Increased density of alpha-adrenoceptors in vas deferens of spontaneously hypertensive rats (SHR), indicated by functional and receptor binding studies

Physiopharmacological properties of the testicular capsule: A concise review

The testicular capsules of different mammalian species exhibit spontaneous motor activity. In addition, contractions can be mediated by neuronal stimulation or exogenous drug administration. However, the physiological role of testicular capsule motor activity is still not well understood. Nevertheless, there is evidence for putative roles in spermatozoa transport from the testis to the caput epididymis, control of interstitial/intratesticular pressure and testicular blood flow. In this review, we have collated information about the agents that regulate testicular capsule motor activity, their receptors and second messengers as well as the impact of altered testicular capsule function on the male reproductive system. Furthermore, we highlight the knowledge gaps in the physiology and pharmacology of the testicular capsule as indicators of future research directions that may lead to a better understanding of the physiological role of testicular capsule motor activity and its importance in male fertility.

Purinergic contraction of the rat vas deferens in L-NAME-induced hypertension: effect of sildenafil

Hypertension (HTN) is a risk factor for erectile dysfunction, but its effect on vas deferens (VD) contractility and the ejaculatory response has not been delineated. NG-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, was used for induction of nitric oxide (NO)-deficient HTN. Our aim was to evaluate the effects of L-NAME-induced HTN on rat VD contractility and to determine whether sildenafil affects VD contractility. A total of 36 male rats were divided into (1) control, (2) L-NAME-HTN, (3) sildenafil treated L-NAME-HTN groups. Group 2 was treated with L-NAME (40 mg kg(-1) per day) in drinking water for 4 weeks. Group 3 received sildenafil (1.5 mg kg(-1) per day, by oral gavage) concomitantly with L-NAME. The prostatic portion of the VD was subjected to electrical field stimulation (EFS, 1-20 Hz), and the P2X(1) agonist alpha,beta-methylene ATP (alpha,beta-meATP, 100 micromol L(-1)-1 micromol L(-1)) and the alpha1-adrenoceptor agonist phenylephrine (Phe, 100 micromol L(-1)-1 mmol L(-1)) were used to construct concentration-response curves. These experiments were repeated in the presence of P2X receptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, 30 micromol L(-1)). VD contractions in response to EFS, alpha,beta-meATP and Phe were significantly enhanced by L-NAME. Sildenafil treatment in the L-NAME group improved the contractile response of VD to EFS (20 Hz). In the presence of PPADS, the enhanced contractile response of VD to EFS and alpha,beta-meATP in hypertensive rats was reversed. In the rat model of chronic NO depletion, the purinergic and adrenergic components and EFS affect VD contractility. The VD contractile response may be mediated more by the purinergic system than the adrenergic system, and sildenafil may alter the ejaculatory response in men with PE.

Functionomics: the analysis of a postgenomic concept on the basis of pregenomic pharmacological studies in smooth muscle

The term functionomics (Amin 2003, Neumann et al. 2004) refers to a postgenomic integrated Systems Biology (Attur et al. 2002) using a multidimensional approach for cells, tissues and organs. It considers current or future involvement among genomics, proteomics or metabolomics, including the main factors that cause biological responses and modulation under different conditions. Our objective in the present review is to summarize the contemporary understanding of functionomics of smooth muscle pharmacology, based on the results obtained on the pregenomic era during several years in our laboratory. The present approach is based on the knowledge of the dynamics of the receptor system, which comprises a cascade of phenomena, leading from the drug administration to the final biological response. We will describe several conditions in which the final effect is modified, based on perturbations induced on drug absorption, distribution, metabolism, interaction with receptors and mobilization of second messengers, as well as by interactions with a second receptor system. We will also discuss the gaps that need to be fulfilled in order to obtain a clear and better understanding of the receptor system in smooth muscle, and to narrow the bridge between ourknowledge of the function of biological systems, genomics, and other recently introduced areas.

Sympathetic neurotransmission in the rat testicular capsule: functional characterization and identification of mRNA encoding alpha1-adrenoceptor subtypes

The rat testicular capsule is a thin tissue surrounding the testis, whose precise function is still unknown. We have studied the contractile effects of electrical field stimulation, noradrenaline, and the blockade by antagonists of adrenergic receptors, in order to characterize sympathetic neurotransmission, and adrenoceptor subtypes. In addition, reverse transcription polymerase chain reaction (RT-PCR) assays were made to check for the expression of the three known subtypes of alpha(1)-adrenoceptors. The effects of electrical field stimulation (2 to 20 Hz, 1 ms, 60 V) were almost totally abolished by depletion of neuronal noradrenaline storage with reserpine (10 mg/Kg), but not by the purinergic receptor antagonist suramin (10(-5) M), indicating that noradrenaline, but not ATP, was involved in contractions. The selective alpha(1)-adrenoceptor antagonist prazosin (10(-7) M) was more effective than the selective alpha(2)-adrenoceptor antagonist idazoxan (10(-7) M) to inhibit contractions induced by electrical field stimulation, pointing out a major involvement of alpha(1)-adrenoceptor. When noradrenaline was used instead of electrical field stimulation, it showed a high potency (pD(2)=7.9). Noradrenaline-induced contractions were competitively blocked by the selective alpha(1A)-adrenoceptor antagonists WB 4101 (pA(2)=8.88), phentolamine (pA(2)=8.39) and by the alpha(1B)-adrenoceptor antagonist spiperone (pA(2)=8.57), indicating the presence of functional alpha(1A)- and alpha(1B)-adrenoceptors. In addition, contractions were not blocked by the selective alpha(1D)-adrenoceptor antagonist BMY 7378 (up to 10(-6) M), while selective alpha(2)-adrenoceptor antagonists showed low pA(2) values (yohimbine, 7.25 and idazoxan, 7.49), suggesting a minor role, if any, for alpha(1D)- and alpha(2)-adrenoceptors. To check the proportionate role of alpha(1A)- and alpha(1B)-adrenoceptors, we blocked alpha(1B)-adrenoceptors with chloroethylclonidine (CEC, 30 microM, 45 min), that reduced the maximal effect of noradrenaline by about 60%. The remnant CEC-insensitive noradrenaline contraction was assumed to be unrelated to alpha(1B)-adrenoceptor, and was inhibited by 5-methyl-urapidil (pA(2)=8.94) and by the Ca(2+) channel blocker nifedipine (3 microM), confirming the involvement of alpha(1A)-adrenoceptors. The presence of mRNA encoding alpha(1A)- and alpha(1B)-adrenoceptor was also shown on RT-PCR assays. Unexpectedly, alpha(1D)-transcripts were also detected in these assays. Taken together, our results show that ATP co-transmission could not be detected, and that neurotransmission involves the interaction of noradrenaline with both alpha(1A)- and alpha(1B)-, but not with alpha(1D)- or alpha(2)-adrenoceptor. The fact that the functional alpha(1D)-adrenoceptor could not be detected in spite of the presence of the corresponding mRNA, remains to be investigated.

Rho-kinase inhibition suppresses bladder hyperactivity in spontaneously hypertensive rats

AIMS

Spontaneously hypertensive rats (SHR) exhibit overactive bladder (OAB) symptoms and have an up-regulated calcium sensitizing RhoA/Rho-kinase pathway in their vascular smooth muscle tissues. This study examined the role of RhoA/Rho-kinase pathway in bladder hyperactivity by evaluating the effect of a specific Rho-kinase inhibitor (Y-27632) on SHR bladder function.

METHODS

Adult male SHR (n = 9) and their normotensive controls (Wistar-Kyoto; WKY) (n = 8) were anesthetized and the carotid artery cannulated for blood pressure monitoring. A catheter was fixed into the bladder dome and connected to a pressure transducer and an infusion pump. After equilibration, systemic and bladder pressure were recorded. Continuous filling cystometrograms (CMGs) were performed and threshold pressure (TP), peak pressure (PP), and number of voids and non-voiding contractions (NVCs) per unit time recorded. Each SHR then received Y-27632, 10 mumol intra-arterially. After 10 min, CMG was repeated and the same measurements recorded. Bladder tissues were evaluated immunohistochemically (IHC) for RhoA protein expression.

RESULTS

SHR exhibited significantly higher number of voids and NVCs than normotensive WKY rats (P < 0.05). In SHR, Y-27362 administration significantly decreased the number of voids (29%, from 0.83 +/- 0.3 to 0.63 +/- 0.17 voids/min) and NVCs (61%, from 1.8 +/- 0.54 to 0.64 +/- 0.167 NVC/min). IHC showed significantly higher RhoA protein expression in SHR bladder tissues.

CONCLUSIONS

Overexpression of RhoA may play a role in hypertension-related OAB. Inhibition of Rho-kinase activity with Y-27632 produced a significant suppression of bladder overactivity. Identification of Rho-kinase isoforms that are bladder-tissue specific and their selective inhibitors may help to disassociate the unwanted hypotensive effects of this approach.

Enhancement of purinergic neurotransmission by galantamine and other acetylcholinesterase inhibitors in the rat vas deferens

Galantamine, a mild acetylcholinesterase inhibitor and an allosteric ligand of nicotinic receptors, enhanced in a concentration-dependent manner the amplitude of purinergic twitch contractions of the electrically stimulated rat vas deferens (0.2 Hz, 1 ms, 60 V). Other acetylcholinesterase inhibitors also increased the twitches, showing a hierarchy of potencies of galantamine>physostigmine>tacrine>rivastigmine=donepezil. The potentiations seem to be unrelated to the ability to inhibit acetylcholinesterase, since the hierarchy of potencies to block the enzyme in vas deferens was tacrine>physostigmine>rivastigmine>donepezil>galantamine. Acetylcholine also increased the twitches; such effect was produced by a low range of concentrations of acetylcholine (10(-10)-10(-7) M). This facilitatory effect of acetylcholine on twitches was significantly potentiated by galantamine (10(-7)-10(-6) M), but not by rivastigmine or donepezil. A striking enhancement of twitches was also caused by charybdotoxin, a blocker of high-conductance Ca2+-activated K+ channels, and by 4-aminopyridine, a non-specific blocker of K+ channels; in addition, apamin, a blocker of small-conductance Ca2+-activated K+ channels, induced a lower potentiation. The antagonist mecamylamine (10(-7)-10(-6) M) reduced by 80% the potentiation by galantamine, indicating the involvement of nicotinic receptors. Therefore, it is suggested that, besides an inhibition of acetylcholinesterase, some additional mechanisms, such as blockade of Ca2+-dependent K+ channels, or activation of nicotinic receptors of nerve terminals, might be involved in twitch potentiation. These results are relevant in the context of the clinical use of galantamine to improve cognition and behaviour in patients with Alzheimer's disease.

Stimulation of the α-adrenoceptor triggers the venom production cycle in the venom gland of Bothrops jararaca

The noradrenergic innervation of Bothrops jararaca venom gland is thought to be important in the production and secretion of venom. We investigated the characteristics of the α-adrenoceptor in the venom gland and its role in venom production. This receptor had relatively low sensitivity to noradrenaline (pD2=4.77±0.09, N=7)and to phenylephrine (pD2=3.77±0.06, N=11). The receptor became desensitized just after venom extraction (pD2 to phenylephrine fell to 3.27±0.02, N=6) and the sensitivity remained low for at least 15 days, returning to normal 30 days after venom extraction, by which time the snake was ready for a new cycle of venom production. Incubation of secretory cells with noradrenaline(10–4 mol l–1 for 5 min) reducedα-adrenoceptor sensitivity to the level seen after venom extraction. Blockade of catecholamine production with reserpine abolished the enlargement of the rough endoplasmic reticulum and the activation of the Golgi apparatus that are normally seen after venom extraction, and the venom production was restored by a single subcutaneous (s.c.) injection of phenylephrine (100 mg kg–1) immediately after venom extraction. Our data suggest that stimulation of the α-adrenoceptor during or shortly after biting is essential for the onset of the venom production cycle.

Up-regulation of Ca(2+) channels in vas deferens after chronic treatment of newborn rats with nifedipine

Radioligand binding and contraction techniques were used to verify if L-type Ca(2+) channels are modified in rat vas deferens after treatment with the blocker nifedipine (15 microg), injected at 7, 14, 21 and 28 days after birth. Vas deferens tissue was used 10, 30 and 90 days after the last injection, to verify if modifications are persistent. Binding studies with cell membranes, using [(3)H]isradipine, showed an increase of the density (B(max)) of Ca(2+) channels by more than 60%, after 10 and 30 days, without changes of affinity (K(d)). Maximal contractions (E(max)) of KCl, were increased by 106% and 37%, respectively, after 10 and 30 days, without changes of apparent affinity (pD(2)). After 90 days, the values of B(max), K(d), E(max) and pD(2) were not different from the controls. Differences were also not found for rats injected when adult. It is concluded that treatment of newborn, but not of adult, rats with nifedipine produced a long-lasting, though reversible, up-regulation of L-type Ca(2+) channels.

