Extraglandular hormonal steroidogenesis in aged rats.

We have examined the metabolism in vitro of [4-¹⁴C]pregnenolone by the following organs of 2.4-year-old rats: submandibular gland, stomach, duodenum, liver, lung, heart, spleen, kidney, skin, prostate, testis and adrenal. All tissues converted pregnenolone to progesterone, the highest yields being observed with adrenal, testis and skin. Androgen formation was intense in the testis and absent in the adrenal. Moreover, 17α-hydroxylation of pregnenolone occurred moderately in kidney, skin and submandibular gland and markedly in duodenum and stomach, which also produced high amounts of dehydroepiandrosterone and/or 5-androstene-3β,17β-diol. Extratesticular synthesis of androstenedione and testosterone was very low. A significant formation of 20α-dihydropregnenolone was observed in all tissues but stomach, duodenum and steroidogenic endocrines. Corticosteroids were not synthesized extraadrenally, except a small amount of 11-deoxycorticosterone in the testis. These results indicate that key steroid-biosynthetic enzymes, such as 3β-hydroxysteroid dehydrogenase/Δ⁵-Δ⁴ isomerase, 17β- and 20α-hydroxysteroid dehydrogenases and steroid 17α-monooxygenase/17,20-lyase are also expressed extraglandularly in the rat.