Experimental studies on the neurocardiovascular effects of urapidil

Antihypertensive Effect of 5-HT1A Agonist Buspirone and 5-HT2B Antagonists in Experimentally Induced Hypertension in Rats

We investigated the antihypertensive effect of 5-HT1A agonist (buspirone) and 5-HT2B antagonists (SB204741 and SB200646) in deoxycorticosterone acetate (DOCA)-salt-induced hypertensive rats. Experiments were divided into two sets: in the first set, sham-operated control and DOCA-treated hypertensive rats received buspirone (1 mg/kg/day p.o. for 4 weeks) and in the second set, in vivo and in vitro studies were carried out. In the case of in vivo studies, sham-operated control and DOCA-treated hypertensive rats received SB204741 or SB200646 (1 mg/kg/week i.v. for 4 weeks). Blood pressure was measured weekly by tail-cuff method. After completion of the treatment schedule, blood pressure and vascular reactivity to various agonists like 5-HT, noradrenaline and adrenaline were recorded. Chronic administration of buspirone, SB204741 and SB200646 produced a significant reduction in blood pressure and vascular reactivity to agonists in DOCA-salt hypertensive rats, implying an antihypertensive effect. However, chronic administration of the same drugs in sham control rats did not alter blood pressure and vascular reactivity to various agonists. For in vitro studies a similar treatment schedule was followed as in vivo studies and a cumulative concentration response curve of 5-HT was recorded on isolated thoracic aorta. Treatment with 5-HT2B antagonists shifted the concentration response curve of 5-HT to the right on isolated aorta. We conclude that 5-HT1A agonist and 5-HT2B antagonists possess an antihypertensive effect.

Modifications hémodynamiques cérébrales et systémiques au moment du réveil en neurochirurgie

Major complications after intracranial surgery occur in 13-27% of patients. Among multiple causes, haemodynamic and metabolic changes of anaesthesia recovery may be responsible for intracranial complications. Recovery from neurosurgical anaesthesia is followed by an increase in body oxygen consumption and catecholamines concentrations. However, in normothermic patients, theses changes are usually mild and not prevented by a 2-h recovery delay. Systemic hypertension is common after neurosurgery and a link between perioperative hypertension and intracranial haemorrhage has been established. The cerebral consequences of recovery associate cerebral hyperaemia and increased ICP in patients with a tight brain at the end of surgery. Cerebral hyperaemia may promote or exacerbate cerebral haemorrhage or oedema. This has been demonstrated in patients operated for subdural haematoma removal or undergoing carotid surgery. Prevention of hypothermia and pain are key factors to prevent metabolic changes. Beta-blockers seem to be suitable agents to obtain haemodynamic control in neurosurgical patients.

Intracoronary-administered urapidil does not influence myocardial contractility, metabolic activity, or coronary sinus blood flow in humans

OBJECTIVE

To compare the acute effect of intracoronary administration of urapidil and saline on myocardial contractility and metabolic activity.

DESIGN

Prospective, controlled, open-label study.

SETTING

University teaching hospital.

PARTICIPANTS AND INTERVENTIONS

Eight patients with stable coronary artery disease (CAD) undergoing elective percutaneous transluminal coronary angioplasty (PTCA) received normal saline followed by urapidil, 4 mg, injected directly into the left main coronary artery.

MEASUREMENTS AND MAIN RESULTS

Because local intracoronary administration is a non-steady-state condition, an in vitro model was used before the clinical experiments to establish the kinetic effects of acute administration of urapidil. The clinical experiments were performed in eight patients with CAD after PTCA. Measurements included a complete hemodynamic profile, coronary sinus blood flow (continuous thermodilution), left ventricular (LV) peak (+) dP/dt, LV peak (-) dP/dt, LV dP/dt/P(D)40, and LV end-diastolic pressures. Arterial and coronary venous blood samples were also obtained for the calculation of myocardial oxygen consumption. Baseline measurements I were first obtained, followed by intracoronary injection of 2 mL of saline. Additional measurements were obtained 1, 5, and 10 minutes after administration of saline. After a resting period (15 minutes), baseline measurements II, and intracoronary injection of urapidil, 4 mg (dissolved in 2 mL saline), additional measurements were obtained 1, 5, and 10 minutes later. Heart rate decreased 2.7+/-3.5 beats/min after injection of saline, whereas heart rate increased 2.0+/-1.8 beats/min after intracoronary urapidil, resulting in a significant difference in treatment effect (p = 0.003). There were no additional differences in treatment effect for any of the other measured or calculated parameters reflecting systemic hemodynamics, LV contractility, coronary dynamics, and myocardial metabolic activity.

