The effect of ketanserin, a 5-HT2-receptor antagonist, on 5-hydroxytryptamine-induced irreversible platelet aggregation in patients with cardiovascular diseases

N-[1-(2-Phenylethyl)pyrrolidin-3-yl]-1-adamantanecarboxamides as novel 5-HT2 receptor antagonists

A series of 1-adamantanecarboxamides was synthesized and examined for their potency as a selective 5-HT2 receptor antagonist. We found (S)-N-[1-[2-(4-fluorophenyl)ethyl]pyrrolidin-3-yl]-1-adamantane carboxamide hydrochloride hydrate (10-(S), Y-39241) to have a high affinity and selectivity for 5-HT2 receptors, and this potent anti-platelet effect of Y-39241 was confirmed both in vitro and in vivo.

Effect of milrinone in human platelet shape change, aggregation and thromboxane A2 synthesis: an in vitro study

Milrinone (MIL; a cAMP-specific phosphodiesterase type-III inhibitor), added in vitro to achieve concentrations below the therapeutic levels, inhibited agonist-induced platelet shape change (PSC). Arachidonic acid (AA)-induced PSC was significantly more inhibited by a combination of MIL and indomethacin (INDO; a cyclooxygenase inhibitor) than by either alone. PSC induced by 5-hydroxytryptamine was inhibited by MIL but not by INDO; and this effect of MIL was not augmented by INDO. Whole blood-platelet aggregation (WB-PA) and platelet-rich plasma aggregation induced by potent stimulators of thromboxane A2 (TXA2) synthesis such as AA and calcium ionophore and by less potent agonists (e.g. ADP and U46619) were inhibited by MIL at or near therapeutic concentrations. WB-PA induced by collagen was significantly more inhibited by the MIL and INDO combination than by either of these agents alone whereas with ADP-induced WB-PA no additional effect could be shown when both MIL and INDO were co-incubated. MIL and similar types of drugs may be of benefit in conditions associated with platelet hyperactivity and some of these effects may be enhanced by cyclooxygenase inhibitors.

Serotonin-induced platelet aggregation predicts the antihypertensive response to serotonin receptor antagonists

The 5-HT2-receptor antagonist ketanserin (20-40 mg b.i.d.) was administered to 62 patients of both sexes with uncomplicated primary hypertension. After 4 weeks of treatment about 50% of the patients had reached the target diastolic blood pressure of 90 mm Hg or below. Interindividual variability was large. In a retrospective analysis the variability could not be explained by sex or the dose of ketanserin. There was a weak association between age and systolic blood pressure response (r = 0.24; P = 0.06), which could be entirely accounted for by the higher base line blood pressure in the elderly patients. In one group of patients (n = 12), the ex vivo aggregation to serotonin (10(-6) M) was studied during treatment with placebo and ketanserin. Ketanserin completely inhibited 5-HT-induced aggregation in all patients. There was a close correlation between the area under the 5-HT-induced platelet aggregation curve during placebo and the subsequent reduction in diastolic blood pressure after 4 weeks of treatment with ketanserin. The present data suggest that the blood pressure response to ketanserin can be predicted from the ex vivo sensitivity of platelets to serotonin. By implication, they also support a role for serotonergic mechanisms in hypertension.

Characterization of rat platelet serotonin receptors with tryptamine agonists and the antagonists: ketanserin and SCH 23390

Current literature suggests that the platelet 5-HT2 receptor, thought to be the only active platelet serotonin (5-HT) receptor, may be both heterogeneous and not the sole 5-HT receptor subtype on platelet membranes. The present studies used more selective tryptamine agonists, and the antagonists ketanserin and SCH 23390 to characterize rat platelet 5-HT receptors in vitro. The present studies also addressed anticoagulant effects (citrate versus heparin) on platelet 5-HT aggregation in the rat. 5-HT was less potent at enhancing ADP-induced aggregation in heparinized rat platelet rich plasma (PRP) as compared to citrated PRP. However, potency and maximum aggregation to ADP were greater in heparinized platelets. In citrated rat PRP, the selective tryptamine agonists, 5-carboxamidotryptamine (5-CT) and 2-CH3-5-HT, produced little change in the baseline ADP-induced aggregation and induced platelet shape change only in higher concentrations (greater than 1 microM). In contrast, alpha-CH3-5-HT-induced shape change and enhancement of ADP aggregation were superimposable with that of 5-HT itself suggesting 5-HT2 receptor activation. The antagonists, ketanserin and SCH 23390, inhibited 5-HT enhancement of ADP-induced aggregation with affinity constants consistent with the presence of 5-HT2 receptors as well. Studies with heparinized rat PRP did not unmask activity to 5-CT or 2-CH3-5-HT. Thus, although reports of multiple platelet 5-HT receptors exist, the only detectable, functional 5-HT receptor to enhance aggregation in rat platelets was probably of the 5-HT2 type.

Comparison of ketanserin and enalapril in the treatment of mild-to-moderate essential hypertension

In a double-blind 3-month study in mild-to-moderate essential hypertensive patients over 50 years of age, ketanserin, a selective S2-serotoninergic antagonist with additional alpha 1-adrenergic blocking properties, has been compared with enalapril, an angiotensin-converting enzyme inhibitor. Supine and upright blood pressures and heart rates were recorded for placebo and during active treatment (-4, -2, 0, 2, 4, 6, 8, 10, and 12 weeks). Metabolic profile (plasma glucose, creatinine, sodium, potassium, total and HDL-cholesterol, triglycerides, uric acid) was monitored during treatment with placebo and at the end of the study. Mean blood pressure was equally and significantly (p less than 0.001) lowered by both drugs from 2 weeks of treatment, whereas no changes occurred in mean heart rate or in biochemical variables. Dizziness was observed in three patients on ketanserin and in one patient on enalapril, whereas headache occurred in only one patient on enalapril. These data indicate that ketanserin is as effective and well tolerated as enalapril in hypertensive patients over 50 years of age.

