Differential effects of potassium channel blockers on neurohypophysial release of oxytocin and vasopressin. Evidence for frequency-dependent interaction with the endogenous opioid inhibition of oxytocin release

Summary Isolated rat neurohypophyses were fixed by their stalks to a platinum wire electrode and superfused with Krebs-HEPES solution. Vasopressin and oxytocin released into the medium were determined by specific radioimmunoassays. Hormone secretion was increased by electrical stimulation of the pituitary stalk at different frequencies. The effects of several potassium channel blockers, tetraethylammonium (TEA) ions, 4-aminopyridine (4-AP) and 3,4-diaminopyridine (3,4-DAP) were tested.The release of vasopressin and oxytocin evoked by electrical stimulation with 900 pulses at 15 Hz (about 900 and 1,000 U, respectively) was about 10 times higher than that evoked by 900 pulses at 3 Hz. Both 10 and 30 mmol/l TEA enhanced the release of vasopressin evoked by stimulation at 3 and 15 Hz, by 25- and 2-fold, respectively, to attain a maximum release of about 1,800 U per stimulation. The stimulated release of oxytocin attained a maximum of about 9,000 U at 15 Hz in the presence of 10 mmol/l TEA or at 3 Hz with 30 mmol/l TEA. Thus, in the presence of maximally effective concentrations of TEA both stimulation frequencies (3 and 15 Hz) were equieffective in evoking release of vasopressin and oxytocin. 4-AP or 3,4-DAP enhanced the release of vasopressin evoked by 15 Hz stimulation maximally to about 1,600 U and that evoked by 3 Hz stimulation to about 900 U. In the presence of 4-AP or 3,4-DAP the release of oxytocin evoked by stimulation at 15 Hz increased maximally to about 8,000 U and that evoked by stimulation at 3 Hz to about 1,500 U. Thus, in the presence of maximally effective concentrations of 4-AP or 3,4-DAP stimulation at 15 Hz induced a significantly higher release of vasopressin and oxytocin than stimulation at 3 Hz. Naloxone (1 mol/l) increased the release of oxytocin evoked by stimulation at 15 Hz to about 3,000 U and that evoked by stimulation at 3 Hz to about 700 U. The release of oxytocin evoked by stimulation at 15 Hz in the presence of 10 mmol/l TEA or 1 mmol/l 4-AP (about 8,000–9,000 U) was not further enhanced by naloxone. However, during stimulation at 1 or 3 Hz in the presence of 10 mmol/l TEA, naloxone increased the release of oxytocin from about 3,700 and 6,300 U, respectively, to the maximum of about 9,000 U. Likewise, during stimulation at 3 Hz in the presence of 1 mmol/14-AP, naloxone increased the relase of oxytocin from about 1,500 to 9,000 U. Under all condition studied, naloxone did not affect the release of vasopressin.In conclusion, neurosecretory nerve endings are endowed with different types of potassium channels. Blockade of potassium channels can oppose the opioid inhibition of oxytocin release in a complex frequency-dependent manner.Abbreviations 4-AP 4-aminopyridine - 3,4-DAP 3,4-diaminopyridine - TEA tetraethylammonium ions Send offprint requests to. K. Racké at the above address     

Frequency-dependent effects of activation and inhibition of protein kinase C on neurohypophysial release of oxytocin and vasopressin

