A series of 6-(omega-methanesulfonylthioalkoxy)-2-N-methyl- 1,2,3, 4-tetrahydroisoquinolines: cysteine-reactive molecular yardsticks for probing alpha2-adrenergic receptors

A series of 6-(omega-methanesulfonylthioalkoxy)-2-N-methyl-1,2,3, 4-tetrahydroisoquinolines (7a-d) was prepared and characterized as SH-reactive molecular yardsticks useful in probing alpha2-adrenergic receptors. Rapid displacement of the methanesulfonyl group by a cysteine residue in dilute aqueous solution with concomitant formation of a disulfide conjugate was verified by MALDI-TOF mass spectrometric analysis of the reaction of 7a with a cysteine-containing decapeptide. 7a-d all showed a marked affinity for the three different variants of human alpha2-adrenergic receptors: H alpha(2A)wt, H alpha(2B)wt, and mutant H alpha(2A)Ser201Cys197. However, only the mutated receptor (H alpha(2A)Ser201Cys197) was irreversibly inactivated, and the extent of inactivation in this case was linearly dependent on the length of the side chain of 7a-d. These results show that the molecular yardstick approach tested here can provide useful information for modeling receptor proteins.

Adrenergic alpha2C-receptors modulate the acoustic startle reflex, prepulse inhibition, and aggression in mice

Studies on animal models of stress, anxiety, aggression, and sensorimotor gating have linked specific monoamine neurotransmitter abnormalities to the cognitive and behavioral disturbances associated with many affective neuropsychiatric disorders. Although alpha2-adrenoceptors (alpha2-ARs) have been suggested to have a modulatory role in these disorders, the specific roles of each alpha2-AR subtype (alpha2A, alpha2B, and alpha2C) are largely unknown. The restricted availability of relevant animal models and the lack of subtype-selective alpha2-AR drugs have precluded detailed studies in this area. Therefore, transgenic mice were used to study the possible role of the alpha2C-AR subtype in two well established behavioral paradigms: prepulse inhibition (PPI) of the startle reflex and isolation-induced aggression. The alpha2C-AR-altered mice appear grossly normal, but subtle changes have been observed in their brain dopamine (DA) and serotonin (5-HT) metabolism. In this study, the mice with targeted inactivation of the gene encoding alpha2C-ARs (alpha2C-KO) had enhanced startle responses, diminished PPI, and shortened attack latency in the isolation-aggression test, whereas tissue-specific overexpression of alpha2C-ARs (alpha2C-OE) was associated with opposite effects. Correlation analyses suggested that both the magnitude of the startle response and its relative PPI (PPI%) were modulated by the mutations. In addition, the differences in PPI, observed between drug-naive alpha2C-OE mice and their wild-type controls, were abolished by treatment with a subtype nonselective alpha2-agonist and antagonist. Thus, drugs acting via alpha2C-ARs might have therapeutic value in disorders associated with enhanced startle responses and sensorimotor gating deficits, such as schizophrenia, attention deficit disorder, post-traumatic stress disorder, and drug withdrawal.

Chloroethylclonidine binds irreversibly to exposed cysteines in the fifth membrane-spanning domain of the human alpha2A-adrenergic receptor

The alpha2-adrenergic receptors (alpha2-ARs) mediate signals to intracellular second messengers via guanine nucleotide binding proteins. Three human genes encoding alpha2-AR subtypes (alpha2A, alpha2B, alpha2C) have been cloned. Several chemical compounds display subtype differences in their binding and/or functional activity. Site-directed mutagenesis and molecular modeling are new tools with which to investigate the subtype selectivity of ligands. In this study, we introduce a new approach to mapping of the binding site crevice of the human alpha2A-AR. Based on a three-dimensional receptor model, we systematically mutated residues 197-201 and 204 in the fifth transmembrane domain of the human alpha2A-AR to cysteine. Chloroethylclonidine, an alkylating derivative of the alpha2-adrenergic agonist clonidine, binds irreversibly to alpha2A-ARs by forming a covalent bond with the sulfhydryl side chain of a cysteine residue exposed in the binding cavity, leading to inactivation of the receptor. Irreversible binding of chloroethylclonidine was used as a criterion for identifying introduced cysteine residues as being exposed in the binding cavity. The results supported a receptor model in which the fifth transmembrane domain is alpha-helical, with residues Val197, Ser200, Cys201, and Ser204 exposed in the binding pocket. Residues Ile198, Ser199, Ile202, and Gly203 face the lipid bilayer of the plasma membrane. This approach emerges as a powerful tool for structural characterization of the alpha2-ARs.

A comparison of gasless mechanical and conventional carbon dioxide pneumoperitoneum methods for laparoscopic cholecystectomy

Carbon dioxide (CO2) insufflation with increased intraabdominal pressure (IAP) has adverse hemodynamic, pulmonary, and renal effects. To avoid these problems, an abdominal wall lift method with a retractor was used to provide the surgical view without CO2 insufflation. Twenty-six patients undergoing elective laparoscopic cholecystectomy were randomly allocated to either the gasless, retractor group, or conventional CO2 pneumoperitoneum group (CPP). Hemodynamic data, ventilatory variables, urine output, urine oxygen tension, and blood samples for determining stress hormones were collected throughout the perioperative period. Patients in the retractor group had lower mean arterial pressure, heart rate, and central venous pressure (P < 0.001). They also had higher pulmonary dynamic compliance and needed a lower minute volume of ventilation to achieve normocarbia (P < 0.001). Urine output and oxygen tension in urine were higher (P < 0.05) with the retractor method than with CPP. Increase in plasma renin activity (P < 0.05) and decrease in core temperature (P < 0.001) were smaller with the gasless method than with CPP. The gasless method for laparoscopic cholecystectomy might be beneficial, especially in patients with compromised cardiorespiratory or renal function.

IMPLICATIONS

Totally gasless laparoscopic cholecystectomy was compared with conventional pressure pneumoperitoneum with CO2 insufflation. The gasless method resulted in more stable hemodynamics and pulmonary function, as well as higher urine, output than conventional pressure pneumoperitoneum. No changes in renal oxygenation was seen with the gasless method, compared with conventional pressure pneumoperitoneum.

Assessment of alpha2-adrenoceptor antagonist potency with GTPase assay

Membranes from Chinese hamster ovary (CHO) cells expressing high densities of alpha2A-, alpha2B- or alpha2C-adrenoceptor subtypes were used to monitor potencies of alpha2-adrenoceptor antagonists with a GTPase assay. Receptor-activated high-affinity GTPase activity was determined by measuring the rate of release of 32P from [gamma-32P]GTP. Concentration-response curves to the full agonist (-)-noradrenaline were obtained in the presence of different antagonist concentrations and pA2 values were calculated by Schild analysis. Three antagonists (rauwolscine, prazosin and chlorpromazine) showed subtype-selectivity, which agrees with earlier radioligand binding results. We suggest that the GTPase assay described here is useful for characterization of the functional potency and subtype-selectivity of alpha2-adrenoceptor antagonists.

Postoperative pharmacokinetics and sympatholytic effects of dexmedetomidine

Dexmedetomidine is a selective alpha2-adrenoceptor agonist with centrally mediated sympatholytic, sedative, and analgesic effects. This study evaluated: 1) pharmacokinetics of dexmedetomidine in plasma and cerebrospinal fluid (CSF) in surgical patients; 2) precision of a computer-controlled infusion protocol (CCIP) for dexmedetomidine during the immediate postoperative period; and 3) dexmedetomidine's sympatholytic effects during that period. Dexmedetomidine was infused postoperatively by CCIP for 60 min to eight women, targeting a plasma concentration (Cp) of 600 pg/mL. Before, during, and after infusion, blood was sampled to determine plasma concentrations of norepinephrine, epinephrine, and dexmedetomidine, and CSF was sampled to determine dexmedetomidine concentrations (C[CSF]). Heart rate and arterial blood pressure were measured continuously from 5 min before until 3 h after the end of infusion. During the infusion, Cp values generally exceeded the target value: median percent error averaged 21% and ranged from -2% to 74%; median absolute percent error averaged 23% and ranged from 4% to 74%. After infusion, C(CSF) was 4% +/- 1% of Cp. Because C(CSF) barely exceeded the assay's limit of quantitation, CSF pharmacokinetics were not determined. During the infusion, norepinephrine decreased from 2.1 +/- 0.8 to 0.7 +/- 0.3 nmol/L; epinephrine decreased from 0.7 +/- 0.5 to 0.2 +/- 0.2 nmol/L; heart rate decreased from 76 +/- 15 to 64 +/- 11 bpm; and systolic blood pressure decreased from 158 +/- 23 to 140 +/- 23 mm Hg. We conclude that infusion of dexmedetomidine by CCIP using published pharmacokinetic parameters overshoots target dexmedetomidine concentrations during the early postoperative period. Hemodynamic and catecholamine results suggest that dexmedetomidine attenuates sympathetic activity during the immediate postoperative period.

