Urinary excretion of taurine as a function of taurine intake: potential for estimating taurine bioavailability in the adult cat.

Abstract

Urinary taurine excretion increases markedly when excess taurine is consumed. Experiments were designed to characterize this response in an attempt to develop an assay system for taurine bioavailability in common cat foods using an adult cat model. Initial studies investigated the time course of changes in urinary taurine excretion in response to alterations in taurine intake. The rate of urinary taurine excretion decreased rapidly when cats were switched from a casein diet supplemented with 0.2% crystalline taurine to a diet containing no supplemental taurine, reaching steady-state in 2 d. In contrast, urinary taurine excretion by cats switched from low to high taurine did not plateau until 6 to 7 d. Subsequently, cats (n = 18) were fed a casein diet containing graded levels of crystalline taurine (0, 0.025, 0.05, 0.10, 0.15 or 0.20%). After a 7-d adjustment period, urinary taurine excretion was quantified over a 5-d collection period and also by cystocentesis, and blood taurine levels were measured on d 6. Plasma taurine increased linearly (r = 0.88) as taurine intake increased, while whole-blood taurine increased asymptotically, reaching 95% of maximum concentration at a taurine intake of 93 mu mole/(kg body weight.d). The rate of urinary taurine excretion increased only slightly as taurine intakes increased to 96 mu mol/(kg body weight.d), but increased markedly (15-fold) thereafter. The same pattern was observed whether urinary taurine excretion was expressed as mu mole/(kg body weight.d) from total urine collection or as mu mole/g creatinine from cystocentesis.(ABSTRACT TRUNCATED AT 250 WORDS)