[Proton pump inhibitors: impact of professional practice evaluation on prescriptions pertinence]

OBJECTIVE

To improve the quality of proton pump inhibitors (PPI) prescription in an orthopaedic department.

STUDY DESIGN

Prospective professional practice evaluation study.

PATIENTS AND METHODS

A specific protocol concerning the best practice for using PPI in the perioperative period was established by anaesthesiologists and validated by all prescribers, according to recent recommendations published by French Afssaps. PPI prescription pertinence, mainly using the oral route, was based upon the presence of clearly identified risk factors. PPI mensual consumption and severe gastric complications were analyzed and compared with those obtained from the previous year. Ten months after the beginning of the protocol, the pertinence of PPI prescription was analyzed in 20 randomly selected medical records. Data are expressed in defined daily dose (DDD).

RESULTS

After one year, a 35.5% decrease in oral PPI consumption was noted (901 ± 211 before vs 581 ± 235 DDD, after, P<0.05). A similar trend to a decrease in intravenous PPI consumption was observed (40 ± 23 vs 22 ± 26, P=0.06). During the same period, the overall incidence of severe gastric complication remained stable. The PPI prescription was pertinent in 85% of selected medical records.

CONCLUSION

This study confirmed the interest of professional practice evaluation protocols to improve PPI prescription. A strong implication of all medical staff members is mandatory to maintain such benefits over time.

Prise en charge de la migraine en médecine générale

INTRODUCTION

A national survey has been conducted with 349 general practitioners in order to analyze the management of concerned episodic headache in general practice.

METHOD

This survey enabled collection of data from 2537 headache patients. The main data concered IHS diagnosis, severity of headache using the MIGSEV scale, management, practices and the impact on daily living (QVM and HIT-6 scales).

RESULTS

Out of the 2537 included patients, 52 percent were migraine sufferers according to IHS criteria (code 1.1/1.2), 34 percent presented with migrainous disorders (code 1.7), and 14 percent were non-migraine headache patients. The distribution of management practices showed that 71 percent of them were given non-specific treatments, 46 percent of them specific treatments and 27 percent of them prophylactic treatments. Analysis of the impact of headache using the QVM or the HIT-6 demonstrated a relationship between diagnosis, migraine severity and disability. Analysis of the correlation between the severity of the last migraine attack as evaluated by the patient and that estimated by the doctor showed that the practitioner tended to underestimate the patient's pain. These results highlight the importance of communication between practitioners and migraine sufferers.

CONCLUSION

Training of general practitioners in the use of simple tools such as the HIT-6 scale, should be helpful for a better evaluation of the impact of headache on daily living, and hence should lead to more optimal therapeutic management of headache patients.

[Clinical pharmacology of triptans]

The 5HTI receptor antagonists currently used for the treatment of migraine headache all belong to the "triptan" group of drugs and have a chemical formula derived from serotonin. This structural similarity explains in part the MAO-A metabolism of certain triptan drugs used in human medicine. Chemical substitutions explain the variable role of different cytochrome P450 isoenzymes and differences in terms of drug interactions. Beyond the analysis of clinical trials, the pharmacologist must examine the epidemiological data on triptans. Prescription studies show an erroneously frequent use of sumatriptan for non-migraine headache. A low percentage of patients consume a large proportion of the sumatriptan prescribed and could be considered as "drug abusers". Epidemiological observation provides better knowledge of adverse effects and a better statistical definition of risk. The high cost of triptans, compared with older drugs, suggests the need to examine the pharmacoeconomical aspects of the question. Much more costly than ergot derivatives, triptans have a favorable cost-benefit and cost-usefulness ratio as is demonstrated by the reduction in loss of productivity, improved quality of life, and cost effectiveness studies.

Glucose-induced sympathetic activity and energy expenditure during acute alpha2-adrenergic antagonism in obese subjects

OBJECTIVE

To determine the effect of an alpha2-adrenoceptor antagonist, idazoxan, on the sympathetic nervous system and on energy expenditure responses after an oral glucose load, in obese patients. (idazoxan acts as an indirect sympathomimetic drug through blockade of presynaptic alpha2-adrenoceptors).

