Inhibitory adenosine A1-receptors on rat locus coeruleus neurones

Summary Intracellular recordings were performed in ₁-pontine slice preparation of the rat brain containing the locus coeruleus (LC). Adenosine (100, 300 mol/l) and its structural analogues, namely (–)-N⁶-(R-phenyliso-propyl)-adenosine (R-PIA; 3 – 30 mol/l) and S-PIA (10, 30 mol/l), as well as 5-N-ethylcarboxamido-adenosine (NECA; 3–30 mol/l) inhibited the firing rate of spontaneous action potentials and produced hyperpolarization; their rank order of potency was RPIA - NECA > S-PIA > adenosine. When applied by superfusion, all agonists strongly desensitized the LC cells; the hyperpolarization never surmounted 6 mV. Upon pressure ejection of adenosine 10 mmol/l from ₁- micropipette positioned close to an LC neurone, the membrane potential was raised by 14 mV and the apparent input resistance decreased by 20%. When the membrane potential was hyperpolarized by current injection to ₁- similar extent as adenosine did, the fall in input resistance was only 7%. The adenosine uptake inhibitor S-(p-nitrobenzyl)-6-thioguanosine (NBTG) 30 mol/l decreased the frequency of action potentials alone; on simultaneous bath-application with adenosine 300 mol/l it potentiated the hyperpolarization caused by the purine derivative. 8-Cyclopentyl-1,3-dipropylxanthine (CPDPX) 0.1 mol/l had no effect on its own, but it antagonized both R-PIA 30 mol/l and NBTG 30 mol/l. A higher concentration of CPDPX (1 mol/l) facilitated the spontaneous firing. In conclusion, both exogenous and endogenous adenosine activates somatic and/or dendritic A₁-receptors of LC neurones leading to an enhancement of potassium conductance and thereby to ₁- decreased firing rate and ₁- hyperpolarization. Send offprint requests to P. Illes at the above address     

On the role of rate of brain norepinephrine release in the antibenzoquinolizine action of desipramine

Summary Desipramine (DMI) antagonizes and even reverses in rats autonomic and behavior changes of the reserpine-like syndrome elicited by reserpine and synthetic benzoquinolizines. The degree of this antagonism is related to the rate of brain norepinephrine-release and not to the degree of depletion of the monoamine. Since increasing the dose of the sedative benzoquinolizines (tetrabenazine, RO 4-1284, P-2565) enhances the rate of brain-norepinephrine-release, higher doses of the tranquilizers paradoxically increase in DMI-pretreated rats the score of total antagonism and the percentage of animals displaying the reversal phenomenon. The data are in keeping with the view that desipramine enhances the effect of free norepinephrine at central adrenergic effector sites.Presented in part before the American Society for Pharmacology and Experimental Therapeutics at Lawrence, Kansas, August, 1964.     

Differential effects of α-β-methylene ATP on responses to nerve stimulation in SHR and WKY tail arteries

Summary The effects of ,-methylene-adenosine triphosphate, (,-methylene ATP, a P₂-receptor desensitising agent) have been evaluated on vasoconstrictor responses elicited by exogenous agonists or electrical field stimulation in isolated perfused SHR or WKY tail arteries and on tritium release elicited by electrical field stimulation in SHR-tail arteries pre-labeled with ³H-noradrenaline.Exposure to ,-methylene ATP (0.1 mol/l) significantly inhibited vasoconstrictor responses to electrical field stimulation in SHR tail arteries. These inhibitory effects were not further increased at a higher concentration of ,-methylene ATP (1 mol/l). In WKY tail arteries, ,-methylene ATP (1 mol/l) failed to significantly inhibit vasoconstrictor responses to electrical stimulation.In SHR tail arteries prelabelled with ³H-noradrenaline, ,-methyleneATP (1 mol/l) did not inhibit the stimulation evoked release of tritium. However, at this concentration, ,-methylene ATP significantly antagonized the vasoconstrictor responses of SHR tail arteries induced by exogenous ATP (1 mol/l), ,-methylene ATP (30 mol/l), a stable agonist at P₂-receptors, or 60 mmol/l KCl. These effects of ,-methylene ATP on contractile responses to KCl were not observed in WKY-tail arteries.In tail arteries obtained from reserpine pretreated SHR, despite a 85–95% decrease in endogenous noradrenaline tissue content, the vasoconstrictor responses induced by periarterial field stimulation were greatly diminished, but not abolished. These residual responses to periarterial field stimulation were not antagonized by prazosin (0.1 mol/l), but were practically abolished by the addition of ,-methylene ATP (1 mol/l).In tail arteries from WKY rats pretreated with reserpine, exposure to prazosin (0.1 mol/l) further reduced the residual responses elicited by electrical field stimulation. In these WKY-tail arteries, addition of ,-methylene ATP (1 mol/l) did not further inhibit the remaining vasoconstrictor response obtained in the presence of prazosin.While our results suggest a significantly greater cotransmitter role for ATP with noradrenaline in tail arteries of SHR compared with control normotensive WKY rats, additional effects of ,-methylene ATP not involving P₂ receptors cannot be entirely excluded.     

Dopamine inhibits prostaglandin F2α-induced depolarization of rabbit jejunal arteries via activation of DA1-receptors

Summary In rabbit jejunal arteries, the membrane potential of single smooth muscle cells decreased on the application of noradrenaline 3 mol/1. LY 171555 1 mol/1 did not change, whereas SKF 38393 10 mol/1 reversed the effect of noradrenaline. When prostaglandin F₂ (PGF₂) was used to evoke depolarization in the presence of prazosin 0.1 mol/1, rauwolscine 1 mol/1 and propranolol 1 mol/1, both SKF 38393 10 mol/1 and dopamine 10 mol/1 repolarized the membrane. SCH 23390 1 mol/1 antagonized the effects of SKF 38393 10 mol/1 and dopamine 10 mol/1. Thus, the change in membrane potential is mediated by a DA₁-recep-tor.     

Differential Effects of Sulfate and Sulfobutyl Ether of β-Cyclodextrin on Erythrocyte Membranes in Vitro

The hemolytic activity of -cyclodextrin (-CyD) on rabbit erythrocytes was reduced by the introduction of negatively-charged groups onto the hydroxyls of -CyD; the membrane disrupting abilities decreased in the order of -CyD > 2-hydroxypropyl--CyD (HP--CyD) > sulfobutyl--CyD (SB--CyD) >> -CyD sulfate (S--CyD). Under pre-hemolytic concentrations, both -CyD and SB--CyD induced shape changes of membrane invagination on the erythrocytes. In sharp contrast, S--CyD showed biphasic effect on the shape of the erythrocytes; i.e. the crenation at relatively low concentrations and the invagination at higher concentrations. The S--CyD-induced membrane crenation arose from a direct action on the membranes rather than cell metabolism-mediated effects. Unlike -CyD, S--CyD was found to bind to the erythrocytes and may be confined to the outer surface of the membrane bilayer, which may expand the exterior layer relative to the cytoplasmic half, thereby inducing the cells to crenate. On the other hand, the membrane invagination mediated by the three - CyDs was initiated by extracting specific membrane lipids from the cells, depending upon their inclusion abilities, subsequently leading to the lysis of the cells. These results indicate that SB--CyD and S--CyD interact with the erythrocyte membranes in a differential manner and possess lower membrane disrupting abilities than the parent -CyD and HP--CyD.     

Presynaptic dopamine DA2-receptors in rabbit jejunal arteries

Summary Excitatory junction potentials (e.j.ps) evoked by nerve stimulation with 15 pulses at 1 Hz were recorded from muscle cells of rabbit isolated jejunal arteries. LY 171555 1 mol/l, SKF 38393 10 mol/l, dopamine 10 ol/l and clonidine 0.1 mol/l depressed all e j.ps in the train. The percentage inhibition was inversely related to the number of pulses. S- and R-sulpiride, 10 mol/l, domperidone 1 mol/l, SCH 23390 1 mol/l and rauwolscine 1 mol/l did not change, or even depressed the first e j.ps. Of these compounds only S- and R-sulpiride, 10 mol/l and rauwolscine 1 mol/l facilitated the late e.j.ps. The percentage facilitation increased with the number of pulses until a maximum was reached; rauwolscine 1 ol/l had the largest effect. S- and R-sulpiride, 10 mol/l, as well as domperidone 1 ol/l antagonized the action of LY 171555 1 mol/l. S-Sulpiride was more potent than its R-isomer. SCH 23390 1 mol/l and rauwolscine 1 mol/l blunted the effect of SKF 38393 10 mol/l. Rauwolscine 1 mol/l slightly reduced the inhibition by dopamine 10 mol/l; S-sulpiride 10 mol/l was antagonistic only in the presence of rauwolscine 1 mol/l. When rauwolscine 1 mol/l, prazosin 0.1 mol/l, propranolol 1 mol/l and cocaine 10 mol/l was added to the medium, dopamine 10 mol/l continued to produce the same depression of e j.ps, as in the absence of these compounds. Under such conditions S-sulpiride 10 mol/l also counteracted dopamine 10 gmol/l. Rauwolscine 1 mol/l prevented the effect of clonidine 0.1 mol/l. The antagonists were not absolutely selective against only one type of agonist. We suggest that both presynaptic DA₂- and postsynaptic DA₁-receptors are present in rabbit jejunal arteries. The activation of either receptor-type may depress the e j.ps. Dopamine interferes with neuroeffector transmission due to ₂-adrenoceptor agonist properties; its DA₂-effect is unmasked only after ₂-adrenoceptor blockade. There was no evidence for a co-transmitter function of dopamine. Send offprint requests to P. Illes at the above address     

Scopolamine effects on go-no go avoidance discriminations: influence of stimulus factors and primacy of training

Rats were trained in a shuttle-box to perform four go-no go avoidance discrimination tasks, with various combinations of active and passive avoidance signals: 1) light go, noise-light no go; 2) light go, noise no go; 3) noise go, light-noise no go; 4) noise go, light no go. The first task was learned with great average difficulty, and showed a large passive avoidance deficit after scopolamine treatment. The other tasks were much easier to learn, and scopolamine exerted little or no effect on their performance. However, relationships between task difficulty and sensitivity to drug were practically absent within groups.After the completion of discrimination tests, active avoidance retraining was carried out with former passive avoidance cues. This was to obtain an indirect measure of possible differences in the amount of response suppression by these cues. Retraining with noise as CS showed identical acquisition rates in the groups which had previously performed with light as active avoidance signal, and either noise or noise-light as passive avoidance signal. Retraining with light as CS showed faster acquisition in the former noise go, light no go group, as compared with the former noise go, light-noise no go group.An additional experiment showed that the elimination of active avoidance pretraining before discrimination training reduced the passive avoidance deficit and enhanced the active avoidance deficit provoked by scopolamine in the light go, noise-light no go task. In spite of such elimination of the primacy of training in favour of active responses, however, the passive avoidance deficit remained greater than the active avoidance deficit.The relative merits of various neuropsychological interpretations of the effects of central antimuscarinic agents (reappearance of responses to biologically irrelevant stimuli, response disinhibition, set perseveration, amnesia, state-dependency) are discussed. The role of built-in hierarchies between stimulus-response relationships, and of response hierarchies (both innate and dependent on training history) are emphasized.On leave from the Department of Pharmacology of the Medical Faculty, Bul. JNA 18, Beograd (Yugoslavia).     

Toxic effects of some “mono-n-butyl-tin compounds” on white mice

The toxic effects of mono-n-butyl-tin-trichloride, mono-n-butyl-tin-tris-(2-ethyl-hexyl-mercaptoacetate), mono-n-butyl-tin acid and mono-n-butyl-thiotin acid on white mice were investigated. These compounds were administered to white mice by means of a stomach tube in a single dose of 4000 mg/ kg b.w. at the start of the experiment. All mice were sacrificed 24 hours after the administration.The clinical course as well as the macroscopic findings in all experimental groups indicated general signs of an acute intoxication. The histological findings in the mono-n-butyl-tin-trichloride group showed pronounced changes in the digestive tract, where haemorrhages in the mucous membrane and in the inner layer of the gastric and intestinal walls had been found. In the mice of the other experimental groups, steatosis of the hepatocytes and an irregular steatosis of the renal tubular epithelium were observed.     

The selective P2X purinoceptor agonist, β,γ-methylene-L-adenosine 5′-triphosphate,discriminates between smooth muscle and neuronal P2X purinoceptors

The effects of the putative selective P_2X purinoceptor agonist, ,-methylene-l-adenosine 5-triphosphate (me-l-ATP), were determined at rat neuronal and smooth muscle P_2X purinoceptors.Me-l-ATP had no effect on the extracellularly recorded membrane potential of the rat isolated vagus nerve preparation at concentrations up to 300 M. In contrast, the archetypal P_2X purinoceptor agonist, , methylene ATP (meATP;1–100 M), produced concentration-related depolarisation responses with a mean EC₅₀ value of 10.8 M. The depolarising effects of meATP were not attenuated by me-l-ATP (100 M). In voltage clamp experiments on single nodose ganglion neurones, ATP (100 M), but not me-l.-ATP (1–300 M), evoked rapid ( < 20 ms onset) inward currents when applied using a concentration-clamp method. In receptor binding studies to rat brain membranes, me-d-ATP and meATP competed with high affinity for [³H]Lx meATP binding sites, with mean pIC₅₀ values of 7.7 and 8.3, respectively. However, me-l-ATP possessed low affinity for these sites and competed only at concentrations in excess of 10 M (mean pIC₅₀ value 4.1).In prostatic segments of the rat vas deferens, me-l-ATP (1–100 M) and meATP (0.3–100 M) each produced concentration-related contractile responses with mean EC₅₀ values of 17.1 and 3.6 M, respectively. Me-l-ATP (1–10 M) evoked fast inward currents in freshly dispersed vas deferens smooth muscle cells, indicative of an action at ligand-gated ion channels. Binding sites in vas deferens membranes labelled using 1 nM [³H]meATP exhibited high affinity for me-l-ATP, meATP and me-d-ATP with mean PIC₅₀ values of 7.7, 8.4 and 7.3, respectively.These results indicate that me-l-ATP exhibits neither agonist nor antagonist properties at P_2X purinoceptors on rat vagal neurones and possesses only very low affinity for [³H]meATP binding sites in rat brain. In contrast, me-l-ATP is a potent, high affinity agonist at smooth muscle P_2X purinoceptors of the rat vas deferens. This selective agonist action of me-l-ATP suggests that P_2X purinoceptors in smooth muscle and neurones are different and represent distinct P_2X purinoceptor subtypes.     

Evidence for a displaceable non-specific [3H]neurotensin binding site in rat brain

Summary Levocabastine is a potent antihistamine drug, structurally unrelated to neurotensin. In rat and mouse brain but not in other animal species, it inhibited 60% of the [³H]neurotensin binding displaced by unlabelled neurotensin or neurotensin (8–13).The levocabastine-sensitive site or site 1 displayed high affinity properties for levocabastine (IC₅₀=25 nM) and was highly stereospecific (IC₅₀-value higher than 10 M for one of the isomers). Binding to the site 1 in rat brain corresponded to the [³H]neurotensin binding displaceable by 1 M levocabastine, whereas binding to the site 2 corresponded to the binding displaced by 1 M neurotensin when the site 1 was occluded by 1 M levocabastine.Both site 1 and site 2 appeared to be saturable. Scatchard plots obtained in rat bulbus olfactorius allowed to calculate a K _D-values of 7.1 nM and a B _max-values of 37.2 fmol/mg original tissue for site 1, while site 2 displayed a K _D-value of 0.7 nM and a B _max-value of 16.3 fmol/mg original tissue. The regional distributions of both sites showed marked differences. The site 1 was homogeneously distributed throughout all rat brain areas, whereas the amount of site 2 binding was markedly different in separate brain areas: bulbus olfactorius and substantia nigra had the highest amounts (8.9 and 7.8 fmol/mg tissue) while cerebellum had the lowest (0.4 fmol/mg tissue).In spite of its high affinity and stereospecificity, site 1 has to be considered as an acceptor or recognition site for [³H]neurotensin because of its species-link, low saturability and homogeneous distribution in all rat brain areas.On the other hand, site 2 had the characteristics of a physiological receptor: high affinity, saturability in the low nanomolar range and marked regional distribution in rat brain. Site 2 corresponds therefore most probably to the physiological neurotensin receptor. The foregoing experiments provide evidence for the presence of a drug displaceable, non-specific (=unrelated to a physiological receptor) neurotensin binding site in rat brain; levocabastine should be an important tool to occlude this site in order to reveal, by means of in vitro binding assays, the specific neurotensin binding site in rat brain.     

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.     

Effects of suramin and α,β-methylene ATP indicate noradrenaline-ATP co-transmission in the response of the mouse vas deferens to single and low frequency pulses

Summary Vasa deferentia from mice were field-stimulated by trains of 10 pulses delivered at 0.5 Hz. The pulses elicited separate twitches, the first of which (corresponding to a single pulse) exceeded the following ones in height and width and often was clearly biphasic. , -Methylene-ATP 1 mol/1 and suramin 100 mol/1 caused almost identical changes. They reduced the height of the first twitch in the train by about one half and also reduced its width in a manner indicating that only the second, slow phase remained, but reduced much more markedly the following twitches in which now a small second, slow phase also became detectable. Idazoxan 0.1 mol/1 or yohimbine 0.1 mol/l, when added in the presence of a, -methylene-ATP or suramin, further decreased the first twitch but enhanced twitches No. 2 to 10. These responses were then almost abolished by prazosin 0.1 mol/l. Successive addition of prazosin 0.1 mol/l and idazoxan 0.1 mol/1 to previously untreated vasa deferentia depressed the response to the first pulse by about one half in a manner indicating that only the first, rapid phase remained, but had comparatively little effect on the responses to the subsequent pulses. Suramin 100 mol/l almost abolished the contractions remaining in the presence of prazosin and idazoxan. The results indicate that the first, rapid phase of the neurogenic contractions elicited by single or low frequency pulses is mediated by ATP which substantially contributes to all responses in a train. The second, slow phase is mediated by noradrenaline which substantially contributes to the response to the first pulse only. The adrenergic contribution seems to be mediated by postjunctional ₁- as well as a ₂-adrenoceptors. Prejunctional ₂-adrenergic autoinhibition depresses the release of both ATP and noradrenaline. Send offprint request to I. v. Kügelgen at the above address     

NMR Studies of Retinoid-Protein Interactions: The Conformation of [13C]-β-Ionones Bound to β-Lactoglobulin B

Purpose. Vitamin A (retinol) and its metabolites comprise the natural retinoids. While the biological action of these molecules are thought to be primarily mediated by ca. 55 kDa nuclear retinoic acid receptors, a number of structurally similar 15-20 kDa proteins are involved in the transport, and possibly metabolism, of these compounds. The milk protein -lactoglobulin B (-LG) is an 18 kDa protein which binds retinol and may be involved in oral delivery of retinol to neonates. -LG also binds drugs and other natural products and is of potential interest as a protective delivery vehicle. Methods. To examine the conformation of the model retinoid -ionone both in solution and when bound to -LG, NMR and computational methods have been employed. Results. Taken together, NMR studies of -ionone in solution measuring scalar and dipolar coupling, as well as CHARMm calculations, suggest -ionone prefers a slightly twisted 6-s-cis conformation. Isotope-edited NMR studies of ^l3C-labeled -ionones bound to -LG, primarily employing the HMQC-NOE experiment, suggest -ionone also binds to -LG in its 6-s-cis conformation. Conclusions. The methods employed here allow estimates of protein-bound ligand conformation. However, additional sites of ligand labeling will be necessary to aid in binding site localization.     