CONCLUSION

The results suggest that intracoronary bolus administration of preservative-free urapidil, 4 mg, is not associated with any detectable effect on myocardial contractility or coronary smooth muscle in awake nonsurgical patients with CAD, after PTCA.

Influence of Vasodilator Drugs on Perioperative Blood Pressure

Survey results are given of the incidence and the etiology of perioperative hypertension in patients sub jected to coronary artery surgery. Over the years, numer ous types of antihypertensives have been used for intravenous administration with the aim of preventing or treating perioperative hypertension. Nitrovasodilator compounds such as sodium nitroprusside and nitroglyc erin (NTG), a few calcium antagonists (nifedipine, nicar dipine and isradipine), the short-acting β-blocker esmo lol, clonidine, and the multifactorial compounds labetalol and ketanserin are discussed in detail. Perioperatively, there is an increasing level of plasma catecholamines, causing α-adrenoceptor stimulation. This indicates that α-adrenoceptor blockade with appropriate antagonists is a logical approach for the treatment of perioperative hypertension. For this reason, the multifactorial agent urapidil, which is an α-adrenoceptor blocker and a 5-HT1A agonist, is discussed extensively.

Vascular alpha-1 adrenergic receptor subtypes in the regulation of arterial pressure

Alpha 1 (alpha 1)-adrenoceptors can be found at numerous end organs in the autonomic nervous system, especially vascular smooth muscle. The tonic sympathetic activation of vascular alpha 1-adrenoceptors maintains vascular resistance and is vital to the regulation of arterial pressure. Recent evidence clearly demonstrates that alpha 1-adrenoceptors are a heterogenous class of receptors and that each subtype may subserve specific cardiovascular functions. Elucidation of the physiological role of each subtype in the regulation of vascular resistance and arterial pressure will enhance our understanding of the cardiovascular system and may facilitate the development of therapeutics with improved efficacy and tolerability.

Different types of centrally acting antihypertensives and their targets in the central nervous system

The central regulation of blood pressure and other cardiovascular parameters may involve the baroreceptor reflex are, including both adrenergic and serotonergic pathways, as well as amino acids, as neurotransmitters. Both adrenergic and serotonergic pathways have been recognized as targets for clinically relevant, centrally acting antihypertensives, such as clonidine, guanfacine, and alpha-methyl-DOPA. The central components of the hybrid drugs urapidil and ketanserin also involve serotonergic pathways and receptors. For urapidil the stimulation of 5-HT1A-receptors is assumed to induce peripheral sympathoinhibition, whereas for ketanserin the central mechanism is unknown in detail. More recently central imidazoline (I1) receptors have been proposed as the major target for the newer antihypertensives rilmenidine and moxonidine. Clonidine, however, is assumed to be mixed I1- and alpha2-receptor agonist. The distinction between central I1- and alpha2-receptors may potentially offer the design of new antihypertensives, acting like clonidine but with fewer side effects. Finally, the amino acid pathways should be considered as potential targets for centrally acting antihypertensives. Experimental compounds on this basis are available but clinical implications appear to be very remote. In the present survey an outline is given of the various pathways, neurotransmitters, and receptors involved in the central regulation of blood pressure. The different types of centrally acting antihypertensives are subsequently discussed on this basis.

Urapidil permeates the intact blood-brain barrier

OBJECTIVE

To determine the plasma and cerebrospinal fluid (CSF) levels of urapidil after i.v. administration and the effect on CSF serotonin and 5-hydroxyindoleacetic acid (5-HIAA) concentrations.

DESIGN

Open, single-dose study.

SETTING

Post-surgery following neurosurgical removal of the hypophysis (n = 5) or aneurysm clipping (n = 1).

PATIENTS

6 patients, aged 32-71 years, with intact blood-brain barrier (BBB); 1 patient was studied twice.