IMPLICATIONS

We studied the pharmacokinetic and sympatholytic effects of dexmedetomidine during the immediate postoperative period and found that during this period, the published pharmacokinetic data slightly overshoot target plasma dexmedetomidine concentrations. We also found that heart rate, blood pressure, and plasma catecholamine concentrations decrease during dexmedetomidine infusion.

Lack of adverse interactions between concomitantly administered selegiline and citalopram

We have evaluated the risk for pharmacokinetic and/or pharmacodynamic interactions of concomitantly administered selegiline, a selective monoamine oxidase type B inhibitor, and citalopram, a widely used selective serotonin uptake inhibitor antidepressant. Two parallel groups of healthy volunteers received 20 mg of citalopram (n = 12) or placebo (n = 6) once daily for 10 days in a randomized, double-blind fashion, followed by concomitant selegiline 10 mg once daily for 4 days. The safety of this drug combination was assessed by measurements of blood pressure, heart rate, body temperature, and inquiries for adverse events. Blood samples were taken for the analysis of serum concentrations of both study drugs and their metabolites and plasma prolactin, adrenaline, noradrenaline, and 3,4-dihydroxyphenylglycol (DHPG); urinary excretion of serotonin and 5-hydroxyindoleacetic acid (5-HIAA) were assessed. After a 5-week washout, the 12 subjects who took citalopram in the first part of the study received 10 mg of selegiline once daily for 4 days to compare the pharmacokinetics of selegiline with and without concomitant citalopram. The safety analysis showed no significant differences in vital signs or the frequency of adverse events between the study groups. Plasma prolactin concentrations were increased by 40% after 10 days' treatment with citalopram (p = 0.03); this was not potentiated by concomitantly administered selegiline. The comparison of plasma concentrations of noradrenaline, adrenaline, and DHPG and the amount of serotonin and 5-HIAA excreted into urine between the study groups indicated no signs of subclinical pharmacodynamic interaction between selegiline and citalopram. The relative bioavailability of selegiline was slightly reduced (by 29%; p = 0.008) when citalopram was coadministered compared with selegiline alone. However, no indication of a pharmacokinetic interaction was found in the analysis of serum concentrations of the three main metabolites of selegiline. The pharmacokinetics of citalopram remained unaffected by concomitant selegiline. The present results indicate lack of clinically relevant pharmacodynamic or pharmacokinetic interactions between selegiline and citalopram.

Alpha2-adrenoceptor regulation of adenylyl cyclase in CHO cells: dependence on receptor density, receptor subtype and current activity of adenylyl cyclase

Chinese hamster ovary (CHO) cells stably transfected to express different densities of the human alpha2A-, alpha2B- and alpha2C-adrenoceptor subtypes, were used to characterize the regulation of adenylyl cyclase activity by alpha2-adrenoceptor agonists. In isolated cell membranes, activation of alpha2A- and alpha2C-adrenoceptors did not affect basal enzyme activity, but activation of alpha2B-adrenoceptors stimulated adenylyl cyclase activity. The extent of stimulation was dependent on the receptor density and was insensitive to pertussis toxin treatment. In the presence of 10 microM forskolin all three receptor subtypes mediated inhibition of adenylyl cyclase activity in a pertussis toxin-sensitive manner. In experiments performed with intact cells the same pattern could be seen: the basal production of cAMP was not affected when alpha2C-adrenoceptors were activated, but activated alpha2B-adrenoceptors mediated stimulation of cAMP production. In the presence of forskolin, both receptor subtypes mediated inhibition of cAMP production. Our results suggest that alpha2B-adrenoceptors are coupled to both Gi and Gs proteins. The signal transduction pathway to which the receptor is coupled is not dependent on receptor density, but its effect on adenylyl cyclase regulation is dependent on the current activity of adenylyl cyclase. The results also suggest that the alpha2A- and alpha2C-subtypes are preferentially coupled to Gi and transduce only inhibition of adenylyl cyclase activity in transfected CHO cells. At low densities of alpha2C-adrenoceptors, clonidine was a partial agonist, but in clones expressing high levels of alpha2C-adrenoceptors, clonidine acted as a full agonist by inhibiting cAMP accumulation with the same efficacy as (-)-noradrenaline. This demonstrates that receptor reserve can mask partial agonist activity.

Enalaprilat decreases plasma endothelin and atrial natriuretic peptide levels and preload in patients with left ventricular dysfunction after cardiac surgery

OBJECTIVE

To study the acute effects of angiotensin-converting enzyme inhibition by intravenous enalaprilat infusion in patients with left ventricular dysfunction after cardiac surgery.

DESIGN

Prospective, consecutive sample, before-after trial.

SETTING

Surgical intensive care unit in a tertiary care university hospital.

PARTICIPANTS

Eight patients with left ventricular dysfunction after cardiac surgery. Patients were defined as having left ventricular dysfunction if the pulmonary capillary wedge pressure persisted above 18 mmHg in spite of conventional vasoactive medication (inotropic or vasodilating and diuretic drugs) and intermittent mandatory ventilation during the first postoperative week.

INTERVENTIONS

Enalaprilat was infused initially at 1 mg/ hour. The rate was doubled every 30 minutes until pulmonary capillary wedge pressure decreased at least 20% or until a maximum total dose of 10 mg was achieved.

MEASUREMENTS AND RESULTS

Central hemodynamics, systemic oxygenation, and hormonal regulation of circulation (plasma renin activity, plasma endothelin, atrial natriuretic peptide, norepinephrine, epinephrine, and vasopressin concentrations, serum angiotensin-converting enzyme activity, and serum levels of aldosterone) were assessed at baseline before enalaprilat infusion, and repeatedly over 2 hours after the infusion. Enalaprilat infusion (median dose, 2.0 mg; infusion time, 48 minutes) caused a significant decrease in pulmonary capillary wedge pressure (p = 0.004), lasting until the end of the 2 hours' follow-up. This coincided with inhibition of serum angiotensin-converting enzyme activity (p < 0.001), an increase in plasma renin activity (p = 0.022), and decreases in plasma endothelin (p = 0.035), atrial natriuretic peptide (p = 0.005), and serum aldosterone (p = 0.001) concentrations. Cardiac output, venous admixture, and oxygen delivery and consumption remained unchanged.

CONCLUSIONS

Adding enalaprilat to conventional therapy makes it possible to unload the left ventricle and to relieve overt neurohormonal activation temporarily while maintaining cardiac function and systemic oxygenation.

Gene targeting--homing in on alpha 2-adrenoceptor-subtype function

The alpha-adrenoceptor was subdivided into three subtypes: alpha 2A-, alpha 2B- and alpha 2C-adrenoceptors almost ten years ago. Since then, the search has been on to discover and develop subtype-selective agonists and antagonists, but as yet no major breakthrough has been made. In the past year, several strains of genetically engineered mice have become available, either overexpressing, totally lacking or expressing heavily modified alpha 2-adrenoceptor subtypes. Ewen MacDonald, Brian Kobilka and Mika Scheinin describe how these mice may be utilized to elucidate the physiological functions of the receptor subtypes and the properties of future subtype-selective drugs.

