Which drug for which orthostatic hypotension?

Power spectral analysis of heart rate variability in cynomolgus monkeys in safety pharmacology studies: comparative study with beagle dogs

INTRODUCTION

Power spectral analysis of heart rate variability is a tool known to provide information of interest on the autonomic control of heart rate in human. However, its use and its conditions of application and interpretation for safety purposes are not well defined for cardiovascular safety pharmacology studies. Likewise, data of power spectral analysis of heart rate variability in cynomolgus monkeys, a species often appropriate for use as second non rodent species in preclinical safety programmes, are not available. This study was designed to evaluate the relevance of this biomarker in this non human primate species, and to compare results with those from beagle dogs under the conditions of safety evaluation studies.

METHODS

Power spectral analysis of heart rate variability was performed on data collected in both species by telemetry following a standard design for cardiovascular safety pharmacology studies. Various pharmacological agents were tested in order to compare the profile of responses in both species after modifying the autonomic nervous balance.

RESULTS

Heart rate variability in cynomolgus monkeys is mainly driven by the parasympathetic nervous system as in beagle dogs although vagal tone is less than in dogs. Power spectral analysis of heart rate variability allows detection of interaction with the autonomic nervous system in both species in all investigated situations, i.e. sympatholytic/sympathomimetic and parasympatholytic/parasympathomimetic drug induced effects. However, due to species difference in the autonomic control of heart rate, cynomolgus monkeys are likely to be more sensitive than beagle dogs for assessment of sympatholytic properties.

DISCUSSION

This study confirms that power spectral analysis of heart rate variability from data derived from ECG recordings in telemetry studies is applicable in cardiovascular safety pharmacology studies and may provide relevant information about possible interaction with the autonomic nervous system when new drug entities are evaluated in either species. However, interspecies differences in autonomic control must be taken into account when interpreting possible drug effects.

Orthostatic hypotension in the anesthetized rabbit in the sitting position exceeds cerebral autoregulation

BACKGROUND

Orthostatic hypotension and cerebral autoregulation have been extensively studied in the rabbit. However, these physiologic responses have not been previously studied utilizing a rabbit in the sitting position under anesthesia.

METHODS

This unusual position was obtained as the preferred orientation based on geometry requirements of associated equipment for a study of osteoarthritis of the knee. Rabbits for this experiment did not survive and an additional experimental condition was developed to elucidate the mechanism and cause of death. The carotid artery pressure was measured under general anesthesia with incremental tilt testing to achieve the sitting position.

RESULTS

Under this condition, rabbits developed orthostatic hypotension and did not survive.

CONCLUSIONS

According to previous studies of orthostatic hypotension and limits of cerebral autoregulation, it is concluded that orthostatic hypotension in the anesthetized rabbit in the sitting position exceeds cerebral autoregulation.

Pharmacological options in the management of orthostatic hypotension in older adults

Orthostatic hypotension (OH) is a common disorder in older adults with potentially serious clinical consequences. Understanding the key underlying pathophysiological processes that predispose individuals to OH is essential when making treatment decisions for this group of patients. In this article, we discuss the key antihypotensive agents used in the management of OH in older adults. Commonly, midodrine is used as a first-line agent, given its supportive data in randomized, controlled trials. Fludrocortisone has been evaluated in open-label trials and has long-established usage in clinical practice. Other agents are available and in clinical use, either alone or in combination, but larger randomized trial evaluations are yet to be published. It is important to bear in mind that a patient may be taking medications that predispose to or exacerbate the symptoms of OH. Withdrawal of such medications, where possible, should be considered before commencing other pharmacological agents that attenuate the symptoms of OH.

Ruscus aculeatus (butcher's broom) as a potential treatment for orthostatic hypotension, with a case report

CONTEXT

Chronic orthostatic hypotension (OH) is frequently a severely debilitating disease that affects large groups of the population with autonomic insufficiency--the elderly; patients with diabetes, Parkinson's disease, and chronic fatigue syndrome; and anyone on drugs that affect the autonomic nervous system. Unfortunately, even though more than 60 medications are currently being used to treat OH, none of them is particularly or consistently effective. Ruscus aculeatus, a phytotherapeutic agent that is well known in Europe, may, however, change this. Its vasoconstrictive and venotonic properties make it ideally suited to treat the pooling of blood in the limbs, lack of venous tone, and lack of neurally mediated vasoconstriction that frequently characterize OH. Although it has never been suggested as a treatment for OH, it already has a long, proven record of use in Europe for treating a variety of circulatory disorders.

