The in vivo pharmacological profile of eletriptan (UK-116,044): a potent and novel 5-HT(1B/1D) receptor agonist.

The anti-migraine drug, eletriptan [(R)-3-(1-methyl-2-pyrrolidinylmethyl)-5-[2-(phenylsulphonyl )ethyl]-1 H-indole; UK-116,044], is a novel 5-HT(1B/1D) receptor agonist. In this paper, the regional vasoconstrictor profile of eletriptan, in comparison with sumatriptan, was examined in the anaesthetised dog. The inhibitory actions of eletriptan on neurogenic inflammation in rat dura mater were also assessed. In the anaesthetised dog, eletriptan (1-1000 microg kg(-1) i.v.) produced a dose-dependent reduction of carotid arterial blood flow with a similar potency and maximum effect to sumatriptan (ED(50) values: eletriptan and sumatriptan, 12 and 9 microg kg(-1), i.v., respectively). However, eletriptan exhibited a significantly lower potency than sumatriptan in reducing coronary artery diameter (ED(50) values: 63 and 19 microg kg(-1), i.v., respectively, P<0.05). In the femoral circulation, sumatriptan caused a significant reduction in arterial blood flow (ED(50) 35 microg kg(-1) i.v.) whereas eletriptan (1-1000 microg kg(-1) i.v.) had no significant effect upon femoral arterial blood flow when compared to vehicle-treated animals. In rats, eletriptan (30-300 microg kg(-1) i.v.) administered prior to electrical stimulation of the trigeminal ganglion produced a dose-related and complete inhibition of plasma protein extravasation in the dura mater (mean extravasation ratio: control 1.9; eletriptan 1.0, minimum effective dose 100 microg kg(-1), P<0.05). The potency and maximum effect of eletriptan was identical to that of sumatriptan in this model. When administered during a period of continual stimulation of the trigeminal nerve, eletriptan (100 microg kg(-1) i.v.) produced a complete inhibition of plasma protein extravasation. The ability to reduce canine carotid arterial blood flow and inhibit neurogenic inflammation in rat dura mater suggests that vascular and neurogenic mechanisms may contribute to eletriptan's clinical efficacy in migraine patients. In addition, eletriptan exhibits some selectivity for reducing carotid arterial blood flow when compared with femoral arterial blood flow and coronary artery diameter, in the anaesthetised dog.

The in vivo pharmacological profile of a 5-HT1 receptor agonist, CP-122,288, a selective inhibitor of neurogenic inflammation.

1. The aim of the present study was to investigate the in vivo pharmacological profile of CP-122,288, an indole-derivative with a conformationally restricted N-methylpyrrolidinyl basic side chain in the C-3 position. This C-3 substituent structurally differentiates CP-122,288 from the 5-HT1D receptor agonist sumatriptan, which possesses an N,N-dimethylaminoethyl group. [Formula: see text] 2. When administered prior to electrical stimulation of the trigeminal ganglion, CP-122,288 (0.3-300 ng kg-1, i.v.) produced a dose-related inhibition of plasma protein extravasation in rat dura mater (minimum effective dose, MED, 3 ng kg-1 i.v., P < 0.05; maximal inhibition of plasma extravasation at 30 ng kg-1 i.v., P < 0.01). Sumatriptan produced a similar inhibition of plasma leakage in the dura, but at much higher dose levels (MED, 100 micrograms kg-1 i.v., P < 0.05). Thus, CP-122,288 is of the order of 10(4) fold more potent than sumatriptan. 3. At all doses tested, CP-122,288 did not inhibit plasma protein extravasation measured in extracranial tissues such as the lower lip, eyelid, and conjunctiva. 4. In a separate series of studies in the anaesthetized rat, CP-122,288 (0.003-3 micrograms kg-1 i.v.) produced no change in either heart rate or mean arterial blood pressure, thus demonstrating that doses of CP-122,288 which inhibit plasma protein leakage in rat dura, are devoid of hemodynamic effects. 5. Following a 5 min period of electrical stimulation of the trigeminal ganglion, a 20 min period of sustained neurogenically-driven plasma extravasation, occurring in the absence of electrical stimulation, was initiated. By administration of the compound 5 min after completing the phase of electrical stimulation, this protocol permitted the evaluation of the activity of CP-122,288 on an ongoing and established inflammatory event. CP-122,288 (30 and 300 ng kg-1, i.v., P < 0.01 and P < 0.05, respectively) produced a complete inhibition of plasma protein leakage which was consistent with its effects when administered prior to trigeminal ganglion stimulation. 6. In the anaesthetized dog, CP-122,288 and sumatriptan, at 1-300 micrograms kg-1, i.v., produced a dose-dependent reduction in carotid arterial blood flow and coronary arterial diameter. These data demonstrate that sumatriptan inhibits neurogenic inflammation in the rat (MED, 100 micrograms kg-1, i.v.), and produces vasoconstriction in the dog, over a similar dose-range. Interestingly, doses of CP-122,288 that inhibit neurogenic inflammation in rat dura mater (0.3-300 ng kg-1) were demonstrated to be devoid of vasoconstrictor activity in either the carotid or coronary vascular beds of dog. 7. These data demonstrate that in the rat, CP-122,288 is a highly potent and selective inhibitor of neurogenic inflammation in intracranial tissues, at doses which are devoid of vasoconstrictor activity in dog. Potentially, CP-122,288 may be of use for the acute treatment of migraine, without the risk of cardiovascular side-effects.

