Fenfluramine-induced thermogenesis in adult domestic fowl (Gallus domesticus): Elimination by propranolol,a beta-blocker

1. Intra-muscular injection of DL-fenfluramine, a 5-hydroxytryptamine agonist, increased heat production by a mean of 16% over the following 6hr in adult domestic fowl.2. Propranolol, a beta-receptor blocker, completely eliminated the effect of fenfluramine on thermogenesis.3. Respiratory quotient (RQ) was significantly reduced by fenfluramine injection, whether or not this was preceded by injection of propranolol. Injection of propranolol alone produced a decline of RQ to 0.71 within 1 hr, followed by an immediate steady increase to 0.90 over the next 5 hr.4. Extension and lowering of the wings, which augments surface area for heat loss, was observed within 30 min of fenfluramine injection and persisted for several hours. This thermolytic effect of fenfluramine was not eliminated by prior injection of propranolol. Polypnea occurred only when both propranolol and fenfluramine had been injected.5. Food intake over the whole day of measurement was significantly reduced by fenfluramine injection, whether or not this had been preceded by injection of propranolol. Water intake over the same period was unaffected by any of the treatments.6. Fenfluramine reduced spontaneous activity by almost half. The reduction was slightly greater when fenfluramine injection followed propranolol. Propranolol given alone had no effect on activity.