Evaluation of pituitary responsiveness to LHRH as a pregnancy test in ewes

Pregnant and nonpregnant ewes were injected with luteinizing hormone-releasing hormone (LHRH). Pituitary responsiveness, based on serum luteinizing hormone (LH), and follicle stimulating hormone (FSH) concentration, 2 hr after injection was then determined for each ewe, by radioimmunoassay (RIA) and correlated with the physiological reproductive state of each ewe. The serum LH release in pregnant ewes was significantly lower than that in nonpregnant ewes. Serum LH concentrations of pregnant ewes were further categorized according to whether the ewes were multiple (ML) or single lambing (SL). The responses by ML ewes were lower for LH than the SL responses. Follicle stimulating hormone responses were not different between pregnant or nonpregnant groups. Luteinizing hormone responses between pregnant ewes which were grouped according to 3 stages of pregnancy (1 to 5, 5 to 10 and 10 to 15 weeks pregnant) were not different from each other. Pregnancy diagnoses were made based on a fixed cut-off value, to which the LH response of each ewe to 5 mug LHRH was compared. Ewes whose response fell below this cut-off were diagnosed as pregnant. Accuracy of the diagnoses were determined by known lambing data. Diagnostic accuracy ranged from a low of 60% for nonpregnant, to a high of 95% for ML ewes. Accuracy for SL ewes (64%) was lower than for the overall pregnant group (79%), as well as that for ML ewes. Doses of LHRH, higher than 5 mug per ewe, generally produced LH release in pregnant ewes which was not significantly suppressed relative to responses of nonpregnant ewes. These results lead to the conclusion that gonadotropin response to exogenous LHRH injection is not an effective tool for pregnancy diagnosis.     

Selective release of follicle-stimulating hormone and luteinizing hormone by 5 alpha-dihydroprogesterone and 3 alpha, 5 alpha-tetrahydroprogesterone in pregnant mare's serum gonadotropin-primed immature rats exposed to constant light

The effects of 5 alpha-dihydroprogesterone (5 alpha-DHP) and 3 alpha, 5 alpha-tetrahydroprogesterone (3 alpha, 5 alpha-THP) on follicle-stimulating hormone (FSH) and luteinizing hormone (LH) release were examined in the pregnant mare's serum gonadotropin (PMSG)-primed immature female rat (8 IU PMSG at 28 days of age) maintained in constant light. Control rats kept in 14L:10D conditions exhibited proestrous-like surges of LH and FSH release with peak levels attained at 1800 h on the second day after PMSG treatment. In rats exposed to constant light, the PMSG-induced surges of LH and FSH were not only delayed until 1000 h on the third day after PMSG, resulting in a delay in ovulation, but were also significantly attenuated when compared to the gonadotropin surges that occurred on Day 2 in rats kept under normal light-dark conditions. The administration of 5 alpha-DHP significantly enhanced the release of FSH at 1000 h on Day 3 when compared to constant light-exposed controls, but had no effect on LH. Treatment with 3 alpha, 5 alpha-THP selectively potentiated the release of LH at 1000 h on Day 3 and had an attenuating effect on FSH release on Days 2 and 3. These observations confirm earlier findings in the immature ovariectomized estrogen-primed rat and suggest that 5 alpha-DHP and 3 alpha, 5 alpha-THP may have significant roles in the regulation of FSH and LH secretion.     

Basal gonadotropin hormone release rates during the period of selective follicle-stimulating hormone release in the juvenile female rat

There are situations in which adult female rats release increased amounts of follicle-stimulating hormone (FSH) independent of increased luteinizing hormone (LH) release. This results from, at least in part, a selective increase in the basal FSH release rate. We investigated whether an increase in the basal FSH release rate is contributory to the rise in serum FSH levels which occurs independent of a rise in serum LH levels in the immature female rat. Rats had high serum FSH concentrations on days 7 and 15 after birth, low serum FSH levels on day 23, and low serum LH levels on all three days. In contrast, anterior pituitary gland (APG) FSH and LH concentrations and contents increased from day 7 to day 15 and the contents increased further from day 15 to day 23. Similarly, basal FSH and LH release rates per mg APG or per APG, as assessed by measurement of FSH and LH released into culture medium containing APG(s) from different aged rats, increased from day 7 to day 15 but did not increase further between days 15 and 23. The results indicate that unlike situations observed to date in adult female rats, a mechanism(s) other than an increase in the basal FSH release rate is involved in selective FSH release in the immature female rat.     

