How does the urothelium affect bladder function in health and disease? ICI-RS 2011

The urothelium is a multifunctional tissue that not only acts as a barrier between the vesical contents of the lower urinary tract and the underlying tissues but also acts as a sensory organ by transducing physical and chemical stresses to the attendant afferent nervous system and underlying smooth muscle. This review will consider the nature of the stresses that the urothelium can transduce; the transmitters that mediate the transduction process; and how lower urinary pathologies, including overactive bladder syndrome, painful bladder syndrome and bacterial infections, are associated with alterations to this sensory system. In particular, the role of muscarinic receptors and the TRPV channels system will be discussed in this context. The urothelium also influences the contractile state of detrusor smooth muscle, both through modifying its contractility and the extent of spontaneous activity; potential pathways are discussed. The potential role that the urothelium may play in bladder underactivity is introduced, as well as potential biomarkers for the condition that may cross the urothelium to the urine. Finally, consideration is given to vesical administration of therapeutic agents that influence urinary tract function and how the properties of the urothelium may determine the effectiveness of this mode of delivery.

Voltage-dependent effects of barnidipine in rat vascular smooth muscle

The effects of the dihydropyridine nifedipine and its more lipophilic congener, barnidipine, were investigated in smooth muscle preparations from the rat in resting and depolarizing conditions. Both drugs relaxed precontracted aortic rings more potently in depolarizing conditions, barnidipine being more potent than nifedipine. Currents through Ca2+ channels in rat vascular smooth muscle cells (A7r5) and in isolated rat cardiomyocytes were reduced more potently by both drugs at a holding potential of -40 mV than at -80 mV. However, barnidipine and nifedipine were more effective in reducing the current in A7r5 cells than in cardiomyocytes. The IC(50) obtained in aortic rings and in A7r5 cells were similar for barnidipine but an order of magnitude different for nifedipine. The results show that, in depolarizing conditions, barnidipine was more effective than nifedipine. It is suggested that the higher potency of barnidipine acting in vascular smooth muscle is related to both a higher affinity to the inactivated state of vascular Ca2+ channels and to a more lipophilic property as compared with nifedipine.

Barnidipine, a long-acting slow onset calcium antagonist

Barnidipine is a stereochemically pure dihydropyridine calcium antagonist with a high potency. The drug showed a slow onset and long-lasting vasorelaxating effect in vitro, and strong antihypertensive activity in hypertension models. Barnidipine was shown to have a high vasoselectivity and offered protection in cardiac and renal ischaemia models. The in vitro drug:drug interaction profile suggests a low potential for clinically relevant interactions with concomitant medication. It can be anticipated that barnidipine is an attractive calcium antagonist, offering good blood pressure control without compensatory baroreflex activity.

BPS epilepsy joint symposium. 18 November 1999, London, UK

This symposium, jointly organized by the British Pharmacological Society, the Pharmaceutical Sciences Group of the Royal Pharmaceutical Society and the National Society for Epilepsy, provided comprehensive information on anti-epileptic therapy and drug development issues. The spectrum of medical imaging techniques was evaluated for application in patient classification and diagnosis, therapeutic or surgical options, and for studying sites and mechanisms of drug action. The value of established therapeutics, as opposed to recent new drug interactions and therapeutics awaiting registration, were discussed in view of their clinical pharmacology, therapeutic use and drug-drug interaction properties. There were discussions on clinical drug testing problems in relation to trial design, and drug screening strategies from the perspective of perceived unmet clinical needs, such as refractory epilepsy and epileptogenesis. New developments, especially in the field of glutamate modulation, were reviewed for anti-epileptic drug potential. The conclusion was that in spite of progress, rational drug development of anti-epileptic drugs is still far away. Possible reasons for this could be that during drug screening, the focus is on drug properties in isolated rather than integrated neuronal circuits. In addition, there is a poor translation of drug effects in models for seizures and convulsions compared with epilepsy and epileptogenesis in man, and also the obstacle of rigidity in drug registration trials. It was a very valuable meeting for those who wanted to be informed about the frontiers and challenges in the development of anti-epileptic drugs.

In vitro investigation of the bladder-vascular selectivity of levcromakalim and YM934 in human tissues

OBJECTIVE

To examine the potencies of the potassium-channel openers (KCOs) levcromakalim and YM934 as relaxing agents on human detrusor and human mesenteric artery smooth muscle, and to determine their bladder-vascular selectivity in vitro.

