General pharmacology of a new potent 5-hydroxytryptamine antagonist

The potential of the investigational 5-hydroxytryptamine (5HT3) antagonist, LY277359, to alter cardiovascular, central nervous system (CNS), smooth muscle, and gastrointestinal functions at multiples of pharmacologically active doses, was examined to provide a profile of possible secondary pharmacological effects. In the anesthetized dog, significant cardiovascular effects were observed at doses 100-1000 and 4-15 times those found to be pharmacologically active at 5HT3 receptors in vivo in rats and dogs, respectively. These effects were limited to decreased heart rate (approximately 20%) at intravenous doses of 1.75 and 3.5 mg/kg and prolonged Q-Tc intervals (approximately 20 to 50%) at doses of 0.438 to 3.5 mg/kg. At an oral dose of 135 mg/kg (representing 1500-4500 times the pharmacologically active dose in rats), LY277359 induced hypoactive behavior and reduced body temperature in mice. Seizure activity was potentiated at high oral doses of LY277359 (45 and 135 mg/kg). A single oral dose of 135 mg/kg increased hexobarbital-induced sleep time. In smooth and cardiac muscle tissue studies in vitro, LY277359 was essentially inactive: it did not alter contractile activity or receptor function of the guinea pig ileum, rat vas deferens, rat uterus, or guinea pig atria at concentrations of 10(-5) to 10(-10) mol/l. At a concentration 50,000 times the 5HT3 antagonistic level in vitro (10(-4) mol/l), LY277359 inhibited the response of the ileum to field stimulation, acetylcholine and angiotensin I, and suppressed the rate of the spontaneously beating guinea pig atria in a noncompetitive manner.(ABSTRACT TRUNCATED AT 250 WORDS)