Depo-Provera increases neural activity in the central amygdala of reindeer bulls

Reindeer bulls are difficult to manage and dangerous to handlers during the rutting period. Progesterone agonists have been used anecdotally in the field to favorably influence behavior, but effects on reproductive signaling have not been determined. The objective of this study was to determine the effects of Depo-Provera (medroxyprogesterone acetate) on neural activity in the amygdala of reindeer bulls in the early (n = 4) and full (n = 4) rut. Treated bulls (n = 4) were injected with a single injection of Depo-Provera (400 mg i.m.) approximately 2 wk before rut was initiated. Control bulls were untreated. Bulls were exsanguinated and brains collected. Neural activity in the amygdala was determined using c-fos immunohistochemistry. Neural activity did not differ by treatment (P ≥ 0.5), collection period (P ≥ 0.5), or their interaction (P ≥ 0.3) in the medial and cortical amygdala nuclei. A treatment × time interaction (P = 0.009) was observed in the central amygdala. The amygdala nuclei are interconnected allowing for integration of sensory stimuli with a direct connection between the medial amygdala and the olfactory bulb. The central amygdala is responsible for alerting, fear, and initiating a state of arousal towards nonspecific stimuli in the surrounding environment. In wildlife, the central amygdala has a role in recognizing threats in the environment such as predators. During the rut, bulls normally have a decreased sense of fear and elevated aggressive behavior with Depo-Provera treatment seemly able to diminish that aggression. Although it is unlikely that this observed change in neural activity fully explains the decreased aggressive behavior noted in bulls treated with Depo-Provera, neural networks of aggression include the amygdala. It is possible that further changes in c-fos activity will be noted in other areas of the brain known to be necessary for processing social cues. Bulls treated with Depo-Provera maintain sexual interest and have offspring. Depo-Prevera increases the neural activity within the central amygdala and may partially account for their altered aggressive behavior during the rut.

144 EFFECT OF ANTRAL FOLLICLE COUNT IN BEEF HEIFERS ON IN VITRO FERTILIZATION/PRODUCTION

Our objective has been to compare the IVF and in vitro production (IVP) of embryos from low and high antral follicle count (AFC) heifers. This is the fourth year of the study with years 1 to 3 reported individually. For this report, we add data for the fourth year and present a combined analysis (years 1 to 4) for the first time. Each year, AFC was determined on ~120 Angus heifers using transrectal ultrasonography. Ten heifers with the lowest AFC and 10 heifers with the highest AFC and all with evidence of oestrous cyclicity were synchronized with two 5-mL injections of PGF2α 11 days apart. Half were harvested on Day 5 to 6 and half on Day 15 to 16 of the oestrous cycle. The IVF procedure was slightly modified each year. For year 4, the IVF procedure included protocols for semi-defined media and was as described (IVP Protocol, P. J. Hansen’s Laboratory, University of Florida). Cumulus-oocyte complexes (COC) from follicles less than 8 mm in diameter were cultured in maturation medium (5% CO2; 38.5°C) for 24 h. Matured COC were fertilized using thawed frozen semen from a bull that was purified using isolate. Motile spermatozoa were added to COC in fertilization medium at a final concentration of 1 × 106 spermatozoa per mL. About 24 h later, presumptive zygotes were placed in micro drops of development medium under oil, and cultured (5% CO2; 5% O2; balance N2; 38.5°C). On Day 3 and 8 after fertilization, cleavage and blastocyst development rates, respectively, were assessed. Data were analysed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC, USA) and the model included the effects of year (1 to 4), group (high or low AFC), and their interaction. The year × group interaction was not significant (P > 0.10). Low AFC heifers, compared with high AFC heifers, had fewer numbers of COC (P < 0.0001; 12.8 ± 1.83 v. 31.9 ± 1.86), fewer numbers of COC that cleaved (P < 0.0001; 8.0 ± 1.38 v. 21.6 ± 1.40), and fewer numbers of COC that developed to the blastocyst stage (P < 0.0001; 1.7 ± 0.58 v. 5.7 ± 0.58). Year affected the numbers of COC that cleaved (P < 0.003) and the numbers of COC that developed to the blastocyst stage (P < 0.0001). Year also influenced the percentage of COC that cleaved (P < 0.0002) and the percentage of COC that developed to blastocysts (P < 0.0001). Group (AFC) did not influence (P > 0.19) the percentage of COC that cleaved (61.2 ± 2.83 v. 66.4 ± 2.83%, for low v. high AFC, respectively). Low AFC heifers had a lower (P < 0.002) percentage of COC that developed to blastocysts (10.3 ± 1.52%) than high AFC heifers (17.6 ± 1.52%). These results indicate that high AFC heifers, compared to low AFC heifers, have more COC recovered, more COC cleaved, and more COC developed to the blastocyst stage. The percentage of COC cleaved did not differ between AFC groups; however, the percentage of COC that developed to the blastocyst stage was greater for high than low AFC heifers. This suggests a potential advantage in maternal to embryonic transition for high compared with low AFC heifers.

181 IN VITRO FERTILIZATION (IVF) USING SEMI-DEFINED CULTURE CONDITIONS FROM LOW OR HIGH ANTRAL FOLLICLE COUNT PUBERTAL BEEF HEIFERS

To compare the in vitro fertilization (IVF) and production (IVP) of embryos from low and high antral follicle count (AFC) heifers, AFC were determined on 106 heifers using transrectal ultrasonography. Ten heifers with the lowest AFC (avg. 13.2) and 10 heifers with the highest AFC (avg. 27.4) with evidence of oestrous cyclicity were synchronised with 2 injections of prostaglandin F2α (PGF2α); half were harvested on Days 5 to 6 and half on Days 15 to 16 of the oestrous cycle. The IVF procedures included protocols for semi-defined media and were as described (IVP Protocol, P. J. Hansen’s Laboratory, University of Florida, Gainesville, FL, USA). Cumulus-oocyte complexes (COC) from follicles less than 8 mm in diameter were cultured in maturation medium (5% CO2; 38.5°C) for 24 h. Matured COC were fertilised using thawed frozen semen from a crossbred bull that was purified using Percoll gradient separation procedures. Motile spermatozoa were added to COC in fertilization medium at a final concentration of 1 × 106 spermatozoa per mL. About 24 h later, presumptive zygotes were placed in microdrops of development medium under oil, and cultured (5% CO2, 5% O2, balance N2, 38.5°C). On Days 3 and 8 after fertilization, cleavage and blastocyst development rates, respectively, were assessed. Data were analysed using the mixed procedure of SAS (SAS Institute, Cary, NC, USA) and the model included the effects of collection day, group (high or low AFC), and their interaction. More COC (P < 0.0005) were collected from high than low AFC heifers (30.3 v. 9.3 ± 3.12 per heifer). Both the number and percentage of COC that cleaved had an interaction between collection day and group (P < 0.03). The interaction appeared to be due to low cleavage and development rates on 1 of 4 collection days (appeared not related to day of oestrous cycle). Although high compared to low AFC heifers had more COC that cleaved (18.7 v. 4.4 ± 1.84 per heifer), the percentage of cleaved COC did not differ (59.2 v. 49.8 ± 3.36%). There were no significant differences between high and low AFC heifers in the number of blastocysts (3.1 v. 0.6 ± 1.21 per heifer) or in the percentage of COC that developed to blastocysts (8.8 v. 5.2 ± 3.60%). In previous replicates (years), we reported that high AFC heifers had more COC collected, more COC that cleaved, and more COC that developed to blastocysts than low AFC heifers. In contrast, in this study numbers of COC that developed to blastocysts did not significantly differ between high and low AFC heifers. Additionally, the percentage of COC that cleaved, and that developed to blastocyst have been similar between high and low AFC heifers. Therefore, high compared to low AFC heifers may produce more IVP embryos; however, AFC does not appear to affect the competence of an oocyte to develop and mature to the blastocyst stage.

142 EFFECT OF HIGH AND LOW ANTRAL FOLLICLE COUNT IN PUBERTAL BEEF HEIFERS ON IVF

Pubertal heifers can be classified between those with high (n = 25) or low (n = 15) antral follicle counts (AFC). The objective of this study was to determine oocyte development and maturation (e.g. fertility) in an IVF system for high- and low-AFC heifers. From a pool of 120 heifers, 10 high- and 10 low-AFC heifers were determined by transrectal ultrasonography; all heifers with evidence of oestrous cyclicity (i.e. pubertal) were synchronized with two 5-mL injections of prostaglandin F2α 11 days apart. Heifers were euthanized over 4 days on Days 15 to 16 of the synchronized oestrous cycle. A total of 15 heifers (n = 7 high and n = 8 low AFC) were at the appropriate stage of the oestrous cycle. Ovaries were collected and transported to the laboratory. Follicles less than 8 mm in diameter were aspirated. The IVF procedures and media were as previously described (Miles et al. 2004. Biol. Reprod. 71, 1919–1926). Cumulus-oocyte complexes (COC) were identified and washed in oocyte collection medium and then in maturation medium and were cultured (5% CO2; 38.5°C) for 24 h. Following maturation, COC were transferred and washed in fertilization medium. Thawed frozen semen from a crossbred bull was subjected to the swim-up procedure. Motile spermatozoa were collected and added to COC to yield a final concentration of spermatozoa per milliliter of fertilization medium. About 24 h later, presumptive zygotes were washed in development medium, placed in microdrops of development medium, and cultured for 8 days. On Days 3 and 8 after fertilization, cleavage and blastocyst development, respectively, were assessed. Data were analysed using the Proc Mixed procedure of SAS (SAS Institute Inc., Cary, NC, USA) and the model included the effects of day of collection (n = 4), group (n = 7 high- or n = 8 low-AFC heifers), and the interaction. The interaction did not differ (P = 0.10). Day of collection influenced (P < 0.05) the number of COC and the number of oocytes cleaved. High- compared to low-AFC heifers had the greater (P < 0.05) numbers of COC (42.7 ± 4.66 v. 22.1 ± 4.59), oocytes that cleaved (28.1 ± 3.60 v. 15.9 ± 3.55), and developed to blastocysts (13.2 ± 1.71 v. 6.2 ± 1.69). However, there was no difference (P > 0.10) in the percentage of COC that cleaved (65.3 ± 5.58 v. 66.2 ± 5.50%, high v. low, respectively) or that developed to blastocysts (46.7 ± 6.75 v. 42.2 ± 6.65%). In conclusion, AFC did not appear to affect oocyte maturation and development through the blastocyst stage.

