Lithium treatment regimens induce different changes in [3H]paroxetine binding protein and other rat brain proteins

Rats were treated with lithium administered either via the food or by intraperitoneal injection. Lithium administration via the food results in a rather stable serum lithium concentration, whereas lithium injection results in a varying serum lithium concentration whereby a sharp increase shortly after the injection is followed by an exponential decline until the next injection (Plenge et al. 1981) After 5 months of lithium treatment the 5HT transport protein, the-adrenergic receptor and several other brain proteins were determined. The 5HT transport protein, labelled with [³H]paroxetine, was found to be decreased in the lithium-injected rats (B_max=347 fmol/mg protein) but was unchanged in the lithium-fed rats (B_max=389 fmol/mg protein), as compared with control rats (B_max=396 fmol/mg protein), and therefore probably is a specific effect only seen with varying lithium concentration. In contrast, the neuronal membrane marker protein D3 was decreased in the lithium-fed rats (88% of the control value), and showed a trend towards decrease in the lithium-injected rats. The decrease in D3 in the lithium-fed rats may indicate some neuronal damage due to the continous presence of lithium. This damage may be more pronounced than in rats, where periods of low lithium concentration enable repair to take place. The-adrenergic receptor and the neural cell adhesion molecule NCAM were unaffected by the different lithium treatment regimens. Lithium has been reported to inhibit the 5HT1B receptor (the serotonin autoreceptor). We postulate that the two effects, i.e. overall lithium-induced inhibition of the 5HT autoreceptor and the down-regulation of the 5HT transport protein in rats with changing lithium concentration shown in the present study, may combine to augment the 5HT concentration in the synaptic cleft; increased 5HT in the cleft possibly being relevant in prophylactic lithium treatment of manic depressive disorders.     

The effect of repeated electroconvulsive shock on corticosterone responses to centrally acting pharmacological stimuli in the male rat

The effect of repeated and single electroconvulsive shocks (ECS) on the corticosterone response to pharmacological stimuli has been studied in male rats. Plasma corticosterone concentrations are elevated by oxotremorine, a muscarinic agonist, and by 5-hydroxy-l-tryptophan, a precursor of serotonin. Both these agonists probably stimulate corticotrophinreleasing-factor release from the hypothalamus. The log dose-response curves of the corticosterone response to oxotremorine and to 5-hydroxy-l-tryptophan are shifted to the left after a single ECS given daily for 10 days compared with sham-shocked controls. Plasma corticosterone concentrations are elevated by treatment with -methyl-p-tyrosine methyl ester (400 mg/kg IP). This rise is suppressed by clonidine. The log dose-response curve for the corticosterone response to clonidine after -methyl-p-tyrosine methyl ester is also shifted to the left by repeated ECS, compared with controls. There is no difference in the corticosterone response of ECS and sham-treated groups given vasopressin, which is thought to act directly on the pituitary to release ACTH.A single ECS produces a slight enhancement of the response to 5-hydroxy-l-tryptophan, a slight decrease in the response to oxotremorine and no change in the response to clonidine after -methyl-p-tyrosine.The disappearance of the difference in response between ECS and sham-treated animals was also studied 1,3, and 6 days after a series of ten ECS or sham procedures. Significant differences in the corticosterone responses to oxotremorine, 5-hydroxy-l-tryptophan and clonidine after -methyl-p-tyrosine between ECS and sham-treated animas were found 24 h after the last ECS or sham shock. These differences were in decline 3 days after the last procedure and had completely disappeared by day 6. The decline was largely due to an increase in plasma corticosterone responsiveness to pharmacological stimuli of the shamshocked controls. Responses in the ECS-treated groups remained constant.It is apparent that the anaesthetic procedure suppresses the effect of oxotremorine, 5-hydroxy-l-tryptophan and clonidine after -methyl-p-tyrosine on corticosterone concentrations in plasma. This effect is spontaneously reversible. Repeated ECS reverses the effect of the anaesthetic procedure but produces no reversible enhancement of its own.     

