Effect of various pretreatments on the hypothermic activity of repin in naive rats

Repin is a sesquiterpene lactone found in Centaurea solstitialis, a plant responsible for Parkinson-like disease in horses. Repin, on intraperitoneal (i.p.) injection, produces a dose-dependent and highly significant hypothermia in naive rats. The hypothermia is long-lasting with a peak 3 h after the injection and a return to normal temperature after more than 8 h. The effects of atropine sulfate, atropine methylbromide, propranolol, metergoline, ketanserin, diphenhydramine and apomorphine pretreatment on repin-induced hypothermia were investigated. None of the pretreatments directly antagonized repin's hypothermic effect. However, partial but significant reversals of hypothermia by atropine sulfate, metergoline, ketanserin, diphenhydramine and apomorphine were observed 2-4 h after the repin injection. These late-onset effects are probably due to secondary physiological mechanisms. On the other hand, propranolol, at 20 mg/kg i.p., clearly accentuated both the early-onset (30-90 min) and late-onset (2-4 h) hypothermic effects of repin.