1 The effects of the P2-purinoceptor agonists, adenosine 5'-triphosphate (ATP), a,fl-methylene ATP (a,f,-MeATP), fl,y-methylene ATP (fi,y-MeATP), L-fi,y-methylene ATP (L-fi,y-MeATP), adenosine-5'-O-(2-thiodiphosphate) (ADPfS), and 2-methylthio ATP (2-MeSATP) were investigated on the isometric tension of the rat anococcygeus muscle.2 Non-cumulative additions of ATP (100-1500MM), a,f,-MeATP (1-300yM), 13,'y-MeATP (10-300 pM), L-fy-MeATP (3-100 pM) and ADPfS (1-100 gM) produced concentration-dependent contractions, whereas 2-MeSATP (1-100pM) had no effect. The rank order of potency was a,,f- 6 The findings suggest that in the rat anococcygeus, smooth muscle cells are endowed with two distinct P2-purinoceptors which subserve contractions: a P2x-purinoceptor activated by ATP and its analogues, and another type of P2-purinoceptor activated by ADPfiS.

1. The pharmacological actions of the oxidized and reduced forms of nicotinamide-adenosine dinucleotide (NAD, NADH) and nicotinamide-adenosine dinucleotide phosphate (NADP, NADPH) were studied on rat isolated anococcygeus muscles. 2. The actions of the two nucleotides were different, but there were no apparent qualitative differences between the oxidized and reduced forms of each. 3. In fully relaxed anococcygeus muscles, NADP(H) produced transient contractions that were subject to desensitization, but NAD(H) had no effect. 4. NADP(H) slightly enhanced contractions elicited by noradrenergic nerve stimulation. In contrast, noradrenergic contractions were inhibited by NAD(H). NADH reduced the stimulation-induced release of noradrenaline, but enhanced contractions elicited by exogenous noradrenaline. 5. In anococcygeus muscles partly contracted with guanethidine, NAD(H) produced a further sustained increase in tone; in contrast, NADP(H) mainly produced transient relaxations to which there was immediate desensitization. 6. Relaxations of anococcygeus muscle elicited by nitrergic nerve stimulation were not affected by NAD. In contrast, NADP(H) reduced them. 7. The actions of NAD(H) were generally the same as those of adenosine and can be attributed to activation of P1-purinoceptors since they were blocked by the selective antagonist 8-sulphophenyltheophylline. 8. The actions of NADP resembled those of the P2-purinoceptor agonist ATP to some extent, but there were some differences. As suggested by others, NADP may act on a unique receptor.