Feeding-induced increases in insulin do not suppress secretion of growth hormone.
Secretion of growth hormone (GH) is reduced for several hours after feeding when access to feed is restricted to a 2-hr period each day. We hypothesized that increased secretion of insulin after feeding inhibits release of GH from the anterior pituitary gland. Our objectives were to determine whether: 1) alloxan prevents concentrations of insulin from increasing after feeding steers; 2) concentrations of GH remain high after feeding alloxan-treated steers; and 3) GH-releasing hormone (GHRH) stimulates greater release of GH in alloxan-treated, than in control, steers after feeding. Steers were injected iv with either saline (control) or with alloxan (110 mg/kg) (n = 4 per group). Concentrations of insulin were not different (P = 0.61) between control and alloxan-treated steers before feeding (87.5 +/- 33.6 pmol/l). However, alloxan prevented insulin from increasing (P < 0.001) after feeding (131.8 pmol/1) compared with control steers (442.0 pmol/l) (pooled SEM = 47.5). Overall, GH was higher (P < 0.05) in alloxan-treated (6.4 ng/ml) than in control steers (3.7 ng/ml) (pooled SEM = 0.7), but GH decreased (P < 0.001) after feeding in both groups. Iv injection of GHRH stimulated release of GH 1 hr before, but not when injected 1 hr after feeding (P < 0.001). In addition, net areas under the GH curve were not significantly different between control and alloxan-treated groups. We conclude that increased concentrations of insulin after feeding do not mediate feeding-induced suppression of GH secretion in steers.
McMahon
C D
CD
Department of Animal Science, Michigan State University, East Lansing 48824-1225, USA.
Chapin
L T
LT
Lookingland
K J
KJ
Radcliff
R P
RP
Tucker
H A
HA
D000496:Alloxan / Q000494:pharmacology; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002417:Cattle / Q000502:physiology*; D004435:Eating / Q000502:physiology*; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D007328:Insulin / Q000097:blood*; D008297:Male; D019518:Postprandial Period
D001786:Blood Glucose; D007328:Insulin; D000496:Alloxan; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone