Amplified androstenedione enzymeimmunoassay for the diagnosis of cryptorchidism in the male horse: comparison with testosterone and estrone sulphate methods

An amplified enzymeimmunoassay (EIA) was validated for androstenedione in the serum of male horses. We will use the assay as a tool for the diagnosis of equine cryptorchidism. We will compare androstenedione EIA to the currently used methods (testosterone and estrone sulphate determinations). The study was conducted on 115 horses of pure Spanish and Arabian breeds, that included 30 geldings, 60 bilateral cryptorchids and 25 stallions. Androstenedione standard curve covered a range between 0 and 1 ng per well. Low detection limit was 1.54 pg/ml. Intra- and inter-assay coefficients of variation (CV%) were <8.2 and <9.3, respectively (n=10). Recovery rate of known androstenedione concentrations averaged from 96.62+/-2.69 to 97.63+/-1.87%. Androstenedione mean+/-S.E. serum concentrations were 10.52+/-1.36 ng/ml in stallions (n=25), 0.51+/-0.04 ng/ml in cryptorchids (n=60), and 0.03+/-0.01 ng/ml in geldings (n=30). Diagnostic validation parameters in basal samples showed for estrone sulphate the lower positive predictive value (0.85) with the higher number of false positives, and lower specificity (0.84). Testosterone showed the higher number of false negatives with a negative predictive value of 0.85, and lower sensitivity (0.85). Among the three hormones evaluated, androstenedione presented the best results with the smaller number of horses diagnosed as false positives (0.93) or negatives (0.91). This technique also resulted in higher sensitivity, specificity and efficiency over the other two methods assayed. We concluded that our amplified EIA is a highly sensitive and specific assay that provides a rapid, simple, and inexpensive alternative to other methods.

Measurement of serum and peritoneal fluid LH concentrations as a diagnostic tool for human endometriosis

A rapid, sensitive enzymeimmunoassay for the measurement of LH concentrations in serum and peritoneal fluid samples of healthy women and women with endometriosis is reported. The ligand (LH) was captured by a readily available, widely used and well-characterized monoclonal antibody (mAb, 518B7) generated against the beta subunit of bovine LH. This mAb, although specific for LH, shows very little species specificity and detects LH by radioimmunoassay in humans. A polyclonal antiserum raised in rabbits against hCG was conjugated to horseradish peroxidase and was used as the second antibody signal. This anti-hCG antiserum crossreacts with LH. The enzymeimmunoassay uses the standard human LH (hLH) preparations (NIADDK-hLH-I-3, AFP-827OB) and results are based on the relative concentrations of LH in serum and peritoneal fluid. Total assay time was < 3 h. The range of the standard curve was 0.002-0.500 ng LH per well and the lowest concentration of hLH that could be distinguished from zero concentration was 0.15 +/- 0.02 ng ml(-1) serum and 0.058 +/- 0.021 ng ml(-1) peritoneal fluid. Clinical diagnostic parameters for the LH enzymeimmunoassay showed a sensitivity of 85.71%, specificity 92.50%, efficiency 88.54%, positive predictive value 94.11% and negative predictive value 82.22%. The study was retrospective. Serum LH concentrations of women with endometriosis were 13.67 +/- 7.21 ng ml(-1), whereas serum LH concentrations of women in the control group were 4.52 +/- 2.03 ng ml(-1). One-way ANOVA showed significant differences (P < 0.001) between women with endometriosis and control groups. Women in the control group had peritoneal fluid LH values of 5.65 +/- 2.43 ng ml(-1), whereas peritoneal fluid LH values of 64.06 +/- 16.44 ng ml(-1) were obtained in women with endometriosis (P < 0.001). A cycle-dependent pattern of serum and peritoneal fluid LH concentration was observed in women in the control group, which was not observed in the peritoneal fluid of the group with endometriosis. The application of this assay to serum or peritoneal fluid samples provides the attractive possibility that it could be included in the panel of markers used for diagnosis of endometriosis.

