Opposite modulation of noradrenaline and ATP release in guinea-pig vas deferens through prejunctional beta-adrenoceptors: evidence for the beta 2 subtype

Physiological and pharmacological aspects of the vas deferens-an update

The vas deferens, a muscular conduit conveying spermatozoa from the epididymis to the urethra, has been used as a model tissue for smooth muscle pharmacological and physiological advancements. Many drugs, notably α-adrenergic antagonists, have effects on contractility and thus normal ejaculation, incurring significant side effects for patients that may interfere with compliance. A more thorough understanding of the innervation and neurotransmitter pharmacology of the vas has indicated that this is a highly complex structure and a model for co-transmission at the synapse. Recent models have shown clinical scenarios that alter the vas contraction. This review covers structure, receptors, neurotransmitters, smooth muscle physiology, and clinical implications of the vas deferens.

Involvement of G-protein βγ subunits on the influence of inhibitory α2-autoreceptors on the angiotensin AT1-receptor modulation of noradrenaline release in the rat vas deferens

The influence of alpha2-autoreceptors on the facilitation of [3H]-noradrenaline release mediated by angiotensin II was studied in prostatic portions of rat vas deferens preincubated with [3H]-noradrenaline. Angiotensin II enhanced tritium overflow evoked by trains of 100 pulses at 8 Hz, an effect that was attenuated by the AT1-receptor antagonist losartan (0.3-1 microM), at concentrations suggesting the involvement of the AT1B subtype. The effect of angiotensin II was also attenuated by inhibition of phospholipase C (PLC) and protein kinase C (PKC) indicating that prejunctional AT1-receptors are coupled to the PLC-PKC pathway. Angiotensin II (0.3-100 nM) enhanced tritium overflow more markedly, up to 64%, under conditions that favor alpha2-autoinhibition, observed when stimulation consisted of 100 pulses at 8 Hz, than under poor alpha2-autoinhibition conditions, only up to 14%, observed when alpha2-adrenoceptors were blocked with yohimbine (1 microM) or when stimulation consisted of 20 pulses at 50 Hz. Activation of PKC with 12-myristate 13-acetate (PMA, 0.1-3 microM) also enhanced tritium overflow more markedly under strong alpha2-autoinhibition conditions. Inhibition of Gi/o-proteins with pertussis toxin (8 microg/ml) or blockade of Gbetagamma subunits with the anti-betagamma peptide MPS-Phos (30 microM) attenuated the effects of angiotensin II and PMA. The results indicate that activation of AT1-receptors coupled to the PLC-PKC pathway enhances noradrenaline release, an effect that is markedly favoured by an ongoing activation of alpha2-autoreceptors. Interaction between alpha2-adrenoceptors and AT1-receptors seems to involve the betagamma subunits released from the Gi/o-proteins coupled to alpha2-adrenoceptors and protein kinase C activated by AT1-receptors.

Interaction between adenosine A 2B-receptors and alpha2-adrenoceptors on the modulation of noradrenaline release in the rat vas deferens: possible involvement of a group 2 adenylyl cyclase isoform

In the prostatic portion of rat vas deferens, activation of adenosine A 2B-receptors, beta2-adrenoceptors, adenylyl cyclase or protein kinase A caused a facilitation of noradrenaline release. Blockade of alpha2-adrenoceptors with yohimbine (1 microM) attenuated the facilitation mediated by adenosine A 2B-receptors and by direct activation of adenylyl cyclase with forskolin but not that mediated by beta2-adrenoceptors or by direct activation of protein kinase A with 8-bromoadenosine-3',5'-cyclicAMP. The adenosine A 2B- and the beta2-adrenoceptor-mediated facilitation was prevented by the adenylyl cyclase inhibitors, 2',5'-dideoxy-adenosine (3 microM) and 9-cyclopentyladenine (100 microM), at concentrations that also attenuated the release enhancing effect of forskolin, but were not changed by the phospholipase C inhibitor 1-[6-[((17beta)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1H-pyrrole-2,5-dione (U-73122, 1 microM). Facilitation of noradrenaline release mediated by adenosine A 2B-receptors was also attenuated by activation of protein kinase C with the phorbol ester 12-myristate 13-acetate (1 microM) and by inhibition of Gbetagamma subunits with an anti-betagamma peptide; facilitation mediated by beta2-adrenoceptors was mainly attenuated by the calmodulin inhibitor calmidazolium (10 microM) and by the calmodulin kinase II inhibitor (N-[2-[N-(4-chlorocinnamyl)-N-methylaminomethyl]phenyl]-N-(2-hydroxyethyl)-4-methoxybenzene-sulfonamide phosphate (KN-93, 5 microM). The results suggest that adenosine A 2B- but not beta2-adrenoceptor-mediated facilitation of noradrenaline release is enhanced by an ongoing activation of alpha2-adrenoceptors. They further suggest that adenosine A 2B-receptors and beta2-adrenoceptors are coupled to distinct adenylyl cyclase isoforms what may explain the different influence of alpha2-adrenoceptor signalling pathway on the facilitatory effects mediated by the two adenylyl cyclase coupled receptors.