Effect of a 5-HT1 receptor agonist, CP-122,288, on oedema formation induced by stimulation of the rat saphenous nerve.

Neurogenic oedema formation in the rat hind paw skin induced by electrical stimulation of the saphenous nerve and measured by extravasation of [125I]-albumin, was inhibited by the 5-HT1B receptor agonist, CP-93,129, and the novel tryptamine analogue, CP-122,288. Significant inhibition of up to 66% of control was observed with CP-122,288 (2 x 10(-14) - 2 x 10(-7) mol kg-1) and CP-93,129 (5 x 10(-7) - 5 x 10(-6) mol kg-1), with the minimum effective dose for CP-122,288 being about 10(7) fold less than that for CP-93,129. Oedema formation induced by the intradermal administration of exogenous mediators (substance P and histamine) in rat dorsal skin was not inhibited by CP-122,288 (2 x 10(-10) mol kg-1). These results suggest that CP-122,288 is a potent inhibitor of neurogenic inflammation in rat skin and that the effect may be due to a prejunctional inhibition of neuropeptide release.

Renal effects of neutral endopeptidase inhibition in euvolemic and hypervolemic rats.

Candoxatrilat is a potent and selective inhibitor of neutral endopeptidase (EC 3.4.24.11), the enzyme responsible for the degradation of atrial natriuretic factor (ANF). In these studies, the renal effects of candoxatrilat were investigated in euvolemic and hypervolemic anaesthetised rats. In euvolemic rats, candoxatrilat (675 micrograms/kg per h) had no effect on urine output, sodium and potassium excretion or urinary cyclic GMP excretion. However, in hypervolemic rats, the natriuretic and diuretic responses to volume expansion were markedly potentiated by the candoxatrilat infusion, with a concomitant increase in urinary cyclic GMP. Acute volume expansion was characterised by natriuresis, diuresis and increased levels of plasma ANF and cyclic GMP (1.5-fold and 2-fold increases respectively, when compared to euvolemic rats). The results presented suggest that plasma ANF levels and volume status modulate responses to neutral endopeptidase inhibition. The development of the neutral endopeptidase inhibitor, candoxatrilat, provides the opportunity to exploit endogenous ANF effectively in disease states with elevated ANF.

Effects of hydrochlorothiazide and captopril on the survival and heart weight of cardiomyopathic hamsters.

The current study investigated the effect of hydrochlorothiazide (HCTZ), and of captopril, on the survival and heart weight of cardiomyopathic hamsters (CMH). Groups of 51 CMH (about 200 days old) were orally treated with HCTZ (6 mg/kg), captopril (30 mg/kg), a combination of both drugs or vehicle alone (control group), for 217 days. Then survivors were sacrificed and the hearts weighed. The survival of the animals treated with HCTZ alone or in combination with captopril was similar, and was clearly increased when compared to controls (more than 70 days increase in median survival time). A more modest increase in survival occurred in animals treated with captopril alone. The efficacy of the diuretic therapy was consistent with fluid retention being the primary cause of death in CMH and demonstrated the usefulness of the model for the testing of new diuretics. HCTZ or captopril alone had no effect on the heart weight of survivors. However a reduction of cardiac hypertrophy (-18%) was seen when captopril and HCTZ were coadministered. This effect of the ACE inhibitor was considered to result from antagonism of the compensatory activation of the renin-angiotensin system occurring in response to diuretic therapy.