Genetic alteration of alpha 2C-adrenoceptor expression in mice: influence on locomotor, hypothermic, and neurochemical effects of dexmedetomidine, a subtype-nonselective alpha 2-adrenoceptor agonist

alpha 2-Adrenergic receptors (alpha 2-ARs) regulate many physiological functions and are targets for clinically important antihypertensive and anesthetic agents. Three human and mouse genes encoding alpha 2-AR subtypes (alpha 2A, alpha 2B, and alpha 2C) have been cloned. We investigated the involvement of the alpha 2C-AR in alpha 2-adrenergic pharmacology by applying molecular genetic techniques to alter the expression of alpha 2C-AR in mice. The effects of dexmedetomidine, a subtype-nonselective alpha 2-AR agonist, on monoamine turnover in brain and on locomotor activity were similar in mice with targeted inactivation of the alpha 2C-AR gene and in their controls, but the hypothermic effect of the alpha 2-AR agonist was significantly attenuated by the receptor gene inactivation. Correspondingly, another strain of transgenic mice with 3-fold overexpression of alpha 2C-AR in striatum and other brain regions expressing alpha 2C-AR showed normal reductions in brain monoamine metabolism and locomotor activity after dexmedetomidine, but their hypothermic response to the alpha 2C-AR agonists was significantly accentuated. The hypothermic effect of alpha 2-AR agonists thus seems to be mediated in part by alpha 2C-AR. Some small but statistically significant differences between the strains were also noted in brain dopamine metabolism. Lack of alpha 2C-AR expression was linked with reduced levels of homovanillic acid in brain, and mice with increased alpha 2C-AR expression had elevated concentrations of the dopamine metabolite compared with their controls.

Plasma levels of atrial natriuretic peptide and endothelin-1 in experimental fat embolism

In order to understand the role of vasoactive peptides in fat embolism, arterial plasma atrial natriuretic peptide (ANP) and endothelin-1 concentrations were investigated in an experimental study. Nine anesthetized and mechanically ventilated pigs received an intracaval infusion of allogeneic bone marrow suspension at a dose of 100 mg/kg (fat embolism group); 9 control pigs received saline. The observation period was 5 h. In the fat embolism group, cardiac index and heart rate decreased within 30 min, whereas mean arterial pressure remained stationary. Pulmonary capillary wedge pressure rose transiently and central venous pressure rose slightly in time, while mean pulmonary arterial pressure, pulmonary vascular resistance and pulmonary shunt increased immediately and persistently after the bone marrow suspension infusion. Simultaneously, arterial oxygen tension and arterial hemoglobin oxygen saturation decreased markedly. Arterial plasma ANP and endothelin-1 concentrations remained stable in the fat embolism animals, whereas in the controls ANP and endothelin-1 levels decreased at 3 and 5 h. Arterial epinephrine concentrations were stable in animals receiving bone marrow suspension, while in the controls arterial epinephrine concentrations decreased towards the end of the experiment. Arterial norepinephrine concentrations remained unchanged in both groups. To conclude, impaired pulmonary function and consequent systemic hypoxemia distinguish the present fat embolism model. Unchanged arterial ANP and endothelin-1 concentrations in the fat embolism group suggest that these circulating vasoactive hormones have a minor impact on the pathogenesis of the current experimental fat embolism.

Randomized comparison of the neuroendocrine response to laparoscopic cholecystectomy using either conventional or abdominal wall lift techniques

Increase in plasma renin activity and noradrenaline concentration occur in response to carbon dioxide insufflation during laparoscopic cholecystectomy. In a randomized study the conventional carbon dioxide pneumoperitoneum was compared with the abdominal wall lift method for laparoscopic cholecystectomy, with special reference to neuroendocrine changes and renal function. The total mean(s.d.) volume of carbon dioxide insufflated was 42(23) litres with the conventional method and 9(7) litres with abdominal wall lift (P < 0.001). Mean(s.d.) intra-abdominal pressure after 15 min of insufflation was 11(2) and 3(9) mmHg respectively (P < 0.01). In the conventional group mean(s.d.) plasma renin activity increased slightly from 5.5(2.1) to 6.1(2.0) ng ml-1 during the first 55 min of laparoscopic cholecystectomy. In the abdominal wall lift group plasma renin activity decreased from 5.3(2.7) to 3.8(0.9) ng ml (P < 0.01 between the groups). Plasma antidiuretic hormone concentration increased similarly in both groups. Diuresis was significantly less with conventional pneumoperitoneum during the first 35 min of the operation compared with the abdominal wall lift method (P < 0.001). There were significant increases in plasma noradrenaline concentration in both groups (P < 0.001), but the increase was slightly higher in the conventional group during the first 15 min of insufflation. The abdominal wall lift method with minimal carbon dioxide insufflation was associated with smaller neuroendocrine responses and better preservation of renal function compared with conventional carbon dioxide pneumoperitoneum.

Biochemical and clinical assessment of histamine blockade

The effects of antihistamines on biochemical stress indicators and on psychomotor and physiological functions were studied in 60 healthy patients receiving in a randomized, double-blind study either 25 mg promethazine, 150 mg ranitidine, both drugs or placebo (n = 15 in each group). Different aspects of the premedications were evaluated by determining various hormone, neurotransmitter and neurotransmitter metabolite levels in blood and cerebrospinal fluid, and subjectively using questionnaires concerning the quality of the preoperative night's sleep and visual analogue scales, and objectively by measuring changes in blood pressure and heart rate, impairment of vigilance with the Maddox wing apparatus and the critical flicker fusion threshold test. The relationships between the subjective assessments and the biochemical stress indicators were also investigated. There were no differences between the study groups in the quality of the preoperative night's sleep, estimated fear, apprehension or dizziness, or in the various physiological stress indicators. Only few statistically significant correlations were found between the subjective and biochemical assessments. It is concluded that histamine receptor antagonists used in clinical doses do not interfere with the biochemical, clinical preoperative, and physiological responses.

COMT inhibition by entacapone does not affect growth hormone or prolactin secretion in healthy volunteers

We studied the effects of entacapone, a novel inhibitor of the enzyme catechol-O-methyltransferase (COMT), on spontaneous and levodopa (LD) modulated secretion of growth hormone (GH) and prolactin (PRL) in 12 healthy male volunteers. The study had a double-blind, cross-over design with two experimental settings. In the first setting the subjects received a single oral dose of 400 mg of entacapone or matching placebo in a randomized order. In the second setting, a single oral dose of 300 mg of LD and 75 mg of carbidopa was administered concomitantly with either 400 mg of entacapone or matching placebo in a randomized order. Entacapone had no effect on resting levels of GH, but PRL concentrations in plasma were slightly lower after entacapone than after placebo. As expected, LD/carbidopa increased the concentration of GH and decreased that of PRL. The effects of LD were not influenced by concomitant administration of entacapone. Compared with the administration of LD/carbidopa together with placebo, concomitant administration of entacapone increased the AUC of LD by 29% and reduced the AUC of 3-O-methyldopa (a metabolite of LD produced by COMT) by 69%. Entacapone appears not to enhance the effects of LD on hypothalamic-pituitary function, although the LD dose used may have been bigger than optimal for detection of a small modulatory influence.

Simultaneous inhibition of catechol-O-methyltransferase and monoamine oxidase A: effects on hemodynamics and catecholamine metabolism in healthy volunteers

OBJECTIVE

To evaluate the effects of simultaneous pharmacologic inhibition of catechol-O-methyltransferase (COMT) and monoamine oxidase type A (MAO-A) on hemodynamics and catecholamine metabolism in healthy volunteers at rest and during exercise.

BACKGROUND

Entacapone, a COMT inhibitor, is studied as an adjunct to levodopa treatment in patients with Parkinson's disease. Moclobemide, an MAO-A inhibitor, is already in clinical use as an antidepressant. It is likely that entacapone and moclobemide will be used concomitantly in the future in patients who have both Parkinson's disease and depression. It was therefore considered to be important to investigate the tolerability of combined COMT and MAO-A inhibition with entacapone and moclobemide.