Summary Isolated rat neurohypophyses were superfused in vitro and the release of vasopressin and oxytocin into the medium was determined by specific radioimmunoassays. Hormone secretion was increased by electrical stimulation of the pituitary stalk at different frequencies. The effects of several phorbol esters, known to activate (phorbol 12,13-dibutyrate, PDB) or not to affect (4a-phorbol 12,13-dideconate and phorbol 12-monoacetate) protein kinase C, and of the direct protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7) were tested.Electrical stimulation with 450 pulses caused the release of about 45 U vasopressin and 55 U oxytocin, when a frequency of 3 Hz was applied, and of about 500 U vasopressin and oxytocin, when a frequency of 15 Hz was used.PDB (1 gmol/l) increased the release of vasopressin evoked by 15 Hz stimulation maximally by about 40–50% and that evoked by 3 Hz stimulation by about 150%. The release of oxytocin evoked by 15 Hz stimulation was increased by about 150% and that evoked by 3 Hz stimulation by about 400–500% in the presence of PDB. Both inactive phorbol esters had no effects on the evoked release of vasopressin or oxytocin. The effect of PDB on the release of vasopressin and oxytocin was blocked by H7 (10–30mol/1). H7 (30 ol/1) alone reduced the release of vasopressin evoked by stimulation at 15 Hz by 50%. The release of oxytocin was not significantly affected by H7. In the presence of naloxone (1 ol/1) the release of oxytocin evoked by 3 and 15 Hz stimulation was increased by about 175 and 105%, respectively. In the presence of naloxone, H7 (30 mol/1) had no effect on the release of oxytocin evoked by stimulation at 15 Hz, but PDB caused an increase of the release of oxytocin similar to that in the absence of naloxone. Inactivation of protein kinase C by prolonged exposure of isolated neurohypophyses to PDB (1 mol/1) for 4 h reduced the release of vasopressin evoked by stimulation at 15 Hz by about 45%.In conclusion, activation of protein kinase C can facilitate impulse-induced hormone secretion from neurosecretory nerve endings. Under the present in vitro conditions, an endogenous activation of protein kinase C appears to be involved, in part, in the frequency-dependent facilitation of vasopressin, but not of oxytocin secretion. In addition, the inhibition of oxytocin release by endogenous opioids appears not to be associated with effects on protein kinase C.Abbreviations DMSO dimethylsulphoxide - H7 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine - PDB phorbol 12,13-dibutyrate Send offprint requests to K. Rack at the above address     

The effect of isoprenaline on plasma concentrations of immunoreactive β-endorphin and β-lipotropin in the conscious rat

Summary The effect of the -adrenoceptor agonist isoprenaline on the plasma concentrations of -endorphin (-E) and -lipotropin (-LPH) was investigated in conscious rats. Isoprenaline (i.m.) elevated plasma -endorphin-like immunoreactivity (-EI) as measured by radioimmunoassay of unextracted plasma, with peak values 24 min after drug administration. This effect was dose-dependent. The lowest effective dose of isoprenaline was 15 g kg^–1; 240 g kg^–1 exerted a maximum effect, raising plasma -EI about ten-fold above control values. Plasma vasopressin concentrations also increased in response to isoprenaline following a timecourse identical to that of plasma -EI. (±)-Propranolol (1 mg kg^–1) but not phentolamine (10 mg kg^–1) rendered isoprenaline (240 g kg^–1) injections almost ineffective. Because of the cross-reactivity of -LPH in the radioimmunoassay used, plasma was extracted by means of a cation exchange resin and subjected to gel chromatography on a Sephadex G-50 column, avoiding artefactual degradation of the peptides. In isoprenaline-treated rats about 50% of the -EI behaved similar to human -LPH, whereas 45% co-migrated with human -E; immunoreactivity corresponding to -LPH or -E comprised about 70% or 30%, respectively, in the plasma extract of vehicle-treated rats. Dexamethasone pretreatment reduced the isoprenaline-induced increase in plasma -EI by 87%, but left the simultaneous elevation of plasma vasopressin concentrations unchanged.These data demonstrate that isoprenaline stimulates -LPH and -E release in vivo. The possibility of an interrelationship between vasopressin and -E release is discussed.     

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.     

European drug information centres ‐ survey of activities

A questionnaire survey of European drug information centres (DICs) was conducted. DICs mentioned in the ESCP directories and other sources were identified and contacted. Information on basic characteristics was obtained: affiliation, the scope of activities, employees, questionanswer service characteristics, information sources and the economic aspects of the DICs' work. Information from 84 DICs was analysed (return rate = 71.3%). DICs are mainly affiliated to hospitals (68%), rather rarely with faculties of pharmacy (6%) or with faculties of medicine (8.3%). Activities of DICs mainly include: questionanswer service (98%), issue of bulletins (68%), participation in P&T committees (63%), tuition (61%) and druguse evaluation (52%). Pharmacists, 12 full or parttime, are the most frequent employees working in the DICs. When the questionanswer service was analysed, it was found that 56% of the DICs are open only to the healthcare professionals and 43% provide a service to the lay public. Questions are mainly concerned with the side effects, indication/therapeutic use and the dosage of the drugs. The majority of DICs (91%) document their activities, very often on a computer database. Quality assurance is provided by almost 75% of DICs, usually by a review (58 %) or a feedback questionnaire (32%). Information sources listed as most frequently used include Martindale The Extrapharmacopeia, journals such as Lancet, Medline and Micromedex databases. DICs are usually financially supported by the organizations to whom they are affiliated. Fees are charged, for special activities, by 9.5% of DICs.     

