Involvement of NK receptors and beta-adrenoceptors in nitric oxide-dependent relaxation of rabbit aorta rings following electrical-field stimulation

The effect of morphine in rat small mesenteric arteries

We investigated the effect of morphine in phenylephrine (PE)- or KCl-precontracted rat small mesenteric arteries. Morphine (10(-6)-10(-4) M) administration caused concentration-dependent relaxation responses in small mesenteric arteries precontracted by PE or KCl. Removal of endothelium did not significantly alter the relaxation responses to morphine. The relaxant responses to morphine were partially inhibited by pre-treatment of tissues with naloxone (NAL, 10(-5) M) for 20 min. The inhibitory effect of NAL on relaxant responses to morphine in PE- or KCl-precontracted arteries did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation of endothelium-intact or endothelium-denuded arterial segments with NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) or cyclooxygenase (COX) inhibitor indomethacin (10(-5) M) or histamine H(1)-receptor blocker diphenhydramine (10(-6) M), for 20 min did not inhibit the relaxation responses to morphine. Small mesenteric arterial segment contractions induced by stepwise addition of calcium to high KCl solution with no calcium were almost completely inhibited by morphine. These findings suggested that morphine-induced relaxation responses in isolated rat small mesenteric arteries were neither dependent on endothelium nor blocked by NOS or COX inhibition but they rather seem to depend on an interaction of morphine with calcium influx pathways.

Ca2+-activated K+ channels in the endothelial cell layer involved in modulation of neurogenic contractions in rat penile arteries

The present study was designed to investigate the functional K+ channels involved in contractions induced by electrical field stimulation in isolated rat penile arteries. Blockers of Ca2+-activated K+ channels (KCa), tetraethylammonium, and of large-conductance KCa channels, charybdotoxin and iberiotoxin, as well as a blocker of voltage-dependent K+ channels (KV), 4-aminopyridine, increased resting tension in penile small arteries. In the presence of propranolol and NG-nitro-L-arginine (L-NOARG), electrical field stimulation evoked prazosin-sensitive contractions. In endothelium-intact preparations, these latter contractions were enhanced in the presence of tetraethylammonium and charybdotoxin. However, these blockers did not enhance contractions evoked by exogenously added noradrenaline. Endothelial cell removal increased the neurogenic contractions but tetraethylammonium had no further potentiating effect in these preparations. In the presence of an inhibitor of cyclooxygenase, indomethacin, and inhibitor of nitric oxide (NO) synthase, L-NOARG, acetylcholine evoked relaxations, which were abolished in the presence of either tetraethylammonium or charybdotoxin. In phenylephrine-contracted arteries treated with guanethidine and atropine, electrical field stimulation evoked relaxations, which were partially inhibited by L-NOARG and tetraethylammonium, without any additive effect of these drugs. These observations suggest that both large-conductance KCa channels and KV channels sensitive to iberiotoxin/tetraethylammonium and 4-aminopyridine, respectively, are directly involved in the modulation of myogenic tone of rat penile arteries. Furthermore, activation of endothelial intermediate-conductance KCa channels sensitive to tetraethylammonium and charybdotoxin leads to release of a non-NO nonprostanoid factor, which inhibits release of the neurotransmitter, noradrenaline, but these channels do not appear to be involved in inhibition of contraction evoked by exogenously applied noradrenaline in rat penile arteries.

The effect of nitric oxide synthase blockade on responses to morphine in rat aortic rings

1 It has been suggested that opioids may play an indirect role in the regulation of the peripheral circulation through the control of nitric oxide (NO) release in vascular tissue. The current study was undertaken to investigate the effect of nitric oxide synthase (NOS) blockade on responses to morphine in phenylephrine (PE)- or KCl-precontracted rat aortic rings. 2 Morphine (3 x 10(-8) - 3 x 10(-5) M) administration did not cause any significant effect on basal tonus of endothelium-intact or endothelium-denuded preparations. Morphine produced concentration-dependent relaxation responses in endothelium-intact as well as in endothelium-denuded rat aortic rings precontracted by PE or KCl. Removal of endothelium did not significantly alter the relaxation responses to morphine. 3 The relaxant responses to morphine were significantly and partially inhibited by pretreatment of tissues with naloxone (NAL, 3 x 10(-5) M) for 5 min. The inhibitory effect of NAL on relaxant responses to morphine in PE- or KCl-precontracted rings did not differ significantly between endothelium-intact and endothelium-denuded preparations. 4 Incubation of endothelium-intact or endothelium-denuded rat aortic rings with NOS inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) for 20 min did not cause a significant inhibition on relaxation responses to morphine. 5 These findings confirmed the presence of opiate receptors in rat thoracic aorta, but suggested that mechanisms other than NO release play a role in the relaxant effect of morphine on rat aortic rings.

