Efeito da temperatura sobre as interações cardiorrespiratórias em sapos Rhinella schneideri

Abstract

For adequate blood supply to match metabolic demand, vertebrates regulate blood pressure (BP) in order to maintain adequate perfusion of target organs avoiding ischemia and tissue damage like edema. Effective short-term BP regulation in anuran amphibians occurs through adjustments in heart rate (HR), peripheral vascular resistance, and changing pulsatile frequency of lymph hearts. In addition, pulmonary ventilation in anurans is directly linked to blood volume homeostasis by facilitating lymph fluid movement back into the cardiovascular system which takes place by changing pressure and volume within anurans' lymphatic sacs. It is apparent that an interaction between baroreflex regulation and breathing control exists in anuran amphibians. In the present study I used pharmacological methods (phenylephrine and sodium nitroprusside; infusion ramp and in bolus methods) to investigate baroreflex sensitivity at different temperatures in the cururu toad Rhinella schneideri. I evaluated the degree to which arterial baroreflex plays a role in pulmonary ventilation in the cururu toad. Baroreflex regulation in the toad R. schneideri was temperature dependent and influenced the toad’s ventilation. Hypotension and hypertension resulted in increases and decreases in HR, respectively, as well as increases and decreases in pulmonary ventilation mainly through adjustments in breathing frequency. In contrast to data from the literature, anuran amphibians seem to defend lower BP events primarily rather than hypertension independent of temperature. Anurans exhibit higher rates of transcapillary fluid filtration which means during hypertension fluid filtration is increased and excess interstitial fluid formation will be reclaimed by an efficient lymphatic system. Therefore, besides pulmonary ventilation's role in matching O2 delivery to demand (e.g. temperatures) in anurans, it also plays a role in BP regulation possibly owing to an interaction between baroreflex control and respiratory areas in the brain.