Acute haemodynamic effects of pinacidil in man

Phenylcyanoguanidines as inhibitors of glucose-induced insulin secretion from beta cells

3,5-Disubstituted-phenylcyanoguanidines have been identified as activators of SUR1/Kir6.2 potassium channels and as potent inhibitors of insulin release from pancreatic beta cells in vitro.

Effect of pinacidil on renal haemodynamics, tubular function and plasma levels of angiotensin II, aldosterone and atrial natriuretic peptide in healthy man

The effects of pinacidil on renal haemodynamics, tubular function evaluated by the lithium clearance technique and the plasma levels of angiotensin II (Ang II), aldosterone (Aldo) and atrial natriuretic peptide (ANP) have been evaluated in 12 healthy volunteers given pinacidil 0.1 mg/kg IV in comparison with a placebo given to 13 different healthy volunteers. Pinacidil induced significant reductions in glomerular filtration rate (-5%), renal plasma flow (-12%), urine output (-35%), urinary sodium excretion (-20%), and the fractional excretion of sodium (-17%) and potassium (-29%). Lithium clearance and proximal and distal absolute and fractional reabsorption of sodium were not significantly changed. Ang II and Aldo were significantly increased (80% and 115%, respectively) and ANP was unchanged. The mean arterial blood pressure was not significantly changed by pinacidil, but the heart rate was increased (22%). It is concluded that bolus IV injection of pinacidil in healthy subjects reduced renal blood flow, urine volume and the urinary excretion of sodium and potassium, whereas segmental tubular function was unchanged. The increase in heart rate and activation of the renin-angiotensin-aldosterone system are most likely to be secondary to stimulation of the sympathetic nervous system caused by the vasodilator effect of pinacidil.

Effects of pinacidil on guinea-pig isolated perfused heart with particular reference to the proarrhythmic effect

1. The effects of pinacidil (10, 30, 50 microM) on contractility (+dP/dtmax), coronary perfusion pressure (cP), and ECG intervals (PR, QRS, QT) have been studied on constant-flow perfused guinea-pig hearts, driven at four frequencies (2.5, 3, 3.5, 4 Hz). 2. Pinacidil decreased +dP/dtmax, cP and the QT interval in a dose-dependent manner, whereas the PR interval was increased. QRS duration was not modified. All these effects were independent of driving frequency. Pinacidil decreased the interval from Q-wave to T-wave peak (QTpeak) to a greater extent than the QT interval, thus decreasing the QTpeak/QT ratio. This effect, unlike that on QT interval, was more evident at the highest frequency of stimulation. 3. In 4 out of 20 hearts treated with pinacidil sustained ventricular fibrillation (VF) occurred following a short run of premature ventricular beats (R on T phenomenon). 4. In separate experiments, an attempt to induce VF electrically was made at drug concentrations ranging from 10 microM to 100 microM (8 experiments for each concentration). In control conditions and at the lowest concentrations of pinacidil tested (10 microM) VF could never be induced; in the presence of 30 microM pinacidil VF was induced in 5 out of 8 experiments. Drug concentrations higher than 50 microM permitted the induction of VF in every case. 5. Although the concentrations of pinacidil producing ventricular fibrillation are 30-40 times higher than those found in patients under long term treatment with this agent, it is suggested that caution should be used in prescribing this drug, at least in patients suffering from myocardial ischaemia.

Acute hemodynamic effects of pinacidil in hypertensive patients with and without propranolol pretreatment

To study the systemic and regional hemodynamic effects of the new antihypertensive agent pinacidil, the authors administered intravenously two doses of pinacidil (0.1 mg/kg) to patients with hypertension after 3 days of randomized, double-blind pretreatment with either propranolol or placebo. Pinacidil administration decreased systemic arterial pressure and total peripheral vascular resistance in both groups of patients. It also decreased pulmonary artery wedge pressure, and increased cardiac output, heart rate, and plasma norepinephrine levels; the changes in cardiac output and heart rate were attenuated by propranolol pretreatment. In addition, propranolol-pretreated patients responded to pinacidil with a decrease in forearm blood flow. In contrast, pinacidil administration exerted no significant effects on right atrial pressure, stroke volume, or mean pulmonary arterial pressure alone or in combination with propranolol. The results show that pinacidil is a potent arterial dilator but has little effect on the venomotor tone in patients with hypertension.

