Exogenous LHRH Research Articles

Effect of modulating endogenous prolactin secretion on testosterone production in the adult male bonnet monkey (Macaca radiata):

Adult male bonnet monkeys maintained under regulated light: dark conditions exhibit a nycthemeral surge of testosterone. The present study attempts to determine the effect of administration of drugs that modulate prolactin levels like ergobromocriptine (EBC) and chlorpromazine (CPZ) on testosterone production. The injection of EBC, a known inhibitor of prolactin secretion, could abolish nocturnal testosterone surge irrespective of the drug being given at 8.00 or 17.00 h. Testosterone surge could likewise be inhibited by treating animals with CPZ, a potent stimulator of prolactin secretion. This suggests that alteration in endogenous prolactin level from the normal effects nycthemeral surges of testosterone. The in vivo responsiveness of the testes of monkeys injected either CPZ oder EBC to exogenous LH or LHRH stimulation was tested. While LH could completely override the CPZ induced inhibition in testosterone production it could only partially reverse the EBC effect.

Alteration of gonadotrophin and steroid hormone release, and of ovarian function by a GnRH antagonist in gilts

This study examined the impact of the gonadotrophin-releasing hormone (GnRH) antagonist Antarelix™ on LH, FSH, ovarian steroid hormone secretion, follicular development and pituitary response to LHRH in cycling gilts. Oestrous cycle of 24 Landrace gilts was synchronised with Regumate ® (for 15 days) followed by 800 IU PMSG 24 h later. In experiment 1, Antarelix™ ( n=6 gilts) was injected i.v. (0.5 mg per injection) twice daily on four consecutive days from day 3 to 6 (day 0=last day of Regumate ® feeding). Control gilts ( n=6) received saline. Blood was sampled daily, and every 20 min for 6 h on days 2, 4, 6, 8 and 10. In experiment 2, gilts ( n=12) were assigned to the following treatments: Antarelix™; Antarelix™ + 50 μg LHRH on day 4; Antarelix™ + 150 μg LHRH on day 4 or control, 50 μg LHRH only on day 4. Blood samples were collected daily and every 20 min for 6 h on days 2, 4 and 6 to assess LH pulsatility. Ovarian follicular development was evaluated at slaughter. Antarelix™ suppressed ( P<0.05) serum LH concentrations. The amount of LH released on days 4–9 (experiment 1) was 8.80 versus 36.54 ng ml −1 (S.E.M.=6.54). The pattern of FSH, and the preovulatory oestradiol rise was not affected by GnRH antagonist. Suppression of LH resulted in a failure ( P<0.05) of postovulatory progesterone secretion. Exogenous LHRH (experiment 2) induced a preovulatory-like LH peak, however in Antarelix™ treated gilts the LH surge started earlier and its duration was less compared to controls ( P<0.01). Furthermore, the amount of LH released from day 4 to 5 was lower ( P<0.01) in Antarelix™, Antarelix™ + 50 and Antarelix™ + 150 treated animals compared to controls. No differences were estimated in the number of LH pulses between days and treatment. Pulsatile FSH was not affected by treatment. Mean basal LH levels were lower ( P<0.05) after antagonist treatment compared to controls. Antarelix™ blocked the preovulatory LH surge and ovulation, but the effects of Antarelix™ were reduced by exogenous LHRH treatment. The development of follicles larger than 4 mm was suppressed ( P<0.05) by antagonist treatment. In conclusion, Antarelix™ treatment during the follicular phase blocked preovulatory LH surge, while FSH and oestradiol secretion were not affected. Antarelix™ failed to alter pulsatile LH and FSH secretor or pituitary responsiveness to LHRH during the preovulatory period.

Luteinizing hormone secretion as affected by hypophyseal stalk transection and estradiol-17β in ovariectomized gilts

