Effects of taurine and a taurine antagonist on some respiratory and cardiovascular parameters

Respiratory performance, heart rate and blood pressure were studied in halothane anesthetized rats after administration of taurine and the putative taurine antagonist 6-aminomethyl-3-methyl-4H-1,2,4-benzothiadiazine-1, 1-dioxide hydrochloride (TAG). Intracerebroventricular (i.c.v.) taurine depressed ventilation due to decreased inspiratory neural drive and depression of respiratory timing mechanisms. I.c.v. administration of 1-100 micrograms TAG caused no changes in the respiratory and circulatory parameters studied except at the highest dose interval where respiratory frequency and minute ventilation were depressed. The respiratory depression induced by taurine (0.2 mg) or beta-alanine (1 mg) was antagonized by administration of TAG (100 micrograms). However, TAG did not antagonize the respiratory effects induced by i.c.v. glycine or gamma-aminobutyric acid (GABA) in equipotent respiratory depressant doses. The decline in inspiratory neural drive as well as in "respiratory timing" after i.c.v. taurine was restituted toward control values by TAG. The hypotension and bradycardia induced by taurine were also antagonized by TAG. It is concluded that TAG seems to antagonize the depressant action of taurine and beta-alanine but not of GABA and glycine on respiratory performance. TAG might also possess some partial agonist activity in higher doses.