Nicotine and smoking: Effects upon subjective changes in mood

A Mood Adjective Check List and an activation scale were used to measure subjective reports on mood changes in 24 male habitual smokers before and after smoking cigarettes with known content of nicotine, at different times of day and rates of puffing. Ratings on pleasantness were dose related. Aggression and anxiety showed effects attributable to circadian influence and slight decreases in both factors occurred after smoking the highest nicotine cigarette. The MACL scores were greatly affected by the experimental procedure. Levels of inner tension were found related to the nicotine inhaled. The heuristic value of the concept of activation in these studies is suggested.This work was supported by the Tobacco Research Council, and carried out at the Institute of Psychiatry, London.     

Chronic administration of a selective dopamine D-2 agonist: factors determining behavioral tolerance and sensitization

The locomotor stimulant effects of sustained administration of a potent and selective dopamine (DA) D-2 receptor agonist, [+]-4-propyl-9-hydroxynaphthoxazine (PHNO), in rats were assessed 24 h a day during 12 h light-dark cycles. PHNO was administered continuously with subcutaneous implants of Alzet osmotic minipumps (5 g/h), for 12 h a day with modified osmotic minipumps (5 g/h), or by daily injections (15 g, SC). Tolerance was observed to occur only with 24 h continuous infusions and only during the light period. The other treatment regimens produced sensitization of the locomotor response. Daytime tolerance to continuous infusions of PHNO was reversed following reversal of the light-dark cycle. A normally arousing stimulus also reversed (temporarily) daytime tolerance. The present results indicate that the temporal pattern of administration of DA agonists, the phase of the circadian cycle and environmental stimuli associated with arousal are important determinants of the behavioral consequences of long-term treatment.     

Pharmacokinetics of digoxin and its 4‴-acetyl-and methylderivates in the rat

Summary The kinetics of absorption, of changes in blood concentration, and of biliary excretion after the i.v. and i.d. administration of 40 Ci each, of digoxin, 4-acetyldigoxin and 4-methyldigoxin were studied in biliary fistula rats. The highest blood concentrations were found after the i.v. administration of 4-methyldigoxin, which decline with a half life time of 10 h, compared with 5.6 and 4.5 h for 4-acetyldigoxin and digoxin respectively. 71%, 55% and 17% of the dose were excreted in the bile within 12 h after the i.v. administration of digoxin, 4-acetyldigoxin and 4-methyldigoxin. The blood concentrations observed after the i.d. administration of digoxin and 4-acetyldigoxin show almost identical pharmacokinetics with respect to height and elimination velocity (half life 7.0 h for digoxin and 7.5 h for 4-acetyldigoxin). In contrast, following the i.d.administration of 4-methyldigoxin, blood concentrations, which were twice as high, were observed and declined with the same half life as after the i.v. administration.Determination of the disappearance rates of these glycosides from the intestinal lumen reveals a biphasic course of absorption. A first phase, with k values of 0.4, 0.5, 1.2 for digoxin, 4-acetyldigoxin and 4-methyldigoxin respectively is followed by a second phase with k values of 0.04, 0.04, 0.001 for digoxin, 4-acetyldigoxin and 4-methyldigoxin. Thus, 4-methyldigoxin is almost completely absorbed within the first two hours, while digoxin and 4-acetyldigoxin continue to be absorbed during the following hours. The absorption velocity of digoxin from the ileum was found to be one half of that seen in the duodenum. But this slow absorption, as well, follows a biphasic course.The data indicate that 4-methyldigoxin is absorbed at a distinctly higher rate than 4-acetyldigoxin and digoxin. Acetylation in 4 position evidently provides no important advantage with respect to absorption. While this study allows the determination of absorption and excretion velocities, no account of absorption quotes is given.     

