Steroidogenesis and prostaglandin synthesis by cultured bovine blastocysts

Bovine blastocysts were collected at Days 13, 15 and 16 and placed in TCM-199 supplemented with 5% fetal calf serum; some blastocysts were immediately frozen while the others were cultured for 48 h and then frozen. Samples (tissue + medium, 5--12/group) were thawed, homogenized and analysed by radioimmunoassays. Measurable amounts of progesterone were found in all blastocysts but values were higher (P less than 0.01) after culture. Testosterone was not found in the cultured or uncultured blastocysts at Day 13, but was detectable on Days 15 and 16 and in greater amounts (P less than 0.05) in the cultured blastocysts. PGF and PGE-2 were increased (P less than 0.05) in the cultured blastocysts in all 3 days. Oestradiol was measurable in some but not all blastocysts. It is suggested that PG synthetase and enzymes capable of synthesizing progesterone, testosterone and, possibly, oestradiol are present in these early bovine blastocysts.

Prostaglandin F2alpha induced luteolysis, hypothermia, and abortions in beagle bitches

Luteal phase plasma progesterone was radioimmunoassayed in samples collected before, during, and after a 72 hr treatment period during which Beagle bitches received repeated i.m. injections of prostaglandin F2alpha (n=17) or saline (n=3). PGF2alpha (20 ug/kg every 8 hr or 30 ug/kg every 12 hr) was administered to 7 pregnant and 8 nonpregnant bitches during the mid or late luteal phase of the cycle (Day 25-58) and to 2 nonpregnant bitches during the early luteal phase (Days 5 and 20). Progesterone was depressed from pretreatment levels (3-40 ng/ml) in each of the 15 bitches given PGF2alpha after Day 25 of the cycle. Mean progesterone (ng/ml plasma) at -24, 0, 12, 24, 36, 48, 60, 72 and 96 hr from the initial PGF2alpha injection were 16.6, 15.6, 9.3, 5.1, 2.1, 1.5, 1.4, 1.1 and 1.1 (+/- 0.9, n=15). Thereafter, progesterone was nondetectable in the 8 nonpregnant bitches and in 4 pregnant bitches that aborted. Abortions occurred when progesterone was depressed to 0.6-1.4 ng/ml, 56-80 hr after starting PGF2alpha treatment on Days 33-53 of the cycle. Three pregnant bitches did not abort when progesterone was depressed to a mean low value of 2.1 ng/ml during PGF2alpha treatments begun on Day 31-40 of pregnancy. Progesterone in these bitches recovered to 5-10 ng/ml and was maintained until the normal prepartum decline. Since PGF2alpha can induce complete luteolysis it may be of use as an abortifacient in the bitch. A transient fall in rectal temperature occurred in each of 12 luteal phase bitches injected with PGF2alpha (20 ug/kg, i.m.). The hypothermia was detectable within 15 min, maximal at 45-60 min, and averaged 1.39 degrees similarly treated. In six luteal phase bitches, plasma progesterone fell 20-45% within the 15 min required to observe a consistent decline in rectal temperature following PGF2alpha administratic effect and dependent on a fall in progesterone.

Hormonal changes associated with experimentally produced cystic ovaries in the cow

Cystic ovaries were experimentally produced by i.m. injection of 5 mg oestradiol valerate on Day 16 of the oestrous cycle or by s.c. injection of 100 ml antiserum to bovine LH before the onset of oestrus. The length of the cycle after both treatments was altered. The cysts formed after oestradiol injection were relatively small (2-5-3 cm diameter) and thin-walled, and were accompanied by relatively low plasma oestrone and high oestradiol levels; those after LH antiserum treatment were large (5-0-6-0 cm) and firm and associated with relatively low oestradiol and high oestrone levels. The results of the hormone assays after treatment support the theory that cystic ovaries could result from premature LH release or an insufficiency of LH at the time of ovulation.

