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Most sheep are seasonal estrus, and they breed in autumn when the days get shorter. Seasonal estrus is an important factor that affects the productivity and fertility of sheep. The key point to solve this problem is to explore the regulation mechanism of estrus in sheep. Therefore, in this study, transcriptomic sequencing technology was used to identify differentially expressed mRNAs in the hypothalamus, pituitary and ovary of Small Tail Han sheep (year-round estrus) and tan sheep (seasonal estrus) among luteal, proestrus and estrus stages. There were 256,923,304,156 mRNAs being identified in the hypothalamus, pituitary and ovary, respectively. Functional analysis showed that the photosensor, leucine and isoleucine biosynthesis pathways were enriched significantly. It is speculated that photoperiod may initiate estrus by stimulating the corresponding pathways in hypothalamus. ODC1 , PRLH , CRYBB2 , SMAD5 , OPN1SW , TPH1 are believed to be key genes involved in the estrogen process. In conclusion, this study expanded the database of indigenous sheep breeds, and also provided new candidate genes for future genetic and molecular studies on the seasonal estrus trait in sheep.

Background: As the milk production of dairy cows increases, the reproductive capacity gradually declines. Ovarian quiescence has become one of the concerns of the dairy industry., Objective: To explore the different plasma metabolite levels between estrus and anestrus in energy balanced (EB) dairy cows., Methods: Ten estrous and 10 anestrus EB Holstein cows in early lactation were selected for the study. 1 H nuclear magnetic resonance technology was used to detect plasma metabolites and screen different plasma metabolites between anestrous and estrous cows at 60-90 days postpartum using multivariate statistical analysis., Results: Within an elective waiting period of 60-90 days postpartum mean plasma concentration of total estrogens was significantly higher in estrus cows as compared to anestrus cows (71.2 ± 26.0 and 42.4 ± 16.7 pg/mL, respectively). Seven plasma metabolites (isoleucine, leucine, valine, alanine, arginine, choline and phosphatecholine) demonstrated significant decreases in estrous dairy cows relative to anestrous subjects. The main pathway was leucine, isoleucine and valine biosynthesis., Conclusion: Anestrus in dairy cows is accompanied by alterations in amino acid, glucose and lipid metabolism based on 1 H NMR analysis.

In order to clarify the effect of exogenous corticotropin-releasing factor (CRF) on catecholaminergic and serotoninergic system activity in the mediobasal hypothalamus-median eminence (MBH-ME) of ewes the changes in extracellular levels of noradrenaline (NA) and serotonin (5HT), and main metabolites of monoamines, 4-hydroxy-3-methoxyphenylglycol (MHPG), 3,4-dihydroxy-phenylacetic acid (DOPAC), homovanilic acid (HVA), and 5-hydroxy-indolo-3-acetic acid (5-HIAA) were quantified in the perfusates collected from MBH-ME. NA, 5-HT and monoamine metabolites in the perfusates were analyzed using high performance liquid chromatography with electrochemical detection. CRF induced a rise in extracellular concentration of NA and 5-HT only in the estrous ewes prior to a preovulatory LH surge. CRF treatment caused a heterogenous effect on extra-cellular concentrations of 5-HT in ewes during the preovulatory LH surge. Except for DOPAC and HVA in some estrous ewes during the preovulatory LH surge, CRF caused an increase in monoamine metabolites levels in the MBH-ME in anestrous and estrous animals. These results indicate that CRF facilities NA release in the MBH-ME during the presurge LH period in ewes, and that CRF increases metabolic activities of the monoaminergic systems in this structure in the anestrous and estrous ewes, except dopaminergic system in the ewes during the preovulatory LH surge. It is suggested that: 1) the responses of monoaminergic systems activity in the MBH-ME to CRF in large degree is dependent upon physiological state of ewes and 2) in some endocrinological phases CRF may affect LHRH and other hypothalamic hormone secretion indirectly by altering monoaminergic system activity in the MBH-ME.

