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.     

Comparative behavioral characterization of the neuroactive steroids 3α-OH,5α-pregnan-20-one and 3α-OH,5β-pregnan-20-one in rodents

Pregnan steroids have been shown to possess anesthetic, hypnotic, anticonvulsant and anxiolytic properties. In this study, two endogenous neuroactive steroid isomers, 3-hydroxy-5-pregnan-20-one (3,5-P) and 3-hydroxy-5-pregnan-20-one 3,5-P), were studied for differences in their pharmacological properties using behavioral assays. 3,5-P and 3,5-P were similar in their potencies and efficacies in blocking pentylenetetrazol-induced seizures in mice (ED₅₀: 3,5-P=2.8 mg/kg and 3,5-P=3.0 mg/kg). Similarly, both neuroactive steroids produced roto-rod deficits within the same range of potency (TD₅₀:3,5-P=18.8 mg/kg and 3,5-P=21.2 mg/kg). However, in animal models of anxiety, subtle differences were observed between the two isomers. In both the light/dark transition test and elevated plus-maze, 3,5-P was more efficacious than 3,5-P, though both compounds had similar potencies. In the Geller-Seifter test, 3,5-P was more potent and efficacious than 3,5-P. Neither compound had significant effects on unpunished responding within the dose range tested. Both compounds produced similar biphasic curves in the locomotor test. All together, the data indicate that 3,5-P and 3,5-P have similar anticonvulsant activity, but the 5-isomer possesses more potent and efficacious anxiolytic properties than the 5-isomer.     

Enzyme kinetics of zearalenone biotransformation: pH and cofactor effects

The aim of the present study was to investigate the hepatic biotransformation of the mycotoxin zearalenone (ZEA) in vitro using subcellular fractions of pig livers. The dependencies of the enzymatic reactions involved on the enzyme velocity, on the cofactor and on pH were analysed in both the microsomal fraction and the post-mitochondrial cell fraction. Finally, the inhibitory effects of various endogenous substrates on the enzymes involved (3- and 3-hydroxysteroid dehydrogenase) were examined. Significant differences were observed between the individual subcellular fractions in terms of prevailing metabolites and absolute amounts of the metabolites produced. Moreover, this study also demonstrated that the reactions for both subcellular fractions of porcine liver are dependent on the cofactor, as -zearalenol (-ZOL) formation increased in the presence of NADPH, whereas -zearalenol (-ZOL) production only increased in the presence of NADH (P<0.001). The optimal pH for -ZOL production was pH 5.6 and that for -ZOL formation pH 7.4. Subsequent inhibition studies showed significant inhibitory effects for 5-androstanedione>androstanedione>pregnenolone on -ZOL formation, whereas -ZOL production was only inhibited by pregnenolone. Finally, the contributions of 3- and 3-hydroxysteroid dehydrogenase during the bioconversion of ZEA are discussed in the context of these experiments.     

Prevention of heterotopic ossification after total hip replacement with NSAIDs

Introduction: non steroidal antiinflammatory drugs ((NSAIDs) and prophylactic radiotherapy can prevent ectopic bone formation around the hip after total hip arthroplasty. Methods: We retrieved from Medline, Embase and the Cochrane Register (clinical)) trials and other relevant literature on the prevention of heterotopic ossification (HO) from 19902002 for further review.Results: Review of these clinical trials shows that HO is effectively prevented by a postoperative NSAID treatment with indomethacin for at least seven days. The best evidence is available for indomethacin, although naproxen, diclofenac and ibuprofen are also well documented. Short term use of ibuprofen is not effective. If NSAIDs are contraindicated, preoperative or postoperative radiotherapy is a very effective therapeutic option to prevent HO. Discussion and conclusion: Because of the potential of serious gastrointestinal side effects of NSAIDs and their interaction with anticoagulant drugs, rofecoxib and other COX2 specific NSAIDs may be a safer option for the treatment of HO. However, randomised controlled studies are needed to confirm the results of the rofecoxib study.     

