Time course and pattern of compensatory ingestive behavioral adjustments to lysine deficiency in rats

We and others have demonstrated that rats deficient in an essential amino a cid (EAA) will consume sufficient quantities of the lacking nutrient to pro duce repletion when it is made available in solution. In the current series of experiments, we made rats deficient in lysine (LYS) by limiting the lev el of this EAA in the diet. We then examined licking behavior during simila r to 23-h two-bottle intake tests over 4 consecutive days. In three separat e experiments, rats were presented with the following: 1) 0.1 mol/L LYS and water, 2) 0.2 mol/L threonine (THR) and water and 3) 0.1 mol/L LYS and 0.2 mol/L THR, Lysine-deficient (LYS-DEF) rats drink significantly more LYS th an did nondepleted controls (CON) when this amino acid was available. Meal pattern analysis revealed that the enhanced intake of LYS occurred as a fun ction of a greater number of ingestive bouts, not changes in bout size. A c umulative analysis of LYS intake between CON and LYS-DEF rats revealed that a potentiation of intake developed within 30 min of sampling the solution when LYS and water were available and within 90 min when LYS and THR were t he contrasting choices. In conclusion, increased LYS intake in the deficien t rats occurs relatively rapidly and appears to be at least somewhat specif ic. Moreover, LYS deficiency does not seem to enhance the palatability of t he limiting amino acid as judged by behaviors such as lick rate and bout si ze. Instead, LYS-DEF rats relieve the deficiency by increasing the number o f drinking episodes initiated.