DESIGN

Double-blind randomized placebo-controlled cross-over study. Idazoxan (40 mg) or placebo were administered orally 90 min before a 100 g oral glucose load.

SUBJECTS

Twelve long-standing obese subjects (six men and six women, age range from 24 to 45 y, body mass index range from 30.2 to 41.3 kg/m2).

MEASUREMENTS

Energy expenditure was derived from oxygen consumption and carbon dioxide production according to indirect calorimetry. Plasma samples were obtained for plasma adrenaline and noradrenaline, glucose, non-esterified fatty acid (NEFA), glycerol and insulin determinations.

RESULTS

The plasma noradrenaline concentration response to the glucose load was significantly higher after idazoxan than after placebo administration. The time-course of glucose load-induced thermogenesis was not significantly different after administration of idazoxan nor placebo. Idazoxan administration did not modify the insulin, non-esterified fatty acids or glycerol concentration responses to the glucose load. Neither heart rate nor blood pressure values were modified by idazoxan when compared to placebo. However, idazoxan significantly improved glucose tolerance.

CONCLUSION

The alpha2-adrenergic antagonist idazoxan increases glucose-induced sympathetic activity but not energy expenditure in obese subjects. These data do not argue for the development of alpha2AR antagonist compounds as anti-obesity treatment.

[Utilization of heart rate at the ventilatory threshold for the prescription of intensity of exercise training in cardiac failure]

Physical exercise is a treatment for cardiac failure but a large range of intensities of exercise is proposed. The aims of this study were to determine the range of intensities of effort used and to individualize the intensities used. Thirty patients with stable cardiac failure (NYHA Classes II-III, age: 53 +/- 2.1 years, ejection fraction: 31 +/- 1.4%) underwent a cardiorespiratory exercise stress test before and after individualized training at the ventilatory threshold. However, before and after the training period, standard methods of calculation of the intensities at the ventilatory threshold showed individual differences greater than +/- 2 standard deviations, indicating different metabolic stimulations. After the individualized training programme, peak oxygen consumption on exercise (1679 +/- 100 vs 1487 +/- 89 ml.min-1, p = 0.0001) and at ventilatory threshold increased (1365 +/- 85 vs 1133 +/- 65 ml.min-1, p = 0.0001), the ventilatory threshold/peak exercise ratio increased (81.2 +/- 1.3 vs 76.7 +/- 1.4%, p = 0.0008), and there was a decrease in heart and ventilatory rates at submaximal metabolic levels (p = 0.0001). The authors conclude that protocols using intensity of effort at the ventilatory threshold give similar results with respect to improvement of aerobic capacity as other methods of indirect calculation, based on maximal heart rate of oxygen consumption. The value of this particular method lies in the adequation between aerobic capacity of the patient and the intensity of training. The results obtained attain the physiopathological aims of rehabilitation.

Changes in short-term variability of blood pressure and heart rate during the development of obesity-associated hypertension in high-fat fed dogs

OBJECTIVE

To investigate the nature and time course of autonomic nervous system changes elicited by a 21-week ad libitum high-fat diet (HFD) in dogs.

RESULTS

The HFD increased body weight (+22.0+/-2.8% at week 21) with an abdominal circumference gain significantly more elevated than the thoracic one. The increases in insulin and free fatty acid plasma levels were correlated with body weight changes. Systolic and diastolic blood pressures and heart rate significantly increased (+23+/-6, +28+/-5 and 19+/-9% respectively). Arterial hypertension was characterized by an increase in cardiac output (+22.3+/-7.7%), in left ventricular mass (+18.1+/-5.0% at week 21) and a decrease in spontaneous baroreflex efficiency (-55+/-6%). The time course of autonomic changes (using spectral analysis of systolic blood pressure and heart rate) showed the existence of time-dependent modifications, which were linked with food intake. The initial rise in arterial blood pressure during body weight increment (observed between the 1st and 8th week of HFD) was associated with a transient increase in the low frequency band of systolic blood pressure variability and noradrenaline plasma levels associated with a long-lasting decrease in the high frequency band of heart rate variability. Early changes in short-term variability were significantly correlated with free fatty acid plasma levels. In contrast, the steady-state of obesity-related hypertension was associated with a decreased high frequency band of heart rate variability, without significant changes in noradrenaline plasma levels.

CONCLUSIONS

This study shows that the HFD induces abdominal obesity, hyperinsulinaemia and arterial hypertension, with a left ventricular hypertrophy associated with a biphasic changes in autonomic activity: an early and long-lasting decrease in parasympathetic nervous system activity and an early but transient increase in sympathetic activity. The present data suggest that autonomic nervous system changes are dependent on the time course of obesity development.

[Functional decoupling of left ventricular beta-adrenoceptor in a canine model of obesity-hypertension]

OBJECTIVE

To assess cardiac beta-adrenoceptors (beta-AR) in an obesity-hypertension model.

METHODS

Six male beagle dogs (aged 35 +/- 5 months) receiving during 30 weeks a high-fat diet with 60% uncooked beef fat were compared to 6 normal beagle dogs. With right auricular and left ventricular samples we analysed cardiac beta-AR density through binding study using [125I]-cyanopindolol. beta 1 and beta 2 densities were obtained by competition with CGP 20712A. Affinity state of beta-AR was assessed by competition with isoproterenol. Noradrenaline plasma level was assayed by HPLC. Left ventricular mass (LV mass) was measured by echocardiography. Results are expressed as mean +/- SE. All comparisons were performed using a variance analysis (*: p < 0.05).

RESULTS

Systolic blood pressure was significantly higher in obesses (245 +/- 8 vs 197 +/- 10 mmHg in controls). Diastolic blood pressure did not differed between both groups (93 +/- 3 vs 84 +/- 3 mmHg in controls). Noradrenaline plasma levels were similar in both groups (276 +/- 30 vs 235 +/- 50 pg/mL in controls). Obesses were characterized by higher LV mass (80 +/- 24 vs 67 +/- 15 g in controls*). Right auricular and left ventricular beta-AR densities were not different in obesses (57 +/- 6 and 67 +/- 4 fmoles/mg protein) and in controls (68 +/- 7 and 63 +/- 9 fmoles/mg protein). The beta 1-AR proportion was the same in obesses and controls in right auricule (63 +/- 4 vs 64 +/- 3% in controls) and left ventricule (59 +/- 3 vs 60 +/- 4% in controls). The proportion of beta-AR receptors in a high affinity state was similar in right auricular samples (69 +/- 4 vs 67 +/- 3%) in controls) but was significantly different in left ventricule (28 +/- 6 vs 74 +/- 6%) in controls).

CONCLUSION

Left ventricular beta-adrenoceptors came under a specific desensibilisation independent of plasma noradrenaline levels. This functional decoupling of beta-adrenoceptors may account for the progressive systolic dysfunction of hypertensive cardiomyopathy.

[Apropos of recent antidepressant drugs: some pharmacological comments]

Since the discovery of imipramine by Kübn in 1958, several hypotheses have been developed in order to explain the antidepressant properties of thymoanaleptic drugs. These hypotheses have successively used the results of predictive psychopharmacology, biological psychiatry and more recently biochemistry of depression. These data have led to the discovery of new products with clear antidepressant properties but with a stereotyped 'mono' aminergic mechanism of action. Among these drugs, the currently most prolific family is the group of 'selective' serotonin reuptake inhibitors (SSRI). This review discusses the mechanism of action of the recently marketed antidepressant drugs, their selectivity, drug-induced changes in the synaptic cleft after short and long term treatment, the differences in pharmacodynamics, pharmacokinetics, pharmacogenetics and drug surveillance between the different agents as well as the perspective for the development of new antidepressants.

