Insulin suppressive effects of aminotetralin analogs and of dopamine

The study concerned the effects of 2-amino-6,7-(OH)2-1,2,3, 4-tetrahydronaphthalene (A-6,7-DTN), dipropyl-A-6,7-DTN and dopamine on plasma levels of immunoreactive insulin (IRI) in cattle. During infusions of A-6,7-DTN, dipropyl-A-6,7-DTN and dopamine, the circulating levels of IRI decreased. In response to A-6,7-DTN, the levels of glucose increased whereas non-esterified fatty acids did not change. The decrease of IRI during additional infusions of A-6,7-DTN was not modified by prolonged administration of A-6,7-DTN. During infusions of A-6,7-DTN there was no increase in response to the administration of glucose and tolbutamide. However, if the beta-adrenergic agonist isoproterenol was infused, IRI increased in the presence of A-6,7-DTN. During, infusions of the alpha-adrenergic blocking agent, phentolamine, levels of IRI increased within minutes while glucose did not change. Concomitant infusions of A-6,7-DTN and phentolamine caused IRI to decrease and the rise in glucose levels seen in the absence of phentolamine was inhibited. In conclusion, enhanced dopaminergic activity inhibited IRI secretion. The suppressive effects of A-6,7-DTN were due primarily to its dopaminergic properties, but A-6,7-DTN also possessed some characteristics of an alpha-adrenergic agonist. beta-Adrenergic stimulation reversed the suppressive effects of A-6,7-DTN on IRI secretion.