Uterine tissue samples were collected from 47 ewes at various stages of the oestrous cycle and early pregnancy (until day 21) and during seasonal anoestrus. Cryostat sections were immunostained to determine the localization of oestradiol and progesterone receptors using specific monoclonal antibodies. Oxytocin receptors were localized by autoradiography in sections from the same ewes using the 125I-labelled oxytocin antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH2(9)]- vasotocin. Plasma progesterone measurements were made during the preceding cycle up to the time of slaughter. Oestradiol receptor concentrations were maximal in all regions of the tract at oestrus. Immunostaining of the luminal epithelium, superficial glandular epithelium, stroma and myometrium decreased in the early luteal phase but was maintained for longer in the deep glands. Progesterone receptor immunostaining in the luminal epithelium and superficial glands developed in the early luteal phase (days 1-2) with a somewhat later appearance in the deep glands (days 5-7). Progesterone receptor concentrations in the stroma and myometrium also reached a maximum in the early luteal phase. Myometrial staining was clearly maintained throughout the luteal phase whereas stromal staining was variable between ewes. For both oestradiol and progesterone receptors no differences were apparent between pregnant and non-pregnant ewes between days 2 and 12, but pregnant ewes did not show the general increases in oestradiol receptor staining associated with luteolysis on days 14-15. Oxytocin receptors first developed in the luminal epithelium of non-pregnant ewes on day 14 of the cycle and spread to the superficial glands, caruncular stroma, deep glands and myometrium at oestrus before decreasing in reverse order on days 1-2. Specific binding was not detectable on days 5-12 of the cycle or on days 14 or 21 of pregnancy. The appearance of oxytocin receptors in the luminal epithelium on day 14 preceded that of both the oestradiol and progesterone receptors in the epithelial cells and the fall in plasma progesterone. It was followed by the development of oestradiol and oxytocin receptors in the superficial glands, deep glands, caruncular stroma and myometrium, with the two receptor populations showing a significant positive association in these tissues. The loss of oxytocin receptors in all regions occurred as plasma progesterone levels were increasing, but the association between these two variables was only significant in the superficial glands. The development of progesterone receptors in different tissues could not be explained on the basis of either oestradiol receptor content or plasma progesterone.(ABSTRACT TRUNCATED AT 400 WORDS)

Pituitaries were collected from late follicular phase (n = 5), mid-luteal phase (n = 5), and anestrous ewes (n = 4) to assess changes in intrapituitary LH heterogeneity at selected reproductive states. After homogenization, an aliquot of each pituitary extract was desalted by flow dialysis against water and chromtofocused on a pH 10.5 to 4.0 gradient. Concentrations of LH in pituitary extracts and chromatofocusing fractions were determined by RIA. The LH in pituitary extracts resolved into 13 isoforms during chromatofocusing, which were coded with letters beginning with the most basic isoform. Follicular and mid-luteal phase ewes exhibited similar distributions of intrapituitary LH among its isoforms. Relative to follicular and luteal phase ewes, anestrous ewes had lower percentages of isoforms D and E as well as higher percentages of isoforms G, H, J and K. Isoform F, the predominant molecular form of LH, constituted a similar percentage in all treatment groups (P > .05). Thus, the distribution of intrapituitary LH among its isoforms did not change significantly between the mid-luteal and follicular phases of the estrous cycle, but higher percentages of the weakly basic and acidic forms of LH were present during anestrus. These observations suggest that intrapituitary LH heterogeneity changes minimally throughout the estrous cycle of ewes during the breeding season.

In this study we investigated immunohistochemically the distribution of VIP in ampullary and isthmic segments of the rabbit oviduct at different hormonal stages in order to correlate the presence of VIP with the morphological and functional differences between the two oviduct segments. Noticeable changes in the VIP-positive sites emerged between corresponding oviduct segments during the stages examined. A reduction in VIP presence was noted in oestrus and the lowest VIP values occurred one and three days after mating in the ampulla and the isthmus respectively. In the subsequent stages an increase of VIP was noted in both tracts which showed features comparable to that described in anoestrus. The levels and distribution of VIP is correlated with the functions of the oviduct segments concerned with egg transport and formation of a mucopolysaccharide envelope around blastocysts.

