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Biomedical subjects

J G Riddell

Publications and source records attributed to J G Riddell.

48 records · Page 3Linked to original sources
PubMed1985

Effects of the beta 2-adrenoceptor antagonist ICI 118,551 on exercise tachycardia and isoprenaline-induced beta-adrenoceptor responses in man.

ICI 118,551, 5 to 80 mg orally, did not significantly alter resting heart rate or blood pressure. In doses less than 40 mg the reduction in exercise tachycardia was under 10 beats/min. ICI 118,551, 10 to 40 mg, did not appear to reduce the maximum rise in systolic pressure with isoprenaline but did attenuate the changes in diastolic pressure, forearm blood flow and finger tremor. It also attenuated the isoprenaline-induced changes in serum glucose, insulin and potassium. On these observed changes, the effect of ICI 118,551 20 mg was similar to that of 40 mg and of propranolol 10 mg, but greater than that of atenolol 25 mg. An isoprenaline tachycardia was attenuated by all doses of ICI 118,551 studied. After atropine (0.04 mg/kg) ICI 118,551 20 mg still significantly reduced the effects of isoprenaline suggesting that functional beta 2-adrenoceptors may be present in the human heart. In doses less than 40 mg, ICI 118,551 appears to be a selective and competitive antagonist of beta 2-adrenoceptors in man.

Adrenergic beta-Antagonists↗
PubMed1985

Effects of azepexole and clonidine on baroreceptor mediated reflex bradycardia and physiological tremor in man.

The effects of oral administration of azepexole 10 mg, clonidine 300 micrograms and placebo on baroreceptor mediated reflex bradycardia and physiological tremor were investigated in six healthy volunteers. Both azepexole and clonidine reduced (P less than 0.05) systolic (120.5 +/-2.5 to 105.0 +/- 3.3 mm Hg; 115.8 +/- 2.6 to 104.7 +/- 2.8 mm Hg respectively) and diastolic (52.5 +/- 2.6 to 47.2 +/- 1.4 mmHg; 53.7 +/- 1.6 to 49.0 +/- 1.5 mmHg respectively) pressure when compared to placebo and to pre-treatment values. This reduction in pressure was not accompanied by a change in heart rate. Both azepexole and clonidine enhanced (P less than 0.05) baroreflex sensitivity to increases in systolic arterial pressure with phenylephrine. Clonidine facilitated (P less than 0.05) baroreflex sensitivity during the strain phase of the Valsalva manoeuvre, whereas azepexole reduced it (P less than 0.05). Neither clonidine nor azepexole altered finger tremor when compared to placebo or pre-treatment values. Azepexole produced (P less than 0.05) sedation compared to placebo but not when compared to pre-treatment values. Clonidine caused significant increases in sedation when compared to both placebo and to pre-treatment values. The differences between azepexole and clonidine may be due to the greater specificity of azepexole for the alpha 2-adrenoceptor than clonidine.

Adrenergic alpha-Agonists↗
PubMed1984

A new method for constant plasma drug concentrations: application to lidocaine.

Optimal intravenous drug therapy often requires the rapid achievement and maintenance of therapeutic plasma drug concentrations. Simple regimens (single bolus and maintenance infusion) can produce wide variations in plasma drug concentrations early in therapy, and more complex regimens require a series of precisely timed infusion rate changes to minimize such variability. A new simple method of delivering an infusion produces a delivery rate that declines exponentially, thereby providing stable plasma concentrations after a bolus dose. The method requires no specialized equipment and no intervention once started. The method has been tested both ex vivo and in normal volunteers receiving lidocaine. Stable lidocaine plasma concentrations are rapidly achieved and maintained within the therapeutic range. Further evaluation of this approach in patients is indicated.

Humans↗
PubMed1981

Alinidine reduces heart-rate without blockade of beta-adrenoceptors.

Alinidine is a new drug which reduces heart-rate in animals by an unknown mechanism. Oral administration of 40 and 80 mg significantly reduced an exercise tachycardia in healthy people, with small reductions in heart-rate in the standing and supine positions. Alinidine 80 mg reduced arterial pressure in the standing and supine positions. The reduction in exercise tachycardia produced by 80 mg alinidine was similar to that after 40 mg propranolol, but alinidine had no effect on an isoprenaline tachycardia. These observations indicate that alinidine reduces heart-rate without blocking beta-adrenoceptors and may be useful in patients with angina and in patients with tachyarrhythmias.

