Differential effects of alpha-adrenoceptor blockade on essential, physiological and isoprenaline-induced tremor: evidence for a central origin of essential tremor

Differential effects of propranolol on head and upper limb tremor in patients with essential tremor and dystonia

Propranolol is used as the first-line treatment in essential tremor and it has also been proposed as a treatment for tremor in dystonia. However, several issues remain uncertain. For example, it is still not clear whether propranolol exerts a beneficial effect on head tremor. Moreover, no studies have investigated whether the effect of propranolol on head and upper limb tremor in essential tremor differs from that in dystonia. We aimed to assess the effects of propranolol on tremor in different body parts in essential tremor and in patients with tremor and dystonia. Twenty-nine patients with head and upper limb tremor were enrolled in the study, 14 with essential tremor, and 15 with dystonia. Participants underwent a clinical and kinematic analysis of tremor in two sessions, i.e., without (baseline) and 'on therapy' with propranolol. We found that head tremor was more severe in patients with dystonia, while upper limb tremor was more evident in patients with essential tremor (P < 0.05). Propranolol had no effect on head tremor in either group (all Ps > 0.05), but it did reduce upper limb tremor in patients with essential tremor. The present study demonstrates differential effects of propranolol on head and upper limb tremor in patients with essential tremor. The lack of effect on head and upper limb tremor in patients with dystonia suggests that the pathophysiological mechanisms underlying tremor in these two conditions and in different body parts may be distinct.

Beta-adrenergic modulation of tremor and corticomuscular coherence in humans

Coherence between the bioelectric activity of sensorimotor cortex and contralateral muscles can be observed around 20 Hz. By contrast, physiological tremor has a dominant frequency around 10 Hz. Although tremor has multiple sources, it is partly central in origin, reflecting a component of motoneuron discharge at this frequency. The motoneuron response to ~20 Hz descending input could be altered by non-linear interactions with ~10 Hz motoneuron firing. We investigated this further in eight healthy human subjects by testing the effects of the beta-adrenergic agents propranolol (non-selective β-antagonist) and salbutamol (β(2)-agonist), which are known to alter the size of physiological tremor. Corticomuscular coherence was assessed during an auxotonic precision grip task; tremor was quantified using accelerometry during index finger extension. Experiments with propranolol used a double-blind, placebo-controlled crossover design. A single oral dose of propranolol (40 mg) significantly increased beta band (15.3-32.2 Hz) corticomuscular coherence compared with placebo, but reduced tremor in the 6.2-11.9 Hz range. Salbutamol (2.5 mg) was administered by inhalation. Whilst salbutamol significantly increased tremor amplitude as expected, it did not change corticomuscular coherence. The opposite direction of the effects of propranolol on corticomuscular coherence and tremor, and the fact that salbutamol enhances tremor but does not affect coherence, implies that the magnitude of corticomuscular coherence is little influenced by non-linear interactions with 10 Hz oscillations in motoneurons or the periphery. Instead, we suggest that propranolol and salbutamol may affect both tremor and corticomuscular coherence partly via a central site of action.

Characteristics of tail-tremor induced by nicotine in rats

To characterize the tail-tremor and locomotor hyperactivity induced by repeated nicotine administration, the effects of nicotinic, alpha-adrenergic and dopaminergic blockers were investigated in rats. Daily administration of nicotine (0.5 mg/kg, s.c.) induced tail-tremor from the 4th day, which became more marked in intensity by subsequent administration. Locomotor hyperactivity was also induced by nicotine, which was enhanced by daily administration. The tail-tremor and locomotor hyperactivity induced by repeated nicotine administration were inhibited by mecamylamine (0.1-1 mg/kg, i.p.) but not by hexamethonium (0.5 and 1 mg/kg, i.p.). Clonidine (0.02 and 0.04 mg/kg, i.p.) and prazosin (0.5 and 1 mg/kg, i.p.) reduced tail-tremor more markedly than hyperactivity. However, haloperidol (0.05-0.2 mg/kg, i.p.) and chlorpromazine (1-5 mg/kg, i.p.) reduced hyperactivity more markedly than tail-tremor. These results suggest that nicotine-induced tail-tremor and hyperactivity are due to an increased susceptibility of central nicotinic receptors of nicotine followed by catecholaminergic mechanisms, and that tail-tremor may be more associated with the noradrenergic system than the dopaminergic system.