[Effects of octreotide on experimental orthostatic neurogenic hypotension]

The synthetic somatostatin analogue, octreotide, has recently been proposed for the treatment of both postprandial and orthostatic hypotension (OH) in humans with autonomic failure related to multiple system atrophy (MSA) or diabetes mellitus. However, pharmacodynamic data are not still available in experimental models of orthostatic hypotension. We investigated in a model of neurogenic orthostatic hypotension, obtained by chronic sinoaortic denervation (SAD) in chloralose-anaesthetized dogs, the effects of octreotide (0.1 mg/kg, subcutaneous route) during a double-blind cross-over study vs placebo. Blood pressure (BP) and heart rate (HR) average values, SBP and HR short-term variabilities (using fast Fourier transformation) in both low (LF: 50-150 mHz) and high frequency range (respiratory rate +/- 50 mHz) and plasma noradrenaline (NA) levels (HPLC) were measured in supine position and during head-up tilt test (HUT: 80 degrees, 10 min) before and 45 min after drug administration. In controls, as expected, head-up tilt test induced a significant increase in DBP (+14 +/- 8 mmHg), HR (+36 +/- 21 beat/min), NA (296 +/- 118 vs 141 +/- 63 pg/ml), SBP-LF (25 +/- 5 vs 14 +/- 3%) whereas HR-HF significantly decreased. The changes during head-up tilt test were not modified after placebo or octreotide administration. In SAD dogs, head-up tilt test elicited a dramatic fall in SBP (-74 +/- 39 mmHg), DBP (-20 +/- 15 mmHg) without any significant change in HR (-5 +/- 12 beat/min), NA (708 +/- 213 vs 606 +/- 331 pg/ml), SBP-LF (16 +/- 3 vs 16 +/- 3%), HR-HF (8 +/- 2 vs 7 +/- 1%). Octreotide or placebo failed to significantly modify any of the measured parameters during head-up tilt test performed 45 min after drug administration. At the dose used, octreotide elicited a 80% decrease in insulin plasma levels after 45 min in both normal and SAD dogs. These results suggest that 1) this experimental model of orthostatic hypotension in SAD dogs is reproductible and can be used to investigate the pharmacological effects of antihypotensive drugs, 2) cardiovascular and biochemical characteristics of the SAD model are similar to those observed in MSA and 3) octreotide, in these experimental conditions, is not able to correct the BP fall during head-up tilt test.

[Experimental hypertension induced by hypercaloric diet]

Obesity, hypertension and hyperinsulinism are frequently related and constitute morbid elements of human athero-thrombogenic syndrom. To elucidate physiopathologic mechanisms linking these symptoms, we have developped an experimental model reproducing the morbid triptyque: obesity-hypertension-insulin resistance were induced by hyperlipidic hypercaloric diet. The aim of this study was to investigate cardiovascular modifications elicited by high fat diet. Four male Beagle-Harrier dogs were used in this preliminary study. We investigated before and 7 weeks after the beginning of the hypercaloric hyperlipidic diet morphologic measures, systemic blood pressure (BP) and heart rate (HR), pulmonary blood pressure, cardiac output (CO), systolic ejection volume (SEV), peripheral arterial resistance (PAR) and HR variability on 24 hours' electrocardiogram obtained by Holter method. Echocardiographic modifications of left ventricule was also studied after 20 weeks. Body weight increased (+15.4%) after 7 weeks and remained stable the whole experimental period. This gain was associated with an increase of thoracic and abdominal circonferences (respectively +5.9% and 14.3% at the 7th week). The abdominal increase was significantly more elevated than the thoracic one. This abdominal obesity was associated with an increase in diastolic (+17.9%) and mean (+16.4%) (but not systolic) BP. High fat diet failed to modify arterial pulmonary blood pressures but induced an increase in both CO (3.0 +/- 5.2 vs 4.3 +/- 0.4 ml/min) and SEV (32.4 +/- 5.2 vs 40.8 +/- 2.7 ml/beat). PAR decreased (43.1 +/- 5.9 vs 33.0 +/- 3.2 UW; p = 0.08). Holter method showed a non significant increase of HR (82.0 +/- 7.8 vs 99.5 +/- 5.6 beat/min; p = 0.1) explained by a significant decrease of parasympathetic HR variability (PNN50: 53.5 +/- 4.1 vs 40.9 +/- 4.1%). No echocardiographic modification of left ventricule was found after 20 weeks of high fat diet. This preliminary study shows that, like in humans, high fat diet in dogs induced abdominal obesity with systemic hypertension but failed to provoke left cardiovascular hypertrophy after 20 weeks. This model will allow to characterize the links between cardiovascular and endocrinometabolic alterations occurring during the development of obesity and hypertension.

Effects of acute levodopa administration on blood pressure and heart variability in never treated parkinsonians

The effects of levodopa on autonomic nervous system (ANS) were investigated through the measurement of blood pressure (BP) and heart rate (HR) variability in 15 de novo parkinsonian who never received dopaminergic drugs. BP and HR were obtained using digital photoplethysmography in supine and standing positions. Measurements were achieved 90 min after administration, in a double blind cross-over way, of placebo or levodopa (200 mg)+benserazide (50 mg). Spectral analysis was performed using fast Fourier transformation (FFT) on 512 consecutive SBP and HR values. Spectral modulus was integrated for calculation of total spectra and of low frequency (LF: 66-129 mHz) or high frequency band (HF: respiratory frequency +/- 50 mHz). After placebo, orthostatism was followed by a significant increase in BP and HR whereas relative variabilities in LF and HF remained unchanged. After levodopa, BP was significantly lower in supine position without changes in HR and LF. During orthostatism, changes observed in BP and in FFT were similar to those observed during placebo period. These data indicate that levodopa reduces supine and standing BP but does not impair orthostatic adaptation. This effect is not due to modification of BP or HR variability and appears to independent of any direct effect on ANS.

Cardiac beta-adrenoceptors and adenylyl cyclase activity in human left ventricular hypertrophy due to pressure overload

The effect of left ventricular hypertrophy (LVH) due to chronic pressure overload on right atrial (RA) and left ventricular (LV) myocardial beta-adrenergic receptor (beta-AR) density and subtypes, adenylyl cyclase (AC) activity and ADP-pertussis toxin ribosylated proteins was investigated in humans with LVH due to aortic stenosis and in patients without LVH undergoing heart surgery for mitral stenosis or coronary artery disease taken as controls. Both groups presented normal systolic function or plasma catecholamine levels. In LVH and controls, beta-AR density was similar in RA (62 +/- 6 vs 77 +/- 12 fmol.mg-1 protein) and LV (39 +/- 7 vs 32 +/- 2 fmol.mg-1 protein). In LVH, beta 1-AR percentage was < than in controls in LV (35 +/- 11 vs 73 +/- 5%, P < 0.05) but not in RA (79 +/- 5 vs 73 +/- 8%). Basal AC activity in RA (19 +/- 4 vs 21 +/- 6 pmol.mg-1 protein) and LV (22 +/- 5 vs 27 +/- 3 pmol.mg-1 protein) was similar in LVH and in controls. Isoprenaline-induced stimulation of AC in RA was similar in LVH and in controls (51 +/- 18 vs 36 +/- 18%) but < in LV of LVH (7 +/- 6 vs 45 +/- 6%, P < 0.05). In the presence of ICI-118,551 (a beta 2-adrenoceptor antagonist), isoprenaline failed to induce any increase in cAMP in LVH. The quantification of ADP-pertussis toxin ribosylated proteins indicated a lower concentration of substrates in LV myocardial membranes from LVH. These data indicate that in LVH due to pressure overload, there is a down-regulation of beta 1-AR and an increase in beta 2-AR density. This is associated with alterations of the transmembrane signalling marked by a decreased capacity of isoprenaline to stimulate AC and an impaired expression of Gi proteins.