Effect of dexamethasone on plasma concentrations of LH, FSH and testosterone in women with hirsutism.

Thirty sexually mature women with hirsutism were treated with 3 x 1.5 mg dexamethasone per day over a period of three days. Before and after treatment, plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone were determined. While an effect of dexamethasone on LH plasma levels could not be established statistically, FSH and testosterone plasma concentrations decreased significantly in comparison to their initial values (p less than 0.01). Special attention is directed to the different effects of dexamethasone on LH and FSH plasma concentrations.     

Dissociation of copulation from ovulation in pregnant rabbits

Experiments were designed to determine why copulation in the pregnant rabbit does not terminate pregnancy while treatment with ovulatory doses of luteinizing hormone (LH) human chorionic gonadotropin (hCG) or luteinizing hormone-releasing hormone (LHRH) is known to do so. Pregnant rabbits (Day 8) were mated or were injected with hCG (25 IU/doe) or LHRH (1, 10 micrograms/kg). Serial blood samples were collected over the next 72 h and analyzed for content of LH, follicle-stimulating hormone (FSH) and progesterone. At sacrifice, uteri and ovaries from these animals were examined for viability of the embryos and for signs of recent ovulation. Injection of hCG or LHRH into pregnant animals led to ovulation and to patterns of LH, FSH and progesterone secretion like those which precede ovulation in estrous rabbits. However, mating the pregnant does did not lead to ovulation or to any changes in the circulating hormones. To investigate whether the elevated levels of progesterone during pregnancy were responsible for the dissociation of coitus from ovulation, nonpregnant rabbits were injected with progesterone (2 mg/kg) and then mated or injected with hCG or LHRH. In virtually every respect, the numbers of ovulations and the patterns of hormone secretion in the progesterone-treated, nonpregnant rabbits mimicked those observed in the 8-day pregnant animals; injection of hCG or LHRH caused ovulation and hormonal surges while hCG caused ovulation only. Mating did not lead to ovulation or any change in blood levels of LH, FSH or progesterone. Taken together, the results show that the elevated circulating levels of progesterone, characteristic of pregnancy, are probably responsible for the dissociation of copulation from gonadotropin release in pregnant rabbits.     

LH- and FSH response to long-term application of LH-RH analogue in normal males.

The effect of luteinizing hormone-releasing hormone (LHRH) analogue after subcutaneous application over a 12-day period was evaluated in 15 normal males to determine whether gonadotropin secretion is influenced by longterm application. After 1.25 mcg/day, LH increases were measurable 3 hours after daily receipt of the analogue. After 2.5 mcg/day, the release of LH secretion was even greater, although this stimulation was markedly reduced in the 2nd week. After 5 mcg in 2-day intervals, a clearly induced LH increase was observed on the day of administration and was maintained for 10 hours. Similar results were noted for follicle-stimulating hormone (FSH). There was a response of FSH after 1.25 mcg and 2.5 mcg, but this response decreased in the 2nd week. After application of 5 mcg every other day, there was a consistent FSH increase that subsided on the treatment-free day and continued into the 2nd week of treatment. These findings suggest that LHRH analogues should be administered in low doses subcutaneously or intranasally at daily intervals to enable a longterm effect on gonadotropin release.     

Acute effect of suckling on gonadotropin, prolactin and glucocorticoid concentrations in serum of intact and ovariectomized beef cows

Suckling may prolong the anovulatory period postpartum by 1) a neural-mediated inhibition of luteinizing hormone-releasing hormone (LHRH)-induced gonadotropin secretion, or 2) an inhibitory effect of hormones released by suckling on gonadotropin secretion and/or action at the ovary. In the present investigation we considered whether a suckling event caused 1) acute inhibition of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion, and 2) release of glucocorticoids and/or prolactin (PRL). Six Hereford cows remained intact and six were ovariectomized (ovx) on day 7 postpartum. Calves remained with their dams continuously. Cows were bled at 10-min intervals during 6 consecutive hr on days 14, 28 and 42 postpartum. Both LH and FSH were released episodically by day 14 in intact and ovx cows, but suckling did not acutely affect LH and FSH secretion. A PRL release accompanied suckling 67, 96 and 95% of the time. However, among all instances where PRL was released on days 14, 28 and 42 postpartum, 67, 29 and 37% occurred independent of a suckling event. Glucocorticoids were not released by suckling in intact cows but were released in ovx cows. We conclude that suckling does not acutely affect LH or FSH concentrations in serum of cows postpartum, that PRL concentrations usually increase in serum coincident with suckling but can be released at other times, and suckling-induced glucocorticoid release depends upon the presence of the ovary.     

