Effect of the adrenergic beta 3-agonist, BRL37344, on heat production by brown adipocytes in obese and in older rats.

Heat production by isolated brown adipocytes, from hypothalamic obese rats and from older rats, was investigated by microcalorimetry. The obese and older rats were 12 and 40 weeks-old, respectively. The basal heat production by the brown adipocytes was significantly less in the obese and older rats than in control rats 12 weeks of age. Isoproterenol and a novel adrenergic beta 3-agonist, BRL37344, increased heat production in a concentration-dependent manner in all rats. The effects of isoproterenol were significantly less in the obese group than in the controls, while BRL37344 stimulated heat production in all rats almost identically. These results suggest that (1) the heat producing capacity of brown adipocytes is reduced by hypothalamic obesity and aging, and (2) BRL37344 might be useful as an anti-obesity drug.