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

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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 by detectable in blood of cattle in vivo.