Modulation of (3)H-noradrenaline release by presynaptic opioid, cannabinoid and bradykinin receptors and beta-adrenoceptors in mouse tissues

Release-modulating opioid and cannabinoid (CB) receptors, beta-adrenoceptors and bradykinin receptors at noradrenergic axons were studied in mouse tissues (occipito-parietal cortex, heart atria, vas deferens and spleen) preincubated with (3)H-noradrenaline. Experiments using the OP(1) receptor-selective agonists DPDPE and DSLET, the OP(2)-selective agonists U50488H and U69593, the OP(3)-selective agonist DAMGO, the ORL(1) receptor-selective agonist nociceptin, and a number of selective antagonists showed that the noradrenergic axons innervating the occipito-parietal cortex possess release-inhibiting OP(3) and ORL(1) receptors, those innervating atria OP(1), ORL(1) and possibly OP(3) receptors, and those innervating the vas deferens all four opioid receptor types. Experiments using the non-selective CB agonists WIN 55,212-2 and CP 55,940 and the CB(1)-selective antagonist SR 141716A indicated that the noradrenergic axons of the vas deferens possess release-inhibiting CB(1) receptors. Presynaptic CB receptors were not found in the occipito-parietal cortex, in atria or in the spleen. Experiments using the non-selective beta-adrenoceptor agonist isoprenaline and the beta(2)-selective agonist salbutamol, as well as subtype-selective antagonists, demonstrated the occurrence of release-enhancing beta(2)-adrenoceptors at the sympathetic axons of atria and the spleen, but demonstrated their absence in the occipito-parietal cortex and the vas deferens. Experiments with bradykinin and the B(2)-selective antagonist Hoe 140 showed the operation of release-enhancing B(2) receptors at the sympathetic axons of atria, the vas deferens and the spleen, but showed their absence in the occipito-parietal cortex. The experiments document a number of new presynaptic receptor locations. They confirm and extend the existence of marked tissue and species differences in presynaptic receptors at noradrenergic neurons.

Effects of omega-conotoxin GVIA and diltiazem on double peaked vasoconstrictor responses to periarterial electric nerve stimulation in isolated canine splenic artery

The actions of omega-conotoxin (omega-CTX) and diltiazem on adrenergic and purinergic components of double peaked vasoconstrictor responses to periarterial nerve stimulation have been investigated in the isolated, perfused canine splenic arterial preparation. Double peaked vasoconstrictions (biphases of vasoconstrictors) were consistently observed in the conditions of 30 s trains of pulses at 1 - 10 Hz frequencies. omega-CTX (1 - 30 nM) produced similar inhibitory effects on the first phase and second phase responses in a dose-related manner. Thirty nM omega-CTX almost completely inhibited the biphasic vasoconstrictions at any used frequencies but did not affect the vasoconstrictor responses to exogenous applied ATP (0.01 - 1 micromol) and noradrenaline (0.03 - 3 nmol). Intraluminal application of a large dose of diltiazem (3 - 10 microM) also produced a dose-dependent inhibitory effect on biphasic vasoconstrictions at any used frequencies. Three microM diltiazem exerted rather a larger inhibitory effect on the second phase than the first phase response at low frequencies (1 - 3 Hz), but a similar inhibition on first and second phasic responses at high frequencies (6 - 10 Hz). An extremely high dose of diltiazem (10 microM) almost completely inhibited the biphasic vasoconstrictor responses to nerve stimulation, and slightly inhibited the contractile responses to exogenous applied ATP (0.01 - 1 micromol) and noradrenaline (0.03 - 3 nmol). The present results indicate that omega-CTX selectively acts prejunctionally to inhibit the release of transmitters from sympathetic nerve terminals, and omega-CTX-sensitive calcium channels may produce a parallel controlling of purinergic and adrenergic components of sympathetic cotransmission. A large dose of diltiazem has inhibitory effects on both prejunctional and postjunctional sympathetic co-transmission. British Journal of Pharmacology (2000) 129, 47 - 52

