Antagonism of the effects of 5-hydroxytryptamine on the rabbit isolated vagus nerve by BRL 43694 and metoclopramide

Summary Depolarization and reduction in the C fibre compound action potential (C spike) in response to 5-HT were recorded simultaneously from rabbit isolated vagus nerve. 5-HT (0.1–100 mol/l) was applied cumulatively and EC₅₀ and IC₅₀ values measured from individual concentration-response curves. Blockade of 5-HT responses by the 3-indazole carboxamide, BRL 43694, was investigated and compared with the blocking action of metoclopramide. BRL 43694 was a selective antagonist of 5-HT responses. A concentration of 10 nmol/l BRL 43694, which nearly abolished the depolarization and reduction of the C spike evoked by 5-HT (100 mol/l), had no effect on similar responses evoked by DMPP (100 mol/l) or GABA (100 mol/l). Blockade of 5-HT responses by BRL 43694 (0.3 nmol/l) was slow in onset, a plateau blockade occurring after equilibrium of tissue with antagonist for 2 to 3 h. Metoclopramide induced a blockade of rapid onset. The maximal blockade was apparent within 30 min of application. Full recovery in the responsiveness of the tissue to 5-HT was observed within 30 min of washing out metoclopramide. BRL 43694 at concentrations of 0.3, 1, 3 and 10 nmol/l caused a progressive rightward shift of the concentration-response curves to 5-HT. At the highest concentration of antagonist, there was some depression of the maximal 5-HT response. The apparent pA₂ estimated from the Schild equation was 10.03 ± 0.09 (mean ± SEM, n = 20) against 5-HT depolarization and 10.31 ± 0.1 against C spike reduction. Schild plots had slopes not significantly different from 1.0. The slopes and extrapolated pA₂ fitted by linear regression were 0.91 (0.58 – 1.24) and pA₂ 10.16 (9.74–10.58; mean and 95% confidence levels) for the depolarizations. For reduction in C spikes the slope was 0.74 (0.39–1.08) with a pA₂ of 10.86 (10.24–11.49). There was no apparent use-dependent element to the blockade by BRL 43694. Blockade of 5-HT depolarization or C spike reduction by BRL 43694 (0.3 nmol/l) was not significantly different on repeated testing in the presence of the antagonist or without testing of 5-HT until 3 h incubation had elapsed. Metoclopramide at concentrations of 0.3, 1, 3, or 10 mmol/l progressively shifted concentration-response curves to the right. However, the response maximum, especially that for depolarization, was enhanced in the presence of the antagonist. The apparent pA₂ values from the Schilde equation were 7.04 ± 0.04 (n = 20) against 5-HT depolarization and 7.13 ± 0.06 (n = 16) against C spike reduction. Schild plots had slopes significantly less than unity. The lines fitted to the relationship gave pA₂ values of 7.41 (7.25–7.57) with a slope of 0.79 (0.69–0.9) against depolarization and 7.63 (7.28–7.97) with a slope of 0.74 (0.54–0.93) against C spike reduction. Metoclopramide at concentrations above 30 mol/l directly reduced C spike amplitude; the IC₅₀ for the local anaesthetic action was 158 ± 40 mol/l (mean ± SEM). It is concluded that BRL 43694 is a potent and selective antagonist of 5-HT₃ receptors on the rabbit vagus nerve. At concentrations below 10 nmol/l, BRL 43694 appeared to behave as a competitive antagonist while at 10 nmol/l the antagonism was unsurmountable, suggesting a pseudo-irreversible antagonism due to slow dissociation of antagonist from the receptor. Although metoclopramide behaved as a surmountable antagonist, the low slope of the Schild plots and the increase in maximal response amplitude in the presence of the antagonist are unexplained features of its blocking action.Send offprint requests to D. I. Wallis at the above address     

Effects of (+)- and (±)-sotalol on repolarizing outward currents and pacemaker current in sheep cardiac Purkinje fibres

