酪氨酸对男子血清促性腺激素和睾酮浓度的影响

给成年男子(n=5)口服酪氨酸300mg/日,共6天,第四天肌注 LRH-A 150μg/人,用RIA 法测定其血清 LH、FSH 和睾酮浓度。与对照组(n=5)相比,酪氨酸对 LH 和 FSH 的基础水平和 LRH-A 诱发的 LH 峰和 FSH 峰均无明显影响。睾酮的基础水平稍有升高,而酪氨酸对 LRH-A 引起的睾酮水平升高有明显的抑制作用。结果提示,酪氨酸可不通过垂体而直接作用于睾丸以影响睾酮的分泌。     

Pituitary gonadotropins regulate spermatogonial differentiation and proliferation in the rat‡

The relative regulatory roles of the pituitary gonadotropins, luteinizing hormone and follicle stimulating hormone in the spermatogonial proliferation has been studied using specific antibodies against these hormones in the immature rats. Immunoneutralization of lu teinizing hormone for 7 days resulted in significant reduction in tetraploid cells and total absence of haploid cells,while there was a relative increase in the diploid population. This was also accomopanied by a decrease in spermatogonial proliferation as indicated by a decrease in [³H] thymidine incorpor-ation into DNA by purified spermatogonia. Administration of follicle stimulating hormone a/s for 7 days also caused a significant decrease in the rate of spermatogonial proliferation. Withdrawal of follicle stimulating hormone led to a significant reduction in tetraploid and haploid cells. However interestingly,it failed to totally abolish the appearance of these cells. Administration of testosterone (3 mg/day/rat) for 2 days along with the gonadotropin a/s could partially reverse the effect on spermatogonial proliferation. It is concluded that (i) both luteinizing hormone and follicle stimulating hormone are involved in spermatogonial proliferation, (ii) lack of testosterone consequent of the neutralization of luteinizing hormone prevented the entry of spermatogonial cells into meiosis, (iii) testosterone may be involved in spermatogonia] proliferation providing a mitotic signal and (v) both follicle stimulating hormone and testosterone act synergistically and lack of any one of the hormones results in impairment of spermatogonial proliferation. A part of the data was presented at the 16th International Congress of Biochemistry and Molecular Biology, New Delhi, September 1994.     

Role of Non-Aromatizable Androgens in the Central Control of Pubertation of Female Rats

In 30-postnatal day-old rat females we created a decreased or increased level of 5-reduced (non-aromatizable) androgens, using injections of an inhibitor of 5-reductase or exogenous dihydrotestosterone, respectively. In these animals, we measured the levels of noradrenaline (NA) and serotonin (5-HT) in the hypothalamus, those of gonadotropins in the hypophysis, and testosterone and estradiol in the blood plasma; the process of pubertation was also monitored. In rats with a deficiency of non-aromatizable androgens, the NA level increased, while that of 5-HT dropped. In animals with an excess of these hormones, the 5-HT level remained stable against the background of a certain increase in the NA level. In the first group of animals, the estradiol level in the blood increased by a factor of 3, while the testosterone level increased insignificantly. The beginning of pubertation in these animals was not shifted, while the first ovulation occurred somewhat earlier, as compared with the control. In the second group of rats, treatment with exogenous dihydrotestosterone accelerated the beginning of pubertation, but the interval between opening of the vagina and first ovulation even somewhat increased. The neurotransmitter hypothalamic mechanisms mediating acceleration of an initial phase of the female pubertation and retardation of its final phase under the influence of non-aromatizable androgens are discussed.     

Cloning of FSH-β, LH-β and glycoprotein hormone α subunits in pejerrey Odontesthes bonariensis (Valenciennes): expression profile and relationship with GnRH expression and plasma sex steroid levels in male fish

Three cDNAs encoding pejerrey Odontesthes bonariensis follicle stimulating hormone-β (FSH-β), luteinizing hormone-β (LH-β) and glycoprotein-α (GPH-α) subunits were cloned and characterized. Gene expression of these subunits was analysed by real-time polymerase chain reaction (PCR) and compared with the brain gene expression of endogenous gonadotropin-releasing hormones (GnRHs): Pacific salmon GnRH (GnRH-III), pejerrey GnRH (GnRH-I) and chicken GnRH-II (GnRH-II) and plasma sex steroid levels in adult males. The nucleotide sequences of the FSH-β, LH-β and GPH-α subunits are 466, 558 and 677 base pairs long, encoding for mature peptides of 102, 118 and 98 amino acids respectively. Maturing males had high expression of FSH-β and GPH-α subunits, and intermediate levels of LH-β when compared with running ripe and spent stages. These animals had the lowest plasma testosterone (T) and 11-ketosterone (11-KT) values as well as low expression of sGnRH, cGnRH-II and pjGnRH. Running ripe males had the lowest expression of FSH-β and the highest expression of LH-β and GPH-α subunits, and of the three GnRH genes. At this stage, the highest values of T and 11-KT were observed. Spent males showed low expression of the three gonadotropin (GtH) subunits, sGnRH, pjGnRH and low levels of T. At this stage, 11-KT levels and cGnRH-II expression showed a tendency to decrease but the values were not statistically significant ( P < 0·05) to running ripe stage. The present results would suggest that T and 11-KT modulate the expression of the FSH subunits. The expression of the anterior brain GnRH variants, sGnRH and pjGnRH is correlated with LH-β expression and reinforce the importance of the forebrain GnRH variants on the regulation of pituitary function.     

