Catecholamine and nitric oxide systems as targets of chronic low-level lead exposure in inducing selective functional impairment

Rats were exposed for ten months to 60 ppm of lead (Pb, as acetate) in drinking water to further assess cardiovascular effects of chronic Pb exposure. At the end of the treatment, mean blood Pb was 3.1+/-0.3 microg/dL in the control rats and 22.8+/-1.2 microg/dL in the Pb-exposed rats (means+/-SE, n=12 in each group); these values were not comparable to those of humans. Pb greatly increased plasma levels of noradrenaline (NA) and adrenaline (A), but not those of L-DOPA and dopamine; monoaminoxidase activity was augmented by Pb, mostly in the aorta and in the liver; the aorta, liver, heart and kidney showed discrete histopathological alterations in the Pb-exposed rats, in which plasma levels of nitric oxide (NO, determined as L-citrulline) were reduced. Pb was able to induce blood hypertension, resulting from increase of cardiac inotropism and, mostly, total peripheral resistance. These data were discussed also in relation to those obtained in our previous studies carried out in rats exposed to Pb in drinking water (15-60 ppm) for periods ranging from five to eighteen months. Pb appeared to increase both sympathetic nerve activity by central mechanisms (thus increasing plasma NA and A) and cyclic adenosine monophosphate (cAMP)-dependent availability of calcium ions (Ca++) for contractile mechanisms in the vascular and cardiac myocells (also through an increased vascular alpha2- and myocardial beta1-adrenoreceptor reactivity). The reduction of plasma NO, contributing to increase vascular resistance and cardiac inotropism, was explained as a result of actions of Pb on enzyme activities concerned with the kallikrein-kinin (KK) and renin-angiotensin-aldosterone (RAA) systems. It was concluded that chronic Pb exposure is able to affect selective neuroendocrine (i.e., catecholamine), au- tacoidal (i.e., KK and RAA) and transductional pathways (i.e., cAMP, NO, Ca++) involved in the cardiovascular function.