The objectives were to determine hypothalamic regulation of pulsatile luteinizing hormone (LH) secretion in female pigs and the biphasic feedback actions of estradiol-17β (E 2-17β). In the first study, the minimum effective dosage of E 2-17β that would induce estrus in ovariectomized gilts was determined to be 20 μg/kg body weight. In the second study, ovariectomized gilts were assigned randomly on day 0 to treatments: (a) hypophyseal stalk transection (HST), (b) cranial sham-operated control (SOC), and (c) unoperated control (UOC). On day 3, gilts from each group received a single i.m. injection of either E 2-17β (20 μg/kg body weight) or sesame oil. Blood was collected from an indwelling jugular cannula at 15 min intervals for 3 h before (day −2) and after treatment (day 2) from HST, SOC and UOC gilts. On day 3, blood was collected at 2 h intervals for 12 h after E 2-17β or sesame oil injection and at 4 h intervals thereafter for 108 h. Pulsatile LH secretion in all gilts 2 days after ovariectomy exhibited a frequency of 0.9±0.06 peaks/h, amplitude of 1.3±0.13 ng/ml, baseline of 0.8±0.07. Serum LH concentrations from SOC and UOC gilts were similar on day 2 and profiles did not differ from those on day −2. In HST gilts pulsatile LH release was abolished and mean LH concentration decreased compared with controls (0 versus 0.9±0.06 peaks/h and 0.77±0.03 versus 1.07±0.07 ng/ml, respectively; P<0.05). E 2-17β or sesame oil did not affect serum LH concentration in HST gilts, and LH remained constant throughout 120 h (0.7±0.07 ng/ml). In SOC and UOC control gilts, E 2-17β induced a 60% decrease ( P<0.05) in LH concentration within 12 h, and LH remained low until 48 h, then increased to peak values ( P<0.05) by 72 h, followed by a gradual decline to 120 h. Although pituitary weight decreased 31% in HST gilts compared with controls (228 versus 332 mg, P<0.05), an abundance of normal basophils was evident in coronal sections of the adenohypophysis of HST comparable to that seen in control gilts. The third and fourth studies determined that hourly i.v. infusions of LHRH (2 μg) and a second injection of E 2-17β 48 h after the first had no effect on the positive feedback action of estrogen in UOC. However, in HST gilts that received LHRH hourly, the first injection of E 2-17β decreased ( P<0.05) plasma LH concentrations while the second injection of E 2-17β failed to induce a positive response to estrogen. These results indicate that both pulsatile LH secretion and the biphasic feedback action of E 2-17β on LH secretion depend on hypothalamic regulatory mechanisms in the gilts. The isolated pituitary of HST gilts is capable of autonomous secretion of LH; E 2-17β will elicit direct negative feedback action on the isolated pituitary gland if the gonadotropes are supported by exogenous LHRH, but E 2-17β at high concentrations will not induce positive feedback in isolated pituitaries. Thus, the direct effect of E 2-17β on the pituitary of monkeys cannot be mimicked in pigs.

Inhibition of nitric oxide facilitates LH release from rat pituitaries

We examined the effects of nitric oxide (NO) modulators on rat pituitary LH content in vivo and studied their response to LHRH-stimulated LH secretion in vitro in ovariectomized adult female Sprague Dawley rats. Alzet mini pumps (flow rate 10 μl/h) delivering either normal saline (Group I), 1.2 mg nitroglycerin, a donor of NO (Group II) or 50 mg of nitro-L-Arginine methyl ester, a NO synthase (NOS) inhibitor (Group III), were subcutaneously implanted into experimental animals. Following 36 h infusion, pituitaries were removed and either frozen for LH quantitation, or fragmented and challenged in the superfusion system with 10 min pulses of LHRH (1 ng/ml) at 90 min intervals for 10 hours. LH was assayed by radio-immunoassay (RIA) in the homogenates of pituitaries and in aliquots of the superfusate collected every 10 mins. Significantly lower pituitary LH levels were noted in Group III (150.3 ± 18.6 ng) in comparison to Groups I (215.6 ± 5.5 ng; p < 0.04) or II (221.2 ± 14.9 ng; p < 0.01), suggesting that low levels of NO stimulate LH secretion in vivo. The pituitary LH contents were not significantly different in Groups I and II. In vitro studies reveal that exogenous LHRH stimulated response, measured as average pulse response (90 minute period after LHRH), and total LH released during the 10 hour perfusion, was 290 ± 23.6 ng and 1646.7 ± 270.8 ng, respectively, in Group III; 57.9 ± 3.1, and 344.7 ± 24.3 ng in Group I, and 105.3 ± 6.3, and 633.7 ± 77.1 mg in Group II. Thus, our in vitro studies demonstrate significantly enhanced (p < 0.05) LHRH- stimulated LH secretion in Group III in comparison to Groups I and II, while Group II shows higher responsiveness than Group I (p < 0.05). The results of the current studies provide evidence that NOS inhibition facilitates pituitary LH secretion. The differential responses to LHRH-stimulated LH secretion in vitro in the 3 groups suggest a possible role of NO in modulating pituitary LHRH receptor concentrations. However, this will have to be tested by further studies.

Lack of suppressive action of luteal factors from sheep corpus luteum on LH response to exogenous LHRH in ovariectomized, pregnant and post-partum ewes.

