The in-vitro and in-vito effects of diethylstilbestrol on testicular synthesis of testosterone.

The effect of diethylstilbestrol (DES) on the percent conversion of a 14C-progesterone (14C-P) substrate to 14C-testosterone (14C-T) when added to incubates fo rat testicular homogenates has been measured. Similarly the effect of DES administered parenterally to intact adult rats at 9 dose regimens on such conversion has been evaluated. In addition, in the latter group serum luteinizing hormone (LH) levels were assessed simultaneously. DES added in-vitro significantly reduced T formation at every level. Only the large parenteral dose of DES affected T synthesis after 24 hours, while every parenteral dose significantly reduced T synthesis with 4 and 8 day regimens. Mean serum LH levels failed to reflect a significant decrease at the 1 and 4 day dose level, but did decrease significantly in 2 of 3 groups on the 8 day regimen. These results suggest that there is a direct effect of DES at a testicular level inhibiting T synthesis not associated with a simultaneous drop in mean serum LH levels. A measurable decrease in LH concentration does occur with continued treatment.