Effect of dietary crude protein source on hormone and follicle characteristics in beef heifers

Ground, raw soybeans (SB), or dried distillers grain plus solubles (DDGS) were utilized in heifer development diets to determine the effect of dietary fat and protein source on hormone and follicle characteristics and ADG. The experiment was conducted over 2 yr with 100 June-born heifers (199 +/- 2 kg initial BW, n = 50 per yr). The experimental periods were 157 and 207 d in yr 1 and 2, respectively. Heifers were provided a dietary supplement (DM basis) of 1.23 kg of SB and 0.40 kg of corn or 1.65 kg of DDGS between weaning and breeding. Estrus was synchronized with 2 injections of PGF(2alpha) 14 d apart. Dominant follicles were measured and aspirated via transvaginal ultrasonography 60 h after the second PGF(2alpha) injection. Heifers were exposed to bulls beginning 14 d after aspiration for 45 d. Heifer ADG was greater (P = 0.02) for DDGS heifers in yr 1, but was similar (P = 0.47) in yr 2. However, there was no difference (P = 0.35) in final BW in either year. There was no difference (P >or= 0.67) in follicle size, follicle hormone concentrations, or pregnancy rate (88%) between yr 1 and 2. Serum estrogen at 48 or 60 h after PGF(2alpha) injection were similar (P >or= 0.91); however, LH at 60 h in yr 2 tended to be greater (P = 0.07) for DDGS heifers. The percentage of heifers experiencing an LH surge 48 and 60 h after PGF(2alpha) injection was not affected (P >/= 0.40) by treatment. Calf production was not affected (P >or= 0.20) by developmental diet. In summary, DDGS and SB have similar effects on hormone and follicle characteristics at the inclusion rates used in these studies.

A proposed role for VEGF isoforms in sex-specific vasculature development in the gonad

Many scientists have expended efforts to determine what regulates development of an indifferent gonad into either a testis or ovary. Expression of Sry and upregulation of Sox9 are factors that initiate formation of the testis-specific pathway to allow for both sex-specific vasculature and seminiferous cord formation. Migration of mesonephric precursors of peritubular myoid cells and endothelial cells into the differentiating testis is a critical step in formation of both of these structures. Furthermore, these events appear to be initiated downstream from Sry expression. Sertoli cell secretion of growth factors acts to attract these mesonephric cells. One hypothesis is that a growth factor specific for these cell linages act in concert to coordinate migration of both peritubular and endothelial cells. A second hypothesis is that several growth factors stimulate migration and differentiation of mesonephric 'stem-like' cells to result in migration and differentiation into several different cell lineages. While the specific mechanism is unclear, several growth factors have been implicated in the initiation of mesonephric cell migration. This review will focus on the proposed mechanisms of a growth factor, Vascular Endothelial Growth Factor, and how different angiogenic and inhibitory isoforms from this single gene may aid in development of testis-specific vascular development.

Utilization of soybeans or corn milling by-products in beef heifer development diets

Whole raw soybeans (SB), wet corn gluten feed (WCGF), and corn dried distillers grains (DDG) are sources of protein in heifer development rations. The objectives of this study were to compare puberty status before synchronization of estrus, response to synchronization, and AI and final pregnancy rates in heifers developed on diets containing SB, WCGF, or DDG that were formulated to be similar in energy and CP. These ingredients vary substantially in fat content, which may affect reproductive performance. Rate of gain during the feeding period and post-AI performance were also compared. In a preliminary experiment, 104 crossbred heifers were fed diets containing either 1.25 kg of SB/d or 2.0 kg of WCGF/d for 110 d (DM basis), beginning at 10 mo of age. In Exp. 1, 100 crossbred heifers received either 1.25 kg of SB/d or 2.5 kg of WCGF/d from approximately 7 to 10 mo of age (91 d; 4 pens/diet), and then were fed 1.25 kg of SB/d for an additional 114 d (4 pens/diet). In Exp. 2, 1.25 kg of SB/d or 1.25 kg of DDG/d was fed to 100 crossbred heifers for 226 d, beginning at 6 mo of age (4 pens/diet). At approximately 13 mo of age, heifers were fed melengestrol acetate (0.5 mg/d) for 14 d, followed by an i.m. injection of PGF(2 alpha) (25 mg) 19 d later to synchronize estrus. Heifers (14 mo of age) received AI for 5 d after PGF(2 alpha), at which time the dietary treatments were ended. Heifers were commingled while grazing on native pasture and were exposed to bulls for approximately 60 d beginning 10 d after the last day of AI. Pregnancy to AI was determined by ultrasound 45 d after the last day of AI. Heifers fed SB in the preliminary experiment had a lower (P < 0.05) synchronization rate (81 vs. 96%) and longer interval (P = 0.05) from PGF(2 alpha) to estrus (76.6 vs. 69.2 h) compared with heifers fed WCGF. In Exp. 1, the age at which the heifers were begun on SB diets did not alter (P > 0.10) the synchronization rate (79%) or timing of estrus after PGF(2 alpha) (77.8 h). In Exp. 2, the synchronization rate (86%) and timing of estrus after PGF(2 alpha) (69.3 h) did not differ (P > 0.10) because of diet. No differences (P > 0.10) were due to diet for AI conception rates (overall mean for each experiment: 76.5, 60, and 68.5%), percentage of all heifers becoming pregnant to AI (67, 46, and 59%), or final pregnancy rates (92, 90, and 90%) in the preliminary experiment, Exp. 1, or Exp. 2, respectively. In summary, SB, DDG, and WCGF can be used as sources of protein in heifer development diets at the inclusion rates used in these studies.

Utilization of dried distillers grains for developing beef heifers1,2,3

A 2-yr study was conducted at 2 locations to determine if supplementing beef heifers with dried distillers grains (DDG) as an energy source affected growth or reproduction. Spring-born crossbred heifers (n = 316) were blocked by age or sire and age and assigned randomly to DDG or control (dried corn gluten feed, whole corn germ, urea) supplement. Heifers received prairie hay in amounts sufficient for ad libitum intake and 0.59% of BW DDG or 0.78% of BW control supplement (DM basis). Supplements were formulated to be isocaloric, but protein degradability differed. Supplemental undegradable intake protein intake from DDG averaged 267 g/animal daily and reached 318 g/animal daily; control supplemental undegradable intake protein intake averaged 90 g/animal daily and peaked at 107 g/animal daily. Initial pubertal status was determined by 2 blood samples collected 10 d apart, and monthly BW were collected from November through January; then biweekly BW and blood samples were collected from February until May yearly. Heifers were synchronized with 2 injections of PGF2alpha 14 d apart; estrus was detected and heifers were artificially inseminated for 5 d and placed with bulls 10 d later. Conception and pregnancy rates were determined via transrectal ultrasonography. Initial age, BW, and BCS did not differ (P > 0.92) for control and DDG heifers. Final BW, ADG, and final BCS also were not affected (P > 0.31) by supplementation. Estimated age and BW at puberty did not differ (P > 0.23) between treatments, and the proportions of pubertal heifers did not differ at the initiation of the experiment (P > 0.82), at the beginning of the 14-d sampling intervals, or before synchronization. Estrus synchronization rate (75.9%), time of estrus, and overall pregnancy rate (89.5%) were not affected (P > 0.14) by treatment. However, a greater proportion (P = 0.008) of DDG than control heifers conceived to AI (75.0 vs. 52.9%), resulting in greater (P = 0.07) AI pregnancy rates for DDG heifers (57.0 vs. 40.1%). Body weight or BCS at pregnancy diagnosis did not differ (P > 0.52) between DDG and control heifers. Supplementing beef heifers with DDG during development did not affect age at puberty but improved AI conception and pregnancy rates compared with an isocaloric control supplement.

Frequency of luteinizing hormone pulses in cattle influences duration of persistence of dominant ovarian follicles, follicular fluid concentrations of steroids, and activity of insulin-like growth factor binding proteins

The objectives of the present study were to determine how varying frequency of LH pulses as controlled by varying treatments with progesterone (P4) in cattle would affect: (1) concentration of steroid hormones and activity of insulin-like growth factor binding proteins (IGFBPs) in the ovarian follicular fluid and blood plasma, and (2) duration of persistence of largest ovarian follicles. There were four treatment groups (n=7 per group) and a control group (n=5) of mature, non-lactating beef cows. Treatments were: (1) two progesterone releasing intravaginal devices (PRIDs) for 16 days (2PRID); (2) a half PRID for 16 days (0.5PRID); (3) two PRIDs for 8 days, then a half PRID for 8 days (2-0.5PRID); or (4) a half PRID for 8 days, then two PRIDs for 8 days (0.5-2PRID). Treatment was initiated on the fifth day of the estrous cycle, which was designated as Day 0, and continued for 16 days. All P4-treated females were administered prostaglandin F2alpha on Day 0 and 1 to regress their corpora lutea. Frequency of LH pulses was greater during treatment with the smaller dose of P4 compared with treatment with the larger dose of P4 and the control group. Ovarian follicles were classified into five categories based on ultrasonographic observations: growing (G); atretic (A); growing dominant (GD); growing persistent (GP); or atretic persistent (AP). At ovariectomy on Day 16, the largest and second largest follicles collected were re-classified into five categories based on follicular concentration of steroids. Classification of the largest follicle collected on Day 16 was influenced by treatment (P<0.005), with the 2PRID group having A follicles, the 2-0.5PRID group GP follicles, the 0.5-2PRID group AP follicles, and the 0.5PRID group GD and GP follicles. Concentrations of 17beta-estradiol (E2) were greatest in GD and GP follicles (P<0.05). There was less (P<0.05) activity of IGFBP-2 in GD follicles and less (P<0.05) activity of IGFBP-3 in GD and GP follicles than other follicles. Activity of IGFBP-4 and -5 was greater (P<0.05) in A and AP follicles than G, GD, and GP follicles. Maintenance of a frequent release of LH pulses over a 16-day period did not result in maintenance of persistent follicles throughout this period indicating that duration of dominance of these follicles is finite even when there is frequent release of LH pulses. Follicular atresia is associated with greater activity of IGFBP-2, -4, -5, and greater concentrations of P4 in follicles, whereas growing dominant and persistent follicles contained greater concentrations of E2, androstenedione (A4), and less IGFBP-2 activity than follicles of other classes. Follicle classifications based on ultrasonography or follicular concentration of steroids did differ (P<0.05) for the largest follicles from the 2PRID group. Two follicles in this group appeared as GD follicles by ultrasonography, but these were atretic based on follicular steroid contents. Objective 1 of the present study yielded the conclusion that concentrations of steroid hormones in follicular fluid and blood plasma could be predictably controlled by regulating the frequency of LH pulses with varying doses of P4. Objective 2 yielded the conclusion that maintain frequent release of LH pulses over a 16-day period could not maintain persistent follicles throughout this period, indicating that duration of dominance of these follicles is finite even when there is frequent release of LH pulses. Follicular atresia in the present study was associated with increased follicular fluid activity of IGFBP-2, -4, -5, and P4, whereas growing dominant and persistent follicles contained greater concentrations of E2, A4, and less IGFBP-2 activity than follicles of other classes.

