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 cavity after hormonal stimulation, while related preparatory events occur in the oviducts. We have reported an association between the biological activity of the pars recta (PR), the female reproductive cycle, and ultrastructural modifications of PR epithelium induced by steroid hormones in Bufo arenarum. This article describes (1) the electron microscopic features of PR epithelium and its secretions after ovariectomy; and (2) the effect of either 17β-estradiol, 5α-dihydrotestosterone, progesterone, or a combination of progesterone plus 17β-estradiol on PR epithelium and secretions in ovariectomized animals. Our results indicate that treatment solely with 5α-dihydrotestosterone, 17β-estradiol or progesterone is ineffective in counteracting the effect of ovariectomy, although some effect was noted. The PR secretions of ovariectomized control and ovariectomized animals stimulated with any one of the steroid hormones analyzed, are composed of flocculent material and membranous vesicles. By contrast, treatment of ovariectomized animals with a combination of 17β-estradiol and progesterone, restores the appearance of the pars recta epithelium to that of the nonovariectomized control animals. Progesterone, in the presence of 17β-estradiol, appears to be responsible for triggering the release of secretory granules into the PR lumen. J. Morphol. 231:1-10, 1997. © 1997 Wiley-Liss, Inc.