Growth hormone releasing hormone induced release of growth hormone in aging male rats: dependence on pharmacological manipulation and endogenous somatostatin release.
These studies were designed to assess whether a decline in pituitary response to growth hormone-releasing factor (GRF) contributes to the decline in amplitude of growth hormone (GH) pulses with age. Atrial cannulated young (3-4 months), middle-aged (12-14 months) and old (20-22 months) Fischer 344 male rats were anesthetized with pentobarbital to suppress pulsatile release of GH. One hour later, animals were injected with hpGRF(1-44) (10 micrograms/kg) and blood samples were removed at 0, 5, 10, 20, 40 and 80 min. Animals were then passively immunized with somatostatin antiserum and hpGRF(1-44) was reinjected. Samples were removed at the time intervals previously described. In response to 10 micrograms/kg GRF, plasma GH in young and middle-aged animals increased to 921 +/- 105 and 866 +/- 126 ng/ml, respectively, at 10 min and declined. In old animals, GH concentrations only increased to 654 +/- 80 ng/ml (p less than 0.05 compared to young rats). This represents a 28% reduction in the peak GH response to GRF. Despite passive immunization with somatostatin antiserum, the peak GH response to a second injection of GRF was diminished in all age-groups. However, integration of the area under the response curve indicated that GH secretion was similar in young and old animals during the 80-min sampling period after somatostatin antiserum. In another study, diethyldithiocarbamate (DDC; 250 mg/kg, i.v.), a dopamine-beta-hydroxylase inhibitor, was used to inhibit pulsatile GH release. One hour later, animals were injected with hpGRF(1-44) (50 micrograms/kg, i.v.) and blood samples were removed as previously described.(ABSTRACT TRUNCATED AT 250 WORDS)
Sonntag
W E
WE
Department of Physiology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, N.C.
Gough
M A
MA
D000375:Aging / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D004050:Ditiocarb / Q000494:pharmacology; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000502:physiology*; D007116:Immunization, Passive; D008297:Male; D010424:Pentobarbital / Q000494:pharmacology; D011863:Radioimmunoassay; D051381:Rats; D011916:Rats, Inbred F344
D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D004050:Ditiocarb; D010424:Pentobarbital