Central arterial hemodynamics in larval bullfrogs (Rana catesbeiana): developmental and seasonal influences.

Central arterial hemodynamics (blood pressure and velocity) as a function of ontogeny and season were determined in larval Rana catesbeiana (body mass 0.3-8.7 g, 20-22 degrees C). Ventricular systolic pressure increased from 1.8 mmHg at stage (St) II to 11.9 mmHg at St XIII, while ventricular diastolic pressures usually were less than 1.0 mmHg. In early stages (up to St V-VII) of fall/winter larvae, the pressure waveform in the conus arteriosus was often biphasic. The first peak was due to weak ventricular contraction (sometimes inadequate to eject blood into the arterial tree), and a stronger second peak resulted from conal contraction. In these young fall/winter larvae, the conus--not the ventricle--was the major circulatory pump. Older larvae (greater than St X) showed "adultlike" central hemodynamics, with the ventricle ejecting blood through the conus into the central arterial circulation. Systolic blood pressure was considerably higher in young spring/summer (April-June) larvae, and the ventricle rather than the conus was the main circulatory pump at all stages, in contrast to fall/winter larvae. Thus both season and development have profound influences on the central hemodynamics of bullfrog larvae.