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

1. Purinergic and adrenergic components of the contractile response to electrical field stimulation (EFS) have been investigated in epididymal and prostatic portions of Wystar Kyoto (WKY) and spontaneously hypertensive rat (SHR) vas deferens. 2. In both halves of SHR and WKY vas deferens, EFS (40 V, 0.5 ms for 30 s, 0.5-32 Hz) evoked frequency-related contractions. The neurogenic responses were biphasic, consisting of a rapid non-adrenergic response, dominant in the prostatic portion, followed by a slow tonic adrenergic component, dominant in the epididymal half. 3. Phasic and tonic components of the frequency-response curves evoked by EFS were significantly higher in the epididymal but not in the prostatic portion of vas deferens from SHR compared to WKY rats. 4. The alpha1-adrenoceptor antagonist prazosin (0.1 microM) was more effective against both components of the contractile response in the epididymal end of SHR than in WKY rats. 5. Inhibition by alpha, beta-methylene adenosine 5'-triphosphate (alpha,beta-meATP 3 and 30 microM) was higher in both components of the contractile responses in WKY preparations than in SHR. 6. Combined alpha1-adrenoceptor and P2x-purinoceptor antagonism virtually abolished the EFS-evoked contractile response in both strains. The degree of inhibition by prazosin (0.1 microM) after P2x-purinoceptor blockade was higher in SHR than in WKY rats. 7. These results demonstrate a modification in the purinergic and noradrenergic contribution to neurogenic responses in SHR and WKY animals besides a co-participation of ATP and noradrenaline in both contractile components of the response to EFS.

Spinal and peripheral mechanisms contributing to hyperactive voiding in spontaneously hypertensive rats

The influence of noradrenergic mechanisms involved in micturition in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats was investigated using continuous cystometry in in vivo and in vitro studies on isolated bladder and urethral tissues. Compared with WKY rats, SHR had a significantly lower bladder capacity (SHR: 0.7 +/- 0. 05 ml; WKY rats: 1.3 +/- 0.06 ml; P < 0.001), micturition volume (SHR: 0.4 +/- 0.04 ml, WKY rats: 1.2 +/- 0.05 ml; P < 0.001), and an increased amplitude of nonvoiding (unstable) bladder contractions. The effects of intrathecal and intra-arterial doxazosin on cystometric parameters were more pronounced in SHR than in WKY rats. There was a marked reduction in nonvoiding contractions after intrathecal (but not intra-arterial) doxazosin in SHR. Norepinephrine (0.1 microM-1 mM) failed to evoke contractions in bladder strips from WKY rats, in contrast to a weak contractile response in SHR. The response to electrical field stimulation was significantly less in bladder strips from SHR than from WKY rats. In WKY rats, norepinephrine produced concentration-dependent inhibition (87 +/- 5%, n = 6) of nerve-evoked bladder contractions. Almost no inhibition (11 +/- 8%, n = 6) was found in SHR. Alterations in bladder function of SHR appear to be associated with changes in the noradrenergic control of the micturition reflex, in addition to an increased smooth muscle and decreased neuronal responsiveness to norepinephrine. The marked reduction in nonvoiding contractions after intrathecal doxazosin suggests that the bladder hyperactivity in SHR has at least part of its origin in supraspinal and/or spinal structures.

Functional properties of agmatine in rat vas deferens

Experiments were performed with rat vas deferens to verify whether agmatine, an endogenous ligand for adrenoceptors and imidazoline receptors, can influence sympathetic neurotransmission, with respect to contractions induced by transmural nerve stimulation, contractions induced by exogenous noradrenaline, and overflow of endogenous noradrenaline. It was shown that agmatine (a) caused a dose-dependent potentiation of electrically induced twitches, up to about 70% in relation to controls, (b) shifted to the right the inhibitory concentration-response curves for clonidine on electrically induced twitches, indicating competitive antagonism at presynaptic alpha-adrenoceptors, with a pA2 value of 4.12 +/- 0.10, (c) shifted to the right the concentration-response curves for noradrenaline-induced contractions, indicating competitive antagonism at postsynaptic alpha-adrenoceptors as well, with a pA2 value of 4.03 +/- 0.10, and (d) caused a dose-dependent increase of KCI-induced overflow of noradrenaline, up to about 90% in relation to controls. It is concluded that agmatine has multiple effects on sympathetic neurotransmission in rat vas deferens.

Indirectly acting agonists. A model for the functional interaction of released endogenous double agonists

A theoretical model is presented to describe the functional interaction of an endogenous double agonist released by an indirectly acting agonist. The model takes into account the functional interaction of a released double (dualistic) agonist and describes both functional synergism and antagonism. It was shown that receptor density plays an important role in determining the profiles of concentration-effect curves and that it is necessary that the model should incorporate a parameter which describes receptor density. The model predicted that the shape of the concentration-effect curves may be sigmoid or bell-shaped. The theoretical predictions are comparable with experimental results.