MATERIALS AND METHODS

Strips of human detrusor muscle and mesenteric artery (with the endothelium removed) were set up in physiological salt solution and the tension developed by the tissues recorded. Tissues were precontracted with a concentration of carbachol (detrusor) or phenylephrine (artery) which caused 80% of maximal contraction, and relaxation responses to levcromakalim and YM934 were then obtained.

RESULTS

Both KCOs caused relaxation of the bladder detrusor muscle and the mesenteric artery. Maximal responses, when plotted as a percentage of the precontraction, were greater for both KCOs in the bladder muscle than the artery, but the differences were small and not statistically significant. The sensitivity (drug potency) of the detrusor muscle to the KCOs was more than twice that of the artery but this selectivity was only statistically significant for YM934.

CONCLUSIONS

Only minor bladder-vascular selectivity for levcromakalim and YM934 could be detected in vitro. This suggests that neither drug would be tolerated clinically, although the results suggest that further development of bladder-selective KCO agents appears feasible.

Relaxant effects of potassium-channel openers on normal and hyper-reflexic detrusor muscle

OBJECTIVE

To compare the effects of the potassium-channel openers, levcromakalim and YM934, in isolated human detrusor muscle from normal and hyper-reflexic bladders.

MATERIALS AND METHODS

Strips of human detrusor muscle from normal and hyper-reflexic bladder were pre-contracted with carbachol and the potassium-channel openers (0.1-0.3 mumol/L) were added cumulatively to the organ baths. Other strips were field-stimulated at frequencies producing 25% and 75% of the maximum response to field stimulation. Contractions could be abolished by atropine (10 mumol/L) and tetrodotoxin (1 mumol/L).

RESULTS

The hyper-reflexic bladder was significantly more sensitive to carbachol than the normal bladder but the maximum response was significantly lower in the hyper-reflexic tissue. There was no significant difference between the potency of the potassium-channel openers in normal and hyper-reflexic detrusor muscle. Hyper-reflexic bladder was significantly more sensitive to electrical field stimulation than was normal bladder: maximum responses to field stimulation were not significantly different. Concentration-response curves for the potassium-channel openers were displaced to the left in hyper-reflexic bladder at both 25% and 75% maximum frequencies: however, only with levcromakalim at 75% of the maximum frequency was the shift significant.

CONCLUSION

The greater sensitivity of hyper-reflexic bladder to carbachol and field stimulation supports existing evidence for post-junctional supersensitivity in detrusor instability. The results of this study also suggest that there are no appreciable changes in KATP channel function in the unstable bladder.

The effects of tamsulosin, a high affinity antagonist at functional alpha 1A- and alpha 1D-adrenoceptor subtypes

1. The actions of the alpha 1-adrenoceptor antagonist tamsulosin have been examined at functional alpha 1-adrenoceptor subtypes and compared with those at the human prostate receptor. 2. At the alpha 1D-adrenoceptors of the rat aorta, tamsulosin acted as a competitive antagonist with a high affinity (pKB = 10.1). 3. At the alpha 1B-adrenoceptor of the rat spleen and rabbit corpus cavernosum penis, tamsulosin again acted as a competitive antagonist but with a significantly lower affinity (pKB = 8.9-9.2). 4. Tamsulosin acted as an unsurmountable antagonist of the alpha 1A-adrenoceptor-mediated responses of the rat and human vas deferens, reducing maximal responses to phenylephrine by 20% and 50%, respectively, at an antagonist concentration of 1 nM. Responses of depolarized (100 mM KCl) rat vas deferens preparations were unaffected by 10 nM tamsulosin but this concentration reduced maximal responses to 5-hydroxytryptamine (5-HT) in this tissue. 5. When longer antagonist incubation periods (> or = 60 min) were used, tamsulosin behaved as a competitive antagonist on the human prostate with a significantly higher affinity (pKB = 10.0) than obtained at the alpha 1B-adrenoceptor. 6. The data demonstrate that tamsulosin is a high affinity antagonist at functional alpha 1-adrenoceptors with a selectivity alpha 1D > or = alpha 1A > alpha 1B. In some tissues the compound exhibits an additional unsurmountable antagonist action, the clinical significance of which is unknown.