Sex differences in the medication choice for hypertension in general practice. A study with written case simulations

The objective of this study was to explore explanations for the preference of physicians to prescribe blockers to hypertensive men and diuretics to hypertensive women.A qualitative study among 12 family physicians was conducted with a combination of written case simulations, semistructured interviews and statements on attitudes of physicians towards antihypertensive drug choice.Among the male hypertensive cases the most frequently prescribed drugs were blockers, whereas among the female hypertensive cases diuretics were more often prescribed. Physician characteristics associated with a preferred prescribing of blockers to hypertensive men and diuretics to hypertensive women were: older age (no residency in family medicine), the believe that blockers are more effective in men with regard to lowering blood pressure and that diuretics are more effective in women, a nonevidence based attitude and a sexrelated attitude towards the choice of blockers and diuretics in general, and in particular towards the prescribing of blockers to hypertensive men because men have a higher absolute risk of coronary heart disease than women. An additional explanation for these findings may be the higher prevalence of ankle oedema among women. Patient characteristics associated with more prescribing of blockers to hypertensive men and diuretics to hypertensive women were: current employment and a "highrisk" profile in terms of blood pressure level and additional cardiovascular risk factors.Although, most considerations underlying a preferred prescribing of blockers to hypertensive men and diuretics to hypertensive women were not evidencebased, the actual choice of antihypertensive drug (diuretic or blocker) was evidencebased. These considerations may also play a role in the sex difference in the choice of calcium antagonists and angiotensin converting enzyme inhibitors and require further investigation.     

Pre- and postjunctional adrenoceptor types in the circular muscle of the guinea-pig caecum

Summary The sucrose gap technique was used to study the effects of applied adrenoceptor agonists on membrane potential and non-adrenergic, non-cholinergic inhibitory junction potentials (IJPs), in the smooth muscle of the circular coat of guinea-pig caecum. Noradrenaline (10 nmol/1–100 mol/l), phenylephrine (1–100 mol/l) and isoprenaline (0.1–100 mol/l) caused hyperpolarisations of the smooth muscle membrane which were rapid in onset and effect. The magnitudes of hyperpolarisations elicited by noradrenaline were significantly reduced by the non-specific -adrenoceptor antagonist phentolamine (10 gmol/l), the₁-adrenoceptor antagonist prazosin (1 mol/l) and the -adrenoceptor antagonist propranolol (5 gmol/1). The ₂-antagonist yohimbine (10 gmol/l) did not significantly reduce the magnitude of the hyperpolarisations induced by noradrenaline. Noradrenaline application caused a reduction in UP amplitude, during hyperpolarisation, by up to 50%. The reduction of the UP amplitude elicited by noradrenaline was significantly antagonised by yohimbine and phentolamine, but not by prazosin or propranolol. Clonidine caused a reduction of UP amplitude by up to 20%, but neither phenylephrine nor isoprenaline caused any significant reduction in UP amplitude. It is concluded that the hyperpolarising responses to exogenous noradrenaline in the circular muscle of guinea-pig caecum are mediated by postjunctional ₁- and -adrenoceptors, and that the inhibition of UP amplitude is mediated by prejunctional ₂-adrenoceptors. Send offprint requests to G. Burnstock at the above address     

New therapeutic targets for rheumatoid arthritis

New insights into the pathogenesis of rheumatoid arthritis (RA) and consequently new targets of therapy are covered in a broad overview fashion. Shortterm significant beneficial effect on RA disease activity has been established in a small but rapidly growing number of doubleblind placebocontrolled trials now including recombinant human IL1 receptor antagonist, chimeric (mouse/human) monoclonal antibodies (mAb) against TNFa (cA2), humanised (human/mouse) antiTNFa mAb (CDP571) and recombinant human TNFreceptorFc fusion protein (TNFR : Fc). Placebocontrolled trials of antiT cells agents such as chimeric antiCD4 mAb (cMT412) and antiCD5 immunoconjugate, did not demonstrate clinical benefit. A placebocontrolled study of the antiT cell derived cytokine IL2 (DAB486IL2) showed only modes clinical improvement. Other antiT cell approaches such as autologous T cell vaccination and induction of tolerance by oral type II collagen have been unsuccessful. The one controlled trial with an antiinflammatory cytokine, recombinant human IFNg, showed modest clinical benefits. Controlled trials with IL4 and IL10 and with antiadhesion molecules are awaited.     

Clockwise hysteresis or proteresis

The authors propose the word proteresis to designate the clockwise hysteresis, i.e., when an effect increases more rapidly than the observed drug concentrations. Such a phenomenon has been recently described for aspirin and nicotine. Indeed hysteresis means which comes after, while proteresis, the greek symmetrical word, means which comes earlier, a more appropriate term for the described situation.     