Changes in rates of salivary estriol increases before parturition at term

OBJECTIVE

The aim of this study was to characterize the increases of salivary estriol concentrations before the onset of labor at term.

STUDY DESIGN

Salivary estriol concentrations were measured in weekly patient-collected samples by means of a sensitive (mean +/- SD threshold, 0.025 +/- 0.001 ng/mL; coefficient of variation, 3.8%) direct enzyme immunoassay in a microtiter plate format. The salivary estriol concentrations in 16 healthy pregnant women were characterized from 30 weeks' gestation until the time of parturition and delivery. Samples were stored frozen at collection and analyzed in batches after delivery.

RESULTS

The median salivary estriol concentration profile revealed a nonlinear rise beginning from 30 weeks' gestation (0.89 ng/mL) until term (2.70 ng/mL, an increase of 201%). At 35 weeks' gestation the salivary estriol concentration median value increased sharply (positive inflection point, 50%-93% increase) at a demarcation between a slower increase during early pregnancy and a more rapid increase during late pregnancy. This positive inflection point associated with a late pregnancy increase characterized subgroups of pregnancies according to the lengths of gestation as follows: early term (delivered at <38 weeks 1 day's gestation), middle term (delivered at 38 weeks 1 day-40 weeks' gestation), and late term (delivered at >40 weeks' gestation). Five weeks before delivery the mean (+/-SEM) rate of rise in salivary estriol concentration was 0.50 +/- 0.13 ng/mL per week to 0.84 +/- 0.26 ng/mL per week in the early term group. The increase in rate for the middle term group was 0.32 +/- 0.06 ng/mL per week to 0.37 +/- 0.26 ng/mL per week, whereas in the late term group the rate of salivary estriol concentration rise was 0.37 +/- 0.03 ng/mL per week to -0.03 +/- 0.25 ng/mL per week.

CONCLUSION

These data demonstrate in normal pregnancies (1) that a direct, nonradiometric measure of salivary estriol concentration can be used to monitor the late pregnancy increase in estriol production, (2) that 35 weeks' gestation marks a positive inflection point of the onset of increased estriol production, and (3) that the late pregnancy rise in salivary estriol concentration shows distinct patterns that tend to be characteristic of the length of pregnancy. These data support the concept that the rate of increase of estriol production is related to the timing of the onset of labor.

ELISA for the measurement of serum and urinary chorionic gonadotropin concentrations in the laboratory macaque

A rapid, sensitive, enzyme-linked immunosorbant assay (ELISA) for the measurement of chorionic gonadotropin (CG) in serum and urine samples of laboratory macaques is reported. The ligand (CG) is captured by a readily available, widely used, and well-characterized monoclonal antibody (Mab, 518B7) generated against the beta subunit of bovine luteinizing hormone (LH). This Mab, while specific for LH, shows very little species specificity, and has been shown to detect LH and CG by radioimmunoassay (RIA) in both human and non-human primates. A polyclonal antiserum raised in rabbits against human chorionic gonadotropin (hCG) is conjugated to horseradish peroxidase, and is used as the second antibody signal. This anti-hCG antiserum cross reacts with CG secreted by both the human (hCG) and macaque (mCG). The ELISA utilizes hCG as the standard, and results are based on the relative concentrations of mCG in serum and urine. Total assay time is less than 5 hours. Range of the standard curve is 0.002 to 0.5 ng hCG/well, and the least detectable concentration of hCG is 0.0023 +/- 0.0007 ng/well. Pregnancy was detected in early pregnant macaques (M. fascicularis) on 9 (N = 1/16), 10 (N = 1/16), 11 (N = 1/16), 12 (N = 6/16), 13 (N = 1/16), 14 (N = 4/16), and 15 (N = 2/16) days following the pre-ovulatory urinary estrone conjugate peak. The detection of pregnancy by urinary mCG occurred approximately 24 to 72 hours after its detection in serum.

