EFFECTS OF FASTING ON THE RESPIRATORY METABOLISM OF NORMAL AND HYPOPHYSECTOMIZED YOUNG PIGEONS

Abstract

Repeated measurements of the respiratory exchange were made under basal conditions, at both 25[degree] and 30[degree] C., on 43 normal and 37 hypophysectomized young Carneau pigeons subjected to a 10-day fast. Neither prolonged fasting nor hypophysectomy caused any apparent shift of the zone of thermal neutrality. The fasting produced a moderate acetonemia, a slight reduction of both liver and muscle glycogen below the 24-hr. fasting level, little or no change in the total store of liver fat, and probably no decrease in total reducing substances in the blood. Respiratory quotients of 0.63-0.68 were frequently found in both types of birds after a fast of 48 or more hrs.; a few quotients of 0.74-0.79 persisted to the end of the fast. The many low quotients obtained and the available information from earlier studies on fowls indicate that birds tend to produce quotients lower than 0.69 from combustion of their own protein. The caloric value of O2 utilized by birds in burning protein has not been determined with acceptable accuracy. On the assumption that the O2 used had a value of 4.686 cal. per 1., irrespective of the R. Q. obtained, the heat production of 39 normal pigeons was reduced from a 24-hr. fasting value of 4.33 to 3.10 cal./ kg./hr., a reduction by ,28.6% in 9 additional days of fasting. Hypophysectomized fasting pigeons showed a comparable decrease of only 22.3%.