Steroid synthesis by ovarian follicles in response to LH and PGF2alpha

Ovarian follicles isolated from bovine ovaries at the 16th and 17th days of the estrous cycle were minced, pooled, and incubated in Krebs-Ringer bicarbonate buffer at 37degrees for 2 hr. Samples were analyzed for testosterone, estrogens, and progesterone by radioimmunoassays. Incubation alone failed to cause an increase in testosterone (12.1 vs 29.3 ng/g of tissue; P is greater than 0.05). Additions of 5 mug/ml of bovine LH or prostaglandin F2alpha caused increases in testosterone synthesis to 125.0 (Pis less than 0.01) and 103 ng/g (P is less than 0.01). Estradiol synthesis was also stimulated by LH (P is less than 0.01). However, stimulation due to addition of PGF2alpha (5.1 to 15 ng/g) was not significant (P is greater than 0.05). PGF2alpha also caused a slight but nonsignificant increase in estrone secretion. Incubation failed to increase the progesterone concentration (623 vs 774 ng/g of tissue; P is greater than 0.05). There was no increase in progesterone synthesis due to addition of either LH or PGF2alpha (P is greater than 0.05). The results show that bovine follicles produce much more testosterone than estrogen and that both LH and PGF2alpha significantly stimulate testosterone synthesis in bovine follicular tissue without increasing net progesterone biosynthesis.

Lipoprotein lipase activity in the bovine corpus luteum during the estrous cycle and early pregnancy

Lipolytic activity measured at pH 8.6 in bovine corpora lutea exhibited classical properties of lipoprotein lipase (LPL) in terms of serum and heparin stimulation and NaCl inhibition. LPL activity was measured in 23 corpora lutea collected at different stages of the estrous cycle and early pregnancy. The LPL activity in cyclic corpora lutea (mumole FA released/hr/100 mg acetone powder) was low at Days 4-8 of the estrous cycle (3.1 +/- 1.5: mean +/- SE) and at Days 19-20 (1.6 +/- 0.6). However, high activity of the enzyme was found at Days 12-15 of the cycle (11.8 +/- 1.8); these concentrations were significantly (P less than 0.01) elevated over those found at Days 4-8 and 19-20. The enzyme activity began to decline at Days 16-18 of the estrous cycle (5.1 +/- 1.7). Low enzyme activity was found in the corpora lutea removed from two cows at Day 22 of pregnancy. Progesterone concentrations were measured in 16 of the 23 corpora lutea and a good correlation (r = 0.75, P less than 0.01) was found between lipoprotein lipase and progesterone concentrations of the tissue. The data suggest that LPL may be involved in controlling the transfer of fatty acids, including arachidonic, from plasma lipoproteins to luteal tissue.

Influence of human chorionic gonadotropin on pregnancy rates in lactating dairy and beef cows

Single subcutaneous injection of 1500 IU human chorionic gonadotropin or placebo injections were given at the time of insemination in lactating dairy and beef cows to determine their effects on rates of pregnancy. Pregnancy rates at first service in 161 control and 145 treated dairy cows were 52.8% and 44.8%, respectively. Similar rates for 136 control and 145 treated beef cows were 54.4% and 54.5%. Injections of human chorionic gonadotropin were not effective in stimulating conception rates in lactating dairy or beer cows under field conditions.

Plasma growth hormone and insulin during early lactation in cows fed silage based diets

Peripheral plasma insulin, growth hormone, and blood glucose were determined in 24 dairy cows during early lactation. Blood samples were obtained at 4-day intervals during the first 56 days of experimental lactations 1 and 3 of a 3-lactation experiment. The cows were divided equally among three groups and fed one of the following forage rations for three consecutive lactations: corn silage (18.2 kg/day) plus alfalfa-timothy hay ad libitum; corn silage (18.2 kg/day) plus alfalfa-timothy silage ad libitum; or corn silage ad libitum. These diets were continued throughout the intervening dry periods except in the latter group where corn silage intake was limited if individual animals exhibited excessive body weight gain. Four animals in each group received prepartum supplemental concentrates. The remaining four animals received no prepartum concentrate supplementation. Following parturition, concentrates were fed in increasing amounts to a maximum of 14.6 kg/day during the first 56 days of lactation. Plasma insulin, growth hormone, and blood glucose were not affected by forage diet or prepartum supplemental concentrate feeding. Plasma insulin and blood glucose increased and plasma growth hormone decreased with time after parturition. These changes were correlated with nutrient intake which increased during the experiment. Changes in plasma insulin and growth hormone are related to metabolic adjustments during early lactation.