Effects of topical treatment with budesonide on parameters for epidermal proliferation, keratinization and inflammation in psoriasis

Corticosteroids are important in the treatment of inflammatory dermatoses, such as psoriasis. They have anti-inflammatory, anti-proliferative and immunosuppressive effects. In this study, the effect of budesonide on proliferation, inflammatory cells and cytokines in psoriasis was investigated. In order to elucidate the time course of the different effects of corticosteroid treatment in psoriasis, six patients were treated for 3 weeks with budesonide 0.025% ointment (Preferid), and biopsies were studied immunohistochemically, before treatment and after 1 and 3 weeks of treatment. Clinical scores together with staining with antibodies indicating proliferation, keratin 16, keratin 10, T-lymphocytes, monocytes, polymorphonuclear leukocytes, Langerhans cells, interleukin-1alpha (IL-1alpha), interleukin-6 (IL-6), interleukin-8 (IL-8), tumor necrosis factor-alpha (TNF-alpha), and intercellular adhesion molecule-1 (ICAM-1) were performed. 'Psoriasis area' and 'severity index' (PASI) scores were significantly reduced after 1 week and 3 weeks of treatment. Epidermal hyperproliferation (Ki-67 binding) and suprabasal keratin 16 (Ks8.12) expression decreased within 1 week, while keratin 10 (RKSE60) expression did not change. Five out of 6 patients showed cytokine levels (IL-1alpha, IL-6, IL-8, and TNF-alpha; detected immunohistochemically) in the normal range, while 1 patient had highly increased cytokine levels. In this patient, cytokine levels decreased during treatment. In 4 patients, showing high dermal ICAM-1 expression before treatment, a consistent reduction of ICAM-1 on endothelial cells was observed. The inflammatory infiltrate (T-lymphocytes (T11), monocytes/macrophages (WT14), polymorphonuclear leukocytes (PMN, anti-elastase)) was reduced to some extent after 3 weeks. The number of Langerhans cells (OKT6) did not change. These results indicate that the psoriatic lesions, although clinically comparable, show interindividual differences in cytokine expression. Corticosteroid treatment for 1-3 weeks improves clinical scores and hyperproliferation. Cytokine levels are reduced during steroid treatment in the patient who showed high levels before treatment. To suppress the infiltrate entirely, longer steroid treatment is probably necessary. This may explain the relapse seen after short term corticosteroid therapy.

[Toxicological and pharmacological effects of the use of bovine somatotropin in dairy farming]

Some possible toxicological and pharmacological consequences of the use of bovine growth hormone (BST) synthesised using recombinant DNA techniques are discussed in the present paper. Three spheres of interest are reviewed. Target species: When BST is used correctly, negative effects on the target species are unlikely to occur. Obscurity may to some extent remain as regards the effect of BST on the immune system. Residues of BST and IGF: There is nothing to suggest that the BST levels in the milk will increase significantly following BST treatment. Slight elevations of the levels of IGF-1 (one of the so-called somatomedins) in the milk following treatment with BST have been reported. However, the concentration of IGF-1 that is reached after the correct use of BST is still lower than that in milk collected during early stages of lactation. As a result of the peptide character of BST and IGF-1, absorption by healthy human individuals is unlikely to occur. The relevance of the problem of BST and/or IGF-1, absorption from milk by some individuals such as young infants is also discussed in this paper. Interaction with the metabolism of drugs: A possible interaction between BST and drugs which are administered to the animal at the same time, as is observed in rats and occasionally also in human subjects could have consequences for the clinical effectiveness, side-effects and drug residues in food products of animal origin. So far, however, an interaction of this type could not be detected in ruminants. At the present time, this phenomenon is being studied in greater detail.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha 1-adrenoceptors: the ability of various agonists and antagonists to discriminate between two distinct [3H]prazosin binding sites

