Significant Increase In Serum LH Research Articles

Marked Seasonal Changes in Response to the Negative Feedback Action of Estradiol on Luteinizing Hormone Secretion in the Female Japanese Monkey

The seasonal changes in response to the negative feedback action of estradiol on LH secretion were studied in two groups of ovariectomized Japanese monkeys (Macaca fuscata fuscata; n = 6). Blood samples were collected two to three times a week, and changes in serum concentrations of LH, estradiol, and progesterone were examined. Before ovariectomy (OVX), serum LH was maintained at about 320 pg/ml regardless of the season (breeding season: autumn and winter). After OVX and simultaneous treatment sc with a Silastic implant of estradiol during the first breeding season, serum LH increased rapidly and remained high. As spring arrived, serum LH decreased abruptly and remained low. The removal of implants during the subsequent nonbreeding season resulted in an increase in serum LH similar to that during the previous breeding season after OVX and estradiol treatment. After the reinsertion of implants during the same nonbreeding season, serum LH reverted to previous low levels. As autumn arrived (second breeding season), serum LH rose again and remained high under the presence of implants. In the first subset of animals (n = 3), the implants were left in place until the subsequent mid-nonbreeding season when they were removed, and reinserted during the same non-breeding season. The findings closely corresponded to the previous results. In these animals, the implants were removed during the third breeding season, which resulted in a significant increase in serum LH. The second subset of animals (n = 3) underwent removal of implants during the second breeding season, which resulted in a further increase in serum LH, but the difference was not significant. In both subsets of animals, the timing of the increase and decrease in serum LH under the presence of implants virtually coincided with the onset and end of the breeding season in ovary-intact animals. Serum estradiol after OVX was maintained at levels similar to those in intact animals (80-100 pg/ml) under the presence of implants, but removal of implants resulted in decrease in serum estradiol to around 30 pg/ml within 1 week. Serum progesterone after OVX was maintained at low levels (less than 0.2 ng/ml) regardless of the presence of estradiol implants. These results clearly indicate a marked seasonal difference in serum LH concentrations in ovariectomized monkeys in response to constant serum estradiol. It is suggested that seasonal breeding of the Japanese monkey is governed by biannual changes in the response of the hypothalamo-hypophysial axis to the negative feedback action of estradiol.

Effects of cyclosporine on the hypothalamic-pituitary-gonadal axis in the male rat: mechanism of action.

In the intact adult male rat, cyclosporine (CsA) induces a significant decrease in serum testosterone (T), serum LH, and intratesticular T. To elucidate the mechanism of action of this CsA-induced hypogonadotropic hypogonadism, castrated male rats were treated with oral CsA (30 mg/kg.day) or vehicle alone, and serum LH was measured after 1, 2, and 4 weeks of treatment. Surprisingly, serum LH was higher in these CsA-treated castrated rats at 1, 2, and 4 weeks than in castrated controls. To provide insight into the cause of this increase in serum LH, a T implant (8 mm) was inserted (at week 5 of treatment) in both CsA-treated and control castrated animals, and serum LH was measured 1 week after insertion of the T implant. Serum LH levels decreased to control values after insertion of the T implant. Subsequently, two other groups of rats received 8-mm T implant at the time of castration and were then treated up to 4 weeks with either CsA or vehicle alone. Serum LH showed a significant decrease in these CsA- plus T-treated animals compared to the vehicle- plus T-treated animals. A GnRH stimulation test performed after 2 weeks of CsA/vehicle treatment showed a significant increase in serum LH in all the rats 30 min after GnRH administration (1, 10, 30, and 100 ng/100 g BW, ip), indicating a normal pituitary response. The increase in LH after exogenous GnRH treatment was more significant in CsA-treated intact rats than in the controls. There was no difference in creatinine clearance between intact and castrate T-treated rats regardless of whether they received CsA. These studies indicate that the hypogonadotropic hypogonadism induced by CsA in intact male rats is mediated through the hypothalamic-pituitary axis, primarily at its hypothalamus end, does not seem to be due to the nephrotoxicity of CsA, and is modulated by T and/or its metabolites.

ICI 176,334: a novel non-steroidal, peripherally selective antiandrogen.