Alcohol,anxiolytics and social stress in rats

The main objective was to compare the anxiolytic-like profiles of alcohol, diazepam and gepirone along the stress intensity gradient which characterizes consecutive phases of a social confrontation. The acute social stress situation consisted of initially placing the experimental rat as an intruder into the homecage of a resident while the resident was not present, termed the anticipatory phase, thereafter permitting brief physical agonistic interactions with the re-introduced resident until the intruder was forced into a submissive supine posture and emitted ultrasonic vocalizations (USV), and eventually exposing the intruder to the resident's threats for 1 h, while being shielded from potential injurious attacks. The hyperthermia, measured via telemetry, in the anticipatory phase prior to defeat and in reaction to threats, was decreased by alcohol, gepirone and diazepam; alcohol and gepirone were also effective in attenuating anticipatory tachycardia. Alcohol, like gepirone and diazepam, also decreased defensive responses and ultrasonic vocalizations in the anticipatory phase of the confrontation, but none of these drugs affected defensive reactions to threats which immediately followed defeat. Gepirone had no systematic sedative effects throughout the confrontation; infact, it dose-dependently reduced the stress-induced suppression of locomotor activity during the anticipatory phase. In contrast, at higher doses, alcohol as well as diazepam had marked sedative effects as evidenced by several behavioral parameters (i.e. lie, crouch, walk). The anxiolytic-like profile of hyperthermia, tachycardia, USV and defensive behavior in the anticipatory phase of the confrontation by alcohol, gepirone and diazepam contrasted with the lack thereof during the more intense reactive phase. This differential pattern of effects appears to be relevant to the clinical distinctions between anticipatory anxiety and other affective disturbances.     

Transplacental passage and breast milk concentrations of hydralazine

Summary The concentrations of real and apparent (= real hydralazine + acid-labile hydrazones) hydralazine in maternal and umbilical plasma obtained at delivery of 6 women treated with hydralazine and atenolol for pregnancy hypertension were measured by gas chromatography. In one of the patients, the concentrations of the same substances were subsequently measured in breast milk. Apparent hydralazine reached higher levels in umbilical than in maternal blood. The concentration of real hydralazine seemed to be at least as high in the fetus as in the mother. On the other hand, even though the fraction of real (i.e. presumably active) hydralazine was greater in milk than in plasma, the total concentration was smaller, and the estimated dose per milk feed of 75ml would not exceed 0.013mg. Thus, hydralazine treatment of the pregnant woman would expose her fetus to effective concentrations of the drug, but breast feeding would not result in a clinically relevant concentration in the infant.     

Effect of Cyclodextrins on Protein Binding of Drugs: The Diflunisal/Hydroxypropyl-β-Cyclodextrin Model Case

The binding of diflunisal to hydroxypropyl--cyclodextrin (HPCD), bovine serum albumin (BSA), human serum albumin (HSA), normal human plasma, and mixed solutions of HPCD/ protein was studied at 25°C, pH 7.4, by potentiometry using an electrode selective to diflunisal. The experimental data for diflunisal/ HPCD fit well to the 1:1 binding model. The binding of diflunisal with each of the studied proteins was compatible with a model having two independent classes of binding sites. The binding of diflunisal in mixed solutions HPCD/BSA, HPCD/HSA, and HPCD/plasma increased considerably when the HPCD concentration was increased. The binding behavior of the two biomolecules in the mixed solutions of HPCD/BSA or HPCD/ HSA was described with an additive model formulated on the basis of the estimates of the binding parameters of diflunisal derived from the separate experiments with each one of the binders tested. The lower than theoretical binding observed in HPCD/plasma solutions was ascribed to the competitive displacement of diflunisal from the HPCD cavity by plasma cholesterol.     

Viscoelastic Properties of Bioadhesive,Chlorhexidine-Containing Semi-Solids for Topical Application to the Oropharynx

Purpose. This study examined the viscoelastic properties of bioadhesive, chlorhexidine-containing semi-solid formulations, designed for topical application to the oropharynx. Methods. Oscillatory rheometry was performed using a Carri-Med CSL²-100 rheometer at 20.0 ± 0.1° C in conjunction with parallel plate geometry (2 cm diameter, 0.5 mm sample thickness). Samples were subjected to a constant strain (6.5 × 10^–3 rad) and defined viscoelastic parameters, namely storage modulus (G), loss modulus (G), loss tangent (tan ) and dynamic viscosity (), measured over a defined frequency range (0.01-1.0 Hz). Results. As the oscillatory frequency was increased, G G of all formulations increased, whereas both and tan significantly decreased. The magnitude of increase of G and G as a function of frequency was relatively small, indicating that, in general, the formulations were non-cross-linked elastic systems. Increasing concentrations of HEC, PVP and PC significantly increased G, G, yet decreased tan observations that may be attributed to the physical state of each polymer in the formulations. Formulation elasticity increased (i.e. tan decreased) as a result of increased entanglement of polymeric chains of dissolved components (i.e. HEC and PVP) and the restrained extension of swollen, cross-linked chains of PC. Additionally, in formulations where the saturation solubility of PVP was exceeded and/or insufficient 'free-water' was available for maximal swelling of PC, formulation elasticity increased as a result of the increasing mass of dispersed solid particles of PVP and/or PC. Formulation increased due to the attendent effects of polymer chain entanglement and polymer state on overall formulation viscosity. Conclusions. Following application to the oropharynx, the formulations will behave as elastic systems. Thus, these formulations would be expected to offer advantageous clinical properties, e.g., prolonged drug release, increased bioadhesion. However, it is noteworthy that the final choice of formulation for clinical evaluation will involve a compromise between viscoelastic characteristics and acceptable textural properties, e.g. ease of product application. This study has shown the applicability of oscillatory rheometry for both the characterisation and selection of candidate, topical bioadhesive formulations for clinical evaluation.     

Dopaminergic factors in human prolactin regulation: A pituitary model for the study of a neuroendocrine system in man

This study in normal male subjects further investigates the effects of dopaminergic-antidopaminergic interactions as manifested by the prolactin response to dopamine and neuroleptic drugs. Incremental doses of dopamine hydrochloride (4 g/min, 15 g/min, 60 g/min, 300 g/min) were infused fused at a constant rate over 90–120 min after a fixed dose of a neuroleptic drug (sufficient for about half of the maximal prolactin response) had been given IV. A dose of dopamine in the order of 15–60 g/min appeared to match the los of endogenous dopaminergic inhibition due to the antidopaminergic effect of the neuroleptic drug. The lactotrophic cells of the pituitary gland are suggested to serve as a model in man for the study of some basic neurohormonal mechanisms.     

Comparative pharmacology of human β-adrenergic receptor subtypes—characterization of stably transfected receptors in CHO cells

Although many ₁-receptor antagonists and ₂-receptor agonists have been used in pharmacotherapy for many years their pharmacological properties at all three known subtypes of -adrenergic receptors are not always well characterized. The aim of this study was, therefore, to provide comparative binding characteristics of agonists (epinephrine, norepinephrine, isoproterenol, fenoterol, salbutamol, salmeterol, terbutalin, formoterol, broxaterol) and antagonists (propranolol, alprenolol, atenolol, metoprolol, bisoprolol, carvedilol, pindolol, BRL 37344, CGP 20712, SR 59230A, CGP 12177, ICI 118551) at all three subtypes of human -adrenergic receptors in an identical cellular background. We generated Chinese hamster ovary (CHO) cells stably expressing the three -adrenergic receptor subtypes at comparable levels. We characterized these receptor subtypes and analyzed the affinity of routinely used drugs as well as experimental compounds in competition binding studies, using the non-selective antagonist ¹²⁵I-cyanopindolol as a radioligand. Furthermore, we analyzed the -receptor-mediated adenylyl cyclase activity in isolated membranes from these cell lines. The results from our experiments show that all compounds exhibit distinct patterns of selectivity and activity at the three -receptor subtypes. In particular, a number of ₂- or ₃-receptor agonists that are inverse agonists at the other subtypes were identified. In addition, ₁-receptor antagonists with agonistic activity at ₂- and ₃-receptors were found. These specific mixtures of agonism, antagonism, and inverse agonism at different subtypes may have important implications for the therapeutic use of the respective compounds.     

