Day-night variations in blood and intracellular pH in a lizard,Dipsosaurus dorsalis

Blood pH, \(P_{{\text{CO}}_2 } \) and \(P_{O_2 } \) ofDipsosaurus dorsalis were measured during the day and at night. Lizards at constant body temperatures (25, 37°C) and lizards experiencing diurnal changes in body temperature similar to those in nature were studied. In lizards at constant body temperatures, blood pH was about 0.1 unit less and blood \(P_{{\text{CO}}_2 } \) was 4–7 Torr higher at night compared to day. Similar patterns were seen in lizards on natural thermal cycles (Figs. 1 and 2). Intracellular pH (pH_i) of skeletal muscle, esophagus and liver was about 0.2 units lower at night than day but myocardial pH_i was unchanged (Table 1). Reduction in breathing frequency, and thus a relative hypercapnia from hypoventilation was consistent with the nocturnal acidification of the blood and intracellular compartments (Fig. 3). Nocturnal acidification (CO₂ retention) corresponds to periods of minimum metabolism. The possible impacts of diurnal shifts in hydrogen ion concentration on energy metabolism and metabolic regulation are discussed.