Expression, action, and regulation of transforming growth factor alpha and epidermal growth factor receptor during embryonic and perinatal rat testis development

The objective of the current study was to extend previous observations and examine the expression pattern and effects of transforming growth factor alpha (TGFalpha) and epidermal growth factor receptor (EGFR) on embryonic testis morphogenesis and growth. The expression of TGFalpha was determined after morphological sex determination (seminiferous cord formation at embryonic day 13 [ED13]) through perinatal testis development (postnatal day 5 [PD5]) with a quantitative reverse transcription-polymerase chain reaction procedure. Expression of messenger RNA (mRNA) for TGFalpha appeared to be more dynamic during testis development when compared with the expression of mRNA for EGFR. Message for TGFalpha was reduced at ED16 and PD4, and was elevated at PD0 during testis development. In contrast, EGFR mRNA levels were negligible at ED15 and were elevated constitutively from ED16 through PD5. Immunohistochemistry was conducted at ED14, ED16, ED19, PD0, PD3, and PD5 to localize cellular expression of both TGFalpha and EGFR. At ED16, positive staining for EGFR was localized to the cords, and by ED19, was mainly in the cords with slight expression in the interstitium. From PD0 to PD5, positive staining for EGFR was detected in the germ, Sertoli, and interstitial cells. Immunohistochemistry for TGFalpha detected localization at ED14 and ED16 to the Sertoli cells and to specific cells in the interstitium. From ED19 through PD5, TGFalpha was detected in the Sertoli, germ, and interstitial cells, and in endothelial cells within the interstitium. To determine the effects of TGFalpha on embryonic testis growth and seminiferous cord formation, ED13 testis organ cultures were treated with sense and antisense TGFalpha oligonucleotides. Antisense TGFalpha inhibited testis growth by 25%-30% in ED13 testis organ cultures when compared with sense oligonucleotide control pairs. To examine the effects of TGFalpha on perinatal testis growth, PD0 testis cultures were treated with different doses of TGFalpha. TGFalpha increased thymidine incorporation into DNA in PD0 testis cultures. Therefore, TGFalpha appears to have actions on both embryonic and perinatal testis growth. The regulation of TGFalpha and EGFR mRNA levels were examined using PD0 testis cultures treated with hormones that stimulate testis growth. Follicle-stimulating hormone (FSH) stimulated (P < .05) and testosterone tended to stimulate (P < .07) mRNA expression of EGFR. Epidermal growth factor stimulation of PD0 testis cultures did not affect levels of mRNA expression for EGFR, but did suppress expression of mRNA for TGFalpha. These results taken together demonstrate that TGFalpha can act to regulate early embryonic and perinatal testis growth. Furthermore, TGFalpha and EGFR expression can be regulated through growth stimulatory hormones such as FSH and testosterone.

Actions of the endocrine disruptor methoxychlor and its estrogenic metabolite on in vitro embryonic rat seminiferous cord formation and perinatal testis growth

The current study examines the actions of methoxychlor and its estrogenic metabolite, 2, 2-bis-(p-hydroxyphenyl)-1, 1, 1-trichloroethane (HPTE), on seminiferous cord formation and growth of the developing rat testis. The developing testis in the embryonic and early postnatal period is likely more sensitive to hormonally active agents than at later stages of development. Embryonic day 13 (E13) testis organ cultures were treated with either 0.2, 2, or 20 microM methoxychlor or 1, 3, 6, 15, 30, or 60 microM HPTE to examine effects on cord formation. No concentration of methoxychlor completely inhibited cord formation. However, cord formation was abnormal with the presence of a reduced number of cords and appearance of "swollen" cords at the 2 and 20 microM concentrations of methoxychlor. The swollen cords were due to an increase in the number of cells in a cord cross section and reduction of interstitial cell numbers between cords. Treatment of embryonic day 13 (E13) testes with HPTE caused abnormal cord formation at the 3 microM and 6 microM concentrations, and completely inhibited cord formation at the 15, 30, and 60 microM concentrations. In addition to the estrogenic metabolite HTPE, methoxychlor can also be metabolized into anti-androgenic compounds. Therefore, to determine the spectrum of potential actions of methoxychlor on testis development, different concentrations of estradiol, testosterone, and an anti-androgen (flutamide) were utilized to determine their effects on E13 testis organ culture morphology. Estradiol (1 microM) and flutamide (0.1microM) both inhibited seminiferous cord formation in E13 testis organ cultures. Therefore, methoxychlor may be acting through the androgen and/or estrogen receptors to elicit its actions on seminiferous cord formation. Reverse transcription polymerase chain reaction (PCR) (RT-PCR) confirmed the presence of estrogen receptor alpha (ERalpha) mRNA from embryonic day 14 (E14) through postnatal day 5 (P5) while estrogen receptor beta (ERbeta) mRNA did not appear until approximately E16 of testis development. Androgen receptor (AR) expression was present from E14 through P5 of testis development, but at apparently reduced levels at E14 and E16. Immunohistochemical analysis localized ERalpha to the cells of the seminiferous cords at E14 though P5 while ERbeta was present in cells of the interstitium at E16 and P0. Androgen receptor was localized to germ and interstitial cells. The effects of methoxychlor, HPTE, estradiol, and testosterone on cell growth of perinatal testes was determined with a thymidine incorporation assay in postnatal day zero (P0) testis cell cultures. Methoxychlor (0.002, 0.02, and 0.2 microM) and HPTE (2 and 20 microM) stimulated thymidine incorporation in P0 testis cell cultures in a similar manner to estradiol (0.01, 0.1, and 1 microM). In addition, testosterone (0.1 microM) also stimulated thymidine incorporation in P0 testis cultures. Observations suggest that methoxychlor and its metabolite HPTE can alter normal embryonic testis development and growth. The actions of methoxychlor and HPTE are likely mediated in part through the steroid receptors confirmed to be present in the developing testis.

Expression and action of neurotropin-3 and nerve growth factor in embryonic and early postnatal rat testis development

The current study examines the expression and potential actions of neurotropin-3 (NT3), nerve growth factor (NGF), and their receptors during morphological sex determination (seminiferous cord formation) and perinatal rat testis development. The expression of neurotropins and their receptors was analyzed with immunohistochemistry. Cellular localization of neurotropin ligand and receptor proteins changed during embryonic testis development. Neurotropin-3 was localized to Sertoli cells at Embryonic Day 14 (E14), was present in gonocytes at Postnatal Day 0 (P0), and after birth became localized to the interstitium and Sertoli cells (P3-P5). The expression of trk C (the high affinity receptor for NT3) was localized to mesonephric ducts and cells surrounding the cords (E14-E18). In addition, Sertoli cells and preperitubular cells surrounding the cords at E14 also stained for trk C. Neurotropin-3 was expressed in gonocytes and Sertoli cells at P0-P5. Nerve growth factor was detected in Sertoli cells at E14, was clearly in Sertoli and interstitial cells at E16 and E18, and in Sertoli, germ, and interstitial cells from P0-P5. The expression of trk A (the high affinity receptor for NGF) was located in Sertoli and interstitial cells at E16-P5. To determine the actions of neurotropins during embryonic and perinatal testis development, experiments were conducted on E13 and P0 testis. Antisense oligonucleotide experiments with NT3 were used on E13 testis organ cultures to determine effects on seminiferous cord formation. Cord formation was inhibited in 40% of the organ cultures treated with the antisense NT3 oligonucleotides, while no inhibition was observed with sense oligonucleotides. In P0 testis cultures, both NT3 and NGF alone and in combination stimulated thymidine incorporation into DNA. Therefore, the neurotropins are involved in embryonic morphological events (cord formation; NT3) and in growth of the perinatal testis (P0; NT3 and NGF). To define further the growth effects of neurotropins on testis development, expression of transforming growth factor alpha and beta (TGF alpha and TGF beta) were examined in response to neurotropins. The P0 testis cultures were treated with neurotropins, and expression of mRNA for TGF alpha and TGF beta was analyzed utilizing a quantitative reverse transcription-polymerase chain reaction assay. Nerve growth factor and NT3 alone or in combination inhibited expression of mRNA for TGF alpha while NT3 increased mRNA expression of epidermal growth factor receptor. The combination treatment of neurotropins inhibited expression of TGF beta 1 and increase expression of TGF beta 3. In summary, observations suggest that NT3, NGF, trk A, and trk C are localized to cells critical to seminiferous cord formation and appear to be important regulators of morphological sex determination. In addition to these morphological effects, both NT3 and NGF stimulate P0 testis growth and may elicit their action through altering the expression of locally produced growth factors such as TGF alpha and TGF beta. Taken together these results suggest that neurotropins are regulators of paracrine cell-cell interactions that result in morphological sex determination and perinatal testis growth.

