Lack of melatonin action on testosterone production by superfused rat interstitial cells

The direct effect of increasing doses of melatonin (10−8 to 10−5 m) on testosterone production by superfused rat interstitial cells was studied. A constant basal testosterone output was observed for approximately 3 h after the initial high release. A continuous hypothalamo-pituitary stimulation induced a rapid testosterone response reaching peak values in 40–60 min, then decreasing progressively. Basal testosterone release was not modified by 20 or 140 min melatonin infusions. Furthermore, melatonin induced no alteration of the stimulative testosterone response when directly infusing the cells. This study demonstrates that melatonin in vitro has no direct effect on testosterone production by adult rat interstitial cells. It would seem, therefore, that the well known inhibitory influence of melatonin on rat reproductive function is not produced by a direct effect on Leydig cells.

Age-related changes in [125I]hLH specific binding to rat interstitial cells

Enriched Leydig cell suspensions were prepared from rats ranging from 5 to 80 days of age. The cells were incubated with [125I]hLH in vitro, and the proportion of LH binding cells determined by means of autoradiography. The proportion of 3β-hydroxy-steroid-dehydrogenase (3β-HSD) positive cells was also determined. By means of Scatchard analysis and determination of grain counts of LH positive cells, an increase in LH receptors per LH binding cells with increasing age was found. LH binding cells from animals 5 and 10 days of age had few LH receptors, more than a doubling occurred between day 10 and day 20, a significant increase was seen between day 20 and 40 whereas only a slight increase in LH receptors per LH binding cell was seen thereafter. Scatchard analysis and grain count analysis of labelled cells gave essentially the same results. The grain count distribution showed cells distributed around low grain values in animals of all ages, whereas a subpopulation of cells with high grain counts appeared in maturing and mature animals. Only a small fraction of LH positive cells had detectable levels of 3β-HSD activity in animals 5 and 10 days of age. With increasing age the proportion of 3β-HSD positive cells approached that of LH binding cells, indicating that rat interstitial cells aquire LH receptors well before any 3β-HSD activity can be traced.

Direct effects of medroxyprogesterone acetate (MPA) and megestrol acetate (MGA) on rat testicular steroidogenesis

The effects of MPA and MGA on rat testicular steroidogenesis were examined by studying: 1) serum testosterone in hCG primed animals treated with MPA or MGA, 2) testosterone synthesis in rat Leydig cells cultured with MPA or MGA, 3) MPA and MGA binding to rat testis microsomal cytochrome P-450 and 4) MPA and MGA inhibition of enzymes of rat testicular steroidogenesis. In immature rats receiving 1.0 IU of hCG per day 20 mg/kg of MPA or MGA reduced serum testosterone by 57 and 56%, respectively. In mature male rats receiving 50.0 IU of hCG per day 20 mg/kg of MPA or MGA reduced serum testosterone by 40 and 29%, respectively. In rat interstitial cells cultured with 10 ng of rat LH, 1 μm MPA or MGA inhibited testosterone production by 32 and 23%, respectively. Addition of MPA or MGA to microsomal preparations resulted in a type I cytochrome P-450 difference spectrum. MPA and MGA inhibited rat testicular 17α-hydroxylase, 17,20-lyase, and the 3β- and 17β-hydroxysteroid dehydrogenases. These findings suggest that MPA and MGA inhibit rat testicular steroidogenesis in vivo and in vitro.