Light-dark differences in [3H]-paroxetine binding to rabbit platelet membranes

Summary [³H]-Paroxetine binding to rabbit blood platelet membranes from samples obtained under light and dark conditions was examined. Animals were kept on a 14 h light (L) — 10 h dark (D) schedule and blood samples were collected at L + 7 and D + 5 h. Significant differences were found for B _max values of [³H]-paroxetine binding, with low B _max values during the light period and high B _max values during the dark period. The K _d values were not significantly different. These results confirm previous observations on light-dark differences of [³H]-imipramine binding in rabbit blood platelets suggesting the existence of a circadian rhythm for the 5-HT transporter complex.Send offprint requests to S. Z. Langer at the above address     

The role of a low β1-adrenoceptor selectivity of [3H]CGP-12177 for resolving subtype-selectivity of competitive ligands

Summary On the basis of saturation binding studies on rat cardiac microsomes, which contained a mixed population of -adrenoceptor subtypes, [³H]CGP-12177 is presumed to be a non-selective -adrenergic radioligand. However, saturation binding studies carried out in the presence of subtype-saturating concentrations of the ₂-selective antagonist ICI 118,551 and the ₁-selective antagonist ICI 89,406, respectively, revealed a K _D for ₁-adrenoceptors of 0.33 ± 0.02 nmol/l and a K _D for ₂-adrenoceptors of 0.90 ± 0.14 nmol/l. Competition experiments with the highly selective antagonists revealed greatly different competition binding curves in the presence of either [³H]CGP-12177 or (–)[¹²⁵I]iodocyanopindolol (ICYP), a -adrenergic radioligand considered to be as non-selective as [³H]CGP-12177. The following results are further suggestive for a selectivity of [³H]CGP-12177 for ₁-adrenoceptors: (1) Using non-linear regression analysis, a significantly lower selectivity (expressed as the ratio of the IC₅₀ for ₂-adrenoceptors to the IC₅₀ for ₁-adrenoceptors) as well as a larger proportion of ₁-adrenoceptors were calculated by competition of the ₁-selective antagonist ICI 89,406 with [³H]CGP-12177 binding than by competition of ICI 89,406 with ICYP binding; (2) reducing the [³H]CGP-12177 concentration from 2 to 0.4 nmol/l, competition experiments with ICI 89,406 led to an increase in the estimated selectivity of the competitor and in the estimated proportion of ₁-adrenoceptors; (3) reverse findings were obtained with ICI 118,551, a ₂-selective antagonist. Theoretical competition data assuming a varying selectivity of the radioligand were generated using an equation which describes inhibition of the binding of a selective radioligand by a selective competing ligand. Analysis of these data by the model which assumes that the radioligand is entirely non-selective revealed a logarithmic relationship between the distortion of the true selectivity of the competing ligand and the degree of selectivity of the radioligand. For instance, the selectivity of ICI 89,406, estimated against [³H]CGP-12177 binding, was 23% of its selectivity estimated against ICYP binding. Hence, non-linear fits of competition curves with subtype-selective unlabeled ligands will result in serious distortion in the estimates of affinity of the competing ligands and in the size of subtype populations if [³H]CGP-12177 is considered entirely non-selective.Abbreviations and code names CGP (–)4-(3-t-butylamino-2-hydroxypropoxy)-benzimidazol-2-one - ICYP (–)[¹²⁵I]-iodocyano-pindolol - ICI erythro-DL-1-(7-methylindane-4-yloxy)-3- isopropylaminobutanol - ICI 1-(2-cyanophenoxy)-3-(3-phenylureido)-ethylamino-2-propanol - HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - Gpp(NH)p guanylyl imidodiphosphate Send offprint requests to C. Nanoff     

Identification of harman in the rat arcuate nucleus

Summary This communication describes the presence of 1-methyl--carboline (harman) in the hypophysiotropic area of the hypothalamus which incorporates the arcuate nucleus. Diethyl ether extracts of boratebuffered arcuate homogenates were subjected to silica column chromatography and thin-layer chromatography (TLC). Identification of the -carboline was accomplished by use of fluorescent spectrometry, gas chromatography (GC), mass spectrometry (MS) and combined gas chromatography-mass spectrometry (GC-MS).Presented in a preliminary report at the 10th Annual Meeting of the American Society for Neurochemistry, Charleston, South Carolina, USA, March 1979     