Role of transforming growth factor-alpha and the epidermal growth factor receptor in embryonic rat testis development

Embryonic testis development requires the morphogenesis of cords and growth of all cell populations to allow organ formation. It is anticipated that coordination of the growth and differentiation of various cell types involves locally produced growth factors. The current study was an investigation of the hypothesis that transforming growth factor-alpha (TGF-alpha) is involved in regulating embryonic testis growth. TGF-alpha has previously been shown to function in the postnatal testis. TGF-alpha and other members of the epidermal growth factor (EGF) family act through the epidermal growth factor receptor (EGFR) to stimulate cell proliferation and tissue morphogenesis. To understand the potential actions of TGF-alpha in the embryonic testis, general cell proliferation was investigated. Characterization of cell proliferation in the rat testis throughout embryonic and postnatal development indicated that each cell type has a distinct pattern of proliferation. Germ cell growth was transiently suppressed around birth. Interstitial cell growth was high embryonically and decreased to low levels around birth. A low level of Sertoli cell proliferation was observed at the onset of testis cord formation. Sertoli cell proliferation in early embryonic development was low; the levels were high later in embryonic development and remained high until the onset of puberty. Both TGF-alpha and the EGFR were shown to be expressed in the embryonic and postnatal rat and mouse testis. Perturbation of TGF-alpha function using neutralizing antibodies to TGF-alpha on testis organ cultures dramatically inhibited the growth of both embryonic and neonatal testis. TGF-alpha antibodies had no effect on cord formation. The TGF-alpha antibody was found to be specific for TGF-alpha in Western blots when compared to EGF and heregulin. Testis growth was also inhibited by perturbation of EGFR signaling using an EGFR kinase inhibitor. Therefore, TGF-alpha appears to influence embryonic testis growth but not morphogenesis (i.e., cord formation). Treatment of embryonic testis organ cultures with exogenous TGF-alpha also perturbed development, leading to an increased proliferation of unorganized cells. Testis from EGFR and TGF-alpha knockout mice were analyzed for testis morphology. TGF-alpha knockout mice had no alterations in testis phenotype, while EGFR knockout mice had a transient decrease in the relative amount of interstitial cells before birth. Observations suggest that there may be alternate or compensatory factors that allow testis growth to occur in the apparent absence of TGF-alpha actions in the mutant mice. In summary, the results obtained suggest that TGF-alpha is an important factor in the regulation of embryonic testis growth, but other factors will also be involved in the process.

Role of neurotropins in rat embryonic testis morphogenesis (cord formation)

The process of seminiferous cord formation is the first morphological event that differentiates a testis from an ovary and indicates male sex determination. Cord formation occurs by embryonic Day 14 (Day 0 = plug date; E14) in the rat. A series of experiments were conducted to determine if neurotropins and their receptors are important for the process of rat embryonic cord formation. The expression of low affinity neurotropin receptor (p75/LNGFR) was determined by immunohistochemistry on sections of both testis and ovary from E13 through birth (Day 0, P0) with an antibody to p75/LNGFR. The staining for p75/LNGFR was present in the mesonephros of E13 gonads and in a sex-specific manner appeared around developing cords at E14 in the embryonic testis. At birth, staining for p75/LNGFR was localized to a single layer of cells (i.e., peritubular cells) that surrounded the seminiferous cords. The genes for both neurotropin 3 (NT3) and for corresponding high affinity neurotropin trkC receptor were found to be expressed in the E14 rat testis, as well as other neurotropins and receptors. Immunocytochemical analysis of E14 rat testis demonstrated that NT3 was localized to the Sertoli cells and trkC was present in individual cells of the interstitium at E16 and in selected preperitubular cells at E18. Previously, the peritubular cells adjacent to the cords were demonstrated to be derived from migrating mesonephros cells around the time of cord formation. To determine if neurotropins were involved in cord formation, the actions of neurotropins were inhibited. A high affinity neurotropin receptor (trk)-specific kinase inhibitor, K252a, was used to treat organ cultures of testes from E13 rats prior to cord formation. Treatment of E13 testis organ cultures with K252a completely inhibited cord formation. K252a-treated organ cultures of E14 testis that contained cords did not alter cord morphology. A second experiment to inhibit neurotropin actions utilized a specific antagonist trk-IgG chimeric fusion protein and E13 testis organ cultures. The trk-IgG molecules dimerize with endogenous trk receptors and inhibit receptor signaling and activation of ligand function. Forty percent of E13 testis organ cultures treated with trkC-IgG had significantly reduced cord formation. TrkA-IgG had no effect on initiation of cords; however, in fifty percent of the treated organs, a "swollen" appearance of the cord structures was observed. Experiments using trkB-IgG chimeric protein on E13 organ cultures had no effect on cord formation or cord morphology. The testes from trkC and NT3 knockout mice were examined to determine if there were any morphological differences in the testis. NT3 knockouts appeared to have normal cord morphology in E15 and E17 testis. TrkC knockout mice also had normal cord morphology in E14 and P0 testis. Both NT3 and trkC knockout-mice testis had less interstitial area than wild-type controls. In addition, the trkC knockout mice have an increased number of cells expressing p75LNGFR within the cords when compared to controls or NT3 knockout mice. Combined observations suggest compensation between the different neurotropin ligands, receptors, and/or possibly different growth factors for this critical biological process. In summary, results suggest a novel nonneuronal role for neurotropins in the process of cord formation during embryonic rat testis development. The hypothesis developed is that neurotropins are involved in the progression of male sex differentiation and are critical for the induction of embryonic testis cord formation.

Expression and action of transforming growth factor beta (TGFbeta1, TGFbeta2, and TGFbeta3) during embryonic rat testis development

The objective of the current study was to determine the role of transforming growth factor beta (TGFbeta) during seminiferous cord formation and embryonic testis development. The expression pattern of mRNA for TGFbeta isoforms was evaluated during testis development through a quantitative reverse transcription-polymerase chain reaction (QRT-PCR) procedure. Expression of mRNA for TGFbeta1 was highest at postnatal day 0 (P0) and P10. In contrast, TGFbeta2 was high at embryonic day 15 (E15), declined at E16, and showed a transient increase at P0 through P3 of testis development. Interestingly, expression of mRNA for TGFbeta3 was high during embryonic development and then declined after P3. Immunohistochemical localization of TGFbeta1 and TGFbeta2 demonstrated expression in Sertoli cells at E14 and in the seminiferous cords at P0. Selective interstitial cells expressed high concentrations of TGFbeta1 and TGFbeta2 in P0 testis. TGFbeta3 was expressed in selective cells at the junction of the E14 testis and mesonephros. The cells expressing TGFbeta3 in the testis appeared to be preperitubular cells that resided around the seminiferous cords. TGFbeta3 was localized to gonocytes in P0 testis. TGFbeta1 was found to have no influence on seminiferous cord formation in embryonic organ cultures of E13 testis. In contrast, growth of both E13 and E14 embryonic organ cultures was inhibited by TGFbeta1 and resulted in reduced testis size (40% of controls) with fewer cords present. A P0 testis cell culture and thymidine incorporation assay were used to directly examine the effects of recombinant TGFbeta1. TGFbeta1 alone had no influence on thymidine incorporation in P0 testis cell cultures when compared to controls. Interestingly, TGFbeta1 inhibited epidermal growth factor (EGF), and 10% calf serum stimulated P0 testis cell growth but not FSH-stimulated growth. Therefore, TGFbeta1 appears to inhibit testis growth in both the embryonic and early postnatal periods. The hormonal regulation of TGFbeta expression was measured using P0 testis cell cultures and a QRT-PCR procedure for each TGFbeta isoform. High concentrations of EGF stimulated expression of mRNA for TGFbeta1 after 24 h but suppressed expression of TGFbeta3. In contrast, there was no effect of FSH on TGFbeta isoform expression. In summary, TGFbeta regulates embryonic and P0 testis growth through inhibiting the actions of positive growth factors such as EGF. In addition, EGF but not FSH appears to regulate TGFbeta isoform expression. Combined observations from the present study demonstrate that TGFbeta isoforms are differentially expressed and appear to be regulators of testis growth during the embryonic and early postnatal periods.

Action of retinoids on embryonic and early postnatal testis development

The current study investigates the hypothesis that retinoids have a role in embryonic testis development. The action of retinoids on testis development and the expression of retinoic acid receptors (RAR alpha, RAR beta, RAR gamma) were examined. In embryonic day 13 (E13; plug date = E0) testis organ cultures an RAR-selective agonist and all-trans retinoic acid completely inhibited seminiferous cord formation. In contrast, an RAR alpha-selective antagonist had no effect. RT-PCR demonstrated that RAR alpha messenger RNA (mRNA) was expressed at all developmental time points evaluated, which included embryonic day 14 (E14) through postnatal day 30 (P30). Expression of RAR beta mRNA was present at E15 through P2, whereas RAR gamma mRNA was expressed at E18 through P2. Cellular localization of receptors by immunohistochemistry indicated that RAR alpha was localized to the interstitium at E18 and to the seminiferous cords by P0. RAR beta and RAR gamma were detected in both interstitium and cords at E16 and by E18 were mainly expressed in the cords. At P0 RAR beta and RAR gamma were localized to the germ cell populations. To examine retinoid actions, the growth of P0 testis cultures were investigated. Interestingly, retinol and retinoic acid did not inhibit growth of P0 testis cultures but did inhibit the action of growth stimulators. Retinoic acid inhibited FSH, EGF, and 10% calf serum stimulated growth in P0 testis cultures. The hypothesis tested was that the inhibitory effects of retinoids on P0 testis growth may be mediated through the growth inhibitor, transforming growth factor-beta (TGF beta). The action of retinoids on TGF beta mRNA expression was examined in P0 testis cultures. Retinoic acid stimulated TGFbeta3 mRNA expression within 24 h and increased expression of TGFbeta1 and TGFbeta2 after 72 h. Retinol increased expression of TGFbeta1 and TGFbeta2 but not TGFbeta3 after 72 h of treatment. These observations indicate that retinoic acid can influence seminiferous cord formation and testis growth. The inhibitory actions of retinoids may in part be mediated through increased expression of TGFbeta isoforms.