Summary This study was aimed to differentiate the action of (+)- and (±)-sotalol (10–1000 mol/l) on membrane currents which are active during the repolarization of cardiac action potentials Effects where studied in shortened sheep cardiac Purkinje fibres with the two-microelectrode voltage-clamp technique Action potentials were activated at a frequency of 0.25 Hz and membrane currents at 0.03 Hz or 0.05 Hz in most experiments.Out of the currents investigated the transient outward current (i_to) reacted most sensitively to (+)- and (±)-sotalol. I_to-amplitude was decreased on the average to 77% of reference at 10 mol/l and to 53% at 1000 mol/l (+)- or (±)-sotalol. The maximally available ito-current was decreased but the voltage-dependent control of inactivation was left nearly unchanged. The initial inwardly rectifying current (i_Ki), which propels the last repolarization phase of the action potential and controls resting potential to a large extent was reduced on the average to 93% of reference at 10 mol/l and to 62% at 1000 mol/l (+)- or (±)-sotalol. Time-dependent (delayed) outward current (i_K) was on the average not affected by (+)- or (±)-sotalol up to 100 mol/l and was decreased to 84% of reference current under the influence of 1000 mol/l. An initial outward current, which is activated at positive membrane potentials (i_inst) was not clearly affected by (+)- or (±)-sotalol at concentrations up to 1000 mol/l Pacemaker current (i_f) was not influenced by the drugs up to 100 mol/l. Only at 1000 mol/l was the amount of available i_f-current decreased to 79% of reference. (The potential-dependent control of activation was not affected) Time constants of time-dependent currents i_to, i_K and i_f did not change in concentrations up to 1000 mol/l of the drug.Action potential duration increased at (+)- or (±)-sotalol concentrations 10 mol/l and maximal prolongation was achieved at concentrations of 100–300 mol/l Resting potential remained nearly unchanged at these concentrations, but the membranes depolarized at 1000 mol/l. According to our data action potential prolongation in sheep Purkinje fibres under the influence of (+)- and (±)-sotalol correlates to the drug-induced block to i_to-current and inwardly rectifying i_K1-current.Supported by the Deutsche Forschungsgemeinschaft SFB 242, C 1 Send offprint requests to U. Borchard at the above address     

The depolarizing action of 5-hydroxytryptamine on rabbit isolated preganglionic cervical sympathetic nerves

Summary This study describes a depolarizing action of 5-hydroxytryptamine (5-HT) on rabbit isolated preganglionic cervical sympathetic nerves using an extracellular recording technique. From cumulative concentration-response curves for 5-HT (1 mol/1-1 mmol/1), the mean maximal depolarization was shown to be 277 ± 32 V and EC₅₀ was 9.4 mol/l(6.5–13.6 mol/l, geometric mean, 95% confidence limits, n = 42). The responses to 5-HT displayed marked tachyphylaxis. When cumulative concentration-response curves to 5-HT and 2-methyl-5-HT were determined in the same preparations (n = 4), the mean maximal response to 5-HT was 519 ± 167 V, EC₅₀ 32.2 mol/l (8.8–118 mol/l) and the mean maximal response to 2-methyl-5-HT was 317 ± 63 V, EC₅₀ 35.1 mol/l (12.9–95.5 mol/l, geometric means, 95 % confidence limits). The action of selective 5-HT antagonists was tested on repeated cumulative concentration-response curves to 5-HT. Neither methiothepin (0.1–1 mol/l, _n = 3) nor ketanserin (0.1–1 mol/l, n = 3) had an action on 5-HT responses. The selective 5-HT₃ antagonists MDL 72222, ICS 205-930 and SDZ 206–830 were all potent antagonists of the 5-HT depolarizations. The action of these antagonists was quantified by determining the apparent pA₂ from the dose ratios and a Schild plot. For MDL 72222 (1 nmol/1-0.1 mol/l), the apparent pA₂ was 9.1 ± 0.1 (n = 12), Schild plot: 9.2; for ICS 205–930 (0.1 nmol/l–3 nmol/1), the apparent pA₂ was 10.4 ± 0.1 (n = 11), Schild plot 10.3, and for SDZ 206–830 (0.03 nmol/l-1 nmol/1), the apparent pA₂ was 11.2 ± 0.1 (n = 12), Schild plot 11.2. 5-HT depolarizations were unaffected by hexamethonium (0.5 mmol/1). 5-HT depolarizations were reduced by superfusion with both Na-free (42 ± 8% of controls, n = 4) and Na/Ca-free media (35 ± 7% of controls, n = 4). It is concluded that 5-HT depolarizations of rabbit preganglionic cervical sympathetic nerve are mediated by 5-HT₃ receptors. The data with selective 5-HT₃ receptor antagonists suggest that the receptor profile may be more like that for the 5-HT₃ receptor on the terminals of sympathetic nerves than that for the 5-HT₃ receptor on the soma of superior cervical ganglion cells or on vagal afferent neurones. Send offprint requests to D. I. Wallis at the above address     

Mechanisms of the contractile effects of flosequinoxan

In guinea-pig papillary muscles the positive inotropic effect of flosequinoxan (BTS) starting at 100 mol/1 amounted to 287.6 ± 34.2% at 300 mol/l without any effects on time to peak tension (103.9 ± 2%) and relaxation time (107.1 ± 6.7% of predrug value, respectively). 10 mol/l carbachol attenuated the positive inotropic effect of 300 mol/l to 166.5 ± 11.6% (n = 10). The phosphorylation state of the inhibitory subunit of troponin (TnI) and phospholamban(PLB) in [³²P]-labeled guinea-pig ventricular myocytes was increased starting at 100 mol/l amounting to 142.5 ± 12.6% and 130.9 ± 2.2% at 300 mol/l, respectively (n = 5). Furthermore, BTS (300 mol/l) decreased phosphorylase phosphatase activity by 23.1%. It is concluded that the contractile effects of BTS are accompanied by enhanced phosphorylation of regulatory proteins which could in part be due to inhibition of phosphorylase phosphatase activity.     