In vivo studies have provided evidence of a non-steroidal factor from ovine corpora lutea (CL) of pregnancy called LH-release inhibiting factor (LH-RIF), which specifically inhibits tonic LH release without affecting FSH secretion. To study the possible pituitary site of action of LH-RIF and other factors from sheep CL of pregnancy, the LH response to LHRH was investigated in ovariectomized (OVX) ewes pretreated with ovine luteal extract (oLE) from CL of mid-pregnancy, and in pregnant and post-partum ewes from which the CL were removed at mid-pregnancy. In view of the fact that human follicular fluid (hFF) contains a non-steroidal factor, called gonadotrophin surge-attenuating factor, which attenuates the LHRH-induced LH release, it was clearly important to examine the LHRH-induced LH release in OVX ewes pretreated with oLE or hFF In experiment 1, the LH and FSH responses (the maximum LH and FSH concentrations, the time to maximum LH and FSH concentrations and the area under the LH and FSH response curves) to a single i.v. injection of 5 microg of the LHRH agonist buserelin was not significantly different between ewes pretreated with oLE and ewes pretreated with BSA. Although the LHRH-induced LH and FSH release was slightly attenuated in OVX ewes pretreated with hFF as compared with OVX ewes pretreated with BSA, the maximum LH and FSH concentrations and the area under the LH and FSH response curves were not significantly different between the two groups of ewes. In experiment 2, the LH responses to a single i.v. injection of 0.5 microg LHRH on days 80 and 100 of pregnancy were not significantly different between intact ewes and ewes from which the CL were removed on day 70 of pregnancy. In both groups of ewes the maximum LH concentration and the area under the LH response curve were significantly lower (P <0.02) on day 100 than on day 80 of pregnancy. In experiment 3, the LH responses to a single i.v. injection of 50 microg LHRH on day 140 of pregnancy and on day 10 post-partum were not significantly different between intact ewes and ewes from which the CL were removed on day 70 of pregnancy. In both groups of ewes the maximum LH concentration and the area under the LH response curve were significantly lower (P <0.01) on day 140 of pregnancy than on day 10 post-partum. These experiments provide evidence for a lack of suppressive action of luteal secretory products from the ovine CL of pregnancy on the pituitary LH response to LHRH in OVX, pregnant and post-partum ewes.

Reduction of glucose availability suppresses pulsatile luteinizing hormone release in female and male rats.

Glucose availability controls reproductive activity through modulation of LH secretion. The aim of the present study was to determine whether the glucoprivic suppression is potentiated by gonadal steroids and if glucoprivic suppression of pulsatile LH release is sexually differentiated. Pulsatile LH secretion was examined in rats after peripheral (jugular) administration of the competitive inhibitor of glycolysis, 2-deoxyglucose (2DG). Fourteen days after gonadectomy, blood samples were collected every 6 min for 3 h. One hour after the onset of sampling, 2DG was administered peripherally (200, 400, or 800 mg/kg BW, iv), and food intake was determined after 2DG injection in gonadectomized males and females in the presence or absence of sex steroids (testosterone or estradiol). To test the ability of the pituitary to produce LH under glucoprivic conditions, LHRH was injected every 30 min for 2.5 h in ovariectomized (OVX) rats 30 min after treatment with 400 mg/kg 2DG. At all peripheral doses of 2DG in females and at the middle and high doses of 2DG in males, mean plasma LH and LH pulse frequency decreased (P < 0.05) in the presence of steroids. However, in the absence of sex steroids, the lowest dose in females and the middle dose in males were not effective. Pituitary function appeared normal, because increases in mean plasma LH in response to the exogenous LHRH occurred in OVX rats treated with the middle dose of 2DG. Food intake significantly (P < 0.05) increased after 2DG injection in all groups except estrogen-treated OVX females at the low and high doses of 2DG. These findings suggest that glucoprivic suppression of LH pulses is potentiated by gonadal steroids in both sexes. Moreover, the hypothalamo-hypophyseal axis of the female rat seems to be more sensitive to the decreased glucose availability induced by 2DG than that of the male.

Continued desensitization of the pituitary gland in young bulls after treatment with the luteinizing hormone-releasing hormone agonist deslorelin.