Recently, it has been demonstrated that two distinct alpha 1-adrenoceptor binding sites showing high and low affinity for WB-4101 (2-(2,6-dimethoxyphenoxy)ethyl-aminomethyl-1,4-benzodioxane) and 5-methyl-urapidil can be distinguished. In the present study we examined the ability of several agonists and antagonists to discriminate between these alpha 1-adrenoceptor binding sites. [3H]Prazosin binding to membranes of rat liver, heart, cerebral cortex and hippocampus was inhibited monophasically by butanserine, I-BE 2254 (2-(3-(4-hydroxy-3-iodophenyl)ethylaminomethyl)tetralone-hydrochloride), prazosin, rauwolscine and verapamil. In contrast, competition curves of adrenaline, oxymetazoline, amidephrine and YM-12617 (5-[2-[[2-(o-ethoxy-phenoxy)ethyl]-amino]propyl]-2- methoxybenzenesulfonamide HCl) were best described by a model of two binding sites. Chloroethylclonidine (CEC), a compound shown to irreversibly eliminate binding sites with low affinity for WB-4101, increased the proportion of high affinity binding sites for oxymetazoline and amidephrine, whereas the binding data for prazosin and adrenaline remained unchanged. These results indicate that amidephrine, oxymetazoline and YM-12617, but not the other drugs tested discriminate between different alpha 1-adrenoceptor recognition sites labelled by [3H]prazosin.

Effect of trenbolone and testosterone on the plasma elimination rates of sulfamethazine, trimethoprim, and antipyrine in female dwarf goats

Plasma elimination rates of sulfamethazine (100 mg/kg of body weight, IV), trimethoprim (20 mg/kg, IV), and antipyrine (35 mg/kg, IV) were studied in adult female dwarf goats (n = 5) before and after implantation with trenbolone acetate (5 mg/kg). Pretreatment with trenbolone caused a significant decrease in the elimination rate of the drugs tested: for sulfamethazine, 5 times; for antipyrine, 3 times; and for trimethoprim, 2 times. After treatment with testosterone (1 mg/kg, SC, twice weekly for 2.5 weeks), female goats (n = 5) had a similar decrease in the elimination rate of sulfamethazine. Other induced effects included a change in social behavior, a lower voice, and the development of a typical billy goat-like odor. Plasma creatinine concentrations after androgen administration were significantly higher than those before androgen administration; changes were not observed in plasma urea values. Because of the differences observed, we believe that more attention should be paid to the effects of androgenic agents on drug kinetic properties, with particular reference to studies on clinical efficacy, side effects, and drug residues in food products.

Some pharmacokinetic data of aditoprim and trimethoprim in healthy and tick-borne fever infected dwarf goats

Aditoprim (AP) is a new dihydrofolate reductase inhibitor, which is structurally related to trimethoprim (TMP). The pharmacokinetics of AP (10 mg/kg) and TMP (20 mg/kg) were assessed in healthy dwarf goats. Therapeutic efficacy against rickettsial infections was tested in tick-borne fever (TBF) infected goats. The animals were given TMP (n = 5) or AP (n = 5) by i.v. injection, and subsequently the drugs were administered orally (same groups, similar doses). Finally, both groups were infected with TBF and the i.v. experiment was repeated. Plasma concentration-time curves for both drugs followed first-order two-compartment decay. For TMP, mean t1/2 beta +/- SEM (h) was 0.84 +/- 0.06 (i.v. control) and 0.90 +/- 0.06 (i.v. infected), respectively, whereas for AP values of 8.00 +/- 0.31 (i.v. control) and 10.28 +/- 0.67 (i.v. infected) were obtained (P less than 0.05). Mean Vd beta +/- SEM values (l/kg) were 3.84 +/- 0.27 (i.v. control) and 4.07 +/- 0.85 (i.v. infected) for TMP (NS) and 7.02 +/- 0.63 vs 9.29 +/- 0.21 (P less than 0.05) for AP. After i.v. injection, rumen fluid concentrations of AP were significantly (P less than 0.05) higher and more persistent than those of TMP. For AP, the plasma and rumen fluid concentrations at 3 h were 1.20 +/- 0.06 micrograms/ml and 0.85 +/- 0.17 microgram/ml, respectively. After oral administration of TMP, Cmax in plasma was 0.12 +/- 0.01 microgram/ml and the maximum was reached after 1.2 +/- 0.16 h; systemic bioavailability (F) was 10.3% (relative to AUC i.v.). Oral treatment with AP resulted in a Cmax value of 0.21 +/- 0.02 microgram/ml with Tmax of 22.5 +/- 1.65 h and a F value of 71%. Based on WBC, serum ALP and rectal temperature responses, it was concluded that both TMP and AP were inactive against Ehrlichia phagocytophila.