Cardiac ventricular β2-adrenoceptors in guinea-pigs and rats are localized on the coronary endothelium

Summary In mammalian heart tissue ₂ are known to coexist with ₁. In the present study, evidence that ₂ in guinea-pig and rat ventricles are primarily localized on the coronary endothelium is provided by competition binding studies with the subtype-selective -adrenoceptor antagonists ICI 89.406 (₁) and ICI 118.551 (₂) on four different plasma membrane preparations. (1) Following density gradient centrifugation of cardiac ventricular microsomes from rats or guinea-pigs, endothelial plasma membranes migrated at slightly higher density than the sarcolemmal membranes, as verified by endothelial (angiotensin converting enzyme) and sarcolemmal markers (adenylate cyclase, [³H] ouabain binding). At the activity peak of angiotensin converting enzyme, the relative amount of ₂ in guinea-pigs and rats was 25% and 65%, respectively. (2) On sarcolemmal membranes corresponding to the activity peak of adenylate, cyclase, -adrenoceptors consisted of the ₁ exclusively (guinea-pig), or to at least 90% (rat). (3) Cultures of coronary endothelial cells derived from guinea-pigs revealed only ₂. (4) Isolated guinea-pig cardiomyocytes contained only ₁, a finding recently established in rat myocytes as well.     

Effect of chronic lithium administration on adrenoceptor binding and adrenoceptor regulation in rat cerebral cortex

Summary Lithium (Li) at a concentration, which exerts prophylactic effects in affective disorders is known to alter noradrenaline turnover and the -adrenoceptor-dependent cAMP accumulation. In the present study the action of chronic Li administration (at least 5 weeks) on agonist and antagonist binding to adrenoceptors and on the regulation of adrenoceptors was investigated in rat cerebral cortex. Li treatment caused a small but significant decrease in the number of -adrenoceptor binding sites by 10% (³H-dihydroalprenolol binding) leaving the number of ₁- and ₂-adrenoceptor binding sites (³H-prazosin and ³H-rauwolscine, respectively) unchanged. The affinity of the radioligands as well as the affinity of agonists to these binding sites were not altered. The up-regulation of -adrenoceptor binding sites produced by repeated reserpine injections was inhibited by 32% in rats treated concomitantly with Li, although the noradrenaline depleting effect of reserpine was not impaired. In contrast, Li treatment had no effect on the up-regulation of -adrenoceptor binding induced by 6-OH-dopamine, nor did it alter the -adrenoceptor down-regulation following chronic administration of desipramine. The up-regulation of ₁-adrenoceptor binding sites caused by reserpine or 6-OH-dopamine also remained unaffected by Li. It is concluded that chronic Li has limited effects on cortical adrenoceptors and their regulation. The inhibition of -adrenoceptor up-regulation caused by reserpine may reflect an action of Li on non-adrenergic systems rather than a general stabilizing effect on adrenoceptors proposed previously.Send offprint requests to: G. Gross     

Involvement of central β-adrenoceptors in the regulation of yawning responses

Summary A behavioral study was performed in an attempt to understand the role of central -adrenoceptors in yawning in rats. Yawning was evoked by apomorphine and piribedil, mixed dopamine D₁/D₂-receptor agonists, but not by SK&F 38393 [1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8diol], a dopamine Dr-receptor angonist. The apomorphine-induced yawning was increased by pindolol, propranolol, indenolol, alprenolol and bukumolol which block the central -adrenoceptors, but not by the peripheral -adrenoceptor antagonists, carteolol and atenolol. These -adrenoceptor antagonists given alone did not elicit yawning. Conversely, the yawning was inhibited by salbutamol, a -adrenoceptor agonist, without being affected by prazosin, an -adrenoceptor antagonist. The combined administration of SK&F 38393 and the -adrenoceptor antagonists did not induce yawning. The yawning elicited by either apomorphine or piribedil in combination with pindolol was suppressed by spiperone and YM-09151-2 [cis-N-(1-benzyl-2-methylpyrrolidin-3-yl)-5-chloro-2-methoxy-4-methylaminobenzamide], dopamine D₂-receptor antagonists, and scopolamine, a muscarinic receptor antagonist, but not by SCH 23390 [R(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol], a dopamine D₁-receptor antagonist. Physostigmine or pilocarpine induced yawning, which was also enhanced by pindolol and propranolol. This enhanced yawning was inhibited by scopolamine, but not by spiperone, YM-09151-2 and SCH 23390. The present results suggest that the \-adrenoceptor blockade facilitates the occurrence of yawning induced by dopaminergic and cholinergic agonists. Therefore, the central adrenergic neuron systems may participate in the regulation of yawning responses.Send offprint requests to K. Yamada at the above address     

