Effect of dipivalyl derivatives of catecholamines on cardiovascular function in the conscious dog

Dipivalyl derivatives of epinephrine, norepinephrine and isoproterenol were injected intravenously into conscious dogs while cardiovascular variables were monitored. The dipivalyl compounds produced cardiovascular effects that were comparable to those produced by their respective parent catecholamines except that the responses had a delayed onset and a prolonged duration. The catecholamines were more potent than their derivatives; norepinephrine was 28 times, epinephrine 15 times and isoproterenol 1.7 times as effective as their respective dipivalyl derivatives. Alpha or beta adrenergic responses to the dipivalyl compounds were attenuated or abolished after alpha adrenergic blockade (phenoxybenzamine or phentolamine), or beta adrenergic blockade (propranolol), respectively, or combined alpha and beta blockade. Since other evidence indicates that the dipivalyl derivatives themselves are inactive, our results suggest that these compounds act as prodrugs that exert their cardiovascular effects only after they are biotransformed to catecholamines.