The pharmacokinetics of 125I-atrial natriuretic factor in anaesthetized rats. Effects of neutral endopeptidase inhibition with candoxatrilat and of ANF-C receptor blockade.

The effects of candoxatrilat (cis-4-([2-carboxy-3-(2-methoxyethoxy)propyl]-1-cyclopentanecarbonyla mino)- 1-cyclohexane carboxylic acid) and the ring-deleted atrial natriuretic factor (ANF) analogue C-ANF4-23 (des[Gln18, Ser19, Gly20, Leu21, Gly22]ANF4-23-NH2) on the clearance of (3-[125I]iodotyrosyl28)ANF (125I-ANF) were studied in both intact and nephrectomized anaesthetized rats. HPLC analysis was used to verify that the 125I-labelled material isolated by solid phase extraction of rat plasma was intact ANF. In intact animals, clearance of 125I-ANF was biphasic with a T1/2 alpha of 17 sec and T1/2 beta of 95 sec. Volume of distribution (Vd) was 564 mL/kg and plasma clearance (Clp) 248 mL/min/kg. Candoxatrilat, over the dose range 0.01-10 mg/kg i.v., increased T1/2 beta (by a maximum of 56%) and decreased Clp (by up to 52%) with no effect on T1/2 alpha or Vd. C-ANF4-23 (10 micrograms/kg+1 microgram/kg/min i.v.) reduced Vd (by 57%) and Clp (by 54%) with no effect on T1/2 beta, whilst abolishing the T1/2 alpha phase in over 50% of animals. Increasing the dose of C-ANF4-23 did not increase the effect on any of these parameters, apart from a small increase in T1/2 beta. Combining the two agents resulted in a substantial decrease in Clp (76%) whilst the reduction in Vd and increase in T1/2 beta were comparable to those seen with C-ANF4-23 and candoxatrilat alone, respectively. In nephrectomized rats, the pharmacokinetics of 125I-ANF and the changes induced by candoxatrilat were similar to those observed in intact animals, whilst the effects of C-ANF4-23 alone were greater than in intact animals. The combination of C-ANF4-23 and candoxatrilat again produced a substantial increase in T1/2 beta (153%) and decreases in Vd (55%) and Clp (78%) in nephrectomized animals, although these changes could not be distinguished from those seen in intact animals treated with the same combination. Our studies indicate that neutral endopeptidase and ANF-C receptors are both major, and approximately equal, clearance mechanisms for 125I-ANF, together accounting for at least 75% of the total clearance of this peptide in the rat.

Inhibition of neutral endopeptidase (EC 3.4.24.11) leads to an atrial natriuretic factor-mediated natriuretic, diuretic and antihypertensive response in rodents.

1. Atrial natriuretic factor is metabolized by neutral endopeptidase (atriopeptidase; EC 3.4.24.11) in vitro. Inhibitors of this enzyme have been reported to prolong the half-life of atrial natriuretic factor in vivo and to potentiate the renal and haemodynamic effects of exogenous atrial natriuretic factor. 2. (+/-)-Candoxatrilat, a selective neutral endopeptidase inhibitor, potentiated the natriuretic and diuretic response to volume loading in anaesthetized rats. Part of the response to volume loading and the potentiation by (+/-)-candoxatrilat was prevented by a polyclonal atrial natriuretic factor antiserum. The diuretic and natriuretic responses evoked by hydrochlorothiazide were not altered by the antiserum. 3. (+/-)-Candoxatrilat reduced systolic blood pressure of one-kidney deoxycorticosterone acetate-salt hypertensive rats for over 5 h. This response was abolished by pretreatment with atrial natriuretic factor antiserum. 4. These data demonstrate that the neutral endopeptidase inhibitor (+/-)-candoxatrilat has natriuretic/diuretic and antihypertensive effects in rodents, and that these effects are mediated via endogenous atrial natriuretic factor.