Pharmacological analysis of vasoconstrictor responses to periarterial purinergic nerve stimulation

1. Periarterial electrical nerve stimulation at a low frequency (1 Hz) readily induced a vasoconstrictor response of the canine splenic artery in a pulse number-related manner (1-30 pulses of trains). The vasoconstrictor response to trains of up to 10 pulses at 1 Hz of stimulation appeared to be monophasic, whereas it became clearly distinguished into two phases at a longer train of 30 pulses. 2. The monophasic vasoconstrictor responses to trains of 1, 3 or 10 pulses were not modified by an alpha1-adrenoceptor blocking agent, prazosin (0.1 microM), but were completely inhibited by the P2X receptor desensitization with alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-methylene ATP; 1 microM). The 1st phase of vasoconstriction induced by a train length of 30 pulses was not influenced by the treatment with prazosin, but was abolished by alpha,beta-methylene ATP. The 2nd phase response was markedly inhibited by prazosin, and the remaining response of this phase was blocked by alpha,beta-methylene ATP. 3. Rauwolscine (0.3 microM), an alpha2-adrenoceptor antagonist, enhanced the vasoconstrictor responses to trains of 1, 3 or 10 pulses. Particularly at 10 pulses of electrical stimulation, the vasoconstrictor responses were significantly potentiated. The blockade of neuronal uptake of noradrenaline with imipramine (1 microM) did not affect the vasoconstrictor responses to trains of 1, 3 or 10 pulses. 4. It is concluded that short pulse trains of stimulation at a low frequency may selectively activate a purinergic component of sympathetic cotransmission, and the prejunctional alpha2-adrenergic feedback mechanism may tonically participate into the modulation of ATP release. Imipramine-sensitive neuronal uptake mechanism may not play an important role in regulating vascular responses to periarterial purinergic nerve stimulation.

Dissociation of inhibitory effects of guanethidine on adrenergic and on purinergic transmission in isolated canine splenic artery

The aim of this study was both to investigate the effects of progressive inhibition of adrenergic neurons by increasing concentrations of guanethidine (0.1-10 microM) on the double-peaked vasoconstrictor responses to electrical periarterial nerve stimulation in the isolated and perfused canine splenic artery, and to clarify whether release of noradrenaline is presynaptically separate from release of adenosine 5'-triphosphate (ATP). Double-peaked vasoconstrictions (biphases of vasoconstrictions) were consistently observed under the conditions of 30-s trains of pulses at 1-10 Hz frequencies. Guanethidine, at a lower concentration (0.1 microM) did not modify the first (1st) phase vasoconstriction at low frequencies (1-2 Hz), but markedly inhibited the second (2nd) responses. On the other hand, it slightly but significantly inhibited the double-peaked vasoconstrictor responses at high frequencies (6-10 Hz). Furthermore, a 10-fold increase of concentration of guanethidine (1 microM) almost completely inhibited the 2nd phase responses at any frequencies used but did not completely inhibit the 1st phase response. A further increased concentration of guanethidine (10 microM) failed to enhance the 1 microM guanethidine-induced inhibition. The 1 microM guanethidine-resistant 1st phase responses at any frequencies used (1-10 Hz) were sensitive to tetrodotoxin (30 nM). Treatment with 0.1 microM prazosin did not modify the 1st phase response at any frequencies used in the 1 microM guanethidine-treated preparation. The responses remaining after 1 microM guanethidine and 0.1 microM prazosin were completely suppressed by a subsequent application of 1 microM alpha,beta-methylene ATP at any frequencies used. The results indicated that guanethidine, an adrenergic neuron blocker, may exert a dominant inhibitory effect on adrenergic rather than on purinergic components of sympathetic nerve co-transmission, indicating that guanethidine-sensitive mechanisms may mainly contribute to determine noradrenaline secretion from neurosecretory vesicles rather than ATP secretion.

