Steroidogenesis-Stimulating Activity in the Gonads: Comparison of Rat Testicular Fluid with Bovine and Human Ovarian Follicular Fluids1

Abstract

The steroidogenesis-stimulating activities of ovarian follicular fluid from bovine (bFF) and human (hFF) sources, were compared with those of adult rat testicular fluid (rTF) using an in vitro bioassay system based on stimulation of testosterone production by purified adult rat Leydig cells during a 20-h incubation. Rat TF and bFF were charcoal-treated to remove steroids prior to assay, and the major active fraction of hFF was collected after gel-permeation chromatography. All three fluid samples stimulated both basal and maximal hCG-stimulated testosterone production, although the resulting log dose-response lines of bFF and the hFF extracts were not parallel with those of rTF. Both rTF and bFF were active over a similar dose range (5.2-150 microliters and 9.7-150 microliters, respectively) and both had a more than additive interaction with hCG on testosterone production. The stimulatory activity of the hFF extract was considerably greater than that of either rTF or bFF in the absence of hCG, but hFF extract had only an additive effect with hCG in stimulating testosterone production. Moreover, unlike rTF activity, which was inhibited by co-incubation with the protein synthesis inhibitor, cycloheximide, the activity of the hFF extract was not affected by cycloheximide. The factors responsible for activity in all three fluids were of a large molecular size (greater than 30 kDa), as determined by ultrafiltration or gel-permeation chromatography. However, in contrast to both rTF and bFF, hFF extract activity was removed by charcoal extraction. Human FF extract was inactivated by heat (100 degrees C, 30 min), whereas rTF activity was partially (70%) heat-labile and bFF was not affected by heart.(ABSTRACT TRUNCATED AT 250 WORDS)