Oxytocin release and its relationship to dihydro-15-keto PGF2alpha and arginine vasopressin release during parturition and to suckling in postpartum mares

Pituitary blood was collected from the intercavernal sinus in five mares before and during parturition, and in nine mares immediately after parturition to investigate oxytocin patterns during parturition and early lactation, and to determine the relationship between oxytocin, prostaglandin and arginine vasopressin during parturition. In four mares in which sample collection began at least 6 h before rupture of the chorioallantois, a significant increase (P < 0.05) in PGF(2alpha) concentration was detected before a significant increase in oxytocin concentration. Cross-correlation analysis of log-transformed oxytocin and PGF(2alpha) concentrations revealed a significant correlation (P < 0.05) at a 6 min lag period, indicating that in the 2 h before delivery of the foal, an increase in prostaglandin was followed 6 min later by an increase in oxytocin. A significant effect of suckling on oxytocin release by the mare was detected in only two of nine mares, when oxytocin concentrations were evaluated 0-3 min after suckling. When foals were prevented from sucking for 1 h, by being either muzzled (n = 2) or separated from the mare (n = 2), there was no significant association between resumption of suckling and oxytocin release by the mare. The results of these studies show that: (i) oxytocin secretion from the maternal posterior pituitary gland begins before, or in association with, the onset of the second stage of labour, and that prostaglandin increases in the peripheral circulation before oxytocin release; and (ii) suckling is not significantly related to oxytocin release in mares.

Rapid enzyme immunoassay for measurement of bovine progesterone

Reproductive management is a primary financial concern of the dairy industry with missed estrus detection one of the major causes of lost income. A rapid enzyme immunoassay (EIA) was developed for on-line measurement of progesterone in bovine milk with a biosensor for detection of estrus. The EIA was developed using covalent binding microtiter wells, monoclonal antibody, horseradish peroxidase, and 3,3',5,5'-tetramethylbenzidine (TMB). The EIA took 8 min and had a dynamic response for progesterone in buffer and milk between 0.2 and 20 ng/ml.

Steroid-level response to insulin-like growth factor-1 in oocytes matured in vitro

The objective was to establish the influence of insulin-like growth factor-1 (IGF-1) on steroid production and nuclear maturation during oocyte in vitro maturation (IVM). Immature-selected rabbit follicular oocytes, divided as cumulus-oocyte complexes (COC) and denuded oocytes (DO), were cultured in Brackett's medium with different concentrations of IGF-1 at 0, 50, 100 and 200 ng/ml. After 8 and 16 h of culture, the oocytes were assessed for nuclear maturation by acetic-orcein stain, and media were analyzed by enzyme-immunoassay (EIA) for 17 beta-estradiol (E), progesterone (P), androstenedione (A) and testosterone (T) content. After culture treatments with IGF-1 significantly increased (P < 0.01) the incidence of nuclear activation (germinal vesicle breakdown stage, GVBD) and nuclear maturation (metaphase II stage); maximum stimulation occurred at 100 ng IGF-1/ml (86.9 vs. 49.3% in control). Compared to controls, the presence of IGF-1 in cultures was associated with a significant increase of E and A production by COCs (P < 0.01). However, P and T levels were not significantly influenced by the IGF-1. In addition, positive correlations between E/T and E/A ratios and nuclear maturation rates were only found in the IGF-1 treatments. Regarding the DOs, neither positive effects in nuclear maturation rates nor increase of steroid levels in culture were observed for any treatment. These results suggest that: (1) IGF-1 had a significant effect on E and A production during oocyte maturation; (2) the addition of IGF-1 enhanced nuclear maturation significantly in rabbit oocytes; and (3) all these effects are only possible in oocytes surrounded by cumulus cells.

