AJP - Endocrinology and Metabolism, Vol 241, Issue 1 51-E56, Copyright © 1981 by American Physiological Society
Role of follicle wall in meiosis reinitiation induced by insulin in Rana pipiens oocytes
C. A. Lessman and A. W. Schuetz
The involvement of the ovarian follicle wall in insulin induction of Rana
pipiens oocyte maturation in vitro was examined. Complete removal of the
follicle wall significantly decreased, but did not obliterate, oocyte
maturation (i.e., germinal vesicle breakdown, GVBD) induced by insulin.
Dose-response studies of GVBD induction revealed that oocytes within intact
follicles were at least 100 times more sensitive to insulin than denuded
oocytes. Addition of cyanoketone, a steroid biosynthesis inhibitor, to
intact follicles also suppressed insulin-induced GVBD. Inhibitory effects
of either follicle wall removal or cyanoketone were not observed when
denuded oocytes were treated with progesterone. Addition of either
progesterone or pregnenolone to insulin-treated denuded oocytes augmented
the oocyte GVBD response compared to either steroid alone and essentially
replaced the effect of the follicle wall. In summary, steroidogenesis in
the follicle wall appears to be a major factor contributing to the ability
of insulin to induce GVBD. However, whether insulin stimulates follicle
wall steroidogenesis or simply augments the biological activity of
endogenous basal steroid levels is unresolved. The in vitro results show
that oocyte maturation can be modulated by the combined actions of several
hormones. Such steroid-insulin interactions may also be relevant to
understanding the control of oocyte maturation in amphibians and other
vertebrates, including mammals, under physiological conditions in vivo.
