Influence of lead on rat thoracic aorta contraction and relaxation

Low levels of lead, but not high levels, produce hypertension. This mystery has not yet been resolved. In this study we compared the in vitro vasoresp onsiveness in rat thoracic aorta to low dose (10(-8) mol/L) and high dose ( 10(-5) mol/L and 10(-4) mol/L) lead acetate. In addition to the direct resp onse to lead, we examined reactivity to norepinephrine, acetylcholine, isop roterenol, phorbol ester, and calcium in the presence and absence of lead. Neither low-dose nor high-dose lead directly affected aortic contractile or relaxant responses. However, lead, only at the highest concentration (10-4 mol/L), increased the contractions to calcium at all submaximal calcium co ncentrations. We conclude that low-dose lead must increase blood pressure i ndirectly through a humoral effect. The reasons for the failure of high-dos e lead to influence blood pressure remain to be explored. (C) 2001 American Journal of Hypertension, Ltd.