Effect of ASTA Z 7557 (INN mafosfamide) a precursor of 4-hydroxy-cyclophosphamide on human T-lymphocytes' Fc-receptors and immunoregulatory functions

Summary The precursor ASTA Z 7557 of the in vivo active metabolite 4-hydroxy-cyclophosphamide (4OH-Cy) of cyclophosphamide (Cy) was tested for selective effects on human T-lymphocytes' Fc-receptor expession and certain immunoregulatory functions. It has been found that ASTA Z 7557 does not alter the expression of Fc-F or Fc-I-receptor on the T-cell membrane nor does it exhibit differential toxicity for either T-cell sub-population. PWM-induced B-cell proliferation is inhibited by ASTA Z 7557, whereas B-cells' Ig-synthesis as well as ConA-driven T-cell proliferation is only blocked with higher doses of the reagent. Final concentrations above 1 g/ml may therefore abrogate ConA-induction of suppressor T-lymphocytes. Already ConA-activated suppressor cells of PWM-driven B-cell cultures, however, are not inhibited even with high doses of ASTA Z 7557.     

The subjective,behavioral and cognitive effects of subanesthetic concentrations of isoflurane and nitrous oxide in healthy volunteers

A prospective, crossover, double-blind trial was conducted in nine healthy volunteers in which the subjective, psychomotor and memory effects of isoflurane (0.0, 0.3 and 0.6%) and nitrous oxide (N₂O) (0, 20 and 40%) were examined. Dependent measures included visual analog scales and a standardized drug effects inventory (subjective effects), reaction time and eye-hand coordination (e.g., psychomotor performance), and immediate and delayed free recall (memory). There were some similarities in subjective effects between the two inhaled drugs (e.g., increased ratings of drunk and spaced out), but isoflurane had effects which N₂O did not have. Isoflurane but not N₂O increased visual analog scale ratings of confused, sedated, and carefree, and decreased ratings of in control of thoughts and in control of body. An odor was detected with isoflurane and it was disliked. Psychomotor performance was more grossly impaired during isoflurane inhalation than during N₂O inhalation. Psychomotor recovery from both agents was rapid and complete so that 5 min after the inhalation period had ceased, performance had returned to baseline levels. Both isoflurane and nitrous oxide impaired immediate and delayed free recall. The feasibility of using isoflurane in conscious sedation procedures is discussed.     

Role of brain amines in learning associated with “amphetamine-state”

Conditional avoidance responses acquired under amphetamine were recalled without deficit only when tested under amphetamine (amphetaminestate dependent learning). Hydroxyamphetamine was devoid of this property. Dihydroxyphenylalanine (DOPA) but not 5-hydroxytryptophan (5-HTP) substituted for amphetamine while reserpine but not syrosingopine eliminated the amphetamine-state. DOPA and 5-HTP, only when given together, restored the amphetamine-state in reserpinized animals. DOPA alleviated the deficit in retention which was caused by methyl-p-tyrosine. 5-HTP alleviated the similar deficit caused by p-chlorophenylalanine. Chlorpromazine or cyproheptadine antagonized the amphetamine-state. It is suggested that amphetamine, but not hydroxyamphetamine is capable of producing an asymmetric behavior-controlling state. The amphetamine-state is related to the stimulation of central and not peripheral amine-receptors and depends on newly synthesized catecholamines which stimulate central catecholamine receptors through serotonin modulation in this case.     

Interactions of three inotropic agents,ASL-7022, dobutamine and dopamine,with α- and β-adrenoceptors in vitro