A sensitive EIA for 17 beta-estradiol and progesterone in culture medium for oocyte in vitro maturation procedures

A sensitive heterologous enzyme immunoassay (EIA) was validated to determine 17 beta-estradiol (E2) and progesterone levels, without previous extraction, in culture medium from rabbit oocytes matured in vitro with and without the addition of IGF-I. Polyclonal E2 (C902), and progesterone (C914) antibodies were raised in rabbits using 6-keto-17 beta-estradiol 6-carboxymethyloxime:BSA, and 11 alpha-hydroxyprogesterone 11 alpha-hemisuccinate:BSA. Horseradish peroxidase was used as label, conjugated to 17 beta-estradiol 3-hemisuccinate, and to progesterone 3-carboxymethyloxime. Standard dose response curves covered a range between 0 and 1 ng/well (100 microliters). The low detection limits of the technique were 1.99 pg/well for E2, and 13.21 pg/well for progesterone. Intra- and interassay coefficient of variation percentage (% CV) were < 6.3 and < 7.8 for E2 and progesterone, respectively (n = 10). The recovery rate of known E2 or progesterone concentrations added to a pool of culture maturation medium averaged 96.39%, and 98.65%, respectively. Compared with RIA, EIA values were in close agreement for E2 (n = 15, R = 0.96, P < 0.001), and progesterone (n = 15, R = 0.99, P < 0.001). Medium samples were obtained after oocyte maturation in vitro for 16 h. Use of IGF-I significantly elevated steroids production in the oocyte surrounded cumulus cells. The EIA described here is highly sensitive and specific assay, and provides a rapid, simple, inexpensive, and non-radiometric alternative to RIA for determining E2 and progesterone levels in oocyte culture medium.

Enzyme immunoassay for testosterone and androstenedione in culture medium from rabbit oocytes matured in vitro

Two enzyme immunoassays (EIAs) were validated to determine testosterone and androstenedione levels in culture medium (Brackett's medium with or without the addition of IGF-I, hormone and serum-free), without previous extraction, from rabbit oocytes matured in vitro. Polyclonal testosterone (C917), and androstenedione (C9111) antibodies were raised in rabbits using testosterone 3-carboxymethyloxime:BSA, and androstenedione 3-carboxymethyloxime:BSA. Horseradish peroxidase was used as label, conjugated to testosterone 3-carboxymethyloxime, and to androstenedione 6-hemisuccinate. Standard dose response curves covered a range between 0 and 1 ng/well. The low detection limits of the technique were 11.43 pg/ml for testosterone, and 2.32 pg/ml for androstenedione. Intra- and inter-assay coefficient of variation percentages were < 6.4 and < 7.1 for testosterone, and < 5.1 and < 6.3 for androstenedione, respectively (n= 10). The recovery rate of known testosterone or androstenedione concentrations added to pools of culture maturation medium samples averaged 97.58 +/- 2.11%, and 95.73 +/- 1.59%, respectively. Compared with RIA, EIA values were in close agreement for testosterone (n= 15, r= 0.96, P< 0.001), and androstenedione (n= 15, r= 0.94, P< 0.001). Culture medium samples were obtained at the end of oocyte in vitro maturation (14-16 h). Mean +/- SE culture maturation medium concentrations (ng/ml) were 1.80 +/- 0.09 and 0.52 +/- 0.01 for testosterone, and 1.70 +/- 0.04 and 0.24 +/- 0.01 for androstenedione in both the oocytes with and without cumulus cells, respectively. We concluded that our EIA is a highly sensitive and specific assay that provides a rapid, simple, inexpensive and nonradiometric alternative to RIA for determining testosterone and androstenedione concentrations in oocyte maturation culture medium.

An enzyme immunoassay for serum and urinary levonorgestrel in human and non-human primates