The effect of testosterone and rutting on the metabolism and pharmacokinetics of sulphadimidine in goats

After testosterone pretreatment of castrated goats and during the rutting season of adult entire male goats, the oxidative metabolism of sulphadimidine (SDM) was inhibited markedly compared with the castrated control state of these animals. The oxidation of the 5 position (yielding 5-hydroxysulphadimidine) and of the 6-hydroxymethyl group (yielding 6-carboxysulphadimidine) was decreased equally, with that of the methyl group at the pyrimidine side chain itself being 6-hydroxymethylsulphadimidine (CH2OH), whereas the acetylation pathway was unaffected by testosterone. The consequence of altered metabolism by testosterone was a prolongation of SDM presence in the body. Effects on protein binding of the CH2OH metabolite and on the renal clearance of SDM were also investigated.

Interaction of calmodulin antagonists with alpha-adrenergic responses in pithed rats and in the perfused hindquarters of the rat

The effect of calmodulin antagonists was studied on the alpha 1- and alpha 2-adrenoceptor-mediated increase in diastolic blood pressure in pithed rats and on the alpha 1-adrenoceptor-mediated reduction of flow in the perfused hindquarters of the rat. B-HT 920 was used as a selective alpha 2-adrenoceptor agonist in the pithed rat experiments, whereas cirazoline was used as a selective agonist for alpha 1-adrenoceptors. The latter was used after pretreatment with nifedipine (1 mg/kg) or phenoxybenzamine (30 micrograms/kg), revealing calcium influx-insensitive and -sensitive mechanisms of vasoconstriction, respectively. Papaverine, calmidazolium and W-7 did not influence the dose-response curves for the agonists in the pithed rat experiments. The modest effects of high doses of flunarizine and bepridil on the dose-response curve for B-HT 920 and of trifluoperazine on the dose-response curve for cirazoline can be explained by the well-known calcium entry (flunarizine) and alpha 1-adrenoceptor-blocking (bepridil) effects of these drugs. Bepridil and calmidazolium caused an elevation of the cirazoline dose-response curves in the perfused rat hindquarters; flunarizine and trifluoperazine showed a parallel and dose-dependent displacement of the cirazoline dose-response curve to the right, whereas W-7 was inactive. Our results do not implicate calmodulin-associated effects in the alpha-adrenoceptor-mediated vasoconstriction in pithed rats and in the perfused rat hindquarters.

Inhibition of vasoconstriction to cirazoline by calcium-entry blockade after phenoxybenzamine in rat perfused hindquarters

The effects of phenoxybenzamine and benextramine were assessed with respect to the vasoconstriction to cirazoline in rat perfused hindquarters. Experiments were performed with and without restriction of inward calcium flux by addition of nifedipine (10(-9)-10(-6) M) to the standard physiological solution (PS), or by omission of calcium chloride from the PS. Addition of nifedipine or omission of Ca2+ did not affect the maximal response or potency of the selective but partial alpha 1-adrenoceptor agonist, cirazoline in rat perfused hindquarters. Upon pretreatment with phenoxybenzamine (0.03-30 micrograms/kg, i.v. at -1 h) or benextramine (1 mg/kg, i.v. at -2 h) both the slope and the maximal response to cirazoline were depressed. After phenoxybenzamine but not after benextramine the maximal response to cirazoline was depressed further upon addition of nifedipine or omission of Ca2+ from the PS. It is concluded that phenoxybenzamine selectively inhibits that part of the alpha 1-adrenoceptor mediated vasoconstriction that is independent of extracellular calcium, thereby unmasking a calcium-entry sensitive mechanism of vasoconstriction to cirazoline.

Bay k 8644, a calcium entry promoter, as an antidote in verapamil intoxication in rabbits

The effects of the Ca++-entry promoters Bay k 8644 and CGP 28932 were compared with that of the potassium channel blocker 4-aminopyridine (4-AP) in urethane/chloralose anaesthetized rabbits subjected to a severe verapamil overdose. Heart rate (HR), blood pressure, E.C.G., acid-base status and plasma verapamil level were monitored. Intoxication was provoked upon i.a. infusion of verapamil, and resulted in complete atrioventricular (AV) dissociation and reduction of mean arterial pressure (MAP) by 55.6 +/- 2.0% (mean +/- S.E.M., n = 25). One minute after complete AV-dissociation, verapamil infusion was interrupted. Subsequently, treatment was started with an i.a. infusion of either Bay k 8644, CGP 28932 or 4-AP, whereas a control group was left untreated. The effects of treatment were assessed at 15 and 30 min after cessation of the verapamil infusion. The criteria were reversal of AV dissociation, and recovery of HR and MAP (HR, MAP greater than 65% of initial value). With the calcium entry promoter Bay k 8644 satisfactory protection against the deleterious symptoms of verapamil intoxication could be obtained. With respect to antidotal potency the following rank order was observed: Bay k 8644 much greater than CGP 28932 greater than 4-AP.

