O. P. F. Clausen

Prolactin and Leydig Cell Responsiveness to LH/hCG in the Rat

The effects of prolactin and 2-bromo-alpha-ergocryptine (CB-154) on Leydig cell function in intact and hypophysectomized male rats were studied. The conclusions can be summarized as follows: prolactin (1) has a direct stimulatory effect on the number of LH receptors on rat Leydig cells, (2) has no effect on the characteristics of the dose-response curve of isolated Leydig cells (hCG stimulated androgen production) in vitro even after treatment with pharmacological doses in vivo, and (3) acts synergistically with LH to stimulate the quantity of androgen produced by the Leydig cells in response to hCG in vitro and to increase the sensitivity of the hCG-dose-response curve. Treatment of intact rats with CB-154 reduced the quantity of androgen produced by the Leydig cells in vitro after exposure to hCG and decreased LH binding to the same cells by 50%. These results suggest that under normal conditions, endogenous prolactin plays a key role in maintaining the functional integrity of rat Leydig cells.

Endocrine Correlates of Meiosis in the Male Rat

Changes in the proportion of cells within various DNA classes of dispersed testicular cells from the developing rat were monitored by microflow fluorometry and correlated with changes in the function of the pituitary (FSH), of the Leydig cells (androgens) and Sertoli cells (androgen-binding proteins, ABP). Peaks of androgens and of FSH appeared simultaneously and coincided with an accumulation of tetraploid cells and with the first appearance of haploid cells in the testis and ABP in the epididymis. Estrogen treatment (5 micrograms/day) of developing rats from day 7 completely prevented the appearance of haploid cells in the testis as well as ABP in the epididymis. In these animals the wave of tetraploid cells started and progressed normally, indicating that transformation and progression of germinal cells to the stage of the primary spermatocytes were taking place. A combined treatment with FSH and dihydrotestosterone propionate (DHTP) resulted in a premature start of Sertoli cell secretion of ABP into the epididymis, but in a normal appearance of haploid and tetraploid cells. The time correlation between peaks in FSH/androgens, the start of Sertoli cell secretion, and the occurrence of haploid cells in the testis stresses the importance of these two hormones for normal Sertoli cell function and the importance of a functional Sertoli cell for the completion of meiosis.

Stage Dependent Variation in Mn2+−-Sensitive Adenylyl Cyclase (AC) Activity in Spermatids and FSH-Sensitive AC in Sertoli Cells

The variation of the specific Mn2+-dependent adenylyl cyclase (AC activity in spermatids and follicle stimulating hormone (FSH)-responsive AC activities in Sertoli cells in different stages (I-XIV) of the seminiferous epithelial cycle has been investigated. Maximal Mn2+-dependent AC activity was observed in stages II-III while minimal activity was encountered in stages VII-VIII (spermiation). FSH-responsive AC activity exhibited a pattern that coincided with that of the Mn2+-dependent AC. The stage-dependent variation in spermatid AC activity cannot be explained by altered numbers of haploid cells. This raises the question whether the Sertoli cells may regulate the spermatid AC activity. Sertoli cells in various stages are all exposed to the same concentration of circulatory hormones. Hence the stage-dependent difference in FSH-responsiveness indicates that local influences (from germ cells?) may regulate the response of the AC in Sertoli cells to FSH.

LH Receptors and Leydig Cell Responsiveness to hCG in vitro

The in vitro responsiveness of isolated Leydig cells from 30-day-old rats to hCG was assessed in terms of androgen and cAMP production, under conditions where the quantity of LH/hCG receptors on the Leydig cell membranes was reduced to varying degrees. Reduction in the receptor population was achieved by a single, in vivo injection of 75 IU hCG 3 and 5 days prior to incubation. When receptor binding was reduced by approximately 30%, neither the sensitivity (dose of hCG needed to give a half maximum response) nor the magnitude of the Leydig cell response to hCG in terms of androgen production was affected. However, a reduction in [125I]-hLH receptor binding by 80% was associated with a decrease in the in vitro sensitivity of Leydig cells to hCG, resulting in a displacement of dose-response curve to the right. Maximal quantity of androgen produced was not reduced. In the case of cAMP production, the same reduction in LH binding was associated with a decrease in both sensitivity and magnitude of the maximal ...

Cellular Localization of the Mn2+-Dependent Adenylyl Cyclase in the Human Testis

An examination of the activity of the Mn2+-dependent adenylyl cyclase (AC) in fine needle biopsies from human testes was made. Simultaneously the DNA distribution patterns in suspensions of testicular cells derived from the same patients have been determined. The DNA distribution patterns were estimated by microflow fluorimetry (MFF) after straining with fluorochrome (ethidium bromide). Thus, AC activity could be assessed and correlated with the relative number of haploid (1C = spermatids), diploid (2C = spermatogonia and testicular somatic cells), and tetraploid (4C = primary spermatocytes) cells. Testicular Mn2+-dependent AC activities varied between 0 and 8.4 pmol cyclic adenosine monophosphate (cAMP)/mg protein/min and were highly correlated with the contents of haploid (1C) germ cells (spermatids) (r = 0.62, p less than 0.01). There was no correlation between Mn2+-dependent AC activity and diploid or tetraploid cells. This indicates that the Mn2+-dependent AC activity in the human testis, like in the rat and mouse, may be exclusively localized to haploid germ cells. An inverse correlation between plasma FSH and Mn2+-dependent AC activities indicated reduced inhibin secretion in situations where the Sertoli cells did not maintain the testicular germ cell production.