A study of alpha 1- and alpha 2-adrenoceptor responsiveness in diabetic insipidus dogs

The present study was performed to investigate the participation of circulating vasopressin in alpha-adrenoceptor responsiveness. Thus, we compared the pressor responses induced by selective alpha 1-or alpha 2-adrenoceptor stimulation in two groups of conscious dogs: a) normal animals and b) animals with surgically-induced diabetes insipidus. In addition, platelet alpha 2-adrenoceptors labelled with (3H)RX821002 were compared in the two groups. The pressor response to alpha 1-adrenoceptor stimulation [ie successive doses of noradrenaline (0.5, 1, 2, 4 micrograms/kg i.v.) after propranolol (1 mg/kg i.v.) plus yohimbine (0.5 mg/kg i.v.)] was significantly (P < 0.05) less pronounced in diabetic insipidus than in normal dogs. In contrast, the magnitude of the pressor effects of alpha 2-adrenoceptor stimulation [ie noradrenaline after propranolol plus prazosin (1 mg/kg i.v.)] was the same in the two groups of animals. Bmax and Kd values for (3H)RX821002 binding on platelets were similar in diabetic insipidus and normal dogs. This study shows that alpha 1- (but not alpha 2-) adrenoceptor responsiveness is decreased in diabetic insipidus suggesting the involvement of vasopressin in the mechanisms of the vascular alpha 1-adrenoceptor pressor response.

[Is there any desensitization of presynaptic alpha 2-adrenergic receptors in hypertension? Experimental and clinical studies]

Several authors have discussed an alteration of adrenergic receptivity in arterial hypertension. De Champlain (Hypertension 1990; 8: S77-S85) suggested that postsynaptic alpha 1-adrenergic functions became dominant while beta-adrenergic functions are attenuated in arterial hypertension. However, the status of presynaptic alpha 2-adrenoceptors remains unknown. The present study investigates presynaptic alpha 2-adrenoceptors in hypertension through the measurement of plasma levels of noradrenaline after administration of yohimbine, an alpha 2-adrenoceptor antagonist, in essential hypertension. Yohimbine (0.2 mg/kg per os) induced a 73% increase of plasma levels of noradrenaline in hypertensive patients (n = 12) and a 178% one in normotensive subjects (n = 6, p < 0.05). A similar significant difference was found in experimental neurogenic hypertension observed in awake dogs 3 weeks after sinoaortic denervation: the increase in plasma concentrations of noradrenaline after yohimbine (0.5 mg/kg i.v.) was +279% in hypertensive versus +642% in normotensive dogs (p < 0.05). The results show that the magnitude of the yohimbine-induced sympathetic activation is lower in hypertensives than in normotensives. They suggest the existence of a presynaptic alpha 2-adrenoceptor desensitization in arterial hypertension. The abnormality of this presynaptic inhibitory mechanism can increase the sympathetic tone and help to develop and maintain arterial hypertension.

[Myocardial beta-adrenergic receptors and left ventricular hypertrophy induced by pressure overload in man]

In experimental models, the characteristics of beta-adrenoceptors in left ventricular hypertrophy (LVH) due to pressure overload remain controversial and no data are still available in man. We investigated right auricular (RA) and left ventricular (LV) beta-adrenoceptors characteristics (125 I cyanopindolol binding) in two groups of patients undergoing valve replacement without heart failure (LV ejection fraction > 55%). Height patients with mitral stenosis (mean age: 64 +/- 4 years) and without LVH (LV mass index < 120 g/m2) constituted the control group and 13 patients with aortic stenosis (mean age: 66 +/- 4 years) and LVH (LV mass index > 150 g/m2) the study group. The results are: [table: see text] These results show that, in man, LVH due to pressure overload does not induce variation of total number beta-adrenoceptors, but is associated with a selective decrease in left ventricular beta 1-adrenoceptors.

Myocardial hypertrophy, cardiac beta-adrenoceptors and adenylate cyclase activity during sinoaortic denervation in dogs

