[The rabbit thermo-regulatory system. Effects of high dose of sodium fluoride]

The mechanism of sodium fluoride (NaF) induced hypothermia was investigated on relations between the monoamine synthesis and metabolism in the rabbit brain. Five male rabbits per a group, weighing about 2.5kg and having rectal temperatures of 38.4 to 39.3 degrees C, were used in this experiment. The rectal temperature measurements were made by means of an electric thermometer for 5 hours at intervals of 15 or 30 minutes. Through this experiment, animals were housed in a room kept at 22 to 23 degrees C. The following drugs were used in this experiment: NaF (40 mg/kg i.v.), barbital sodium (0.1 g/kg s.c.), hexamethonium bromide (C6, 10 mg/kg i.v.), ergotamine tartrate (30 mg/kg s.c.), phenoxybenzamine hydrochloride (15 mg/kg i.v.), propranolol hydrochloride (5 mg/kg s.c.), pindolol (0.3 mg/kg s.c.), atropine sulfate (30 mg/kg s.c.), 2, 4-dinitrophenol (DNP, 20 mg/kg i.v.), l-DOPA (20 mg/kg i.v.), 5-HTP (20 mg/kg i.v.) Results 1. Intravenous injection of 30 mg/kg of NaF induced a drop of 0.66 degrees C in rectal temperature. 2. Pretreatment with 0.1 mg/kg of barbital sodium or 10 mg/kg of C6 prominently inhibited the NaF-induced hypothermia. 3. The alpha-blockade caused by ergotamine tartrate and phenoxybenzamine or the beta blockade by propranolol hydrochloride and pindolol resulted in an approximate 50% inhibition of maximum drop in body temperature induced by NaF administration. Both alpha- and beta-blockades caused by ergotamine tartrate and propranolol or by phenoxybenzamine and pindolol, however, made a remarkable inhibition of the NaF effect. Cholinergic blockade brought on by atropine sulfate, on the other hand, had no effect against NaF-induced hypothermia. 4. Bilateral splanchnicotomy completely inhibited drops in rectal temperature. 5. Intravenous injection of NaF 40 mg/kg failed to counteract the rise of rectal temperature caused by DNP 20 mg/kg. 6. Pretreatment with l-DOPA made a prominent inhibition of NaF-induced hypothermia. The inhibiting effects of 5-HTP, however, were slight. 7. Administration of NaF made a significant decrease in norepinephrine levels in the rabbit hypothalamus, but had no effect on 5-HT levels.