Effects of luteinizing hormone releasing hormone on gonadotrophins in the hamster

The changes in serum gonadotrophins in male hamsters following one injection of 15 μg luteinizing hormone releasing hormone (LHRH) (Group A) were compared with those following the last injection of LHRH in animals receiving an injection approximately every 12 hr for 4 days (Group B) or 12 days (Group C). Peak follicle stimulating hormone (FSH) levels (ng/ml) were 1776±218 (Group A), 2904±346 (Group B), and 4336±449 (Group C). Peak luteinizing hormone (LH) values (ng/ml) were 1352±80 (Group A), 410±12 (Group B), and 498±53 (Group C). Serum FSH:LH ratios, calculated from the concentrations measured 16 hr after the last LHRH injections, were higher in Groups B and C than in Group A. Similar injections of LHRH (100 ng or 15 μg/injection) for 6 days elevated the serum FSH:LH ratio in intact males. Five such LHRH injections (100 ng/injection) blunted the rise in serum LH in orchidectomized hamsters. Direct effects of LHRH on gonadotrophin secretory dynamics or altered brain-pituitary-testicular interactions may alter the ratio of FSH to LH in the hamster.     

On the existence and separation of the follicle stimulating hormone releasing hormone from the luteinizing hormone releasing hormone.

Porcine hypothalamic fragments were extracted by 2M AcOH at 4°C, and the extractives were subsequently processed in the presence of one protease inhibitor and one anti-oxidant. Gel filtration was performed on Bio-Gel P-2, and supplementary [³H]-LHRH and [¹⁴C]- 3H]-LHRH, and was differentiated from [¹⁴C]- 相似文献   

Effect of number of receptors for gonadotropin-releasing hormone on the release of luteinizing hormone

The relationship between number of receptors for gonadotropin-releasing hormone (GnRH) and the ability of the anterior pituitary gland to release luteinizing hormone (LH) was examined in ovariectomized ewes. A GnRH antagonist was used to regulate the number of available receptors. The dose of GnRH antagonist required to saturate approximately 50 and 90% of GnRH receptors in ovariectomized ewes was determined. Thirty min after intracarotid infusion of GnRH antagonist, ewes were killed and the number of unsaturated (i.e., those available for binding) pituitary GnRH receptors was quantified. Infusion of 10 and 150 micrograms GnRH antagonist over a 5-min period reduced binding of the labeled ligand to approximately 50 and 12% of controls, respectively. The effect of reducing the number of GnRH receptors on release of LH after varying doses of the GnRH agonist, D-Ala6-GnRH-Pro9-ethylamide (D-Ala6-GnRH) was then evaluated. One of four doses of D-Ala6-GnRH (0.125, 2.5, 50 and 400 micrograms) was given i.v. to 48 ovariectomized ewes whose GnRH receptors had not been changed or were reduced to approximately 50 or 12% of control ewes. In ewes with a 50% reduction in GnRH receptors, total release of LH (area under response curve) was lower than that obtained for controls (P less than 0.01) at the 0.125-micrograms dose of D-Ala (6.1 +/- 0.7 cm2 vs. 13.5 +/- 0.7 cm2) but was not different at the 2.5-, 50- or 400-micrograms doses of D-Ala6-GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)     

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)     

Studies on pituitary lactogenic hormone. The primary structure of the porcine hormone.

The complete amino acid sequence of porcine lactogenic hormone has been elucidated. It consists of 199 amino acid residues with three disulfide bridges formed by residues 4-11, 58-174, and 191-199. The two tryptophan residues are in positions 91 and 150. A high degree of homology exists between the known structure of ovine prolactin and the porcine lactogenic hormone. This led to a re-examination of residues 82-90 in the ovine prolactin structure, where an extra leucine was found in position 88.     