Clinical effects and plasma levels of Δ9-Tetrahydrocannabinol (Δ9-THC) in heavy and light users of cannabis

⁹-Tetrahydrocannabinol (⁹-THC) was administered in a crossover design by smoking and IV injection to groups of heavy and light users of marihuana. Plasma concentrations of ⁹-THC were similar for the groups after IV injection of 5.0 mg ⁹-THC, but the AUC_{0–240 min} showed a trend towards lower values for the heavy user group. To achieve a maximum desired high, both groups smoked similar amounts (about 13 mg) of ⁹-THC. Heavy users tended to have higher plasma levels than light users. The systemic availability of smoked ⁹-THC was significantly higher for the heavy users (heavy users 23±16% vs 10±7% for light users). These results also indicate that heavy cannabis users smoke more efficiently than casual smokers.Both light and heavy users showed more clinical effect following IV administration than after smoking. The response of the heavy users, both with respect to effect on heart and high, was quite comparable to that of light users.The present study does not suggest that tolerance readily develops in heavy users.     

Klinisch-neuroleptische Prüfungen am Beispiel der Butyrophenonderivate Benzperidol und Spiroperidol

Summary The terms Neuroleptic Threshold, Neuroleptic Potency, Neuroleptic-Therapeutic Range and Disposition to Neuroleptic Action, developed by Haase and coworkers as a result of clinical-experimental investigations over the last ten years, are described as well as the clinically more important results obtained by means of a fine motor test, according to Haase, which is described in detail with respect to its use and evaluation.Using the fine motor test, the neuroleptic action of the extremely potent butyrophenone derivatives benperidol and spiroperidol is described as observed on two test groups of female schizophrenic first admission cases (total 60 patients).The average clinical-neuroleptic threshold dosage for benperidol was found to be 0.62 mg daily i.m. (s±0.39), for spiroperidol 0.53 mg daily i.m. (s±0.31). The coefficient of equivalence based on haloperidol is, for benzperidol 8.32 (s±4.67), for spiroperidol 12.25 (s±1.69). The neuroleptic potency based on chlorpromazine=1 is for benperidol =350 and for spiroperidol appx. 400.The results confirm once more that the clinical-experimental investigation of fine motor activity (handwriting) makes it possible to investigate neuroleptic action as an exactly measurable, repeatable and comparable Basic Function as proposed by Panse.

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Herrn Prof. Dr. Fr. Panse ergebenst zum 65. Geburtstag gewidme.     

Neuronally released (−)-noradrenaline relaxes smooth muscle of calf trachea mainly through β1-adrenoceptors : comparison with (−)-adrenaline and relation to adenylate cyclase stimulation

Summary The nature of the receptors that mediate the relaxation of smooth muscle by field stimulation, (–)-noradrenaline and (–)-adrenaline was investigated in calf tracheal smooth muscle. The relation between relaxation, stimulation of the adenylate cyclase and density of -adrenoceptor subtypes was studied with the help of antagonists of ₁- and ₂-adrenoceptors. The question of the existence of catecholamine-containing nerves was also investigated. (1) Nerves with varicosities exhibiting catecholaminergic fluorescence were observed between bundles of smooth muscle cells. (2) Consistent with the existence of adrenergic nerves (–)-noradrenaline was also found. The content of (–)-noradrenaline (1 g · g^–1 w.w.) was the same in smooth muscle strips from the sublaryngeal region and from the region close to the bifurcation of the calf trachea. (–)-Adrenaline was not detected. (3) Smooth muscle relaxation by low (–)-noradrenaline concentration (0.6–2 nmol/l) was mediated through ₁-adrenoceptors. Low concentrations of (–)-adrenaline (0.06–1 nmol/l) relaxed through ₂-adrenoceptors. High concentrations of (–)-noradrenaline and (–)adrenaline also caused relaxation through ₂- and ₁-adrenoceptors respectively. (4) Field stimulation caused relaxation which was half maximal at 0.2–0.8 Hz. Blockade of ₁-adrenoceptors strongly attenuated the relaxant response to field stimulation and shifted the frequency-relaxation curves to 4 times higher frequencies. These results are consistent with a ₁-adrenoceptor-mediated relaxation caused by (–)-noradrenaline released from sympathetic nerve endings at low stimulation frequencies. (5) Blockade of ₂-adrenoceptors failed to reduce smooth muscle relaxation caused by field stimulation at low stimulation frequencies (0.1–1 Hz). However, after ₁-adrenoceptor blockade, additional blockade of ₂-adrenoceptors reduced the relaxant effects observed at high frequencies (2–400 Hz). The results suggest that high concentrations of endogenous (–)-noradrenaline cause relaxation through ₂-adrenoceptors. (6) Binding experiments with ³H-(–)-bupranolol and ³H-ICI 118,551 revealed between 10,000 and 20,000 -adrenoceptors per smooth muscle cell of which 3/4 were ₂ and 1/4 ₁. The equilibrium dissociation constant of (–)-adrenaline for both ₁- and ₂-adrenoceptors and of (–)-noradrenaline for ₁-adrenoceptors was 1 mol/l. The affinity of (–)noradrenaline for ₂-adrenoceptors was 10 to 20 times lower than for ₁-adrenoceptors. (7) The adenylate cyclase of smooth muscle cells was stimulated more through ₂-adrenoceptors by both (–)-noradrenaline (77%) and adrenaline (83%) than through ₁-adrenoceptors. Half maximum stimulation of the cyclase was observed at 2 to 4 times lower catecholamine concentrations than the concentrations that half saturate ₁- or ₂-adrenoceptors. (8) Both the low affinity and low cyclase stimulating potency of the catecholamines suggest considerable amplification of the receptor signals. Half maximum relaxation of tracheal muscle by (–)-noradrenaline is associated with the activation of less than 50 ₁-adrenoceptors per cell producing less than 250 molecules cyclic AMP per second.     

