Time course of temperature effects on arterial acid-base status in Alligator mississippiensis

Temperature effects on extracellular acid-base status in terrestrial poikilotherms are well known. Comparatively less is known concerning the time course of acid-base responses to prolonged changes in temperature. In this study, two questions were addressed: (1) what is the time course of acid-base responses to a temperature change of 5 days duration in Alligator mississippiensis?; and (2) what are the relative contributions of respiratory vs metabolic (strong ion) processes to the acid-base response? The effects of acute (4-6 h) vs chronic (24-120 h) decreases in ambient temperature from 30 to 20 degrees C were determined on arterial blood gases, acid-base status and plasma electrolyte concentrations ([Na+], [K+] and [Cl-]) in 7 awake alligators. In addition, in vivo and in vitro non-bicarbonate buffer values were determined in 6 anesthetized alligators. Acute decreases in temperature decreased PaCO2 (31 to 18 mmHg) and PaO2 (91 to 50 mmHg), increased pH (7.48 to 7.66), but had no significant effect on plasma bicarbonate concentration ([HCO3-]). Chronic exposure to 20 degrees C had no further effect on any variable. dpH/dT ranged between -0.018 and -0.011 U/degrees C, over the duration of the experiment. Temperature did not alter [Na+] or [Cl-] at any time, and had only minor effects on [K+]. In vivo (11.5 +/- 0.7 mEq/L/pH unit) and in vitro (16.1 +/- 0.9 mEq/L/pH unit) buffer values were significantly different, but neither was affected by temperature. Temperature had no effect on the base excess (estimated with either in vitro or in vivo buffer values), nor on estimates of the strong ion difference. We conclude that pH changes during prolonged exposure to decreased temperature occur rapidly and can be explained by changes in PaCO2, CO2 solubility and pK', without major contributions from metabolic or strong ion adjustments.