Acid-Base and Ion Regulation in the Bullfrog Rana catesbeiana during and following Severe Hypoxia

Abstract

This study examined the acid-base and ionoregulatory responses by the skin and kidneys of adult bullfrogs (Rana catesbeiana) during and following hypoxic enforced submergence (38 ± 3 min duration). Two groups were studied: large spring animals and smaller summer animals. Arterial and bladder catheters permitted repetitive blood sampling and continuous urine collection. Enforced submergence initially resulted in a combined respiratory/metabolic acidosis; there were no significant differences in blood parameters between the two groups. A marked lactacidosis ensued, with plasma lactate and nonrespiratory acid () concentrations peaking at 15.2 ± 1.8 and 25.8 ± 6.0 mmol/liter ½ h after emergence. The respiratory component of the acidosis was corrected within 4 h. The metabolic component was mostly corrected by 12 h, owing primarily to metabolic utilization of lactate and proton equivalents and secondarily to renal/cutaneous excretion of acid equivalents. Each group showed a different pattern in its renal and cutaneous parameters at rest and in response to the acid-base disturbance. Cutaneous permeability and renal excretion in the small summer frogs was two- to threefold that of large spring animals, both during control periods and during recovery from the acidosis. In the former group, there were significant correlations between the cutaneous excretion of acid equivalents and influx of Na⁺ and Cl⁻, indicating the potential for acid-base regulation via ion movements across the skin. In the latter, the skin was not an important organ of acid-base regulation via ion exchanges with the external environment, despite evidence for a cutaneous Na⁺/ exchange. It is concluded that bullfrogs are very tolerant of large acid-base disturbances and that the kidneys play a more important role than the skin in acid-base and ion regulation.