DESIGN AND METHODS

This was a randomized, single-dose, double-blind crossover study of 12 healthy male volunteers. The treatments were either placebo, 200 mg entacapone, 150 mg moclobemide, or the combination of entacapone and moclobemide in single doses. Heart rate, blood pressure, impedance cardiography, and plasma concentrations of catecholamines and their metabolites were measured both at rest and during submaximal standardized bicycle exercise.

RESULTS

Entacapone and moclobemide (either alone or in combination) did not change heart rate, blood pressure, or any hemodynamic parameter at rest or during exercise compared with placebo. Neither were the concentrations of norepinephrine and epinephrine in plasma influenced. Both drugs had the expected effects on catecholamine metabolite concentrations in plasma. The decrease in the concentration of 3-methoxy-4-hydroxyphenylglycol (MHPG) induced by moclobemide was not potentiated by entacapone.

CONCLUSION

The combined use of therapeutic single doses of entacapone and moclobemide in healthy volunteers did not affect the hemodynamics or concentrations of unconjugated norepinephrine and epinephrine in plasma. Other mechanisms are capable of regulating the concentrations of norepinephrine and epinephrine in circulating blood (and apparently also at receptors in the heart and vascular tissue) when both COMT and MAO-A activity are inhibited to a significant extent. This was also the case during marked sympathetic stimulation. The changes in the catecholamine metabolite concentrations provide evidence of effective COMT and MAO inhibition. Concentrations of MHPG in plasma are determined mainly by MAO-A activity because COMT inhibition did not have an additional effect on the moclobemide-induced decrease in plasma MHPG.

The sedative and sympatholytic effects of oral tizanidine in healthy volunteers

Tizanidine, an imidazoline derivative with alpha 2-receptor-mediated central muscle relaxant activity, is in widespread clinical use for the treatment of spasticity. To evaluate its possible role in anesthesia we assessed the sedative and sympatholytic effects of orally administered tizanidine in a double-blind, placebo-controlled, randomized, cross-over study in six healthy male volunteers. Three different doses of tizanidine (4, 8, and 12 mg) were tested and compared to clonidine 150 micrograms. The sedative and sympatholytic effects of tizanidine 12 mg were comparable in magnitude to those of clonidine 150 micrograms, but the effects of clonidine were longer lasting. Similarly, the observed decreases in arterial blood pressure (diastolic, 13% and 19%; systolic, 10% and 8% for tizanidine and clonidine, respectively) and salivation were comparable in magnitude but of shorter duration after tizanidine 12 mg than after clonidine. Clonidine and tizanidine 12 mg had also similar effects on the secretion of growth hormone. Our results indicate that the effects of a single 12-mg oral dose of tizanidine resemble those of 150 micrograms oral clonidine, but are of shorter duration. Tizanidine may thus be a useful alternative to clonidine as an orally active, short-acting alpha 2-adrenoceptor agonist in the perioperative period.

beta-blockade, atrial natriuretic peptide and exercise

Changes in the release of atrial natriuretic peptide (ANP) and vasopressin (VP) may contribute to the final outcome of beta-adrenoceptor blocking therapy. Therefore, we administered 2 hours before a bicycle exercise test (a 30-minute exercise with 100 W work load) in a randomized, double-blind, placebo-controlled crossover study orally 50 mg atenolol, 80 mg propranolol or 10 mg pindolol to 15 healthy volunteers. Hormone release and sympathoadrenal activation were estimated by measuring plasma ANP-, VP-, adrenaline and noradrenaline concentrations. beta-blockade and -antagonism were estimated by measuring the reduction of exercise-induced tachycardia and the extent to which the drugs occupied rabbit lung beta 1- and rat reticulocyte beta 2-adrenoceptors in the circulating plasma. We noticed clear differences in the animal beta 1- and beta 2-receptor occupancy between these agents. The agents and placebo during the exercise augmented plasma ANP level similarly, on average by 34-72%. Pindolol administration enhanced the decline of plasma ANP level after exercise (ANCOVA rep meas, pindolol vs placebo, p < 0.05). Although pindolol increased the mean plasma VP level by 25% (ANCOVA rep meas for the increase, pindolol vs placebo, p < 0.05), drug effects on plasma VP-level were generally negligible. In conclusion, in healthy volunteers beta 1- and beta 2-antagonism by pindolol, atenolol and propranolol do not markedly potentiate plasma ANP- and VP-responses to physical exercise. The responses are, however, slightly influenced presumably by the beta-agonist activity of pindolol.

Simultaneous inhibition of catecholamine-O-methylation by entacapone and neuronal uptake by imipramine: lack of interactions

OBJECTIVE

We have evaluated the effects of simultaneous inhibition of catechol-O-methyltransferase (COMT) by entacapone and of neuronal monoamine reuptake by imipramine on haemodynamics and catecholamine metabolism, and the safety and tolerability of the drug combination in healthy women.

METHODS

In a randomized, single-dose, single-blind, cross-over study, 12 healthy women were given placebo, entacapone (200 mg), imipramine (75 mg) or entacapone and imipramine in combination. Heart rate, blood pressure, systolic time intervals, and plasma concentrations of catecholamines and their metabolites were measured at rest and during exercise.

RESULTS

The only drug-related effect on haemodynamics was an increase in heart rate during exercise after imipramine. The increase in heart rate after the combination of entacapone and imipramine was similar to that after imipramine alone. Entacapone alone had no effects on haemodynamics. Imipramine and entacapone had no significant effects on the plasma concentrations of noradrenaline and adrenaline. No interactions between entacapone and imipramine were detected.

The effect of skin incision followed by alfentanil on catecholamine levels and on the T-wave amplitude of ECG during isoflurane anaesthesia

Haemodynamic, ECG T-wave amplitude and plasma potassium changes and plasma catecholamine responses to skin incision followed by alfentanil were studied in 24 ASA I patients. Propofol and vecuronium were used without anticholinergics for induction of anaesthesia followed by isoflurane in 02/air. End-tidal isoflurane concentration was kept constant (0.7%) for 30 min before the skin incision. Five min after the skin incision alfentanil 30 mu g kg-1 was given. Blood samples for catecholamines and plasma potassium concentrations were drawn from right ventricle of the heart one minute before and after the skin incision and two minutes after alfentanil. Heart rate, systolic and diastolic arterial pressures increased after the skin incision (P < 0.001), and decreased after alfentanil (P < 0.001). Plasma adrenaline and noradrenaline concentrations increased slightly after the skin incision (P < 0.05 and P < 0.01, respectively). Noradrenaline levels continued to increase after alfentanil (P < 0.001) despite totally abolished haemodynamic responses to the skin incision. ECG T-wave amplitude changes, measured as R/T ratio, did not correlate to the changes in plasma catecholamine levels: both rapid increases and decreases in R/T ratio were seen. No plasma potassium changes were seen during the trial. T-wave changes, occurring in seconds after the skin incision, are probably produced by a direct catecholamine release from cardiac sympathetic nerve endings.

Effects of dexmedetomidine on coronary hemodynamics and myocardial oxygen balance

OBJECTIVE

alpha 2-adrenergic agonists decrease central sympathetic outflow and maintain normal transmural myocardial blood flow distribution, but intravenous bolus doses of these agents can also induce excessive coronary vasoconstriction and myocardial ischemia. The hypothesis of the present study was that a rapid intravenous bolus of dexmedetomidine, a specific alpha 2-adrenergic agonist, will cause coronary vasoconstriction and accompanying myocardial ischemia in young pigs.

DESIGN

Prospective, controlled study on experimental animals.

SETTING

Animal laboratory of a university cardiorespiratory research center.

PARTICIPANTS

Twelve domestic 8-week-old open-chest pigs, anesthetized with high-dose fentanyl. Another six pigs served as controls.

INTERVENTIONS

Sequential intravenous dexmedetomidine boluses of 3, 10, and 30 mg/kg were administered, and responses were measured during peak changes (2 minutes after injection) and during recovery after each dose.

