Renal hemodynamics in hemorrhagic hypotension: studies on the effects of pre- and postjunctional dopamine receptor agonists.

The present study was conducted to determine if selective prejunctional dopamine receptor agonists will be useful in improving renal hemodynamics in acute hemorrhagic shock in anesthetized mongrel dogs. Both bromocriptine and N-n-propyl-N-n-butyl dopamine (PBDA) effectively increased renal blood flow, due to a decrease in renal vascular resistance in intact anesthetized dogs. However, these two agents failed to increase renal blood flow after acute hemorrhage in the innervated or denervated kidneys. Dopamine was effective in increasing renal blood flow in both intact and hemorrhaged animals. However, this action of dopamine in hemorrhaged animals was associated with a significant increase in arterial blood pressure. These data could be explained based on the observations that the reduction in renal blood flow following hemorrhage was primarily due to a decrease in blood pressure as a result of the decrease in cardiac output and was not due to an increase in renal vascular resistance. Because elevation of sympathetic tone appeared to play little role, prejunctional inhibition by bromocriptine and/or PBDA of sympathetic nerve function was ineffective in altering renal vascular resistance. Dopamine was effective in increasing renal blood flow, not because of its pre- or postjunctional actions on dopamine receptors on renal nerves or vasculature, but because of its ability to increase cardiac output and arterial pressure. Based on the experimental model employed in these studies, it is concluded that agents such as PBDA and bromocriptine, which are considered to be selective prejunctional dopamine agonists, may not be clinically useful in improving renal circulation during hemorrhagic shock.