Metanephrine: Cardiovascular responsiveness in normotensive and renal hypertensive dogs

Metanephrine, infused intravenously into normotensive and renal hypertensive dogs at the rate of 0.02 mg/kg/min, caused a pressor response. The response elicited in chronic hypertensive dogs was significantly higher than the evoked either in normotensive or in acute hypertensive animals, and it was significantly reduced after bilateral adrenalectomy but not after nephrectomy. Moreover, phentolamine and P-286 (a drug which selectively blocks the adrenal discharge of catecholamines) inverted and reduced the pressor response respectively in chronic hypertensive dogs. This strong pressor response was not accompanied by an increase in renin-release from the kidney. The pre-infusion with catecholamines sensitized the normotensive dogs to subsequent infusion with metanephrine.