Effect of gonadotropin-releasing hormone antagonists on serum follicle-stimulating hormone and luteinizing hormone under conditions of singular follicle-stimulating hormone secretion

Previous work has indicated that in long-term ovariectomized rats a potent antagonist to gonadotropin-releasing hormone (GnRH) suppressed serum luteinizing hormone (LH) more successfully than follicle-stimulating hormone (FSH). The present studies examined whether the rise in serum FSH which occurs acutely after ovariectomy, or during the proestrous secondary surge, depends on GnRH. In Experiment A, rats were ovariectomized at 0800 h of metestrus and injected with (Ac-dehydro-Pro1, pCl-D-Phe2, D-Trp3,6, NaMeLeu7)-GnRH (Antag-I) at 1200 h of the same day, or 2 or 5 days later. Antag-I blocked the LH response completely, but only partially suppressed serum FSH levels. Experiment B tested a higher dose of a more potent antagonist [( Ac-3-Pro1, pF-D-Phe2, D-Trp3,6]-GnRH; Antag-II) injected at the time of ovariectomy. The analog suppressed serum LH by 79% and FSH by 30%. Experiment C examined the effect of Antag-II on the day of proestrus on the spontaneous secondary surge of FSH, as well as on a secondary FSH surge which can be induced by exogenous LH. Antag-II, given at 1200 h proestrus, blocked ovulation and the LH surge expected at 1830 h, as well as increases in serum FSH which occur at 1830 h and at 0400 h. Exogenous LH triggered a rise in FSH in rats suppressed by Antag-II. In Experiment D proestrous rats were injected with Antag-II at 1200 h and ovariectomized at 1530 h. By 0400 h the antag had suppressed FSH in controls, but in the ovariectomized rats, a vigorous FSH response occurred.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pituitary and ovarian hormone secretion and ovulation in gilts injected with gonadotropins during and after oral administration of progesterone agonist (Altrenogest)

We determined changes in plasma hormone concentrations in gilts after treatment with a progesterone agonist, Altrenogest (AT), and determined the effect of exogenous gonadotropins on ovulation and plasma hormone concentrations during AT treatment. Twenty-nine cyclic gilts were fed 20 mg of AT/(day X gilt) once daily for 15 days starting on Days 10 to 14 of their estrous cycle. The 16th day after starting AT was designated Day 1. In Experiment 1, the preovulatory luteinizing hormone (LH) surge occurred 5.6 days after cessation of AT feeding. Plasma follicle-stimulating hormone (FSH) increased simultaneously with the LH surge and then increased further to a maximum 2 to 3 days later. In Experiment 2, each of 23 gilts was assigned to one of the following treatment groups: 1) no additional AT or injections, n = 4; 2) no additional AT, 1200 IU of pregnant mare's serum gonadotropin (PMSG) on Day 1, n = 4); 3) AT continued through Day 10 and PMSG on Day 1, n = 5, 4) AT continued through Day 10, PMSG on Day 1, and 500 IU of human chorionic gonadotropin (hCG) on Day 5, n = 5; or 5) AT continued through Day 10 and no injections, n = 5. Gilts were bled once daily on Days 1-3 and 9-11, bled twice daily on Days 4-8, and killed on Day 11 to recover ovaries. Termination of AT feeding or injection of PMSG increased plasma estrogen and decreased plasma FSH between Day 1 and Day 4; plasma estrogen profiles did not differ significantly among groups after injection of PMSG (Groups 2-4). Feeding AT blocked estrus, the LH surge, and ovulation after injection of PMSG (Group 3); hCG on Day 5 following PMSG on Day 1 caused ovulation (Group 4). Although AT did not block the action of PMSG and hCG at the ovary, AT did block the mechanisms by which estrogen triggers the preovulatory LH surge and estrus.     