The atriopeptidase inhibitor (+/-) candoxatrilat reduces the clearance of atrial natriuretic factor in both intact and nephrectomized rats: evidence for an extrarenal site of action.

We have demonstrated that in anaesthetized rats. (+/-) candoxatrilat reduces the clearance of both 125IANF and ANF 5-28, and prolongs the elimination half-life. These effects occur independent of glomerular filtration, since they are not attenuated by nephrectomy. Moreover, they cannot be attributed to blockade of ANF-C receptors. Our findings suggest that (+/-)candoxatrilat exerts its activity in vivo by specific inhibition of atriopeptidase at both renal and extra-renal locations.

Design of an antithrombotic-antihypertensive agent (Wy 27569). Synthesis and evaluation of a series of 2-heteroaryl-substituted dihydropyridines.

An approach to the design of potential combined antithrombotic-antihypertensive agents is described. A series of 1,4-dihydropyridines bearing a 1H-imidazol-1-yl or pyrid-3-yl substituted side chain in the 2-position were synthesized and tested for antihypertensive activity in spontaneously hypertensive rats and for inhibition of TXA2 synthetase in rabbit platelets, in vitro. 1,4-Dihydro-2-(1H-imidazol-1-ylmethyl)-6-methyl- 4-(3-nitrophenyl)pyridine-3,5-dicarboxylic acid 3-ethyl 5-methyl diester (1) was shown to be similar in potency to nitrendipine as an antihypertensive agent. Compound 1 inhibited TXA2 synthetase in rabbit and human platelets in vitro and reduced plasma TXB2 levels in rats at antihypertensive dose levels. The reductions in thromboxane production observed in vivo and in vitro were accompanied by enhanced levels of 6-KPGF1 alpha, reflecting diversion of the arachidonic acid cascade toward prostacyclin synthesis.

Pharmacologic effects of Wy 27569: a combined calcium channel blocker and thromboxane synthetase inhibitor.

Wy 27569 (1,4 dihydro-2-[imidazol-1-yl-methyl]-6-methyl-4- [3-nitrophenyl] pyridine-3,5, dicarboxylic acid 3-ethyl 5-methyl diester) is a combined calcium channel blocker and thromboxane synthetase inhibitor. This article reports the in vivo and in vitro pharmacological studies demonstrating these properties. Wy 27569 evoked rightward shifts and depressed the maximum of calcium dose response curves in potassium depolarised rat aortas [concentration required to inhibit the response by 50% (IC50) = 7.3 nM]. The calcium channel blocker nitrendipine exhibited a similar profile to, although more potent than, Wy 27569 (IC50 = 0.28 nM). Comparison of the data obtained in aortas with the effects of these compounds in electrically stimulated isolated ventricle strips (IC50 for Wy 27569 = 8.3 microM, IC50 for nitrendipine = 0.41 microM) suggests that Wy 27569, like nitrendipine, is a vascular selective calcium channel blocker. Wy 27569 and the thromboxane synthetase inhibitor dazoxiben inhibited the collagen-stimulated production of thromboxane B2 (TXB2, IC50 = 3.9 and 2.8 microM, respectively) and, over the same concentration range, enhanced the production of immunoreactive 6 keto prostaglandin F1 alpha (6 keto-PGF1 alpha) by human platelet rich plasma. Single doses of Wy 27569 (0.3-10 mg kg-1 p.o.) or dazoxiben (3-10 mg kg-1 p.o.) evoked a dose-related reduction of TXB2 and enhancement of immunoreactive 6 keto PGF1 alpha levels in rat plasma and serum. Nitrendipine (0.3-10 mg kg-1 p.o.) had no significant effect on either eicosanoid.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of human and rat CGRP compared in the rat and other species.

In the anaesthetised rat, human and rat CGRP (calcitonin gene-related peptide) which differ by 4 out of 37 amino acids, when given intravenously, lowered blood pressure and increased heart rate. The effects of human CGRP were unaltered by either propranolol or by mepyramine plus cimetidine. In the rat isolated perfused heart the peptides decreased coronary perfusion pressure and evoked a tachycardia. The latter effect was not seen in the rabbit isolated heart, although human CGRP increased coronary flow. The two peptides were equipotent at increasing the rate and force of contraction in the rat isolated right atrium, effects unaltered by propranolol. In the guinea-pig isolated atrium, rat CGRP was 10 times as potent as a chronotropic agent than as an inotrope, unlike human CGRP which was equipotent. In conclusion, human and rat CGRP probably acted directly on the cardiovascular system to produce their qualitatively similar effects.

