Centrally administered ghrelin suppresses sympathetic nerve activity in brown adipose tissue of rats.

To clarify the functional roles of ghrelin in regulating energy balance, we investigated the effects of a central infusion of ghrelin on food intake and the activity of the sympathetic nerve innervating brown adipose tissue (BAT), the site regulating energy expenditure in rodents. A bolus infusion of ghrelin at a dose of 1 nmol/rat into the third cerebral ventricle (i3vt) increased the 4 h cumulative food intake. I3vt infusion of ghrelin (1 nmol/rat) suppressed BAT sympathetic nerve activity, followed by a gradual recovery. In contrast, i3vt infusion of growth hormone (GH) at a dose of 0.5 nmol/rat induced a gradual increase in sympathetic nerve activity. The ghrelin infusion decreased BAT temperature, which recovered gradually, but did not affect rectal temperature. In conclusion, the central administration of ghrelin suppresses energy expenditure and thermogenesis in BAT via its inhibitory effect on BAT sympathetic nerve activity. Simultaneous GH secretion induced by ghrelin treatment may modulate the temporal course of the sympathetic nerve response to ghrelin. The stimulatory and inhibitory effects of ghrelin on energy intake and expenditure, respectively, may induce a positive energy balance, which, in turn, affects adiposity and body weight.