Acute hemodynamic effects of pinacidil and hydralazine in essential hypertension

The antihypertensive effect of pinacidil versus prazosin in mild to moderate hypertensive patients seen in general practice

The antihypertensive effect of a new vasodilating drug, pinacidil, was compared with prazosin in a randomized, open study in general practice including 131 patients with a sitting diastolic blood pressure (DBP) between 100-115 mmHg. At inclusion 108 patients were untreated and the remaining patients were on treatment with thiazide diuretics and/or beta-blockers. The aim was to reduce the sitting DBP to less than or equal to 95 mmHg, which was achieved in 85% of the patients treated with pinacidil and in 77% of the patients treated with prazosin (NS). In the responding patients the reductions were (mean +/- SD) 16 +/- 7 mmHg (p less than 0.001) and 13 +/- 6 mmHg (p less than 0.001) in the pinacidil group (n = 60) and the prazosin group (n = 46), respectively (p less than 0.10). During 5 months of maintenance therapy no statistically significant differences in blood pressures between the two treatment groups were present. Side-effects were typical of vasodilator therapy, i.e. headache, dizziness, tachycardia and edema, leading to discontinuation of therapy in 10 patients in each treatment group. Heart rate (HR) was increased with pinacidil and unchanged with prazosin. Edema was frequently seen with pinacidil and dizziness with prazosin. Because of edema a thiazide diuretic was given to nine patients in the pinacidil group and two patients in the prazosin group. No clinically significant changes in ECG and biochemical variables were observed. In conclusion, the study has demonstrated that pinacidil is as effective an antihypertensive agent as prazosin. Pinacidil may be used as monotherapy. However, the study suggests that pinacidil should be used as add-on therapy to thiazide diuretics.

Ion channels and the control of blood pressure

Ion channels exist in all cells and are enormously varied in structure, function and regulation. Some progress has been made in understanding the role that ion channels play in the control of blood pressure, but the discipline is still in its infancy. Ion channels provide many different targets for intervention in disorders of blood pressure and exciting advances have been made in this field. It is possible that new drugs, as well as antisense nucleotide technology or gene therapy directed towards ion channels, may form a new class of treatments for high and low blood pressure in the future.

Potassium channel activation: a potential therapeutic approach?

The physiological role of K+ channel opening by endogenous substances (e.g., neurotransmitters and hormones) is a recognised inhibitory mechanism. Thus, the identification of novel synthetic molecules that 'directly' open K+ channels has led to a new direction in the pharmacology of ion channels. The existence of many different subtypes of K+ channels has been an impetus in the search for new molecules demonstrating channel and, thus, tissue selectivity. This review focuses on the different classes of openers of K+ channels, the intracellular mechanisms involved in the execution of their effects, and potential therapeutic targets.

Pharmacokinetic-pharmacodynamic modeling between pinacidil or pinacidil-N-oxide plasma levels and systemic and regional hemodynamic effects in healthy volunteers

Pinacidil (P) lowers blood pressure through peripheral vasodilation, but also induces dose-dependent side-effects. In a previous placebo-controlled, randomized, double-blind and crossover study, performed in six healthy male volunteers, we investigated the systemic and regional hemodynamic effects of a single oral administration of 25 mg of P (sustained-release form) and measured the plasma concentrations of P and of its active metabolite, pinacidil-N-oxide (PO). In the present study, our goal has been to investigate the relationships between P and/or PO plasma concentrations and P administration effects on systolic, diastolic and mean arterial pressures (SAP, DAP, MAP), heart rate (HR), cardiac output (CO), total peripheral resistance (TPR), brachial and carotid arteries' diameters (BAD, CAD), flows (BAF, CAF) and vascular resistances (BVR, CVR) which were assessed before and at different time intervals after drug intake. Concentration-effect relationships were investigated using both linear and log-linear multiple regression models with P, PO or both P and PO as independent variables (six models). Significant linear relationships were observed between P and/or PO and SAP, DAP, MAP, TPR, BAD, BAF, BVR, CAD and CVR. For example, TPR (dynes.s/cm5) = 1308-3.031 x P (ng/ml), R = 0.57, P = 0.0037; BVR (mmHg.s/ml) = 58-0.261 x P (ng/ml), R = 0.56, P = 0.0042. Almost similar R values were obtained using P, PO, or both P and PO. The use of log-linear models did not improve the fittings.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Pharmacodynamic model of the haemodynamic effects of pinacidil in normotensive volunteers