Immunofluorescence study of the hypothalamo-infundibular LRH tract and serum gonadotropin levels in the female squirrel monkey during the estrous cycle

Summary The study of LRH reactive neurons of the medial basal hypothalamic group was made with rabbit antisera to unconjugated synthetic LRH, in normally cycling female squirrel monkeys.The specifically immunoreactive material present along the hypothalamo-infundibular LRH tract shows significant modifications that are particularly distinct in the lateral, posterior and anterior labia of median eminence, with a maximum concentration during the early and middle follicular phases, a sudden fall to a minimum concentration during the late follicular and ovulatory phases and with a progressive increase during the luteal and early follicular phases.Serum FSH and LH levels show a progressive decrease from the luteal phase to the late follicular phase, with differential modifications suggesting that a double regulation might take place in cycling squirrel monkeys.A parallel is suggested between the specifically reactive material along the hypothalamo-infundibular tract, serum gonadotropin levels and variations in the medial basal hypothalamic and infundibular LRH concentrations during the estrous cycle in the squirrel monkey.This work was supported by the D.G.R.S.T. (contrat 76-7-1536) and U.E.R. 3 (Faculty of Medicine). We acknowledge the help of A. Pillez (C.N.R.S.) for sectioning and staining the genital tracts     

The bonnet monkey (Macaca radiata): A model for the study of gonadotropin dynamics during fasting in the human

General Hospital and Harvard Medical School, Boston Postmenopausal women excrete significantly greater quantities of radioimmunoassayable luteinizing hormone (LH) and follicle stimulating hormone (FSH) during fasting than during the control or refeeding periods. The concentrations of these gonadotropins in the serum, however, are not affected. In the present studies, ovariectomized Bonnet monkeys (Macaca radiata) and ovariectomized Sprague-Dawley rats were studied to compare the effects of fasting on gonadotropins dynamics in subhuman primates and rodents. Serum LH and FSH concentrations were not reduced by fasting of monkeys or rats. During a 4-day fast, rats excreted significantly (P ? 0.01) less LH, FSH, Na⁺, and K⁺ than during prefast or refeeding periods. Monkeys, on the other hand, excreted significantly (P ? 0.025) greater quantities of LH and FSH during the last 2 day of a 4-day fast as compared to prefast and refeeding periods. Like the human, they conserved Na+ and K+ on refeeding. These results indicate that the monkey is a better animal model than the rat with which to study the effects of fasting on gonadotropin excretion in the human.     

Three‐dimensional environments preserve extracellular matrix compartments of ovarian follicles and increase FSH‐dependent growth

In this study we performed a systematic comparative analysis of two culture environments—flat/adhesive liquid and three‐dimensional collagen gel—upon in vitro ovarian follicle development. We paid particular attention to the effects of in vitro environments upon the preservation of follicular structure and of peri‐ and intra‐follicular extracellular matrix. We show that flat/adhesive environment leads to an obvious distortion of follicle morphology, marked extracellular matrix modifications and high rates of spontaneous, i.e., FSH‐independent, follicle disruption. In contrast, three‐dimensional collagen gel environments are able to maintain follicular structure with an in vivo‐like basal lamina architecture, minimizing spontaneous disruption. Follicle distortions found in flat/adhesive culture systems include a pronounced flattening, causing the follicle horizontal diameters not to adequately reflect follicle volume. Our volume data, based on three‐axis follicle diameter measurements, indicate that three‐dimensional collagen gel environments increase follicle growth, particularly in response to FSH. This study demonstrates that preservation of both peri‐ and intra‐follicular extracellular matrix compartments during the in vitro growth and differentiation of ovarian follicles is highly desirable, and is now possible through the use of appropriate three‐dimensional collagen gel culture environments. This system allows a better understanding of the specific roles played by each of the follicle compartments during development. Mol. Reprod. Dev. 54:163–172, 1999. © 1999 Wiley‐Liss, Inc.     