Temporal relationship of the prolactin-dependent LH-induced LH receptor to the LH stimulus

The time course for LH induction of luteinizing hormone (LH) receptors as reflected in binding of ¹²⁵l-labeled hCG was investigated in hypophysecto-mized adult male rats. A low dose of oLH (10 μg) was administered to hypophysectomized adult male rats following pretreatments with prolactin, follicle-stimulating hormone (FSH), growth hormone (GH), or saline. Testicular binding of hCG was determined at different times following the LH injection using Leydig cell membrane preparations from a testicular homogenate. Seven days after hypophysectomy, hCG binding was at a nadir of 19 ± 7% (mean ± SD) of control values. Pretreatment with prolactin (100 μg/day) for 7 days was associated with a nonsignificantly different hCG binding that was 30 ± 5% of control values. Prolactin pretreatment plus a single 10 μg LH i.p. injection increased ¹²⁵l hCG binding up to 56 ± 10% of control values within 30 minutes of the LH injection. Luteinizing hormone-induced hCG binding persisted at a high level (51 ± 4% of control values) for 2 hours but returned to hypophysectomized control levels 6 hours after the i.p. LH injection. Seven days pretreatment with FSH or GH at 100 μg/day plus 10-μg LH injections was also tested. Neither FSH nor GH had a statistically significant effect on hCG binding nor could they mimic the ability of prolactin to allow for LH induction of hCG binding in the hypophysectomized adult male rats. These studies suggest that the induction or “up-regulation” of Leydig cell hCG binding by ovine LH is rapid and specifically dependent upon pre-exposure to prolactin.     

Standardization of therapeutic,urinary gonadotrophins: An update on the use and availability of International Standards for Menotrophin

The potencies of therapeutic preparations of gonadotrophins of human, urinary origin, which comprise a heterogenous mix of isoforms with follicle-stimulating hormone (FSH) and luteinizing hormone (LH) bioactivities, are standardized by WHO International Standards (IS). We report here, the evaluation, through an international collaborative study, of a candidate preparation, coded 10/286, to replace the 4th IS, 98/704, for human, urinary FSH and LH (Menotrophin) which has been used for many years for the potency assignment of therapeutic preparations using bioassays. The mean FSH and LH bioactivities of 10/286, determined by in vivo bioassays in terms of 98/704, were 183 IU per ampoule (95% confidence limits 165–202) and 177 IU per ampoule (95% confidence limits 159–197), respectively.     

Catecholamine mechanisms in the feedback effects of estradiol benzoate on the release of LH and prolactin

The role of hypothalamic catecholamines and luteinizing hormone releasing hormone (LHRH) in the negative feedback effect of estradiol benzoate (EB) on luteinizing hormone (LH) release was studied in chronic ovariectomized rats. Administration of 10 micrograms EB decreased plasma LH levels and increased LHRH content in the medial basal hypothalamus (MBH) 1 day after injection. Inhibition of dopamine and norepinephrine synthesis with alpha-methyl-p-tyrosine (alpha-MT) reduced the LHRH content in the MBH in both oil- and EB-treated animals and partially reversed the decrease in plasma LH levels. Inhibition of norepinephrine synthesis with fusaric acid decreased LHRH content in both oil- and EB-treated rats but had no effect on plasma LH levels. The results suggest that at least a portion of the inhibitory effect of EB on LH release is due to the stimulation of an inhibitory dopaminergic mechanism which reduces LHRH release from the MBH. This feedback mechanism is apparently not susceptible to dopaminergic receptor blockade since administration of pimozide had no effect on LH levels. The stimulatory feedback effect of EB on prolactin release was studied in the same animals. alpha-MT and EB produced additive effects on plasma prolactin levels whereas fusaric acid blocked the EB-induced increase in plasma prolactin levels. Pimozide appeared to potentiate the effect of EB on prolactin release. The results reconfirm the possible role of noradrenergic neurons in the release of prolactin induced by EB and also suggest that EB stimulates a dopaminergic mechanism which is inhibitory to prolactin release but is normally masked by increased noradrenergic activity.     

Biphasic effect of gonadotropin releasing hormone on progestin secretion by rat granulosa cells

