Effect of atrial natriuretic peptide on diastolic filling in the stage 21 chick embryo.

Atrial natriuretic peptide (ANP) exerts hemodynamic effects by direct venodilation in the chick embryo. We hypothesized that ANP-induced venodilation affects ventricular diastolic filling resulting in reduced ventricular preload. Chick ANP (0.1 microgram in 10 microL of normal saline) was suffused onto the vitelline vascular bed in stage 21 (3 1/2 d) chick embryos. Equivalent aliquots of normal saline were suffused as sham controls, and normal embryos received no suffusion. We measured simultaneously dorsal aortic blood velocity and atrioventricular blood velocity with a 20-MHz pulsed-Doppler velocity meter. Analog wave forms were digitally sampled at 500 Hz, and the dorsal aortic cross-sectional area was used to calculate dorsal aortic blood flow. Passive ventricular filling volume equaled dorsal aortic stroke volume multiplied by the fraction of passive area; active filling volume equaled dorsal aortic stroke volume multiplied by the fraction of active area. Data were summarized as mean +/- SEM (n > or = 7 per group) and analyzed by analysis of variance. Cycle lengths were similar in ANP-suffused, sham control, and normal embryos. Dorsal aortic blood flow decreased from 0.49 +/- 0.04 mm3/S at baseline to 0.27 +/- 0.05 mm3/S at 4 min post-ANP suffusion (p < 0.05) and was unchanged in sham control and normal embryos (p > 0.05). Passive ventricular filling was reduced by ANP suffusion, whereas active filling was unaffected, resulting in a decreased passive/active filling ratio from 0.64 +/- 0.07 at baseline to 0.32 +/- 0.08 at 4 min in ANP-suffused embryos (p < 0.05). Passive/active ratio was unchanged in sham control and normal embryos. Thus, ANP-mediated vasodilation reduces cardiac output via decreased passive ventricular filling in the embryonic heart.