CYCLIC-NUCLEOTIDE CONTENT OF THE RAT ANOCOCCYGEUS DURING RELAXATIONS INDUCED BY DRUGS OR BY NONADRENERGIC, NONCHOLINERGIC FIELD STIMULATION

Low concentrations of sodium nitroprusside (0.2 and 1-mu-M) 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-mu-M) produced greater relaxation (> 60%) and a rise in cGMP but not cAMP. In the presence of the cGMP-phosphodiesterase inhibitor M&B 22948 (10-mu-M), 1-mu-M sodium nitroprusside produced greater relaxation and a selective increase in cGMP. Forskolin (0.5-250-mu-M) 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-mu-M M&B 22948 or 1-mu-M 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.