Pure antiandrogens, like flutamide, antagonize androgen action both peripherally and centrally at the hypothalamic-pituitary axis, which leads to an increase in LH and testosterone secretion. A new non-steroidal antiandrogen ICI 176,334 [2RS)-4'-cyano-3-(4-fluorophenylsulphonyl)-2-hydroxy-2-methyl-3'- trifluoromethyl)propion-anilide) has now been discovered which causes regression of the accessory sex organs but does not increase serum concentrations of LH and androgens. ICI 176,334 binds to rat prostate androgen receptors with an affinity around fourfold that of hydroxyflutamide. When administered s.c. concurrently with testosterone propionate (200 micrograms/kg) for 7 days to immature castrated rats, ICI 176,334 (10 mg/kg) significantly (P less than 0.001) inhibited growth of the seminal vesicles and ventral prostate gland. Oral administration of ICI 176,334 at doses of 1, 5 and 25 mg/kg for 14 days to adult rats caused a dose-related reduction in accessory sex organ weights but had no effect on the testes. None of these doses caused a significant increase in serum LH and testosterone. Flutamide was around fourfold less potent and significantly increased serum LH and testosterone at the higher doses. ICI 176,334 was well tolerated. ICI 176,334 should, therefore, prove useful for the treatment of androgen-responsive benign and malignant diseases.

Clomiphene citrate induces pituitary GnRH receptors in ovariectomized rats: its possible role in induction of ovulation.

Since our previous studies have shown that clomiphene citrate (clomiphene) acts directly on the pituitary gland and exerts a facilitatory role on oestradiol-17 beta (E2)-induced LH surge in chronically ovariectomized rats, the effect of clomiphene on pituitary GnRH receptors was investigated. A single ip injection of either 5 micrograms E2 or 200 micrograms clomiphene did not induce LH release in adult rats ovariectomized 1-2 weeks before the injection. However, a significant increase in serum LH was noted 24 h after a single injection of E2 in the ovariectomized rats, if clomiphene was pre-injected 48 h before the E2 injection. The content of pituitary GnRH receptors in the ovariectomized rats (62 +/- 9 fmol/pituitary) remained almost unchanged until 24 h after a single injection of clomiphene but significantly increased 48 h after the injection (105 +/- 13 fmol/pituitary) without any alterations in the affinity for GnRH. To determine steroid specificity for the increase in pituitary GnRH receptors, other classes of steroids were injected in the ovariectomized rats. A single dose of E2 increased GnRH receptors, but either progesterone or 5 alpha-dihydrotestosterone failed to show any effect on the level of GnRH receptors. These results suggest that clomiphene may augment oestrogen-induced pre-ovulatory LH surge in anovulatory women, at least in part by increasing the number of pituitary GnRH receptors.

Effects of Melatonin and Thyroxine Replacement on Thyrotropin, Luteinizing Hormone, and Prolactin in Male Hypothyroid Hamsters*

The effects of daily evening melatonin injections on plasma and pituitary levels of TSH, LH, and PRL in hypothyroid hamsters maintained under a 14-h light, 10-h dark photoperiod were investigated. Circulating levels of thyroid hormones were monitored, and testicular weights were recorded. Thiourea-induced increases in serum and pituitary TSH were significantly reduced by melatonin injections. Control hamsters, not receiving thiourea, responded to daily evening melatonin injections with a decrease in serum T4. Serum T3 levels were decreased by thiourea and increased by T4 replacement. The pituitary PRL content was significantly reduced below control values in hamsters receiving melatonin injections; the sensitivity to melatonin was inhibited by thiourea and restored by T4 replacement. T4 replacement injections were associated with a significant decrease in serum PRL and a significant increase in serum LH. Melatonin-induced testicular involution was attenuated by thiourea administration; this attenuation was reversed by T4 replacement. Similarly, a melatonin-induced decrease in serum LH was prevented by thiourea administration and restored by T4 replacement. The data suggest that melatonin injections increase the sensitivity of the pituitary to T4/T3 feedback inhibition of TSH. Furthermore, these data show that thyroid status may influence melatonin-induced changes in release of PRL and LH from the hamster pituitary. The data showing an interaction of thyroid hormones in the control of testicular size are interpreted as evidence that thyroid hormones play a major role in the mechanism regulating gonadal cycles in the hamster.

Neonatal androgen abolishes clock-timed gonadotrophin release in prepubertal and adult female hamsters.

