Effects of long-term infusion of growth hormone (GH)-releasing factor on pulsatile GH secretion in the male rat.
The effects of long-term infusion of GRF on pulsatile GH secretion were investigated in conscious, freely-moving male rats. GH-releasing factor (GRF) was intravenously administered for 14 days using an osmotic minipump. Six-hour iv infusion of 0.5 microgram/h GRF significantly increased mean GH concentration in the conscious rats. In contrast, 14-day iv infusion of 0.5 microgram/h GRF significantly inhibited pulsatile GH secretion. The pituitary GH content was significantly increased by the 14-day treatment. The GH response to bolus injection of 1 microgram GRF under urethane anesthesia was enhanced by the 14-day infusion of GRF. Pretreatment with somatostatin (SS) antiserum did not restore the inhibited GH secretion in rats treated with 14-day infusion of GRF. These results suggest that neither pituitary GH depletion nor high somatostatin tone is involved in the GRF-induced GH inhibition.
Sato
M
M
First Department of Internal Medicine, Kagawa Medical School, Miki-Cho, Japan.
Murao
K
K
Niimi
M
M
Tamaki
M
M
Takahara
J
J
D000818:Animals; D013006:Growth Hormone / Q000187:drug effects* / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007262:Infusions, Intravenous; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012636:Secretory Rate / Q000187:drug effects; D013997:Time Factors
D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone