Analysis of the renin-angiotensin system during fasting in adult male rabbits

Summary Caloric deprivation for 3 days in adult male rabbits induced significant increases in daily urinary Na+ excretion, urinary volume and fluid intake as previously reported. These changes were accompanied by: (a) a significant reduction in plasma renin concentration; (b) an unchanged plasma renin activity; (c) a marked increase in the plasma angiotensinogen concentration; (d) a significant reduction in plasma angiotensin I; and (e) a significant increase in plasma angiotensin II. In a separate group of adult male rabbits, 3 days of caloric deprivation significantly increased the amount of converting enzyme in pulmonary parenchymal tissue. These findings correlate with the previously reported enhancement of mineralocortical hormone secretion and limiting effect of the latter on the natriuresis of caloric withdrawal. Since the increased mineralocortical hormone secretion does not prevent the natriuresis, the possibility that these striking changes in the components of the renin-angiotensin system during caloric deprivation may exert intrarenal effects is discussed. The authors wish to thank Dr. R. O. Soffer, Albert Einstein College of Medicine, for his helpful suggestions and for providing us with a preprint of his method for determining the pulmonary converting enzyme. We also thank Mr. John Hegmann for his excellent technical assistance.