OBJECTIVE

To provide evidence for what appears to be an effective, safe, inexpensive botanical therapy for OH and encourage further studies on the efficacy of Ruscus for OH patients.

DESIGN

Review of OH and therapies currently available for OH and evaluation of the properties of Ruscus aculeatus, its mechanism of action, and its suitability as a therapeutic agent for treatment of OH.

RESULTS

A review of the many pharmacologic and nonpharmacologic agents for treating OH reveals that all of the drug therapies are disappointing and marginally useful. Although nonpharmacologic management is preferred, in the many cases in which OH becomes debilitating, pharmacologic intervention becomes a last resort. But drug therapy may not always be necessary, because Ruscus aculeatus, a phytotherapeutic agent containing ruscogenins and flavonoids, may prove useful for the treatment of OH if denervation is not so advanced that it has compromised receptor activity at the venous wall. Ruscus aculeatus is an alpha-adrenergic agonist that causes venous constriction by directly activating postjunctional alpha1- and alpha2-receptors, in turn stimulating the release of noradrenaline at the level of the vascular wall. It also possesses venotonic properties: it reduces venous capacity and pooling of blood in the legs and exerts protective effects on capillaries, the vascular endothelium, and smooth muscle. Its flavonoid content strengthens blood vessels, reduces capillary fragility, and helps maintain healthy circulation. Unlike most of the drug therapies used to treat OH, Ruscus aculeatus does not cause supine hypertension. It also appears to do something no other therapy can offer--alleviate the worsening effects of OH in environmentally hot conditions. Finally, it is an extremely safe, inexpensive, over-the-counter botanical medicine.

CONCLUSION

With proven phlebotherapeutic properties, including vasoconstrictive action and venotonic properties, Ruscus aculeatus shows great promise for ameliorating the symptoms of OH and improving the quality of life for large groups in the population. It clearly deserves to be the object of wider research and study as a treatment for OH.

Fluoxetine in orthostatic hypotension of Parkinson's disease: a clinical and experimental pilot study

Recent clinical studies have reported a beneficial effect of fluoxetine, a serotonin reuptake inhibitor, in patients with severe refractory orthostatic hypotension. The present study was undertaken to investigate the effect of fluoxetine in orthostatic hypotension occurring during Parkinson's disease on both blood pressure values and number of clinical symptoms during orthostatic procedure evaluated using a validated clinical rating scale. In a pilot study performed in fourteen patients with idiopathic Parkinson's disease plus orthostatic hypotension, fluoxetine hydrochloride (20 mg orally daily during one month) significantly reduced the fall in systolic blood pressure [-33 +/- 21 (SD) mmHg before fluoxetine vs -22 +/- 19 mmHg after fluoxetine, P = 0.03] elicited by standing without modifying heart rate. The drug also significantly reduced the number of postural symptoms occurring during the orthostatic procedure [2.9 +/- 1.5 (SD) before fluoxetine vs 1.2 +/- 1.3 after fluoxetine, P = 0.006]. A similar pattern of response was obtained in an experimental model of neurogenic orthostatic hypotension obtained in chronically sino-aortic denervated dogs submitted to an 80 degrees head-up tilt test procedure under chloralose anaesthesia. Fluoxetine did not change plasma noradrenaline levels. This pilot study suggests a slight but clinically significant effect of fluoxetine on both hemodynamic parameters and clinical symptoms in parkinsonian patients suffering from orthostatic hypotension.