Characterization of alpha-adrenoreceptor mediated reduction of flow in a saline-perfused constant pressure model of rat perfused hindquarters

An analysis of vasopressor responses elicited by alpha-adrenoreceptor agonists and KCl in a constant pressure saline perfused model of rat perfused hindquarters is presented. Using methoxamine (alpha 1), cirazoline (alpha 1), B-HT 920 (alpha 2) and St 587 (alpha 1) as alpha-adrenoreceptor agonists, and rauwolscine and prazosin as selective alpha 2- and alpha 1-adrenoreceptor antagonists, respectively, it is concluded that alpha-adrenoreceptor mediated vasoconstriction in this model is mediated by the alpha 1-subtype. Pretreatment of the animals with reserpine (i.p., at various doses and dose-regimens) or addition of angiotensin II (10(-9)-10(-6) M), PGF2 alpha(10(-8) & 5 X 10(-7) M) or KCl (2 & 4 X 10(-3) M), or changing [Mg2+] did not significantly affect the potency or intrinsic activity of the alpha-adrenoreceptor agonists studied. Experiments with the calcium entry blocking drugs gallopamil and nifedipine, or deletion of CaCl2 from the perfusion solution, did not reveal a contribution from the influx of extracellular calcium towards alpha 1-adrenoreceptor-mediated reduction of flow in RPH. KCl-induced vasoconstriction in RPH was found to be sensitive to the blockade of calcium entry by calcium entry blocking drugs, but not to alpha-adrenoreceptor-blocking drugs and calmodulin antagonist. It is concluded that the model described here is of potential value in the characterization of alpha-adrenoreceptor antagonists and calcium entry blocking drugs under in vitro conditions in resistance vessels of the rat.

Characterization of flufylline, fluprofylline, ritanserin, butanserin and R 56413 with respect to in-vivo alpha 1-,alpha 2- and 5-HT2-receptor antagonism and in-vitro affinity for alpha 1-,alpha 2- and 5-HT2-receptors: comparison with ketanserin

The experimental drugs butanserin (R 53393), ritanserin (R 55667), R 56413, flufylline (Sgd 195/78) and fluprofylline (Sgd 144/80) were evaluated with respect to their antagonism at postjunctional alpha 1- and alpha 2-adrenoceptors and 5-HT2-receptors in pithed rats. Moreover, affinity for [3H]mianserin, [3H]prazosin and [3H]yohimbine binding sites was assessed using rat brain preparations. In all experiments ketanserin was taken as a reference compound. It is concluded that of the compounds investigated butanserin is the most potent and selective alpha 1-adrenoceptor antagonist, whereas ritanserin was found to be a potent and selective 5-HT2-antagonist. Of the other compounds, fluprofylline was a very selective though not very potent alpha 1-adrenoceptor antagonist. The other compounds were less active and less selective in this respect.

Influence of respiratory acidosis or alkalosis on pressor responses mediated by alpha 1- and alpha 2-adrenoceptors in pithed normotensive rats