The effects of a potent opioid peptide agonist [D-ala2-Phe4, Met(0)ol5-enkephalin (FK 33-824) on the magnitude of the oestradiol-induced LH surge and on basal plasma LH concentrations were examined in intact and chronically-ovariectomized ewes during the late-anoestrous period. In intact ewes, treatment with FK 33-824 (0.5 mg i.v. every 3 hr) for a 24 hr period commencing at the time of oestradiol-17 beta administration (25 micrograms i.m. bolus) was associated with non-significant 65% reduction in the peak plasma LH level observed and a significant (P less than 0.05) 58% reduction in the total amount of LH released during the surge (calculated from the area under the curve). Concurrent treatment with the opioid antagonist naloxone (10 mg i.v. every 3 hr) partially reversed this suppressive effect on the magnitude of the LH-surge. In ovariectomized ewes no significant effects on the oestradiol-induced LH surge of either FK 38-824 alone or FK 33-824 in combination with naloxone were observed. Administration of FK 33-824 at a 6-fold higher dose rate (0.5 mg every 30 min) failed to modify basal plasma LH concentration in intact ewes. In ovariectomized ewes, however, a significant (P less than 0.05) 25% fall in basal plasma LH was observed, an effect which was completely reversed by combined treatment with naloxone (10 mg every 30 min). These results support the conclusion that endogenous opioid peptides may contribute to the neuroendocrine mechanism through which oestradiol promotes a preovulatory-like surge in the anoestrous ewe.

In an effort to determine whether anestrus in swine is due to aberrant ovarian feedback control of gonadotropin release, this study contrasted the influence of ovariectomy on LH concentrations in serum of anestrous sows and in sows that returned to estrus following weaning. Blood samples were collected at 6-h intervals from 7 d prior to until 4 d after ovariectomy of 22 anestrous and 24 cyclic sows. Blood samples also were collected at 15-min intervals for 8 h at 2 d prior to and 2 d after ovariectomy. Sampling at 6-h intervals continued until 12 d after ovariectomy and additional 8-h windows of 15-min samples were taken at 7 and 12 d after ovariectomy of seven anestrous and nine diestrous sows. Mean LH concentrations and LH pulse frequencies were greater (P less than .05) 2 d after ovariectomy than 2 d prior to ovariectomy in both anestrous and diestrous sows. Mean pulse amplitude had increased by 2 d after ovariectomy in anestrous sows but did not change in cyclic sows. Baselines as determined from the mean of all LH measurements excluding pulses, remained the same in both anestrous and diestrous sows at 2 d after ovariectomy. Pulse frequency, pulse amplitude, and mean LH concentration were greater (P less than .05) in both anestrous and diestrous sows at 7 and 12 d after ovariectomy than at 2 d prior to and 2 d after ovariectomy. Pulse amplitude on d 7 and 12 after ovariectomy decreased (P less than .05) in both anestrous and diestrous sows relative to those observed at earlier times.(ABSTRACT TRUNCATED AT 250 WORDS)

The changes in the concentrations of proteolytic enzyme inhibitors after the administration of hormones influencing the activity of the ovaries can cause an imbalance in the development of follicles. Important roles are attributed to serine proteases during the development of follicle, ovulation, and activity of the corpus luteum. In order to find out the changes in the trypsin inhibiting activities (TIA) of the blood plasma and cervical mucus after the administration of PGF2 alpha (100 + 100 micrograms in January and 250 + 250 micrograms in May on the 0th and 11th day) and after the single administration of 750 I. U. PMSG on the 10th day, a 14-day trial was performed to investigate the circadian changes. TIA was determined by means of slowing down the hydrolysis of the synthetic substrate N-alpha-tosyl-p-nitro-anilide (TAPA) by bovine trypsin. When the blood plasma TIA is expressed as the percent of the control values, a large drop is observed on the 11th and 12th days of the January trial (total as well as low-molecular TIA). In the May experiment this drop was recorded only on the 11th day in total TIA (c TIA); low-molecular TIA (n TIA), on the other hand, increased, particularly after the administration of PMSG. The average values of plasma TIA's, recorded in the course of the 14-day trial, increased after the administration of PGF2 alpha (c TIA increased to 109.8 +/- 22.1%, n TIA to 135.42 +/- 54.0% in January; c TIA to 112.59 +/- 50.5%, n TIA to 109.48 +/- 55.9% in May). After the administration of PMSG the TIA values remained higher than the controls (c TIA 107.13 +/- 24.0%, n TIA 133.40 +/- 52.1% in January; c TIA 113.87 +/- 51.3%, n TIA 118.33 +/- 55.6% in May). The average TIA values of the cervical mucus increased after PGF2 alpha administration to 3.06 +/- 1.7% in comparison with the control value of 2.59 +/- 1.1%, and also after the administration of PMSG to 2.82 +/- 1.9% (January, TIA per 1 mg of mucus).