The effect of an agonistic gonadotropin releasing hormone (GnRH)-analog (D-Ala6, des-Gly10-NH2-GnRH-ethylamide, GnRHa) on granulosa cell steroidogenesis in the presence or absence of follicle-stimulating hormone (FSH) or luteinizing hormone (LH) was studied. Granulosa cells, isolated from preovulatory follicles of pregnant mare's serum gonadotropin (PMSG)-treated immature rats or from the less mature follicles of untreated immature rats, were cultured for a period of 72 h with daily changes of medium, and progesterone and its metabolite, 20 alpha-dihydro-progesterone (20 alpha-OHP), were assayed in the medium. In granulosa cells from preovulatory follicles, LH and FSH caused a much greater stimulation of steroidogenesis than did GnRHa. There appeared to be no interaction between GnRHa and FSH during the first 10 h, but at 24 h and later the presence of GnRHa clearly inhibited the steroidogenic response to LH and FSH. Steroidogenesis in granulosa cells from immature rats was considerably lower and the effects of GnRHa and FSH alone less pronounced. In these cells, FSH-stimulated progesterone secretion was inhibited by GnRHa only at 72 h. In contrast, 20 alpha-OHP secretion in the same cultures was potentiated by the combined presence of FSH and GnRHa. In conclusion, it seems as though the effects of GnRHa on granulosa cell steroidogenesis varies with exposure time, the initial response being stimulatory and the later inhibitory. Furthermore, the response is also to some extent determined by the maturational stage of the granulosa cells.     

The effects of injecting [D-Ser(But)6] Des Gly-NH2(10) luteinizing hormone releasing hormone ethylamide in early, mid and late seasonal anoestrus on gonadotrophin secretion and luteal function in the ewe

The ability of the luteinizing hormone releasing hormone (LH-RH) analogue [D-Ser(Bu(t))(6)] Des-Gly-NH(2)(10) LH-RH ethylamide to stimulate the secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) and to induce ovulation and luteal function in seasonally anoestrous ewes was investigated by injecting the analogue at three stages of the anoestrus (day 118, day 182 and day 235 of the year). After injection on day 118, eight of nine ewes ovulated and all of the former secreted progesterone during the subsequent 20 days. After injection on day 182, six of the nine ewes ovulated, of which none showed luteal function. Only two of the nine ewes were not already secreting progesterone on day 235. Both of these responded to the analogue by secreting normal luteal levels of progesterone. The mean LH peak heights in response to injection at the three stages showed no significant differences from one another. The mean FSH peak heightafter injection on day 182 was significantly lower than the mean FSH peak height associated with the other two challenges (P < 0.05). On day 116 of the following year, 20 ewes were treated with the analogue as before. The high progesterone levels confirmed the results of the day 118 challenge in the previous year. However, none of the ewes conceived when inseminated artificially 24 and 36 hours after analogue treatment.     

The rapid effects of luteinizing hormone releasing hormone agonists and antagonists on the mouse pituitary in vitro

The effect of luteinizing hormone releasing hormone (LHRH) and its analogs on the release of FSH and LH by 20 day old whole mouse pituitary incubated in vitro for 3-4 hrs was investigated. Three agonistic analogs (AY 25650, 25205 and Buserelin) all of which are reported to be superactive in vivo showed approximately the same potency in this in vitro test system. Preincubation of the pituitaries for 1 h with the antagonistic analogs [Ac Dp Cl Phe1,2, D Trp3, D Phe6, D Ala10] LHRH and [Ac Dp Cl Phe1,2, D Trp3, D Arg6, D Ala10] LHRH inhibited the secretion of LH and FSH induced by 2.5 x 10(-9)M LHRH. The inhibitory response was dose dependent. The continued presence of the antagonists was not required for effective suppression of the LHRH effect. Experiments designed to find out the minimum time required for eliciting suppression of LHRH revealed that preincubation of the pituitary with the second antagonist for 5 mins followed by removal was adequate to produce effective inhibition of gonadotropin release. At lower doses of the antagonist, LH release was more effectively inhibited than FSH release. The results suggest that antagonistic analogs can effectively bind to LHRH receptors in the whole pituitary incubation preventing the subsequent action of LHRH. With the present incubation system assessment of bioactive LH and FSH release is possible within 24 hrs.     

Purification of equine gonadotropins and comparative study of their acid-dissociation and receptor-binding specificity

A method for the simultaneous purification of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from equine pituitaries is briefly described. Different forms of each hormone were obtained. The total yield of LH was 24.2 mg·kg^?1 with a recovery of 22% and the yield of FSH was 26 mg·kg^?1 with a recovery of 34%. The specific activities of both hormones, measured in homologous equine radio-receptor assays are equal to or higher than those of the preparations described so far. In all species studied so far the acid-dissociation curves of LH and FSH are similar; this is an agreement with the view that the binding of the common α-subunit and the specific β-subunits involves polypeptide regions which are identical in both hormones. In contrast, the acid-dissociation pK_a of equine LH was found to be considerably lower (3.9) than that of equine FSH (5.8). The equine gonadotropins exhibit a much lower specificity with receptors of a porcine testicular fraction compared with an equine fraction. Equine LH exhibited a binding activity on FSH receptors from a porcine testicular fraction equal to 20% that of equine FSH instead of only 1% for an equine binding fraction. Similarly, all the equine FSH preparations tested exhibited a five-fold higher binding-activity on porcine LH receptors than on equine LH receptors. In the porcine system, pregnant mare serum gonadotropin behaved like equine LH towards LH and FSH receptors. In contrast, on equine binding fraction, pregnant mare serum gonadotropin was only 4% as active as equine LH and was devoid of FSH activity. All the data we have obtained are consistent with the ‘negative specificity’ model we proposed recently.     