Investigation into the cardioregulatory properties of the alpha 1-adrenoceptor blocker indoramin.

The cardioregulatory properties of the alpha 1-adrenoceptor blocker indoramin have been compared with those of prazosin in the anaesthetized rat. The effects of autonomic blockade on heart rate responses evoked by these two agents and their effects on blood pressure and heart rate after peripheral or central administration have been compared. Cumulative administration of indoramin (0.8-25.6 mg kg-1 i.v.) evoked significant decreases in arterial blood pressure and a concomitant bradycardia. Pithing or autonomic blockade, by pretreatment with a combination of practolol and bilateral vagotomy, prevented the bradycardia evoked by indoramin (0.8-3.2 mg kg-1 i.v.). Atropine sulphate pretreatment abolished the bradycardia until a cumulative dose of 25.6 mg kg-1(i.v.) of indoramin had been reached. Bilateral vagotomy, intravenous administration of atropine methylnitrate or practolol pretreatment attenuated the bradycardia. Prazosin (0.02-0.64 mg kg-1 i.v.) evoked a fall in arterial blood pressure of similar magnitude to that observed following indoramin. A bradycardia was evoked only at a relatively high dose (0.64 mg kg-1 i.v.). Intracisternal injection of indoramin or prazosin evoked bradycardia and hypotension at a dose which had no effect after intravenous injection (25 micrograms). Intracerebroventricular injection of indoramin (25 micrograms) had no significant effect on heart rate or blood pressure compared to control values, whereas prazosin (25 micrograms) evoked a significant tachycardia and hypotension. It is concluded that the bradycardia evoked by indoramin in the rat is not due to a direct action on the heart except possibly at high doses. Central alpha 1-adrenoceptor blockade, possibly in the brainstem region, results in a bradycardia and this may explain the lack of reflex tachycardia following the administration of indoramin.

The effects of a new opioid analgesic, meptazinol, on the respiration of the conscious rat.

In the conscious rat arterial PCO2 was measured as an index of respiratory status. The opioid analgesic meptazinol (7.5 - 30 mg kg-1) evoked small but significant increases in arterial PCO2 which were attenuated by naloxone. Meptazinol significantly reduced the increase in arterial PCO2 evoked by morphine. The respiratory depression induced by meptazinol, but not that induced by morphine, was enhanced by pretreatment with atropine. The (+)-enantiomer, but not the (-)-enantiomer of meptazinol increased arterial PCO2. In contrast, only the (-)-enantiomer reduced the respiratory depressant effect of morphine. It is proposed that the degree of respiratory depression induced by meptazinol is limited by its opioid antagonist and cholinomimetic properties.

The alpha 2-adrenoceptor selectivities and haemodynamic effects of WY26392 and yohimbine in the anaesthetised dog.

The selectivities of WY26392 and yohimbine for prejunctional alpha 2-adrenoceptors have been evaluated in the anaesthetised dog. Clonidine inhibited the tachycardia evoked by cardiac sympathetic nerve stimulation, WY26392 and yohimbine reversed this effect by 50% at doses of 3.3-12 and 7.5-69.5 micrograms/kg respectively, depending upon the frequency of nerve stimulation. The alpha 1-adrenoceptor agonist phenylephrine evoked a pressor response which was reduced by 50% following approximately 1.0 mg/kg of either antagonists. Due to its greater potency at alpha 2-adrenoceptors, WY26392 consistently exhibited a greater selectivity than yohimbine for this receptor. The haemodynamic evaluation of WY26392 and yohimbine revealed that low doses of these compounds (0.03-0.1 mg/kg i.v.) increased systolic blood pressure, heart rate and dp/dtmax. WY26392 evoked a small rise in diastolic blood pressure over this dose range. These increases may be due to an increase in sympathetic nerve activity resulting from alpha 2-adrenoceptor blockade. Higher doses of these compounds reduced these cardiovascular parameters, possibly as a result of alpha 1-adrenoceptor blockade.

The effect of indoramin on plasma lipids in hypercholesterolemic patas monkeys.