Study on didanosine concentrations in cerebrospinal fluid Implications for the treatment and prevention of AIDS dementia complex

It has been hypothesized that didanosine has a low efficacy in the prevention and treatment of patients with the dementia complex of acquired immunodeficiency syndrome (AIDS) because ...the drug has not been detected in the cerebrospinal fluid. We investigated didanosine concentrations in cerebrospinal fluid (CSF) and plasma of four patients with AIDS who were using didanosine chronically. Didanosine levels, 4 h after the last drug administration, averaged 0.16 (±0.03) mol/l in CSF and 0.70 (±0.27) mol/l in plasma. When compared with historical data from patients using zidovudine, didanosine concentrations in CSF appeared to be approximately half (on a molar base) those of zidovudine concentrations in the CSF. Whether this difference in CSF levels is the explanation for the presumed lower efficacy of didanosine in the prevention and treatment of AIDS dementia complex remains to be proven. However, it is clear from this study, in contrast with earlier suggestions, that didanosine is able to pass the blood-CSF barrier in human immunodeficiency virus-infected individuals.     

Isoprenaline-induced increase in mRNA levels of inhibitory G-protein α-subunits in rat heart

Summary Long-term -adrenergic stimulation has been shown to desensitize the -adrenoceptor/adenylyl cyclase signalling pathway at both the receptor and the G-protein level. To further elucidate the cellular mechanism of G-protein regulation we investigated the influence of prolonged infusion of isoprenaline (2.4 mg/kg·d) on myocardial mRNA levels of different G-protein -subunits in rats. For comparison rats were treated with triiodothyronine (T₃; 0.5 mg/kg·d) which induces cardiac hypertrophy like isoprenaline but has different effects on the adenylyl cyclase system. Isoprenaline- and T₃-treated animals developed an increase in heart/body weight ratio of 41±3% and 27±4%, respectively (P<0.05). Isoprenaline increased myocardial total RNA concentration by 39±6% (P<0.05). Hybridization with ³²P-labeled rat cDNAs demonstrated an expression rank order of G_s-mRNA>G_i-2-mRNA>G_i–3-mRNA and no detectable expression of G_i–1-mRNA in rat myocardium. mRNA levels of G_s G_i–2 and G_i–3 were 36.9±1.28, 10.7±1.07 and 3.7±0.19 pg/g total RNA, respectively. Isoprenaline increased G_i–2 ^– and G_i–3-mRNA concentrations per g total RNA by 49±18% and 27±710, respectively (P<0.05). This effect was abolished by simultaneously administered propranolol (9.9 mg/kg·d), indicating a,-adrenoceptor-mediated mechanism. In contrast, T₃-induced cardiac hypertrophy was not accompanied by changes in G_i-mRNA expression. G_sa-mRNA levels were unaffected by either treatment.In conclusion, long-term stimulation with isoprenaline in vivo induces a -adrenoceptor-mediated increase in myocardial G_i–2 ^– and G_i–3-mRNA without affecting G_s-mRNA. These results suggest that similar increases in myocardial G_i–2-mRNA in end-stage human heart failure may be at least partly explained by increased -adrenergic stimulation due to increased sympathetic activity.Parts of this work were presented at the wintermeeting of the Deutsche Gesellschaft fur Pharmakologie und Toxikologie in Hannover, 1990 (Eschenhagen et al.), Naunyn-Schmiedebergs Arch Pharmacol 342 (Suppl):R8. The work was supported by the Deutsche Forschungsgemcinschaft Send offprint requests to: T. Eschenhagen at the above address     