Involvement of ATP in the non-adrenergic non-cholinergic inhibitory neurotransmission of lamb isolated coronary small arteries

1. The involvement of non-adrenergic non-cholinergic (NANC) transmitters, such as nitric oxide (NO) and adenosine 5'-triphosphate (ATP), in the neurogenic relaxation of lamb coronary small arteries was investigated in vessel segments with an internal lumen diameter of 200-550 microns, isolated from the left ventricle of the heart, and suspended for isometric tension recording in microvascular myographs. 2. In both endothelium-intact and -denuded coronary small arteries treated with phentolamine (3 x 10(-6) M), propranolol (3 x 10(-6) M), and atropine (10(-6) M) and contracted to 3 x 10(-7) M of the thromboxane analogue U46619, electrical field stimulation (EFS) evoked frequency-dependent relaxations, which were markedly reduced in the presence of tetrodotoxin (10(-6) M). 3. Exogenous NO added as acidified sodium nitrite (10(-6)-10(-3) M) and L-nitrosocysteine induced potent relaxations of lamb coronary small arteries. However, both inhibition of NO synthase with NG- nitro-L-arginine (L-NOARG, 3 x 10(-5) M), and mechanical endothelial cell removal increased rather than inhibited relaxations to EFS. In small arteries processed for NADPH-diaphorase histochemistry, activity was only observed within endothelial cells. 4. In arteries contracted to U46619, exogenously added ATP caused concentration-dependent relaxations with pD2 and maximum responses of 4.72 +/- 0.12 and 89.6 +/- 3.8% (n = 12), respectively. ADP and the P2Y-agonist, 2-methylthio-ATP, induced relaxations equipotent to ATP, while the P2x-agonist, alpha, beta-methylene ATP (10(-9)-10(-4) M), and the P2U-agonist, UTP (10(-9)-10(-4) M) only caused small transient relaxations at the highest concentrations (10(-4) and 10(-3) M). 5. ATP and EFS-induced relaxations were unchanged in the presence of the P1-purinoceptor antagonist, 8-phenyltheophylline (10(-5) M), while this antagonist inhibited the concentration-dependent relaxations to adenosine. In contrast, the P2-purinoceptor antagonist, suramin (3 x 10(-5) M), markedly reduced the relaxations to EFS. 6. After desensitization of P2x-purinoceptors with alpha, beta-methylene ATP (2 x 10(-5) M), the relaxations to exogenous added ATP were enhanced, but this procedure did not influence the relaxations to EFS. In contrast, the P2y-purinoceptor antagonist, basilen blue E-3G (3 x 10(-5) M, earlier named reactive blue 2) significantly inhibited the concentration-relaxation curves to ATP and almost abolished the EFS-induced relaxations. 7. Mechanical removal of the endothelium significantly inhibited ATP-induced maximal relaxations without affecting sensitivity, pD2 and maximum relaxations being 4.72 +/- 0.12 and 89.7 +/- 3.8% (n = 10), and 5.45 +/- 0.38 and 48.0 +/- 8.6% (P < 0.05, paired t test, n = 10) in endothelium-intact and -denuded coronary small arteries, respectively. However, incubation with L-NOARG did not change relaxations elicited by ATP. 8. The present study suggests that in NANC conditions neurogenic relaxations of coronary small arteries are mediated by ATP, which relaxes coronary small arteries through P2Y-purinoceptors. A prejunctional modulation of these relaxations by endothelial-derived NO cannot be excluded.

Involvement of nitric oxide in the non-adrenergic non-cholinergic neurotransmission of horse deep penile arteries: role of charybdotoxin-sensitive K(+)-channels