MEASUREMENTS AND MAIN RESULTS

Left anterior descending coronary artery blood flow, calculated regional coronary vascular resistance, myocardial extraction of oxygen and lactate, plasma catecholamine levels, and conventional central hemodynamic parameters were measured. The two higher doses of dexmedetomidine induced 21% and 29% immediate increases in left anterior descending coronary artery blood flow. At the same time mean systemic blood pressure and pulmonary capillary wedge pressure increased, and calculated regional coronary vascular resistance increased. Myocardial extraction of oxygen and lactate remained unchanged.

CONCLUSIONS

Large intravenous doses of dexmedetomidine caused moderate regional coronary vasoconstriction without metabolic signs of myocardial ischemia in young domestic pigs at the same time as a marked vasoconstrictive response in the systemic circulation.

Distribution and pharmacology of alpha 2-adrenoceptors in the central nervous system

Three subtypes of the alpha 2-adrenoceptor have been characterized. The drugs currently available which most specifically activate (e.g. dexmedetomidine) or antagonize alpha 2-receptors (e.g. atipamezole, idazoxan) do not show significant differences in their affinities for the subtypes. The drugs which do show some subtype selectivity (oxymetazoline for alpha 2A; prazosin for alpha 2B and alpha 2C) are not useful for in vivo pharmacology due to their relative nonspecificity in binding to other receptors (e.g. alpha 1-adrenoceptors). By examining the distribution of the mRNA coding for the three subtypes, it has been possible to map those regions in the brain which possess cells which synthetize the distinct subtypes. The mRNA coding for alpha 2A receptors is found throughout the brain, especially in locus coeruleus, a region which contains the cell bodies for the ascending and descending noradrenergic neurones. The mRNA for alpha 2B receptors was only found in thalamus. The alpha 2C mRNA had a wider distribution, in basal ganglia its expression was particularly intense. One must hope that the fact that the receptor subtypes are not uniformly distributed throughout the brain means that new subtype selective drugs will not suffer from the same broad diversity of actions of the present alpha 2-agonists and antagonists.

The effect of entacapone on the disposition and hemodynamic effects of intravenous isoproterenol and epinephrine

BACKGROUND

Entacapone is a potent, selective catechol-O-methyltransferase (COMT) inhibitor. Entacapone could potentiate the hemodynamic effects of exogenously administered catecholamines, which are substrates of the COMT enzyme.

DESIGN AND METHODS

Originally, the study was to follow a placebo-controlled, randomized crossover design. Because of two cases of ventricular arrhythmia, a decision was made to terminate the study before its completion. Six subjects went through the isoproterenol and epinephrine infusions while taking placebo and five other subjects while taking entacapone. The actual design was thus one with two parallel groups with random allocation and double-blind drug administration. The subjects were given either a single dose of 400 mg entacapone or placebo 30 minutes before the start of isoproterenol or epinephrine infusions. Four dosages of epinephrine (1.5, 3, 6, or 12 micrograms/min) and isoproterenol (0.5, 1, 1.5, or 2 micrograms/min) were infused (5 minutes for each level). Heart rate and blood pressure were measured and ECG was monitored. The concentrations of isoproterenol and epinephrine in plasma were determined by HPLC.

RESULTS

The maximal increase in heart rate during isoproterenol infusion after entacapone administration (40 +/- 11 beats/min, mean +/- SD) was statistically greater (p = 0.0496) than after placebo administration (27 +/- 7 beats/min). The increase in heart rate during epinephrine infusion was 25 +/- 13 beats/min after entacapone administration and 14 +/- 9 beats/min after placebo administration (p = 0.127). There were no statistically significant differences between entacapone and placebo in blood pressure or in plasma concentrations of isoproterenol and epinephrine.

CONCLUSION

We conclude that entacapone may potentiate the chronotropic and arrhythmogenic effects of exogenously administered isoproterenol and epinephrine.

Molecular pharmacology of alpha 2-adrenoceptor subtypes

alpha 2-adrenergic receptors mediate many of the physiological actions of the endogenous catecholamines adrenaline and noradrenaline, and are targets of several therapeutic agents. alpha 2-adrenoceptor agonists are currently used as antihypertensives and as veterinary sedative anaesthetics. They are also used in humans as adjuncts to anaesthesia, as spinal analgesics, and to treat opioid, nicotine and alcohol dependence and withdrawal. Three human alpha 2-adrenoceptor subtype genes have been cloned and designated alpha 2-C10, alpha 2-C4, and alpha 2-C2, according to their location on human chromosomes 10, 4 and 2. They correspond to the previously identified pharmacological receptor subtypes alpha 2A, alpha 2C and alpha 2B. The receptor proteins share only about 50% identity in their amino acid sequence, but some structurally and functionally important domains are very well conserved. The most obvious functionally important differences between the receptor subtypes are based on their different tissue distributions; e.g. the alpha 2A subtype appears to be an important modulator of noradrenergic neurotransmission in the brain. The three receptors bind most alpha 2-adrenergic drugs with similar affinities, but some compounds (e.g. oxymetazoline) are capable of discriminating between the subtypes. Clinically useful subtype selectivity cannot be achieved with currently available pharmaceutical agents. The second messenger pathways of the three receptors show many similarities, but small functional differences between the subtypes may turn out to have important pharmacological and clinical consequences. All alpha 2-adrenoceptors couple to the pertussis-toxin sensitive inhibitory G proteins Gi and G(o), but recent evidence indicates that also other G proteins may interact with alpha 2-adrenoceptors, including Gs and Gq/11. Inhibition of adenylyl cyclase activity, which results in decreased formation of cAMP, is an important consequence of alpha 2-adrenoceptor activation. Many of the physiological effects of alpha 2-adrenoceptor activation cannot, however, be explained by decreases in cAMP formation. Therefore, alternative mechanisms have been sought to account for the various effects of alpha 2-adrenoceptor activation on electrophysiologic, secretory and contractile cellular responses. Recent results obtained from studies on ion channel regulation point to the importance of calcium and potassium channels in the molecular pharmacology of alpha 2-adrenoceptors.

Targeted inactivation of the gene encoding the mouse alpha 2c-adrenoceptor homolog

alpha 2-Adrenergic receptors (alpha 2-ARs) regulate a wide range of physiological functions and are targets for clinically important antihypertensive and anesthetic agents. Three genes encoding alpha 2-AR subtypes have been cloned in humans and mice, but the physiological significance of each subtype has not been completely characterized. The available agonist and antagonist compounds are not sufficiently subtype selective to allow the unambiguous dissection of these receptors in vivo. As an alternative approach, we have used gene targeting in embryonic stem cells to disrupt the Adra2c gene, which encodes the alpha 2c-AR subtype in mice. Adra2c-/Adra2c- animals do not express a functional alpha 2c-AR transcript, as detected by Northern blotting or reverse transcription-polymerase chain reaction analysis. In addition, these mice have markedly reduced [3H]rauwolscine binding in their caudate putamen and in other brain regions normally expressing Adra2c binding sites. Adra2c-/Adra2c- mice, however, are viable and fertile and appear grossly normal. Expression levels of Adra2a and Adra2b mRNA in brain and kidney are not altered by the Adra2c knockout. These data suggest that up-regulation of Adra2a or Adra2b does not compensate for the Adra2c deficiency and that the receptor encoded by Adra2c is not required for normal mouse development or for survival in a laboratory environment.