Inhibitory and facilitatory presynaptic effects of endothelin on sympathetic cotransmission in the rat isolated tail artery

1. The present study was undertaken to determine the modulatory effects of the endothelin peptides on the neurogenically-induced release of endogenous noradrenaline (NA) and the cotransmitter adenosine 5'-triphosphate (ATP) from the sympathetic nerves of endothelium-free segments of the rat isolated tail artery. The electrical field stimulation (EFS, 8 Hz, 0.5 ms, 3 min) evoked overflow of NA and ATP, in the absence of endothelins, was 0.035+/-0.002 pmol mg(-1) tissue and 0.026+/-0.002 pmol mg(-1) tissue, respectively. 2. Endothelin-1 (ET-1; 1-30 nM) significantly reduced the EFS evoked overflow of both NA and ATP. The maximum inhibitory effect was produced by a peptide concentration of 10 nM, the amount of NA overflow being 0.020+/-0.002 pmol mg(-1) and that of ATP overflow 0.015+/-0.001 pmol mg(-1). Higher peptide concentrations (100 and 300 nM) reversed the EFS-evoked overflow of NA to control levels and that of ATP to above control levels. The inhibitory effect of ET-1 (10 nM) was resistant to the selective ET(A) receptor antagonist cyclo-D-Trp-D-Asp(ONa)-Pro-D-Val-Leu (BQ-123) but was prevented by ET(B) receptor desensitization with sarafotoxin S6c (StxS6c) or by ET(B) receptor blockade with N, cis-2,6-dimethylpiperidinocarbonyl-L-gmethylleucyl-D-1-me thoxycarbonyltryptophanyl-D-norleucine (BQ-788). 3. StxS6c, upon acute application, exerted a dual effect on transmitter release. At concentrations of 0.001-0.3 nM the peptide significantly reduced the EFS-evoked NA overflow, whereas at concentrations of 1-10 nM it caused a significant increase in the evoked overflow of both ATP and NA. Both the maximum inhibitory effect of StxS6c at a concentration of 0.003 nM (approximately 85% reduction of NA overflow and 40% of ATP overflow) and the maximum facilitatory effect of the peptide at a concentration of 3 nM (approximately 400% increase of ATP overflow and 200% of NA overflow) were completely antagonized by either BQ-788 or by StxS6c-induced ET(B) receptor desensitization. 4. ET-3 (10-100 nM) did not affect the EFS evoked overflow of either ATP or NA, but at a concentration of 300 nM significantly potentiated the release of both transmitters (0.118+/-0.02 pmol mg(-1) tissue ATP overflow and 0.077+/-0.004 pmol mg(-1) NA overflow). This effect was prevented either by BQ-123 or by BQ-788. 5. In summary, the endothelin peptides exerted both facilitatory and inhibitory effects on the neurogenically-induced release of the sympathetic cotransmitters ATP and NA in the rat tail artery. Both transmitters were modulated in parallel indicating that the endothelins do not differentially modulate the release of NA and ATP in this tissue.

Beta-adrenoceptor mediated facilitation of noradrenaline and adenosine 5'-triphosphate release from sympathetic nerves supplying the rat tail artery

1. The effects of prejunctional beta-adrenoceptor activation on electrically evoked noradrenaline (NA) and adenosine 5'-triphosphate (ATP) were studied by use of continuous amperometry and conventional intracellular recording techniques. Excitatory junction potentials (e.j.ps) were used as a measure of ATP release, and NA-induced slow depolarizations and oxidation currents as measures of NA release, from postganglionic sympathetic nerves innervating the rat tail artery in vitro. 2. Isoprenaline (0.1 microM) increased the amplitude of e.j.ps, slow depolarizations and oxidation currents evoked by short trains of stimuli at 1 to 4 Hz. The facilitatory effect of isoprenaline on e.j.ps and oxidation currents was most pronounced on responses evoked by the first stimulus in a train. 3. Isoprenaline (0.1 microM) did not detectably alter the amplitude-frequency distribution of spontaneous e.j.ps. 4. The facilitatory effect of isoprenaline on e.j.ps, slow depolarizations and oxidation currents was abolished by the beta-adrenoceptor antagonist, propranolol (0.1 microM). Propranolol alone had no effect on e.j.ps, slow depolarizations or oxidation currents. 5. Thus, activation of prejunctional beta-adrenoceptors increases the release of both NA and ATP from postganglionic sympathetic nerves. The findings are consistent with the hypothesis that NA and ATP are released from the same population of nerve terminals and presumably from the same vesicles.