Experimental and clinical approaches to treatment of hypertension by dopamine receptor agonists

Hypotension and bradycardia, a serious adverse effect of piribedil, a case report and literature review

Background

Dopamine agonists (DAs) are efficacious for the treatment of motor and nonmotor symptoms in patients with Parkinson’s disease (PD). The treatment of PD with DAs is often complicated by adverse drug reactions (ADRs) of dopaminergic and non-dopaminergic origins. The DA piribedil is widely used in Asian, European, and Latin American countries; therefore, its ADRs are pertinent to clinicians. Here we present a rare case of hypotension and bradycardia that is significantly related to the dosage of piribedil.

Case presentation

A middle-aged male, diagnosed with PD, received dopamine replacement with piribedil. When taking 50 mg piribedil daily dose, the patient didn’t feel any discomfort. Two hours after taking 100 mg piribedil he presented with serious concomitant hypotension and bradycardia with a blood pressure (BP) reading of 85/48 mmHg and a heart rate (HR) of 45 beats/min when sitting. After taking 75 mg piribedil, the patient showed the same symptoms with BP reading at 70/45 mmHg and HR of 47 beats/min in the same position. Upon replacing treatment with pramipexole 0.125 mg, 0.25 mg, and 0.375 mg three times a day, no further cardiovascular effects persisted.

Conclusions

No studies have previously reported the simultaneous observation of position-unrelated hypotension and bradycardia after taking small doses of piribedil. More studies are needed to explore the effects of DAs on BP and HR, especially piribedil. Piribedil is efficacious for the treatment of PD, but it is important to weigh the potential risk of hypotension and bradycardia against the clinical benefits of this drug.

Orthostatic hypotension in drug-naïve patients with Parkinson's disease

Background and Purpose

Orthostatic hypotension (OH) is known to be present even in patients with early Parkinson’s disease (PD). To affirm the presence of OH and find correlation between OH and other dysautonomic symptoms in PD, this study has done in newly-diagnosed PD patients.

Methods

Forty-five non-demented patients with no prior history of treatment for PD were recruited (17 men, 63.8 ± 10.1 years of age). All the patients were evaluated for OH before starting medications. Autonomic symptoms were evaluated with structured questionnaires. Clinical characteristics of PD were evaluated (median Hoehn and Yahr stage 2.0 (1–3), 1.3 ± 1.1 years of disease duration), and comorbid medical conditions that could affect blood pressure were also recorded.

Results

OH was prevalent, and eighteen patients (40%) showed orthostatic hypotension, and twenty-seven (60%) did not (normotensive group). There was no significant difference in demographic and clinical characteristics between groups. The presence or severity of symptoms of autonomic dysfunction in the OH group also not differed from those of the normotensive group.

Conclusions

OH was prevalent even in the early stage of PD, and was not related to presence or severity of any other symptoms of autonomic dysfunction. Our findings suggest that clinicians should pay attention to OH from the early stage of disease.

Dopamine and sympathoadrenal activity in man

The sympathetic adrenal (SA) activity can be modulated by dopamine (DA) through D2 receptors. In man, using D2 antagonists, it has been demonstrated that endogenous DA plays an inhibitory modulation of the SA system during high degree of SA activation. D2 agonists are able to induce a decrease in norepinephrine (NE) release either in vitro or in vivo. This effect leads, in vivo, to a decrease in blood pressure (BP) and to an activation of arterial baroreceptors. Therefore, in vivo, the D2 mediated inhibition of epinephrine (E) release, which is clearly demonstrated in vitro, is overwhelmed by the baroreceptor-mediated activation of the splachnic nerve. As a consequence, the in vivo administration of D2 agonists can induce a different effect on the net peripheral sympathetic tone of an organ, depending on the balance between the degree of the baroreceptor-mediated sympathetic activation and the inhibitory D2-mediated inhibition of NE release at the tissue level. In the present paper we investigated the in vivo effect of placebo (PL) or acute oral bromocriptine (BC) administration on plasma CA and on the cardiac sympatho-vagal balance of 7 normal volunteers, as assessed by power spectral analysis of heart rate (HR) variability (autoregressive method), either in resting or sitting position. Low frequency (LF) and high frequency (HF) components, both expressed in normalized units (nU), and LF/HF ratio were calculated. BC caused a decrease in BP, plasma NE and no change in HR in resting and sitting position. Plasma E increased in sitting position. At the heart level, after BC, we observed, during rest, an increase in LF and LF/HF ratio and a decrease in HF while in sitting position LF did not increase further. These data show that BC, while reducing BP through a decrease of plasma NE, increases LF/HF ratio (sympathetic tone) without any change in heart rate. These data seem to confirm that BC causes an inhibitory modulation of the SA system acting predominantly at the periphery through D2 presynaptic receptors.