Arterial vasodilating profile and biological effects of pinacidil in healthy volunteers

1. The effects of pinacidil (25 mg, sustained release formulation) a) on systemic (arterial pressure, cardiac output) and regional (brachial and carotid arteries' diameters and flows) haemodynamics (pulsed Doppler techniques), b) on sympathetic (plasma noradrenaline) and renin-angiotensin (plasma renin activity) systems, and c) on atrial natriuretic factor have been investigated and compared with those of a placebo during the 12 h period following oral administration in a randomized, double-blind and cross-over study performed in six healthy volunteers. Simultaneously, the plasma levels of pinacidil and of its active metabolite, pinacidil N-oxide, were determined. 2. As compared with placebo, pinacidil decreased systemic vascular resistance and arterial blood pressure but cardiac output was not modified. 3. Pinacidil significantly increased brachial and carotid arteries' diameters (by 7 and 8% respectively) and flows (by 60 and 17% respectively) and decreased forearm vascular resistance (by 43%). Thus, pinacidil dilates both large and small arteries, increases large vessels' compliance and redistributes blood flow towards the muscular vascular bed. These effects peaked at 4 h and their duration at the brachial level was 8 h. 4. Pinacidil administration resulted in a stimulation of both sympathetic (increases in heart rate and plasma noradrenaline) and renin-angiotensin systems, and induced a transient increase in atrial natriuretic factor. 5. The duration of pinacidil haemodynamic effects at the brachial level is consistent with the pharmacokinetic data which show that pinacidil and pinacidil N-oxide plasma levels almost plateaued between 3 and 8, and 2 and 8 h respectively after oral administration of the sustained release formulation used.

Pinacidil. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in the treatment of hypertension

Pinacidil is an orally administered antihypertensive drug that acts via direct relaxation of vascular smooth muscle to produce peripheral vasodilatation and a reduction in blood pressure without significant direct effects on cardiac electrophysiology. Pinacidil is unrelated to other antihypertensive drugs in clinical use, either in structure or mechanism of action. It belongs to a new class of agents called 'potassium channel openers' which act via potassium efflux to hyperpolarize cell membranes, indirectly causing a net reduction in intracellular calcium that leads to relaxation of vascular smooth muscle. Pinacidil is indicated in the management of essential hypertension. In clinical trials of up to 1 year duration, pinacidil administered twice daily in a controlled release capsule formulation has been shown to achieve adequate blood pressure control both in previously untreated patients and in those with blood pressure inadequately controlled by beta-adrenoceptor blocking drugs or thiazide diuretics. In long term (up to 1 year) comparative studies pinacidil was at least as effective as hydralazine, prazosin or nifedipine in maintaining blood pressure control. Pinacidil may also have a potential use in the treatment of patients with secondary renal hypertension. Clinical trials to date have usually allowed the addition of a thiazide diuretic and/or beta-adrenoceptor blocking drug to enhance the efficacy of pinacidil and/or to reduce the incidence of adverse effects. The main adverse effects of pinacidil treatment, which result from its peripheral vasodilator activity, are headache, oedema, palpitations and tachycardia. Although the overall incidence of adverse effects is quite high, they are usually mild, transient in nature and respond to a reduction in dose. Nevertheless, these effects may occasionally be severe, necessitating withdrawal from therapy. Thus, pinacidil is an effective antihypertensive drug for the treatment of mild to moderate essential hypertension. Despite its novel mechanism of action pinacidil causes adverse effects typical of peripheral vasodilators; during long term use with twice daily administration of the controlled release capsule formulation, the addition of a diuretic is often necessary to attenuate peripheral oedema and maintain adequate control of blood pressure. Further long term controlled trials are needed to determine the precise role of pinacidil relative to that of the angiotensin converting enzyme (ACE) inhibitors and calcium channel blocking drugs.

