Fig. 5.

Effect of thermoneutrality and β-AR blockade on rectal temperature in A3^−/−A8^−/− and WT chow-fed mice. (A) Six-week-old male A3^−/−A8^−/− and WT mice (n = 8 per group) were maintained at thermoneutrality for 5 wk. Rectal temperatures, body weights, VO₂ consumption, and VCO₂ output were measured as described in the Materials and Methods. (B) Rectal temperatures were obtained in mice fed ad libitum (first 4 bars) or after a 14-h fast (second 4 bars) (n = 6; age 9–12 wk). The mice were then treated with a nonselective β-adrenergic blocker (propranolol; 5 mg/kg) and provided food. Temperatures were monitored as described in Materials and Methods. (C) Male mice (n = 5 per group) were treated chronically with propranolol (0.5 mg/mL in the drinking water) starting at 6 wk of age for 5 wk. Heart rates were measured as a control for propranolol activity. (D) Mice (n = 5 per group; age 7–9 wk) were treated with l-748,337 compound, a β3-receptor blocker (5 mg/kg). (E) Male mice were maintained at thermoneutrality for 5 wk and then injected twice with CL 316,243 (1 mg/kg, 18 h apart) (n = 4; age 16–17 wk). Values are means ± SEM. Group means were compared by using unpaired t tests. Experiments were repeated once, and the results were similar. (F) cAMP levels were measured in tissue lysates from WAT-SQ, BAT, and WAT-Epi of WT and A3^−/−A8^−/− mice fed ad libitum (n = 5; age 8–11 wk). Levels were measured by using an ELISA, as described in Materials and Methods. Values are means ± SEM. Groups were compared by using unpaired t tests. Experiments were repeated once, and the results were similar. CL, CL 316,243; L, l-748,337; P, propranolol. *P < 0.05; **P < 0.01; ***P < 0.001.