Studies on nitrogen metabolism in rats of different age fed on a protein-free diet. 3. Urinary endogenous nitrogen excretion in relation to body size and protein-free feeding duration.

Abstract

The influence of the time (t = 3, 6, 9, 12 and 16 days) of feeding on a protein-free diet (PFD) and the size of shrunk body mass (SB), increasing with age but decreasing with the duration of feeding on PFD, on the excretion of endogenous urinary nitrogen (EUN) were investigated. The experiment was on 350 male rats from 23 to 275 days of age and mean SB from 39 to 430 grammes, divided into 14 age groups (k = 14). The material and the method of the experiment as well as the composition of PFD were described in detail in part one of this work (Beza, 1986). The linear analysis of covariance showed that the EUN excreted after 3, 6, 9, 12 and 16 days on PFD as well as the average daily EUN did not significantly correlate with the initial body mass (SBi). It were calculated: 1. In relationship EUN(t) the slope ratios bk and intercepts ak, differed between the groups of age significantly. The ak values but not the bk, were closely correlated with the initial body mass SBi (r for ak values = 0.947***) indicating that the amount but not the rate of EUN excretion was closely related to SBi; 2. the daily EUN excretion at 1, 3, 6, 9, 12 and 15 days on PFD in relation to body mass in these days-EUNd(SBd) is described by the equation: EUNd = Ad.SBd 0.872 less than 1, in which Ad decreased from 287 mg N/SBd 0.872 on the first day to 167 mg N/SBd 0.872 on the 15th day on PFD; 3. the daily excretion of EUN(y) in relation to the daily body mass (x1) and to the day on PFD (x2) is described by the equation: EUNd(y) = 286.8.x1(0.872).x2(-0.1993); R = 0.987*** with N in mg, SB in kg. There was a directly proportional relationship between EUNd and SB0d 0.872 only (b1 = 1), whereas between EUNd and SBd 0.67 as well as between EUNd and SBd 0.75 the slope ratios b1 were 1.308 and 1.163, respectively and were significantly higher than one. With prolonged feeding on PFD for 15 days, the rate of EUNd excretion decreased in accordance to b2 = -0.1993 less than 0**, independently of the age and the initial SB of the rats.(ABSTRACT TRUNCATED AT 400 WORDS)