AJP - Endocrinology and Metabolism, Vol 250, Issue 6 650-E654, Copyright © 1986 by American Physiological Society
Sex-related differences in GH secretion in rat using reverse hemolytic plaque assay
K. Y. Ho, D. A. Leong, Y. N. Sinha, M. L. Johnson, W. S. Evans and M. O. Thorner
It is not known whether enhanced growth hormone (GH)-releasing factor
(GRF)-stimulated GH release observed in the male reflects differences in
somatotrope numbers and/or secretory response to GRF. We addressed this
question by using the hemolytic plaque assay which allows quantification of
hormone secretion by single pituitary cells. Time-course studies and GRF-GH
concentration-response relationships (0.01, 0.1, 1, 10, 100, 1,000 nM GRF)
in age-matched male and diestrous day 2 female rats were compared by
quantitating the percent of GH plaque-forming cells, and measuring the
plaque areas. The male pituitary contained a greater percent (P less than
0.05) of somatotropes (% of plaque-forming cells 45 +/- 2 vs. 27 +/- 4% in
the female; mean +/- SE). GRF induced a greater concentration-dependent
increase in plaque areas in the male. Maximal responses were attained at 10
nM GRF in both sexes. However, mean maximal plaque area was significantly
greater (P less than 0.001) and the EC50 was significantly lower (P less
than 0.05) in the male (0.25 +/- 0.09 vs. 1.78 +/- 0.64 nM in the female).
The data suggest that the greater percent of somatotropes in the male and
greater secretory capacity and sensitivity to GRF may contribute to
sex-related differences in GH secretion in the rat.