Recombinant human alpha 2-adrenoceptor subtypes: comparison of [3H]rauwolscine, [3H]atipamezole and [3H]RX821002 as radioligands

Kinetic, saturation and competition binding assays were employed to optimize and validate radioligand binding methods for characterization of recombinant human alpha 2-adrenoceptor subtypes and for screening of new subtype-selective ligands. Stable transfected lines of Shionogi 115 mouse mammary tumour cells (S115) and three structurally different antagonist radioligands, [3H]rauwolscine, [3H]atipamezole and [3H]RX821002, were used. Specificity of alpha 2-adrenergic binding was defined with 100 microM (-)-adrenaline. Steady-state was reached with all three radioligands within 15-30 min at 25 degrees C, and the binding was rapidly reversible. The receptor affinities (alpha 2-C10) were highest in glycylglycine, almost equally high in K(+)-phosphate, and lowest in Tris buffer for all three [3H]-ligands. This was mainly caused by different association rates. [3H]RX821002 was bound with high affinity and similar kinetic properties to all three alpha 2-adrenoceptor subtypes in K(+)-phosphate buffer, and had the highest proportion of specific binding (96-98%). [3H]RX821002 and K(+)-phosphate buffer were subsequently used in competition assays. The rank order of affinity of compounds selective for alpha 2-adrenoceptor subtypes was alpha 2-C10 > alpha 2-C4 > alpha 2-C2 for oxymetazoline, alpha 2-C4 > alpha 2-C2 > alpha 2-C10 for prazosin and alpha 2-C2 > alpha 2-C4 > alpha 2-C10 for chlorpromazine. The drug affinities (Ki values) determined in this system were in close agreement with earlier results with [3H]rauwolscine in Tris buffer (r = 0.94). Agonist competition for [3H]RX821002 binding was biphasic in K(+)-phosphate buffer supplemented with 10 mM MgCl2, indicating functional coupling of receptors to G-proteins. Accordingly high-affinity binding of the agonists (-)-noradrenaline and UK14,304 was eliminated by 10 microM Gpp(NH)p in the assays. Our results confirm that [3H]RX821002 is a suitable radioligand for the characterization of all three human alpha 2-adrenoceptor subtypes and for the determination of the subtype-selectivity of new alpha 2-adrenoceptor agonists and antagonists.

Haemodynamic and catecholamine responses to induction of anaesthesia and tracheal intubation in diabetic and non-diabetic uraemic patients

We have studied cardiovascular and catecholamine responses to induction of anaesthesia and tracheal intubation in 13 patients with diabetic nephropathy, in 12 patients with uraemia of other origin and in 12 ASA I control patients. All uraemic patients were undergoing renal transplantation. Cardiovascular autonomic function tests indicated that severe autonomic neuropathy was common in the diabetic patients; less severe impairment of autonomic function was found in the non-diabetic uraemic patients. The systolic pressor response to intubation was greater in diabetic uraemic patients than in the other groups (P < 0.05). Both uraemic groups had higher plasma catecholamine concentrations than the ASA I patients both before and after induction of anaesthesia. The increased plasma concentrations of catecholamines in the uraemic patients may be a result of impaired clearance of catecholamines and higher sympathoadrenal activity needed to maintain cardiac function. The normal systolic pressor response to tracheal intubation in the uraemic patients indicates that the capacity of the cardiovascular system to respond to a stressful stimulus was preserved in these patients also, in spite of autonomic neuropathy. The greater response in the diabetic group may be caused by increased sensitivity to catecholamines and loss of autonomic control.

COMT inhibition by high-dose entacapone does not affect hemodynamics but changes catecholamine metabolism in healthy volunteers at rest and during exercise

We studied the effects of catechol-O-methyltransferase (COMT) inhibition with entacapone on hemodynamics and catecholamine metabolism in healthy volunteers at rest and during a bicycle exercise test. Entacapone was given orally during two periods of seven days each to eleven healthy male volunteers; on the first period 400 mg t.i.d. and on the second 800 mg t.i.d. A submaximal exercise test giving a heart rate of about 163-167 beats/min with the highest predetermined work load was performed on a bicycle ergometer, and blood pressure, heart rate and ECG were recorded. The concentrations of adrenaline, noradrenaline, 3,4-dihydroxyphenylglycol (DHPG), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylacetic acid (DOPAC) in plasma were determined. Blood pressure, heart rate, ECG, and plasma concentrations of unconjugated adrenaline and noradrenaline were not influenced after single and repeated dosing of entacapone. The plasma concentrations of DHPG (a monoamine oxidase (MAO)-dependent metabolite) increased maximally by 245% compared to the control day. DOPAC (a MAO-dependent metabolite) increased maximally by 144% and MHPG (a COMT-dependent metabolite) decreased by 54%. The increase in DHPG and DOPAC was significantly greater with the 800 mg dose than with the 400 mg dose. The decrease in MHPG was significantly greater with the repeated dosing than with the single dose of entacapone. COMT inhibition by entacapone seems not to affect hemodynamics or plasma concentrations of unconjugated adrenaline and noradrenaline in healthy volunteers either at rest or during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Enalaprilat in acute intractable heart failure after myocardial infarction: a prospective, consecutive sample, before-after trial

OBJECTIVE

To evaluate the acute effects of intravenous enalaprilat infusion in critically ill patients with intractable heart failure after acute myocardial infarction.

DESIGN

Prospective, consecutive sample, before-after trial.

SETTING

Medical intensive care unit in a university hospital.

PATIENTS

Eight consecutive patients with intractable acute heart failure after acute myocardial infarction. All study patients continued receiving inotropic, vasodilating, and diuretic medication at a constant rate. Six patients received steady intermittent mandatory ventilation and two patients were on a continuous positive airway pressure mask during the investigation, all with constant positive end-expiratory pressure. Heart failure was defined as intractable if the pulmonary artery occlusion pressure remained > 20 mm Hg despite this conventional therapy.

INTERVENTIONS

Enalaprilat was infused at a rate of 1 mg/hr until the pulmonary artery occlusion pressure decreased by > or = 20%.

MEASUREMENTS AND MAIN RESULTS

Central hemodynamics, oxygenation, and hormonal regulation (plasma renin activity, plasma norepinephrine, epinephrine, endothelin, atrial natriuretic peptide, and vasopressin concentrations, serum angiotensin-converting enzyme activity, and serum concentrations of aldosterone) were assessed at baseline before enalaprilat infusion, and repeatedly during 2 hrs after the infusion. The statistical analysis was performed with analysis of variance for repeated measurements. Enalaprilat infusion (median dose 0.3 mg and infusion time 21 mins) caused significant but short-lasting decreases in pulmonary artery occlusion pressure (p = .007), mean arterial pressure (p = .003), mean pulmonary arterial pressure, and rate pressure product. These findings coincided with inhibition of serum angiotensin-converting enzyme activity, an increase in plasma renin activity, and a decrease in plasma endothelin concentrations (p = .041). Enalaprilat had no significant effects on the other hormones studied. Cardiac output and stroke volume index, venous admixture, oxygen extraction ratio, and mixed venous and arterial oxygen saturations remained unchanged.

CONCLUSIONS

Adding enalaprilat to conventional therapy makes it possible to transiently relieve pulmonary congestion while maintaining cardiac function and systemic oxygenation. The decrease in plasma endothelin concentrations may have further clinical implications, because endothelin is known to have potent vasoconstricting effects on the coronary circulation and it may also contribute to the extension of myocardial infarction. Whether these observed benefits can be maintained with repeated bolus injections or with continuous infusion of enalaprilat, remains to be settled.

Similar ligand binding in recombinant human alpha 2 C2-adrenoceptors produced in mammalian, insect and yeast cells

Ligand binding properties were investigated in recombinant human alpha 2C2-adrenoceptors expressed in three different host systems: Shionogi S115 mouse mammary tumour cells, Spodoptera frugiperda Sf9 insect cells and Saccharomyces cerevisiae yeast cells. The expected 43 kDa alpha 2C2 protein was visualized with immunoblotting using a polyclonal alpha 2C2-receptor antibody. [3H]Rauwolscine binding in cell homogenates or membranes (Bmax 3-11 pmol/mg protein; Kd approximately 5.5 nM) was inhibited by prazosin, oxymetazoline, RX821002, chlorpromazine and (-)-noradrenaline with and without the GTP-analogue Gpp(NH)p with similar Ki values in the different host systems. This indicates that alpha 2C2-adrenoceptors retain their binding characteristics irrespective of the host environment.

