Effect of growth hormone-releasing factor infusion on somatotropin, prolactin, thyroxine, insulin, insulin-like growth factor I and blood metabolites in control and somatostatin-immunized growing pigs.
The aim of this study was to characterize the effects of prolonged infusion of growth hormone-releasing factor (1-29)NH2 (GRF) on plasma concentrations of hormones and metabolites when administered to control pigs and pigs immunized against somatostatin (SRIF). In the first experiment, eight purebred Yorkshire boars averaging 113 +/- 2 kg BW were immunized against SRIF conjugated to bovine serum albumin (BSA) (n = 4) or BSA alone (n = 4). Somatotropin (ST) response to four rates of GRF infusion (0, 1.66, 5 and 15 ng/min/kg BW) for 6 hr was evaluated using a double balanced 4 x 4 Latin square design. During the 4 hr before infusion, SRIF-immunized animals tended (P = 0.06) to have a higher ST release (613 vs 316 ng.min/ml, SE = 232) than controls. During infusion, GRF elicited a dose-dependent increase in ST release in both squares; the ST response was not better in SRIF-immunized animals than in controls (P greater than 0.05) (1435 vs 880 ng.min/ml; SE = 597). In the second experiment, ten purebred Yorkshire boars (5 controls and 5 SRIF-immunized animals) averaging 69 +/- 2 kg BW were continuously infused with GRF at the rate of 15 ng/min/kg BW for six consecutive d. Under GRF infusion, ST concentrations increased (P less than 0.05) from 805 to 4768 ng.min/ml (SE = 507) from day 1 to day 6 in both SRIF-immunized and control animals. Prolactin levels increased (P less than 0.05) with GRF infusion; pattern of increase was different (P less than .01) overtime in control and SRIF-immunized animals. Thyroxine levels increased from 2.53 to 3.45 micrograms/dl (SE = 0.16) after six d of infusion. Insulin-like growth factor I was higher (P less than 0.05) before (139 vs 90 ng/ml; SE = 11) and during (222 vs 185 ng/ml; SE = 11) GRF infusion in SRIF-immunized animals. A transient increase (P less than 0.05) in glucose and insulin was observed in both groups. Immunization against SRIF had no effect on blood metabolites; however, GRF infusion increased free fatty acids from 157 to 204 microEq/l (SE = 11) and decreased blood urea nitrogen from 4.1 to 3.5 mmol/l (SE = 0.2) from day 1 to day 6, respectively. In summary, active immunization against SRIF in growing pigs increased ST and IGF-I concentrations. Infusion of GRF continuously raised ST levels with days of infusion without any sign of decrease responsiveness.
Dubreuil
P
P
Agriculture Canada, Research Station, Lennoxville, Québec.
Petitclerc
D
D
Gaudreau
P
P
Brazeau
P
P
Pelletier
G
G
D000818:Animals; D013006:Growth Hormone / Q000097:blood; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D006728:Hormones / Q000097:blood*; D007114:Immunization / Q000662:veterinary; D007262:Infusions, Intravenous / Q000662:veterinary; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D008297:Male; D011388:Prolactin / Q000097:blood; D013004:Somatostatin / Q000276:immunology*; D013552:Swine / Q000097:blood / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood
D006728:Hormones; D007328:Insulin; D013004:Somatostatin; D007334:Insulin-Like Growth Factor I; D011388:Prolactin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D013974:Thyroxine