REGULATION OF ACID-BASE STATUS IN ECTOTHERMIC VERTEBRATES - THE CONSEQUENCES FOR OXYGEN PRESSURES IN LUNG GAS AND ARTERIAL BLOOD

Extensive literature reports a negative Delta pHa/Delta t in ectotherm ic vertebrates, but data are scarce as to its consequences for O-2 tra nsport. In reptiles, the negative Delta pHa/Delta t results from an el evated lung gas P-CO2 (PA(CO2)) at higher temperatures, implying a cor responding fall of PA(O2). In parallel, arterial P-O2 rises with tempe rature, due to a combination of central vascular shunt and decreasing Hb . O-2 affinity. As a result, the P-O2 gradient between lung gas and blood (PA-a(O2)) becomes reduced at higher temperatures. In amphibian s, the negative Delta pHa/Delta t results from combined cutaneous and pulmonary CO2 elimination. We propose that this leads to a rather temp erature-independent lung gas P-O2. Moreover our calculations suggest t hat resting reptiles and ampihibians maintain a relatively large PA-a( O2) also at high temperatures. The negative Delta pHa/Delta t in teleo st fish is generally considered to be a result of modulated plasma [HC O3-]. Recent data from our laboratory suggest that acute pH adjustment s at high temperatures may involve alterations of Pa-CO2 through gill ventilation, leading to a decrease of Pa-O2 with rising temperature.