The mechanism of anestrus in rats treated with losulazine, a peripheral sympatholytic antihypertensive agent, was investigated by determining its effect on hypothalamic catecholamines and serum sex hormones and by evaluating the influence of bromocriptine on the reproductive functions of rats treated with losulazine. Groups of six female Upjohn Sprague-Dawley rats were treated orally with 10 mg/kg/day of losulazine and/or 18.75 mg/kg/day of bromocriptine for 15 or 27 days. Six rats were treated with losulazine plus 6.25 mg/kg/day of bromocriptine for 16 days followed by losulazine alone for 11 days. Rats treated with losulazine only were depleted of hypothalamic catecholamines, were hyperprolactinemic, and had interrupted estrous cycles and attenuated vaginal mucosa. Treatment with bromocriptine, a dopamine receptor agonist, resulted in suppression of serum prolactin and normal estrous cycles. Rats reverted back to hyperprolactinemia and anestrus shortly after bromocriptine withdrawal. These results suggest that hyperprolactinemia mediated through hypothalamic dopamine depletion is the mechanism of anestrus in rats treated with losulazine.

Two experiments determined how feed restriction and realimentation altered metabolism and ovarian function in gilts. In Exp. 1, cyclic (INTACT-R, n=6) and ovariectomized (OVEX-R, n=6) gilts were fed restricted diets (.23 kg feed.d-1) or ovariectomized (OVEX-C, n=6) gilts were fed control diets (1.81 kg.d-1). Estrous cycles stopped after 46 +/- 9 d of feed restriction. Average weight (WT), backfat thickness (BF) and concentrations of insulin (INS) were lower and free fatty acids (FFA) were greater in OVEX-R than in OVEX-C gilts. Frequency of luteinizing hormone (LH) release (peaks.6 h-1) was reduced by feed restriction (.2 +/- .2, 1.8 +/- 1.0 and 5.8 +/- .2 in INTACT-R, OVEX-R and OVEX-C gilts, respectively). Patterns of secretion of LH and follicle stimulating hormone (FSH) after gonadotropin releasing hormone (GnRH) or estradiol benzoate were not altered by feed restriction. Feed intake was then increased in INTACT-R and OVEX-R gilts beginning on d 80 and 82, respectively. Resumption of estrous cycles in INTACT-R gilts occurred on d 116.0 +/- 4.0 and was preceded by a significant increase in WT, but not BF, and a linear increase in concentration and frequency of release of LH. Increasing feed intake in OVEX-R gilts increased WT and frequency of LH release, while FFA decreased and INS increased to concentrations not different from those of OVEX-C gilts. The hypothesis that nutritionally-induced anestrus resulted from decreased activity of the hypothalamic pulse-generator was evaluated in Exp. 2 by providing 144 hourly pulses (iv) of saline (n=3), GnRH (n=3) or LH (n=4) to nutritionally-anestrous gilts.(ABSTRACT TRUNCATED AT 250 WORDS)

In May mature seasonally anoestrous ewes were implanted with melatonin which advanced the onset of cycles by about 1 month. The LH response to an opioid antagonist, WIN-3, was determined 5, 15, 25 and 60 days after melatonin implantation, by intravenous administration of WIN-3 (12.5 mg/dose) 4 times at 15-min intervals during both the 1st and the 5th hour of an 8-h treatment period. There was no effect of WIN-3 at 5, 15 and 25 days after melatonin implantation. At 60 days LH concentration and pulse frequency were significantly increased (P less than 0.05 and less than 0.01 respectively) in response to WIN-3 treatment, but only in those animals which had begun reproductive cycles, an effect known to be mediated by the presence of progesterone. We were therefore unable to find evidence to support the hypothesis that the influence of melatonin in advancing the breeding season may be via an opioidergic pathway.

