MK-801 alters diaphragmatic activities in unanesthetized rats differently between normoxia and hypoxia.
This study was designed to examine how systemic administration of an N-methyl-d-aspartate (NMDA) receptor antagonist, MK-801, altered respiratory timing in unanesthetized rats under normoxia and hypoxia. To detect fine changes in inspiratory time (TI) and expiratory time (TE), and cycle duration (TTOT), we prepared a diaphragmatic electromyogram (EMGdia). Diaphragm electrodes and arterial and venous catheters were inserted into Wistar rats (n = 8) under pentobarbital anesthesia. The next day, EMGdia was recorded before and after intravenous administration of MK-801 (3 mg/kg) under normoxia and hypoxia (12% O2) without anesthesia, and the respiratory timing (TI, TE, TTOT), respiratory frequency (fR), and amplitude of the integrated EMGdia were measured. Arterial blood gases (ABGs), mean arterial pressure (MAP), and heart rate (fH) were also measured with the EMGdia. Under normoxia, MK-801 increased fR owing to a significant decrease in TE, and elevated both MAP and fH. Under hypoxia, MK-801 suppressed an increase in fR owing to a significant increase in TI, and did not accelerate fH. In both gaseous conditions, on ABGs, MK-801 did not alter partial pressure of O2 (PaO2) or CO2 (PaCO2), and slightly decreased pH (but not less than 7.4). MK-801 significantly decreased hypoxic response (%change from normoxia) in fR, and increased that in EMGdia amplitude, and did not alter a total ventilatory index (fRxEMGdia amplitude). The results suggest that an NMDA receptor-mediated mechanism partially determines fR through significant alterations in respiratory timing, particularly in which the hypoxic ventilatory response was obtained in unanesthetized rats.
Saiki
Chikako
C
Department of Physiology, Nippon Dental University, School of Life Dentistry at Tokyo, 1-9-20 Fujimi, Chiyoda-ku, Tokyo, 102-8159, Japan. chikako@tky.ndu.ac.jp
Miura
Akiko
A
Furuya
Hideki
H
Matsumoto
Shigeji
S
D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000187:drug effects; D003964:Diaphragm / Q000187:drug effects* / Q000503:physiopathology; D016291:Dizocilpine Maleate / Q000494:pharmacology*; D004576:Electromyography; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D000860:Hypoxia / Q000188:drug therapy* / Q000503:physiopathology; D007275:Injections, Intravenous; D008297:Male; D023421:Models, Animal; D012123:Pulmonary Ventilation / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
D018691:Excitatory Amino Acid Antagonists; D016291:Dizocilpine Maleate