A microtiter plate enzyme immunoassay (EIA) is reported for the measurement of levonorgestrel (LNG) in serum and urine samples of human and non-human primates, and the results are compared to data obtained by radioimmunoassay (RIA). Rabbit polyclonal antibodies were raised against the bovine serum albumin conjugate of the 3-O-carboxymethyl oxime (CMO) derivative of LNG. The enzyme label was produced by the conjugation of horseradish peroxidase to LNG at the 3-position by the same CMO bridge used for the immunogen. The assay requires 2.5 hours to perform using 2.2-azino-di-(3-ethylbenzthiazoline sulfonic acid) diammonium salt as the chromogenic substrate. Serum (100 microliters) is extracted with petroleum ether prior to assay, whereas urine samples (25 microliters) are diluted and measured directly. The sensitivity of the assay is 0.25 pg/well with a 50% displacement of label at 7.5-9.5 pg and a linear response through 250 pg/well. Minimum levels of 8.7 and 10.0 pg/ml can be detected in serum and urine samples, respectively. Changes in serum LNG concentrations were measured in women and non-human primates following LNG implantation or injection. In the non-human primate study, serum LNG concentrations began to rise rapidly following i.m. injection of LNG, with peak levels occurring on days 3 to 5, then decreasing to approximately 25-35% of peak levels for the duration of the study. Circulating concentrations of 1.86 +/- 0.18 ng/ml LNG were reached in women the first week post-insertion of Norplant implants and decreased by 50% at 7-10 days, 75% after 14-21 days, followed by a steady decrease during the next 60-70 days to constant low levels that exhibited a high individual variation. Correlation coefficients of EIA and RIA results were 0.988 for human serum, 0.926 for human urine, and 0.972 for non-human primate serum.

Development of a simple, rapid sandwich enzyme immunoassay for the measurement of serum rat LH

The present study describes the development and validation of a rapid, sensitive, specific and precise enzyme immunoassay (EIA) sandwich suitable for measuring luteinizing hormone (LH) in rat serum. Ninety-six well polystyrene microtiter plates were coated with 100 microliters (250 ng/ml) of a well-characterized monoclonal antibody (518B7, Roser, UC Davis) generated against bovine LH. A polyclonal antiserum raised in rabbits against ovine FSH (G4-215B, Papkoff) was conjugated to sodium periodate-activated horseradish peroxidase (HRP), and used as the second antibody of the sandwich assay. This anti-ovine FSH antiserum cross-reacted more than 200% with rat LH. Standards (r-LH-RP-3, NIADDK, range 0 pg/well to 2.5 ng/well or 100 microliters) diluted in a 3(N-Morpholino) propane sulfonic acid (MOPS) buffer, or serum, were incubated with the solid phase antibody for 2 hours. Plates were washed and the anti-oFSH:HRP (100 microliters) in MOPS buffer was added and incubated a further 2 hours before a second wash and the addition of the substrate (TMB, 3,3',5,5'-tetramethylbenzidine dihydrochloride and H2O2). The least detectable concentration of LH was 16.1 +/- 1.42 pg/ml. The recovery of known concentrations of LH added to several samples was 93.5 +/- 1.70%. Mean intra-assay and inter-assay coefficients of variation (%) were less than 10% (n = 20). The anti-FSH:HRP showed less than 8.0% cross reactivity with rFSH in this LH EIA system. The correlation coefficient (r) of samples analyzed by EIA in parallel with RIA was r = 0.90 (p < 0.001, n = 26). Results showed levels between 105.21 and 633.87 pg/ml. This new LH EIA sandwich offers a stable, rapid, and improved EIA system for the measurement of serum LH concentrations of this species over previously reported methods.

Urine and fecal sample collection on filter paper for ovarian hormone evaluations

A practical method for collecting, storing, and transporting liquid biological samples in a dry state for subsequent hormone metabolite analyses is presented. This method employs the use of ordinary filter paper strips that imbibe liquid samples. Samples taken up by the filter paper were allowed to dry and were retained at ambient conditions in capped vials for up to 5 years prior to analysis. Examples presented in the present report include urine samples from human and nonhuman primates as well as solubilized fecal samples from nonhuman primates. Hormone metabolite analysis of the paper-stored samples provided data that were comparable to the results obtained from analyses of the original liquid samples. One year of storage had no effect on hormone concentration. Five years of storage resulted in concentrations that were quantitatively less but qualitatively similar to the concentrations obtained by direct analysis of the initial samples. These data demonstrate the versatility and reliability of paper as a matrix for biological samples that may provide a more convenient approach for collecting and transporting samples collected in the field. © 1995 Wiley-Liss, Inc.

