MICROVASCULAR EFFECTS OF ATRIAL-NATRIURETIC-PEPTIDE (ANP) IN MAN - STUDIES DURING HIGH AND LOW-SALT DIET

Objective: Infusion of ANP in anephric dogs causes a decrease in cardi ac output and a rise in peripheral vascular resistance. This reduced c ardiac output is possibly related to increased resistance to venous re turn generated in the microcirculation by venular constriction. The ai m of the present study was to evaluate in healthy volunteers the effec ts of low-dose ANP infusion on both conjunctival and skin microcircula tion during high or low salt diet. Methods: ANP (7.5 ng/kg/min) and pl acebo were infused (i.v.) for 4 h, in random order on two separate day s, in two groups of 10 healthy male volunteers each. One group was stu died during high salt (ad libitum), and one group during low salt (55 mmol Na+/24 h) diet. Microvascular density and diameters of both conju nctiva and nailfold were studied using intravital videomicroscopy. Nai lfold capillary red blood cell velocity (CBV) was studied using intrav ital videomicroscopy, and skin (thermoregulatory) blood flow (SBF) was studied using laser-Doppler fluximetry. Results: In the high salt gro up ANP induced a 43% reduction in basal SBF as compared to an 18% redu ction by placebo (P<0.01). Parallel to SBF, ANP significantly reduced CBV (P<0.02), Conjunctival capillary density decreased by 5% during AN P, while it increased by 28% during placebo (P<0.05). No such effects of ANP were observed in the low salt group. Blood pressure and heart r ate were not influenced by ANP infusion in either group. Conclusion: I nfusion of low doses of ANP into humans on an ad libitum salt diet res ults in vasoconstriction of the microcirculation, probably on the venu lar side. The lack of effect of ANP On the microcirculation during low salt diet may be related to a higher vascular tone prior to infusion. (C) 1998 Elsevier Science B.V. All rights reserved.