Effect of a2-Adrenergic Agonist Growth Hormone and Insulin-li Concentrations in Barrows

The effects of infusion of clonidine, an a2-adrenergic agonist, on plasma insulin-like growth factor-I (IGF-I) concentrations were investigated with a single growth hormone (GH) injection in pigs. Four barrows were subjected to four treatments: saline infusion with a vehicle injection, clonidine infusion (0.5 nmol/kg/min for 8 h) with a vehicle injection, saline infusion with a bovine GH (bGH:100 tg/kg) injection, and clonidine infusion with a bGH injection. Infusion was started 1 h before the injection. Plasma IGF-I, bGH, porcine GH (pGH), insulin, glucose, non-esterified fatty acid (NEFA), and blood urea nitrogen (BUN) concentrations were measured. Plasma IGF-I concentrations during saline infusion increased after a bGH injection (P<0.05). However, the IGF-1 concentrations during clonidine infusion did not increase after the bGH injection. Plasma endogenous GH (pGH) was not increased during clonidine infusion. The plasma glucose concentration was noticeably increased during clonidine infusion and moderately increased after the GH injection. Despite the extreme increase in plasma glucose during clonidine infusion, plasma insulin did not change. Neither plasma NEFA nor BUN was changed by these treatments. These results demonstrate that the a2-adrenergic agonist clonidine altered the action of GH to increase the plasma IGF-I concentrations.