The effect of luteinizing hormone releasing hormone on the copulatory behavior of hyperprolactinemic male rats

The present study was undertaken to test the hypothesis that the deficits in copulatory behavior observed in hyperprolactinemic male rats may be related to a reduction in hypothalamic release of luteinizing hormone releasing hormone (LHRH). Adult male Fischer 344 rats were made hyperprolactinemic by ectopic pituitary grafts or were sham operated and 30 min prior to being tested for copulatory performance received a single subcutaneous injection of 500 ng LHRH, 100 ng LHRH, or saline. On different occasions, testosterone (T) levels were measured in plasma collected 30 min following identical treatments. Plasma prolactin (PRL) levels were determined in samples collected 30 min after injection of 500 ng LHRH. Pituitary grafting produced the expected, significant increase in plasma PRL levels and significant deficits in copulatory behavior. Treatment of hyperprolactinemic subjects with 500 ng LHRH significantly reduced both the time to first intromission and the time to ejaculation to times comparable with those of sham-operated subjects. The 100-ng dose produced a significant reduction in mount frequency. Plasma T levels were significantly elevated following either dose of LHRH. These results demonstrate that exogenous LHRH can restore normal copulatory performance in hyperprolactinemic male rats and support the hypothesis that a reduction in hypothalamic LHRH release is responsible for the behavioral deficits observed in those animals.     

Effects of hyperprolactinemia on the control of luteinizing hormone and follicle-stimulating hormone secretion in the male rat

Experiments were conducted to determine the effects of acute hyperprolactinemia (hyperPRL) on the control of luteinizing hormone and follicle-stimulating hormone secretion in male rats. Exposure to elevated levels of prolactin from the time of castration (1 mg ovine prolactin 2 X daily) greatly attenuated the post-castration rise in LH observed 3 days after castration. By 7 days after castration, LH concentrations in the prolactin-treated animals approached the levels observed in control animals. HyperPRL had no effect on the postcastration rise in FSH. Pituitary responsiveness to gonadotropin hormone-releasing hormone (GnRH), as assessed by LH responses to an i.v. bolus of 25 ng GnRH, was only minimally effected by hperPRL at 3 and 7 days postcastration. LH responses were similar at all time points after GnRH in control and prolactin-treated animals, except for the peak LH responses, which were significantly smaller in the prolactin-treated animals. The effects of hyperPRL were examined further by exposing hemipituitaries in vitro from male rats to 6-min pulses of GnRH (5 ng/ml) every 30 min for 4 h. HyperPRL had no effect on basal LH release in vitro, on GnRH-stimulated LH release, or on pituitary LH concentrations in hemipituitaries from animals that were intact, 3 days postcastration, or 7 days postcastration. However, net GnRH-stimulated release of FSH was significantly higher by pituitaries from hyperprolactinemic, castrated males. To assess indirectly the effects of hyperPRL on GnRH release, males were subjected to electrical stimulation of the arcuate nucleus/median eminence (ARC/ME) 3 days postcastration. The presence of elevated levels of prolactin not only suppressed basal LH secretion but reduced the LH responses to electrical stimulation by 50% when compared to the LH responses in control castrated males. These results suggest that acute hyperPRL suppresses LH secretion but not FSH secretion. Although pituitary responsiveness is somewhat attenuated in hyperprolactinemic males, as assessed in vivo, it is normal when pituitaries are exposed to adequate amounts of GnRH in vitro. Thus, the effects of hyperPRL on pituitary responsiveness appear to be minimal, especially if the pituitary is exposed to an adequate GnRH stimulus. The suppression of basal LH secretion in vivo most likely reflects inadequate endogenous GnRH secretion. The greatly reduced LH responses after electrical stimulation in hyperprolactinemic males exposed to prolactin suggest further that hyperPRL suppresses GnRH secretion.     

Significance of charge on lysine residue of ovine luteinizing hormone on immunological and biological properties of the hormone

In order to understand the significance of positive charge of lysine residues of ovine luteinizing hormone (oLH) on immunological and biological activity, the epsilon-NH2 group(s) of ovine LH were sequentially modified with 2-iminothiolane (2IT) that preserves the positive charge of the lysine while the overall charge of the hormone remains unchanged. These studies have also been compared with the oLH modified by N-succinimidyl 3-(2 pyridyldithio) propionate (SPDP) and succinimidyl 6-[3-(2-pyridyldithio)propionamido]hexanoate (LC-SPDP) that abolish positive charge of lysine residues. The modification primarily occurs in the alpha-subunit. Sequential modification led to progressive reduction in receptor binding and immunological activities. However, the steroidogenic activity was substantially retained. The immunoreactivity and receptor binding properties of 2IT modified oLH (oLH-2IT) were less affected when compared to SPDP (oLH-SPDP) or LC-SPDP (oLH-LC-SPDP) modified derivatives suggesting that increase in hydrophobic carbon chain in oLH-LC-SPDP molecule resulted in drastic inhibition in immunological and biological properties. But the steroidogenic potential of oLH-2IT, oLH-LC-SPDP or oLH-SPDP was relatively comparable. This suggests that a single -NH2 group modification with 2IT would generate the site in the hormone for conjugation to the toxin/carrier proteins that may retain better immunological and biological activity compared to that of SPDP or LC-SPDP modified oLH.     

