Noradrenergic vasoconstriction of pig prostatic small arteries

The current study investigated the distribution of adrenergic nerves and the action induced by noradrenaline (NA) in pig prostatic small arteries. Noradrenergic innervation was visualized using an antibody against dopamine-beta-hydroxylase (DBH), and the NA effect was studied in small arterial rings mounted in microvascular myographs for isometric force recordings. DBH-immunoreactive nerve fibers were located at the adventitia and the adventitia-media border of the vascular wall. Electrical field stimulation (EFS, 1-32 Hz) evoked frequency-dependent contractions that were reduced by guanethidine and prazosin (adrenergic neurotransmission and α1-adrenoceptors blockers, respectively) and by the α2-adrenoceptor agonist UK 14,304. The α2-adrenoceptor antagonist rauwolscine reversed the UK 14,304-produced inhibition. NA produced endothelium-independent contractions that were antagonized with low estimated affinities and Schild slopes different from unity by prazosin and the α1A-adrenoceptor antagonist N-[2-(2-cyclopropylmethoxyphenoxy) ethyl]-5-chloro-α-α-dimethyl-1H-indole-3-ethanamine (RS 17053). The α1A-adrenoceptor antagonist 5-methyl-3-[3-[4-[2-(2,2,2,-trifluoroethoxy) phenyl]-1-piperazinyl]propyl]-2,4-(1H)-pyrimidinedione (RS 100329), which also displays high affinity for α1L-adrenoceptors, and the α1L-adrenoceptor antagonist tamsulosin, which also has high affinity for α1A- and α1D-adrenoceptors, induced rightward shifts with high affinity of the contraction-response curve to NA. The α1D-adrenoceptor antagonist 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]8-azaspiro[4,5]decane-7,9-dione dihydrochloride (BMY 7378) failed to modify the NA contractions that were inhibited by extracellular Ca2+ removal and by voltage-activated (L-type) Ca2+ channel blockade. These data suggest that pig prostatic resistance arteries have a rich noradrenergic innervation; and NA, whose release is modulated by prejunctional α2-adrenoceptors, evokes contraction mainly through activation of muscle α1L-adrenoceptors coupled to extracellular Ca2+ entry via voltage (L-type)- and non-voltage-activated Ca2+ channels.Fundación Médica Mutua MadrileñaSección Deptal. de Fisiología (Farmacia)Fac. de FarmaciaTRUEpu

Role of neuronal voltage‐gated K+ channels in the modulation of the nitrergic neurotransmission of the pig urinary bladder neck

Background and purpose: As nitric oxide (NO) plays an essential role in the inhibitory neurotransmission of the bladder neck of several species, the current study investigates the mechanisms underlying the NO‐induced relaxations in the pig urinary bladder neck. Experimental approach:Urothelium‐denuded bladder neck strips were dissected and mounted in isolated organ baths containing a physiological saline solution at 37 °C and continuously gassed with 5% CO2and 95% O2, for isometric force recording. The relaxations to transmural nerve stimulation (EFS), or to exogenously applied acidified NaNO solution were carried out on strips pre‐contracted with phenylephrine, and treated with guanethidine and atropine, to block noradrenergic neurotransmission and muscarinic receptors, respectively. Key results:EFS (0.2–1 Hz) and addition of acidified NaNO solution (1 μM–1 mM) evoked frequency‐ and concentration‐dependent relaxations, respectively. These responses were potently reduced by the blockade of guanylate cyclase and were not modified by the K+ channel blockers iberiotoxin, charybdotoxin, apamin or glibenclamide. The voltage‐gated K+ (Kv) channels inhibitor 4‐aminopyridine, greatly enhanced the nitrergic relaxations evoked by EFS, but did not affect the NaNO2 solution‐induced relaxations. Conclusions and implications:NO, whose release is modulated by pre‐junctional Kv channels, relaxes the pig urinary bladder neck through a mechanism dependent on the activation of guanylate cyclase, in which post‐junctional K+ channels do not seem to be involved. Modulation of Kv channels could be useful in the therapy of the urinary incontinence produced by intrinsic sphincteric deficiency.Sección Deptal. de Fisiología (Farmacia)Sección Deptal. de Farmacología y Toxicología (Veterinaria)Fac. de FarmaciaFac. de VeterinariaTRUEpu

Neuronal and non-neuronal bradykinin receptors are involved in the contraction and/or relaxation to the pig bladder neck smooth muscle

Aims: The current study investigates the role played by bradykinin (BK) receptors in the contractility to the pig bladder neck smooth muscle. Methods: Bladder neck strips were mounted in myographs for isometric force recordings and BK receptors expression was also determined by immunohistochemistry. Results: B2 receptor expression was observed in the muscular layer and urothelium whereas B1 expression was consistent detected in urothelium. A strong B2 immunoreactivity was also observed within nerve fibers among smooth muscle bundles. On urothelium-denuded preparations basal tone, BK induced concentration-dependent contractions which were reduced in urothelium-intact samples, by extracellular Ca(2+) removal and by blockade of B2 receptors and voltage-gated Ca(2+) (VOC) and non-VOC channels, and increased by cyclooxygenase (COX) inhibition. On phenylephrine-precontracted denuded strips, under non-adrenergic non-cholinergic (NANC) conditions, electrical field stimulation-elicited frequency-dependent relaxations which were reduced by B2 receptor blockade. In urothelium-intact samples, the B1 receptor agonist kallidin promoted concentration-dependent relaxations which were reduced by blockade of B1 receptors, COX, COX-1 and large-conductance Ca(2+) -activated K(+) (BKCa ) channels and abolished in urothelium-denuded samples and in K(+) -enriched physiological saline solution-precontracted strips. Conclusions: These results suggest that BK produces contraction of pig bladder neck via smooth muscle B2 receptors coupled to extracellular Ca(2+) entry via VOC and non-VOC channels with a minor role for intracellular Ca(2+) mobilization. Facilitatory neuronal B2 receptors modulating NANC inhibitory neurotransmission and urothelial B1 receptors producing relaxation via the COX-1 pathway and BKCa channel opening are also demonstrated.Ministerio de Ciencia e Innovación (España)Fundação para a Ciência e Tecnologia, Ministério da Educação e Ciência (Portugal)Depto. de FisiologíaFac. de FarmaciaTRUEpu