Enhancement of Solubility and Bioavailability of β-Lapachone Using Cyclodextrin Inclusion Complexes

Purpose. To explore the use of cyclodextrins (CD) to form inclusion complexes with -lapachone (-lap) to overcome solubility and bioavailability problems previously noted with this drug. Methods. Inclusion complexes between -lap and four cyclodextrins (-, -, -, and HP-CD) in aqueous solution were investigated by phase solubility studies, fluorescence, and ¹H-NMR spectroscopy. Biologic activity and bioavailability of -lap inclusion complexes were investigated by in vitro cytotoxicity studies with MCF-7 cells and by in vivo lethality studies with C57Blk/6 mice (18-20 g). Results. Phase solubility studies showed that -lap solubility increased in a linear fashion as a function of -, -, or HP-CD concentrations but not -CD. Maximum solubility of -lap was achieved at 16.0 mg/ml or 66.0 mM with HP-CD. Fluorescence and ¹H-NMR spectroscopy proved the formation of 1:1 inclusion complexes between -CD and HP-CD with -lap. Cytotoxicity assays with MCF-7 cells showed similar biologic activities of -lap in -CD or HP-CD inclusion complexes (TD₅₀ = 2.1 M). Animal studies in mice showed that the LD₅₀ value of -lap in an HP-CD inclusion complex is between 50 and 60 mg/kg. Conclusions. Complexation of -lap with HP-CD offers a major improvement in drug solubility and bioavailability.     

Effect of haloperidol on reflex activation of rat α-motoneurones

Summary Effects of haloperidol on rat flexor and extensor -motoneurones were studied in ventral roots of laminectomized rats under halothane anesthesia. The -motoneurones were activated by tetanic stimulation of low-threshold afferents (group I and II), either of the ipsilateral peroneal nerve (flexor -motoneurones) or gastrocnemius-soleus nerve (extensor -motoneurones).Haloperidol, given in the doses of 0.075, 0.15 and 0.30 mg/kg i.p. inhibited the reflex activation of flexor -motoneurones; higher doses seemed to be more effective than lower ones. Apomorphine (2 mg/kg s.c.) partially antagonized the inhibitory action of haloperidol with some latency. Higher doses of haloperidol (0.15–0.60 mg/kg i.p.) also inhibited the reflex activation of extensor -motoneurones; this inhibitory effect was, at least for a short time, antagonized by apomorphine (2 mg/kg s.c.).The threshold for reflex activation both of flexor and extensor -motoneurones was raised by haloperidol and lowered by a subsequent administration of apomorphine.Our results suggest that akinesia and catalepsy, induced in rats by haloperidol might be, at least in part, due to a decrease in sensitivity of -motoneurones to proprioceptive stimuli.     

(±)[125Iodo]cyanopindolol,a new ligand for β-adrenoceptors: Identification and quantitation of subclasses of β-adrenoceptors in guinea pig

