Neuromuscular effects of respiratory and metabolic acid-base changes in vitro with and without nondepolarizing muscle relaxants.
The effects of metabolic (bicarbonate, [HCO3]) and respiratory (carbon dioxide, PCO2) acid-base changes on indirectly elicited twitch tension with and without nondepolarizing neuromuscular blocking agents were compared in a rat phrenic nerve-hemidiaphragm preparation. Ionized calcium [Ca2+] and magnesium [Mg2+] concentrations in the modified Krebs' solution were measured and kept constant. Likewise, twitch was altered when pH changes were produced by altering either PCO2 or [HCO3]. Decreasing pH either by increasing PCO2 or by decreasing [HCO3] significantly decreased (P less than 0.01) twitch, by 9.5 +/- 0.6 (SEM, n = 8) and 10.6 +/- 1.5%, respectively. Increasing pH by decreasing PCO2 or by increasing [HCO3] significantly increased (P less than 0.01) twitch, by 5.6 +/- 0.9 and 7.9 +/- 0.6%, respectively. After a partial depression of twitch by nondepolarizing neuromuscular blocking agents, the effects of PCO2 and [HCO3] changes were again assessed. Decreasing pH by increasing PCO2 or by decreasing [HCO3] intensified d-tubocurarine (dTc) (28.2 +/- 1.6 and 32.0 +/- 2.9%, respectively) and vecuronium (23.0 +/- 1.4 and 36.8 +/- 3.2%, respectively) block, whereas it reversed metocurine (1.2 +/- 2.2% NS and 2.9 +/- 1.3%, respectively) and pancuronium (8.3 +/- 1.5 and 11.5 +/- 3.0%, respectively) block. Conversely, increasing pH by decreasing PCO2 or by increasing [HCO3] antagonised dTc (12.8 +/- 2.2 and 13.6 +/- 1.8%, respectively) and vecuronium (25.3 +/- 1.7 and 25.0 +/- 3.0%, respectively) block, whereas it potentiated metocurine (4.2 +/- 0.6 and 8.0 +/- 1.1%, respectively) and pancuronium (11.0 +/- 1.2 and 17.5 +/- 2.0%, respectively) block. Except where indicated, all changes in block described above were statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)
Ono
K
K
Department of Anesthesiology and Resuscitology, Okayama University Medical School, Japan.
Nagano
O
O
Ohta
Y
Y
Kosaka
F
F
D000137:Acid-Base Imbalance / Q000503:physiopathology*; D000142:Acidosis, Respiratory / Q000503:physiopathology; D000818:Animals; D066298:In Vitro Techniques; D008297:Male; D009469:Neuromuscular Junction / Q000187:drug effects / Q000503:physiopathology*; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology*; D010197:Pancuronium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014403:Tubocurarine / Q000031:analogs & derivatives / Q000494:pharmacology; D014673:Vecuronium Bromide / Q000494:pharmacology
D003473:Neuromuscular Nondepolarizing Agents; D014673:Vecuronium Bromide; D010197:Pancuronium; C032943:metocurine; D014403:Tubocurarine