Using isolated adrenal medulla we observed no difference in basal catecholamine secretion percentile between obese and lean animals. However, the percentile of catecholamine secretion stimulated by high K+ concentration was lower in the obese group. There was a decrease in the tyrosine hydroxylase enzyme expression (57.3%, P<0.004) in adrenal glands of obese mice. Interestingly, the expression of dopamine beta-hydroxylase was also reduced (47.0%, P<0.005). Phenylethanolamine N-methyltransferase expression was not affected.