Summary (±)[¹²⁵Iodo]cyanopindolol (ICYP) is a radioligand which binds with an extraordinarily high affinity and specificity to -adrenoceptors. In contrast to (±)[¹²⁵Iodo]-hydroxybenzylpindolol (IHYP), the new ligand has neither affinity to - nor to 5-HT-receptors. The dissociation constants of ICYP for -adrenoceptors in various tissues range from 27 to 40 pM, thereby exceeding the affinity of IHYP by a factor of 3.ICYP does not discriminate between ₁– and ₂–. Therefore, the densities of the two receptor subtypes can be determined from competition curves of ICYP by drugs previously found to show in vitro selectivity for ₁–adrenoceptors.The guinea pig left ventricle contains only ₁– adrenoceptors, whereas in the lung tissue, the ratio of ₁– to ₂–adrenoceptors is 1 to 4. The calculated affinities of five ₁– selective antagonists for ₁–adrenoceptors were nearly identical in the ventricle and the lung.Kinetic studies of ICYP binding to guinea pig lung membranes indicated that the dissociation reaction consists of two components, a fast process (t _1/2=9 min) and a slower process (t _1/2=8.8 h). A mathematical treatment revealed two possibilities of interpretation: 1. Two forms of the receptor exist which are interconvertible. 2. The (+)- and (–)-enantiomers of ICYP dissociate with different rate constants.The low dissociation constant of ICYP in combination with its high specific radioactivity (2175 Ci mmole^–1) allows binding studies to be carried out with small protein and ligand concentrations, e.g. 3 g protein per assay in guinea pig lung membranes.Abbreviations CYP (±)cyanopindolol, [(±)4-(3-tert-butylamino-2-hydroxypropoxy)-1H-indole-2-carbonitrile] - ICYP (±)-3-[¹²⁵iodo]-cyanopindolol - HYP (±)hydroxybenzylpindolol; IHYP, (±)[¹²⁵iodo]-hydroxybenzylpindolol - ³H-DHA (–)-[³H]dihydroalprenolol Part of this work has been presented in Mainz, March 1980, at the Spring Session of the German Pharmacological Society, and in Brussels, June 1980, at the 4th International Conference on Cyclic Nucleotides     

Hemmung von Adenyl-Cyclase-Präparationen aus der Rattenniere durch Calciumionen und verschiedene Diuretica

Summary Antidiuretic hormone (ADH) increases the permeability to water of certain epithelial membranes. This effect, found in the urinary bladder of the toad and in the distal tubules and the collecting ducts of kidney, is mediated intracellularly by adenosine 35-monophosphate (Ado-35-P). Calcium ions and the diuretic ethacrynic acid are known to inhibit the ADH-induced increase in water permeability of the toad bladder. In adenyl cyclase preparations from rat renal cortex and medulla, the influence of these substances as well as of other diuretics added in vitro has been studied. Adenyl cyclase activity has been determined, excepted as noted, by measuring Ado-35-P formed from 1 mM ¹⁴C-ATP in the presence of 10 mM Mg⁺⁺, an ATP regenerating system, and 5 mM unlabeled Ado-35-P to reduce the enzymatic degradation of the labeled Ado-35-P.Calcium ions reduced the rate of Ado-35-P formation by particles from renal cortex and medulla when the activity was measured in the presence of either Mg⁺⁺ or Mn⁺⁺. With 10 mM Mg⁺⁺, 1 mM Ca⁺⁺ decreased adenyl cylase activity by about 50%. Activities of cortical adenyl cyclase stimulated by parathyroid hormone, thyrocalcitonin or ADH and of medullary adenyl cyclase stimulated by ADH were also reduced by about 50% in the presence of 1 mM Ca⁺⁺. The inhibition was independent of the ATP concentration, but was influenced by the Mg⁺⁺ content of the incubation medium.Adenyl cyclase activities of cortical and medullary membrane preparations were reduced by about 50% by 0.2 mM ethacrynic acid. The extent of this inhibition was essentially the same whether the enzymatic activity was determined in the absence or presence of stimulating hormones. The inhibitory action of ethacrynic acid was partially prevented by simultaneous addition of dithioerythritol (DTE). A derivative of ethacrynic acid, L 589420-0-2, also inhibited renal adenyl cyclase, but its action was not influenced by the addition of DTE. Adenyl cyclase from both parts of the kidney was inhibited by about 90% by 0.2 mM mersalyl. This action was almost completely prevented by the addition of 1 mM DTE. The pharmacological significance of adenyl cyclase inhibition by these diuretics is still uncertain since the role of Ado-35-P in the regulation of sodium transport is as yet unclear.Other diuretics, hydrochlorothiazide, furosemide, mefruside, amiloride, and the non-diuretic benzothiadiazine, diazoxide, had essentially no effect on cortical and medullary adenyl cyclase preparations when they were added in 0.1–0.5 mM concentration.The methylxanthines, theophylline and caffeine, which are known to inhibit nucleoside 35-monophosphate phosphodiesterase, reduced the rate of Ado-35-P formation. The unstimulated and the hormone-stimulated adenyl cyclases were inhibited to the same extent by theophylline. When adenyl cyclases was stimulated by fluoride, however, we found only a very small inhibition by theophylline. Inhibition of the medullary adenyl cyclase was greater than that of the enzyme prepared from renal cortex. At a concentration of 1 mM these methylxanthines significantly inhibited the medullary enzyme, but the inhibition became asymptotic at about 50% when concentrations up to 20 mM were used. Therefore, it is likely that inhibition by these substances varies in different cell types and tissues.Instead of phosphodiesterase inhibitors, unlabeled Ado-35-P can be used in the assay of adenyl cyclase activity to reduce the degradation of enzymatically formed labeled Ado-35-P. This addition, though, can also influence adenyl cyclase activity. In a medullary enzyme preparation 0.2 mM Ado-35-P reduced the adenyl cyclase activity by 13%, 5 mM Ado-35-P by 35%.