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.     

Opposite modulation of ouabain cardiotoxicity by hexamethyleneamiloride and phenylephrine

Summary To see whether the Na/H antiporter plays a role in digitalis cardiotoxicity, we investigated the influence of modulators of Na/H exchange on the toxic effects of ouabain in isolated, paced (0.4 Hz) rat left atria. Ouabain (1 mmol/l) caused a transient positive inotropic effect followed by toxic events, including a complete loss of developed force and a gradual increase in resting force. In the presence of hexamethyleneamiloride (3 and 10 mo1/l), an inhibitor of Na/H exchange, ouabain (1 mmol/l) caused a sustained positive inotropic effect without toxicity. By contrast, phenylephrine (100 mol/ 1) an -adrenoceptor agonist reported to stimulate the antiporter, hastened the development of ouabain's toxicity. Neither ouabain, at a subtoxic concentration (650 ol/l), nor phenylephrine (100 mol/l) affected diastolic force, but in their combined presence, a substantial contracture developed and twitch contractions disappeared. Phenylephrine (30 or 100 mol/l) or adrenaline (30 mol/l), in the presence of a -adrenoceptor antagonist, increased the intracellular pH by up to 0.15 pH unit, as measured using ion-selective microelectrodes in quiescent preparations. This effect on pH₁ was prevented by hexamethyleneamiloride (10 mol/l). Consistent with phenylephrine's ability to stimulate Na⁺ influx via the Na/H antiporter, phenylephrine (100 mol/l) increased intracellular Na⁺ activity by about 3 mmol/l in ouabain (650 mol/l)-treated atria. These findings indicate that modulators of Na/H exchange affect the cardiotoxicity of digitalis glycosides and imply that the stimulation of myocardial -adrenoceptors may aggravate digitalis toxicity.This work was conducted in part under the auspices of the Association for US/French Biomedical Cooperation Send offprint requests to S. M. Vogel at the above address     

Über die Wirkung einiger herzwirksamer Bisguanylhydrazone auf den Veratrineffekt am Frosch-Sartoriusmuskel

Zusammenfassung Die Wirkung einiger Guanylhydrazone sowie von Tyramin auf die Veratrine-Response des Froschsartoriusmuskels wurden untersucht. Von den drei herzglykosidartigen Bisguanylhydrazonen zeigten BG 60 und BG 31 den unspezifischen Veratrinantagonismus des Chinidins. BG 85 hingegen beeinflußte die VR herzglykosidartig. Von den drei tyraminartigen Substanzen BG 81, MG 41 und Tyramin wirkten die letzten zwei chinidinartig, während BG 81 trotz seiner tyraminartigen Wirkung die VR herzglykosidartig beeinflußte.

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Summary A series of guanylhydrazones was synthesized, some of the substances had a cardiac glycoside-like activity on the mammalian heart whereas other ones acted tyramine-like. The effect of some guanylhydrazones of each kind of action on the veratrine response (VR) of the frog's sartorius muscle should be investigated. Following substances were synthesized: 1. with cardiac glycoside-like activity 3,3-dimethyl-4,4-diacetyldiphenylbisguanylhydrazone (BG 60), progesteronebisguanylhydrazone (BG 31), p-aceto-m-methyl-phenyl-acetonyl-ether-bisguanylhydrazone (BG 85) 2. with sympathomimetic activity: p-aceto-phenyl-acetonyl-ether-bisguanylhydrazone (BG 81) and p-hydroxybenzaldehyd-monoguanylhydrazone (MG 41). The characteristic influence of the cardiac glycosides on the VR was only to be seen with BG 85 and BG 81. BG 60, BG 31 and BG 41 showed a quinidine-like effect on the VR. That means that from 3 guanylhydrazones with cardiac glycoside-like activity on the mammalian heart two of them had a quinidine-like effect on the VR and only one of them showed the typical cardiac glycoside-like effect on the VR. On the other hand among the guanylhydrazones with tyramine-like activity on the mammalian heart there is one, BG 81, which influenced the VR like a cardiac glycoside.