Testosterone propionate (100 micrograms) or oil was injected within 24 h of birth. At 25 days of age blood samples were obtained at 14:00, 17:00 and 20:00 h. There was a significant increase in serum LH, FSH and progesterone concentrations between 14:00 and 17:00 h in the controls, followed by a decrease at 20:00 h. These rhythms were absent in testosterone propionate-injected animals. Ovariectomy of adults was followed by similar increases of LH and FSH in androgenized and oil-injected females (gonadectomy response) but the large surge of gonadotrophins observed in controls 1 day after implantation of an oestradiol-containing capsule (positive feedback) was not detectable in androgenized females. These results show that the initial effects of neonatal androgenization on cyclic gonadotrophin release in the female are present before puberty and are separable from effects on steroid modulation of gonadotrophin secretion.

Interrelationship between pituitary-testicular axis activity and raised environmental temperature in the rat.

The relationship between the testes and the adenohypophysis in rats exposed to heat was assessed by (1) the determination of adenohypophysial concentrations of FSH, LH and prolactin as well as serum levels of prolactin and testosterone in rats maintained at 35 degrees C for various periods of time and (2) the elucidation of the responsiveness to stimulation with gonadotrophin releasing hormone (GnRH) or human chorionic gonadotrophin (hCG) of the rat acclimatized for 40 days to a temperature of 35 degrees C. The results demonstrated that while heat exposure caused a transient change in the concentration of FSH and LH in the adenohypophysis, the level of prolactin increased by twofold within 24 h and remained significantly higher than in control animals. A concurrent significant decrease in the concentrations of prolactin and testosterone in the serum of rats exposed to heat was also observed. Challenging the rat with exogenous GnRH resulted in a significant increase in serum LH and FSH concentrations in control rats and rats exposed to heat, but the magnitude of the rise in LH was greater in the latter group. However, this phenomenon was not accompanied by a rise in serum testosterone concentration in the rat exposed to heat. Challenging the animals with hCG provoked an increase in serum testosterone, but the magnitude of the rise was greater by far in the control rats. It is concluded that exposure of the intact rat to increased environmental temperatures is accompanied by accumulation of prolactin in the lactotrophs, reduced serum prolactin concentration, decreased capacity of the testes to synthesize testosterone and consequently reduced serum testosterone concentration. These phenomena are independent of the capacity of the adenohypophysis to synthesize LH.

An acute increase in serum prolactin does not modify gonadotropin release in female rats.

Attempts were made to find out whether hyperprolactinemia has an effect on the hypothalamo-pituitary response to estrogen feedback and LHRH stimulation. Adult female rats of Wistar strain were ovariectomized and received subcutaneous injection of 20 micrograms estradiol benzoate (EB) 3-4 weeks later (day-0). A second injection of 20 micrograms EB, when administered at noon on day-3, induced a highly significant increase in serum LH (p less than 0.001 vs. basal values), but not FSH, estimated at 1800 h on the same day. This EB-promoted LH release was not altered by pretreatment with rat PRL (5 micrograms/day), which was administered subcutaneously daily in the morning (1100 h) between day-1 and day-3. No statistical difference in the serum LH concentration was found when compared with the values for the control animals pretreated with 0.9% saline alone. Serum gonadotropins 15 min after LHRH administration (100 ng/100 g BW) in 32-day-old female rats were not statistically different between the animals pretreated with 5 micrograms PRL, which was given subcutaneously daily (at 0800 h) for 3 days, and the controls pretreated with 0.9% saline. These results suggest that an acute increase in serum PRL may not exert a negative effect on the gonadotropin release induced by estrogen feedback and LHRH stimulation.

Direct evidence in men for a role of endogenous oestrogens on gonadotrophin release.

In six healthy subjects serum oestradiol was selectively decreased by administering an aromatase activity inhibitor, hydrotestolactone (HT). After HT administration serum oestradiol (Oe2) decreased from 18.7 +/- 2.3 (SEM) to 6.7 +/- 0.6 pg/ml whereas testosterone (T) and dihydrotestosterone (DHT) blood levels were not modified. These oestradiol changes were associated with a significant increase in serum LH and FSH concentrations (P less than 0.001). The administration of tamoxifen, an oestrogen antagonist, to 5 subjects caused a sharp increase in LH and FSH levels (P less than 0.001). Oe2 was unchanged after the treatment with tamoxifen, whereas T levels were significantly higher. The sum of these data suggests that oestradiol under physiological conditions plays a specific role in the feedback mechanism of gonadotrophin release.

The stimulatory roles of catecholamines and acetylcholine in the regulation of gonadotropin release in ovariectomized estrogen-primed rats.