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Abkürzungen Ado-35-P Adenosin-35-monophosphat - Guo-35-P Guanosin-35-monophosphat - ADH antidiuretisches Hormon, Vasopressin - PTH Parathormon - TCT Thyreocalcitonin - DTE Dithioerythrit - EDTA Äthylendiamintetraessigsäure Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.Über einen Teil der Ergebnisse wurde auf der 11. Frühjahrstagung der Deutschen Pharmakologischen Gesellschaft berichtet (Jakobs et al., 1970). Einige der vorliegenden Ergebnisse sind der Inauguraldissertation von K. H. J. (Medizinische Fakultät der Universität Heidelberg, 1971) entnommen.     

The effect of gamma-butyrolactone on locomotor activity in the rat

The effect of -butyrolactone (GBL) on locomotor activity in the rat was studied. Low doses of GBL (100 and 200 mg/kg) had a biphasic effect on activity. Initially, the activity of the rats was reduced, and this reduction was then followed by a period of hyperactivity. The effect of -flupenthixol (50 g/kg -FPT), atropine (10 mg/kg), benztropine (25 mg/kg), protriptyline (15 mg/kg), and clomipramine (25 mg/kg) was investigated on this biphasic effect. -FPT reduced the hyperactivity while benztropine potentiated it; atropine, clomipramine, and protriptyline had little effect. It is concluded that the increase in activity could be due to a release of dopamine.     

Enhancement by α-fluoromethylhistidine of the thiopental sleep-prolonging action of Δ9-tetrahydrocannabinol

The effect of -fluoromethylhistidine (-FMH), a specific inhibitor of histidine decarboxylase, on the potentiation of thiopental-induced sleep by ⁹-tetrahydrocannabinol (THC), which inhibits the histamine turnover in the brain, was examined in mice and rats. The sleeping time after injection of thiopental sodium (40 mg/kg, IV) was prolonged by THC (10 mg/kg, IP, 1 h before) to approximately twice the control value. -FMH (50 mg/kg, IP) administered alone had no significant influence on the thiopental sleeping time. However, -FMH given 1 or 3 h before THC treatment markedly enhanced the THC potentiation of thiopental-induced sleep. Such an enhancement by -FMH was not observed when -FMH was administered 15 h before THC treatment. The brain histamine level decreased by 60% during the first 4 h after -FMH injection and remained low until 15 h after the treatment. The thiopental sleep-potentiating action of morphine, chlorpromazine and diazepam was not affected by pretreatment with -FMH. The transient enhancing effect of -FMH on the THC potentiation of thiopental-induced sleep suggests that the histaminergic system is one of the activating transmitter systems in the brain.     