INTERVENTIONS

Single dose of 25 mg urapidil i.v. as prophylaxis of BP increase during extubation or as treatment of hypertensive episodes.

MEASUREMENTS AND RESULTS

Urapidil, serotonin and 5-HIAA were measured by HPLC in CSF during 8 h after urapidil administration. Urapidil was detected in CSF as soon as 5 min after injection in 3 patients. The concentration ratio of plasma/CSF after the distribution phase was about 5:1. No significant effect on serotonin and 5-HIAA in CSF was seen.

CONCLUSION

After administration of a therapeutic dose, urapidil permeates the BBB and may interact with central 5-HT1A-receptors.

Pharmacological evidence for interactions between 5-HT1A receptor agonists and subtypes of alpha 1-adrenoceptors on rabbit aorta

This study was designed to determine if alpha 1-adrenoceptors are involved in the vascular responses to 5-HT1A receptor agonists. Buspirone (3.1 x 10(-7)-3.1 x 10(-5) M) and 8-hydroxy-2(di-N-propylamino)tetralin (8-OH-DPAT; 3.1 x 10(-6)-10(-4) M) elicited contractions of rabbit aorta rings which were blocked by prazosin (10(-9)-5.6 x 10(-9) M), but which were unaffected by reserpine pretreatment (1 mg/kg i.p.). 5-Methylurapidil (10(-7) and 10(-6) M) blocked contractions elicited by 8-OH-DPAT and by buspirone, whereas chloroethylchonidine (10(-5) and 10(-4) M) inhibited only the effect of buspirone. In addition, these 5-HT1A receptor agonists relaxed arteries precontracted with alpha-adrenoceptor agonists in a similar range of concentrations in which they elicited contraction. Moreover, 8-OH-DPAT and buspirone protected the alpha-adrenoceptors from the irreversible blockade provoked by phenoxybenzamine (10(-7) M), as judged by the norepinephrine contraction and stimulated phosphatidylinositol labeling. According to these results the contractile and relaxant effects elicited by 5-HT1A receptor agonists are a consequence of a direct interaction with alpha 1-adrenoceptors. The contraction elicited by 8-OH-DPAT may be mediated by alpha 1A-adrenoceptors, whereas both alpha 1A- and alpha 1B-adrenoceptors may mediate the effect of buspirone in rabbit aorta.

Blood pressure management during aortic surgery: urapidil compared to isosorbide dinitrate

The efficacy and hemodynamic effects of urapidil, an arteriolar vasodilator, and isosorbide dinitrate, a venodilator, were compared, when used for blood pressure control during abdominal aortic surgery. Urapidil is an alpha-adrenergic receptor antagonist with serotonin-1A receptor-agonist activity in the central nervous system. Hemodynamic profiles were recorded before and after the administration of the study drug (+/- 10 minutes before aortic clamping), 3 and 10 minutes following aortic clamping, and before and 3 and 10 minutes following the removal of the aortic clamp. Arterial and mixed venous oxygen contents were compared. Both groups of 18 patients were similar with respect to demographic profiles, anesthetic technique, and perioperative fluid therapy. Identical heart rate and blood pressure profiles were obtained. In contrast to isosorbide dinitrate, urapidil produced a 17% (P < 0.05) increase in cardiac index as a result of a 30% (P < 0.001) decrease in systemic vascular resistance before placement of the aortic clamp. In patients treated with urapidil, cardiac index was higher (P < 0.05) 10 minutes after aortic clamping, before removal of the clamp, and 10 minutes later. The arterio-venous oxygen content difference decreased from 3.2 +/- 0.8 mL O2/dL to 2.4 +/- 1.0 mL O2/dL (P < 0.01) following urapidil, but did not change during the administration of isosorbide dinitrate. It is concluded that urapidil is an effective and safe drug for the prevention of the hemodynamic consequences of aortic clamping. Compared to a venodilator (isosorbide dinitrate), urapidil offers the advantage of improving cardiac output and oxygen delivery.

Serotonergic receptors and drugs in hypertension

The possible role of 5-hydroxytryptamine (5HT) and 5HT-receptors in hypertension, already suggested by Page in 1954, has been subject to a renaissance of interest owing to the development of antihypertensive drugs which interact with 5HT-receptors. These drugs, like ketanserin, urapidil and flesinoxan are used as tools to study the role of 5HT and its receptors in hypertension. Some arguments would plead in favour of a certain role of 5HT and 5HT-receptors in the pathogenesis and maintenance of hypertension: hyperresponsiveness of blood vessels from hypertensive patients and animals to 5HT-induced constriction; the antihypertensive/vasodilator activity of the 5HT2-receptor antagonist ketanserin; enhanced sensitivity of platelets from hypertensives to 5HT. However, there are also several arguments which do not support a causal role of 5HT in hypertensive disease: 5HT is not a generally accepted pressor agent, whereas its concentration in the circulating blood is subthreshold; the 5HT2-receptor antagonist ketanserin is the only agent of this type which lowers blood pressure, other 5HT2-receptor blockers (ritanserin; LY 53587) being inactive. The various data and arguments available do not unequivocally support a relevant role of peripheral 5HT and its receptors in hypertensive disease. 5HT2-receptor blockade may, however, have a favourable effect on the microcirculation under pathological conditions. The stimulation of central 5HT1A-receptors by drugs like urapidil, 8-OH-DPAT or flesinoxan, has been demonstrated to induce peripheral sympathoinhibition and a fall in blood pressure. This mechanism appears to be a novel target for centrally acting antihypertensives, clearly different from that of clonidine and related drugs, which are centrally acting alpha 2-adrenoceptor agonists.

Influence of α1-adrenoceptor blockade and/or 5-HT1Aagonism on blood pressure and heart rate at rest and during exercise in hypertensive dogs

1. Antihypertensive effects resulting from alpha 1-adrenoceptor blockade and stimulation of central nervous 5-HT1A receptors were compared with the effects arising from stimulation of 5-HT1A receptors alone during arterial hypertension. 2. Urapidil and 5-methyl-urapidil were less effective in decreasing arterial blood pressure than the lowest dose of the selective 5-HT1A receptor agonist, flesinoxan. After the higher dose of urapidil, a certain dampening of barareceptor reflex was found which was also seen with flesinoxan. 3. Flesinoxan was the only drug which did not reduce the exercise-induced increase in systolic arterial blood pressure. 4. Stimulation of 5-HT1A receptors alone, which is assumed to occur with flesinoxan, exerted antihypertensive activity only at low doses, without inducing reflex tachycardia at rest. 5. Only the combined effects of alpha 1-adrenoceptor blockade and 5-HT1A receptor stimulation, as assumed to occur with urapidil and 5-methyl-urapidil, lead to both a decrease in arterial blood pressure at rest and during exercise.

Cardiovascular and side effects of flesinoxan in conscious hypertensive dogs. Modulation by prazosin

Previous studies on anaesthetized animals indicate that flesinoxan exerts hypotensive effects via stimulation of central 5-HT1A receptors. The purpose of the present study was to investigate the cardiovascular and side effects of flesinoxan in conscious, renal hypertensive dogs at rest and during exercise. Animals were pretreated with prazosin (2.5 or 7.5 nmol/kg) to verify a reduction of dose-dependent side effects, as occurred in normotensive dogs. A decrease in blood pressure without reflex tachycardia was observed only with the lower dose of flesinoxan (0.1 mumol/kg). The higher dose (0.2 mumol/kg) led to an increase in blood pressure and heart rate. The increase in heart rate during exercise was diminished by 0.2 mumol/kg flesinoxan. Pretreatment with prazosin resulted in an additive hypotensive effect at rest. Side effects, occurring primarily after the higher dose of flesinoxan, were not influenced by prazosin. It is concluded that flesinoxan is not likely to be efficacious in antihypertensive therapy.

The effect of urapidil on responses to phenylephrine, angiotensin and isoprenaline in man

Intravenous urapidil, 40 mg bolus followed by an infusion of 18 mg.h-1 for 2 h was administered to 6 female non-patient volunteers. Randomised cumulative dose response curves to angiotensin, phenylephrine and isoprenaline were performed before and commencing 30 min after the start of the infusion of urapidil. Urapidil significantly reduced supine systolic blood pressure, 118.5 mm Hg to 105.3. The diastolic blood pressure was not significantly reduced, heart rate was not affected. Urapidil did not affect the responses to angiotensin or isoprenaline. Urapidil inhibited the pressor response to phenylephrine. The dose required to increase systolic blood pressure by 20 mm Hg increased from 156.9 micrograms.min-1 before to 685 micrograms.min-1 during urapidil; Dose ratio from individual values of 4.58. Urapidil concentrations were not significantly different before and after each agonist infusion. It is concluded that urapidil has alpha 1-adrenoceptor blocking activity in man without any non specific vasodilator action and that it is devoid of beta adrenoceptor blocking action.

[3H]5-methyl-urapidil labels 5-HT1A receptors and alpha 1-adrenoceptors in the rat CNS. In vitro binding and autoradiographic studies

The tritiated derivative of the potent antihypertensive agent, 5-methyl-urapidil, was used as a radioligand in binding studies with rat brain membranes and tissue sections. Serotonin and prazosin inhibited [3H]5-methyl-urapidil binding to membranes from the rat hippocampus, cerebral cortex and brainstem biphasically, leading to the definition of serotonin high-affinity and prazosin high-affinity [3H]5-methyl-urapidil binding sites. Comparison of these serotonin-sensitive [3H]5-methyl-urapidil binding sites with the 5-HT1A sites labelled by [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT) revealed striking similarities regarding pharmacological properties, respective densities and regional distribution. On the other hand, the prazosin-sensitive [3H]5-methyl-urapidil binding sites should correspond to the alpha 1A-subtype of adrenoceptors which has recently been defined. Detailed autoradiographic investigations allowed the detection of 5-HT1A sites labelled by both [3H]5-methyl-urapidil and [3H]8-OH-DPAT in the posterior raphe nuclei (pallidus and obscurus) which are possibly involved in the hypotensive action of 5-methyl-urapidil. These data demonstrate that [3H]5-methyl-urapidil is a useful radioligand for the visualization and quantification of both 5-HT1A serotonin receptors and alpha 1A-adrenoceptors in the central nervous system.

The mechanism of the sympathoinhibitory action of urapidil: role of 5-HT1A receptors

1. An investigation was carried out to determine if the sympathoinhibition caused by urapidil is due to activation of 5-HT1A receptors by investigating whether it could be reversed by the non-selective 5-HT1A receptor antagonist spiperone. To control for the possibility of functional antagonism by spiperone, the ability of spiperone to reverse the sympathoinhibition caused by clonidine was also investigated. These experiments were carried out in anaesthetized prazosin-pretreated cats to prevent the alpha 1-adrenoceptor antagonist action of urapidil and spiperone from masking any effects observed. 2. Cats were anaesthetized with alpha-chloralose and simultaneous recordings were made of whole cardiac, splanchnic and renal nerve activities, blood pressure, heart rate and femoral arterial flow (from which conductance was derived). All animals were initially pretreated with prazosin (1 mg kg-1, i.v.) given in divided doses (0.75 followed 10 min later by 0.25 mg kg-1), then either urapidil (0.75 mg kg-1, i.v.) or clonidine (10 micrograms kg-1, i.v. in two divided doses) followed by 3 separate injections of spiperone (1 mg kg-1, i.v.). In another set of experiments urapidil was given followed by injections of the appropriate vehicle for spiperone, while in another set urapidil was replaced with an injection of the appropriate vehicle followed by injections of spiperone. In the experiments with clonidine, the alpha 2-adrenoceptor antagonist Wy 26392 (0.3 mg kg-1) was given after the last injection of spiperone. 3. The prazosin pretreatment caused a fall in blood pressure associated with femoral vasodilatation, a small bradycardia and little change in cardiac, splanchnic or renal nerve activities. Urapidil or clonidine injection after prazosin caused sympathoinhibition associated with an additional bradycardia. However, only urapidil caused an additional fall in blood pressure. Spiperone injections reversed the sympathoinhibition caused by urapidil but not that caused by clonidine. The sympathoinhibition caused by clonidine was reversed by the alpha 2-adrenoceptor antagonist Wy 26392. 4. These results show that the sympathoinhibition caused by urapidil in prazosin-pretreated cats can be reversed by spiperone. The reversal of this sympathoinhibition is not due to functional antagonism. It is concluded that urapidil can cause sympathoinhibition by activation of 5-HTlA receptors.

Alpha 1-adrenoceptor blockade and/or 5-HT1A agonism during treadmill exercise in dogs

1. The hypotensive effects of alpha 1-adrenergic blockade and/or stimulation of central nervous 5-HT1A receptors were studied using drugs with different affinity for central nervous 5-HT1A and peripheral alpha 1-adrenoceptors. Urapidil, 5-methylurapidil, flesinoxan and 8-OH-DPAT were compared under states of different activation of the autonomic nervous system, i.e. at rest and during graded treadmill exercise. 2. The rank order of hypotensive potency as derived from the most extensive decrease in resting diastolic arterial blood pressure was urapidil greater than 5-methylurapidil greater than flesinoxan much greater than 8-OH-DPAT. 3. The reflex increase in heart rate due to the decrease in arterial blood pressure at rest was suppressed after 0.1 mumol kg-1 flesinoxan. 4. The reflex increase in heart rate due to the decrease in arterial blood pressure at rest was less accentuated after high doses of urapidil and 5-methylurapidil. 5. During exercise both 5HT1A receptor agonists, flesinoxan and 8-OH-DPAT, decreased sympathetic tone. 6. The combined effects of alpha 1-adrenoceptor blockade and 5-HT1A receptor stimulation (urapidil and 5-methylurapidil) result in distinct decreases in blood pressure and slight suppression of reflex tachycardia at rest after high doses. Stimulation of 5-HT1A receptors alone (flesinoxan) suppresses reflex tachycardia by modulation of baroreceptor reflex and at high dose also diminishes exercise-induced increase in sympathetic tone.

Stimulation of serotonin2 receptors in the ventrolateral medulla of the cat results in nonuniform increases in sympathetic outflow

Topical application of the serotonin2 agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane or DOI, in a dose of 30 micrograms/side to the intermediate area of the ventrolateral surface of the medulla produced a significant increase in mean arterial pressure with no significant change in heart rate both in intact animals (n = 8) and in cervically vagotomized animals (n = 3). The pressor response of DOI was blocked by pretreatment of the intermediate area with ketanserin, a serotonin2 antagonist (n = 7). Pretreatment with intravenous phentolamine did not block the pressor response of DOI (n = 3). However, this pressor response could be counteracted by intravenous propranolol (n = 5) or by bilateral stellate ganglionectomy (n = 3). These data suggest that sympathoexcitation by centrally applied DOI selectively increased cardiac inotropy but not chronotropy. Further studies indicate that DOI increased contractile force without increasing heart rate and that the positive inotropic effect of DOI could be counteracted by bilateral stellate ganglionectomy. Bilateral microinjections of DOI into the subretrofacial nucleus in a dose of 100 ng (n = 3) and a dose of 300 ng (n = 3) increased mean arterial blood pressure by 23 +/- 2 and 44 +/- 6 mm Hg, respectively, without producing any changes in heart rate. These data suggest that DOI has a central site of action in the ventrolateral medulla, presumably at the subretrofacial nucleus, which leads to selective sympathoexcitation of the cardiac ventricles.

Effect of urapidil on the performance of ischemic myocardium in anesthetized dogs

Urapidil (URA) is used to treat acute hypertension in patients with coronary artery disease, but the effect of URA on the performance of ischemic myocardium has not yet been investigated. The present study was intended to assess the function of ischemic myocardium following URA administration. In eight anesthetized (piritramide) open-chest dogs systolic contraction (dL) and end-diastolic length (edL) of myocardium supplied by the left descending (LAD) and circumflex (LCA) coronary arteries were measured by sonomicrometry simultaneously with aortic pressure (AoP), left ventricular end-diastolic pressure (LVedP), heart rate (HR), stroke volume (SV), and LAD-flow (QLAD). QLAD was reduced by LAD stenosis to about 50% of control, decreasing dLLAD by 55%. Concomitantly, edLLAD increased by about 9% and LVedP by 22%, whereas AoP decreased by 5%. Then, URA was given i.v. (0.25 + 0.25 + 0.50 + 1.0 mg/kg) in 15-min intervals. Following URA, the performance of the non-ischemic area was not systematically affected, but dLLAD increased by about 50%. This could neither be related to the significant reduction in afterload (AoP: -8%), nor to an increase in preload (LVedP and edLLAD did not change significantly), nor to an improved oxygen supply via the LAD (QLAD even decreased), although an increased collateral flow the LCA could not be excluded. The increase in systolic shortening correlated very closely to a decrease in heart rate (r = -0.92). It is concluded that the improved function of ischemic myocardium following urapidil resulted from a reduced oxygen demand in consequence to the decrease in heart rate.

Pharmacology of antihypertensive agents with multiple actions

Compounds with two or more different pharmacodynamic activities in a single molecule are designated as hybrid drugs. If several stereoisomers with different pharmacodynamic activities exist in one molecule, the term pseudo-hybrid drug is applied. In the treatment of hypertension, the use of hybrid drugs enables a considerable reduction in the number of tablets to be taken per day. Conversely, the dose of each individual component cannot be tritrated. Most hybrid drugs used in antihypertensive treatment are beta-blockers with an additional vasodilator component, caused by different mechanisms such as alpha-adrenoceptor blockade, beta 2-adrenoceptor agonism, ACE inhibition or direct relaxation of vascular smooth muscle. Examples include labetalol (in fact, a mixture of four stereoisomers), carvedilol, celiprolol, dilevalol, tertatolol and BWA-575 C. A combination of beta-receptor blockade and vasodilation may be beneficial from a hemodynamic point of view. More recently it has been recognized that urapidil and ketanserin are hybrid drugs, each containing at least two pharmacodynamic activities in their molecules.

Drugs affecting serotonin neurons

Advances in serotonin pharmacology, the development of drugs that intervene at specific sites to modify serotonergic function, have accompanied advances in the understanding of physiologic roles of serotonin present in neurons and elsewhere and of serotonin receptors that are widely distributed in brain and many peripheral tissues. The pharmacologic advances have sometimes been stimulated by developments in serotonin physiology, such as the recognition of multiple serotonin receptor subtypes, and in other cases have been a major factor in providing new insights into physiologic roles of serotonin. Drugs that modify serotonin function have a variety of therapeutic applications currently and many more potential therapeutic uses to be explored in the future. Having drugs that act with high specificity or selectivity on particular enzymes in serotonin biosynthesis, on particular serotonin receptors, or at other sites such as uptake carriers for serotonin not only offers the hope of improved clinical therapy in diseases caused by abnormal serotonergic function or in which alteration of serotonergic function can alleviate symptoms, but also provides valuable pharmacologic tools for learning more about serotonin physiology and probing the functional status of serotonergic systems. The next few years promise to yield important new serotonergic drugs.

Urapidil, a multiple-action alpha-blocking drug

Investigations in animals indicate that urapidil has a number of actions that may be relevant to its antihypertensive effect. It has an alpha 1-blocking action, a weak beta 1-blocking effect, an interaction with a serotonin receptor and a central depression of sympathetic tone. Urapidil is well absorbed orally with a bioavailability of about 70% and a time to peak concentration of about 4 hours after a sustained release capsule. It is metabolized in the liver at a half-life of 4.7 hours. Peripheral alpha 1-blocking activity has been demonstrated in humans. A shift to the right in the dose-response curve to phenylephrine has been found after urapidil, whereas responses to angiotensin are not affected. Evidence for beta 1-blocking activity is marginal. Urapidil does not inhibit the exercise increase in heart rate. Some investigators have suggested a possible inhibition of isoprenaline tachycardia; others have found no evidence. There is some evidence suggestive of a central action of urapidil in humans as lower single doses result in a decrease in blood pressure and an increase in heart rate. With higher doses the hypotensive effect continues but the tachycardia no longer occurs. However, urapidil has been reported to increase noradrenaline levels, although there has been a report with a high dose reducing vanillylmandelic acid excretion. Evidence for changes in renin is inconsistent. Hemodynamic studies have revealed findings that are compatible with peripheral alpha 1 blockade. After intravenous administration, peripheral resistance is reduced along with arterial pressure, and cardiac output is increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of brain 5-HT1A receptors in the hypotensive response to urapidil

Stimulation of serotonin-1A (5-hydroxytryptamine) (5-HT1A) receptors in the brain stem has been suggested to contribute to the antihypertensive action of the alpha 1-adrenoceptor antagonist urapidil. This hypothesis was tested by analyzing the influence of the 5-HT1A receptor antagonist spiroxatrine on the hypotensive responses to urapidil and the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT). Chloralose/urethane-anesthetized cats underwent thoracotomy and were artificially ventilated. Blood pressure was monitored in the femoral artery. Urapidil (0.01 to 10 mumol/kg) or 8-OH-DPAT (3 to 30 nmol/kg) was injected into a femoral vein and the maximal hypotensive response recorded. A dose-response test with both drugs was performed before and after administration of spiroxatrine (3 and 10 nmol/kg); the latter was given through the vertebral artery, thus delivering the antagonist to the brain stem. Blood pressure was dose-dependently reduced by urapidil and 8-OH-DPAT after intravenous injection. Central administration of spiroxatrine through the vertebral artery shifted the dose-response curves of both drugs markedly and in a dose-dependent manner to the right, while the hypotensive response to the peripheral vasodilator nitroglycerin remained unchanged. The results suggest that the hypotensive response after peripheral administration of urapidil is mediated in part by stimulation of brain 5-HT1A receptors and this effect on central cardiovascular regulation is additive to the blood pressure reduction resulting from peripheral alpha-adrenoceptor blockade.

Acute responses to urapidil in hypertensive persons

Urapidil is a new antihypertensive agent involving both a peripheral and a central mode of action. To evaluate the acute effects of this drug on renal vascular tone and on pressor systems a randomized placebo-controlled crossover study was conducted in 10 patients with uncomplicated essential hypertension. Each subject received, on 2 separate days 1 week apart, an intravenous injection of either placebo or urapidil (25 or, if necessary, 50 mg). Before and after this injection blood pressure and heart rate (Dinamap), renal plasma flow (125I-hippuran), active plasma renin concentration, angiotensin II, aldosterone and catecholamines in plasma were measured. The results show that urapidil, when compared with placebo, greatly reduced blood pressure, while increasing heart rate, renal blood flow, and noradrenaline and adrenaline levels. However, dopamine levels were suppressed. Whereas renin and angiotensin II were only mildly stimulated, aldosterone levels increased significantly. It is concluded that urapidil, given intravenously, has an immediate blood pressure-lowering effect associated with a decrease in renal vascular tone and an increase in renal perfusion. Consequently, both the sympathetic and renin-angiotensin systems are stimulated, although the latter only to a mild degree. The increase in aldosterone may be partially related to the decrease in dopamine levels.

Evidence for the interaction of urapidil with 5-HT1A receptors in the brain leading to a decrease in blood pressure

Current knowledge about the role of serotonin (5-HT) in central cardiovascular regulation is reviewed. Results from experiments with the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) suggest that activation of somatodendritic 5-HT1A receptors in the medulla oblongata decreases the firing of serotoninergic neurons and thus reduces their excitatory input to the sympathetic neurons in the intermediolateral cell column. As a consequence, blood pressure is reduced by 5-HT1A receptor agonists. Urapidil is an antihypertensive drug that has a dual mode of action: peripheral alpha-adrenoceptor antagonism and interaction with 5-HT1A receptors in the brain. This profile can adequately explain the vasodilation and lack of significant sympathetic activation observed during urapidil treatment.

Effect of urapidil on steady-state serum digoxin concentration in healthy subjects

In an open, randomized, two-period change-over study the effect of urapidil, an antihypertensive agent, on steady-state serum digoxin levels was investigated in 12 healthy male volunteers. The subjects were given digoxin 0.25 mg once daily for 4 days to produce a steady-state digoxin level in serum. At the end of that time the subjects received either digoxin monotherapy or digoxin and concomitant treatment with urapidil 60 mg b.d. for a further 4 days. Subsequently the treatments were changed over. The absorption characteristics Cmax and tmax of digoxin were not altered by concomitant urapidil treatment. The geometric mean and nonparametric 95% confidence limits of digoxin relative bioavailability were 97% (93%-103%). Therefore, concomitant administration of urapidil with digoxin treatments did not appear to alter the rate and extent of absorption of the glycoside.