Pre-abstinence smoke intake and smoking motivation as predictors of severity of cigarette withdrawal symptoms

Twenty-nine cigarette smokers completed a smoking motivation questionnaire and had expired-air carbon monoxide (CO) and plasma nicotine concentrations measured prior to abstaining from smoking for 24 h. Before and after the abstinence period, the subjects rated mood and physical symptoms known to be affected by cigarette abstinence (e.g. irritability, restlessness). Scores on the dependent smoking subscale of the smoking motivation questionnaire correlated significantly with overall withdrawal severity, craving, and increased irritability. Indulgent smoking scores correlated positively with increased hunger. Pre-abstinence plasma nicotine concentration significantly pedicted craving, hunger, restlessness, inability to concentrate and overall withdrawal severity, while expired-air CO predicted craving and restlessness only. Usual daily cigarette consumption did not significantly predict any withdrawal effects. The data indicate that pre-abstinence measures of smoking motivation and smoke intake may provide a guide to withdrawal severity on smoking cessation and that smokers with a high pre-abstinence nicotine intake experience the greatest discomfort.     

Target sites for the inhibition of prostacyclin effect in guinea-pig ileum

Summary In the guinea-pig terminal ileum a maximally effective concentration of prostacyclin (PGI₂) (1 ol/l) induced contractions that were partially resistant to tetrodotoxin (TTX) 0.1 mol/l, to low temperature (20°C) and to atropine (30 nmol/l). Half maximum contractions evoked by PGI₂ (20 nmol/l) were abolished by TTX and by low temperature, which did not modify the response to exogenous acetylcholine (ACh), as well as by atropine. Procaine (5–500 ol/l) caused a concentration-dependent inhibition of contractions induced by PGI₂ (20 nmol/l and 1 mol/l) and by equieffective concentrations of ACh (20 nmol/l and 0.4 ol/l, respectively). The order of magnitude for this inhibition was ACh 20 nmol/l = PGI₂ 20 nmol/l > PGI₂1 mol/l > ACh 0.4 mol/l. In preparations exposed to TTX or to low temperature procaine (50 mol/l) did not affect the residual response to PGI₂ (1 mol/l). Quercetin (1 and 5 ol/l) inhibited the effect of PGI₂ and, at higher concentrations, it also caused partial depression of the responses to ACh. Quercetin did not alter TTX-resistant and low temperature-resistant contractions induced by PGI₂ 1 mol/l. Carbonyl cyanide-trifluoromethoxyphenyl hydrazone (FCCP) (0.1–1 ol/l) reduced the effect of PGI₂ and of ACh to approximately the same extent and inhibited the residual response to PGI₂ 1 mol/l in preparations treated with TTX or expressed to low temperature. The present results show that PGI₂, besides acting on cholinergic neurons, also exerts a direct effect on smooth muscle cells and FCCP can be used to block this effect. In contrast procaine and quercetin selectively inhibit the ACh-mediated component of PGI₂ action. Send offprint requests to R. M. Gaion     

Evidence against a causal relationship between increase in c-AMP and induction of tyrosine hydroxylase in the rat adrenal medulla

Summary It was the purpose of the present experiments to establish whether the reserpine-mediated changes in adrenomedullary c-AMP result from - or -adrenergic activation of adenylate cyclase by catecholamines liberated from adrenal chromaffin cells and whether a causal relationship exists between these changes and subsequent induction of tyrosine hydroxylase (TH).The reserpine-mediated increase in c-AMP was blocked by neither - nor -adrenergic blocking agents. However, propranolol abolished the increase in c-AMP by a mechanism which is not related to the -blocking properties of this drug. Although propranolol abolished the reserpine-mediated increase in c-AMP it did not interfere with the subsequent TH induction. Moreover, administration of aminophylline together with reserpine produced a larger and more prolonged increase in c-AMP in denervated adrenals than reserpine alone in intact glands. Denervation prevented TH induction in spite of the more extensive increase in c-AMP in the adrenal medulla after the combined treatment. It is concluded that there is no causal relationship between the overall increase in c-AMP in the adrenal medulla and the subsequent TH induction. However, the possibility that a small pool of c-AMP which is overshadowed by the non-related overall changes may be involved in trans-synaptic TH induction cannot be excluded.     