Regulation of adenylate cyclase activity in hamster adipocytes

Summary In ghosts of hamster adipocytes, the regulation of adenylate cyclase (ATP: pyrophosphate lyase, cyclizing; EC 4.6.1.1) activity by prostaglandins, -adrenergic agonists and nicotinic acid was studied. These three classes of antilipolytic agents caused adenylate cyclase inhibition without an apparent lag phase. Maximal inhibitions observed ranged between about 45% (by -adrenergic agonists) and 60% (by prostaglandins and nicotinic acid). The order of potency for the inhibitory prostaglandins (PG) was PGE₁ PGE₂>PGF₂PGI₂>PGD₂>6-keto PGF₁. The IC₅₀ values obtained were about 0.007, 0.06, 0.3 and 1 M for PGE₁, PGF₂, PGD₂ and 6-keto PGF₁, respectively. -Adrenergic agonists, studied in the presence of the -adrenergic blocking agent, propranolol (30 M), inhibited the fat cell enzyme with the order of potency (1)-adrenaline > (1)--methylnoradrenaline (1)-noradrenaline > clonidine tetryzoline > (1)-phenylephrine. The IC₅₀ values obtained for (1)-adrenaline and (1)-noradrenaline were about 3 and 10 M, respectively. The inhibitory effect of (1)-adrenaline was blocked by the -adrenergic antagonists with the potency order yohimbine phentolamine > prazosin. These findings suggest that an ₂ of receptors is involved in this catecholamine-induced inhibition. Nicotinic acid (10 M) reduced adenylate cyclase activity by about 60% with half-maximal effectiveness at about 0.6 M. The nicotinic acid derivatives, nicotinamide, -pyridylcarbinol and NAD (up to 100 M), had no effect on enzyme activity.Inhibition of the hamster adipocyte adenylate cyclase by the antilipolytic agents required the presence of both GTP, which reduced basal activity by about 80% at 10 M, and sodium ions, which specifically activated the GTP-affected from of the enzyme. Inhibition was also observed in the presence of ACTH, which in a GTP-dependent manner increased adenylate cyclase activity. Pretreatment of the enzyme preparation with NaF (10 mM) partially reduced the inhibitory effect, and preactivation with the stable GTP analogue, guanylyl 5-imidodiphosphate (100 M), abolished the adenylate cyclase inhibition by the antilipolytic agents.Abbreviations PG prostaglandin - GMP-P(NH)P guanylyl 5-imidodiphosphate Some of the data were presented in abstract form (Aktories et al., 1979a)     

The functional pool of brain catecholamines: Its size and turnover rate

Behavioral data are reviewed that give evidence for an indiscriminate involvement of brain catecholamines (CA), especially dopamine (DA), in nervefunction, regardless of the time elapsed from their synthesis. Critical analysis of biochemical and pharmacological studies shows that a clear-cut distribution of brain catecholamines in two compartments [newly synthesized (NS) and main storage] is not at all established, and moreover that there is no adequate proof that the difference in turnover rates attributed to these two supposed pools is due to a preferential extraneuronal release of NS-CA during nerve function rather than to a preferential (nonfunctional) intraneuronal deamination of NS-CA, or at least of NS-DA.     

Cardiostimulatory effects of cyclic 3′,5′-adenosine monophosphate and its acylated derivatives