Effects of pinacidil on the sympatho-adrenal system in dogs

1. The aim of the present work was to study the antihypertensive effect of pinacidil, a potassium channel opener, in sinoaortic denervated (SAD) conscious dogs and to investigate whether the involvement of the sympathetic nervous system induced by this vasodilator compound is only of baroceptor reflex origin. 2. Pinacidil (0.1, 0.2, 0.4 mg kg-1 i.v.) induced a dose-dependent decrease in blood pressure in normal as well as in SAD dogs. In contrast, the induced-tachycardia observed in normal dogs was not found in SAD animals. 3. Since pinacidil induced an increase in plasma catecholamines, free fatty acids, glucose, plasma renin activity and aldosterone in SAD dogs it is suggested that this sympathetic activation is independent of the baroreceptor reflex pathways. 4. The sympathetic activation is mainly of peripheral origin, since pinacidil (0.7 mg kg-1 i.v.) induced an increase in adrenaline release from the adrenal gland after section of the great splanchnic nerve in anaesthetized dogs. This increase is probably due to an effect that does not involve K+ channel opening. However, this effect of pinacidil was not observed during splanchnic nerve stimulation (in this case, the involvement of K+ channel opening is suggested).

Pinacidil uptake and effects in the isolated rabbit heart

The myocardial accumulation of pinacidil showed one-compartment characteristics with a half-time of 1.11 min., whereas the disposition followed three-compartment kinetics with half-times for the relevant two redistributory and the terminal phases of 0.39, 1.51 and 5.44 min., respectively. At a steady-state drug concentration in the perfusate of 6.12 nmol ml-1, the average concentration of pinacidil in the myocardium was 20.6 nmol g-1. The accumulated amount could predictically be referred with 57% to a central and 31 and 12% to two peripheral (deeper) drug pools. The pharmacodynamic effects of pinacidil in the isolated perfused rabbit heart were studied at stepwise increasing concentrations from 0.15 to 100 microM. Coronary flowrate increased initially up to 24.5% at 1.5 microM pinacidil and then gradually decreased. Amplitude and velocity of contraction were both inhibited in a biphasic way up to 92.7 and 94.1%, respectively. Apparent dynamic steady states developed within 13-15 min. The computer-derived inhibitory Em-values related to the first phase were 49.2 and 52.4% and those related to the second phase were 111.7 and 108.3%, respectively. Heart frequency decreased monophasically and exhibited an inhibitory Em-value of 19.6%. Oxygen consumption decreased at pinacidil concentrations higher than 15 microM and the Em-value was 69.7%. The frequency-corrected QT-interval decreased biphasically and the related inhibitory Em-values were 8.6 and 58.7%. The QRS-interval did not change and the PQ-interval only showed a minor increase at the highest pinacidil concentration. Our findings are compatible with the concept of pinacidil being a potassium channel opener.

Hypotensive and peripheral vascular effects in healthy volunteers of repeated oral administration of pinacidil

The hypotensive and peripheral vascular effects of two different oral formulations of pinacidil were investigated in twelve healthy male volunteers. Arterial blood pressure, heart rate and calf blood flow were measured on Days 1 and 7. The vasodilator activity of both formulations was confirmed by a significant increase in calf blood flow on both days, which was correlated with a significant decrease in diastolic blood pressure. There was no differences between the tablet and the pellet.

Antihypertensive effects of pinacidil in patients with and without indomethacin pretreatment

To determine the potential role of prostaglandins in mediating the hypotensive action of the new antihypertensive agent pinacidil, we measured the blood pressure, regional blood flow and neurohumoral responses to pinacidil in thirteen hypertensive patients randomly assigned to receive pretreatment with either indomethacin (75 mg) or placebo. After baseline measurements had been obtained, each patient received an oral dose of pinacidil to which he had previously demonstrated a therapeutic response. The doses of pinacidil administered between the two groups did not differ. Serial measurements of blood pressure and heart rate over two hours revealed no attenuation of the hypotensive effect of pinacidil in the indomethacin-pretreated patients (-12.7 +/- 4.1 mm Hg) compared to the placebo group (-9.3 +/- 3.2 mm Hg). While significant vasodilation was not observed in the forearm, renal vasodilation occurred and was not different between the two groups. Pinacidil had no effect on glomerular filtration rate. Neither did pinacidil significantly increase plasma catecholamines or renin activity. The results indicate that prostaglandins probably do not play a major role in the vasodilator action of pinacidil, and that therapeutic doses of the drug have a differential effect on regional blood flows that result in hypotension, but not significant neurohumoral stimulation, in patients with mild to moderate hypertension.