AJP - Endocrinology and Metabolism, Vol 263, Issue 4 E748-E751, Copyright © 1992 by American Physiological Society
Differences in GH secretion from individual somatotropes in rats genetically selected for fast and slow growth
J. R. Arbona, C. H. Rahe, R. L. Kelley, Y. N. Sinha, D. R. Strength, D. N. Marple and D. R. Mulvaney
Department of Animal and Dairy Sciences, Auburn University, Alabama 36849.
A reverse hemolytic plaque assay was used to examine effects of selection
for fast (F) and slow (S) growth on growth hormone (GH) secretion by
individual somatotropes. Anterior pituitaries (AP) from 32 male Charles
River CD strain rats selected for F and S growth for 20 generations were
used. Four rats per line were used at 4, 6, 8, or 10 wk of age. Body weight
(P < 0.0001) of F rats was greater compared with S rats. AP (P <
0.05) were heavier at 8 and 10 wk of age in F compared with S line rats.
Percentages of GH-secreting cells were unaffected by age (range =
32.7-35.5%) and line [F = 33.1 +/- 1.2% (SE) vs. S = 34.5 +/- 1.2%] or by
human GH-releasing factor (hGRF). At 8 and 10 wk, mean plaque-forming area
was greater (P < 0.0001) in F compared with S rats under both
nonstimulated (2,704 +/- 202 vs. 1,648 +/- 202 microns2) and
hGRF-stimulated secretion (4,503 +/- 202 vs. 2,682 +/- 202 microns2).
Results indicate that differences in growth observed in the two lines may
be due to a greater secretory capacity of individual somatotropes rather
than to a greater percentage of somatotropes or sensitivity of somatotropes
to secretagogue.