β-endorphin-sensitive opioid receptors in the rat tail artery

Summary Isolated tail arteries of rats were perfused and field-stimulated every 2 min with 2 pulses at 1 Hz. Different opioid peptides depressed the contractile responses to stimulation; their concentration-response curves showed a maximum at about 40% inhibition. The rank order of potency of the peptides was -endorphin (IC₅₀ = 97 nmol/1) BAM-22P > FK-33824 > DAGO > [d-Ala²,d-Leu⁵]-enkephalin metorphamide > dynorphin A-(1-13) [Met⁵]enkephalin. All these substances have in common a certain activity at opioid -receptors, although the enkephalins are preferential -, and the dynorphins preferential -agonists. However, the selective -agonist [d-Pen²,l-Pen⁵]enkephalin was ineffective at up to 10 mol/l, and the -agonists ethylketocyclazocine and U-50488 acted only at concentrations higher than 3 mol/l. Whereas the effects of -endorphin, DAGO and [d-Ala²,d-Leu⁵]enkephalin could be reduced by the -preferential antagonist naloxone, the effects of ethylketocyclazocine and U-50488 were not changed. The -selective antagonist ICI 174864 did not influence the action of [d-Ala²,d-Leu⁵]enkephalin. Naloxone in a concentration (1 mol/l) which nearly abolished the effect of DAGO 3 mol/l, slightly enhanced responses to stimulation. Neither -endorphin nor DAGO influenced vasoconstriction evoked by the application of noradrenaline or adenosine triphosphate; U-50488 reduced it. In arteries preincubated with [³H]noradrenaline DAGO depressed, whereas naloxone enhanced the tritium overflow and vasoconstriction evoked by field stimulation (0.4 Hz, 24 pulses every 14 min). In addition, naloxone antagonized the effect of DAGO. We suggest that the axon terminals of postganglionic sympathetic neurones in the rat tail artery possess -endorphin-sensitive opioid receptors of the -type. The activation of these receptors by exogenous or endogenous opioids inhibits the release of the neuroeffector transmitter.This work was supported by the Deutsche Forschungsgemeinschaft (SFB 325) Send offprint requests to P. Illes at the above address     

Effects of dichlorvos (DDVP) inhalation on the activity of acetylcholinesterase in the bronchial tissue of rats

The experiments presented here deal with the effects of the inhalation of dichlorvos [dimethyl-(2,2 dichlorvinyl)-phosphate, DDVP] vapor on acetyl-cholinesterase (ACHE) activity in rat bronchial tissue. Exposure to DDVP concentrations of 0.8 and 1.8 g/l for 3 days reduced ACHE activity in the bronchial tissue (62.8±0.8 and 51.6±1.6% of the control), but did not elicit any changes in blood ACHE activity (101±4.5% of the control each). Higher concentrations (4.3 g/l) induced a decline in ACHE activity also in the blood (38.2±1.1% of the control). In the histochemical preparations used to demonstrate CHE activity in bronchial tissue (thiolacetic acid method), a staining of the bronchial glands and smooth muscles characteristic of the enzyme activity was strongly reduced after exposure of the animals to even the lowest dose applied (0.2 g/l). The question of whether localized inhibition of ACHE in the bronchial tissue might cause increases in airway resistance due to activation of a broncho-bronchial reflex is discussed. This efferent cholinergic mechanism has been found to be at least partly responsible for maintenance of bronchospasm and hypersecretion in chronic obstructive deseases of the respiratory system.     

β 1- andβ 2-adrenoceptor binding and functional response in right and left atria of rat heart

Summary The properties of ₁- and ₂-adrenoceptors in right and left atria of rat heart, and their roles in mediating chronotropic and inotropic responses to-adrenoceptor agonists were examined. [¹²⁵I](-)-pindolol (¹²⁵IPIN) bound saturably and specifically to a single class of high affinity sites in homogenates of both right and left atria. Thek ₁'s for association in right and left atria were 6.5×10⁹ l/mol-min and 2.3×10⁹ l/mol-min respectively, while thek _–1's for dissociation were 0.20 min^–1 and 0.17 min^–1. The kinetically determinedK _D's were 75 pmol/l in right and 30 pmol/l in left atria and were similar to the equilibriumK _D's determined from Scatchard analysis of saturation isotherms of specific¹²⁵IPIN binding. Inhibition of¹²⁵IPIN binding by-adrenoceptor antagonists was stereoselective and the order of potency was timolol > 1-propranolol > d-propranolol > sotalol. Inhibition by ₁- and ₂-adrenoceptor subtype selective antagonists yielded flat displacement curves with low Hill coefficients. Nonlinear regression analysis of displacement by ₁-selective (practolol, atenolol and metoprolol) and ₂-selective (ICI 118,551) antagonists gave estimates of the proportion of ₁- and ₂-adrenoceptors present in rat atria. Right atria contained 67±4.2% ₂-adrenoceptors and 33±4.2% ₂-adrenoceptor, while left atria contained 67±2.8% ₁- and 33±2.8% ₂-adrenoceptors. Increases in the rate of spontaneously beating right atria and the force of electrically driven left atria caused by-adrenoceptor agonists were also measured. pA₂ values for non-subtype selective-adrenoceptor antagonists in inhibiting isoprenaline-induced increases in rate and force were highly correlated withK _D values determined for specific¹²⁵IPIN binding. pA₂ values for ₁- and ₂-selective antagonists in inhibiting isoprenaline-induced increases in rate and force correlated well with the pK _D values of these drugs in binding to ₁-adrenoceptors, but not with the pK _D values in binding to ₂-adrenoceptors. Dose-response curves for stimulation of both rate and force by the ₂-selective agonists procaterol and zinterol were shifted to a much greater extent by selective blockade of ₁-adrenoceptors with metoprolol than by selective blockade of ₂-adrenoceptors with ICI 118,551, suggesting that these compounds caused their effects by activating ₁-adrenoceptors. These results suggest that ₁- and ₂-adrenoceptors coexist in both left and right atria of rat heart in approximately a 21 ratio, however only ₁-adrenoceptors mediate the chronotropic and inotropic effects of-adrenoceptor agonists.Supported by a grant from the American Heart Association — Georgia Affiliate     