Adult↗
PubMed1980

Effects of thyroid dysfunction on propranolol kinetics.

Propranolol kinetics was studied in six hyperthyroid and six hypothyroid patients who received single oral and intravenous doses of propranolol when they had thyroid dysfunction and again when they had become euthyroid. Change in thyroid status from hyperthyroid to euthyroid produced no change in the elimination half-life (t 1/2) of oral propranolol (3.2 +/- 0.5 to 4.1 +/- 0.7 hr), the oral clearance (38.4 +/- 7.3 to 27.4 +/- 2.4 ml/min/kg), the elimination t 1/2 of intravenous propranolol (2.5 +/- 0.3 to 3.5 +/- 0.7 hr), and the apparent volume of distribution (4.8 +/- 0.4 to 3.8 +/- 0.5 l/kg). The systemic clearance of propranolol, however, was greater when the patients were hyperthyroid (20.8 +/- 2.5 ml/min/kg) than when they had become euthyroid (11.7 +/- 1.7 ml/min/kg). The elimination t 1/2 after oral propranolol was longer in the hypothyroid (3.7 +/- 0.5 hr) than in the euthyroid state (2.0 +/- 0.1 hr). No other changes were observed in the kinetic parameters measured when these hypothyroid patients had become euthyroid. Adequate beta-adrenoceptor blockade in hyperthyroid patients may require higher propranolol dosage than expected.

Adult↗
PubMed1978

Catecholamine sensitivity in hyperthyroidism and hypothyroidism.

1. Catecholamine sensitivity in hyper- and hypothyroidism has been studied using a standardised isoprenaline sensitivity test. 2. Seven patients with hyperthyroidism and seven with hypothyroidism were tested both when showing evidence of thyroid dysfunction and again when euthyroid. 3. No significant differences were seen in heart rate responses to isoprenaline when patients became euthyroid compared to their response when either hyperthyroid or hypothyroid. 4. These results indicate that sensitivity to catecholamines is not altered in thyroid dysfunction and, in particular, that hypersensitivity does not occur in spontaneous hyperthyroidism.

Adult↗
PubMedDate not supplied

Effects of alinidine, a novel bradycardic agent, on heart rate and blood pressure in man.

The effects of the oral administration of alinidine (ST567) were studied on heart rate and blood pressure in healthy subjects in the supine and standing positions and on an exercise tachycardia. Exercise tachycardia was reduced by the three doses (20, 40 and 80 mg) of alinidine, and supine and standing heart rate by 80 mg alinidine. The maximum reductions in heart rate occurred at 1 to 2 h but were still present at 6 h. Systolic and diastolic pressure in the supine and standing positions was significantly reduced by alinidine, 80 mg. A comparison of the effects of placebo, alinidine (80 mg), propranolol, (40 mg), and clonidine (0.1 mg) showed that the effects of alinidine on heart rate and blood pressure in the supine and standing positions and after exercise were similar to those of propranolol; clonidine had little effect on these parameters. Alinidine, 40 and 80 mg, had no effect on an isoprenaline tachycardia, which was competitively antagonised by propranolol, 40 mg. The oral administration of alinidine, 40 mg once daily and 40 mg twice daily, for 8 days reduced heart rate in supine and standing positions and on exercise tachycardia with small reductions in systolic and diastolic pressure. The effect of the twice-daily regimen was greater. Some subjects had a dry mouth after alinidine, and 8-9 h after 80 mg all subjects felt drowsy an sleepy. Tiredness was reported during the first 2 days of the chronic-dosing study. One subject had a visual disturbance after 40 mg. These studies show that alinidine reduces heart rate in man without blocking Beta-adrenoceptors. This is a novel pharmacological action warranting further investigation.U

Adult↗
PubMedDate not supplied

Computer-assisted measurement of peripheral blood flow.

An automated system for the measurement of peripheral blood flow using venous occlusion plethysmography based on the low-cost Apple II microcomputer, together with purpose-built compressor unit and data acquisition interface, has been developed. The computer performs the dual role of controlling the timing of inflation and deflation of the occluding cuffs and recording the resulting increase in limb circumference. Ten 8 s epochs of data are acquired and analysed per session. Flow rate is computed using a least squares fit between 0.5 and 4.0 s after cuff inflation, giving on-line indication of blood flow. Venous capacitance and digital systolic pressure may be measured using additional algorithms. The system has been used for the investigation of circulatory disorders and in the assessment of drugs acting on the peripheral circulation.

Blood Pressure↗