Involvement of hypothalamic somatostatin in glucagon-induced suppression of growth hormone secretion in conscious rats.
The role of central glucagon in regulating GH secretion was studied in conscious male rats with chronic indwelling intra-atrial and intracerebro-ventricular (ICV) cannulae. Repeated blood sampling every 20 min from 1000 hr to 1700 hr showed two major GH bursts occurring at regular intervals (3.6 +/- 0.1 hr) around 1200 hr and 1540 hr. The ICV (lateral ventricle) injection of glucagon (10 micrograms/rat) at 1100 hr inhibited spontaneous GH secretion, and the mean (+/- SE) plasma GH levels from 1120 hr to 1700 hr were lower than those in controls injected ICV with the vehicle solution only (31.9 +/- 7.8 ng/ml vs. 157.1 +/- 13.4 ng/ml, p less than 0.01). The GH bursts did not appear until 5 hr after the injection. The intravenous (IV) injection of glucagon (10 micrograms/rat) did not change plasma GH levels or the occurrence of spontaneous GH bursts. The glucagon-induced suppression of GH release was attenuated when anti-somatostatin serum (ASS), but not normal rabbit serum (NRS), was given IV in a volume of 0.25 ml immediately before the ICV injection of glucagon (10 micrograms/rat) (mean GH levels at 1120-1700 hr: ASS + glucagon, 133.6 +/- 26.7 ng/ml vs. NRS + glucagon, 30.5 +/- 7.4 ng/ml, p less than 0.01). These findings suggest that central glucagon may play an inhibitory role in regulating GH secretion by stimulating SRIF release from the hypothalamus in the rat.
D000818:Animals; D003243:Consciousness / Q000502:physiology; D005934:Glucagon / Q000494:pharmacology*; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism*; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000378:metabolism*
D013004:Somatostatin; D013006:Growth Hormone; D005934:Glucagon