Tissue specificity of SNS response to exercise in mice exposed to low temperatures

The present study was carried out to investigate the tissue specificity of the sympathetic nervous system (SNS) response to acute exercise in adult mice exposed to four ambient temperatures. SNS activity estimates in heart, pancreas, and brown adipose tissue (BAT) were obtained from the measurement of the dopamine (DA) tissue contents 1 h after the inhibition of the DA-beta-hydroxylase with 1-cyclohexyl-2-mercaptoimidazole (CHMI). DA was measured by electrochemical detection after the separation of the monoamine using high-performance liquid chromatography. In both heart and pancreas, temperature and activity influenced DA tissue contents after the CHMI injection. In these tissues, and regardless of whether mice were resting or exercising, the DA contents gradually increased while the ambient temperature was dropped from a thermoneutral temperature of 32 to 5 degrees C. In BAT, however, there was a significant interaction between temperature and activity on the tissue DA content; in contrast to what was observed in resting animals, DA did not uniformly augment in exercising mice when the temperature was decreased from 32 to 5 degrees C. In summary, the present results show that exercise can attenuate the stimulating effect of cold on SNS activity in BAT. This effect is seemingly specific to BAT because, in mice exposed to low ambient temperatures, SNS activity in both heart and pancreas is not lower in exercising than in resting animals.