The objective in this study was to evaluate pituitary and testicular function in young bulls during and after treatment with the LHRH agonist deslorelin. The primary focus was to ascertain the period required for a return to typical LH and testosterone secretion after cessation of treatment with deslorelin, in order to establish whether desensitization was a phenomenon restricted to the pituitary or also occurred at the testes. Brahman bulls, 13.0 +/- 0.6 mo of age and 224 +/- 5 kg, were allocated to four groups and received treatment as follows: group C (n = 5), control, received no treatment; group C + LHRH (n = 5), control, received LHRH tests (50 micrograms LHRH i.m.) at the same times as group D + LHRH below; group D (n = 5), received deslorelin (approximately 200 micrograms/day) for 28 days; group D + LHRH (n = 5), received deslorelin for 28 days and were given LHRH test (50 micrograms LHRH i.m.) on Day 28 of treatment and on Days 2, 4, 8, 12, 16, and 20 after treatment. Deslorelin induced acute increases (p < 0.01) in plasma concentrations of LH and testosterone within 2 h, after which concentrations of both hormones declined by 24 h. From Day 6 to Day 28 of the treatment period, plasma LH concentrations were similar for treated and control bulls. During the same period, concentrations of plasma testosterone were greater (p < 0.01) in treated than in control bulls. Mean concentrations of both LH and testosterone were lower in treated than in control bulls for approximately one week after cessation of deslorelin treatment. Bulls treated with deslorelin did not exhibit a release of LH in response to exogenous LHRH on Day 28 of treatment. A relatively small but significant (p < 0.05) release of LH occurred on Day 4 after cessation of treatment with deslorelin (group D + LHRH, 0.49 +/- 0.11 ng/ml; group C + LHRH, 7.17 +/- 0.90 ng/ml). LH release in response to LHRH in bulls previously treated with deslorelin increased to Day 12 and then remained constant to Day 20 after cessation of treatment. However, LH release in these bulls remained significantly lower compared with that of control bulls during the 20 days after cessation of treatment with deslorelin. Bulls treated with deslorelin had a typical release of testosterone after administration of LHRH on Days 2-20 after discontinuation of treatment, even though there were relatively small releases of LH. Therefore, the pituitary in bulls remained desensitized to LHRH for at least 20 days after cessation of treatment with an LHRH agonist. In contrast, desensitization did not occur at the testes, which retained the capacity for a typical testosterone response to the LH that was released after administration of LHRH.

Pituitary function, ovarian follicular growth, and plasma concentrations of 17 beta-estradiol and progesterone in prepubertal heifers during and after treatment with the luteinizing hormone-releasing hormone agonist deslorelin.

Pituitary function, ovarian follicle growth, and plasma steroid concentrations were determined in prepubertal heifers during and after treatment with the LHRH agonist deslorelin. Brahman heifers, 13 mo of age and 204 +/- 5 kg, were allocated to 4 groups with treatments as follows: group C (n = 6), control, received no treatment; group C + LHRH (n = 6), control, received LHRH tests at the same times as group D + LHRH below; group D (n = 6), received deslorelin (approximately 300 micrograms/day) for 28 days; group D + LHRH (n = 6), received deslorelin for 28 days were given LHRH tests (50 micrograms LHRH i.m.) on Day 28 of treatment and on Days 2, 4, 8, 12, 16, and 20 after treatment. Number and size of ovarian follicles were determined by rectal ultrasonography. Deslorelin induced an increase in plasma concentrations of LH within 2 h (p < 0.001); LH remained greater (p < 0.05) for heifers treated with deslorelin for 48 h, but from Day 4 to 28 of treatment, LH in treated and control heifers did not differ. Ovarian follicles of heifers treated with deslorelin were characterized by increased (p < 0.05) maximum size, and also tended to have a greater rate of growth, compared with those of control heifers. Heifers treated with agonist had greater (p < 0.05) plasma concentrations of 17 beta-estradiol from Day 0 to 28 of treatment, and 17 beta-estradiol in these heifers showed cyclical fluctuations that appeared to be related to cycles of growth and regression of ovarian follicles. After cessation of deslorelin treatment, plasma LH was similar for heifers in group C and group D. Heifers in group C + LHRH had significant (p < 0.05) LH responses to exogenous LHRH at all times. In contrast, heifers in group D + LHRH did not show an LH release in response to exogenous LHRH on Day 28 of treatment and also failed to have a significant (p < 0.05) release of LH until Day 12 after treatment. A significant increase in plasma 17 beta-estradiol after LHRH injection also occurred on Day 12 after treatment in heifers in group D + LHRH. The findings indicated that LHRH agonist treatment in prepubertal heifers is associated with an acute LH response followed by a return of LH to concentrations similar to those of control heifers. Size of the largest ovarian follicle is greater in heifers treated with LHRH agonist and is associated with increased plasma concentrations of 17 beta-estradiol. After cessation of agonist treatment, the pituitary remains desensitized to LHRH for approximately 12 days. This study is the first demonstration of enhanced ovarian follicular growth and increased 17 beta-estradiol secretion during treatment with an LHRH agonist.

