On the use of the nephrectomized rat for the study of rapid changes in nitrogen metabolism.

With the exception of some recent applications of the isotope technique (l), studies concerned with endocrine influences over nitrogen metabolism have depended largely on the use of the conventional nitrogen balance technique or on measurements of tissue nitrogen. While these methods have yielded valuable information about over-all changes in nitrogen metabolism, they do not offer much opportunity to detect small or transient shifts in protein metabolism or to establish time relationships with hormone action when the latter are rapid or of brief duration. The importance of being able to measure such small and rapid changes in nitrogen metabolism is emphasized by recent studies which indicate that certain of the hormones concerned in nitrogen metabolism, and particularly the adrenal cortical hormones, act more rapidly than had been once thought (2). Evidences of adrenal cortical activity can be demonstrated as soon as 20 minutes following the injection of potent cortical hormone or after administration of adrenocorticotropic hormone. By the conventional methods for studying nitrogen metabolism it is not possible. to detect the earliest changes attendant on hormone action. Furthermore, the 12 to 24 hour urinary nitrogen excretion may reflect not only the effects of the hormone itself, which may be short lived, but the secondary homeostatic changes as well. Accurate collections of urine for less than 12 hours are difficult when small animals such as rats are used. In order to obtain more information concerning factors involved in the endocrine control of nitrogen metabolism, this investigation of use of the nephrectomized rat for the s%udy of rapid changes in nitrogen metabolism was begun. Since urea, the end-product of protein catabolism, is freely diffusible throughout the body water, measurement of its rate of accumulation in