Coupling of human alpha 2-adrenoceptor subtypes to regulation of cAMP production in transfected S115 cells

Stable S115 mouse mammary tumour cell lines, expressing separately alpha 2A-C10, alpha 2B-C2 and alpha 2C-C4 adrenoceptors were used to compare the receptor binding properties of alpha 2-adrenoceptor agonists with their potency in inhibiting cAMP production. All tested agonists detected high and low affinity binding sites in all three receptor subtypes. In the presence of the GTP analogue Gpp(NH)p (10 microM), all displacement curves were shifted to the right and were best modelled by one-site fits, suggesting that the receptor subtypes are coupled to G-proteins. The extent of the Gpp(NH)p-induced shift was greatest in the alpha 2A-C10 subtype, smaller in alpha 2C-C4, and minimal in alpha 2B-C2. All three receptor subtypes were also coupled to inhibition of forskolin-stimulated cAMP production through pertussis toxin-sensitive G-proteins. For the full agonists noradrenaline, UK 14,304, and dexmedetomidine, the maximal inhibitory effect on cAMP production was smaller in the alpha 2B-C2 subtype (35%) than in the alpha 2A-C10 and alpha 2C-C4 subtypes (50-70%). After treatment of cells expressing alpha 2B-C2 receptors with pertussis toxin, cAMP production was increased by up to 58% by alpha 2-adrenoceptor agonists. Similar stimulation of adenylyl cyclase activity could not be demonstrated at the other two receptor subtypes. In conclusion, these results demonstrate that (1) alpha 2-adrenoceptor agonists may be characterized by an agonist-type binding pattern in homogenates of transfected S115 cells, (2) all three alpha 2-adrenoceptor subtypes are coupled to inhibition of adenylyl cyclase in S115 cells through pertussis toxin-sensitive G-proteins, (3) the receptor-effector coupling in S115 cells is different among the subtypes so that the alpha 2A-C10 subtype is coupled with high efficacy but with low sensitivity, the alpha 2B-C2 subtype with low efficacy but high sensitivity, and the alpha 2C-C4 subtype with both high efficacy and high sensitivity, and (4) at least alpha 2B-C2 receptors may also be coupled to stimulation of adenylyl cyclase activity, presumably through Gs.

Distribution of alpha 2-adrenergic receptor subtype gene expression in rat brain

alpha 2-Adrenergic receptors in brain are important presynaptic modulators of central noradrenergic function (autoreceptors) and postsynaptic mediators of many of the widespread effects of catecholamines and related drugs. alpha 2-Adrenergic agonists are currently used as antihypertensives and preanesthetic agents, but new subtype-selective alpha 2-adrenoceptor agonists and antagonists have additional therapeutic application potential. Three genes encoding specific alpha 2-adrenoceptor subtypes (alpha 2A, alpha 2B, and alpha 2C) have been isolated and characterized. RNA blotting indicates that all three are expressed in rat brain. This study used in situ hybridization with 35S-labeled RNA probes to map the distribution of alpha 2-adrenoceptor subtype gene expression in rat brain. alpha 2A mRNA was most abundant in the locus coeruleus, but was also widely distributed in the brain stem, cerebral cortex, septum, hypothalamus, hippocampus and amygdala. alpha 2B mRNA was observed only in the thalamus. alpha 2C mRNA was mainly localized to the basal ganglia, olfactory tubercle, hippocampus, and cerebral cortex. These mRNA distributions largely agree with previous findings on the alpha 2-adrenoceptor distributions in the rat brain, but suggest that the localization patterns for each receptor subtype are unique. The expression of alpha 2A mRNA in noradrenergic neurons indicates that this subtype mediates presynaptic autoreceptor functions. Furthermore, the localization of alpha 2A mRNA in noradrenergic projection areas suggests that this receptor may also have an important role in mediating postsynaptic effects. The precise physiological and pharmacological roles of the alpha 2-adrenoceptor subtypes are still largely unknown, but it is expected that in situ hybridization coupled to various methods to identify the transmitter phenotypes of the subtype-expressing neurons will help to clarify these important issues in the near future.

Monoamine metabolite and catecholamine measurements in cerebrospinal fluid in determining the quality of the pre-operative night's sleep

Temazepam 20 mg (n = 18), midazolam 15 mg (n = 14), placebo (n = 15) or no medication (n = 20) were given orally as pre-operative hypnotic in healthy patients operated on under spinal analgesia. The quality of the pre-operative night's sleep assessed subjectively was significantly better in patients receiving temazepam (P = < 0.05) and midazolam (P = < 0.05) compared with those receiving no drug. The concentrations of cortisol and monoamine neurotransmitters or their metabolites in cerebrospinal fluid were of no value in monitoring the quality of the pre-operative night's sleep.

The effects of the COMT inhibitor entacapone on haemodynamics and peripheral catecholamine metabolism during exercise

1. Catechol-O-methyltransferase (COMT) inhibition might be assumed to potentiate the effects of circulating catecholamines, particularly under conditions of enhanced catecholamine release. 2. The purpose of the present study was to establish whether the novel COMT inhibitor, entacapone, changes haemodynamic responses and catecholamine metabolism during exercise. 3. Entacapone was given orally to 12 healthy male subjects (age 23-30 years) in increasing single doses from 0 mg (control day) to 200 mg. A submaximal exercise test was performed on a bicycle ergometer, and blood pressure, heart rate and ECG were recorded. The concentrations of noradrenaline, adrenaline, DHPG (3,4-dihydroxyphenylglycol), MHPG (3-methoxy-4-hydroxyphenyl-glycol) and, DOPAC (3,4-dihydroxyphenylacetic acid) in plasma were determined. 4. Entacapone did not influence haemodynamics or ECG at rest or during exercise. 5. Entacapone did not influence plasma catecholamine levels, either at rest or during exercise. However, it altered the metabolic profile of catecholamines, which was shown by increases in the plasma concentrations of the monoamine oxidase-dependent metabolites DHPG (by up to 100%) and DOPAC (by up to 53%), and by a decrease of the COMT-dependent metabolite MHPG (by up to 29%).

Effects of monoamine oxidase inhibition by selegiline on concentrations of noradrenaline and monoamine metabolites in CSF of patients with Alzheimer's disease

A double-blind, cross-over trial with 12 patients with Alzheimer's disease (AD) was carried out primarily to test the suitability of this design in the investigation of the clinical effects of selegiline (10 mg/day) in AD. Cerebrospinal fluid (CSF) samples for the determination of concentrations of noradrenaline (NA) and several monoamine metabolites were collected at baseline and at the end of both four-week treatment periods (placebo and selegiline). The severity of dementia was assessed using Ferm's and Gottfries-Bråne-Steen (GBS) dementia scales. The concentrations of the dopamine metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) and the NA metabolites, 3,4-dihydroxyphenylglycol (DHPG), and 3-methoxy-4-hydroxyphenyl glycol (MHPG) decreased significantly during selegiline treatment. There was a clear trend of reduction in concentrations of homovanillic acid (HVA) during selegiline treatment, whereas the concentrations of NA, 5-hydroxyindoleacetic acid (5-HIAA), and tryptophan did not differ significantly. The study design was not suitable for the analysis of the clinical results as there was a significant carry-over effect in both scales. As only the first period data could be used in the analysis, there were no significant differences in the scores of Ferm's or GBS scales, but clear positive trends could be detected in favour of selegiline.

Cloning and expression of a fish alpha 2-adrenoceptor

1. Pigment granule aggregation in specialized cells (melanophores) from the skin of teleost fishes has been shown to be mediated by receptors with an alpha 2-adrenoceptor pharmacology. We now report the cloning of the alpha 2-F, a fish skin alpha 2-receptor from the cuckoo wrasse (Labrus ossifagus). 2. Degenerate oligonucleotides corresponding to conserved regions of the human alpha 2-adrenoceptor subtypes were used in a polymerase chain reaction (PCR) with cDNA prepared from mRNA isolated subtypes were used in a polymerase chain reaction (PCR) with cDNA prepared from mRNA isolated from the skin of the cuckoo wrasse. An 876 base pair (bp) product was obtained that was homologous with that of the human alpha 2-adrenoceptor and was used to screen a genomic library from the cuckoo wrasse. 3. A clone (pTB17BS) consisting of approximately 5 kb of genomic DNA was obtained which contained the nucleotide sequence of the initial PCR product. In addition, it contained an open reading frame that encoded a protein of 432 amino acids and approximately 2 kb of 5'untranslated sequence. The deduced amino acid sequence of this protein showed 47-57% identity with the human alpha 2-adrenoceptors and thus appeared to encode a fish alpha 2-adrenoceptor. 4. In the 5'-untranslated region of the gene, nucleotide sequences were present suggesting that transcription of the alpha 2-F might be regulated by cyclic AMP, calcium and/or steroids. 5. The alpha 2-F was expressed in COS-7 cells and radioligand binding studies were performed with [3H]-rauwolscine. The binding was of high affinity and it was saturable with a KD of 0.8 +/- 0.1 nM and a Bmax of 5.7 +/- 1.0 pmol mg-1 of protein.6. Competition curves for the displacement of specific [3H]-rauwolscine binding showed the following order of potency: for agonists, medetomidine > clonidine >p-aminoclonidine> B-HT 920> (- )-noradrenaline;for antagonists, rauwolscine > atipamezole > yohimbine > phentolamine > prazosin.7. These results show that alpha2-F has characteristics of both the human alpha2-CIO and alpha2-C4 and that it might represent an ancestral alpha2-adrenoceptor subtype.