The concentration-effect relationships of pinacidil, a peripheral vasodilator, have been measured in 12 healthy adults who received placebo or pinacidil 25 mg daily for 1 week in a cross-over experiment. Diastolic blood pressure (DBP) and heart rate (HR) were recorded and blood samples were taken on days 1 and 7. Plasma drug concentration-time data were fitted by a biexponential function with zero-order input. The pharmacokinetic model was incorporated into a combined pharmacokinetic-dynamic model (PK-PD) using the Hill equation, which has three parameters: n, the sigmoidicity parameter, Emax the maximum effect and EC50 the concentration which gives 50% of Emax. For delta DBP, the parameter medians were estimated as n = 5, EC50 = 44.6 ng.ml-1 and Emax = 13.5 mmHg. A hysteresis loop was found when delta HR was plotted against concentration, which could be fitted by a linear effect compartment model. Simulations showed that experimental delta DBP points on Day 7 could be predicted from a simulated curve computed by the model using parameters estimated on Day 1. Using the simulation, it was possible to suggest an optimal dosage regimen for pinacidil tablets.

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.

The initial hemodynamic response to newer antihypertensive agents at rest and during exercise: review of visacor, doxazosin, nisoldipine, tiapamil, perindoprilat, pinacidil, dilevalol, and carvedilol

Antihypertensive drugs may lower blood pressure through very different mechanisms, initially as well as during chronic use. This article is a review of the immediate hemodynamic changes induced by a beta blocker (visacor), an alpha-receptor blocker (doxazosin), two calcium antagonists (tiapamil and nisoldipine), an angiotensin-converting enzyme inhibitor (perindoprilat), two double-acting compounds (dilevalol and carvedilol), and placebo studied in 126 patients with mild to moderately severe essential hypertension. The patient populations of the different treatment groups were comparable. The invasive hemodynamic technique, including intraarterial blood pressure (BP) recording and measurements of cardiac output by cardiogreen, was the same in all studies. All antihypertensive compounds examined induced a rapid reduction in blood pressure both at rest and during exercise, while no significant changes occurred in the placebo group. This review shows the scope of hemodynamic responses, ranging from peripheral vasodilation to a reduction of heart rate and blood flow. Furthermore, different counterregulatory effects blunting the immediate BP reduction are demonstrated.

Potassium channel openers and vascular smooth muscle relaxation

Potassium channel openers comprise a diverse group of chemical agents which open plasma-lemmal K-channels. They show selectivity for smooth muscle, although K-channels in cardiac and skeletal muscle, neurones and the pancreatic beta-cell are also affected at relatively high concentrations. In addition, at least one endogenous K-channel opener of vascular origin--endothelium-derived hyperpolarizing factor--exists and in man plays a role in modulating blood vessel tone. The type of K-channel involved in the actions of both exogenous and endogenous K-channel openers is still uncertain, although a prime candidate in smooth muscle seems similar to the [ATPi]-modulated K-channel in the pancreatic beta-cell. This review focuses attention on the action of these agents in vascular smooth muscle and on the possible clinical exploitation of their powerful vasorelaxant properties.

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.

Clinical pharmacokinetics of pinacidil, a potassium channel opener, in hypertension

Pinacidil is a potassium channel opener that decreases blood pressure by reducing peripheral arterial resistance. In two multicenter trials, we studied the concentrations and apparent clearance of pinacidil (406 patients) and concentrations of its pyridyl-N-oxide metabolite (147 patients). Responding patients had plasma samples collected hourly for 12 hours on 2 occasions after weeks to months of treatment. Pinacidil dose was titrated from 12.5 to 75 mg b.i.d. The peak concentration of pinacidil and N-oxide and the area under the concentration-time curve (AUC) were proportional to the dose of pinacidil, with an average pinacidil concentration of 268 micrograms/L (1.02 microM) and N-oxide concentration of 172 micrograms/L (0.65 microM) for every 1 mg/kg pinacidil administered. Clearance of pinacidil (Clp = Dose/AUC) was 31 L/hr in patients younger than 45 years and 27 L/hr in those older than 60. Clp was significantly smaller in white patients compared with other races (Clp = 28 vs. 34 L/hr). Clp was significantly less in patients taking hydrochlorothiazide (27 vs. 31 L/hr) and greater in smokers (33 vs. 29 L/hr). Concomitant propranolol use did not influence Clp.

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.

