Studies on nitrogen metabolism in rats of different age fed on a protein-free diet. 2. The feed intake

Changes in the intake of dry matter (DM) of the protein-free diet (PFD) fed ad libitum were studied on male rats in relation to the shrunk body mass (SB) and duration of protein-free feeding (t). The intake of DM and changes of SB were investigated on the same rats and during the same experimental periods. The mean intake of DM in relation to PFD feeding periods t = 3, 6, 9, 12, 16 days and the daily DM intake (DMd) in relation to the daily shrunk body mass (SBd) were calculated on logarithmical values according to a model of linear regression y = a + bx and to a model of multiple regression y = b0 + b1x1 + b2x2. The rate of DM intake in relation to the duration of PFD feeding (t) did not differ significantly between age groups (k = 14) but the ak differed significantly. The common coefficient bc = 0.871 +/- 0.012 was less than 1***. This relationship is described by the equation: DM intake = Ak X t0.871, where: DM intake = the sum of intake in the periods of 3, 6, 9, 12 and 16 days (in grams), k = age group, t = PFD feeding period. No significant correlation (P less than 0.05) was found between bk and the initial body mass (SBi) or age of rats (r = -0.21 and -0.02, respectively) but between ak and SBi or age the correlation was highly significant (r = 0.960 and 0.832). This indicates that the amount but not the rate of DM intake depended on the initial body mass or age. The relation between DMd and SBd, the latter increasing with age but decreasing with the duration of PFD feeding, is described by equation: DMd intake = Ad X SBd0.503, where: DMd intake in grams, d = day 1 to 15 of PFD feeding, SBd = daily shrunk body mass in kilograms. The values of Ad decreased with the duration of PFD feeding. The using of multiple regression permitted to describe DMd intake as a function of SBd and (d) by a common equation: DMd intake = 27.02 X SBd0.503 X d-0.103; R = 0.976. Thus the daily DM intake was closely positively correlated with SBd and negatively correlated with the duration of protein-free feeding regardless of the age of rats.(ABSTRACT TRUNCATED AT 400 WORDS)