Adrenergic and purinergic components in bisected vas deferens from spontaneously hypertensive rats

Regulation of nerve-evoked contractions of the murine vas deferens

Stimulation of sympathetic nerves in the vas deferens yields biphasic contractions consisting of a rapid transient component resulting from activation of P2X1 receptors by ATP and a secondary sustained component mediated by activation of α1-adrenoceptors by noradrenaline. Noradrenaline can also potentiate the ATP-dependent contractions of the vas deferens, but the mechanisms underlying this effect are unclear. The purpose of the present study was to investigate the mechanisms underlying potentiation of transient contractions of the vas deferens induced by activation of α1-adrenoceptors. Contractions of the mouse vas deferens were induced by electric field stimulation (EFS). Delivery of brief (1s duration) pulses (4 Hz) yielded transient contractions that were inhibited tetrodotoxin (100 nM) and guanethidine (10 µM). α,β-meATP (10 µM), a P2X1R desensitising agent, reduced the amplitude of these responses by 65% and prazosin (100 nM), an α1-adrenoceptor antagonist, decreased mean contraction amplitude by 69%. Stimulation of α1-adrenoceptors with phenylephrine (3 µM) enhanced EFS and ATP-induced contractions and these effects were mimicked by the phorbol ester PDBu (1 µM), which activates PKC. The PKC inhibitor GF109203X (1 µM) prevented the stimulatory effects of PDBu on ATP-induced contractions of the vas deferens but only reduced the stimulatory effects of phenylephrine by 40%. PDBu increased the amplitude of ATP-induced currents recorded from freshly isolated vas deferens myocytes and HEK-293 cells expressing human P2X1Rs by 93%. This study indicates that: (1) potentiation of ATP-evoked contractions of the mouse vas deferens by α1-adrenoceptor activation were not fully blocked by the PKC inhibitor GF109203X and (2) that the stimulatory effect of PKC on ATP-induced contractions of the vas deferens is associated with enhanced P2X1R currents in vas deferens myocytes.

Nitric oxide decreases the biological activity of norepinephrine resulting in altered vascular tone in the rat mesenteric arterial bed

Nitric oxide (NO) reacts with catecholamines resulting in their deactivation. In this study, we demonstrated that coincubation of NO donors with sympathetic neurotransmitters decreased the amount of norepinephrine detected but not ATP or neuropeptide Y (NPY). Furthermore, we found that the ability of norepinephrine to increase perfusion pressure in the isolated perfused mesenteric arterial bed of the rat was attenuated by the incubation of norepinephrine with the NO donor diethylamine NONOate. Conversely, the vasoconstrictive ability of NPY and ATP was unaffected by incubation with NONOate. Periarterial nerve stimulation in the presence of the NO synthase (NOS) inhibitor Nω-nitro-l-arginine methyl ester (l-NAME) resulted in an increase in both perfusion pressure response and norepinephrine levels. This was prevented by l-arginine, demonstrating that the effects of l-NAME were indeed specific to the inhibition of NOS. To confirm that NO was not altering the release of norepinephrine from the sympathetic nerve via presynaptic activation of guanylate cyclase, we repeated the experiments in the presence of the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]-quinoxaloine-one (ODQ). Unlike l-NAME, ODQ infusion did not increase norepinephrine overflow, demonstrating that modulation of norepinephrine by NO at the vascular neuroeffector junction of the rat mesenteric vascular bed is not the result of presynaptic guanylate cyclase activation. These results demonstrate that, in addition to being a direct vasodilatator, NO can also alter vascular reactivity at the sympathetic neuroeffector junction in the rat mesenteric bed by deactivating the vasoconstrictor norepinephrine.

In vivo and in vitro pharmacological studies of a new hypotensive compound (QF0301B) in rat: comparison with prazosin, a known alpha1-adrenoceptor antagonist

In this work, we studied the in vivo and in vitro pharmacological effects of the novel compound QF0301B (2-[2-(N-4-o-methoxyphenyl-N-1-piperazinyl)ethyl]-1-tetralone) and compared with those of prazosin. In anaesthetized normotensive rats, both QF0301B and prazosin (0.1-0.2 mg/kg iv) caused a pronounced and prolonged fall in mean arterial blood pressure accompanied by bradycardia. Neither QF0301B nor prazosin (0.2 mg/kg iv) significantly modified the cardiovascular effects of either 5-hydroxytryptamine (serotonin, 5-HT, 75 microg/kg iv) or the selective alpha(2)-adrenoceptor agonist B-HT 920 (0.2 mg/kg iv), but both markedly inhibited the hypertensive effect of noradrenaline (5 microg/kg iv), a nonselective alpha-adrenergic receptor agonist. In isolated rubbed rat aorta rings, QF0301B and prazosin showed marked alpha(1)-adrenoceptor blocking activity, with pA(2) values of 9.00+/-0.12 and 9.75+/-0.14, respectively. In addition, QF0301B reversed and competitively antagonized the inhibitory action produced by clonidine in electrically stimulated rat vas deferens and inhibited the force and rate of contraction in rat isolated atria (pA(2)=5.91+/-0.43), competitively antagonized the contractile effect of 5-HT in rat aorta (pA(2)=6.75+/-0.06) and in rat stomach fundus (pA(2)=7.13+/-0.48) and the contractions induced by histamine in isolated guinea pig longitudinal ileal muscle (pA(2)=7.40+/-0.40). QF0301B showed noncompetitive low action in 5-HT(3), muscarinic and nicotinic receptors, or as Ca(2+) antagonist. These results indicate that a alpha(1)-adrenoceptor blocking lead has been obtained with a new chemical structure and interesting pharmacological properties, which only alpha(1)-adrenoceptor blocking activity seems to be responsible for its cardiovascular effects.

P2X2 receptor expression by interstitial cells of Cajal in vas deferens implicated in semen emission

Male reproduction is dependent upon seminal emission mediated by vas deferens contraction. This drives spermatic fluid to the prostatic urethra during ejaculation. We localize interstitial cells of Cajal (ICC), which express P2X2 receptor, subunits of ATP-gated ion channels, to rat, mouse and guinea-pig vas deferens submucosa. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of rat vas deferens resolved two functional splice variant transcripts of the P2X2 receptor subunit. The P2X2 receptor mRNA was localized principally within the lamina propria (submucosal) region of the rat vas deferens using in situ hybridization (ISH) and in situ RT-PCR-ISH. Immunohistochemistry using rat, mouse and guinea-pig vas deferens tissues confirmed expression of P2X2 receptor protein within the lamina propria, particularly within a dense column of small spindle-shaped cells adjacent to the columnar epithelial cells which line the lumen. This immunoreactivity was co-localized with neurone-specific enolase (NSE) and c-Kit protein expression, gene markers for ICC. Mucosal mast cells were distinguished from ICC by toluidine blue staining. Choline acetyltransferase immunoreactivity, a marker for post-ganglionic parasympathetic innervation, occurred on the lateral margin of the lamina propria and extended into the inner longitudinal muscle layer. P2X1 receptor immunolabelling was associated with sympathetic innervation of the smooth muscle in the outer longitudinal and circular muscle layers, but not the inner longitudinal layer. The physiological significance of the vas deferens ICC which express P2X2 receptors remains to be established. Possible roles include regulation of smooth muscle activity or mucosal secretion utilizing local ATP signaling, both of which would affect semen transport.