Cause of hypophosphatemia in hyperthermic dogs

¹ Department of Physiology, Albany Medical College of Union University, Albany, New York

The plasma inorganic phosphate (P) fell from 3.9±0.4 mg % to 1.6±0.3 mg % in eight unanesthetized dogs exposed to an air temperature of 48°C for 2 hours. It was shown previously that this alteration in P was not due to renal excretion. There appeared to be an inorganic-organic P shift in hyperthermia. Dehydration in the absence of hyperthermia and panting did not cause hypophosphatemia. Induction of hyperthermic hypophosphatemia was not inhibited by anesthesia. Hyperthermia was eliminated as the causative agent in three anesthetized, hyperthermic dogs which were curarized and artificially ventilated so as to maintain normal pH. With panting absent, no fall in inorganic P occurred. The effect of the altered pH on phosphate was tested in five anesthetized, curarized, normothermic dogs which were hyperventilated with a respiratory pump. The pH was elevated to an average value of 7.61. In all cases hypophosphatemia occurred. It therefore appears that the increase in pH, due to panting, is the major factor in causing the fall in plasma inorganic P observed in dogs exposed to heat.

Note:
With the Technical Assistance of R. H. Lubinski and I. M. Mielens