Improvement of metabolic disorders and visceral fat obesity by the beta 3-adrenoceptor agonist (R*,R*)-(+/-)-methyl-4-[2-[2-hydroxy-2 -(3-chlorophenyl)ethylamino]propyl]-phenoxyacetate hydrobromide (BRL35135A) in genetically obese rodents.

The effects of BRL35135A ((R*,R*)-(+/-)-methyl-4-[2-[2-hydroxy-2 -(3-chlorophenyl)ethylamino]propyl]-phenoxyacetate hydrobromide), a beta 3-adrenoceptor agonist, on visceral and subcutaneous fat weight and metabolic disorders were studied in genetically obese C57BL/KsJ db/db mice and Zucker fa/fa rats. In db/db mice, four weeks of oral administration of BRL35135A (0.5 and 5 mg/kg/day) decreased body weight gain and reduced white fat weight. The rates of reduction of white fat weight were in the order mesenteric fat > retroperitoneal fat > subcutaneous fat. In fa/fa rats, daily administration of BRL35135A (0.05 mg/kg/day)) for 6 weeks reduced the visceral white fat weight/total energy intake ratio, particularly for mesenteric fat, without any clear effect on body weight gain. This tendency of the compound to exert effects on visceral fat was consistent with the findings that the effect of BRL37344 ((R*,R*)-(+/-) -methyl-4-[2-[2-hydroxy-2-(3-chlorophenyl)ethylamino]propyl]-phenoxyacet ic acid), an active metabolite of BRL35135A, on the lipolytic activity of isolated adipocytes and the tissue concentration of [14C]BRL37344 in male Wistar rats were each greater in visceral fat than in subcutaneous fat. Moreover, BRL35135A at 0.05 mg/kg/day elevated serum insulin levels and improved hyperglycemia in db/db mice without reducing body weight gain, whereas at doses of 0.5 and 5 mg/kg/day it ameliorated hyperglycemia and hyperlipidemia, and tended to decrease serum insulin levels. In fa/fa rats, BRL35135A (0.005 mg/kg/day) was also effective in improving hyperinsulinemia, glucose intolerance, and hypertriglyceridemia without any effect on body weight gain or fat distribution. These findings suggest that the improvement of metabolic disorders by BRL35135A may be due to improvement in insulin resistance as well as reduction of visceral fat weight.