The effect of respiratory acidosis and alkalosis on the vasoconstriction to alpha 1- and alpha 2-adrenoceptor stimulation was studied in pithed normotensive rats. The selective alpha 1-adrenoceptor agonists (-)amidephrine, cirazoline, (+/-)erythro methoxamine, (-)phenylephrine, Sgd 101/75 and St 587 were used, as well as the selective alpha 2-adrenoceptor agonists B-HT 920, B-HT 933, DP-6,7-ADTN, M-7 and UK 14,304. The non-selective alpha-adrenoceptor agonists xylazine, noradrenaline and adrenaline were included as well. The latter two were also studied under selective doses of the antagonists rauwolscine and prazosin, thus yielding the respective alpha 1- and alpha 2-adrenoceptor components of the vasoconstriction to these agonists. The effect of acid-base balance disturbances on presynaptically released noradrenaline elicited by electrical stimulation of preganglionic nerves was studied as well. Dose response curves for the agonists were generated under various conditions of ventilation, yielding either alkalotic, normal or acidotic values of arterial blood pH. Pressor responses to all agonists were maximally affected by changes in acid-base status at the low doses of the agonists. Acidosis was found to inhibit increases in diastolic pressure mediated by the alpha 1-as well as the alpha 2-adrenoceptor agonists studied, although not to the same extent. Alkalosis exerted either an obvious potentiation or did not significantly influence alpha 1-adrenoceptor mediated pressor responses. On the basis of acid-base sensitivity the following groups of agonists were distinguished: Cirazoline, phenylephrine, methoxyamine, electrically released noradrenaline from presynaptic sites, of which pressor responses are obviously potentiated and attenuated by alkalosis and acidosis, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity of WY 26703 for central and peripheral alpha 1- and alpha 2-adrenoreceptors in the rat; comparison with yohimbine

The antagonist activity of Wy 26703 at vascular postjunctional alpha-adrenoreceptors was quantified against the methoxamine and B-HT 920-induced increase in diastolic pressure in pithed rats. For Wy 26703 pA2-values (= -log dose antagonist evoking a 2-fold shift for the agonist dose-response curve) of 4.96 and 6.43 are found, respectively, whereas for yohimbine values of 5.72 and 6.83 have been reported. The blocking potencies of Wy 26703 and yohimbine have been compared at cardiac prejunctional alpha 2- adrenoreceptors in rats. pA2-values of 6.84 and 6.97, respectively, resulted for the antagonism against the B-HT 920-induced inhibition of stimulation-induced tachycardia. At central alpha-binding sites Wy 26703 and yohimbine were compared for their ability to displace [3H]-prazosin, [3H]-yohimbine and [3H]-clonidine from their specific binding sites in rat brain homogenates. For both compounds binding data indicated a preferential affinity for cental alpha 2- over central alpha 1-binding sites. Wy 26703 exhibited a greater selectivity for cental alpha 2- as compared with central alpha 2-sites than did yohimbine. It is concluded that Wy 26703 behaves as a potent alpha 2-adrenoreceptor blocking agent, that is more selective than yohimbine for postjunctional and central alpha 2-adrenoreceptors as compared with alpha 1-adrenoreceptors. At cardiac prejunctional alpha 2-adrenoreceptors both blocking drugs appeared to be equipotent.

Calcium influx-dependent and -independent alpha 1-adrenoceptor-mediated processes of vasoconstriction in vivo do not operate via different alpha 1-adrenoceptor subtypes

In pithed rats, the selective alpha 1-adrenoceptor agonists St 587 and cirazoline show preponderant calcium influx-dependent and -independent vasoconstriction, respectively. By using these agonists, selective (competitive) antagonists for either process of vasoconstriction were sought. For this purpose, antagonism was analyzed for eight structurally different antagonists (prazosin, BE 2254, AR-C239, R 28935, corynanthine, phentolamine, sulpiride, and chlorpromazine) opposing the pressor responses evoked by cirazoline and St 587. Where pA2 values (-log dose antagonist evoking a twofold shift for the agonist dose-response curve) could be calculated, no significantly different pA2 values against either agonist resulted. However, with respect to the slopes of the Schild plots, deviations from unity were found for prazosin, R 28935, AR-C239, sulpiride, and chlorpromazine, but not uniformly against both agonists. Following treatment with phenoxybenzamine (PB) (30 micrograms/kg) and nifedipine (1 mg/kg), which produced calcium influx-sensitive and -insensitive vasoconstriction to cirazoline, respectively, Schild plots were constructed for BE 2254, prazosin, and chlorpromazine. Using cirazoline as an agonist, unity slopes were now obtained for prazosin and chlorpromazine. The Schild plots of BE 2254 versus cirazoline after PB or nifedipine administration, however, exhibited a slope deviating from unity. For prazosin and chlorpromazine, identical pA2 values still resulted against both processes of vasoconstriction to cirazoline. The results are compatible with the view that alpha 1-adrenoceptors mediating calcium influx-dependent and -independent vasoconstriction in vivo are not distinctly different entities, but are separate recognition sites of the same receptor.