Some Effects of Fasting on the Composition of the Blood and Respiratory Exchange in Fowls

Abstract

The occurrence of a peak in the true blood-sugar curve of the fasting fowl on the 3rd or 4th day, as found in previous work, was confirmed. No correlation was found to exist between this increase in blood sugar and the concentration of protein (uric acid and non-protein nitrogen) or fat (cholesterol and lecithin) metabolites in the blood, or between it and the muscle glycogen; in regard to liver glycogen and the R.Q. the results were inconclusive. After glucose ingestion the hyperglycaemic response and the rate of oxidation of sugar decreased as length of the previous fast was increased. These effects were probably due to a falling off in the rate of absorption and to utilisation of increasing proportions of absorbed sugar to restore the glycogen deposits. Adrenalin produced a greater degree of hyperglycaemia in fowls fasted for 96 hours than for shorter periods, and the corresponding liver glycogen values indicated that only about one-fourth of the extra sugar could have come from the original glycogen stores. The R.Q. during luxus absorption of carbohydrate was near or above unity, thus indicating conversion of sugar into fat. The R.Q. rapidly fell to below 0·700 and then remained steady during a fast of 7 days; the fasting quotient was not appreciably altered by protein meals or by maintenance on a protein diet, but was raised by ingestion of pure fat. Uric acid formed, during fasting, 50 per cent. or more, and after a protein meal 30 per cent. or more of the urinary nitrogen, and the low R.Q. is believed to be due to the loss of O₂ incurred in the synthesis of uric acid. The Zuntz-Schumburg tables are, therefore, inapplicable to the fowl. In fasting, ketosis did not occur, and the metabolic rate was higher in the morning than in the evening. One of us (K. M. H.) is indebted to the Medical Research Council for a personal grant.