Injections of 2 mg of progesterone into ovariectomized estrogen-primed rats significantly increased serum LH and FSH concentrations 3, 5 and 8 hr later. Receptor blockers of noradrenaline (NA), dopamine (DA) or acetylcholine (ACH), phenoxybenzamine (20 mg/kg body weight), pimozide (1mg/kg body weight) or atropine (700 mg/kg body weight), respectively, prevented the progesterone-induced gonadotropin release. On the other hand, none of them blocked the gonadotropin release following unilateral electrochemical stimulation (100 microA for 60 sec) of the medial preoptic area which occurred 0.5 and 1.5 hr later, although pimozide or atropine reduced serum LH concentrations at 4.0 hr after stimulation. Furthermore, the sites of action of NA, DA and ACH with respect to LH release were examined by intracerebral implantation in ovariectomized estrogen-primed rats DA or ACH, when implanted unilaterally into the medial preoptic urea, induced a significant increase in serum LH 5 hr later, whereas NA decreased LH levels. Implantations of NA or ACH into the bed nucleus of the stria terminalis or the medial amygdala increased serum LH although the effect of NA into the latter was not statistically significant. Only implantations of NA among the three substances into the lateral septum induced LH release. These results suggest that all of NA, DA and ACH play stimulatory roles in the regulation of gonadotropin secretion, and that there are regional differences of their effectivenesses in releasing LH within the limbic-preoptic area.

Data on the sites of stimulatory feedback action of gonadal steroids indispensable for luteinizing hormone release in the rat.

The sites of the stimulatory feedback action of gonadal steroids on LH release were investigated in estrogen-primed ovariectomized rats. Either estradiol benzoate (E2) or estrone (E1) injections 72 h after E2 priming induced a significant increase in serum LH 30 h later, whereas injections of progesterone (P) did so 6 h later. Horizontal sections placed above the medial preoptic area prevented the increase after E2 injections but not after E1 and P injections. Retrochiasmatic sections or bilateral lesions placed in the medial-basal part of the suprachiasmatic area prevented any increases in serum LH induced by steroid injections. Intracerebral implantations of E2 and P in E2-primed ovariectomized rats induced a similar significant increase in serum LH when E2 was implanted into the bed nucleus of stria terminalis (BST), the lateral septum (l-SEPT) and the preoptic suprachiasmatic area (POSC), and when P was implanted in to the medial amygdala, the diagonal band of Broca (DBB), the POSC, the l-SEPT and the anterior hypothalamic area (AHA). These results suggest that the stimulatory feedback effect of E2 is exerted on the limbic structures, especially the BST and the l-SEPT, while the main sites of the stimulatory feedback action of P are located in the DBB, the POSC, and the AHA.

Effect of progesterone and its 5 alpha-reduced metabolites on gonadotropin levels in estrogen-primed ovariectomized rats.

In an effort to determine whether the metabolic conversion of progestrone may be important in the feedback effects of this steroid, serum LH and FSH levels were measured after administration of progesterone, 5 alpha-dihydroprogesterone or 3 alpha-hydroxy-5 alpha-pregnan-20-one to estrogen-primed ovariectomized rats. A single injection of 2 or 4 mg progesterone, 4 mg 5 alpha-dihydroprogesterone, or 4 mg 3 alpha-hydroxy-5 alpha-pregnan-20-one 72 h (Day 3) after estrogen pretreatment induced a highly significant increase in serum LH and FSH 6 h later (1800 h). Although serum gonadotropin levels had begun to decrease 12 h after administration of the progestins, they were still significantly higher than control values and did not return to baseline levels until noon on Day 4. When either progesterone or 3 alpha-hydroxy-5 alpha-pregnan-20-one was administered at noon on Days 3 and 4, there was a significant reduction in LH levels 6 h after the second injection. In contrast, serum LH levels were slightly elevated 3 to 6 h (1500 to 1800 h) after the second injection of 5 alpha-dihydroprogesterone and did not decrease until 2100 h. There was no effect on FSH concentrations after a second injection of any of the progestins. Loss of uterine luminal fluid was observed within 24 h after a single injection of progesterone. Neither of the 5 alpha-reduced metabolites had an effect on uterine ballooning until after the second injection, and, even then, nonfluid-filled uteri were observed in only 20 to 30% of the animals. The results suggest that the conversion of progesterone to 5 alpha-dihydroprogesterone and 3 alpha-hydroxy-5 alpha-pregnan-20-one by neuroendocrine tissues may be necessary for the positive and negative feedback effects of progesterone on gonadotropin secretion. Thus, the diverse effects of progesterone may be due to progesterone per se (e.g., in the uterus) and/or its metabolites (e.g., in the hypothalamus and pituitary).

