Pulmonary vascular responsiveness to histamine: exquisite sensitivity of small intrapulmonary arteries.

The contractile responses of cylindrical segments of the central and peripheral pulmonary arteries of the rabbit and the guinea pig to norepinephrine and histamine were studied. Concentration-response curves demonstrated that the relative sensitivity of the pulmonary arteries of both species to the 2 agents increased as the internal diameter of the arterial segments decreased, except in very small arterial rings obtained from the rabbit, which did not respond at all to norepinephrine, but responded quite vigorously to histamine. These data suggested that histamine and other vasoactive substances may play an important role in the regulation of blood flow in the periphery of the lung, and, perhaps, in the response of the peripheral vasculature to hypoxia.