Atrial, B-type, and C-type natriuretic peptides cause mesenteric vasoconstriction in conscious dogs

Cardiovascular responses were compared with equimolar infusions of B- type (BNP) and C-type (CNP) with atrial natriuretic peptide (ANP) in conscious, instrumented dogs. On separate days, each natriuretic peptide or vehicle was infused (intravenously) at step-up doses of 2, 5, 10, and 20 pmol · kg^-1 · min^-1 (20 min each dose) to increase circulating levels of the infused peptide from ~2- to 20-fold. Like ANP, infusions of BNP caused dose- related increases (P < 0.05) in mesenteric vascular resistance, urine flow, natriuresis, and hematocrit (changes at highest doses were 60 ± 9, 334 ± 113, 313 ± 173, and 12 ± 2%, respectively). BNP also lowered (P < 0.05) plasma renin activity (-43 ± 11%) and arterial pressure (-10 ± 3%). Effects of BNP were independent of reflex sympathetic activation, since autonomic ganglion blockade did not attenuate the responses. CNP infusions had little effect except to increase (P < 0.05) mesenteric vascular resistance (27 ± 10%) and plasma ANP (41 ± 7%). Cardiovascular actions of BNP, like those of ANP, counteract the renin-ANG system and may protect the heart by lowering cardiac preload (venous return) and afterload (arterial pressure) while maintaining blood flow to extrasplanchnic regions.