Effect of epinine on tension of human renal arteries

Background: The present study aimed to characterize the effects of epinine, the active metabolite of ibopamine on tension development in human renal arteries.Methods and results: Experiments were performed on isolated human renal arteries rings obtained during surgery due to kidney tumors (n = 12). Epinine concentration-dependently relaxed isolated precontracted (PGF₂) human renal artery rings (P < 0.05) in the presence of phentolamine, as effectively (epinine – 30 +/– 4 mN, dopamine – 31 +/– 5 mN) and with the same potency as dopamine (epinine EC₅₀ 0.7 mol/l (0.4–1.2 mol/l), dopamine 0.5 mol/l (0.2–1.7 mol/l)). This effect was antagonized by the specific D₁-receptor-antagonist SCH 23390. Effective -adrenoceptor antagonistic concentrations of propranolol did not affect epinine-induced vasorelaxation. In the absence of -and -adrenoceptor-antagonists the potency of epinine to contract renal artery rings was significantly higher compared to dopamine indicating a higher affinity of epinine to -adrenoceptors.Conclusion: The present study provides evidence for direct vasodilatory effects of epinine via activation of D₁-receptors on human renal arteries.     

The transport of (+)-amphetamine by the neuronal noradrenaline carrier

Summary PC-12 cells (a clonal line of rat phaeochromocytoma cells) take up noradrenaline by a transport system which is identical with the neuronal amine transport system (uptake₁). The uptake of ³H-noradrenaline into reserpine-pretreated PC-12 cells (monoamine oxidase inhibited) was saturable (K_m=0.6±0.1 mol/l), dependent on sodium and chloride, and competitively inhibited by (+)-amphetamine (K_i=0.18±0.04 mol/l), cocaine (K_i=0.55±0.15 mol/l) and desipramine (K_i=4.3±0.6 nmol/l). The uptake and accumulation of ³H (+)-amphetamine showed characteristics comparable to those of ³H-noradrenaline, since the uptake of ³H (+)-amphetamine (0.1 mol/l) was reduced by omission of sodium or chloride from the incubation medium. The sodium-sensitive component of uptake and accumulation of ³H (+)-amphetamine was fully inhibited by cocaine and desipramine. The IC₅₀ of desipramine for inhibition of the sodium-sensitive component of the 1-min uptake of ³H (+)-amphetamine (20 nmol/l) was about 2 nmol/l, i.e., identical with the K_i for inhibition of uptake of ³H-noradrenaline. At concentrations above 1 mol/l, desipramine additionally caused an inhibition of the sodium-independent permeation of ³H (+)-amphetamine into PC-12 cells.Hence, by using a homogeneous population of cells endowed with uptake₁, it is possible to demonstrate — besides a pronounced lipophilic entry — a carrier-mediated uptake of ³H (+)-amphetamine.Some of the results were communicated to the German Pharmacological Society (Bönisch 1981). This study was supported by the Deutsche Forschungsgemeinschaft (Bo 521)     

Vasopressin stimulates release of β-lipotropin and β-endorphin in conscious rats as measured by radioimmunoassay of unextracted plasma

Summary Using a newly developed radioimmunoassay to determine the -endorphin-like immunoreactivity (-EI) in unextracted plasma, the effect of vasopressin injections on plasma -EI was investigated in conscious rats. Arginine vasopressin caused a dose-dependent increase of plasma -EI from 34.5±7.8 fmol ml^–1 (n=6) in vehicle-treated animals to 205.0±36.1 fmol ml^–1 (n=7) after injection of the highest vasopressin dose employed (486 ng/100 g b.w.). In view of the appreciable cross-reactivity of -lipotropin (-LPH) in the radioimmunoassay used, plasma was extracted and subjected to gel chromatography on a Sephadex G-50 column. On average, about 70% of the -EI co-eluted with human -LPH and about 30% with human -endorphin in plasma extracts obtained from both control and vasopressin-treated rats. No peripheral conversion of human -LPH occurred under the experimental conditions, since after i.v. bolus injection of human -LPH 97% of the -EI comigrated with human -LPH during gel filtration. A similar blood pressure increase to that induced by the vasopressin injections, when elicited by noradrenaline or angiotensin II i.v., was not followed by an elevation of plasma -EI.These data indicate that vasopressin stimulates -lipotropin and -endorphin release into the systemic circulation in vivo.     