1. The involvement of nitric oxide (NO) and the signal transduction mechanisms mediating neurogenic relaxations were investigated in deep intracavernous penile arteries with an internal lumen diameter of 600-900 microns, isolated from the corpus cavernosum of young horses. 2. The presence of nitric oxide synthase (NOS)-positive nerves was examined in cross and longitudinal sections of isolated penile arteries processed for NADPH-diaphorase (NADPH-d) histochemistry. NADPH-d-positive nerve fibres were observed in the adventitia-media junction of deep penile arteries and in relation to the trabecular smooth muscle. 3. Electrical field stimulation (EFS) evoked frequency-dependent relaxations of both endothelium-intact and denuded arterial preparations treated with guanethidine (10(-5) M) and atropine (10(-7) M), and contracted with 10(-6) M phenylephrine. These EFS-induced relaxations were tetrodotoxin-sensitive indicating their non-adrenergic non-cholinergic (NANC) neurogenic origin. 4. EFS-evoked relaxations were abolished at the lowest frequency (0.5-2 Hz) and attenuated at higher frequencies (4-32 Hz) by the NOS inhibitor, NG-nitro-L-arginine (L-NOARG, 3 x 10(-3) M). This inhibitory effect was antagonized by the NO precursor, L-arginine (3 x 10(-3) M). NG-nitro-D-arginine (10(-4) M) did not affect the relaxations to EFS. 5. Incubation with either the NO scavenger, oxyhaemoglobin (10(-5) M), or methylene blue (10(-5) M), an inhibitor of guanylate cyclase activation by NO, caused significant inhibitions of the EFS-evoked relaxations, and while oxyhaemoglobin abolished the relaxations to exogenously added NO (acidified sodium nitrite, 10(-6) - 10(-3) M), there still persisted a relaxation to NO of 24.4 +/- 5.1% (n = 6) in the presence of methylene blue. 6. Glibenclamide (3 x 10(-6) M), an inhibitor of ATP-activated K(+)-channels, did not alter the relaxations to either EFS-stimulation or NO, while the blocker of Ca(2+)-activated K(+)-channels, charybdotoxin (3 x 10(-8) M), caused a significant inhibition of both the electrically-induced relaxations and the relaxations to exogenously added NO. Furthermore, charybdotoxin blocked relaxations induced by the cell permeable analogue of cyclic GMP, 8-bromo cyclic GMP (8 Br-cyclic GMP). 7. These results suggest that relaxations of horse deep penile arteries induced by NANC nerve stimulation involve mainly NO or a NO-like substance from nitrergic nerves. NO would stimulate the accumulation of cyclic GMP followed by increases in the open probability of Ca(2+)-activated K(+)-channels and hyperpolarization leading to relaxation of horse penile arteries.

The distribution and co-localization of immunoreactivity to nitric oxide synthase, vasoactive intestinal polypeptide and substance P within nerve fibres supplying bovine and porcine female genital organs

The distribution of nitric oxide synthase-immunoreactive (NOS-IR) axons and their relationship to structures immunoreactive to vasoactive intestinal polypeptide (VIP), substance P (SP) and tyrosine hydroxylase (TH) were studied by means of the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) technique or double-labelling immunofluorescence in the genital organs of cow and pig. Relevant neurons were also investigated in the pig. NOS-containing neural structures were TH-immunonegative in bovine or porcine genital organs, or in the studied ganglia. In the bovine ovary, NOS-IR nerves were neither VIP-IR nor SP-IR, whereas in the pig, most NOS-containing axons were also VIP-IR. The oviduct was supplied by single NOS/VIP- or NOS/SP-containing nerves, whereas in the uterus, NOS-IR axons were moderate in number, often being immunoreactive for VIP or SP. Numerous NOS/VIP-IR and NOS/SP-IR nerves were found in the vagina of both species. In all tissues studied, NOS-IR axons were mainly related to vascular smooth muscle. Most of the neurons of the paracervical ganglia and some neurons in dorsal root ganglia exhibited strong NOS activity. Only single neurons in sympathetic ganglia were NADPH-d-positive. Most nitrergic neurons in the autonomic ganglia were VIP-IR but SP-immunonegative. The sensory neurons were mostly NOS/SP-IR, whereas only single neurons co-expressed NOS and VIP immunoreactivity.

Existence and co-existence of vasoactive substances in nerve fibres supplying the abdomino-pelvic arterial tree of the female pig and cow

The occurrence and co-localization of several presumed vasoactive neuropeptides, serotonin, and catecholamine-synthesising enzymes--tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H) and phenylethanolamine-N-methyltransferase (PNMT)--were investigated in perivascular nerves supplying the systemic and distributing arteries of the abdomino-pelvic arterial tree of the female pig and certain arteries supplying female reproductive organs in the cow. As revealed by single immunofluorescence, perivascular axons immunoreactive for TH, D beta H, neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP) and Leu-enkephalin (LENK) occurred in both species examined, whereas galanin-immunoreactive (GAL-IR) nerve fibres were found exclusively in the pig. PNMT-, serotonin-, dynorphin A-, alpha-neoendorphin-, bombesin- or cholecystokinin-IR nerve terminals were not observed. The following classes of perivascular nerve fibres might be distinguished in the present study: 1) noradrenergic (i.e. TH/D beta H-IR), 2) NPY-, 3) GAL- (pig only), 4) LENK-, 5) VIP-, 6) SP-, 7) VIP/NPY-, 8) SP/CGRP-, 9) SP/GAL- (pig only), 10) SP/VIP- (cow only), 11) TH/D beta H/NPY- and 12) TH/D beta H/NPY/LENK-IR. Distinct differences in the distribution of LENK- and SP-IR axons around particular parts of the studied arterial tree in individual species were also observed. The present data indicate that the abdomino-pelvic arterial tree of the pig and cow receive perivascular nerve fibres that exhibit diverse chemical codes, and that different chemical coding of perivascular nerve fibres in individual species may depend on the target organ of the particular artery.