Summary Three inotropic agents, ASL-7022, dobutamine and dopamine, were evaluated for their -and -adrenoceptor mediated effects in vitro in a variety of isolated organs and in radioligand binding studies. All compounds were ₁-adrenoreceptor agonists in rat and guinea pig aortae, but the rank orders of potency were exactly opposite in these two tissues. Only the rank potency order of dobutamine>ASL-7022>dopamine obtained in rat aorta was consistent with the results obtained in radioligand binding studies to ₁-adrenoreceptors in rat cerebral cortex and to previous results obtained in vivo in the pithed rat. The results obtained in guinea pig aorta did not parallel the radioligand binding studies in rat brain or our previous results in pithed rat, and suggests that species differences exist between postsynaptic vascular ₁-adrenoreceptors in rat and guinea pig aorta, consistent with previous conclusions. ASL-7022 was found to be a potent ₂-adrenoreceptor agonist in field-stimulated guinea pig ileum, and was approximately 10-fold more potent than dobutamine in this respects, which was also confirmed by radioligand binding studies to ₂-adrenoreceptors in rat cerebral cortex. The ₁-adrenoreceptor mediated effects of these compounds were evaluated in guinea pig atria, where the rank order of potency was dobutamine>ASL-7022>dopamine. An identical rank order of affinity was established for these compounds by displacement of ³H-dihydroalprenolol from ₁-adrenoreceptors in rat cerebral cortex. The ₁-adrenoreceptor mediated effects of dobutamine and ASL-7022 in guinea pig atria were completely direct in nature and not secondary to the release of endogenous catecholamines. In contrast, a major component of the ₁-adrenoreceptor mediated tachycardia produced by dopamine in guinea pig atria was indirect in nature as evidenced by the marked attenuation in potency that occurred following catecholamine depletion with reserpine. All three compounds elicited ₂-adrenoreceptor mediated inhibition of tone in rat uterus, with the rank order of potency being ASL-7022>dobutamine>dopamine. Again, this rank order of ₂-adrenoreceptor potency was also reflected in ₂-adrenoreceptor affinity as assessed by displacement of ³H-dihydroalprenolol from ₂-adrenoreceptors in rat cerebellum. Based on these results, it may be concluded that for -adrenoceptors, dobutamine is a selective ₂-adrenoreceptor agonist, ASL-7022 is a selective ₂-adrenoreceptor agonist, and dopamine is a nonselective -adrenoceptor agonist. For -adrenoceptor mediated effect, ASL-7022 is a selective ₂ agonist, while dobutamine and dopamine are nonselective -adrenoceptor agonists. It is likely that the complex inotropic and hemodynamic activities of ASL-7022, dobutamine and dopamine result from the sum of their individual effects at the -and -adrenoceptor subtypes.     

Toxicity and 7-ethoxyresorufin O-deethylase-inducing potency of coplanar polychlorinated biphenyls (PCBs) in chick embryos

The toxicities of the coplanar polychlorinated biphenyls 3,3,4,4-tetrachlorobiphenyl (TCB), 3,3,4,4,5-pentachlorobiphenyl (PeCB) and 3,3,4,4,5,5hexachlorobiphenyl (HCB) were compared in a 72-h study on chick embryos. The substances were injected into the air sacs of hens' eggs preincubated for 7 days. Mortality was measured 72 h later and corresponding LD₅₀ values were calculated. The rank order of toxicity was PeCB> TCB>HCB. Using the same injection procedure, the potencies of these chlorobiphenyls with regard to their induction of hepatic 7-ethoxyresorufin O-deethylase activity were compared. The ranking order of the substances as inducers was the same as their order when ranked according to toxicity. The three coplanar chlorobiphenyls were considerably more toxic and potent as inducers than the nonplanar 2,2,4,4,5,5-hexachlorobiphenyl. In a 2-week toxicity study, PeCB and HCB were injected into the yolks of hens' eggs preincubated for 4 days. PeCB was about 50-fold more potent than HCB in causing embryonic death. Both substances caused abnormalities, including edema, liver lesions, microphthalmia and beak deformities.     

Pharmacological evidence for the possible coexistence of multiple receptor sites for mammalian tachykinins in rabbit iris sphincter smooth muscle

Summary Contractile responses to neurokinin and neurokinin were characterized and compared with those to substance P (a SP-P agonist) and eledoisin (a SP-E agonist) in isolated rabbit iris sphincter. Neurokinin a and neurokinin as well as substance P and eledoisin produced atropine- and tetrodotoxin-resistant contractions of the iris sphincter in nanomolar concentrations, and the rank order of sensitivity was eledoisin > substance P = neurokinin = neurokinin . After prolonged cold-storage of the preparations, responses to capsaicin, a releaser of tachykinins from sensory nerve endings, were nearly absent, but responses of considerable magnitude to carbachol and the tachykinins persisted. On wash-out of the tachykinins, responses faded at characteristic rates (neurokinin a > eledoisin > neurokinin substance P). From the Schild analyses, [abetd-Arg¹, abetd-Pro², abetd-Trp^7,9, Leu¹¹]-substance P, a potent substance P antagonist, competitively antagonized the response to substance P, had no significant effect on the response to neurokinin , and antagonized the response to neurokinin and eledoisin in a more complex manner. Taken together, these results suggest that there coexist multiple receptor sites for mammalian tachykinins in rabbit iris sphincter smooth muscle. Send offprint requests to I. Takayanagi at the above address