The effect of the doses of 750, 1000, and 1500 I. U. PMSG (Antex Leo) on changes in the trypsin-inhibition activities (TIA) of the blood plasma and cervical mucus of ewes was found to vary: a) in the times (from PMSG administration) of recording the minimum values of total TIA (72, 48, 24 hours); b) in the values of the average total TIA on individual days of the trial (40.3-141.4% of the control values); c) in the fractions of low-molecular TIA after administration of 750 and 1500 I. U. PMSG, the fractions exhibited minimum values after 24 hours, and of 1000 I. U. after 72 hours (53.0 and 60.4, and 69.7% of the control values, respectively); d) in the highest values of the fractions of low-molecular TIA recorded after 96 hours (96.1-183.7% of the control values); e) in the average values for 96 hours of the trial, which ranged from 64.1% (1500 I. U.) to 77.1% (750 I. U.) for total TIA and from 89.6% (750 and 1000 I. U.) to 122.8% (1500 I. U.) for low-molecular TIA; f) in the ratio of atretic and non-atretic (A/N) tertiary follicles, which grew with increasing PMSG doses; this was indirectly correlated with the average values for total TIA; g) in the weights of uteri and ovaria which increased from 176.8 to 322.3% of the control values after the stimulation; h) in the epithelium thickness of cervix and cervical glands increasing from 118% to 316% of the control values; i) in the average TIA values of cervical mucus ranging from 53.3 to 125% of the control values.

The preovulatory gonadotropin surge in the sheep was recently characterized by a divergent pattern of LH beta and FSH beta mRNAs immediately preceding this event. It is not clear whether this pattern is due to estradiol (E2), inhibin or other effectors. In this study, to determine if E2 may be involved in the divergent beta mRNA patterns seen during the surge, gonadotropin surges were induced in anestrous ewes (An) by E2 (An + E2) and several parameters were then measured. These included the amounts of alpha, LH beta, and FSH beta mRNAs, as assessed by solution hybridization assays, plus pituitary and serum gonadotropin concentrations. The values were compared with those observed in control, An ewes, to assess the effect of E2. The E2 treatment resulted in LH and FSH surges that appeared to be similar to the normal surges seen during the breeding season. Concomitantly, the E2 treatment lowered pituitary concentrations of FSH (P less than 0.05), while LH amounts did not change. Although the effect of E2 on gonadotropin subunit mRNA amounts varied depending upon the individual subunit, the changes that were observed paralleled changes reported during the preovulatory surge of the cycle. Specifically, alpha mRNA amounts increased significantly (P less than 0.001) while FSH beta mRNA amounts fell dramatically (P less than 0.001). Moreover, LH beta mRNA amounts were slightly increased, although not significantly by E2. These results demonstrate that E2 effects changes in the amounts of the gonadotropin subunit mRNAs during an induced gonadotropin surge in An ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

In sheep, secretion of oestradiol by the ovary is stimulated by pulses of LH but the factors controlling ovarian inhibin secretion are not well understood. We have investigated the effect of a single injection of LH on the ovarian secretion of inhibin. Six anoestrous Finn-Merino ewes which had one ovary autotransplanted to a site in the neck had jugular and timed ovarian venous blood samples collected at 10-min intervals for a total of 5 h. The secretion rates of both inhibin (1-3 ng/min) and oestradiol (0.5-8 ng/min) were similar to those observed during the breeding season indicating significant follicular development in these animals. After injection of 2.5 micrograms NIH-LH-S25 intravenously the concentration of LH in plasma rose from a baseline of 1.8 +/- 0.1 (S.E.M.) microgram/l to a peak of 3.9 +/- 0.3 micrograms/l (P less than 0.01). This LH pulse stimulated a corresponding increase (P less than 0.01) in oestradiol secretion from a basal level of 0.9 +/- 0.2 ng/min to a peak of 4.6 +/- 0.6 ng/min that occurred within 30 min of injection. Although inhibin secretion was episodic in nature, increases were not related to either exogenous or endogenous LH pulses. We conclude that, in contrast to oestradiol, the secretion of inhibin by the ovary is not controlled acutely by changes in plasma levels of LH during anoestrus.

