AJP - Endocrinology and Metabolism, Vol 249, Issue 4 380-E384, Copyright © 1985 by American Physiological Society
Adenohypophyseal response to hypophysiotropic hormones in male obese Zucker rats
M. L. Heiman, J. R. Porter, M. V. Nekola, W. A. Murphy, A. D. Hartman, V. A. Lance and D. H. Coy
Description of the recessive, homozygote obese Zucker rat (fafa) includes
disorders of growth and reproduction. The aim of this study was to compare
responsiveness of adenohypophyseal cells, obtained from male fafa rats and
from their lean siblings, to growth hormone-releasing factor (GRF) and to
luteinizing hormone-releasing hormone (LHRH). Pituitary cells were cultured
for 4 days and were then challenged with either GRF-29 (the NH2-terminal 29
amino acid GRF peptide that expresses full biological activity of its
parent 44 amino acid molecule) or [D-Trp6]LHRH (LHRH-A, an LHRH agonist).
Medium was assayed for growth hormone (GH), luteinizing hormone (LH), and
follicle-stimulating hormone (FSH) by radioimmunoassay. Dose-response
curves were compared using the computer program ALLFIT. The median
effective GRF-29 concentration (EC50) computed for hypophyseal cells
cultured from lean animals (0.30 +/- 0.01 fM; means +/- SE of 4
experiments) was less (P less than 0.01) than that calculated for cells
obtained from fafa rats (15.8 +/- 6.7 fM). In contrast, cells derived from
lean littermates required a larger (EC50) concentration of LHRH-A than did
gonadotrophs cultured from obese rats [58.2 +/- 1.2 vs. 10.7 +/- 1.2 pM (P
less than 0.01) and 59.4 +/- 10.4 vs. 15.7 +/- 7.6 pM (P less than 0.05)]
to secrete LH and FSH, respectively. Our data describe an attenuated
pituitary response to GRF-29 and an enhanced response to LHRH-A in the
fafa.
