INHIBITORY EFFECTS OF N-ALKANOLS ON THE HORMONAL INDUCTION OF MATURATION IN FOLLICLE-ENCLOSED XENOPUS-OOCYTES - IMPLICATIONS FOR GAP JUNCTIONAL TRANSPORT OF MATURATION-INDUCING STEROID

In fishes and amphibians, the induction of oocyte maturation by gonadotropin is mediated by follicle cell production of maturation-inducing steroid. This steroid appears to be progesterone in the frog Xenopus laevis. It is also known that full-grown oocytes of X. laevis are cytoplasmically linked to follicle (granulosa) cells via gap junctions, and that these gap junctions are enhanced by whole-animal injections of gonadotropin (human chorionic gonadotropin, hCG). However, the specific role of this heterocellular gap junctional communication is unclear, especially in regard to its possible involvement in the regulation of oocyte maturation. Therefore, the objective of this study is to examine the role of follicle cell-oocyte gap junctional coupling during maturation of the ovarian follicle of X. laevis. For this purpose, we determined the in vitro effects on oocyte maturation of the known gap junction uncouplers 1-heptanol and 1-octanol, alone or in combination with maturational concentrations of hCG or progesterone. The n-alkanols alone did not have any effect on maturation. However, both heptanol and octanol at 1 mM blocked the hCG and progesterone induction of maturation in follicle-enclosed Xenopus oocytes. At least in the case of heptanol, the inhibition of hormone-induced maturation was not accompanied by changes in the steroidogenic response of intact follicles to hCG or in the responsiveness of defolliculated oocytes to exogenous progesterone. These latter observations seem to rule out nonspecific effects of the alcohols on follicle cell or oocyte function. Therefore, our results suggest that gap junctional coupling between follicle cells and the oocyte is required for maturational steroid signaling in amphibian ovaries. © 1993 by Academic Press, Inc.