Normal and abnormal corpora lutea were recovered from anoestrous Romney Marsh ewes on Days 3, 4, 5 and 6 after treatment with small-dose (250 ng) multiple injections of GnRH followed by a bolus injection (125 micrograms) with (+P) and without (-P) progesterone pretreatment and a study made of their characteristics in vitro. Plasma progesterone concentrations initially rose concurrently in all animals but abnormal luteal function occurred in 70% of the -P ewes and was defined on Day 5 when plasma progesterone concentrations declined relative to those in the +P ewes. All corpora lutea recovered on Days 3 and 4 appeared macroscopically similar and there were no significant differences between the +P and -P groups in terms of luteal weight, progesterone content and binding of 125I-labelled hCG on these days. However, corpora lutea from the -P animals only exhibited a decline in progesterone production in vitro on Day 4 (P less than 0.01), and morphological differences became apparent on Days 5 and 6 when the abnormal corpora lutea from the -P animals also decreased in weight (P less than 0.01) and progesterone content (P less than 0.001). Binding of 125I-labelled hCG increased on Day 5 in the normal corpora lutea only. These results show that, although abnormal luteal function induced by GnRH treatment of anoestrous ewes could not be distinguished from normal corpora lutea before Day 5 by measurement of progesterone in peripheral plasma, a significant decline in progesterone production in vitro occurred on Day 4 in the abnormal corpora lutea. This was followed by significant decreases in weight and progesterone content and a failure to increase 125I-labelled hCG binding. Abnormal corpora lutea are therefore capable of some initial growth and progesterone production, before undergoing a rapid and premature regression from Day 4, which has similar characteristics to natural luteolysis.

We studied the effect of short (acute (20 min/h, for 4 h) and intermittent, long-term (20 min/h for 9 h on 3 consecutive days) electric foot shocks on the immunocytochemical localization of CRH and SRIH in the hypothalamus and of ACTH, beta-endorphin, GH and PRL in the pituitary of the anestrous ewe. Acute stress greatly reduced immunoreactive (ir) CRH in the median eminence and cellular irACTH, beta-endorphin and PRL, as well as the proportion of these cell types in the pituitary. A slight reduction of irSRIH in the median eminence was also observed. After long-term stress, reduction of irCRH in the median eminence was still observed. However, ACTH/beta-endorphin cells in the pituitary gland displayed increased secretory activity, manifested by hypertrophy and hyperplasia. A marked depletion of irSRIH in the nerve terminals of the median eminence was observed. The proportion of PRL cells but not their ir content returned to control levels. No effects were observed on the features of the GH cells. This study indicates that there are differences in the effect of short- and long-term stressful stimuli on the activity of hormonal systems in the anestrous ewe. Short-term stress immediately activates the CRH/ACTH/beta-endorphin axis. Prolonged stress appears to augment the activation of the SRIH hypothalamic system and probably has a restraining effect on ACTH/beta-endorphin release.

During pregnancy the hypothalamic-hypophysial axis is suppressed by the high concentrations of progesterone and oestradiol in the circulation. The high concentrations of these steroids appear to inhibit secretion of GnRH from the hypothalamus, resulting in inadequate stimulation of pituitary gonadotrophs to maintain synthesis of LH. This produces a depletion of LH in the anterior pituitary gland that must be restored after parturition before normal oestrous cycles can begin.

