Exogenous growth hormone inhibits bovine but not murine pituitary growth hormone secretion in vitro: evidence for a direct feedback of growth hormone on the pituitary.
To test the hypothesis that one aspect of growth hormone (GH) regulation involves a direct effect of GH on its own secretion at the level of the pituitary, we evaluated the effects of human GH on basal and GH-releasing factor (GRF)-induced GH secretion in rat and bovine pituitary cell cultures. Both 4 h (acute) and 24 h (chronic) exposure of bovine pituitary cells to exogenous human GH significantly (p less than 0.001) reduced GH secretion. Acute treatment resulted in a decrease in GH secretion from 579 +/- 24 to 500 +/- 17 ng/ml 4 h (mean +/- SEM, n = 24) while chronic treatment resulted in a GH decrease from 595 +/- 21 to 483 +/- 17 ng/ml/4 h. In contrast, human GH treatment of rat somatotropes had no effect on basal GH secretion. GRF-stimulated GH secretion was not affected by either acute or chronic GH exposure in either species. These results demonstrate that there are species-specific differences in the ability of GH to regulate its own secretion and provide evidence for a direct inhibitory effect of GH at the level of the bovine pituitary.
Rosenthal
S M
SM
Department of Pediatrics, University of California, San Francisco.
Silverman
B L
BL
Wehrenberg
W B
WB
D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D005246:Feedback; D013006:Growth Hormone / Q000378:metabolism / Q000494:pharmacology*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D008297:Male; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone