piperidines and 8-(4-sulfophenyl)theophylline

1. The aim of the present study was to examine the modulator influence of muscarinic M(2) receptors on responses of rat urinary bladder detrusor muscle evoked by endogenous stimuli, i.e. by stimulation of the bladder innervation. 2. Responses were evoked by electrical field stimulation (EFS; 2-20 Hz, 0.8 ms, 60 V) of isolated strip preparations mounted in organ baths. The tension of the muscle strips was recorded digitally. EFS was performed by applying stimulation with either a short duration (5 s) or a longer duration (to reach peak response; approximately 20 s). 3. Effects of muscarinic receptor antagonists (muscarinic M(1)/M(3) receptor selective: 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP); muscarinic M(2) receptor selective: methoctramine), a beta-adrenergic antagonist (propranolol) and an adenosine receptor antagonist (8-p-sulfophenyltheophylline) were assessed on contractile activity and on poststimulatory relaxations. 4. Low concentrations of methoctramine (10(-8) m) reduced or tended to reduce the EFS-induced contraction, e.g. at 2 Hz by 12% while methoctramine at 10(-7) m had no significant effect. In addition, in the presence of 4-DAMP (10(-9) m), which tended to inhibit contractions at all frequencies (2-20 Hz; -17 to -25%), methoctramine at 10(-8) and 10(-7) m induced a further reduction of the contractile responses (-5 to -10%; 2-20 Hz). 5. The beta-adrenergic receptor antagonist propranolol (10(-6) m) and the adenosine receptor antagonist 8-p-sulfophenyltheophylline (10(-6) m) both increased contractile responses by 9-21% (2-10 Hz, long duration; P < 0.05-0.001) as a consequence of antagonizing relaxatory stimuli. Neither antagonist affected the contractile responses to EFS with the short duration stimulation. Poststimulatory relaxations were reduced by 30-60% (P < 0.05) by propranolol and by 40-60% (P < 0.001) by 8-p-sulfophenyltheophylline, but for 8-p-sulfophenyltheophylline only after stimulation with the short duration. 6. In the presence of methoctramine (10(-7) m), the 8-p-sulfophenyltheophylline-induced increases of the contractile response to long duration EFS were significantly enhanced at 10 Hz (+12 +/- 4%; P < 0.05), whereas no such enhancement of the propranolol inhibitory effect occurred in the presence of methoctramine. However, poststimulatory beta-adrenoceptor-evoked relaxations after short duration EFS were increased by about 35% in the presence of methoctramine, but not those after long duration. 7. Thus,

Topics: Animals; Diamines; Electric Stimulation; In Vitro Techniques; Muscarinic Antagonists; Muscle Contraction; Muscle Relaxation; Muscle, Smooth; Parasympatholytics; Piperidines; Propranolol; Rats; Rats, Sprague-Dawley; Receptor, Muscarinic M2; Theophylline; Time Factors; Urinary Bladder; Vasodilator Agents

Adenosine 5'-triphosphate (ATP) has important roles in the cardiovascular system, modulating vascular tone by acting as both a vasoconstrictor and a vasodilator. The dilator function of ATP is traditionally thought to be monophasic and mediated primarily by nitric oxide (NO). Here we have identified the endothelium-dependent biphasic nature of ATP-induced vasodilatation of the rat isolated mesenteric bed and investigated the two distinct pathways involved. ATP, at doses of 1x10(-11) to 1x10(-8) moles, induced transient relaxations that were inhibited by the NO synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME: 1x10(-4) M), the soluble guanylyl cyclase inhibitor, 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ: 3x10(-6) M) and KCl (6x10(-2) - 1.2x10(-1) M). At doses upwards of 1x10(-8) moles (1x10(-8) - 3x10(-7) moles), ATP also induced prolonged vasodilatations which were unaltered by L-NAME, L-NAME (1x10(-3) M) and indomethacin (1x10(-5) M), or by ODQ, but were abolished in the presence of KCl. In addition, the cannabinoid CB(1) receptor antagonist SR141716A (1x10(-5) M) was found to inhibit the second prolonged phase of vasodilatation. However, at the concentration used SR141716A is reported to be non-selective. A second CB(1) receptor antagonist, AM251 (1x10(-6) M), had a small but significant inhibitory effect on the second phase of ATP-induced vasodilatation. SR141716A, AM251 and KCl (6x10(-2) - 1.2x10(-1) M) all inhibited anandamide-induced relaxation of the isolated mesenteric bed. These observations demonstrate that ATP stimulates vasodilatation of the mesenteric bed by two distinct mechanisms involving the release of NO and an EDHF. In the absence of better pharmacological tools we can only speculate as to the involvement of an endogenous CB(1) receptor ligand in these responses.

Topics: Adenine; Adenosine; Adenosine Triphosphate; Animals; Arachidonic Acids; Capsaicin; Dose-Response Relationship, Drug; Endocannabinoids; Endothelium, Vascular; Enzyme Inhibitors; Guanylate Cyclase; Histamine; In Vitro Techniques; Male; Mesenteric Arteries; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Oxadiazoles; Piperidines; Polyunsaturated Alkamides; Potassium Chloride; Pyrazoles; Pyrilamine; Quinoxalines; Rats; Rats, Wistar; Rimonabant; Signal Transduction; Stereoisomerism; Theophylline; Vasodilation

The functional effects of muscarinic receptor and purinoceptor agonists and antagonists were studied on isolated strip preparations of the rat urinary bladder. The muscarinic "M3/M1-selective" receptor antagonist 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP) most conspicuously inhibited the carbachol-evoked contractile responses (pA2=9.8), while the muscarinic "M1-selective" receptor antagonist pirenzepine and the muscarinic "M2-selective" receptor antagonist methoctramine were less potent (pA2=7.0 and 6.5, respectively). Administration of 4-DAMP in combination with methoctramine in selective dosages gave no significant additional reduction of carbachol-evoked contractile responses. Adenosine 5'-triphosphate (ATP) elicited transient dose-dependent contractile responses and it caused relaxation of the carbachol-contracted detrusor strips. The relaxatory response was enhanced in the presence of methoctramine and furthermore, was attenuated by the adenosine receptor antagonist 8-p-sulfophenyltheophylline. Administration of 2-chloro-adenosine to pre-contracted strips tended to cause dose-dependent relaxations, which were significantly increased in the presence of methoctramine. The purinergic contractile response, on the other hand, was not affected by methoctramine. Thus, the results are consistent with the cholinergic contractile response in the rat urinary bladder being exerted via activation of muscarinic M3 receptors, while the muscarinic M2 receptors exerted a modulator effect on purine-evoked relaxations in the rat urinary bladder.

Topics: 2-Chloroadenosine; Adenosine; Adenosine Triphosphate; Animals; Carbachol; Diamines; Dose-Response Relationship, Drug; In Vitro Techniques; Male; Muscarinic Agonists; Muscarinic Antagonists; Muscle Contraction; Piperidines; Pirenzepine; Purinergic Agonists; Purinergic Antagonists; Rats; Rats, Sprague-Dawley; Receptor, Muscarinic M2; Receptors, Muscarinic; Receptors, Purinergic; Theophylline; Urinary Bladder