Effects of yohimbine, an alpha 2-adrenoceptor antagonist, on experimental neurogenic orthostatic hypotension

Yohimbine has been proposed for the treatment of neurogenic orthostatic hypotension; however, no controlled trial has been performed in experimental models of orthostatic hypotension or in patients with autonomic failure. The aim of the present study was to compare the effects of yohimbine (0.05 mg/kg, intravenously [i.v.]) and placebo (saline) in a new model of neurogenic orthostatic hypotension obtained by sinoaortic denervation (SAD) in chloralose-anaesthetized dogs. Blood pressure, heart rate, noradrenaline plasma levels and systolic blood pressure and heart rate short-term variabilities (calculated on low frequency [40-50 MHz] and high frequency [390-490 MHz] bands) were measured in supine position and after a 10 min 80 degrees head-up tilting. The drugs were administered in a double-blind cross-over randomized fashion. The head-up tilting performed in normal animals increased diastolic blood pressure (+12 +/- 4 mmHg), heart rate (+39 +/- 12 beats per minute [bpm]), the low frequency band of systolic blood pressure and noradrenaline plasma level, without changing systolic blood pressure or heart rate variability. In SAD dogs, a marked fall in systolic (-80 +/- 11 mmHg) and diastolic (-43 +/- 4 mmHg) blood pressures was observed within 1 min after placebo, without modification in heart rate, systolic blood pressure and heart rate short-term variabilities and noradrenaline plasma levels. In SAD dogs, yohimbine (0.05 mg/kg, i.v.) delayed the blood pressure fall elicited by head-up tilting, but failed to modify its magnitude. These results show that, in the model of orthostatic hypotension obtained by SAD, yohimbine, at an alpha 2-adrenoceptor selective dose (0.05 mg/kg), delays the fall in blood pressure elicited by head-up tilting. The effect of yohimbine can be explained by an increase in sympathetic tone.

Midodrine. A review of its therapeutic use in the management of orthostatic hypotension

Midodrine is a prodrug which undergoes enzymatic hydrolysis to the selective alpha 1-adrenoceptor agonist desglymidodrine after oral administration. Oral midodrine significantly increases 1-minute standing systolic blood pressure compared with placebo. The drug also improves standing time and energy level and clinical symptoms of orthostatic hypotension including dizziness, light-headedness and syncope. Comparative studies have shown midodrine to have similar efficacy to dihydroergotamine mesylate, norfenefrine, fludrocortisone and etilefrine, and to be more effective than dimetofrine and ephedrine in patients with orthostatic hypotension. Midodrine is well tolerated, with the most commonly reported adverse events being piloerection, pruritus, paraesthesias, urinary retention and chills. The risk of supine hypertension, which is associated with midodrine therapy in up to 25% of patients, can be reduced by taking the final daily dose at least 4 hours before bedtime. Thus, oral midodrine is an effective therapeutic option for the management of various forms of orthostatic hypotension. This well-tolerated agent is likely to be useful in conjunction with standard nonpharmacological care.

Effects of octreotide on experimental neurogenic orthostatic hypotension in anaesthetized dogs

This paper investigates the effects of octreotide (0.1 mg/kg, subcutaneous) on cardiovascular adaptation during head-up tilt test in an experimental model of neurogenic orthostatic hypotension (OH) obtained by chronic sinoaortic denervation in anaesthetized dogs. Blood pressure (BP), heart rate (HR), spectral variability (Fast Fourier transformation on 512 consecutive points, delta t: 2 Hz) and plasma catecholamine levels were measured in a double blind cross-over randomized study versus placebo, in supine position and during a head-up tilt test (80 degrees, 10 min) in six sinoaortic denervated and six control (normal) dogs. In normal dogs, head-up tilt test significantly increased HR and diastolic blood pressure (DBP). Plasma noradrenaline levels and energy of the low frequency band (40-150 mHz) of systolic blood pressure (SBP) significantly increased whereas the energy of the low frequency band of HR significantly decreased. Placebo and octreotide failed to modify supine and head-up tilt values of the measured parameters (except the value of low frequency band of SBP, which increased after octreotide). In sinoaortic denervated dogs, supine values of BP, HR and plasma noradrenaline levels were significantly higher than in controls whereas the energy of the low frequency spectral band of HR and SBP was similar to controls. Head-up tilt test induced a dramatic decrease in BP. HR, plasma noradrenaline levels and energy of the low frequency band of SBP and HR remained unchanged during head-up tilt tests. Neither supine nor head-up tilt values of these parameters were modified 45 min after octreotide or placebo administration. These results show that sinoaortic denervation is a reproducible model of OH characterized by a lack of activation of sympathetic efferent pathways during head-up tilt tests. Octreotide at the dose used remains ineffective to prevent the fall in BP under these experimental conditions.