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Relationship between muscarinic receptor subtypes and cyclic nucleotides in pons-medulla oblongata
Aim:
To study the relationship between muscarinic receptor (M-R) subtypes and cyclic nucleotides in pons-medulla oblongata (MeOb).
Methods:
The contents of cGMP and cAMP in Sprague-Dawley rat pons-MeOb, cerebellum and cerebral cortex were assayed by radioimmunoassay and competitive protein-binding assay, respectively, after ip injections of drugs. Control rats were given ip normal saline.
Results:
M1-R agonist pilocarpine (6, 15 mg kg-1, ip) increased the content of cGMP in the pons-MeOb and cerebral cortex, but did not bring about any noticeable change in the cAMP content. The increase of cGMP was antagonized by ip pirenzepine or scopolamine. On the other hand, ip M2-R agonist 6 beta-acetoxy nortropane (6 beta-AN) 25 micrograms kg-1 reduced not only cAMP contents in the pons-MeOb and cerebellum but also cGMP contents in the pons-MeOb and cerebral cortex, while 6 beta-AN 12 micrograms kg-1 only lowered cAMP content. The decreases of cGMP and cAMP induced by 6 beta-AN were antagonized by ip AF-DX 116 or atropine, respectively.
Conclusion:
Stimulation of M1-R causes the increase of cGMP and that of M2-R induces the decreases of both cGMP and cAMP in the pons-MeOb.