Central cardiovascular effects of taurine: comparison with homotaurine and muscimol.

The central cardiovascular effects of taurine were compared with those of homotaurine and muscimol. The drugs were injected i.c.v. in cumulative doses into pentobarbital-anesthetized cats. Muscimol (0.1-30 microgram/kg) produced dose-dependent hypotension and bradycardia, with a maximum effect of 70 +/- 5 mm Hg and 75 +/- 5 beats/min, respectively. Homotaurine led to a dose-related fall in blood pressure and heart rate; maximum effects were obtained with 300 microgram/kg and averaged 55 +/- 3 mm Hg and 73 +/- 3 beats/min. For both drugs, the dose-response curves were shifted to the right by pretreatment with 10 microgram/kg of bicuculline i.c.v. This antagonism confirms that the central cardiovascular effects of muscimol and homotaurine are mediated by a stimulation of gamma-aminobutyric acid receptors. Taurine produced dose-related hypotension and bradycardia. The depressive effects of taurine started at a dose of 10 microgram/kg; at a dose of 1000 microgram/kg, the maximum effects observed were a 55 +/- 7 mm Hg hypotension and a 53 +/- 8 beats/min bradycardia. These effects were not affected by bicuculline pretreatment, but strychnine (i.c.v) prevented the effects of taurine. These findings indicate that glycine-type receptors may be involved in the taurine effects rather than gamma-aminobutyric acid type receptors. However, these results do not exclude the involvement of taurine-type receptors for which the specific antagonists is not yet available.