Blood levels, clearance rates and effects of epinephrine and norepinephrine on insulin and metabolites during alpha- and beta-adrenergic blockade in cattle in vivo, and in vitro degradation of dopamine in bovine blood.

Abstract

To study possible modifications of norepinephrine and epinephrine kinetics (metabolic clearance rate and half-times) by inhibition of binding to alpha- and/or beta-adrenergic receptors, norepinephrine and epinephrine were iv infused in the absence or presence of the alpha-adrenergic blocking agent phentolamine, the beta-adrenergic blocking agent propranolol, and during the combined administration of phentolamine and propranolol. In addition, recovery experiments were performed to investigate the in vitro degradation of dopamine, norepinephrine and epinephrine. Blood levels and kinetics of epinephrine were not modified by alpha- and beta-adrenergic blockade, whereas norepinephrine clearance was reduced by alpha-adrenergic blockade, and was greater than epinephrine clearance. alpha- and beta-adrenergic blockade markedly modified insulin, glucose and non-esterified fatty acid responses to epinephrine and norepinephrine. Norepinephrine and epinephrine could fully be recovered when added to bovine blood plasma. In contrast, dopamine obviously was immediately destructed by bovine, but not by human blood plasma, and should therefore barely be detectable in blood of cattle in vivo.