Periovulatory LHRH, LH and FSH secretion in cyclic rats treated with RU486: effects of exogenous LHRH and LHRH antagonist on LH and FSH secretion at early oestrus

The antiprogesterone RU486 injected on the morning of pro-oestrus blunts the preovulatory secretion of LH and FSH and abolishes the secondary secretion of FSH during oestrus without affecting ovulation in the rat. To ascertain whether the secretion of LHRH is involved in these effects, we studied the effects of RU486 (4 mg/0.2 ml oil), given s.c. at 0800 h on pro-oestrus, on LHRH secretion into the pituitary stalk blood vessels and on peripheral plasma concentrations of LH and FSH at 1800 h on pro-oestrus and 0200 h on oestrus. Furthermore, we determined the effects of an s.c. injection of 1 mg of an LHRH antagonist (LHRH-A; ORG30276) at 2000 h on pro-oestrus and those of an i.p. injection of 100 ng LHRH (Peninsula 7201) at 0100 h on oestrus on serum concentrations of LH, FSH and oestradiol at 0200 h on oestrus in oil- and RU486-treated rats. RU486 decreased LHRH secretion at 1800 h on pro-oestrus while this was increased at 0200 h on oestrus. While the reduction of preovulatory LHRH secretion in RU486-treated rats coincided with a reduction in both LH and FSH surges during the evening of pro-oestrus, the increased LHRH secretion during the early hours of oestrus was only accompanied by an increased concentration of LH. An injection of LHRH stimulated, while that of LHRH-A inhibited serum concentrations of LH at 0200 h on oestrus in both oil- and RU486-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential gonadotropin responses to N-methyl-D,L-aspartate in intact and castrated male rats.

Peripheral administration of N-methyl-D,L-aspartate (NMA), a neuroexcitatory amino acid agonist, probably stimulates LH release through an increase in endogenous LHRH secretion. In the present study, NMA and a potent LHRH antagonist were used to determine the degree to which release of FSH is similarly dependent upon the acute secretion of LHRH. A second aim was to compare responsiveness of LHRH neurons to NMA in castrated and intact male rats. Adult male rats were castrated (n = 10) or sham castrated (n = 11) on the morning of Day 0. After 8 days, rats were fitted with atrial catheters between 0900 and 1200 h; at 2100 h they received s.c. either oil vehicle or 100 micrograms of an LHRH antagonist. Starting at 0900 h on Day 9, 0.5-ml blood samples were collected every 10 min for 3 h. After 1 h of sampling each animal received i.v. 5 mg of NMA in 0.5 ml 0.9% saline. An hour later each rat received i.v. 500 ng of LHRH in 0.5 ml saline. Plasma LH, FSH, and prolactin (PRL) levels were determined by RIA. In the oil-treated sham castrates, mean plasma LH levels were increased by 110% (p < 0.01) within 10 min and remained elevated for 30 min after the injection of NMA. The profile of this LH secretory response was similar to or slightly more robust than endogenous LH pulses observed previously. The NMA-induced LH release was completely blocked by pretreatment with LHRH antagonist. In both oil- and antagonist-treated sham-castrated rats, NMA administration failed to elicit a concomitant increase in plasma FSH levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovariectomy Decreases Luteinizing Hormone-Releasing Hormone-Degrading Activities in the Anterior Pituitary in Female Mice.

Changes in the luteinizing hormone-releasing hormone-degrading activities (LHRH-DA) in the anterior pituitary and the hypothalamus after ovariectomy (OVX) were examined in mice. Mice were decapitated at 1000 h on diestrus day 1 (D1) or on day 7, 14 and 21 after OVX. Another group of mice was also killed at 1000, 1200, 1500 and 1700 h on D1 or on day 7 after OVX to determine the change in LHRH-DA during the day. Trunk blood, the anterior pituitary and hypothalamic tissue were collected. LHRH-DA were determined by incubating the exogenous LHRH with tissue extracts at 37C for 30 min. The changes of LHRH-DA in the anterior pituitary were inversely correlated with those of LH secretion: LHRH-DA decreased after OVX when plasma LH levels increased, but did not change when plasma LH levels were kept at a stable level throughout the day on D1 or day 7 after OVX. The present results suggest that the LHRH-DA in the anterior pituitary is involved in its hypersensitivity to the LHRH stimulation after OVX.

Chronic stress induced changes in LH secretion: The contribution of anorexia associated to stress

The effects of chronic intermittent immobilization (IMO) on serum LH levels of adult male rats were studied. Chronic IMO (2 h daily for 13 days) did not alter basal LH levels, but abolished the LH response to acute stressors (IMO and tailshock). The inhibition of LH caused by acute exposure to IMO for 4 or 18 h was similar in control and chronic IMO rats. Also the LH response to exogenous LHRH administration was normal in chronically stressed rats. When a group of rats eating the same amount of food as that eaten by immobilized rats was introduced (pair-fed), an inhibition of LH response to acute stressors quite similar to that found in chronic IMO rats was observed. These data indicate that chronic stress-induced inhibition of LH release caused by short-term exposure to acute stressors was located above the pituitary and was mainly due to anorexia accompanying daily exposure to the stressor.