Unaltered 5-HT- and desipramine-sensitive [3H]imipramine binding and [3H]5-HT uptake in rat brain after chronic imipramine and norzimeldine treatment

Several reports have shown heterogeneity of [³H]imipramine binding to brain membranes. Recently, a high affinity and 5-HT sensitive [³H]imipramine binding site of protein nature, that was suggested to be identical to the substrate recognition site for 5-HT uptake, was demonstrated. Since most studies on the regulation of the [³H]imipramine binding sites by antidepressants have used desipramine displaceable binding, which is heterogenous in nature and contains binding not related to 5-HT uptake sites, the present report studies the possible effects of chronic (3 weeks) administration of imipramine or norzimeldine (10 mg/kg intraperitoneally twice daily) on 5-HT sensitive [³H]imipramine binding sites. For comparison, desipramine sensitive binding was also studied, as well as the physiological correlate 5-HT uptake. There were no changes in either [³H]imipramine binding or 5-HT uptake after the antidepressant treatment.Supported by the Swedish Medical Research Council Offprint requests to: J. Marcusson at Dept. of Geriatric Medicine     

Beta-adrenoceptors in the rat kidney

Summary The direct histochemical detection of -blocker binding sites was studied in sections of rat kidney using an immunohistochemical technique developed in our laboratory.Frozen sections of rat kidney were incubated in a solution of (-)alprenolol, washed, exposed to fluorescent (-)alprenolol antibodies (FAA) and then observed at a fluorescence microscope.Strong fluorescence was found within the wall of renal artery and vein, but primarly in the artery. At the level of blood vessels(-)alprenolol binding sites were located chiefly in the media and in the intima.The renal glomerulus, the loop of Henle and collecting tubules appear to be free of any fluorescence. Consequently they do not have -adrenoceptors.On the contrary, the glomerular afferent and afferent arterioles, the cellular elements of the juxtaglomerular apparatus, proximal and distal convoluted tubules, are rich in (-)alprenolol binding sites. At higher magnifications the immunoreactivity appears to be located in the basal membrane of cellular elements which indicates that (-)alprenolol binding sites are membrane receptors.The direct immunohistochemical detection of -blocker binding sites in the kidney may offer useful information concerning the site of action of -blockers at the level of an important target organ for this class of drugs.     

Pulmonary Absorption of Insulin Mediated by Tetradecyl-β-Maltoside and Dimethyl-β-Cyclodextrin

Purpose. To determine if tetradecyl--maltoside (TDM) and dimethyl--cyclodextrin (DMCD) enhance pulmonary absorption of insulin and to investigate if they do so by a reversible action on respiratory epithelium. Methods. Insulin formulated with saline, TDM, or DMCD was administered intratracheally, after laryngoscopic visualization, as a spray to anesthetized rats. Reversibility studies were conducted in intact rats by administering insulin at different time points after administration of TDM or DMCD. The pharmacodynamics and pharmacokinetics of insulin formulations were assessed by measuring plasma glucose and plasma insulin concentrations. Results. When insulin formulated with increasing concentrations (0.06-0.25%) of TDM or DMCD were administered to anesthetized rats, there was a concentration-dependent decrease in plasma glucose and increase in plasma insulin concentrations. The relative bioavailability of insulin formulations containing TDM was higher (0.34-0.84%) than that of formulations containing DMCD (0.19-0.48%). When insulin was administered 120 min after an agent was administered, in the reversibility study, no significant change in plasma glucose and insulin levels occurred compared to control. Conclusions. Both TDM and DMBCD enhance pulmonary absorption of insulin, with TDM being more efficacious than DMCD in enhancing insulin absorption via pulmonary administration. The effects of TDM and DMCD on respiratory epithelium are reversible, and the epithelium reestablishes its normal physiologic barrier 120 min after exposure to these agents.     

