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.