Concentrations of gonadotropins, estradiol and progesterone in sows selected on an index of ovulation rate and embryo survival

The objective of this study was to determine concentrations of follicle stimulating hormone (FSH), luteinizing hormone (LH), progesterone (P4) and 17beta-estradiol (E2) in sows from a line selected on an index which emphasized ovulation rate (Select) and from a control line. A further classification of the sows in each line was made according to the estimated number of ovulations during an estrous cycle. Sows in the Select line were ranked into a high (HI) or low group (LI) when their estimated number of ovulations were 25 or more and 14 to 15, respectively. Sows of the control line were classified into groups as high (HC) or low (LC) when the estimated values for ovulation rate were 14-15 and 8-9 ovulations, respectively. Blood samples were collected every 12 h during a complete estrous cycle and samples were analyzed for concentrations of FSH and LH. Samples collected every 24 h were assayed for P4 and E2. Mean concentrations of FSH, LH, P4 and E2 did not differ (P > 0.10) between lines or between HI and LI or HC and LC groups. Selection of pigs for ovulation rate and embryonal survival did not affect concentrations of FSH, LH, P4 and E2 in sows during the estrous cycle.

Developmental and hormonal regulation of transforming growth factor-beta1 (TGFbeta1), -2, and -3 gene expression in isolated prostatic epithelial and stromal cells: epidermal growth factor and TGFbeta interactions

Growth factors are postulated to mediate stromal-epithelial interactions in the prostate to maintain normal tissue physiology. Transforming growth factor-beta (TGFbeta) has been shown to influence the prostate and probably mediate stromal-epithelial interactions. TGFbeta1 messenger RNA (mRNA) expression is stimulated after castration and can be suppressed by in vivo treatment with androgens. The hypothesis tested is that TGFbeta is regulated not only by androgen, but also by a network of locally produced growth factors that influence prostatic growth and differentiation. Epithelial and stromal cells from 20-day-old rat ventral prostate were isolated and used to test this hypothesis. The expression of mRNA for TGFbeta1, -2, and -3 was analyzed by a quantitative RT-PCR procedure. Observations from this assay demonstrate that both epithelial and stromal cells express the mRNA for TGFbeta1, -2, and -3. TGFbeta1 mRNA expression was constant during development of the prostate. TGFbeta2 mRNA expression was elevated at birth, then declined and elevated again at 100 days of age. TGFbeta3 mRNA expression was high during puberty and young adult ages then declined at 100 days of age. TGFbeta2 and TGFbeta3 expression are inversely related during prostate development. After castration of 60-day-old rats, both TGFbeta1 and TGFbeta2 mRNA were enhanced. Interestingly, TGFbeta3 mRNA was significantly suppressed after castration. Epidermal growth factor (EGF) stimulated TGFbeta1 mRNA expression in stromal cells (6-fold increase), whereas keratinocyte growth factor stimulated TGFbeta2 mRNA in epithelial cells. TGFbeta inhibited both testosterone- and EGF-stimulated prostatic stromal and epithelial cell growth. EGF and TGFbeta also inhibited prostatic ductal morphogenesis and growth in organ culture. Immunocytochemical localization of TGFbeta in 20-day-old prostate demonstrated predominately stromal localization of the protein. These results indicate that the isoforms of TGFbeta2 and TGFbeta3 are differentially regulated during prostate development, suggesting distinct regulatory mechanisms. Testosterone did not affect TGFbeta expression in cultured prostatic cells. These observations suggest that the in vivo effects of castration on TGFbetas are regulated indirectly through a complex network of growth factors, not simply by direct androgen depletion. The ability of EGF to inhibit prostatic ductal morphogenesis and growth in organ culture is postulated to be in part mediated by the increase in TGFbeta1 expression. In summary, a network of growth factor-mediated stromal-epithelial interactions is needed to maintain prostate growth and development. TGFbeta is postulated to have an important role in this process.

Gonadotropin secretion and development of ovarian follicles during oestrous cycles in heifers treated with luteinizing hormone releasing hormone antagonist

The hypothesis tested was that reduced LHRH stimulation of the anterior pituitary would lead to attenuated development of ovarian follicles as a result of reduced gonadotropin secretion during oestrous cycles of cattle. Twenty heifers were randomly assigned to be treated ( n = 5/treatment) with an antagonist to LHRH (LHRH-Ant) 1) from Day 2 to 7 (Day 0 = behavioural oestrus), 2) Day 7 to 12, 3) Day 12 to 17, 4) or serve as untreated control animals. LHRH-Ant suppressed LH pulses of heifers in all treatment groups from treatment initiation through Day 17 as compared with untreated control heifers [Peters et al., 1994. Luteinizing hormone has a role in development of fully functional corpora lutea (CL) but is not required to maintain CL function in heifers. Biol. Reprod., 51 (1994) 1248-1254]. Circulating concentration of FSH from Day 8 to 10 of the oestrous cycle did not increase in heifers treated with LHRH-Ant from Day 2 to 7 or Day 7 to 12; however, there was increased (P < 0.05) FSH from Day 8 to 10 of the oestrous cycle in heifers treated with LHRH-Ant from Day 12 to 17 and control heifers. Compared with control heifers, heifers treated with LHRH-Ant from the Day 2 to 7 had suppressed (P < 0.05) size and persistence of the first and second dominant ovarian follicles. Heifers treated with LHRH-Ant from Day 7 to 12 had suppressed size (P < 0.05 and tended (P < 0.10) to have a shorter persistence of the second dominant ovarian follicle compared with control heifers. Heifers treated with LHRH-Ant from Day 12 to 17 had a similar (P > 0.10) size and persistence of dominant ovarian follicles but had reduced (P < 0.10) numbers of large follicles compared with control heifers. Heifers treated with LHRH-Ant from Day 2 to 7 had lower (P < 0.01) concentrations of 17 beta-oestradiol during the treatment period and tended (P < 0.10) to have lower concentrations of 17 beta-oestradiol from Day 7 to 12 of the oestrous cycle compared with control heifers. Heifers treated with LHRH-Ant from Day 7 to 12 or Day 12 to 17 had similar (P > 0.10) circulating LH concentrations of l7 beta-oestradiol compared with control heifers. Reduced LHRH stimulation of the pituitary from Day 2 to 12 of the oestrous cycle and the resulting modulation in circulating LH and FSH led to suppressed ovarian follicular development and oestradiol secretion. After Day 12 of the oestrous cycle, reduced LHRH stimulation of the anterior pituitary did not lead to altered ovarian follicular development to the extent as reduced LHRH stimulation before Day 12 although pulsatile release of LH was similarly suppressed by treatment with the LHRH-Ant.

Role of basic-helix-loop-helix transcription factors in Sertoli cell differentiation: identification of an E-box response element in the transferrin promoter

Sertoli cells are critical for testicular function and maintenance of the spermatogenic process. The induction of Sertoli cell differentiation in the embryo promotes testicular development and male sex determination. The progression of Sertoli cell differentiation during puberty promotes the onset of spermatogenesis. The maintenance of optimal Sertoli cell differentiation in the adult is required for spermatogenesis to proceed. The current study was designed to investigate the transcriptional regulation of Sertoli cell differentiation through the analysis of a previously identified marker of differentiation, transferrin gene expression. Sertoli cells produce transferrin to transport iron to developing spermatogenic cells sequestered within the blood-testis barrier. The transferrin promoter was characterized and found to contain two critical response elements, designated Sertoli element 1 (SE1) and Sertoli element 2 (SE2). Through sequence analysis, SE2 was found to contain an E-box response element, which has been shown to respond to basic-helix-loop-helix (bHLH) transcription factors. The bHLH proteins are a class of transcription factors associated with the induction and progression of cell differentiation. bHLH proteins dimerize through the conserved helix-loop-helix region and bind DNA through the basic region. Nuclear extracts from Sertoli cells were found to cause an E-box gel shift when the cells were stimulated to differentiate in culture, but not under basal conditions. The SE2 gel shift of Sertoli nuclear extracts was competed with excess unlabeled SE2 or E-box DNA fragments. Several Sertoli nuclear proteins associate with the SE2 gel shifts, including 70-, 42-, and 25-kDa proteins. Therefore, the critical SE2 element in the transferrin promoter is an E-box element capable of binding bHLH transcription factors. The ubiquitously expressed E12 bHLH protein dimerizes with numerous cell-specific bHLH factors. A Western blot analysis demonstrated that E12 was present in Sertoli cell nuclear extracts and associated with the SE2 gel shift. A ligand blot of Sertoli cell nuclear extracts with radiolabeled E12 had apparent bHLH proteins when the cells were stimulated to differentiate. The E-box sequence in the SE2 fragment of the transferrin promoter was CATCTG and was similar in gel shifts to the consensus E-box elements (CANNTG) previously characterized. A bHLH inhibitory factor (Id) competed and inhibited formation of the Sertoli cell nuclear extract E-box gel shift. To extend this observation, Id protein was overexpressed in cultured Sertoli cells. A transferrin promoter chloramphenicol acetyltransferase construct was used to monitor Sertoli cell function. The presence of Id suppressed the activation of the promoter induced by Sertoli differentiation factors. Therefore, the inhibition of Sertoli bHLH factors by Id suppressed Sertoli cell differentiated function, as measured by transferrin expression. An E-box-chloramphenicol acetyltransferase construct was also found to be active in Sertoli cells when cells were induced to differentiate. Screening the computerized nucleotide data bases demonstrated that putative E-box response elements are present in the promoters of a large number of Sertoli cell differentiated genes. In summary, a critical E-box response element has been identified in the transferrin promoter that can be activated by bHLH factors (e.g. E12) present in Sertoli cells. Inhibition of Sertoli bHLH factors by Id suppresses Sertoli cell differentiated function (i.e. transferrin expression), suggesting that bHLH transcription factors may be important in regulating Sertoli cell differentiated functions.

