Catecholamine release: mechanism of mercury-induced vascular smooth muscle contraction

The mechanism by which mercuric ion (HgCl2) induces contraction of vascular smooth muscle was defined in the kidney of anesthetized dogs and in rabbit aortic strips. In vivo, HgCl2 injected into the renal artery induced a dose-related reduction in renal blood flow (electromagnetic flowmeter) and glomerular filtration rate (creatinine clearance). An intra-arterial infusion of phenoxybenzamine (POB) significantly reduced the vascular response to HgCl2 (P less than 0.001). In vitro, alpha-adrenergic blockade with phentolamine and POB prevented mercury-induced contraction, whereas agents that block serotonin, histamine, acetylcholine, and angiotensin did not do so. Norepinephrine receptor "protection" from phenoxybenzamine blockade sustained the response to HgCl2. Reserpine pretreatment produced a parallel reduction in the response of the aorta to tyramine and mercury. The results are consistent with an indirect action of mercuric ion via release of endogenous catecholamines.