Prolonged intravenous infusions of LH-releasing hormone into normal men.

Five normal men received constant intravenous infusions of luteinizing hormone-releasing hormone (LH-RH), 0.2 mug/min, for 14-19 hours. Serum levels ofluteizining hormone (LH) revealed a biphasic pattern of increase, reaching maximal values by 4 hours after the infusions began, then remained near that level until the infusions ceased. Serum follicle stimulating hormone (FSH) levels rose gradually to maximal values by 6-13 hours and maintained this level until the end of the infusions. Testosterone (T) levels revealed gradual increases throughout the infusions. These results confirm an increase in serum T levels with prolonged endogenous gonadotrophin stimulation. This is in contrast to the inability of several previous studies to demonstrate an increase in T levels following the relatively short gonadotrophin elevation produced by single-shot LH-RH administration. The T increases produced, however, were quantitatively much less than those reported during prolonged LH-RH infusions in rams, suggesting that the human testis is less responsive to endogenous gonadotrophin stimulation than is that of the ram. In addition, prolonged LH-RH stimulation did not cause pituitary refractoriness in men as has been described in animals.     

The follicle-stimulating hormone (FSH) receptor in testis: interaction with FSH, mechanism of signal transduction, and properties of the purified receptor

The follicle-stimulating hormone (FSH) receptor purified from calf bovine testis membranes appears to be an oligomeric glycoprotein, consisting of 4 disulfide-linked monomers of molecular weight about 60,000 each. Polyclonal antibodies to the hormone binding sites of the receptor have been developed. FSH interaction with the receptor seems to involve multiple discrete binding regions, which include amino acids 34-37 and 49-52 of the human FSH beta subunit. The interaction between FSH and the membrane-bound receptor is reversible at low temperatures but becomes increasingly irreversible as the temperature increases. FSH interaction with the soluble receptor is reversible over a wider temperature range. The hydrophobic effect is a significant factor in the initial hormone receptor interaction in each system. FSH bound to membrane receptors on cultured immature rat Sertoli cells is internalized and degraded to the level of amino acids. Current evidence suggests that the membrane receptor may exist as free receptor, and complexed with G-protein. A functional receptor/G-protein/adenylate cyclase complex has been reconstituted in liposomes. The G-protein of testis membranes contains both high and low affinity guanosine triphosphate (GTP) binding sites. Both are capable of modulating FSH receptor binding, whereas only the high affinity sites seem to be required for activation of adenylate cyclase. Although testis membranes contain a phosphatidylinositide hydrolysis system, the latter is not directly influenced by FSH.     

Pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH) responses to gonadotropin-releasing hormone during the rat estrous cycle: an increased ratio of FSH to LH is secreted during the secondary FSH surge

The hormonal interactions required for the generation of a secondary surge of FSH on the evening of proestrus have not been clearly defined. The role of GnRH in driving a surge of FSH has been questioned by findings in previous studies. In the current study, gonadotropin secretion was measured from pituitary fragments obtained from rats at 0900 and 2400 h on each day of the estrous cycle. Pituitary fragments were perifused in basal (unstimulated) conditions or in the presence of GnRH pulses to determine whether a selective increase in basal release of FSH and/or an increase in the responsiveness to GnRH occurs during the secondary FSH surge. Each anterior pituitary was cut into eighths and placed into a microchamber for perifusion. Seven pulses of GnRH (peak amplitude = 50 ng/ml; duration = approximately 2 min) were administered at a rate of one per hour starting at 30 min. Fractions of perfusate were collected every 5 min and frozen until RIA for LH and FSH. The mean total amount of LH or FSH secreted during the hour interval following each of the last six pulses of GnRH (or the corresponding basal hour) was calculated. Analysis of variance with repeated measures indicated that the evening secretion of LH on proestrus (2400 h) dropped significantly (p less than 0.05) from a maximum on the morning of proestrus (0900 h), whereas the FSH secretion remained elevated at this time. Therefore, the ratio of FSH to LH secreted in response to GnRH pulses was highest during the secondary FSH surge and lowest on the morning of proestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Isolation and culture of FSH responsive Sertoli cells.