In patas monkeys fed a high cholesterol diet, chronic dosing with the antihypertensive agent indoramin increases the cholesterol ratio by raising the plasma HDL-C concentration. Epidemiological evidence suggests that increasing HDL-C reduces the incidence of coronary heart disease (CHD). If, therefore, indoramin is able to evoke these changes in man it may be expected to favourably influence the progress of CHD.

Alpha 2-adrenoceptor agonists potentiate responses mediated by alpha 1-adrenoceptors in the cat nictitating membrane.

Alpha 1 but not alpha 2-adrenoceptors mediate contractions of the cat nictitating membrane. The contractions of this tissue evoked by alpha 1-adrenoceptor agonists, but not those evoked by angiotensin II, are potentiated by pre-dosing with alpha 2-adrenoceptor agonists. This potentiation is reversed by the alpha 2-adrenoceptor antagonist, WY 26392. Pressor responses evoked by alpha 1-adrenoceptor agonists or angiotensin II were not affected by alpha 2-adrenoceptor agonists. Contractions of the nictitating membrane evoked by noradrenaline were reduced by pretreatment with WY 26392. These results suggest that in some tissues the role of alpha 2-adrenoceptors may be to modulate responses to alpha 1-adrenoceptors, rather than to evoke a discrete response themselves.

An investigation into the selectivity of a novel series of benzoquinolizines for alpha 2-adrenoceptors in vivo.

The potencies and selectivities of a novel series of benzoquinolizines for the alpha 2-adrenoceptor have been investigated in the rat in comparison with yohimbine and indoramin. Peripheral postjunctional alpha 2- and alpha 1-adrenoceptor blockade was measured as the reversal of B-HT 933 and methoxamine-induced pressor responses, respectively, in the pithed rat. Peripheral prejunctional alpha 2-adrenoceptor blockade was measured as the reversal of B-HT 933-induced inhibition of an electrically evoked tachycardia in the pithed rat. Central alpha 2-adrenoceptor blockade was measured as a reversal of the hypotension induced in anaesthetized rats by central (i.c.v.) administration of clonidine. Wy 25309, Wy 26392, Wy 26703 and yohimbine (0.3-3 mg kg-1 i.v.) evoked dose-dependent shifts to the right of the dose-response curves to B-HT 933 whilst having minimal effects on the methoxamine dose-response curve. The selectivity for alpha 2-adrenoceptors increased with the dose of antagonist administered. In general, the order of selectivity was Wy 25309 greater than Wy 26392 greater than Wy 26703 greater than yohimbine. Indoramin (1 mg kg-1 i.v.) shifted the methoxamine pressor dose-response curve to the right without affecting the B-HT 933 dose-response curves, confirming its selective alpha 1-antagonist activity. Peripheral administration of all three benzoquinolizines (1-100 micrograms kg-1 i.v.) led to a dose-dependent reversal of the hypotension evoked by central administration of clonidine (500 ng i.c.v.). The reversal was incomplete, higher doses causing a further decrease in blood pressure. A similar degree of hypotension induced by the ganglion blocking agent chlorisondamine (1 mg kg- I i.v.) was not reversed by the benzoquinolizines. 9 It is concluded that Wy 25309, Wy 26392 and Wy 26703 are selective alpha 2-adrenoceptor antagonists which readily penetrate the CNS.

alpha 1-Adrenoceptor agonist activity of alpha 2-adrenoceptor antagonists in the pithed rat preparation.

The selective alpha 2-adrenoceptor antagonist, RX781094, evoked a dose-related pressor response in the pithed rat preparation when administered in bolus doses by the intravenous route. This response was enhanced following depletion of endogenous amines by reserpine, and inhibited by the selective alpha 1-adrenoceptor antagonist, prazosin. Two other selective alpha 2-adrenoceptor antagonists, Wy26703 and Wy26392, had no marked effect on the blood pressure of this preparation. Pretreatment of the preparation with Wy26703 had no significant effect on the pressor response evoked by RX781094. It is concluded that RX781094 is an alpha 1-adrenoceptor agonist at similar doses to those at which it exhibits alpha 2-adrenoceptor antagonist properties. The agonist activity exhibited by RX781094 is not a general property of all alpha 2-adrenoceptor antagonists and should be considered when this compound is employed as an alpha 2-adrenoceptor antagonist.