Baroreflex-linked variations of catecholamine metabolism in the caudal ventrolateral medulla: an in vivo electrochemical study.

In vivo electrochemical recordings of the metabolism of catecholamines were obtained in the caudal ventrolateral medulla in anesthetized rats submitted to various experimental changes in systemic arterial pressure. Hypertension induced with phenylephrine and reversal of hypovolemia decreased the catechol metabolic activity. In contrast, controlled or hypovolemic hypotension, induced respectively with sodium nitroprusside or blood withdrawal (30% of blood volume), reversibly elicited the opposite pattern. This was suppressed by deafferentation. The changes in catechol metabolic activity in response to hypovolemia were accompanied by similar trends of variations of plasma vasopressin levels. By contrast with the increased catechol metabolic activity secondary to hypotension induced by either prazosin, sodium nitroprusside or hypovolemia, clonidine elicited a decrease in catechol metabolic activity. These data show a dynamic and specific involvement of the metabolism of catecholamines themselves promoted by changes in systemic arterial pressure. This pattern of functioning of catechol metabolism in the caudal ventrolateral medulla appears to be negatively related to systemic arterial pressure changes, a finding which does not fit with the proposed vasodepressor role of the A1-group.