[4-14C] Testosterone was converted to [14C] oestrone and [14C]17β-oestradiol on incubation with slices of bovine follicles. These metabolites were identified by sequential chromatography, derivative formation and recrystallization to constant 14C/3H ratio. Both Graafian and atretic follicles were able to synthesize these oestrogens from testosterone.
The yield of [14C] oestrone plus [14C] 17β-oestradiol, measured by reverse isotope dilution analysis, varied from 4 μμmoles to 4459 μμmoles in the 19 follicles tested. Differences, much greater than the measured experimental error, were also found in the yields from the two halves of individual follicles. The difficulties imposed by these findings in demonstrating an effect of gonadotrophins are discussed.
On incubation of segments of two follicles, identified histologically as Graafian follicles, in the presence of ovine follicle stimulating hormone, the yield of radioactive oestrone and 17β-oestradiol from [4-14C] testosterone was markedly reduced. In eight other follicles, the majority of which were atretic, the conversion of [4-14C] testosterone was not influenced by gonadotrophin in vitro.
These results would suggest that, in some follicles, follicle stimulating hormone in vitro may modify steroid biosynthesis. In these cases the major locus of action of gonadotrophin on steroid biosynthesis appears to be before the synthesis of testosterone.