Comparison of circulating concentrations of reproductive hormones in boars of lines selected for size of testes or number of ovulations and embryonal survival to concentrations in respective control lines

The objectives of this study were to determine whether circulating concentrations of genadotropins and gonadal hormones of boars were altered as a result of selection of pigs for size of testes or for embryonal survival and(or) number of ovulations. Included in Exp. 1 and 2 were boars with the greatest estimated paired weight of testes (TS) and boars from a control (C) line. Concentrations of FSH were similar (P > .10) in boars from the TS and C lines. In Exp. 3, 4, and 5, circulating concentrations of FSH and 17 beta-estradiol (E2) were evaluated in neonates, during pubertal development, and in mature boars of lines selected for an index of number of ovulations and embryonal survival (I), and data were compared to those for boars from a respective C line. Concentrations of E2 were not different in boars from the I line and those from the C line during the early neonatal period but were greater (P < .05) in boars of the C line than in those from the I line during pubertal development. Concentrations of FSH were greater (P < .05) in mature boars from the I line than in those from the C line. In summary, selection for size of testes did not influence circulating concentrations of FSH in mature boars. The secretory pattern of E2 in boars before puberty changed as a result of selection for embryonal survival and number of ovulations in females of the I line, and the different patterns of circulating E2 early in life may result in enhanced circulating concentrations of FSH in adult boars of the I line compared with boars of the C line.

Changing dose of progesterone results in sudden changes in frequency of luteinizing hormone pulses and secretion of 17 beta-estradiol in bovine females

The aim of the present study was to elucidate the time course according to which changes in circulating concentrations of progesterone influence pulsatile secretion of LH and secretion of 17 beta-estradiol. Our working hypothesis was that changing the dose of progesterone would result in changes in frequency of LH pulses and secretion of 17 beta-estradiol within 72 h. Five days after behavioral estrus, thirty-three cows were randomly assigned to one of five groups: 1) control, no treatment (CONT, n = 5); 2) treatment with two progesterone-releasing intravaginal devices (PRIDs) for 11 days (2PRID, 5-6 ng/ml plasma progesterone, n = 7); 3) treatment with a 0.5 PRID for 11 days (0.5PRID, 1-2 ng/ml plasma progesterone, n = 7); 4) treatment with 2 PRIDs for 8 days followed by treatment with a 0.5 PRID for 3 days (2-0.5PRID, n = 7); and 5) treatment with a 0.5 PRID for 8 days followed by treatment with 2 PRIDs for 3 days (0.5-2PRID, n = 7). Cows subject to PRID treatments received injections of prostaglandin F2 alpha on Days 1 and 2 (Day 0 = day of initiation of PRID treatments, fifth day of the estrous cycle in CONT cows) to lyse the existing corpus luteum. Cows were bled for 12 h at 15-min intervals on Day 7.5 of the treatment period (twelfth day of the estrous cycle in CONT cows). The dose of progesterone was changed on Day 8 in cows that were assigned to the 2-0.5PRID and 0.5-2PRID groups, and blood collections continued an additional 72 h to characterize profiles of circulating concentrations of LH and 17 beta-estradiol. Cows treated with a 0.5 PRID had a greater (p < 0.05) number of LH pulses and higher (p < 0.05) concentrations of 17 beta-estradiol throughout the entire blood collection period than cows in the 2PRID and CONT groups. An increase in the number of LH pulses was detected within 6 h after the change from the high to the low dose of progesterone (2-0.5PRID), and frequency of LH pulses was similar to that of cows in the 0.5PRID group for the remainder of the period of blood collection. LH pulse frequency declined within 6 h after the shift from the low to the high dose of progesterone (0.5-2PRID) and was similar to that of cows in the 2PRID group by 12 h after the dose was changed. Within 6 h after the dose of progesterone was changed, circulating concentrations of 17 beta-estradiol increased (p < 0.05) in cows shifted from the high to low dose (2-0.5PRID) and declined (p < 0.05) after the dose of progesterone was changed from low to high (0.5-2PRID). We conclude that changing the circulating concentrations of progesterone concurrently affects frequency of pulsatile LH release and secretion of 17 beta-estradiol within 6-24 h.

Development of persistent ovarian follicles during synchronization of estrus influences the superovulatory response to FSH treatment in cattle

The synchronization of estrus with synthetic progestins or progesterone (P(4)) results in the development of a large, persistent ovarian follicle. The objectives of the present study were to determine if development of a persistent ovarian follicle during synchronization of estrus suppresses recruitment of additional follicles during FSH treatment. On Day 5 of the estrous cycle (estrus = Day 0), beef cows were treated with 0.5 or 2.0 P(4) releasing intravaginal devices (PRIDs) for 8 d (Experiment 1, n = 20), 5 or 2 d (Experiment 2, n = 44) before initiation of FSH treatment. Prostaglandin F(2alpha) (25 mg) was administered on Days 5 and 6. Superovulation was induced with 24 mg of recombinant bovine FSH (rbFSH, Experiment 1) or 28 mg of FSH-P (Experiment 2) over a 3- or 4-d period, respectively. The PRIDs were removed concurrently with the 5th injection of rbFSH or FSH-P. There was a treatment-by-day interaction (P < 0.001) for the concentration of 17beta-estradiol in cows treated for 8, 5 or 2 d before FSH treatment. In Experiment 1, FSH treatment initiated 8 d after insertion of a 0.5 PRID did not affect the number of CL (6.9 +/- 1.4 vs 6.7 +/- 1.6), ova/embryos (3.7 +/-1.3 vs 3.0 +/- 1.3) and transferable embryos (2.4 +/- 0.9 vs 3.0 +/- 0.9) compared with that of the 2.0 PRIDs. In Experiment 2, FSH treatment initiated 5 d after insertion of a 0.5 PRID decreased the number of CL (4.0 +/- 0.5 vs 8.3 +/- 0.8; P < 0.001), ova/embryos (3.0 +/- 0.6 vs 5.9 +/- 1.2; P < 0.03) and transferable embryos (2.3 +/- 0.6 vs 5.1 +/- 1.0; P < 0.03) compared with that of a 2.0 PRID, respectively. Initiation of FSH treatment 2 d after insertion of a 0.5 PRID compared with a 2.0 PRID had no affect on the number of CL (8.0 +/- 2.1 vs 8.7 +/- 1.2), total ova (4.8 +/- 1.4 vs 6.9 +/- 1.4) and transferable embryos (2.9 +/- 1.2 vs 6.1 +/- 1.7). In conclusion, treatment with low doses of P(4) (0.5 PRID) for 5 d but not for 2 or 8 d before initiation of FSH treatment results in the development of a dominant ovarian follicle, which reduces recruitment of ovarian follicles, and the number of CL, total ova and transferable embryos.

Increasing concentrations of 17 beta-estradiol has differential effects on secretion of luteinizing hormone and follicle-stimulating hormone and amounts of mRNA for gonadotropin subunits during the follicular phase of the bovine estrous cycle

The hypothesis tested was that 17 beta-estradiol (E2) would increase amounts of mRNA for alpha, LH beta, and FSH beta subunits during the follicular phase of the estrous cycle prior to the preovulatory surge of gonadotropins in cows. On Day 16 (Day 0 = estrus) of the estrous cycle, all cows were treated with prostaglandin F2 alpha (PGF2 alpha). Cows served as intact controls (CONT, n = 4) were ovariectomized (OVX, n = 5), or were ovariectomized and administered E2 (OVXE, n = 6) in increasing doses starting at the time of treatment with PGF2 alpha. Cows were bled for 6 h before and for 40 h after PGF2 alpha treatment to characterize pulsatile secretion of LH and FSH. Forty hours after PGF2 alpha treatment, pituitaries were collected for evaluation of amounts of mRNA for alpha, LH beta, and FSH beta subunits. Amplitude of LH pulses was greater (p < 0.05) in cows from the OVXE than from the CONT group. Concentrations of FSH were greater in cows from both the OVXE and OVX (p < 0.01) groups than from the CONT group. Amounts of mRNA for alpha and FSH beta subunits were greater (p < 0.01) in pituitaries of cows from the OVX than from the CONT or OVXE groups. Amounts of mRNA for LH beta subunit in pituitaries of cows from the OVX group tended to be greater (p < 0.08) than from the CONT group. Cows in the OVXE group tended (p < 0.08) to have greater amounts of mRNA for FSH beta subunit than did CONT cows.(ABSTRACT TRUNCATED AT 250 WORDS)

Dosage of the synthetic progestin, norgestomet, influences luteinizing hormone pulse frequency and endogenous secretion of 17 beta-estradiol in heifers

The objective of this study was to determine whether there were doses at which the synthetic progestin, norgestomet, could mimic midluteal phase concentrations of progesterone in regulating the secretion of LH and 17 beta-estradiol in bovine females. Heifers were randomly assigned to one of five groups to receive: 1) one (1Norg, n = 5), 2) two (2Norg, n = 5), 3) four (4Norg, n = 5), or 4) eight (8Norg, n = 5) norgestomet implants or to serve as untreated control heifers (control, n = 5). On Day 7 (Day 0 = behavioral estrus), implants containing norgestomet were inserted, and they remained in place for 10 days. All heifers implanted with norgestomet were treated with 25 mg prostaglandin F2 alpha (PGF2 alpha) on Days 7 and 8 to lyse the CL. Controls were treated with 25 mg PGF2 alpha at the time norgestomet implants were removed from heifers of the other treatment groups. Blood samples were collected every 15 min for 24 h on Days 10 and 16 to determine the frequency of LH pulses. Beginning 24 h after removal of implants, samples of blood were collected at 4-h intervals for 96 h to determine the time of the preovulatory surge of LH. Daily blood samples were collected from Day 2 to Day 48 to determine concentrations of progesterone, and samples collected between Days 2 and 17 were used to determine concentrations of 17 beta-estradiol. Ultrasonography was performed daily from Day 2 until Day 23 to evaluate ovarian follicular development.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of 17 beta-estradiol on distribution of pituitary isoforms of luteinizing hormone and follicle-stimulating hormone during the follicular phase of the bovine estrous cycle

