CARDIORESPIRATORY EFFECTS PRODUCED BY BLOCKADE OF EXCITATORY AMINO-ACID RECEPTORS IN CATS

The aim of our study was to determine the role of excitatory amino aci ds in controlling cardiorespiratory activity. For this purpose we admi nistered an antagonist of both N-methyl-D-aspartate (NMDA) and non-NMD A receptors (kynurenic acid), and an antagonist of the NMDA receptor c omplex (dizocilpine, more commonly known as MK-801) i.v. to chloralose -anesthetized cats while monitoring tracheal air flow, tidal volume, r espiratory rate, inspiratory and expiratory durations, end tidal CO2, arterial blood pressure and heart rate. Administration of kynurenic ac id in doses of 350 and 500 mg/kg produced respiratory depression as re flected by decreases in respiratory minute volume and increases in end tidal CO2. Inspiratory duration was increased with both doses and apn ea (occurring during expiration) was observed with the high dose. Apne a was preceded by an apneustic pattern of breathing. Both doses result ed in an increase in blood pressure and, with the high dose, a later d ecrease in blood pressure was noted. Dizocilpine in doses ranging from 0.03 to 1 mg/kg produced dose-related decreases in respiratory minute volume, and increases in end tidal CO2. In addition, dizocilpine prod uced increases in inspiratory duration, an apneustic pattern of breath ing and apnea (occurring during inspiration). Effects on blood pressur e were similar to those observed with kynurenic acid. It is concluded that blockade of excitatory amino acid receptors results in pronounced effects on cardiorespiratory activity.