Proluminal movement of 3H-androgen across the epididymal epithelium in the rat after hypophysectomy and gonadotropin supplementation

The effects of hypophysectomy and gonadotropin replacement on transepithelial movement of 3H-androgen in the rat epididymis were examined by in vivo microperifusion of 3H-testosterone followed by in vivo micropuncture to obtain peritubular and intraluminal fluid. In the caput epididymidis of normal rats, intraluminal 3H-androgen concentrations were approximately 300% of those in the interstitial space. In contrast, proluminal movement of 3H-androgen into rat caput epididymal tubules was significantly decreased 10 days after hypophysectomy. 3H-Testosterone movement across the caput epididymal epithelium was completely returned to normal by supplementation with 24 micrograms/day follicle-stimulating hormone (FSH) or 24 micrograms/day luteinizing hormone (LH). However, neither 0.12 micrograms/day FSH nor 250 micrograms/day prolactin returned proluminal androgen movement to normal. It is speculated that epididymal uptake of peritubular testosterone is mediated by androgen-binding protein, which is known to be secreted by Sertoli cells after stimulation by FSH or testosterone.     

Placebo-controlled study of effects of epimestrol on the pituitary-testicular axis in normal men

Twenty healthy male volunteers were randomly allocated to the treatment with either 15 mg/day of epimestrol or placebo for 10 days. The plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T), oestradiol (E2) and prolactin (PRL) were measured before, during and 4 days after the medication by radioimmunoassays. Data were statistically evaluated by means of an analysis of covariance. Circulating LH and FSH, and also T and E2 significantly increased in the epimestrol treated subjects. In the placebo treated subjects no significant changes in the plasma hormone levels were observed. There were no significant changes in the plasma levels of PRL in either group.     

Seasonal changes in the endocrine responsiveness of the pituitary and tests of male sheep in relation to their patterns of gonadotropic hormone and testosterone secretion

Pituitary and testicular endocrine responses to exogenous gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH), respectively, were assessed for adult rams in an investigation of the regulation of seasonal changes in the patterns of episodic LH and testosterone secretion. Concurrent variations in testis size and in circulating levels of follicle stimulating hormone (FSH) and prolactin (PRL) were also examined. On 10 occasions throughout the year, serum hormone levels were assessed over 6- to 8-h periods during which time rams were left untreated (day 1) or were injected (iv) with single doses of either 10 micrograms synthetic GnRH (day 2) or 30 micrograms NIH-LH-S18 (day 3); blood samples were collected from the jugular vein at 10- to 20-min intervals. Testicular redevelopment during the summer, as indicated by increasing testis diameter measurements, was associated with increases in mean FSH level and was preceded by a springtime rise in mean PRL level; "spontaneously" occurring LH pulses and those produced in response to GnRH treatment were relatively large during this period. Increases in the magnitude of testosterone elevations in response to both endogenously and exogenously produced LH pulses occurred in August. Mean testosterone levels were elevated fourfold in the fall as a consequence of relatively frequent and small LH pulses stimulating a more responsive testis to produce more frequent and larger testosterone elevations; endogenous LH pulses, however, did not appear to stimulate the testes maximally at this time.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in gonadotrophin and ovarian hormone levels during the estrous cycle of black-tailed deer (Odocoileus hemionus columbianus)

Daily blood samples over a fifteen day period were obtained from two adult female black-tailed deer and circulating levels of progesterone, estrogens, luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin were measured by radioimmunoassay. LH levels showed an apogee at the time when there was observed estrous behaviour. The length of the estrous cycle appeared to be 7 days. Progesterone levels peaked just subsequent to the LH peak. High estrogen levels coincided with high progesterone and prolactin levels. FSH reached maximum levels prior to peak estrogen levels. LH and FSH levels reached maxima on different days. There were two steroid peaks between the LH apogees.