The objective of this study was to examine the influence of 17 beta-estradiol (E2) on distribution of LH and FSH isoforms during the follicular phase of the bovine estrous cycle prior to the preovulatory surges of LH and FSH. On Day 16 of the estrous cycle (Day 0 = estrus), intact controls (CONT; n = 4) were treated with prostaglandin F2 alpha (PGF2 alpha) to induce luteal regression and initiation of the follicular phase. Other cows were also treated with PGF2 alpha and either ovariectomized (OVX; n = 5) or ovariectomized and given E2 implants (OVXE; n = 6) to mimic the pattern of increasing E2 concentrations during the follicular phase of the estrous cycle. Pituitaries were collected 40 h after treatment with PGF 2 alpha or ovariectomy (0 h). Aliquots of pituitary extracts were chromatofocused on pH 10.5-4.0 gradients. The LH resolved into thirteen isoforms (designated A-L and S, beginning with the most basic form) while FSH resolved into nine isoforms (designated I-IX, beginning with the most basic form). The percentage of LH as isoform F (elution pH = 9.32 +/- 0.01) was greater (p < 0.05) in the OVX group (48.5%) than in the OVXE group (45.0%). LH isoforms I (elution pH = 6.98 +/- 0.01) and J (elution pH = 6.48 +/- 0.01) were more abundant (p < 0.05) in cows from the OVXE (2.3 and 5.8%, respectively) than the OVX group (1.4 and 3.7%, respectively). Distribution of LH isoforms in cows from the three groups did not differ (p > 0.10).(ABSTRACT TRUNCATED AT 250 WORDS)

Melengestrol acetate at greater doses than typically used for estrous synchrony in bovine females does not mimic endogenous progesterone in regulation of secretion of luteinizing hormone and 17 beta-estradiol

Our working hypothesis was that doses of melengestrol acetate (MGA) greater than those typically administered in estrous synchrony regimens would regulate secretion of LH and 17 beta-estradiol (E2) as endogenous progesterone (P4) does during the midluteal phase of the estrous cycle. We also hypothesized that endogenous P4 from the CL would interact with MGA to further decrease the frequency of LH pulses and E2. Cows on Day 5 of their estrous cycle (Day 0 = estrus) were randomly assigned to an untreated control group (CONT, n = 5) or to one of six MGA treatment groups (n = 5 per group): 1) MGA administered orally each day via a gelatin capsule at a dose of 0.5 mg MGA/cow with the CL present (0.5CIL); 2) 0.5 mg MGA/cow daily in the absence of CL (0.5NO); 3) 1.0 mg MGA with CL present (1.0CL); 4) 1.0 mg MGA without CL (1.0NO); 5) 1.5 mg MGA with CL present (1.5CL); 6) 1.5 mg without CL (1.5NO). MGA was administered for 10 days (Day 5 = initiation of treatment). To regress CL, cows assigned to groups without CL received injections of prostaglandin F 2 alpha (PGF 2 alpha; 25 mg) on Days 6 and 7 of their estrous cycle. All cows were administered PGF2 alpha at the end of the 10-day treatment period. During the treatment period, daily blood samples were collected to determine concentrations of E2. Serial blood samples were collected at 15-min intervals for 24 h on Days 8, 11, and 14 to determine pattern of LH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Luteinizing hormone has a role in development of fully functional corpora lutea (CL) but is not required to maintain CL function in heifers

We tested the hypothesis that endogenous pulses of LH have a role in development and maintenance of CL during the estrous cycle of the bovine female. Twenty heifers were synchronized to estrus by treating two times with prostaglandin F2 alpha 11 days apart (Day 0 = behavioral estrus). Heifers were then randomly assigned to one of four treatments (n = 5/group). Heifers were treated with an antagonist to LHRH (LHRH-Ant; N-Ac-D-Nal[2]1,4Cl-D-Phe2,D-Pal[3]3,D-Cit6,D-Ala10- LHR H; 10 micrograms/kg body weight) or vehicle (5% mannitol) once every 24 h: 1) LHRH-Ant Days 2-7, 2) LHRH-Ant Days 7-12, 3) LHRH-Ant Days 12-17, 4) no LHRH-Ant (control). Blood samples were collected from the jugular vein twice daily on Days 0-24, and area under the profile of progesterone in circulation during the luteal phase of the estrous cycle was characterized from the start of each treatment period until the demise of CL or Day 24, whichever came first. Luteolysis was considered to have occurred when three consecutive samples contained less than 1 ng progesterone/ml plasma. Areas under the profile of progesterone in circulation during the luteal phase of the estrous cycle were compared to those of heifers from the control group for the same period. LHRH-Ant treatment diminished LH pulses in all treatment groups compared to control (p < 0.05). Treatment with LHRH-Ant on Days 2-7 diminished function of CL (3.72 +/- 0.93 vs. 7.36 +/- 1.02 units, respectively; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Ovarian follicular development in prepubertal heifers is influenced by level of dietary energy intake

Objectives were twofold: 1) to determine the chronology of development of dominant ovarian follicles during the peripubertal period in heifers and 2) to determine whether feeding a diet with low energy content that delays onset of puberty alters chronology of dominant ovarian follicular development in peripubertal heifers. Ten heifers of composite breeding (1/4 Angus, 1/4 Hereford, 1/4 Red Poll, 1/4 Pinzgauer) were randomly assigned, at 8 mo of age, to receive a diet designed to produce 0.9 (n = 5) or 0.3 (n = 5) kg body weight gain per day for the duration of the experiment. To characterize changes in size of ovarian follicles, real-time linear ultrasonography of ovaries was conducted in all heifers every other day until puberty occurred. Blood samples were collected weekly to determine concentrations of progesterone and 17 beta-estradiol. Determination of time of puberty was based on increased concentrations of progesterone, ultrasound depiction of ovulation, and subsequent presence of a corpus luteum. Size of the dominant ovarian follicles differed prior to puberty (p < 0.03); diameter of the dominant ovarian follicle was greater in all heifers as the first ovulation approached as compared to earlier in prepuberty. Heifers fed the greater amount of energy exhibited larger dominant ovarian follicles at a younger age in comparison to heifers fed the lower amount of energy.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential regulation of gonadotropin synthesis and release in ovariectomized ewes after treatment with a luteinizing hormone-releasing hormone antagonist

Our working hypothesis was that synthesis and release of LH, but not FSH, were solely dependent on LHRH. Twenty ovariectomized (OVX) ewes were randomly assigned to one of five treatments (n = 4 per group). Ewes were administered a low (10 micrograms/kg) or high (100 micrograms/kg) dose of LHRH antagonist (LHRH-Ant) at 24-h intervals for 3 or 6 days. Control ewes received vehicle (5% mannitol) at 24-h intervals for 6 days. Blood samples were collected every 15 min for 4 h before LHRH-Ant or vehicle and every 2 h during the period of treatment to determine concentrations of LH and FSH. Twenty-four hours after the last treatment with LHRH-Ant or vehicle, anterior pituitaries were collected and divided in half along the midsagittal plane; the number of receptors for LHRH, pituitary content of LH and FSH, and relative amounts of mRNA for alpha, LH beta, and FSH beta subunits were determined. Concentrations of LH in serum decreased (p < 0.05) from 25.4 +/- 4.3 ng/ml before LHRH-Ant to less than 0.5 ng/ml within 4 h after the first treatment of LHRH-Ant and remained low (< 0.5 ng/ml) throughout the study. Serum concentrations of FSH declined gradually during the 3- or 6-day period of treatment with LHRH-Ant, from 37.3 +/- 2.4 and 26.5 +/- 4.8 ng/ml to 19.9 +/- 1.8 and 13.7 +/- 2.1 ng/ml, respectively. The magnitude of decline in serum concentrations of LH and FSH did not differ among ewes treated with low or high doses of LHRH-Ant.(ABSTRACT TRUNCATED AT 250 WORDS)

Pregnancy rate is greater when the corpus luteum is present during the period of progestin treatment to synchronize time of estrus in cows and heifers

Our hypothesis was that conception in bovine females would be enhanced if the corpus luteum was present during the period of progestin treatment to synchronize estrus. In this study, 67 heifers (one replicate) and 124 cows (two replicates) were randomly assigned to one of two treatment groups. Seven days after estrus (Day 0), all animals were implanted with norgestomet and the implant remained in place for 10 days. All implants were removed on Day 17. Cows and heifers in one group received prostaglandin F2 alpha (PGF2 alpha) on Day 7 of the estrous cycle (PG 7; norgestomet without corpus luteum), and animals in the second group received PGF2 alpha on Day 17 (day of implant removal; PG 17; norgestomet with corpus luteum). All heifers and cows exhibiting behavioral estrus were artificially inseminated 12 h after estrus was detected during a 7-day period following removal of norgestomet. Blood samples were collected from cows of replicate 1 to determine serum concentrations of progesterone and 17 beta-estradiol. Percentage of females that had calves as a result of artificial insemination was greater (p < 0.01) in the PG 17 group (87% and 78% cows [two replicates] and 58% heifers) compared to the PG 7 group (31% and 44% cows [two replicates] and 41% heifers).(ABSTRACT TRUNCATED AT 250 WORDS)

Increasing exogenous progesterone during synchronization of estrus decreases endogenous 17 beta-estradiol and increases conception in cows

