Differential effects of dopamine on glucoregulatory hormones in rats

The effect of dopamine at different doses on serum concentrations of insulin, glucose and corticosterone and on plasma glucagon concentration was investigated in rats. Dopamine was given intravenously over 6 h with infusion rates of 2.5, 7.5, 15, and 60 μg/kg · min and in combination with phentolamine. Serum insulin concentration was unchanged at low doses of dopamine. It was significantly increased from 6.0 ± 0.7 ng/ml to 13.7 ± 2.3 ng/ml ( P < 0.01) when 7.5 μg/kg · min of dopamine were used, whereas it was significantly depressed to 3.96 ± 0.89 and to 4.0 ± 0.34 ng/ml ( P < 0.01), respectively, at the high doses of dopamine. This latter effect could be reversed to 6.7 ± 1.19 ng/ml and inverted to 9.2 ± 1.7 ng/ml ( P < 0.01) by simultaneously applied phentolamine at appropriate dosages. Serum glucose levels were markedly elevated from 154 ± 7 to 234 ± 42 mg/dl ( P < 0.01) by the higher doses of dopamine. A significant alteration of glucagon plasma concentrations from 18.9 ± 2.8 to 42.3 ± 14 pg/ml ( P < 0.01) was elicited only by 7.5 μg/kg · min of dopamine. The data clearly demonstrate that exogenous dopamine acts differently on glucose homeostasis according to the dosage. The study provides strong evidence that dopamine decreases insulin levels via α-adrenergic receptor stimulation. This effect may contribute to the deterioration of glucose homeostasis with high doses of dopamine.