The dose dependency of the alpha-adrenoceptor antagonist and beta-adrenoceptor partial agonist activity of dilevalol and labetalol in man

1. The alpha-adrenoceptor antagonist, beta 1-adrenoceptor antagonist and beta 2-partial agonist activity of dilevalol, a beta-adrenoceptor antagonist with vasodilating properties and labetalol were investigated in two studies. 2. In the first study, six healthy male subjects received serially increasing concentrations phenylephrine after single oral doses of dilevalol 200 mg, labetalol 400 mg and placebo at weekly intervals in a randomised double-blind manner. An exercise step test was performed at the end of the infusions. 3. The doses of phenylephrine required to increase systolic and diastolic blood pressures by 20 mmHg (PS20 and PD20 respectively) were increased by labetalol 400 mg (P < 0.05) but unchanged by dilevalol 200 mg. The dose ratios for PS20 (means +/- s.d.) were: dilevalol 200 mg 1.1 +/- 0.1, labetalol 400 mg 2.2 +/- 0.1. There was no difference in the percentage reduction in exercise tachycardia between dilevalol and labetalol. 4. In the second study, 10 healthy male subjects received infusions with serially increasing concentrations of phenylephrine and angiotensin II before and after single oral doses of dilevalol 200, 400 and 800 mg, labetalol 200 mg and placebo at weekly intervals in a double-blind randomised manner. Finger tremor was measured (piezoelectric accelerometer) with each infusion. An exercise step test was performed at the end of the infusions. 5. The PS20 and PD20 of phenylephrine were increased by labetalol 200 mg and unchanged by dilevalol. The dose ratios for PS20 were: dilevalol 200 mg 1.1 +/- 0.2. dilevalol 400 mg 1.1 +/- 0.4, dilevalol 800 mg 1.4 +/- 0.4 and labetalol 200 mg 2.5 +/- 0.7. The dose ratios for PD20 were: dilevalol 200 mg 1.1 +/- 0.4, dilevalol 400 mg 0.9 +/- 0.3. dilevalol 800 mg 1.3 +/- 0.4 and labetalol 200 mg 2.3 +/- 0.9. 6. The PS20 and PD20 of angiotensin II were unchanged by any of the drugs. 7. Exercise heart rate was reduced by dilevalol 200 mg (130 +/- 13 beats min-1), 400 mg (123 +/- 12 beats min-1), 800 mg (125 +/- 9 beats min) and labetalol 200 mg (143 +/- 12 beats min-1) vs placebo (161 +/- 17 beats min-1). 8. Finger tremor was significantly increased by dilevalol 800 mg (13.17 +/- 10.51 vs 6.62 +/- 4.51 centivolts for placebo: P < 0.01). Neither phenylephrine nor angiotensin II had an effect on finger tremor. 9. In conclusion, dilevalol 200, 400 and 800 mg demonstrated beta 1-adrenoceptor antagonist activity with no evidence of alpha 1-adrenoceptor antagonist activity. Labetalol 200 and 400 mg showed both beta 1- and alpha 1-antagonist activity. Dilevalol 800 mg demonstrated significant partial beta 2-adrenoceptor agonist activity by increasing finger tremor.

Propranolol, clonidine, urapidil and trazodone infusion in essential tremor: a double-blind crossover trial

Accelerometric tremorgrams were recorded from 25 subjects affected by essential tremor and analysed by a Berg-Fourier frequency analyser before and during venous infusion of the following drugs: propranolol (beta-blocker), clonidine (alpha-presynaptic adrenergic agonist), urapidil (alpha-postsynaptic blocker), trazodone (adrenolytic agent) and placebo. The washout interval between infusions was 3 days. Recordings and data analyses were performed in a double-blind crossover trial. Tremor was classified as: at rest; postural (arms hyperextended); and intention (finger-nose test). Analysis of the results showed that propranolol and clonidine reduced significantly (P = 0.01 and P = 0.009, respectively) the power spectrum of postural tremor, but left at rest and intention tremors unchanged. No significant effects on the tremor power spectrum were observed after placebo, urapidil or trazodone administration. None of the drugs had any effect on tremor frequency.

The tremorolytic action of beta-adrenoceptor blockers in essential, physiological and isoprenaline-induced tremor is mediated by beta-adrenoceptors located in a deep peripheral compartment

The effects of intravenous propranolol 100 micrograms kg-1, sotalol 500 micrograms kg-1, timolol 7.8 micrograms kg-1, atenolol 125 micrograms kg-1 and placebo on essential, physiological and isoprenaline-induced tremor were studied. These beta-adrenoceptor blocker doses produced equal reduction of standing-induced tachycardia in essential tremor patients. Atenolol produced significantly less reduction of essential and isoprenaline-induced tremor than the non-selective drugs, confirming the importance of beta 2-adrenoceptor blockade in these effects. Propranolol and sotalol produced equal maximal inhibition of isoprenaline-induced tremor but propranolol was significantly more effective in reducing essential tremor. The rate of development of the tremorolytic effect was similar in essential, physiological and isoprenaline-induced tremors but all tremor responses developed significantly more slowly than the heart rate responses. It is proposed that these results indicate that the tremorolytic activity of beta-adrenoceptor blockers in essential, physiological and isoprenaline-induced tremor is exerted via the same beta 2-adrenoceptors located in a deep peripheral compartment which is thought to be in the muscle spindles.