Use of recombinant human alpha 2-adrenoceptors to characterize subtype selectively of antagonist binding

Cloning of the genes encoding three subtypes of human alpha 2-adrenoceptors allows the separate heterologous expression of each subtype. We have generated stably transfected Shionogi S115 mouse mammary tumour cell lines expressing the human alpha 2-adrenoceptor subtypes alpha 2-C10, alpha 2-C2, and alpha 2-C4 at densities of 0.2-7 pmol/mg total cellular protein. Binding of [3H]rauwolscine was inhibited by co-incubation of S115 cell homogenates with ten alpha 2-adrenoceptor antagonists and oxymetazoline, a partial agonist known to discriminate the receptor subtypes. Other useful agents for discrimination of subtypes were prazosin, chlorpromazine, phentolamine, and yohimbine. The most sensitive indices for differences between the three subtypes were the binding inhibition coefficient (Ki) ratios chlorpromazine/oxymetazoline (alpha 2-C10: 202; alpha 2-C2: 0.004; alpha 2-C4: 0.8), prazosin/oxymetazoline (430; 0.03; 0.5) and chlorpromazine/atipamezole (1612; 5.8; 77). Correlation analysis between our results for human-type receptors and published data for their rat alpha 2-adrenoceptor homologues demonstrated excellent general agreement, with some interspecies differences in the affinity of rauwolscine, phentolamine and oxymetazoline. The use of recombinant human receptors produced in stably transfected cell lines should facilitate the development of new, subtype-selective alpha 2-adrenoceptor ligands.

Hormonal responses to physical exercise in patients with polycystic ovarian syndrome

OBJECTIVE

To examine the effects of obesity and polycystic ovarian syndrome (PCOS) on the endocrine responses to physical exercise.

SETTING

Outpatient clinic of reproductive endocrinology at the University Central Hospital of Turku and the Department of Pharmacology, University of Turku, Turku, Finland.

PATIENTS

Nine oligomenorrheic women with PCOS (body mass index [BMI] 19.5 to 46.0 kg/m2) and eight control women with regular menstrual cycles (BMI 20.0 to 53.5 kg/m2).

INTERVENTIONS

A bicycle ergometer test was performed at 8 A.M.

RESULTS

The only hormone response that was different between PCOS patients and controls was the exercise-induced increase in circulating GH levels. This response was significantly greater in controls than in PCOS patients. There was also a negative correlation between the GH response and BMI. The increases in the concentrations of adrenaline, noradrenaline, 3,4-dihydroxyphenylglycol, glucose, and insulin:C-peptide ratios during the bicycle ergometer test were correlated negatively to BMI.

CONCLUSION

Obesity is an important determinant of the hormonal responses to physical exercise. This applies also to women with PCOS. Taking obesity into account in the analysis of exercise-induced hormone responses, only little, if any, of the variation in the hormonal responses measured by us could be attributed to PCOS per se. The only hormone response that was different between PCOS patients and controls was the GH response.

The effects of the COMT inhibitor nitecapone for one week on exercise haemodynamics and catecholamine disposition

We have studied resting and exercise haemodynamics and catecholamine disposition after catechol-O-methyl-transferase (COMT) inhibition with nitecapone 100 mg t.d.s. for 7 days in 15 healthy men (aged 21 to 28 y) in a placebo-controlled, cross-over study. Nitecapone did not alter resting or exercise heart rates, blood pressure, or plasma catecholamine concentrations, but it altered the metabolic profile of endogenous catecholamines, as shown by: (1) a fall in the concentrations of the COMT-dependent metabolite 3-methoxy-4-hydroxy-phenylglycol (MHPG) by 22% (P < 0.01), (2) increases in plasma concentrations of the monoamine oxidase-dependent metabolites 3,4-dihydroxyphenylglycol (DHPG) by up to 90% (P < 0.001) and 3,4-dihydroxyphenylacetic acid (DOPAC) by 67% (P < 0.05), (3) a three-fold increase in the concentration of circulating conjugated adrenaline (P < 0.001).

Reduced turnover of dopamine and 5-hydroxytryptamine in discrete dopaminergic, noradrenergic and serotonergic rat brain areas after acutely administered medetomidine, a selective alpha 2-adrenoceptor agonist

Monoamine metabolism and turnover were investigated in discrete dopaminergic, noradrenergic and serotonergic brain areas in the rat after acute administration of the selective alpha 2-adrenoceptor agonist, medetomidine. Medetomidine (3, 30 and 100 micrograms/kg subcutaneously) was given 90 min. before decapitation and discrete brain nuclei were punched from frozen brain slices for the analysis of concentrations of noradrenaline (NA), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA). In a separate experiment, the accumulation of 3,4-dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) was measured after inhibition of L-aromatic amino acid decarboxylase by NSD 1015: medetomidine (3, 10 and 100 micrograms/kg subcutaneously) was given 60 min. before NSD 1015 (100 mg/kg intraperitoneally), and the rates of DOPA and 5-HTP accumulation were determined over 30 min. Finally, the antagonistic effect of idazoxan (1 mg/kg subcutaneously), a selective alpha 2-adrenoceptor blocking agent, on the medetomidine-induced changes in monoamine metabolism was investigated. Medetomidine markedly decreased the metabolism and turnover of DA in the nucleus caudatus, but not in the nucleus accumbens or substantia nigra. In all dopaminergic areas, the turnover of 5-HT was markedly inhibited by medetomidine. These effects were significantly counteracted by idazoxan pretreatment demonstrating the alpha 2-receptor mediated action of medetomidine. The turnover of 5-HT was also reduced by medetomidine in the nucleus raphe dorsalis, the A1-C1 area, locus coeruleus, nucleus tractus solitarius and the A5 area. The accumulation of DOPA was markedly inhibited in the A1-C1 area, nucleus tractus solitarius and nucleus raphe dorsalis, but not in locus coeruleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Haemodynamic and catecholamine responses to induction of anaesthesia and tracheal intubation: comparison between propofol and thiopentone

We have studied the haemodynamic changes, QT intervals and catecholamine responses to induction of anaesthesia and tracheal intubation in 24 ASA I patients allocated randomly to receive either propofol 2.5 mg kg-1 or thiopentone 5 mg kg-1 over 60 s. After disappearance of the eyelash reflex, the lungs were ventilated with 100% oxygen for 3 min. The trachea was intubated after administration of vecuronium. With thiopentone, heart rate (HR) was greater than with propofol before intubation (P < 0.05). During induction, systolic (SAP) and diastolic arterial pressure (DAP) decreased more with propofol than with thiopentone. The QT interval was prolonged only during induction with thiopentone. In both groups, HR, SAP, DAP and the QT were increased in response to intubation (P < 0.001). The SAP and QT interval responses to intubation were significantly greater with thiopentone than with propofol (P < 0.05). One patient in the thiopentone group with a significantly prolonged QT interval had episodes of bigeminy and ventricular tachycardia. In both groups, concentrations of noradrenaline in mixed venous plasma increased after intubation (P < 0.001). Concentrations of adrenaline increased after intubation only in the thiopentone group (P < 0.001).