A prototype for ovulation detection: pros and cons

A noninstrumented enzyme immunoassay for urinary estrone conjugates was adapted from an instrumented microtiter plate enzyme immunoassay assay. The end point of the assay was a color change from green to clear, which was visible to the unaided eye. The visible color change was adjusted to allow 80 ng/ml estrone conjugates (on the basis of a sample size of 6.5 microliters urine) to be distinguished from an infinite dilution without instrumentation. The evaluation of human urine collected from ovulatory ovarian cycles demonstrated that early follicular phase concentrations (35.9 +/- 6.8 to 79.4 +/- 14.7 ng/ml, n = 10) produced a dark-green color, whereas late follicular phase concentrations (162.9 +/- 20.1 ng/ml, n = 10) produced no color. Daily urine samples throughout 10 ovulatory ovarian cycles produced parallel profiles when compared to measurements of estradiol in paired blood samples. Complete analysis of the data indicated that ovarian follicular dynamics can be accurately monitored through the noninstrumented analysis of daily estrone conjugates in urine samples.

Relationship of serum estradiol and progesterone concentrations to the excretion profiles of their major urinary metabolites as measured by enzyme immunoassay and radioimmunoassay

Paired daily blood and urine samples were collected from 10 apparently healthy premenopausal women to compare the hormone profiles of estradiol (E2) and progesterone in serum with those of estrone conjugates (E1Conj) and pregnanediol-3-glucuronide (PdG) in urine. Serum hormones were measured by radioimmunoassay (RIA) kits, whereas the urinary steroid metabolites were assessed by both RIA and enzyme immunoassay (EIA). RIA and EIA values for urinary E1Conj and PdG were not different, and both methods produced urinary profiles that paralleled the profile of the parent steroid in serum. However, the simplicity, flexibility, and economy of EIA will make this method more widely applicable. Mean E1Conj values lagged behind concentrations of serum E2 by one day or less, whereas daily urinary PdG profiles lagged behind serum progesterone by one to two days. Mean urinary profiles of E1Conj were similar whether or not creatinine was used to adjust for urine volume; however, creatinine indexing was beneficial when urinary profiles in individual cycles were compared with changes of serum E2.

Relationship of serum estradiol and progesterone concentrations to the excretion profiles of their major urinary metabolites as measured by enzyme immunoassay and radioimmunoassay

Paired daily blood and urine samples were collected from 10 apparently healthy premenopausal women to compare the hormone profiles of estradiol (E2) and progesterone in serum with those of estrone conjugates (E1Conj) and pregnanediol-3-glucuronide (PdG) in urine. Serum hormones were measured by radioimmunoassay (RIA) kits, whereas the urinary steroid metabolites were assessed by both RIA and enzyme immunoassay (EIA). RIA and EIA values for urinary E1Conj and PdG were not different, and both methods produced urinary profiles that paralleled the profile of the parent steroid in serum. However, the simplicity, flexibility, and economy of EIA will make this method more widely applicable. Mean E1Conj values lagged behind concentrations of serum E2 by one day or less, whereas daily urinary PdG profiles lagged behind serum progesterone by one to two days. Mean urinary profiles of E1Conj were similar whether or not creatinine was used to adjust for urine volume; however, creatinine indexing was beneficial when urinary profiles in individual cycles were compared with changes of serum E2.