Studies on the follicle stimulating hormone releasing hormone by radioimmunoassays and by bioassays

An entity (in fractions), separated from the luteinizing hormone-releasing hormone (LHRH), <Glu-OH, and N-Ac-Asp-OH, which released both FSH and LH appeared to show immunoreactivity in the RIA for LHRH. This entity was destroyed by trypsin, but did not yield LHRH, under conditions which (1) converted a synthetic model, [Arg-Lys-Gln¹]-LHRH, of a pro-LHRH to LHRH; (2) did not destroy LHRH. This entity may not be a pro-LHRH, but may be the follicle stimulating hormone-releasing hormone (FSHRH) on the basis of all these data. A second immunoreactive entity had negligible, if any, releasing activity for FSH and LH, and did not yield LHRH on trypsin digestion.     

Investigation on the formation of the hormone reception mechanism

The formation of the hormone receptor mechanism is part of the embryonic development. The perinatal age seems to be critical for the maturation of this system, i.e. the development of the proper hormone selectivity, the number of the receptors, their sensitivity to the adequate hormone. Our team tried to get a closer view on this developmental period examining different parameters in different model systems. We were able to show that during the maturation of the hormonal system similar responses could be elicited by the later specific hormones or by the non-specific ones but structurally similar compounds. Also it became evident that one single hormonal treatment, applied during in the perinatal age, could influence the responsiveness to hormones of the adult animals.     

The influence of age on human pancreatic growth hormone releasing hormone stimulated growth hormone secretion

63 non-obese healthy subjects aged 18 to 95 years were investigated for age-dependence of GHRH-stimulated GH-secretion. In addition, priming of GH-secretion with three oral doses of propranolol (3 x 80 mg, the last dose 2 hours prior to the second GHRH-bolus) was carried out in 15 subjects below 40 years and 13 subjects older than 70 years. We found that mean maximal incremental GH-levels were inversely correlated with chronological age (r = -0.44, P = 0.001) of the probands. Propranolol premedication caused a significant rise of both basal and peak GHRH-induced relative increases in all subjects tested, whereas GHRH-induced relative increases of GH remained unchanged. In a well selected group of non-obese healthy subjects stimulated GH-secretion is found to undergo an aging process that is supposed to be of pituitary and suprapituitary origin. Priming GH-secretion with a beta-Blocker is possible both in young and very old healthy subjects and is likely to affect the basal GH secretory tone and not GHRH-stimulated GH-secretion.     

Studies on the purification of locust adipokinetic hormone

$\text{Locusta}$ adipokinetic hormone (AKH) has been purified from glandular lobes of corpora cardiaca by a series of chromatographic steps that have allowed a 58 to 77% recovery of activity. Methanolic extracts of the glandular lobes were fractionated on Sephadex LH-20 and then on thin-layer plates. The average recovery of AKH activity after separation on Sephadex LH-20 approached 100%, whereas recoveries of between 58 to 77% were obtained after TLC on cellulose plates. In practice, the highest recoveries were obtained with separations of large amounts of the hormone on cellulose plates. In the course of this investigation it was found that AKH activity can be extracted efficiently from aqueous solutions using Florisil. The hormone activity was recovered from the Florisil by eluting with 80% methanol. The purified hormone was found to be homogeneous in composition when subjected to rechromatography on Sephadex LH-20 and to amino acid analysis of the acid hydrolysate. From the amino acid analysis we estimate that one pair of glandular lobes contains on average 188 pmoles of AKH.     

