AJP - Endocrinology and Metabolism, Vol 247, Issue 4 468-E474, Copyright © 1984 by American Physiological Society
Insulin stimulates granulosa cells: increased progesterone and cAMP production in vitro
M. J. Ciancio and A. R. LaBarbera
Granulosa cells (GC) harvested from large (6-12 mm) follicles of cycling
pigs obtained at the abattoir were incubated in the absence or presence of
insulin and/or human chorionic gonadotropin (hCG). The total accumulation
of progesterone and cAMP in the tissue plus medium was quantified by
radioimmunoassay of hexane extracts and trichloroacetic acid extracts,
respectively, and was related to cellular DNA content. Insulin (1
microgram/ml) had little effect on progesterone accumulation by freshly
harvested GC incubated for up to 26 h at 37 degrees C. After preincubation
of GC for 16 h in the absence of hormones, insulin (650 ng/ml) only
enhanced subsequent basal progesterone accumulation after an additional 22
h. However, preincubation of cells for 20 h in the presence of 1
microgram/ml of insulin increased subsequent progesterone accumulation in
both the absence and the presence of hCG (50 ng/ml). The effect of a 20-h
preincubation with insulin on subsequent progesterone accumulation was
related to the insulin concentration. At a maximally effective
concentration of 5 micrograms/ml during the preincubation period, insulin
increased subsequent basal and hCG-stimulated progesterone accumulations
more than twofold. The concentrations of insulin in the preincubation
medium that produced half maximal stimulation (ED50) were 300 and 200 ng/ml
for subsequent basal and hCG-stimulated progesterone accumulations,
respectively. After correction for loss of insulin immunoreactivity in the
incubation medium, the ED50 levels were 60 and 50 ng/ml, respectively.
Insulin elevated hCG-stimulated progesterone accumulation over the entire
range of hCG concentrations; the effect on hCG-stimulated cAMP production
was evident only at higher hCG concentrations.(ABSTRACT TRUNCATED AT 250
WORDS)