Effects of food on the bioavailability of sustained-release pinacidil in humans

The effects of a standard breakfast meal on the bioavailability of a sustained-release tablet formulation of pinacidil [(+/-)-2-cyano-1- (4-pyridyl)-3-(1,2,2-trimethylpropyl)guanidine monohydrate) were investigated in eight healthy volunteers. Concomitant food intake resulted in significantly increased maximum measured serum pinacidil concentrations, Cmax, (172 +/- 21 versus 102 +/- 49 ng/mL, p less than 0.05), and relative bioavailability, measured as AUCo-infinity (904 +/- 189 versus 697 +/- 279 ng.h/mL, p less than 0.05). The time to maximum serum concentration (tmax) was not affected by food (2.3 +/- 1.3 versus 3.3 +/- 1.2 h, p greater than 0.05), and the terminal elimination half-life, (t1/2z) was significantly decreased (4.7 +/- 2.2 versus 2.3 +/- 0.4 h, p less than 0.05).

Long term haemodynamic effects of pinacidil and hydralazine in arterial hypertension

Eight patients with a diastolic blood pressure greater than or equal to 100mm Hg when treated with a diuretic and a beta-blocker participated in a randomised crossover study comparing the haemodynamic effects of adjunctive therapy with pinacidil or hydralazine. The vasodilator dose was increased until the diastolic blood pressure was less than 90mm Hg or the maximum dosage, hydralazine 100mg twice daily, or pinacidil 50mg twice daily, was reached. Treatment continued for 3 to 6 months and a haemodynamic study was performed. After washout, the patients received the alternative treatment. In the upright position, during supine rest and during isometric as well as dynamic exercise, pinacidil lowered blood pressure more effectively than hydralazine. No differences between the 2 treatments were found in heart rate, stroke index, cardiac index, end systolic wall stress or glomerular filtration rate. Pulmonary mean and wedge pressure were lower during treatment with pinacidil. Forearm blood flow was higher and forearm vascular resistance lower during treatment with pinacidil. Cardiac contractility, judged from the systolic time interval ratio PEP: LVET, was lower during treatment with pinacidil compared with hydralazine. The median daily dose of pinacidil was 50mg and that of hydralazine 200mg. It was also noted that during long term treatment, pinacidil seemed more effective in reducing blood pressure than hydralazine.

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.

Chronic effects of direct vasodilation (pinacidil), alpha-adrenergic blockade (prazosin) and angiotensin-converting enzyme inhibition (captopril) in systemic hypertension

Chronic responses of systemic hemodynamics and blood pressure counterregulatory ("pseudo-tolerance") mechanisms were investigated in matched groups of patients with essential hypertension after 1 month of vasodilator therapy with pinacidil (a direct arterial dilator), prazosin (an alpha 1-adrenergic blocking drug) or captopril (an angiotensin-converting enzyme inhibitor). For equivalent decreases in mean arterial pressure compared with placebo baseline (approximately 8 mm Hg supine and 12 mm Hg upright), prazosin and captopril did not increase cardiac index or heart rate. In contrast, marked decreases in systemic vascular resistance with pinacidil (approximately 25%, p less than 0.05) were accompanied by reflex increases in cardiac index (approximately 20%, p less than 0.05). Activity of the sympathetic nervous system, measured by supine and upright plasma norepinephrine (NE), increased approximately 50% with pinacidil and prazosin (p less than 0.001 each), whereas captopril decreased supine plasma NE by 12% (p less than 0.05) and did not change upright plasma NE. All 3 drugs caused an expansion of height-adjusted blood volume (approximately 14%). Pinacidil and prazosin caused reversible weight gains of 0.9 and 0.7 kg, respectively, whereas captopril reversibly decreased body weight by 0.8 kg (p less than 0.05), suggesting differential effects of the 3 drugs on interstitial fluid volume. During chronic therapy, all 3 drugs may require concomitant diuretic therapy, whereas concomitant sympatholytic therapy may be required with the potent vasodilator pinacidil. Captopril may be associated with the lowest cardiac risk because of its lack of stimulatory effects on the sympathetic nervous system and cardiac index.

Liquid chromatographic determination of pinacidil, a new antihypertensive drug, and its major metabolite, pinacidil N-oxide, in plasma

Two procedures are described, one for the determination of pinacidil, the other for the determination of both pinacidil and its metabolite, pinacidil N-oxide, in plasma. When only parent drug levels are required, the plasma proteins are precipitated with acetonitrile, the solids discarded and the supernatant is evaporated to dryness. The residue is then reconstituted for analysis. For the determination of both drug and metabolite, the analytes are selectively retained from plasma on a solid-phase extraction column and eluted with methanol. After evaporation to dryness, the residue is reconstituted in mobile phase. Both procedures utilize reversed-phase liquid chromatographic separations with ultraviolet detection. The limits of detection are 10 ng/ml pinacidil in plasma and 5 ng/ml each of pinacidil and pinacidil N-oxide in plasma for the two procedures, respectively.