Delayed puberty in uremia: pituitary-gonadal function during short-term pulsatile luteinizing hormone-releasing hormone administration.

Pubertal development is frequently delayed or disordered in children with chronic renal failure. Both neuroendocrine and peripheral alterations due to uremia have been hypothesized to explain the impairment in the pituitary gonadal axis. The aim of the present study was to evaluate quantitative (immunological) and qualitative (biological) LH secretion, as well as FSH and sex steroids, before and during 7 days of sc LHRH administration (136-150 ng/kg bw every 120 min) in 5 uremic children (13.1-14.8 yr) with delayed puberty. Six nonuremic children (13.2-17.8 yr) with delayed puberty underwent the same schedule and served as control group. On day 0 mean immunoreactive LH (I-LH) levels were higher in uremic (4.5 +/- 0.9 mIU/ml) than in nonuremic (1.9 +/- 03 mIU/ml; p < 0.05) subjects while no differences were observed in bioactive LH (B-LH) levels (2.9 +/- 0.7 mIU/ml vs 2.4 +/- 0.3 mIU/ml). In both groups of subjects testosterone was at prepubertal levels. Spontaneous I-LH and B-LH pulses were observed sporadically in both uremic and nonuremic subjects. Short-term pulsatile LHRH administration induced significant increases in B-LH, I-LH, FSH and testosterone. The B/I LH ratio increased from day 0 (0.7 +/- 0.2) to day 7 (1.3 +/- 0.4; p < 0.05) in uremics while it showed wide fluctuations in nonuremic subjects. On day 7, 4 uremic and 5 nonuremic subjects showed a pulsatile release of B-LH after exogenous LHRH pulses. Our data document that in uremia there are qualitative as well as quantitative abnormalities in pituitary gonadal secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive endocrinology of macaroni ( Eudyptes chrysolophus) and gentoo ( Pygoscelis papua) penguins : II. Plasma levels of gonadal steroids and LH in immature birds in relation to deferred sexual maturity

Plasma levels of LH, testosterone, estradiol, and progesterone were measured, during the breeding season, in adult and immature macaroni ( Eudyptes chrysolophus) and gentoo ( Pygoscelis papua) penguins, at Bird Island, South Georgia (54°S, 38°W), in relation to deferred sexual maturity. Macaroni penguins do not breed until 6–8 years of age whereas gentoo penguins first breed at 2 years of age. Plasma LH was elevated in 3- to 5-year-old macaroni penguins, but not in 1- to 2-year-old birds nor 1-year-old gentoos. However, 1 year olds of both species responded to an injection of exogenous LH-RH by increasing LH secretion. Some individual 3-, 4-, and 5-year-old macaroni penguins had circulating testosterone levels within the range of peak values in adults, suggesting that in males, gonads were physiologically mature several years in advance of the age of first breeding. One-year-old macaroni penguins had elevated progesterone levels and basal estradiol levels, but in 2–4 year olds plasma levels of both progesterone and estradiol were low. This does not support the hypothesis that high progesterone levels “block” ovarian maturation in immature penguins. Immature gentoo penguins showed a different pattern of hormone secretion. Plasma testosterone was low in all breeding periods, but estradiol levels increased to a peak during the incubation period, 4 weeks later than peak values occurred in adults. In both species, therefore, deferred sexual maturity was associated with delayed and/or reduced secretion of LH and gonadal steroids.

Patterns of Pulsatile Luteinizing Hormone and Follicle-Stimulating Hormone Secretion in Prepubertal (Midchildhood) Boys and Girls and Patients with Idiopathic Hypogonadotropic Hypogonadism (Kallmann's Syndrome): A Study Using an Ultrasensitive Time-Resolved Immunofluorometric Assay

