The effect of propranalol on the calorigenic response in brown adipose tissue of new-born rabbits to catecholamines, glucagon, corticotrophin and cold exposure.

1. Experiments measuring the rate of oxygen consumption of unanaesthetized new-born rabbits and the blood flow in brown adipose tissue of anaesthetized new-born rabbits are described.2. The increase in rate of oxygen consumption caused by I.V. infusion of noradrenaline, adrenaline and isoprenaline (2 mug/kg.min for 10 min) was blocked by propranalol (I.V. 1 mg/kg) but the increase caused by cold exposure was not. A larger dose of propranalol (5 mg) blocked the calorigenic response to cold exposure as well.3. Infusion of glucagon (I.V. 4 mug/kg.min for 10 min) caused a large increase in the rate of the rabbit's oxygen consumption and in blood flow through its brown adipose tissue. These responses, which reached a maximum within 10 min from the start of the infusion, were not blocked by propranalol (1 or 5 mg/kg).4. Infusion of corticotrophin (I.V. 1 i.u./kg.min for 10 min) also caused a large increase in the rate of oxygen consumption of new-born rabbits. The response reached a maximum about 20 min from the start of the infusion and it was not blocked by propranalol (5 mg/kg).5. These results support the conclusion that noradrenaline is released at sympathetic endings in brown adipose tissue and that the increase in blood flow caused by noradrenaline is secondary to its metabolic action on the tissue. They also suggest the possibility that glucagon and corticotrophin may act directly on brown adipose tissue and stimulate heat production during cold exposure.