Antagonism of kynurenine-induced seizures by picolinic, kynurenic and xanthurenic acids.

Picolinic, kynurenic, xanthurenic and anthranilic acids are metabolites of L-kynurenine which, when administered intraperitoneally (i.p.) antagonized (in descending order of potency) the seizures induced by intracerebroventricular (i.c.v.) injections of l-kynurenine sulfate in SHR and C57BL/6 mice. Picolinic and anthranilic acids were also effective after oral administration. Picolinic acid completely prevented seizures. Kynurenic acid, when injected i.c.v. prior to l-kynurenine sulfate, appeared to be more effective than after i.p. administration while picolinic and anthranilic acids were less effective. This suggest that the antikynurenine effect of metabolites of kynurenine (kynurenines) is related to different brain structures, i.e. kynurenic acid predominantly affects structures adjacent to ventricles (e.g. hippocampus, caudate nucleus) while picolinic and anthranilic acids act on other brain structures or the periphery. Xanthurenic, kynurenic and picolinic acids merely prolonged the latency of seizures induced by i.c.v. quinolinic acid (another metabolite of kynurenine) or by subcutaneous strychnine sulfate and i.p. pentylenetetrazole, and did not modify seizures induced by i.p. caffeine and thiosemicarbazide. This selective antagonism of the tested kynurenines against kynurenine might be an important anticonvulsant factor in kynurenine-dependent seizures. It is suggested that increased excretion of xanthurenic, kynurenic and picolinic acids in patients with convulsive states may be manifestations of compensatory processes.