The relationship between parthenogenetic embryonic development and cumulus cell-oocyte intercellular coupling during oocyte meiotic maturation

Intercellular coupling between cumulus cells and oocytes persists after oocyte meiotic maturation has been initiated. The experiments described here focus on the relationship between oocyte-cumulus cell intercellular coupling during maturation and the subsequent embryonic development of spontaneous mouse parthenotes. Several lines of evidence suggest that this coupling during oocyte maturation is required for the acquisition of the capacity for spontaneous mouse parthenotes to develop embryologically. First, the period of time that LT/Sv oocytes remained coupled to cumulus cells during oocyte maturation in vivo corresponded to that required for the acquisition of the capacity for parthenogenetic embryonic development. Second, the longer that cumulus cells were present during Fpontaneous oocyte maturation in vitro, the higher was the percentageofova undergoing subsequent parthenogenetic development. Third, cumulus cell-free oocytes cocultured with cumulus cell-enclosed oocytes during the maturation period in vitro did not develop embryologically. Fourth, intercellular coupling between cumulus cells and oocytes persisted throughout the oocyte maturation period in vitro. Fifth, incubation of oocyte-cumulus cell complexes in medium containing follicle-stimulating hormone (FSH) promoted uncoupling and decreased the percentage of ova undergoing parthenogenetic development. Thus, cell-to-cell communication, mediated via the intercellular coupling pathway between cumulus cells and oocytes, plays an important role during oocyte maturation and relates to subsequent preimplantation development.     

Effects of follicle-stimulating hormone and ovarian steroids during vitro meiotic maturation on fertilization of rat oocytes

The present study examined the effects of gonadotropins and ovarian steroids during in vitro meiotic maturation of rat oocytes on their ability to undergo in vitro fertilization. Fully grown oocytes were isolated from antral follicles of immature rats and cultured as oocyte-cumulus cell complexes (OCC) under conditions in which completion of meiotic maturation occurs spontaneously. They were then exposed to spermatozoa under conditions in which oocytes matured in vivo exhibit high fertilization rates. Compared with oocytes from pregnant mare's serum gonadotropin (PMSG) or follicle-stimulating hormone (FSH)-treated rats, a simiiar proportion of the oocytes (>80%) from untreated rats underwent germinal vesicle breakdown, but such oocytes had a lower rate of fertilization (70% vs. 20%). The presence of FSH during in vitro maturation restored the fertilization rate for oocytes from untreated rats, while a cytochrome P450 inhibitor, aminoglutethimide phosphate abolished this beneficial effect of FSH. The addition of progesterone during the in vitro maturation period duplicated the beneficial effect of FSH on fertilization rate of oocytes from untreated rats; oestradiol-17β was less effective in this regard, and 5α-dihydrotestosterone was ineffective. These findings indicate that FSH and progesterone, although having no apparent effect on nuclear maturation of the oocyte, play an important role during oocyte maturation in enabling normal fertilization to occur.     

The acceleration of reproductive aging in Nrg1flox/flox;Cyp19‐Cre female mice

Irregular menstrual cycles, reduced responses to exogenous hormonal treatments, and altered endocrine profiles (high FSH/high LH/low AMH) are observed in women with increasing age before menopause. In this study, because the granulosa cell‐specific Nrg1 knockout mice (gcNrg1KO) presented ovarian and endocrine phenotypes similar to older women, we sought to understand the mechanisms of ovarian aging and to develop a new strategy for improving fertility in older women prior to menopause. In the ovary of 6‐month‐old gcNrg1KO mice, follicular development was blocked in bilayer secondary follicles and heterogeneous cells accumulated in ovarian stroma. The heterogeneous cells in ovarian stroma were distinguished as two different types: (i) the LH receptor‐positive endocrine cells and (ii) actin‐rich fibrotic cells expressing collagen. Both the endocrine and fibrotic cells disappeared following long‐term treatment with a GnRH antagonist, indicating that the high levels of serum LH induced the survival of both cell types and the abnormal endocrine profile to reduce fertility. Moreover, follicular development to the antral stages was observed with reduced LH and the disappearance of the abnormal stromal cells. Mice treated with the GnRH antagonist regained normal, recurrent estrous cycles and continuously delivered pups for at least for 3 months. We conclude that endocrine and matrix alternations occur within the ovarian stroma with increasing age and that abolishing these alternations resets the cyclical release of LH. Thus, GnRH antagonist treatments might provide a new, noninvasive strategy for improving fertility in a subset of aging women before menopause.