5-Hydroxytryptamine (5-HT) contracts the guinea-pig isolated iliac artery via 5-HT1-like and 5-HT2 receptors

Summary The characterization of 5-hydroxytryptamine (5-HT) receptors mediating contractions of the guinea-pig isolated iliac artery was studied when the basal tone was slightly increased by prostaglandin F₂ (PGF₂).In the presence of ketanserin (1 mol/l), 5-HT and several 5-HT receptor agonists induced contractile responses with the rank order of agonist potency: 5-HT = 5-carboxamidotryptamine (5-CT) = lysergol > ergometrine = methylergometrine > RU 24969 5-methoxytryptamine (5-MeOT) > methysergide > sumatriptan > tryptamine. Concentration-effect curves to the ergot alkaloids, lysergol, ergometrine, methylergometrine and methysergide, were biphasic.In the presence of ketanserin (1 mol/l), contractile responses to 5-HT, 5-CT, RU 24969, 5-MeOT, sumatriptan and tryptamine were antagonized by methiothepin (30 nmol/l) and flesinoxan (3 mol/l) with approximate pK_B values of 8.5–9.0 and 6.0–6.3, respectively. The first phase of contraction produced by the ergot alkaloids, lysergol, ergometrine, methylergometrine and methysergide, were blocked by methiothepin (30 nmol/l) and flesinoxan (3 mol/l), respectively, with approximate pK_B values about 8.4–8.7 and 6.2–6.4, respectively. The mechanism underlying the second phase of contraction remains to be established.Maximum responses of the concentration-effect curves to 5-HT (1 nmol/l-1 mol/l) were concentration-dependently depressed by ketanserin (1 nmol/l-1 mol) and spiperone (30 nmol/l-0.3 mol/l) and reached approximately 60% of the 5-HT maximum response in the presence of ketanserin (1 mol/l) and spiperone (0.1 mol/l), respectively. Agonist potency of 5-HT was not affected by the antagonists. 5-HT (1 nmol/l-1 mmol) produced biphasic concentration-effect curves (first phase: 1 nmol/l-1 gmol/l; second phase: 1 mol/l-1 mmol/l) in the presence of ketanserin (100 and 300 nmol/l), spiperone (100 and 300 nmol/l), (R)--methylketanserin (3 mol/l) and (S)--methylketanserin (10 nmol/l). Contractions mediating the first phase of the effects of 5-HT accounted for approximately 60% of the 5-HT maximum response and were resistant to blockade by the antagonists. pK_B values at the receptor mediating the second phase of the effects of 5-HT were 9.2–9.3 for ketanserin, 9.2–9.6 for spiperone, 10.5 for (S)--methylketanserin and 7.2 for (R)--methylketanserin.It is concluded that 5-HT contracts the guinea-pig isolated iliac artery via a mixture of 5-HT₁-like receptors and 5-HT₂ receptors. At low concentrations contractions are mediated via 5-HT₁-like receptors which accounted for approximately 60% of the 5-HT maximum response. At higher concentrations 5-HT-induced contractions are mediated via 5-HT₂ receptors.     

Antihypertensive effect of E-643, a new alpha-adrenergic blocking agent

Summary To determine whether E-643, a new -blocking agent, would reduce the blood pressure, regardless of the posture, a 1 mg dose was given 3 times daily for 7 consecutive days, to 8 male and 7 female inpatients, aged 37–73 years, with essential hypertension. Blood pressure and pulse rate were measured daily in the supine, sitting and standing positions. Before and after the treatment with E-643, plasma levels of noradrenaline, adrenaline, dopamine--hydroxylase, renin and aldosterone were determined, samples being obtained with the subjects recumbent and after standing upright for 60 min. A significant reduction in the systolic and diastolic blood pressures was evident in the supine (172±31/100±12 151±28/89±14 mmHg), sitting (158±22/101±11 138±28/89±15 mmHg) and standing (153±32/103±21 129±31/89±20 mmHg) positions. The reduction in blood pressure remained unchanged throughout the period of administration of E-643. Pulse rate was not affected when the subjects were supine (67±10 69±10 beats/min), but was increased in the sitting (68±10 73±9 beats/min) and standing (73±10 81±11 beats/min) positions. The increased pulse rate tended to decline during continued administration of E-643. Treatment with E-643 produced no significant change in plasma levels of adrenaline, noradrenaline, dopamine--hydroxylase, renin and aldosterone. The antihypertensive effect of treatment was more prominent in the patients with higher levels of plasma catecholamines and dopamine--hydroxylase, and was less prominent in those with higher plasma renin and aldosterone. Two patients had temporary bouts of dizziness and visual disturbances, but there were no subjective complaints during treatment.