Kynurenic acid inhibits circulatory responses to intracisternally injected L-proline in conscious rats.

To investigate the modes of action of potential neurotransmitters for cardiovascular control, amino acids and an antagonist were injected intracisternally into conscious rats. Blood pressure and superior mesenteric flow were measured with cannulae and electromagnetic flow probes that had been implanted in a previous operation under pentobarbitone anaesthesia. L-Proline, L-glutamate and L-arginine (10, 2 and 10 micromol, respectively) caused similar increases in blood pressure and mesenteric vascular resistance. Prior injection of kynurenic acid (0.1 micromol), a broad spectrum antagonist of ionotropic excitatory amino acid receptors, completely blocked the circulatory effects of L-proline, significantly reduced those of L-glutamate but had little effect on responses to L-arginine. These results suggest that the central pressor pathways activated by L-proline, a potential endogenous neurotransmitter, are mediated by ionotropic excitatory amino acid receptors.