The purpose of this study was to determine the effects of diet-induced thiamine deficiency on tissue protein synthesis. [14C]valine incorporation into total protein of cortex, brainstem, cerebellum and subcortical structures of thiamine-deficient (TD) rats with neurological dysfunction was significantly depressed (P < 0.001) by 52, 49, 50 and 52 per cent as compared to pair-fed (PFC) control values. [14C]valine incorporation into heart, kidney, pancreas and liver protein of TD rats was also depressed (P < 0.001) by 49, 53, 65, and 46 per cent respectively. Incorporation rates were only slightly (10 per cent) (yet significantly, P < 0.05) impaired in the brains of partly fasted PFC animals as compared to controls fed ad lib. In the viscera, only PFC heart incorporation rates were significantly (P < 0.05) reduced (20 per cent) as compared to rats fed ad lib. When neurologic dysfunction and anorexia of TD rats were reversed by three daily injections of 500 μg thiamine. [14C]valine incorporation into protein of all tissues returned to normal except for a residual 8 per cent impairment in the cerebral cortex. Severe thiamine deficiency causes hypothermia. In TD rats with neurologic dysfunction whose body temperature had been restored to the normal value of 38°, valine incorporation rates remained significantly (P < 0.02) less than control values, but the initial (hypothermic) depression in incorporation was reversed by 56-73 per cent in various brain areas and by 29,40, 18 and 35 per cent in heart, kidney, pancreas and liver respectively. Thiamine deficiency had no effect on the specific activity of valine precursor pools in any of the tissues studied. Thus, the observed inhibition in net protein synthesis in vivo in diet-induced thiamine deficiency seems to involve at least three components: (1) hypothermia to an important degree, (2) decreased food assimilation/utilization to a minor degree, and (3) probably an effect of thiamine deficiency per se.
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