The action of luteinizing hormone on the testis

Luteinizing hormone (LH) and human chorionic gonadotrophin (hCG) receptors are coupled to intracellular effector systems, most notably adenylate cyclase, through guanyl nucleotide-binding proteins or G-proteins. The molecular mechanism involved in the dynamic coupling of the LH/hCG receptor however, are not known. It has been postulated that receptor aggregation at the molecular level plays a critical role in this process. There have been attempts to understand the receptor association and dissociation phenomena at the molecular level. One of them involves the participation of the major histocompatibility complex (MHC) class I antigen in the mechanism of receptor activation and/or expression. One molecular basis for these mechanisms consists of a physical interaction between MHC proteins and receptors to form "compound receptors" able to transfer a hormonal signal to the cell. Using a photo-reactive probe we demonstrated that the LH/hCG receptors and the class I antigens are closely associated in the membrane. Thus, it is possible to form covalent complexes of hCG and class I antigens through the binding of the hormone to specific receptors. These findings imply that LH/hCG receptors and the MHC class I antigens may interact at the level of the plasma membrane in the mechanism of LH action. We also performed experiments using a single cell and limiting stimulation to a patch of membrane. The results stimulating the cell in a localized area suggested that even if all components are entirely free to float there is a constraint in the localization of the receptor, G-protein, and/or the effector, supporting the constraint dissociation model. Within a limited area subunits could dissociate, but they would not be free to diffuse throughout the membrane. Moreover the concept of compartmentalization that has been utilized to explain some inconsistencies in second-messenger action now can be proved by experimental design.     

Studies on the enzymic degradation of luteinizing hormone releasing hormone by rat pituitary plasma membranes

Degradation of luteinizing hormone releasing hormone (LH-RH) by purified plasma membranes from rat pituitaries was investigated. Synthetic LH-RH (0.5 mg/ml) was incubated (20 min, 37°C) with pituitary plasma membranes (750 μg protein/ml). The reaction was stopped by centrifugation at 4°C. The degradation products were isolated by high pressure liquid chromatography using a reversed-phase column. Amino acid analysis of the degradation products indicated that the N-terminal tripeptide (pGlu-His-Trp) and the N-terminal hexapeptide (pGlu-His-Trp-Ser-Tyr-Gly) sequence of LH-RH are the main degradation products. These results suggest that the main cleavage sites of LH-RH by the pituitary plasma membrane-bound enzymes are the Gly⁶-Leu⁷ and the Trp³-Ser⁴ bonds of the neurohormone.     

Overlapping effect of thyroid-stimulating hormone and follicle-stimulating hormone on the thyroid gland in baby chicken

Follicle-stimulating hormone (FSH) although quantitatively less effective than thyroid-stimulating hormone (TSH) in the thyroid gland, overlapped with the actions of the latter regarding the indices tested. Thus, it increased the follicular diameter and height of epithelial cells. These findings appear to support our earlier observation demonstrating an overlapping effect of tropic hormones in the gonads and suggest that the overlapping action of tropic hormones with related structure is a general phenomenon in the perinatal period.     

Negative effect of estradiol on luteinizing hormone throughout the ovulatory luteinizing hormone surge in mares

The negative effect of estradiol-17beta (E2) on LH, based on exogenous E2 treatments, and the reciprocal effect of LH on endogenous E2, based on hCG treatments, were studied throughout the ovulatory follicular wave during a total of 103 equine estrous cycles in seven experiments. An initial study developed E2 treatment protocols that approximated physiologic E2 concentrations during the estrous cycle. On Day 13 (ovulation = Day 0), when basal concentrations of E2 and LH precede the ovulatory surges, exogenous E2 significantly depressed LH concentrations to below basal levels. Ablation of all follicles > or = 10 mm when the largest was > or =20 mm resulted in an increase in percentage change in LH concentration within 8 h that was greater (P < 0.03) than for controls or E2-treated/follicle-ablated mares. Significant decreases in LH occurred when E2 was given when the largest follicle was either > or =25 mm, > or =28 mm, > or =35 mm, or near ovulation. Treatment with 200 or 2000 IU of hCG did not affect E2 concentrations during the initial portion of the LH surge (largest follicle, > or =25 mm), but 2000 IU significantly depressed E2 concentrations before ovulation (largest follicle, > or =35 mm). Results indicated a continuous negative effect of E2 on LH throughout the ovulatory follicular wave and may be related to the long LH surge and the long follicular phase in mares. Results also indicated that a reciprocal negative effect of LH on E2 does not develop until the E2 surge reaches a peak.