Cyclic Nucleotide Content of the Rat Anococcygeus During Relaxations Induced by Drugs or by Non-adrenergic, Non-cholinergic Field Stimulation

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Abstract
Low concentrations of sodium nitroprusside (0.2 and 1 μM) relaxed carbachol-induced tone of the rat anococcygeus but did not affect the content of either cGMP or cAMP; higher concentrations (10, 100 and 1000 μM) produced greater relaxation (> 60%) and a rise in cGMP but not cAMP. In the presence of the cGMP-phosphodiesterase inhibitor M&B 22948 (10 μM), 1 μM sodium nitroprusside produced greater relaxation and a selective increase in cGMP. Forskolin (0.5–250 μM) caused relaxation and a selective increase in cAMP; the concentration-response relationships of the two effects were similar. Non-adrenergic, non-cholinergic (NANC) field stimulation (10 Hz; 20 s trains) reduced tone by 52% but had no effect on cyclic nucleotide content; in the presence of 10 μM M&B 22948 or 1 μM sodium nitroprusside, NANC stimulation produced a greater degree of relaxation and increased cGMP but not cAMP content. The results show that NANC stimulation acts like sodium nitroprusside, causing a selective increase in cGMP, and this supports the proposal that NANC transmission in the rat anococcygeus involves an endogenous nitrate; the possibility that multiple pools of cGMP exist in the anococcygeus is discussed.

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