Effects of SK&F 85174, a DA-1/DA-2 receptor agonist, on pre- and postganglionic sympathetic neurotransmission to the heart

Expression and distribution of dopamine transporter in cardiac tissues of the guinea pig

Dopamine transporter (DAT) is a membrane protein that it is a marker for dopaminergic neurons. In the present work, throught Western blot and autoradiographic studies with a selective ligand for DAT ([(3)H] WIN-35428) and noradrenaline transporter (NET) ([(3)H] Nisoxetine), we search the expression and distribution of DAT in comparison with NET, in cardiac tissue of guinea pig in order to support the presence of dopaminergic nerve cells into the heart. Expression of DAT, and NET were evidenced by a bands of 75 and 54 kDa, respectively in the heart. Binding for DAT and NET were found in the four cardiac chambers. However, DAT show heterogeneous distribution with binding in right atria and in both ventricles, whereas NET show homogenous distribution in the four cardiac chambers. The results show the expression of DAT in cardiac tissues with a different distribution compared with NET, being an evidence for the presence of dopaminergic nerve cells into the heart.

Functional and autoradiographic characterization of dopamine D2-like receptors in the guinea pig heart

Dopamine receptors include the D1- (D1 and D5 subtypes) and D2-like (D2, D3, and D4 subtypes) families. D1-like receptors are positively and D2-like receptors negatively coupled to the adenylyl cyclase. Dopamine D2-like (D4 subtype) receptors have been identified in human and rat hearts. However the presence of D2 and D3 receptor subtypes is unclear. Furthermore, their role in cardiac functions is unknown. By autoradiographic studies of guinea pig hearts, we identified D3 and D4 receptors, using the selective radioligands [3H]-7-OH-DPAT and [3H]emonapride (YM-09151-2 plus raclopride). Western blot analysis confirmed D3 and D4 receptors in the right and left ventricle of the same species. Selective agonists of D3 and D4 receptors (+/-)-7-OH-DPAT and PD 168 077 (10(-9) to 10(-5) M, respectively) induced a significant negative chronotropic and inotropic effect in the isolated guinea pig heart preparation. Negative inotropic effect induced by PD 168 077 was associated with an inhibition in cyclase activity. No changes in cyclase activity were found with (+/-)-7-OH-DPAT. The aim of this study is to support the presence of D3 and D4 receptors in the heart. Although our results suggest that D3 and D4 receptors are functionally active in the heart, we need additional information with an antagonist and an agonist of improved potency and selectivity to understand the respective roles of D3 and D4 receptors in the cardiac functions.

Interactions between drugs for erectile dysfunction and drugs for cardiovascular disease

The association of erectile dysfunction (ED) and cardiovascular disease is well-documented in the literature and both conditions share risk factors. Therefore, it is difficult to distinguish the effect of underlying disease and adverse effects of the drugs and/or interactions between ED drugs and drugs implemented for cardiovascular disease. The known interactions of systemic administered drugs for ED with drugs for cardiovascular disease are mainly pharmacodynamic. Thus, nitrates enhance the production of cyclic GMP and combined with phosphodiesterase type-5 inhibitors this can lead to severe hypotension. The same is the case for the treatment with phentolamine in patients treated with beta-adrenoceptor antagonists. Due to increased partial thromboplastin time, the risk of bleeding is enhanced for intracavernous alprostadil injection in heparin-treated patients. Pharmacokinetic interactions of clinical importance have been described for ED drugs with other therapeutic groups such as sildenafil with the antifungal drug, ketoconazole, and apomorphine with the antiparkinson drug, entacapon. Although sildenafil and antihypertensive dihydropyridines like amlodipine are metabolized by the same cytochrome P450 enzyme, CYP3A4 in the liver, the combination of these drugs does not exhibit a synergistic blood pressure lowering action. Unfortunately documentation concerning drug interactions is often poor and occasional.

In vivo canine model comparison of cardiohemodynamic and electrophysiological effects of a new antipsychotic drug aripiprazole (OPC-14597) to haloperidol

The cardiovascular effects of aripiprazole were assessed in comparison with those of haloperidol using a halothane-anesthetized canine model with monophasic action potential monitoring. Aripiprazole (n = 6) or haloperidol (n = 6) was infused over 10 min at escalating doses of 0.03, 0.3, and 3.0 mg/kg with intervals of 20 min between doses. Clinically relevant plasma concentrations were obtained after 0.03-0.3 mg/kg of aripiprazole as well as haloperidol. After 0.03-0.3 mg/kg of aripiprazole, positive chronotropic, inotropic, and dromotropic effects, shortening of the ventricular effective refractory period (ERP) and repolarization phase, and decrease of total peripheral resistance were observed in a dose-related manner. However, in the presence of a beta-blocking dose of esmolol (0.1 mg/kg/min), these changes were not induced. After 3.0 mg/kg of aripiprazole administration, cardiac effects induced by the lower doses were attenuated or disappeared, while the negative chronotropic, dromotropic, and hypotensive actions and prolongation of ERP and repolarization phase were induced. After 0.03 mg/kg of haloperidol, no significant change was observed, except for the decrease of the peripheral resistance. After 0.3-3.0 mg/kg of haloperidol, negative chronotropic, inotropic, and hypotensive actions, intraventricular conduction delay, and prolongation of ventricular ERP and repolarization phase were observed in a dose-related manner accompanied by further decrease of the peripheral resistance. The inhibitory effects of aripiprazole on cardiovascular parameters in dogs were less potent than those of haloperidol at clinically relevant exposures, moreover, aripiprazole, unlike haloperidol, neither induced early afterdepolarization nor prolonged the ventricular electrical vulnerable period. Therefore, aripiprazole can be considered safer to use than haloperidol.