Effect of estradiol on the response to LH-RH in male rats at different times after castration.

SummaryThe effects of pretreatment with estradiol benzoate on the pituitary release of LH and FSH in response to LH-RH were investigated in male rats at various time intervals after castration. In oil-treated control rats, LH-RH brought about a significant increase in serum LH at all the periods after castration. One day after castration, pretreatment with estradiol significantly inhibited the response to LH-RH, as observed in normal male rats. One week after castration estradiol induced a greater response to LH-RH than observed in oil-treated control rats, although the difference was not significant. One and two months after castration, estradiol significantly increased the response to LH-RH.The authors express their gratitude to Dr. G. D. Niswender, Dr. H. Papkoff and to NIAMD, Rat Pituitary Program, for the gift of materials used in radioimmunoassays. Thanks are also given to Mr. L. Garcia, Mrs. M. Esslinger, and Mrs. J. Gauthier for technical assistance.

The gonadotropin-primed rat: a model for testing agents that influence steroid biosynthesis.

Immature female rats were injected with 50 IU pregnant mare serum gonadotropin (PMSG) on day 0 and 25 IU human chorionic gonadotropin (hCG) on day 3. Plasma progestin rose to concentrations ranging from 350 to 625 ng/ml from day 5 to day 17. Expression of plasma progestin concentrations in ng/ml/mg ovary weight showed maximal concentrations of approximately 3 ng/ml/mg ovary weight on days 7 to 11 followed by a gradual decrease through day 19. Although the pituitary glands of D5GPR were significantly larger (5.20 mg ± 0.49 mg SE) than controls (3.65 mg ± 0.15 mg SE), radioimmunoassay indicated serum LH levels were not different than controls. Administration of LHreleasing factor (LRF) to D5GPR caused a significant increase in serum LH and a significant decrease in plasma progestin concentrations 20 min after LRF administration. Injection of ergocornine methanesulfonate did not alter serum LH or plasma progestin concentrations. A minimum iv dose of 3 to 5 μg prostaglandin F2α caused a maximal decrease (appr...

Effect of crude rat hypothalamic extract on serum gonadotropin and prolactin levels in normal and orchidectomized male rats.

Serum LH, FSH, and prolactin concentrations were determined by radioimmunoassay in etherized rats immediately prior to, and 8 min after, the iv injection of hypothalamic extract. There was a significant increase in serum LH in normal and in acute and chronic castrate animals injected with hypothalamic extract, whereas cerebral cortical extract failed to alter serum LH levels. Quantitatively the elevation of LH observed in chronic castrate rats following injection of hypothalamic extract was greater than that observed in normal or acute castrate animals. Hypothalamic extract produced a significant decrease in serum prolactin levels in normal rats, but failed to decrease serum prolactin in acute and chronic castrates to a statistically significant degree. There was a highly significant correlation between preinjection prolactin levels and the decrease of serum prolactin in all types of animals studied. An estimate of prolactin halftime was obtained from the preinjection and postinjection serum levels by ass...

Studies on dose response relationship of luteninizing hormone-releasing hormone (LH-RH) in sheep.

Three ewes, three wethers and one ram were used to study responses to LH-RH purified from porcine hypothalami. The levels of serum LH after LH-RH administration in the ewes were compared during diestrus. Each animal received a dose of 1, 3, 9 and 27 μg LH-RH intracarotidly. Jugular blood samples were collected at intervals before and after the LH-RH injection and serum LH was measured by a double antibody radio-immunoassay. At all dosages of LH-RH studied, each animal exhibited a significant increase in serum LH 2.5 min. after LH-RH administration. The maximal responses in the ewes and ram appeared to be obtained with 3 μg of LH-RH which increased mean serum LH levels 7 to 14 ng/ml over pretreatment levels. Higher levels of LH could not be induced with greater doses (9 or 27 μg) of LH-RH in the ewes or the ram. However, mean serum LH levels were increased by 160 ng/ml in the three wethers after administration of 27 fxg LH-RH. This demonstrates that the pituitary is more responsive to LH-RH in the castrate than in the intact sheep. In the ewes the maximum levels of serum LH detected after administration of LH-RH are well below reported preovulatory levels of LH. This refutes the assumption that LH-RH is solely responsible for LH release prior to ovulation and suggests that the pituitary responsiveness to LH-RH may also be an important factor in the rise of LH prior to ovulation.