Brain tyrosine availability and the depression of central nervous norepinephrine turnover in acute and chronic starvation in adult male rats.

Norepinephrine (NE) and 3-methoxy-4-hydroxyphenylglycol (MOPEG) were determined in medio-basal hypothalamus of adult male rats using high-performance liquid chromatography to study nutritional modulation of noradrenergic turnover. Acute starvation, as well as 3 weeks of semistarvation with a low-protein high-carbohydrate or high-protein low-carbohydrate diet decreased NE turnover significantly, as estimated by MOPEG concentration. Low-protein semistarvation resulted in subnormal concentrations of large neutral amino acids (LNAA), high-protein semistarvation in elevated concentrations. Tyrosine/LNAA ratio and calculated tyrosine flow into brain and brain tyrosine levels were reduced in both types of semistarvation. Corticosterone was low in low-protein and high in high-protein diet. These results suggest that tyrosine availability in brain potentially contributes to reduced NE turnover in starvation.