CARDIAC-OUTPUT AND PERIPHERAL RESISTANCE DURING LARVAL DEVELOPMENT IN THE ANURAN AMPHIBIAN XENOPUS-LAEVIS

Stroke volume (SV) and cardiac output (CO) were measured in anesthetized larvae of Xenopus laevis from hatching (3 mg) to the end of metamorphosis (similar to 1 g). CO and SV were calculated from videotaped images of the intact beating heart; SV increased from 2.4 x 10(-3) mu l at 3 mg body mass to 7.6 mu l at 1 g. CO increased from 0.25 mu l/min at 3 mg to 623 mu l/min at 1 g. With use of CO, along with arterial pressures from another study [P.-C. L. Hou and W. W. Burggren. Am. J. Physiol. 269 (Regulatory Integrative Comp. Physiol. 38): R1120-R1125, 1995], peripheral resistance and cardiac work were also calculated. Resistance decreased rapidly from 701 peripheral resistance units (PRU, mmHg . s . mm(-3)) at 3 mg body mass to 79 PRU at 20 mg and gradually declined toward 0.9 PRU at 1 g. Cardiac work increased from 0.06 dyn . mm at 3 mg body mass to 1.27 dyn . mm at 20 mg and then climbed sharply to 717 dyn . mm at 1 g. The general pattern of change in hemodynamic variables (except heart rate) during larval development-is similar in Xenopus laevis and chick. embryos, suggesting a common pattern for hemodynamic development in vertebrate embryos/larvae.