ULTRASTRUCTURAL STUDIES OF THE EFFECT OF STEROID-HORMONES ON PARS RECTA SECRETIONS IN BUFO-ARENARUM

In amphibians, eggs are released from the ovaries into the coelomic ca vity after hormonal stimulation, while related preparatory events occu r in the oviducts. We have reported an association between the biologi cal activity of the pars recta (PR), the female reproductive cycle, an d ultrastructural modifications of PR epithelium induced by steroid ho rmones in Bufo arenarum. This article describes (1) the electron micro scopic features of PR epithelium and its secretions after ovariectomy; and (2) the effect of either 17 beta-estradiol, 5 alpha-dihydrotestos terone, progesterone, or a combination of progesterone plus 17 beta-es tradiol on PR epithelium and secretions in ovariectomized animals. Our results indicate that treatment solely with 5 alpha-dihydrotestostero ne, 17 beta-estradiol or progesterone is ineffective in counteracting the effect of ovariectomy, although some effect was noted. The PR secr etions of ovariectomized control and ovariectomized animals stimulated with any one of the steroid hormones analyzed, are composed of floccu lent material and membranous vesicles. By contrast, treatment of ovari ectomized animals with a combination of 17 beta-estradiol and progeste rone, restores the appearance of the pars recta epithelium to that of the nonovariectomized control animals. Progesterone, in the presence o f 17 beta-estradiol, appears to be responsible for triggering the rele ase of secretory granules into the PR lumen. (C) 1997 Wiley-Liss, Inc.