Alterations in β-adrenoceptor number and catecholamine content of chick atria after reversible sympathetic denervation with 6-hydroxydopamine

Summary 1. The characteristics of [³H]-dihydroalprenolol (DHA) binding were determined in atria from untreated chicks. [³H]-DHA binding to atrium homogenates was rapid (k1 = 8.52 × 10⁸ 1 mol^–1 min^–1), reversible (k _–1 = 0.47 min^–1), saturable, and of high affinity (K _D = 0.61.–nmol/l). Isoprenaline competed for specific [³H]-DHA binding in a stereoselective manner; IC₅₀ values (mol/l) were: (–)isoprenaline 0.12, (+)isoprenaline 4.7. 2. The number of [³H]-DHA binding sites and catecholamine content of left and right atria were examined after injection of chicks with a single dose of 6-hydroxydopamine hydrobromide (100 mg/kg). There were transient increases in the number of [³H]-DHA binding sites in both the left and the right atrium after 6-OHDA treatment. These increases were quicker in onset and in offset in the right atrium than in the left atrium. [³H]-DHA binding was significantly increased- in the left atrium at 5 and 7 days, and in the right atrium at 3 and 5 days after 6-OHDA injection. 3. Saturation binding isotherms indicated that the increase in [³H]-DHA binding was due to an increase in -adrenoceptor number with no change in affinity for [³H]-DHA. 4. Twenty four hours after 6-OHDA treatment there was a significant (80%) decrease in noradrenaline content of left and of right atria. 5. The decrease in noradrenaline content was reversible, noradrenaline levels returning to 55% of control in left atrium and to 71% of control in right atrium by 21 days after 6-OHDA treatment. These changes are consistent with reversible sympathetic denervation of the atria. 6. Adrenaline levels in the atria were 5 to 18% of total catecholamine (noradrenaline+adrenaline) content and were not significantly altered by 6-OHDA treatment.     

Responses to catecholamines of the rat isolated uterus throughout the natural oestrous cycle

Summary The effects of noradrenaline (NA), adrenaline (Adr) and isoprenaline (Iso) on rat isolated uterus were studied, throughout the natural oestrous cycle. The -inhibitory effects of the catecholamines were measured as a percentage inhibition of a standard acetylcholine (ACh)-induced contraction. Iso produced approximately 80% maximum inhibition of the standard ACh-contraction in all 4 stages of the oestrous cycle. Adr and NA produced 80% maximum inhibition in oestrus only, and 50–60% maximum inhibition in proestrus, metoestrus and dioestrus. The differences in the degree of inhibition produced by the catecholamines were overcome (i.e. the maximum inhibition produced by Adr and NA was increased to become equal to that produced by Iso) when experiments were repeated in the presence of the uptake inhibitors desmethylimipramine (DMI) and normetanephrine (NMN), but not in the presence of an -adrenoceptor antagonist (azapetine 10^–7 M). Variations in the uptake of³H-Iso and³H-NA were observed in the different stages of the oestrous cycle. Small -adrenoceptor mediated motor responses to NA and Adr were observed only in the presence of a -antagonist (propranolol 10^–5 M), in uteri from rats in oestrus, metoestrus and dioestrus, but not proestrus. It is concluded that in the rat isolated uterus, -inhibitory receptors predominate throughout the natural oestrous cycle, although the existence of -excitatory receptors has been shown in 3 of the 4 stages.     

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.     