Summary The effects of cyclic 3,5-AMP and of two acylated derivatives, dibutyryl (DBA) and dihexanoyl-3,5-AMP (DHA) were investigated in isolated perfused hearts of guinea pigs, rats and rabbits.In guinea pig hearts, DBA (Ca- and Na-salt) and DHA-Na in high doses (10 moles) produced strong and long lasting increases in the rate and amplitude of contractions, coronary flow, and moderate increases in phosphorylase activity in the majority of experiments. The positive ino- and chronotropic effects occured 3–5 min after injection of the drug, mostly in a fluctuating manner with several maxima. Theophylline augmented the effects of DBA-Na and revealed positive inotropic actions of non substituted 3,5-AMP.In rat hearts, similar, but more pronounced and dose-dependent effects were observed after 1, 5 and 10 moles DBA-Na. Propranolol (50 g) did not block the action of 10 moles DBA-Na. Non substituted 3,5-AMP, 5-AMP and ATP in doses of 10 moles had no significant positive inotropic effects.In rabbit hearts, DBA-Na (50 moles) produced moderate, non fluctuating rises in the amplitude of contraction.The results provide evidence that under certain conditions cyclic 3, 5-AMP itself, like its acylated derivatives DBA and DHA, may produce strong and direct positive inotropic and chronotropic effects in the heart. These findings support the view that cyclic 3,5-AMP is the cellular mediator of the cardiostimulant actions of substances that increase its rate of production in the myocardial cell.The excellent technical help of Mrs. Vera Bauer is gratefully acknowledged by the authors.     

In Vitro Evaluation of Dexamethasone-β-D-Glucuronide for Colon-Specific Drug Delivery

Dexamethasone--D-glucuronide is a potential prodrug for colonic delivery of the antiinflammatory corticosteroid dexamethasone. Previous studies [T. R. Tozer et al., Pharm. Res. 8:445–454 (1991)] indicated that a glucoside prodrug of dexamethasone was susceptible to hydrolysis in the upper gastrointestinal tract. Resistance of dexamethasone--D-glucuronide to hydrolysis in the upper gastrointestinal tract was therefore assessed. Conventional, germfree, and colitic rats were used to examine enzyme levels along the gastrointestinal tract to compare the stability of two model substrates (p-nitrophenyl--D-glucoside and --D-glucuronide) and to evaluate the prodrug dexamethasone--D-glucuronide. Hydrolytic activity was examined in the luminal contents, mucosa, and underlying muscle/connective tissues in all three types of rats. Enzymatic activity (-D-glucosidase and -D-glucuronidase) was greatest in the lumen of cecum and colon of conventional rats. In contrast, germ-free rats exhibited relatively high levels of -D-glucosidase activity (about 80% of total activity in the conventional rats) in the proximal small intestine (PSI) and the distal small intestine (DSI). Rats with induced colitis (acetic acid) showed reduced levels of luminal -D-glucuronidase activity in the large intestine; however, -D-glucosidase activity was relatively unchanged relative to that of the conventional rat. Mucosal -D-glucuronidase activity was significantly lower in the colitic rats compared with that in the conventional animals. Despite reduced luminal levels of -D-glucuronidase activity in the colitic rats, there was still a sharp gradient of activity between the small and the large intestines. Permeability of the glucoside and glucuronide prodrugs of dexamethasone through a monolayer of Caco-2 cells was relatively low compared to that of dexamethasone. The results indicate that dexamethasone--D-glucuronide should be relatively stable and poorly absorbed in the upper gastrointestinal tract. Once the compound reaches the large intestine, it should be hydrolyzed to dexamethasone and glucuronic acid. Specificity of colonic delivery in humans should be even greater due to lower levels of -D-glucuronidase activity in the small intestine compared with that in the laboratory rat.     

Involvement of tumor necrosis factor-α in sulfur mustard-induced skin lesion; effect of topical iodine