Methods for the isolation and culture of enriched populations of Sertoli cells from 20-60 day old rats are described. The identity of the Sertoli cells was verified by bright light and electron microscopy. Freshly isolated Sertoli cells specifically bound follicle stimulating hormone (FSH) but not luteinizing hormone (LH) and responded to FSH stimulation with dramatic increase in cyclic AMP level. Isolated Sertoli cells, maintained in culture for 11 days, showed no evidence of proliferation but retained their characteristic ultrastructural features and FSH binding ability. Incubation of cultured cells with FSH resulted in a significant stimulation of cyclic AMP and androgen binding protein (ABP). Since the freshly isolated or cultured cells were predominantly (greater than 80%) Sertoli cells, these results provide direct evidence that the Sertoli cells represent a primary target site for FSH activity in the testes. The culture method also provides a valuable in vitro model for the study of chronic effects of various agents on the Sertoli cell.     

Biochemical and biological properties of urinary follicle-stimulating hormone (FSH) from the rhesus monkey (Macaca mulatta)

Follicle-stimulating hormone (FSH) is routinely used for the induction of superovulation in women. Homologous gonadotropin preparations that could be used for reproductive studies in macaques would have valuable research applications. Accordingly, we set out to characterize the physical and biological characteristics of urinary FSH (UFSH) in the ovariectomized rhesus monkey. In urine from 7 monkeys, concentrations of bioactive FSH ranged from 16 to 57 μg/1, relative to cynFSH-RPI (NIDDK). UFSH was contrasted to pituitary FSH (PFSH) by non-reducing SDS-polyacrylamide gel electrophoresis (PAGE), native disc PAGE, and FPLC chromatofocusing. The apparent molecular weights of UFSH and PFSH are similar (approximately 35 kD); however, UFSH is more negatively charged and demonstrates a lower overall isoelectric (pl) range than PFSH. The bioactivity of UFSH was assessed by the stimulation of aromatase activity in cultured Sertoli cells and by induction of follicular maturation in hamsters. Two fractions of pituitary FSH, which differed in isoelectric properties, were obtained by chromatofocusing. The in vivo biological activity of FSH-A (acidic, pl 3.8–4.6) and UFSH (pl 3.5–4.5) were similar, but greater than FSH-B (basic, pl 4.6–5.5). These results support the hypothesis that heavily sialylated, low pl FSH expresses high in vivo bioactivity. This may reflect the well-known effect of sialic acid in prolonging the circulating half-life of glycoproteins. Thus, the quality and quantity of FSH present in ovariectomized rhesus monkey urine indicates that this may be a useful source for the preparation of enriched hormone preparations. © 1992 Wiley-Liss, Inc.     

Studies on prolactin 48: Isolation and properties of the hormone from horse pituitary glands

Isolation of prolactin from equine pituitary glands has been described. It has a potency of 42 IU/mg in the pigeon crop-sac test and consists of 199 amino acids. The hormone has only four half-cystine residues in contrast to other mammalian prolactins which have six residues. From NH₂-terminal sequence analysis and amino acid composition of cyanogen bromide fragments, the NH₂-terminal disulfide loop is missing in the equine prolactin molecule. Circular dichroism spectra indicate that the α-helical content of equine prolactin appears to be lower (50%) than that found in the ovine hormone (65%).     

Proceedings: Interaction between gonadal steroids and LH-releasing hormone to control gonadotropin secretion at the pituitary level

Previously, it was shown that intact or castrated female rats which were pretreated with estradiol for 48-72 hours had an increased sensitivity to exogenous LH-Releasing Hormone (LRF). The findings indicated a biphasic effect of estrogen on the pituitary responsiveness to LRH, probably dependent upon the time of exposure of the pituitary to the steroid. A series of experiments were performed in which pituitary sensitivity to LRF was tested at various times after estradiol treatment in ovariectomized mice. Sensitivity to LRF was significantly decreased 3 hours after estradiol treatment. No difference in anterior pituitary sensitivity to LRF was found between control and experimental groups in 6 hours. 9 hours after treatment, there was a clear increase in response; and in animals treated for 24 hours, there was an even higher response. It has been suggested that progesterone may also alter pituitary sensitivity to LRF, but this was not shown to be true in ovariectomized rats. The biphasic effect of estradiol on pituitary sensitivity to LRF suggests that the changes in sensitivity may play a role during the normal estrous cycle. The time of exposure of the anterior pituitary to estradiol rather than the dose is the important factor in determining the inhibitory or facilitatory response to LRF.