The purpose of this investigation was to evaluate the role of blood pressure in the proliferative response of vascular smooth muscle cells to systemic infusion of angiotensin II (Ang II). Our laboratory has previously shown that infusion of Ang II induces smooth muscle cell proliferation in rat mesenteric vessels and carotid arteries. Ang II, a strong vasopressor, raised systolic blood pressure in rats from 120 to 200 mm Hg at a dose of 435 ng x kg(-1) x min(-1) after 1 week of treatment. The question arises as to whether this development of hypertension is a primary contributor to the replicative activities observed in the arterial wall of the mesenteric arteries or the carotid arteries or whether Ang II alone, without an increase in blood pressure, is sufficient to stimulate proliferation in these vessels. In the previous studies, we found that Ang II stimulated smooth muscle cell replication in the carotid artery and in type III and type I mesenteric microvessels. This study demonstrates that although administration of hydralazine normalizes the animals' blood pressures, it does not suppress the mitogenic effect of Ang II. Thus, it appears that Ang II has a direct effect on cell proliferation.