Effects of M1 and M2 receptor agonists and blockers on dog respiration.
OBJECTIVE
To study the effects of M1 and M2 receptor agonists and blockers on dog respiration.


METHODS
Using thoracic respiratory transducer and RM-86 multipurpose polygraph to determine respiratory rate (RR), tidal volume (TV), and minute ventilation volume (MVV), and DH-100G blood gas analysis instrument to analyze pO2, pCO2 and pH.


RESULTS
Pilocarpine (Pil, an M1-R subtype agonist) 0.5, 1, and 2 mg.kg-1 iv caused increases in RR, MVV, and pO2, and a decrease in pCO2. The excitatory effects of Pil were antagonized by pretreatment with pirenzepine (Pir, 3 mg.kg-1, iv) and scopolamine (Sco, 2 mg.kg-1, iv). The iv injections of a novel M2-R subtype agonist, 6 beta-acetoxy nortropane (6 beta-AN) 2, 5, and 20 micrograms.kg-1 caused decreases in RR, MVV, and pO2 and an increase of pCO2. The actions of 6 beta-AN were antagonized by iv pretreatment with AF-DX116 ¿11-2 [[2-[(diethylamino)methyl]-1-piperidinyl] acetyl]-5, 11-dihydro-6H[2,3-b][1,4]benzodiazepine-6-one, 0.5 mg.kg-1¿ and atropine (Atr, 2 mg.kg-1). Similar results were obtained when smaller doses of Pil (0.2, 0.4, and 0.8 mg.kg-1) and 6 beta-AN (0.25, 0.5, and 1 microgram.kg-1) were injected into the vertebral artery. Pir and Sco also antagonized the excitatory effects of Pil, and AF-DX116 and Atr antagonized the inhibitory effects of 6 beta-AN on respiration.


CONCLUSIONS
Stimulating M1-R of the respiratory center caused excitation of the respiration while stimulating the M2-R subtype caused inhibition of the respiration.
Yao
B
B
Department of Pharmacology, Xuzhou Medical College, China.
Ge
X Q
XQ
Zheng
J L
JL
Qin
W
W
Bian
C F
CF
D000818:Animals; D001784:Blood Gas Analysis; D004285:Dogs; D005260:Female; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology*; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D009662:Nortropanes / Q000037:antagonists & inhibitors; D010862:Pilocarpine / Q000037:antagonists & inhibitors*; D010890:Pirenzepine / Q000031:analogs & derivatives / Q000494:pharmacology*; D012119:Respiration / Q000187:drug effects*; D012601:Scopolamine / Q000494:pharmacology
D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D009662:Nortropanes; D010862:Pilocarpine; C071344:6-acetoxynortropane; D010890:Pirenzepine; D012601:Scopolamine; C048593:otenzepad