METABOLIC, VENTILATORY, AND ACID-BASE RESPONSES ASSOCIATED WITH SPECIFIC DYNAMIC ACTION IN THE TOAD BUFO-MARINUS

Specific dynamic action (SDA), the postprandial increase in metabolic rate that has been well documented in numerous vertebrates, intensifie s demand for O-2 delivery by the ventilatory and cardiovascular system s. Yet the well-documented increase in plasma pH following feeding (th e ''alkaline tide'') should, paradoxically, result in a decrease rathe r than art increase in ventilation. The intent of this study was to in vestigate in the marine toad Bufo marinus whether there is a change in the relationship between metabolism, lung ventilation, and blood pH a ssociated specifically with SDA. We measured VO2, VCO2; respiratory qu otient (R(E)); lung ventilation volume and frequency; arterial pH, PO2 , and hematocrit; and heart rate before and after the induction of SDA by peptone injection directly into the stomach. Levels of VO2 and VCO 2; approximately 40-60 mL . g(-1) . h(-1), doubled 5-6 h after peptone injection and then declined within 24 h. Accompanying this profound p eptone-stimulated SDA, which was dose-dependent, lung ventilation incr eased from about 3,750 mL . kg(-1) . h(-1) to 5,750 mL . kg(-1) . h(-1 ) with a time course similar to that of VO2. Heart rate increased from 36 to 45 beats . min(-1). In spite of these changes, arterial PO2 and pH (approximately 80 mmHg and 7.75, respectively) did nor change duri ng the SDA response. Although the anticipated alkaline tide did not de velop in Bufo, the large increase in lung ventilation without a corres ponding fall in blood pH nonetheless suggests an uncoupling of hyperve ntilation and an acid stimulus during SDA. Respiratory physiology duri ng the postprandial period clearly deserves more investigation.