Sulfur mustard (SM), also termed mustard gas, is a potent vesicant that elicits an inflammatory response upon exposure of the skin. Evaluation of mouse ear 3 h after SM exposure revealed acute inflammatory-cell aggregates in the vascular beds accompanied by strongly TNF--positive neutrophils. Eight hours after SM exposure, this phenomenon became intensified and associated with infiltration into the adjacent dermis. In ear skin topically treated with iodine, however, no inflammatory cells were observed 3 h after SM exposure; 8 h postexposure, blood vessels contained very few TNF--positive inflammatory cells. Since TNF- induction was shown to be associated with reactive oxygen species production, we studied the effect of iodine on activated peritoneal mouse neutrophils. Iodine elicited a concentration-dependent reduction in the oxidative burst of activated neutrophils. Iodine also scavenged hydroxyl radicals generated by glucose oxidase in a concentration-dependent manner. The involvement of TNF- in SM-induced skin toxicity was confirmed by reduction of 49 and 30% in ear edema following administration of 1 and 2 g anti-TNF- antibodies, respectively. These findings were corroborated by quantitative analysis of the histological findings showing 46% reduction in acute inflammation and no signs of subacute inflammation in the treated group, in contrast to the control group treated with SM only. Other epidermal (microblister formation, ulceration, and necrosis) and dermal (neutrophilia, hemorrhage, and necrosis) parameters also showed marked reductions in the antibodies-treated group in comparison to controls. The combination of iodine and antiTNF- antibodies might constitute a new approach for treatment of SM-exposed individuals.U. Wormser is affiliated with David R. Bloom Center for Pharmacy at The Hebrew University.     

Postjunctional α-adrenoceptors

Summary The postsynaptic -adrenoceptors in rat aorta and in pithed rat were investigated according to their sensitivity to nine -adrenergic agonists and to the selective antagonists yohimbine (₂) and prazosin (₁) and the non-selective one, phentolamine. In addition, in radioligand binding studies, the affinity and selectivity of the drugs were determined on rat cerebral cortex using [³H] yohimbine and [³H] prazosin.On rat aorta, prazosin is 1,000 times more potent than yohimbine against each -adrenoceptor agonist, whether ₁- or ₂-selective. Rat aorta probably contains only ₁-adrenoceptors.Pressor effects in pithed rats are mediated by post-junctional ₁- and ₂-adrenoceptors. The dose-response curve for -methylnorepinephrine in the presence of prazosin, using Hofstee's plots, revealed ₁- and ₂-adrenoceptors, respective proportions being 80.5 and 19.5%     

β-Adrenoceptor subtypes in sections of rat and guinea-pig kidney

Summary The present autoradiographical study examines the distribution of the two -adrenoceptor subtypes in sections of rat and guinea-pig kidney. The radioligand [¹²⁵Iodo]-(-)-cyanopindolol was used for the labelling of -adrenoceptors and the selective -adrenoceptor blocking agents ICI 89-406 (₁-antagonist) and ICI 118-551 (₂-antagonist) were utilized to differentiate both subclasses unequivocally. -Adrenoceptors in rat kidney were found to be almost exclusively ₁. They were located mainly on glomeruli and to a lesser extent on the straight part of the distal tubules and on the cortical portion of the collecting ducts. Some ₂-adrenoceptors were localized around the corticomedullary junction. Grain localization in the autoradiograms was absent in the inner medulla and papilla. Glomeruli and distal tubules of the guinea-pig kidney also possess only ₁-adrenoceptors, but, in contrast to the rat, extremely high concentrations of ₂-adrenoceptors were associated with the straight part of the proximal tubules in the cortex and possibly with the cortical portion of the collecting duct. Labelling was not detected on the proximal convoluted tubule in either species.     

Evidence that the aversive effects of opioid antagonists and κ-agonists are centrally mediated

The role of central versus peripheral opioid receptors in mediating the aversive effects of opioids was examined by use of an unbiased place preference conditioning procedure in rats. The non-selective opioid antagonist naloxone (NLX) produced conditioned aversions for the drug-associated place after subcutaneous (SC) as well as intracerebroventricular (ICV) administration. Place aversions were also observed in response to the ICV administration of the selective -antagonist CTOP. In contrast, the selective -antagonist ICI 174,864 and the selective -antagonist norbinaltorphimine (nor-BNI) (ICV) were without effect. Place aversions were also produced by central applications of the selective -agonist U50,488H and the dynorphin derivative E-2078. For those opioid ligands tested, the doses required to produce place aversions were substantially lower following ICV as compared to SC administration. These data confirm that -agonists and opioid antagonists produce aversive states in the drug-naive animal and demonstrate that this effect is centrally mediated. Furthermore, the ability of NLX and CTOP, in contrast to both ICI 174,864 and nor-BNI, to produce place aversions suggests that the aversive effects of opioid antagonists result from the blockade of -receptors.     