To study the ontogeny of spontaneous pulsatile LH and FSH secretion before the onset of puberty, plasma LH and FSH were measured by an ultrasensitive time-resolved immunoflurometric assay in 16 boys and 6 girls, aged 6.5 +/- 0.2 yr (+/- SEM; range, 4.4-8.0) with short stature. Eight male patients with idiopathic hypogonadotropic hypogonadism (Kallmann's syndrome), aged 24.1 +/- 3.4 yr, were also investigated. Blood samples were withdrawn at 10- to 20-min intervals for 12 h from 2000-0800 h. Pituitary responsiveness was assessed by a standard iv LHRH challenge test. LH and/or FSH pulses were detectable in all but two prepubertal subjects. In boys, low amplitude LH (0.16 +/- 0.06 U/L) and FSH (0.19 +/- 0.03 U/L) pulses were detectable at mean frequencies of 2.19 +/- 0.37 and 2.13 +/- 0.46 pulses/12 h, respectively. In girls, low amplitude LH (0.29 +/- 0.18 U/L) pulses, but higher (P less than 0.05 compared to boys) amplitude FSH (1.62 +/- 1.05 U/L) pulses were observed at frequencies of 1.71 +/- 0.56 and 1.67 +/- 0.53 pulses/12 h, respectively. Mean FSH in prepubertal girls (1.95 +/- 0.88 U/L) was significantly (P less than 0.05) higher than that in boys (0.46 +/- 0.07 U/L), but mean LH was not different at 0.17 +/- 0.07 and 0.10 +/- 0.03 U/L, respectively. Patients with Kallmann's syndrome had mean LH and FSH levels indistinguishable from those of prepubertal boys. Nocturnal augmentation of pulsatile LH or FSH secretion was observed in 74% of children (71% in girls and 75% in boys), but in none of the eight patients with Kallmann's syndrome. A close temporal association was observed between sleep onset and the appearance of nocturnal pulsatile gonadotropin secretion. The FSH response to exogenous LHRH in prepubertal girls was significantly greater than that in patients with Kallmann's syndrome and prepubertal boys, but LH responses were not different. Our results show that pulsatile LH and FSH secretion occurs in the majority of boys and girls in midchildhood, with a robust association with nocturnal sleep onset. Between the ages of 4-8 yr, these low amplitude and low frequency pulses are unable to activate gonadal function. The regulation of FSH secretion in prepubertal girls appears to be different from that in prepubertal boys.(ABSTRACT TRUNCATED AT 400 WORDS)

Patterns of Pulsatile Luteinizing Hormone Secretion before and during the Onset of Puberty in Boys: A Study Using an Immunoradiometric Assay

To study spontaneous pulsatile LHRH/LH secretion around the onset of puberty, nocturnal plasma LH was measured by means of a highly sensitive immunoradiometric assay in 30 boys (aged 5.6-16.8 yr) investigated for potential problems with growth and/or development. Blood was withdrawn at 10- to 20-min intervals from 2000-0800 h. Pulse analysis was accomplished by a computerized peak detection algorithm. Pituitary and gonadal responsiveness was assessed by a standard exogenous LHRH challenge and testosterone. Subsequent clinical progress was monitored for a mean duration of 2.08 +/- 0.16 yr and used as the basis for classifying patients retrospectively into three groups: 1) prepubertal (n = 14), 2) peripubertal (n = 11), and 3) pubertal (n = 5). LH pulses were undetectable in 9 and present in 5 prepubertal subjects, the youngest of whom was aged 7.3 yr. In peripubertal and pubertal individuals, 2-7 LH pulses/12 h were detectable. LH pulses were detectable before sleep by midpuberty (Tanner stage 3). There was a highly significant (P less than 0.0001) increase in LH/LHRH pulse frequency from 0.93 +/- 0.38 to 4.55 +/- 0.43/12 h (mean +/- SEM) between the prepubertal and peripubertal groups and a further increase to 6.20 +/- 0.37/12 h in the pubertal group. LH pulse amplitude remained under 1.0 U/L in both the prepubertal and peripubertal groups and only increased significantly to 2.02 +/- 0.17 U/L in pubertal boys. Response to LHRH increased significantly between the prepubertal (2.47 +/- 0.49 U/L) and peripubertal (6.53 +/- 2.02 U/L) patients. T increased significantly at each stage, with the greatest rise between the peripubertal and pubertal stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Luteinizing Hormone (LH)-Releasing Hormone: Chronic Effects on LH and Follicle-Stimulating Hormone Cells and Secretion in Adult Male Rats*

We investigated whether chronic administration of LHRH to normal adult rats could increase the percentages of anterior pituitary gland (APG) cells that contain immunoreactive LH and/or FSH and gonadotropin secretion. Vehicle or 1 microgram LHRH was injected sc twice daily for 6 days, and rats were decapitated 16 h after the last injection. Treatment with LHRH caused nearly a doubling in the numerical density of LH and FSH cells and in the percentage of APG cells that contained LH or FSH. It also caused a shift in the gonadotroph population from LH and LH/FSH cells to LH/FSH cells. It did not change the mean size of gonadotrophs or APG weight. These changes at the light microscopic level were not accompanied by any apparent changes in LH cells at the ultrastructural level. However, they were accompanied by an approximate doubling of the basal serum LH and FSH concentrations, an increase in the APG FSH concentration, and an increase in the basal FSH release rate (measured in vitro). The results indicate that exogenous LHRH can be administered to increase numbers of gonadotrophs in the APG, synthesis of FSH in gonadotrophs, and basal serum LH and FSH concentrations.