Platelet function during long-term treatment with ketanserin of claudicating patients with peripheral atherosclerosis. A multi-center, double-blind, placebo-controlled trial. The PACK Trial Group

In a multi-center, double-blind, placebo-controlled trial in claudicating patients with peripheral atherosclerosis, the effects of 1 year of treatment with ketanserin (20 mg t.i.d. for 1 month, 40 mg t.i.d. thereafter; n = 63 patients) or placebo (n = 84 patients) on platelet function (aggregation in P.R.P. by 5-HT 5 x 10(-6) M, ADP 1 to 5 x 10(-6) M, collagen 2 micrograms/ml; platelet 5-HT content; plasma beta TG- and PF4-levels; serum TXB2) were analyzed. Before treatment, claudicating patients (n = 173) displayed an higher reactivity of platelets to 5-HT and signs of platelet activation/release in vivo (higher plasma beta TG-PF4, lower platelet 5-HT content and decreased platelet aggregation by ADP, collagen) in comparison with healthy controls (n = 50). After 1 year of treatment with ketanserin, but not with placebo, platelet aggregation induced by 5-HT (slope -41.1%) and platelet 5-HT content (-23.7%) were significantly reduced. PF4 and beta TG were significantly higher than their pre-medication values in the two trial groups. The other platelet function tests were not significantly modified by the treatment. Only the small subgroup of patients with initially elevated plasma beta TG levels (greater than 20 ng/ml) also scrutinized for hidden NSAID consumption or technical bias (exclusion of data with serum TXB2 less than or equal to 10000 pg/100 microliters and/or plasma PF4 greater than 10 ng/ml) had significantly lower plasma beta TG levels (-22.7%) than the pre-medication values after treatment with ketanserin, but not with placebo. The present study confirms that ketanserin affects some platelet functions, during long-term administration in claudicating patients with atherosclerosis.

Serotoninergic mechanisms in hypertension. Focus on the effects of ketanserin

Aggregating platelets release serotonin, which induces contraction of most vascular smooth muscle by activation of S2-serotoninergic receptors. Serotonin released in the circulation may contribute to the increase in peripheral resistance of hypertension as the responsiveness of blood vessels from hypertensive animals and humans to the vasoconstrictor action of the monoamine is augmented. The data obtained with the new antihypertensive agent ketanserin may favor that interpretation. Ketanserin is a selective S2-serotoninergic antagonist with additional alpha 1-adrenergic blocking properties. In humans, it has a terminal half-life of 12 to 25 hours and is eliminated predominantly by the liver. The hemodynamic profile of ketanserin is that of a vasodilator drug with actions on both resistance and capacitance vessels. On short-term intravenous administration, it lowers blood pressure in hypertensive patients with minimal reflex changes in cardiovascular function. When given orally long term to hypertensive patients, ketanserin causes a sustained reduction in arterial blood pressure, comparable to that obtained with either beta-adrenergic blockers or diuretics. Several studies have shown a greater efficacy in older (greater than 60 years of age) than in younger patients independent of starting pressure. Side effects mainly consist of dizziness, somnolence, and dry mouth, but they are usually not severe. The mechanism underlying the antihypertensive effect of ketanserin is unclear. It cannot be attributed to either S2-serotoninergic or alpha 1-adrenergic blockade alone, but an interaction between the two effects appears to be required.

The 5-hydroxytryptamine system of blood platelets: physiology and pathophysiology

The 5-hydroxytryptamine (5HT)-system of human blood platelets consists of a relatively specific uptake mechanism for 5HT at the plasma membrane, intracellular storage organelles (dense bodies), a metabolizing enzyme (monoaminoxidase B) and a 5HT2-receptor whose stimulation leads to activation of the phosphatidylinositide turnover, a rise in free cytoplasmic Ca2+, phosphorylation of proteins and a shape change reaction. There is neither a relevant 5HT-biosynthesis nor a marked physiological 5HT-turnover in platelets. Under physiological conditions the platelet 5HT-system may have a role as a scavenger for free extracellular 5HT and in hemostasis. Disturbances which have been described in pathophysiological states include impairment of 5HT-uptake (hypertension, migraine), impairment of 5HT-storage (storage pool deficiencies, thromboembolic disorders, hypertension) and increased sensitivity to activating agents like 5HT (cardiovascular disorders, diabetes). Besides their role in physiology and pathophysiology platelets may be useful partial models for vascular smooth muscle cells.

Effects of ketanserin, a selective 5-HT2 serotonergic antagonist, on the secondary recruitment of human platelets in vitro

Ketanserin, a selective 5-HT2 serotonergic receptor antagonist, reduces in vitro the release-associated human platelet aggregation induced by threshold concentrations of collagen and curtails the second wave of aggregation/release induced by critical concentrations of ADP in particular and, to a lesser extent, of 1-epinephrine. Its inhibitory effect on the second waves becomes more pronounced when the reaction is already attenuated by moderate cyclo-oxygenase inhibition with esculetin, by yohimbine or by propranolol. The first wave of aggregation induced by ADP or 1-epinephrine is not affected. Such an inhibition of secondary platelet recruitment by ketanserin in vitro may be due to an inhibition of the 5-HT2 receptor-mediated amplifying effects of platelet-released 5-HT or to a non-specific interference with the platelet membrane, reducing the release of mediators from the platelets. Reduction of the increased plasma BTG levels in patients after ketanserin may result from such release-inhibiting mechanisms.