Prolactin response in beef cows and heifers suckling one or two calves

Blood was collected, at 5-min intervals for 3 h, via jugular cannulation every 14 days during the first 4 months post partum from beef cows and heifers, 4 suckling 2 calves and 4 suckling 1 calf. Calves were isolated from the dams to prevent suckling for approximately 4 h before and 2 1/2 h during sampling to obtain baseline values for prolactin, measured by radioimmunoassay. During the last 30 min of sampling, calves were allowed to suck. Milk samples were also collected at 28-day intervals from 60 females, 30 with twins and 30 with single calves. beginning 2 weeks after calving and continuing until calves were weaned at 180 days of age. No differences were observed between dams with 1 and 2 calves for baseline plasma prolactin level or for prolactin response to the suckling stimulus by 1 or 2 calves. However, milk prolactin concentration was significantly higher (P less than 0.01) for dams with 2 calves, probably reflecting the more frequent suckling that occurs with twins. Milk prolactin value in this study was not highly correlated with the post-partum interval to first ovulation from another study on these animals. It is concluded that prolactin is not significantly higher (P less than 0.01) for dams with 2 calves, probably reflecting the more frequent suckling that occurs with twins. Milk prolactin value in this study was not highly correlated with the post-partum interval to first ovulation from another study on these animals. It is concluded that prolactin is not significantly higher (P less than 0.01) for dams with 2 calves, probably reflecting the more frequent suckling that occurs with twins. Milk prolactin value in this study was not highly correlated with the post-partum interval to first ovulation from another study on these animals. It is concluded that prolactin is not the primary factor controlling the longer post-partum interval to first ovulation in beef cattle with twins.

Photoperiod induction of fertile oestrus and changes in LH and progesterone concentrations in yearling dairy goats (Capra hircus)

Oestrus and ovulation were induced in a group of 19 yearling dairy goats which had been maintained for 70 days on a 19 h/day photoperiod regimen. Six yearling females, raised under natural photoperiod, served as controls. An intact, light-treated male was introduced to each group 42 days after termination of the artificial lighting. Behavioural, endocrine and kidding observations indicated that 15 of the experimental females (79%) ovulated within 21-30 days after introduction of the male, that 12 (63%) conceived at the induced ovulation, and that 10 (53%) gave birth to live kids, while none of the controls ovulated during this time. The breeding season was advanced between 60 and 80 days. In experimental and control nannies there was a brief, small surge (320 +/- 42 pg/ml) of plasma progesterone which occurred 19.5 days after introduction of the male and which closely preceded oestrus in the nannies that ovulated and at 25 days in control females. Ovulatory surges of LH (to 70 ng/ml plasma) were closely associated with oestrus, and remained above basal levels for 9.0 +/- 0.75 h, in 7 experimental females. Two of 6 control nannies also showed LH surges but they did not ovulate.

Circa-annual rhythms of prolactin secretion in ewes and the effect of pinealectomy

Changes in the plasma concentration of prolactin in intact, pinealectomized, shampinealectomized, ovariectomized and hysterectomized ewes were investigated over a period of 11 months.

The concentrations of prolactin were consistently low (<20 ng/ml) during the winter months (short photoperiod) in the intact, sham-pinealectomized, ovariectomized and hysterectomized animals. In contrast, the concentrations of prolactin were consistently raised (> 50 ng/ml) during the summer months (long photoperiod) in the same groups. During the transitional period from winter to summer the concentrations of prolactin were correlated with the reproductive status of the animals. In the pregnant animals, the prolactin concentrations increased from low values during pregnancy to high values at parturition. During lactation, the concentrations of prolactin in these animals remained high, although they were lower than those found subsequently during the summer months when the ewes were no longer lactating. In the non-pregnant ewes (i.e. the ovariectomized and hysterectomized animals), the prolactin concentrations increased more gradually during the transitional period from winter to summer than was the case in the parturient animals.

In the pinealectomized ewes, the plasma concentrations of prolactin were raised throughout the year, irrespective of whether the animals were pregnant, lactating or in anoestrus. In these animals, the only occasion when prolactin concentrations were consistently low was during the mid-winter period, although they were also low at times during the period of oestrous activity.

It was concluded that the circa-annual pattern of prolactin concentrations in ewes is primarily determined by the photoperiod, and that the pineal gland in the ewe is an important translator of the photoperiod. Parturition and suckling have important, but secondary, influences. Moreover, it was concluded that the secretions from the reproductive tract and the seasonal variations in temperature normally have little influence by themselves on the circa-annual rhythm of prolactin.