1. The long-term effects of sinoaortic denervation on the development of left ventricular hypertrophy (assessed by the measurement of the ratio (R): heart weight/total body weight and LVT: left ventricular thickness), myocardial beta-adrenergic receptivity (measured by [125I]-cyanopindolol binding and adenylate cyclase activity) and plasma catecholamine levels (measured by h.p.l.c.) were investigated in three groups of dogs: normotensive controls (group 1), dogs made hypertensive by sinoaortic denervation and evaluated 1 (group 2) and 18 months (group 3) later. 2. Noradrenaline (NA) and adrenaline (A) plasma levels were 461 +/- 54 and 85 +/- 45 pg ml-1 in controls, 861 +/- 185 and 191 +/- 23 pg ml-1 in group 2 (P less than 0.05). They were normal in group 3 (426 +/- 132 and 110 +/- 16 pg ml-1). 3. R and LVT values were significantly (P less than 0.05) higher in sinoaortic denervated dogs (R = 7.7 +/- 0.1 and 7.8 +/- 0.2; LVT = 13.6 +/- 1.3 and 14.2 +/- 0.9 mm in groups 2 and 3 respectively) than in normotensive dogs (group 1: R = 6.7 +/- 0.1, LVT = 9.3 +/- 0.8 mm). 4. In group 1, the total number of beta-adrenoceptors (Bmax) was 37 +/- 11 and 29 +/- 6 fmol mg-1 protein in the left ventricle (LV) and right auricle (RA) respectively. In group 2, Bmax was significantly lower (10 +/- 3 in LV and 13 +/- 2 fmol mg-1 protein in RA, P less than 0.05) than in group 1. There was no difference between group 1 and group 3 (37 +/- 3 fmol mg-1 prot in LV and 31 +/- 3 fmol mg-1 protein in RA). 5. The percentage of beta 1-adrenoceptors was 82 +/- 4 in LV and 75 +/- 5 in RA in group 1. It was significantly lower (P less than 0.05) in groups 2 (LV: 33 +/- 6 and RA: 33 +/- 5) and 3 (LV: 59 +/- 3 and RA: 55 +/- 4). 6. Basal values of adenylate cyclase activity in LV significantly decreased after sinoaortic denervation.7. These data show that sinoaortic denervation is associated with left ventricular hypertrophy which appears early (1 month) and persists until 18 months despite the normalization of plasma catecholamine levels. The total number of myocardial beta-adrenoceptors is closely related to catecholamine levels but a selective decrease in beta 1-adrenoceptors is observed during cardiac hypertrophy. The fall in basal adenylate cyclase activity suggests that cardiac hypertrophy is associated with an impairment of transmembrane signalling.

Alpha 2-adrenoceptor in HT29 human colon adenocarcinoma cell-line: study of [3H](-)-adrenaline binding

The HT29 human adenocarcinoma cell-line was used to investigate the binding of [3H](-)-adrenaline at alpha 2-adrenoceptors. All aspects of the study indicated that alpha 2-adrenoceptors were specifically labeled. [3H](-)-adrenaline bound with high affinity (KD = 2.28 +/- 0.41 nM) to a single population of non-interacting sites. The rank order of adrenoceptor antagonists (yohimbine greater than phentolamine much greater than prazosin) and agonists (UK-14,304 greater than clonidine greater than (-)-adrenaline greater than (-)-noradrenaline greater than (+)-adrenaline greater than (+)-noradrenaline greater than amidephrine) to compete with [3H](-)-adrenaline binding showed that the labeled sites were alpha 2-selective and stereospecific. Comparison of the binding parameters of [3H](-)-adrenaline with those of [3H]clonidine (partial-agonist) and [3H]yohimbine (antagonist) indicated that [3H](-)-adrenaline and [3H]clonidine labeled a similar number of sites (156 +/- 13 versus 175 +/- 21 fmol/mg protein) and that [3H]yohimbine (Bmax = 246 +/- 22 fmol/mg protein) labeled more sites than the 3H-agonists. Data on the inhibition of [3H]yohimbine binding by (-)-adrenaline was better fitted to a two-site model and revealed (1) that the KiL/KiH ratio was higher for (-)-adrenaline than for clonidine (2) that both agonists recognized the same percentage of high-affinity receptors. The results from a kinetic study of [3H](-)-adrenaline binding were apparently inconsistent with the equilibrium data. Both the association and dissociation were bi-exponential, suggesting a relative heterogeneity of the labeled sites. The tritiated physiological full-agonist was moreover able to induce tight-binding. The practical consequences of this property are discussed.