Modulation of rat brain α-adrenoreceptor populations four weeks after stimulation of the nucleus locus coeruleus

We previously showed that electrical stimulation of the nucleus locus coeruleus was followed 4 weeks later by a greatly improved performance in the acquisition of a food-reinforced operant task. To ascertain whether adrenergic receptors were involved in this long-term behavioral modification, we studied the characteristics of the ₁, ₂, and -adrenoreceptors of the cerebral cortex 4 weeks after stimulation of the locus coeruleus. This stimulation induced a slight (14%) but significant increase in the number of ₁-receptor [(³H) WB 4101 binding sites] as well a rise in the number of ₂-receptor [(³H) clonidine binding sites]. The later rise mainly affected high-affinity ₂ sites (36%) and the number of low-affinity sites remained unchanged. No significant alteration in the number of -receptors [(³H)-dihydroalprenolol binding sites] was observed. To confirm this biochemical result, the effect of very small doses of clonidine (1, 2.5, 5 and 10 g/kg) was tested on locomotor activity in the open-field. In rats stimulated 4 weeks before injection, clonidine induced a biphasic effect, comprising firstly sedation which occurred 30 min after injection, and secondly, long-term hyperactivity which began 24 h after injection. For the 5 g/kg dose, this rebound of activity was detectable 8 days after injection. In implanted, control rats, only the sedative effect was observed. These findings are interpreted in relation to the current theories about -adrenoreceptors.     

Coronary vascular responses to nicotine in the anaesthetized dog

Summary The effect of the intra-coronary (i.c.) injection of nicotine on large coronary artery diameter and coronary blood flow was examined in anaesthetized dogs. In sixteen untreated dogs nicotine (20 g i.c.) had a biphasic effect on arterial pressure (initial increase, 7 ± 2 mmHg; secondary decrease, –8 ± 3 mmHg) which was accompanied by small and variable effects on heart rate and an increase in LV dP/dt. Nicotine increased large coronary artery diameter by 5.8 ± 0.8% but had a biphasic effect on coronary blood flow (initial increase, 41 ± 7 ml/min; secondary decrease, –10 ± 2 ml/min). Bilateral vagotomy or muscarinic receptor blockade with atropine (0.1 mg/kg i. v.) did not significantly affect the nicotine-induced changes in coronary artery diameter or coronary blood flow. The additional antagonism of -adrenoceptors with propranolol (1 mg/kg i. v.) abolished the effect of nicotine in coronary artery diameter ( CD = 0.2 ± 0.2%) and the initial increase in coronary blood flow ( CBF = 1 ± 1 ml/min) but enhanced the secondary decrease in flow ( CBF = –25 ± 3 ml/min). The nicotine-induced decrease in coronary blood flow observed after muscarinic and -adrenoceptor blockade was attenuated by antagonism of ₁-adrenoceptors with prazosin (10 g/kg i. c., CBF = –15 ± 3 ml/min) and abolished after additional antagonism of ₂-adrenoceptors with idazoxan (50 g/kg i. c., CBF = –2 ± 1 ml/min). These results indicate that in the anaesthetized dog intra-coronary injection of nicotine results in -adrenoceptor mediated dilatation of both large and small coronary arteries. In the coronary resistance vessels, but not in the large coronary artery, the dilatation is opposed by ₁-and ₂-adrenoceptor mediated vasoconstriction. Send offprint requests to O. L. Woodman at the above address