The objectives of this study were to determine the effects of dose of exogenous progesterone (P4) prior to artificial insemination on concentrations of 17 beta-estradiol (E2) and on conception rates in bovine females. Heifers (n = 100) and cows (n = 100) received P4-releasing intravaginal devices (PRIDs) to produce two different circulating concentrations of P4. All animals received a single PRID 10 days before (Day-10) the start of the breeding season (Day 0). In animals that received the low dose of P4 (1 PRID, target concentration of 2-3 ng/ml of plasma), the original PRID remained in place for 10 days. In animals that received the larger dose of P4 (2 PRIDs, target concentration of 5-8 ng/ml of plasma), an additional PRID was inserted on Day -9. To maintain concentrations of P4 in the 2-PRID group, the PRIDs inserted on Days -10 and -9 were replaced with new PRIDs on Days -5 and -4, respectively. Prostaglandin F2 alpha (25 mg) was administered to all animals on Days -9 and -3 to remove the endogenous source of P4. Following PRID removal, animals were artificially inseminated 12 h after signs of behavioral estrus were observed. A treatment-by-day interaction (p < 0.0001) was observed for concentrations of P4 in circulation of both heifers and cows. Animals that received 2 PRIDs had greater (p < 0.001) concentrations of P4 by Day-8 of treatment than animals that received 1 PRID. In cows that received 1 PRID, concentrations of E2 increased 2.4-fold from Day-10 (6.8 +/- 1.0 pg/ml) to Day-2 (16.7 +/- 1.4 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Yearling bulls shorten the duration of postpartum anestrus in beef cows to the same extent as do mature bulls

The objective of this study was to determine whether yearling bulls, when pastured with cows, reduced the duration of postpartum anestrus to the same extent as did mature bulls. This experiment was conducted over a 3-yr period. Cows were stratified by parity group to achieve 37% 2-yr-old and 63% mature (> 2-yr-old) cows within each treatment group (approximately 50 cows per treatment per year). Cows were assigned in the order in which they calved to one of three treatment groups: 1) isolated from bulls (NBE; n = 158); 2) exposed to mature bulls that were > 3 yr of age (MBE; n = 154); or 3) exposed to bulls that were 1 yr of age (YBE; n = 152). Beginning the 2nd wk after calving, cows were pastured with either sterile bulls that were 1 yr (YBE) or > 3 yr of age (MBE) (three bulls per treatment group). Blood samples were collected twice weekly from late March until mid-July each year. Cows with serum concentrations of progesterone > 1 ng/mL for two consecutive sampling periods were assumed to have initiated estrous cycles after calving. Duration of postpartum anestrus in cows exposed to yearling bulls (YBE = 61.8 +/- 1.8 d) did not differ (P > .10) from duration of postpartum anestrus in cows exposed to mature bulls (MBE = 59.5 +/- 1.7 d). Duration of postpartum anestrus was shorter (P < .01) for cows exposed to bulls (MBE+YBE = 61.0 +/- 1.7 d) than for cows isolated from bulls (NBE = 72.3 +/- 1.8 d).(ABSTRACT TRUNCATED AT 250 WORDS)

Exogenous progesterone and progestins as used in estrous synchrony regimens do not mimic the corpus luteum in regulation of luteinizing hormone and 17 beta-estradiol in circulation of cows

Our working hypothesis was that the low concentrations of progesterone (P4) and synthetic progestins administered in hormonal regimens to control estrous cycles of cows would have similar effects on secretion of LH and 17 beta-estradiol (E2). In addition, we hypothesized that concentrations of exogenous P4 typical of the midluteal phase of the estrous cycle and the corpus luteum (CL) would have similar effects on LH and E2, and the effects would be different from those of synthetic progestins and low concentrations of P4. Cows (n = 29) were randomly assigned to one of five treatment groups: 1) one Progesterone Releasing Intravaginal Device (1PRID; n = 6); 2) two PRIDs (2PRID; n = 6); 3) norgestomet, as in Syncro-Mate-B regimen (SMB; n = 6); 4) melengestrol acetate (MGA; 0.5 mg/day; n = 5); and 5) control (CONT; n = 6). Treatments were administered for 9 days (Day 0 = initiation of treatment). All cows from 1PRID, 2PRID, SMB, and MGA groups were injected with prostaglandin F2 alpha (PGF2 alpha) on Days 2 and 5 of the treatment period to regress CL. Cows in the 1PRID and SMB groups were also administered exogenous estrogen according to the respective estrous synchronization protocol for these products. Daily blood samples were collected from Day 0 to 35 to determine concentrations of P4. On Day 8, blood samples were collected at 15-min intervals for 24 h to determine pattern of LH secretion. On Day 9, all treatments ceased and cows in the CONT group received injections of PGF2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Circulating gonadotrophins during a period of restricted energy intake in relation to body condition in heifers

Beef heifers, 13 months old, were fed to achieve high (7.6 +/- 0.2 units) or low (3.9 +/- 0.1 units) body condition by feeding them one of two diets for 20 weeks. During week 17 of the growth phase, all heifers were ovariectomized. From week 20 to week 27 (restriction phase), all heifers were fed a daily diet containing 0.071 MJ metabolizable energy kg-1 body weight. At weekly intervals throughout the restriction phase, blood samples were collected at 10-min intervals for 11 h to determine the pattern of secretion of luteinizing hormone (LH), the amount of LH released in response to 750 ng (pituitary responsiveness) and 50 micrograms LH-releasing hormone (LHRH, releasable stores) and mean concentrations of follicle-stimulating hormone (FSH) in the circulation. Body weight declined during the restriction phase in a similar fashion in heifers with high and low body condition and changes in body weight were unrelated to mean concentrations of LH and FSH and frequency of LH pulses. Amplitude of LH pulses and responsiveness to 750 ng LHRH increased in a linear fashion with weight loss in heifers with low but not in those with high body condition. The amount of LH released in response to 50 micrograms LHRH decreased with increasing weight loss in heifers with high but not with low body condition, indicating that releasable pools of LH declined with increased weight loss in heifers with high body condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Steady-state amounts of alpha- and luteinizing hormone (LH) beta-subunit messenger ribonucleic acids are uncoupled from pulsatility of LH secretion during sexual maturation of the heifer

Our primary objective for this study was to determine whether steady-state amounts of alpha- and LH beta-subunit mRNAs in the anterior pituitary are altered during sexual maturation in the bovine female. A secondary objective was to determine whether 17 beta-estradiol (E2) alters amounts of LH subunit mRNAs before onset of puberty. Heifers (7 mo old) were assigned to one of three treatments: 1) ovariectomized (OVX, n = 16); 2) OVX and administered E2 (OVXE, n = 16); or 3) ovary-intact (INTACT, n = 20). Pituitaries were collected at an estimated 120 days before onset of puberty (prepuberty) or 25 days before onset of puberty (peripuberty). Six INTACT heifers were used to determine time of puberty during the experimental period, and their pituitaries were collected 40 h after administration of prostaglandin F2 alpha (postpubertal INTACT group). Relative amounts of mRNAs for LH subunits in each pituitary were determined by Northern analysis and scanning densitometry. Amounts of alpha- and LH beta-subunit mRNAs were lower in pituitaries of INTACT heifers and OVXE heifers, regardless of stage of sexual maturation, than in those of OVX heifers. Amounts of alpha-subunit mRNA were similar in OVXE and INTACT heifers regardless of stage of sexual maturation. Amounts of LH beta-subunit mRNA did not change during sexual maturation in heifers in the INTACT group. Concentrations of E2 were higher and LH beta-subunit mRNA were lower in heifers from the prepubertal OVXE group than in heifers in all other treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)

A similar distribution of gonadotropin isohormones is maintained in the pituitary throughout sexual maturation in the heifer

Our working hypotheses for this study were that 1) the profile of intrapituitary LH and FSH isoforms would be shifted toward acidic forms as sexual maturation progresses in the bovine female; and 2) concentration of 17 beta-estradiol (E2) in circulation during sexual maturation would be a major factor modulating the percentage of the more acidic isoforms. In addition, the biological-immunoreactive (B:I) ratios of each isoform of LH were evaluated at selected stages of sexual maturation. Heifers (7 mo of age) were assigned to one of three treatment groups: 1) ovariectomized (OVX; n = 16); 2) OVX and administered E2 (OVXE; n = 16); or 3) ovary-intact (INTACT; n = 14). Pituitaries were collected from heifers in each group at an estimated 120 days (prepubertal) of 25 days before puberty (peripubertal). A fourth group of 6 heifers remained intact (postpubertal INTACT) to determine time of puberty during the experimental period. Pituitaries of heifers assigned to the postpubertal INTACT group were collected during the follicular phase of the first or second estrous cycle postpuberty. Pituitaries were used for determination of relative amounts of gonadotropin isohormones. Tissue extracts of the pituitaries were chromatofocused on pH 10.5-4.0 gradients. The LH of all pituitaries resolved into thirteen isoforms that were designated isoforms A-L, and S, with isoform A the most basic form. Isoforms F and G (basic pH range) were the predominant isoforms of each chromatofocusing profile and comprised 50-60% of the immunoreactive LH. Isoforms J and K were the major isoforms eluting in the acidic pH range.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of growth rate and exposure to bulls on age at puberty in beef heifers

Two experiments were conducted to test the following hypotheses: 1) exposure of beef heifers to sterile bulls increases the proportion of heifers attaining puberty by 14 mo of age and 2) rate of growth interacts with bull exposure to influence age at puberty in beef heifers. In Exp. I, heifers were assigned to one of two treatments: 1) heifers were exposed to bulls (BE; approximately 70-d period of exposure) or 2) heifers were isolated from bulls (NE) and served as controls. In Exp. II, heifers were assigned to either BE or NE treatments (175-d period of exposure to bulls) and were fed to gain at a moderate (MG; .6 kg/d) or high (HG; .8 kg/d) growth rate. Blood samples were collected twice weekly to determine concentrations of progesterone indicative of onset of corpus luteum function and puberty. In Exp. I a greater (P less than .05) proportion of heifers receiving the BE treatment than of heifers receiving the NE treatment initiated corpus luteum function by 14 mo of age. In Exp. II, there was a bull exposure x growth rate interaction (P less than .05). The effect of bull exposure was greater within the HG groups than within the MG groups. However, heifers fed to attain a moderate or high growth rate and exposed to bulls attained puberty at younger ages than heifers not exposed to bulls and fed to attain a moderate or high growth rate. Mean ages at puberty were 375, 422, 428, and 449 (pooled SEM = 8.6) d for heifers in the BE-HG, BE-MG, NE-HG, and NE-MG groups, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)