Plasma adrenocorticoid response to corticotropin in dairy cattle fed high silage diets

Responses of plasma corticoids to adrenocorticotropic hormone (.32 U/kg body weight) administered during early lactation were measured in dairy cattle consuming large amounts of concentrate feeds and one of the following forage diets: alfalfa-timothy hay plus corn silage, alfalfa-timothy hay crop silage plus corn silage, or corn silage. Concentrations of plasma corticoids increased to maximum in all groups within 60 to 90 min. Concentrations remained at near maximum for 4 to 5 h and then declined to baseline. Maximum corticoid concentrations following adrenocorticotropic hormone injection differed among forage treatment groups. Responses of corn silage and hay crop silage groups (46.7 +/- 1.1 and 50.1 +/- 2.4 ng/ml) did not differ but were less than those in the hay group (65.5 +/- 2.9 ng/ml). Response measured as area under the curve of plasma corticoid response also differed among forage treatments: hay 443 +/- 17 h (ng/ml) is greater than hay crop silage 334 +/- 34 is greater than corn silage 245 +/- 36. Results are discussed in terms of stress susceptibility in dairy cattle consuming diets containing large amounts of silage.

Arachidonic acid and bocine corpus luteum function (38514)

Injections of arachidonic acid directly into the corpora lutea of normal cattle at the 12th or 13th day of the estrous cycle resulted in (a) a decline in jugular vein plasma progesterone levels from an average of 6 ng/ml to 2.5 ng/ml (p smaller than0.05), (b) an immediate rise in PGF levels in ovarian venous plasma, and (c) a sharp rise in jugular vein plasma estrogen levels. Jugular plasma estrogen peaks were associated with each ovarian vein PGF Peak in each animal; jugular plasma LH levels did not change. These results show that the bovine ovary can convert arachidonic acid to PGF and that arachidonic acid administered directly into the corpus luteum results in partial regression of the corpus luteum.PGF appears to stimulate estrogen production by the ovary in the absence of measurable changes of plasma LH.

Levels of prostaglandin F (PGF) in bovine endometrium uterine venous, ovarian arterial and jugular plasma during the estrous cycle (38789)

Prostaglandins F (PGF) were measured in uterine vein, ovarian artery, and jugular vein plasma and in the endometrial tissues at various times during the bovine estrous cycle, and were compared to peripheral plasma progesterone levels. Four groups of heifers at days 1-5, 10-14, 15-17 and 20-0 of the estrous cycle were studied. Low levels of PGF (48 plus or minus 12 ng/g dry tissue were measured in the endometrium on days 1-14 of the cycle. Higher values (131 plus or minus 9.0) were found at days 15 until the day of estrus (p less than 0.001). Similarly, very low levels of PGF were observed in the uterine vein plasma at days 1-14 (0.162) plus or minus 0.044) ng/mlM plus or minus S.E.), whereas on days 15 until the day of estrus the levels ranged from 1.5 to 3.0 ng/ml. The increases in uterine vein PGF on day 15 occurred even while peripheral plasma progesterone levels were still high. However, PGF was not elevated in either the ovarian artery or the jugular vein at any time during the cycle, even when uterine vein levels were greatly elevated. No differences in PGF content were detected in endometrial tissue from uterine horns adjacent or opposite to the functional corpus luteum.

Survival and gonadotrophin responsiveness of luteal cells in vitro

Simplified methods for incubating luteal tissues have been developed. Progesterone biosynthesis in washed, minced bovine luteal tissue is stimulated by added bovine LH. The response is linear in the range 2–200 ng added LH per ml of medium. The use of covariance analysis to correct for differences in time elapsing between mincing the tissue and the beginning of incubation reduces the standard error of the mean and results in marked improvement in the indices of precision. Progesterone biosynthesis in washed, minced bovine luteal tissues appears specific for LH; no other pituitary hormones give a response, and the response is completely negated by adding anti-bovine LH serum to the incubation medium. Prior treatment of cattle from which the incubated corpora lutea are obtained with various levels of human chorionic gonadotrophin, results in greatly increased luteal tissue weights. However, this tissue has a markedly reduced sensitivity to LH added in vitro. No conclusive evidence was found for a feedback inhibition of progesterone on its own synthesis in this system. The incubation system developed is sensitive enough to serve as a bioassay for LH in biological tissues and fluids. Preliminary data suggest that a simplified protein binding assay can be successfully used to measure the progestins synthesized by minced, washed bovine luteal tissue in response to added bovine LH.