Selective and tone-dependent vasodilation of arterial segment in rabbit and feline pulmonary microcirculation in response to ANP.

Using an X-ray television system, we directly measured the changes in internal diameter (ID; 100-600 microns) of small pulmonary arteries and veins in response to intravenous infusion of atrial natriuretic peptide (ANP) in anesthetized rabbits and cats. Under physiological conditions, ANP (0.01-1 micrograms/(kg.min) for 3 min) increased the ID of the small arteries in a dose-dependent manner by 4-9% and by 6-14% in the rabbit and cat, respectively. The maximum increase in ID occurred in the 400-600 microns arteries. In the small veins, however, the peptide had no significant effects on the ID. To simultaneously investigate the ANP-induced responses of pulmonary vessels with different vascular tone in a given lung region, we embolized a part of the rabbit pulmonary vascular tree with micro-beads (80-100 microns diameter) and measured ID responses to ANP (1 microgram/(kg.min) for 3 min) in the embolized vessels with elevated tone and the nonembolized vessels with baseline tone. In the embolized arteries, which had constricted by 31%, ANP induced 27% increase in ID, while in the nonembolized arteries it caused 8% increase in ID. This indicated that in the small arteries, the vasodilator activity of ANP is greatly enhanced under the conditions of elevated vascular tone. In the small veins, however, no significant vasodilation occurred even under the elevated-tone conditions. We concluded that ANP dilates the arterial segments in the rabbit and cat pulmonary microcirculation selectively and in a dose-dependent manner. Furthermore, the pulmonary vasodilator effect of ANP was dependent on the pulmonary vascular tone.