Anti-oestrogenic effect of clomiphene citrate in oestrogen-treated, hypogonadal women

The effect of clomiphene on the pituitary response to exogenous LHRH was investigated in five hypogonadal women during long-term treatment with varying doses of oestrogen. In three of them, basal LH levels were low (less than 10 mIU/ml) and increased significantly after 8 days of treatment with clomiphene (100 mg/day). Clomiphene augmented the LH and FSH response to LHRH (an acute i.v. injection of 100 micrograms) and changed the pattern of response into that seen in the absence of the influence of ovarian steroids. We conclude that clomiphene exerts anti-oestrogenic effects on basal and LHRH-stimulated release of gonadotrophins in hypogonadal women during long-term treatment with oestrogen.

Effect of pulsatile luteinizing hormone — releasing hormone administration on pituitary — gonadal function in elderly man

The effect of short-term pulsatile LHRH administration was studied in 8 healthy subjects ranging from 60 to 81 yr to see if the decrease of pituitary gonadal function could be in part due to changes in the discharge of LHRH from the hypothalamus. Gonadotropin and testosterone (T) secretion was evaluated two weeks before and during LHRH (122-160 ng/kg bw every 120 min sc) infusion. In addition, a bolus dosage of LHRH (50 mu iv) was given both at the beginning and at the end of pulsatile LHRH administration in order to test gonadotrophs sensitivity. A significant increase in gonadotropin levels from day 0 to day 4 was found, and was followed by a subsequent decrease from day 7 to day 14. A slight significant increase in T levels was observed during LHRH administration (p less than 0.01). LH pulses were identified in 5 out of 8 subjects on day 0. On day 14, all the exogenous LHRH pulses were followed by significant LH bursts. There was not a significant decrease in the pituitary LH responsiveness to LHRH test from day 0 to day 14. Our study seems to indicate that pituitary - gonadal unit in normal elderly men can be modulated by pulsatile administration of LHRH. A pulse frequency of LHRH which is probably similar to the physiological one, could induce a slight increase in T levels via qualitative changes in LH activity. We can assume that clinical changes in gonadal activity might also be connected to some disturbances in endogenous LHRH pulsar.

Ontogeny of pulsatile gonadotrophin secretion and pituitary responsiveness in male puberty in man: a mixed longitudinal and cross-sectional study

The onset of puberty is characterized by a sleep-associated increase in pulsatile LH secretion which is not observed in adults. The ontogeny of gonadotrophin secretion during pubertal maturation may reflect changes in endogenous LHRH secretion, pituitary sensitivity to LHRH and/or alterations in gonadal steroid feedback. To understand the interplay between these mechanisms, we have examined the pulsatile pattern of plasma LH, FSH, testosterone, oestradiol and prolactin between 20.00 and 09.00 h and the pituitary response to repeated exogenous LHRH stimulation in 16 boys with delayed puberty (age 16.3 +/- 2.7 (S.E.M.) years) on one to four occasions in a mixed longitudinal/cross-sectional analysis. Physical maturity was determined by Tanner G staging (1-5) and clinical progress followed for a mean duration of 22.4 +/- 8.5 months during which 33 hormone profiles were obtained. Nocturnal (23.00-09.00 h) LH pulse frequency increased to a peak of 0.54 +/- 0.03/h at stage 2 which was followed by a gradual decline to 0.42 +/- 0.04/h at stage 5. The appearance of LH pulses in the evening (20.00-23.00 h), probably representative of the rest of the day, was delayed until mid-puberty from which point frequency increased to a peak of 0.53 +/- 0.08/h at stage 5. LH pulse amplitude showed a linear increase from stages 1 to 5, with nocturnal pulse amplitudes being higher than evening pulses throughout. FSH did not show a clear pulsatile pattern. The LH:FSH ratio reversed from less than 1 to greater than 1 at stage 2. The LH response to exogenous LHRH increased in parallel with LH pulse amplitude. There was no difference in the pattern of LH response to repeated LHRH stimulation as puberty advanced; the first stimulus always elicited a greater response than subsequent doses. In contrast, the FSH response to LHRH was maximal at stage 1 and became attenuated thereafter. The estimated mean nocturnal LHRH concentration or amplitude did not show any increase during pubertal maturation from 20.42 +/- 11.57 at stage 1 to 35.96 +/- 20.83 ng/l at stage 5. In conclusion, the sequential changes in this study suggest that the sleep-entrained increase in LHRH pulse frequency plays a key role at the onset of puberty. By enhancing pituitary responsiveness and setting in motion a cascade of events, this peripubertal augmentation of LHRH pulse frequency can account for most of the subsequent changes in LH, FSH and testosterone secretion during pubertal development in the male without any apparent alteration in LHRH pulse amplitude.