Km. Eisenhauer et al., GROWTH-HORMONE SUPPRESSION OF APOPTOSIS IN PREOVULATORY RAT FOLLICLESAND PARTIAL NEUTRALIZATION BY INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEIN, Biology of reproduction, 53(1), 1995, pp. 13-20
A growing body of evidence suggests that growth hormone IGH) plays a r
ole in regulating ovarian function by augmenting gonadotropin stimulat
ion of granulosa cell differentiation and folliculogenesis. The majori
ty of follicles in the mammalian ovary do not ovulate, but instead und
ergo a degenerative process (atresia) involving apoptotic cell death.
The objective of the present study was to investigate the role of GH i
n regulating follicle apoptosis and to determine whether or not insuli
n-like growth factor-I (IGF-I) mediates GH action in this process. Pre
ovulatory follicles obtained from eCG-primed rats were cultured for 24
h in serum-free conditions with or without hormone treatments. After
culture, follicular apoptotic DNA fragmentation was analyzed by autora
diography of size-fractionated DNA labeled at 3' ends with [P-32]dideo
xy-ATP. Culture of preovulatory follicles resulted in a spontaneous on
set of apoptotic DNA fragmentation that was suppressed by ovine GH (oG
H) in a dose-dependent manner, reaching a maximum of 65% suppression.
To rule out the effect of residual gonadotropin in the oGH preparation
, follicles were also cultured with recombinant bovine growth hormone
(rbGH). Like oGH, rbGH suppressed apoptotic DNA fragmentation. Our ear
lier study indicated that hCG and FSH treatment also suppress apoptosi
s in the present model system, but no additive effect of GH and either
hCG or FSH on the suppression of apoptosis was observed. To determine
whether the observed effect of GH action on follicle apoptosis is med
iated by IGF-I, three types of studies were carried out. First, follic
les were cultured with rbGH in the presence of insulin-like growth fac
tor binding protein-3 (IGFBP-3), which is known to neutralize IGF-I ac
tion. Cotreatment with IGFBP-3 reversed the suppressive effect of GH i
n a dose-dependent manner by up to 75%, suggesting that endogenous IGF
-I is partially responsible for the effects of GH in this system. Foll
icles were also cultured in the presence of GH and IGF-I together, and
no additive effect of these hormones was observed. To further support
this hypothesis, levels of IGF-I mRNA in the follicles were measured;
rbGH treatment increased IGF-I mRNA levels by 1.5-fold. Taken togethe
r, these data suggest that GH acts as an ovarian follicle survival fac
tor by preventing follicle cell apoptosis and that part of the GH acti
on is mediated by locally produced IGF-I.