After Day 6 post-H, the ovaries contained interstitium and viable and atretic small preantral follicles. The viable preantral follicles were histochemically devoid of ⁵-3-hydroxysteroid dehydrogenase (3-HSDH). Histochemically, there were no appreciable changes in lipids in the interstitial gland cells (IGC) until Day 20 post-H, followed by a slight decrease by Day 30. The 3-HSDH activity in the IGC showed no appreciable changes until Day 6 and thereafter decreased gradually until Day 30. Trace amounts of glucose-6-phosphate dehydrogenase were found in the IGC until Day 6 and thereafter the enzyme was undetectable. The IGC contained only trace amounts of acid phosphatase until Day 10, followed by a gradual increase by Day 30.

A single i.p. injection of 5 µg ovine LH on Day 10, 20 or 30 resulted 3 h later in dramatic increases in the concentration of serum progesterone and ovarian progesterone and testosterone but not estradiol-17. Concomitantly, the depletion of lipid droplets in viable interstitial cells was observed by histochemical and ultrastructural criteria. However, lipid accumulations in degenerating interstitial cells and atretic granulosa cells were unaffected by LH treatment.

These data indicate that the interstitium is an active steroidogenic tissue for at least 30 days post-H and that LH can rapidly stimulate synthesis and secretion of progesterone and testosterone by the interstitium in long term hypophysectomized hamsters.