Stereospeciflc High-Performance Liquid Chromatographic Assay of Sotalol in Plasma

A convenient high-performance liquid chromatographic (HPLC) assay was developed for determination of sotalol (STL) enantiomers in plasma. Following addition of the internal standard (IS; racemic atenolol), enantiomers of STL and IS were extracted using ethyl acetate. After evaporation of the organic layer, samples were derivatized with a solution of S-( + )-l-(l-naphthyl)ethyl isocyanate (NEIC). The resulting diastereomers were chromatographed with normal-phase HPLC with chloroform:hexane:methanol [65:33:2 (v/ v)] as the mobile phase at a flow rate of 2 ml/min. The fluorescence detection wavelength was set at 220 nm for excitation with no emission filter. The suitability of the assay for pharmacokinetic studies was determined by measuring STL enantiomers in the plasma of a healthy subject after administration of a single 160-mg oral, racemic dose of STL.     

Lesioning of serotoninergic and noradrenergic nerve fibres of the rat brain does not decrease binding of 3H-clonidine and 3H-rauwolscine to cortical membranes

Summary ₂-adrenoceptors located presynaptically on nerve terminals are known to modulate the release of neurotransmitters from noradrenergic and serotoninergic neurons. The pre- and/or postsynaptic localization of binding sites for ₂-adrenergic radioligands, the agonist ³H-clonidine and the antagonist ³H-rauwolscine, was investigated in the rat cerebral cortex by the use of specific neurotoxins.Intracerebroventricular ijections of 6-hydroxydopamine (6-OH-DA) and 5,7-dihydroxytryptamine (5,7-DHT) were used to destroy the noradrenergic and serotoninergic neurons, respectively, and the success of the treatment was controlled by measurement of tritium accumulation in cortex slices incubated with ³H-noradrenaline or ³H-serotonin.In cortical membranes, ³H-rauwolscine bound to a single site (K _D about 5 nmol/l; B _max 217–247 fmoles/mg protein), whereas ³H-clonidine bound to a high affinity site (K _D 0.6–1.4 nmol/l) and a low affinity site (K _D 6–10 nmol/l). The total number of high plus low affinity ³H-clonidine binding sites was about two thirds of the number of ³H-rauwolscine binding sites.6-OH-DA treatment significantly increased the number of high affintiy ³H-clonidine binding sites without reducing the number of high plus low affinity binding sites, indicating a denervation supersensitivity. K _D- as well as B _max-values for ³H-rauwolscine remained unaltered after 6-OH-DA-treatment. Since an increase in postsynaptic ₂-adrenoceptors due to 6-OH-DA-administration might have masked a loss of presynaptic ₂-adrenergic binding sites, rats were chronically treated with high doses of clonidine in order to prevent a possible supersensitivity of postsynaptic receptors. Even under these conditions 6-OH-DA did not reduce the number of ³H-clonidine and ³H-rauwolscine binding sites.Injection of 5,7-DHT had no influence on binding parameters of ³H-clonidine and ³H-rauwolscine.It is concluded that in the cerebral cortex the number of postsynaptic ₂-adrenoceptors is much greater than that of presynaptic ₂-adrenoceptors. Therefore, the changes in the number of presynaptic ₂-adrenoceptors due to destruction of noradrenergic or/and serotoninergic neurons cannot be detected by equilibrium binding studies with ³H-clonidine or ³H-rauwolscine.     

Effect of repetitive electroconvulsive treatment on sensitivity to pain and on [3H]nitrendipine binding sites in cortical and hippocampal membranes

The effect of electroconvulsive shock (ECS) on the responsiveness to pain (measured by the hot-plate test) and on the characteristics ofl-type calcium channels (measured as [³H]nitrendipine binding sites) in the cortex and hippocampus was tested on the Wistar rat. In animals receiving a single ECS, the calcium channel density and affinity 24 h after treatment did not differ from the controls; the response to pain was also at the control level. Repeated ECS (eight once-daily shocks) resulted in an increased responsiveness to pain (shortening of response latency) and in an increase in the density of cortical, but not hippocampal, calcium channels. The K_D value for [³H]nitrendipine binding sites in either brain region remained unaltered by ECS. The calcium channel antagonist nifedipine, which by itself did not significantly alter the response to pain, prevented the enhancement of pain sensitivity brought about by ECS. The results suggest activation of calcium-dependent mechanisms by repeated ECS and confirm the involvement of calcium channels in pain mechanisms.     

