Hemodynamics and ventricular function in the day-12 rat embryo: basic characteristics and the responses to cardiovascular drugs.

We investigated the basic characteristics of the rat embryonic circulation and also looked at the hemodynamic effects of alpha- and beta-agonists, digitalis, and atrial natriuretic peptide, using a modified organ culture system in which the embryo was placed in oxygenated Hanks' balanced salt solution, blood pressure was measured by a servo-null micropressure system, and blood flow pattern was obtained by a 20-MHz pulsed Doppler velocity meter. The peak pressure was 0.5 +/- 0.04 (SEM) mm Hg at the atrium (n = 6), 2.3 +/- 0.10 mm Hg at the ventricle (n = 15), 1.6 +/- 0.03 mm Hg at the truncus (n = 7), and 1.0 +/- 0.05 mm Hg at the umbilical artery (n = 21). There was a pressure drop from the ventricle to the truncus and then a smaller pressure decrease to the umbilical artery. The atrial a-wave was 20% of ventricular pressure and ventricular inflow blood flow pattern showed very low early-to-late filling ratio, indicating that the ventricle was stiff. These findings were essentially the same as in the chick embryo. We recorded the ventricular image by using a high-speed video system with a frame rate of 200/s, and the ventricular pressure-area loop showed a triangular shape with short isovolumetric phases, which was different from that of the chick embryo at a similar stage.(ABSTRACT TRUNCATED AT 250 WORDS)