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1. The removal of the interscapular brown adipose tissue (IBAT) led to an increase in body-weight of normal, lean mice as compared to anaesthetized controls.2. No significant difference in food consumption could be detected between the two groups of mice over the period of the experiment.3. Fat extraction of the whole carcasses with chloroform: methanol showed a statistically significant increase in fat content in the animals without IBAT.4. There was no apparent failure in the operated animals to sustain core temperature when exposed to a cold stress situation (4° for 24 h).5. There was no difference in the wet weight, protein content or cytochrorne oxidase content of the dorso-cervical brown adipose tissue (DCBAT) between operated and control mice. This is indicative of a lack of proliferation of other brown adipose tissue sites in the operated mice in response to the removal of the IBAT.6. It is suggested that brown adipose tissue is implicated in dietary themiogenesis in the mouse.

Unidirectional 3*Cl-efflux from preloaded isolated brown adipocytes was studied. A norepinephrine-stimulated 36C1-efflux pathway was found which approximately doubled the rate of 36Cl-effl~ from the cells. The response to norepinep~ine was fully i~bit~ by the ar-adrenergic antagonist praxosin, but was una&cted by the padrenergic antagonist propranolol, showing that norepinephrine stimulated the 36CI-efflux pathway via the a,adrenoceptor. The stimulation of 36C1-e8Iux could not be mimicked by the Caz+ ionophore A23187, indicating that the effect was not mediated by elevation of the intracellular Ca 2+ level. It is concluded that brown fat cells possess a specific mechanism for cc,-adrenergic stimulation of Cl-efflux. The possibility is discussed that this Cl-efflux pathway could be the basis for the early a-adrenergic depolarization seen in brown fat cells.