Clinical and economic impact of a pharmacist‐intervention to promote sequential intravenous to oral clindamycin conversion

A multicentre, prospective, controlled study compared the clinical efficacy, safety and economic impact of a pharmacist intervention to promote sequential intravenous to oral clindamycin conversion. A total of 473 patients receiving intravenous clindamycin for at least 72 hours were included in the study. Two groups were established: an intervention group (204 patients) in which an informative sheet recommending the sequential treatment was provided, and a control group (269 patients). Clindamycin was prescribed for respiratory infections in 38.9% and for prophylaxis in surgery in 25.4% of the patients (71% were contaminated surgery). No difference between groups regarding sex, infection severity, health status or clinical progress was observed. Both the stepdown treatments after 72 hours of intravenous clindamycin and the change to the oral route later on, were significantly increased with the intervention (p<0.001, p<0.001 respectively). No significant differences between both groups were found in the number of patients with adverse effects associated with the IV therapy, although the incidence tended to be lower in the intervention group (49/204 intervention versus 85/269 control, p=0.07). Compliance with the recommended clindamycin dosing regimen was significantly higher in the intervention group, in which 1.3 days reduction of intravenous therapy provided an average cost savings of PTA5246 (95%CI 25567935) per treatment. A higher reduction of 1.7 days was achieved in those patients candidates for switch therapy on the third day of intravenous clindamycin. A sequential program with clindamycin may provide a costeffective alternative to conventional therapy and the introduction of an information sheet is a costeffective strategy to promote it.     

Analysis of the β-receptor mediated effect on fast-contracting skeletal muscle in vitro

Summary Subtetanic contractions of the isolated extensor digitorum longus (EDL) of the guinea-pig, a fast-contracting muscle, were evoked by transmural field stimulation. Isoprenaline, adrenaline, terbutaline, and noradrenaline each caused a dose-dependent increase in the force of contraction, their potencies decreasing in that order. Tyramine was without effect in this respect. Curare depressed the contractions of EDL by about 20% but did not appreciably change the response to the -adrenoceptor agonists. The effects of isoprenaline and noradrenaline were blocked by propranolol (unselective) and H 35/25 (1-(p-tolyl)-2-isopropylamino-1-propanol, ₂-selective) but not by practolol (₁-selective). Moreover, the increase in the force of subtetanic contractions of EDL produced by noradrenaline was unaffected by phentolamine. It is concluded that the adrenoceptor mediating the increase in the force of contraction of the isolated EDL is of the ₂-type and that the site of action is direct on the muscle. Its similarity to the receptor mediating the inverse effect on the slow-contracting soleus-muscle is pointed out.Subsidiary to AB Astra, Sweden     

A unique pressor response to isoprenaline in the pithed rat during triiodo-l-thyronine (T3)-induced hyperthyroidism

Summary Thyroid hormone appears to be involved in the regulation of -adrenoceptors affecting cardiovascular performance. In the present study, the influence of hyperthyroidism on -adrenoceptor-mediated response of the cardiovascular system was investigated in vivo using the pithed rat preparation. Hyperthyroidism was induced by triiodothyronine injections (500 g/kg, i.p.) for 6 days. A markedly accelerated basal heart rate and a wider pulse pressure with a significantly elevated systolic blood pressure were observed in hyperthyroid pithed rats. Although the basal and the maximal heart rates were increased in hyperthyroid rats, EC₅₀ of the heart rate response to isoprenaline did not significantly differ between euthyroid and hyperthyroid pithed animals. Markedly different responses of blood pressure to isoprenaline were obtained in the two groups; isoprenaline caused a dose-dependent decrease in diastolic pressure in euthyroid pithed rats, whereas it produced pressor response in hyperthyroid pithed rats. This unique pressor response to isoprenaline observed in hyperthyroid pithed rats was abolished by the ₁-adrenoceptor selective antagonist metoprolol but not by the -adrenoceptor antagonist phenoxybenzamine. The density of myocardial binding sites of the -type was markedly increased after T₃ treatment (65%), whereas that of the mesenteric artery was not altered. The results indicate that thyroid hormone exerts different effects on cardiac and vascular -adrenoceptors, and this different susceptibility to thyroid hormone may in part be responsible for the altered response of blood pressure to isoprenaline seen in hyperthyroid pithed rats.