Thirty beef cows, approximately 3 yr of age, were randomly assigned to be slaughtered on d 7, 14, 28, 42 or 56 postpartum. Each cow suckled one calf until slaughter. Data from cows slaughtered on d 42 and 56 were pooled and further classified as anestrous or cyclic based on the presence of a corpus luteum and elevated serum concentrations of progesterone at slaughter. Specific binding of [3H]naloxone (3H-NAL) to homogenates of tissue from hypothalamus (HYP), preoptic area (POA) and basal forebrain (BF) was assessed using multiple-point Scatchard analyses. Nonspecific binding was estimated in the presence of 10(-6) M naloxone. Separation of bound from free 3H-NAL was achieved by centrifugation at 20,000 X g. Concentration (fmol/mg original tissue wet wt) of 3H-NAL binding sites in POA tissue was higher (P less than .05) on d 28 postpartum in anestrous cows than in cyclic cows on d 42 + 56 postpartum (2.58 +/- .32 vs 1.58 +/- .10). When all anestrous cows were compared with cyclic cows, concentrations of 3H-NAL binding sites in POA tissues and in BF tissue were higher (P less than .05) in anestrous cows (anestrous POA, 2.12 +/- .17, cyclic POA, 1.58 +/- .10; anestrous BF, 2.94 +/- .41, cyclic BF, 2.19 +/- .16). Compared across brain regions for all cows, the concentration of specific binding sites for 3H-NAL was greater (P less than .01) in BF (2.5 +/- .2) than in POA (1.9 +/- .1) and greater (P less than .01) in POA than in HYP (1.5 +/- .1).(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of treatment with estradiol-17 beta (E2) and progesterone (P4) on the neuronal system for gonadotropin-releasing hormone (GnRH) of the ovariectomized ewe during the non-breeding season were examined using immunocytochemical and radioimmunoassay analyses. The majority of GnRH-immunoreactive cell bodies are located in the medial preoptic area (POA). Clusters of labelled cell bodies also are found in the septum and anterior hypothalamus. GnRH fibers projected from the medial POA to a dense fiber plexus in the median eminence (ME). For ewes treated with E2, the percentage of GnRH cell bodies that were multipolar was approximately twice that for ewes not treated with E2 (P less than 0.05). The intensity of immunocytochemical staining in the GnRH cell body, and the incidence of fiber branching close to the cell body also were significantly greater for ewes treated with E2 (P less than 0.01 and P less than 0.05, respectively). The intensity for staining of GnRH in the ME appeared to be greater for ewes not treated with steroid, and this was reflected by a greater density of GnRH fibers in ewes not treated with steroid (P less than 0.05). The mass of GnRH in the ME of the ewes not treated with E2 was approximately twice that for E2-treated ewes; however, there was little difference in the total contents of GnRH in the hypothalamus and POA between E2 and non-E2-treated ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

To determine whether opioid mechanisms modulate the positive feedback effect of oestrogen on LH secretion, anoestrous ewes were given a single injection of 50 micrograms oestradiol benzoate (OB), followed by infusions of morphine or naloxone. All sheep were injected i.m. with 50 micrograms OB at 00.00 h. In experiment 1, sheep were given i.v. infusions of the following: group 1, 12 ml saline/h from 09.00 to 15.00 h (n = 12); group 2, 40 mg naloxone/h from 09.00 to 12.00 h (n = 5); group 3, 40 mg naloxone/h from 10.00 to 14.00 h (n = 5); group 4, 10 mg morphine/h from 09.00 to 15.00 h (n = 5); and group 5, 20 mg morphine/h from 09.00 to 15.00 h (n = 5). Jugular blood samples were taken at 30-min intervals to monitor LH surges, which commenced 13.0 +/- 0.6 h after injection of OB in control (OB plus saline) ewes. The infusions of naloxone or morphine did not affect the timing or magnitude of the oestrogen-induced LH surge. To examine the possibility that opioidergic regulation of the LH surge occurred earlier than the infusion regimens in experiment 1, sheep were infused from the time of the OB injection (00.00 h) until 15.00 h. In this experiment (experiment 2), sheep were given i.v. infusions of the following: group 1, 4.2 ml saline/h (n = 5); group 2, 20 mg naloxone/h (n = 5); and group 3, 20 mg morphine/h (n = 5). As in experiment 1, treatment with neither the opioid agonist or antagonist was able to alter the positive feedback response of OB.(ABSTRACT TRUNCATED AT 250 WORDS)