Bernard-Soulier-like functional platelet defect in myelodysplastic syndrome and in acute myeloblastic leukemia associated with trilineage myelodysplasia

Platelet function was studied in a child with myelodysplastic syndrome (MDS: refractory anemia with an excess of blasts) and a child with acute myeloblastic leukemia (AML-M6) associated with trilineage myelodysplasia (TMDS). An acquired Bernard-Soulier-like platelet defect was considered in both patients with the findings of prolonged bleeding time and abnormally large platelets that failed to aggregate in response to ristocetin. In contrast to findings in von Willebrand's disease, the abnormal response of platelets to ristocetin could not be corrected by the addition of normal flesh plasma. The detection of abnormal platelet aggregation response to ristocetin may be a useful diagnostic finding for clonal disorders causing impaired platelet function in MDS and coexistent TMDS associated with AML. Further studies of ristocetin-induced platelet aggregation in a large number of these patients are required.

5-HT1-like and 5-HT2A receptors mediate 5-hydroxytryptamine-induced contraction of rabbit isolated mesenteric artery

The contractions induced by 5-hydroxytryptamine (5-HT) and the 5-HT1-like receptor agonist, sumatriptan, were investigated in the open ring preparations of rabbit mesenteric artery in order to characterize the 5-HT receptors. 5-HT induced concentration-dependent contractions. Sumatriptan did not induce any contraction of unstimulated rings, whereas it elicited concentration-dependent contractions in preparations given a moderate tone by a threshold concentration of prostaglandin F2 alpha (PGF2 alpha). Pargyline, cocaine or normetanephrine were without significant effect on the contractions induced by 5-HT and sumatripan. The 5-HT concentration-effect curve was clearly biphasic. Methiothepin (0.01 microM) shifted the both phases of the concentration-effect curve to the right. Ketanserin (0.1 microM) shifted the second, low affinity, phase and prazosin did not alter concentration-effect curve to 5-HT. The sumatriptan concentration-effect curve was shifted by methiothepin (0.01 microM) to the right (pKB = 9.19) but not by ketanserin (1 microM). Concentration-effect curves to 5-HT and sumatriptan were not affected by the 5-HT3 receptor antagonist tropisetron (1 microM). These results suggest that 5-HT1-like type receptors are responsible for the first phase of 5-HT-induced contraction and 5-HT2A receptor for the second phase, in rabbit mesenteric artery. Sumatriptan-induced contractions appear to be mediated by 5-HT1-like type receptors in this artery. These results also suggest that this kind of amplification may be a common feature of vascular 5-HT1-like type receptor as has been shown in other vascular segments such as rabbit femoral, iliac and renal arteries, and guinea-pig iliac artery.

Effect of nitrovasodilators on the rhythmic contractions of guinea-pig isolated sphincter of Oddi

The effects of amyl nitrite (CAS 8017-89-8) isosorbide dinitrate (CAS 87-33-2) and sodium nitroprusside (CAS 14402-89-2), on the acetylcholine-induced tachyrhythmia (greater than 9 waves/min) were investigated in the isolated guinea-pig sphincter of Oddi. Acetylcholine (10(-3) mol/l) produced an initial rapid rise in tension, the peak being followed by a gradual decrease associated with the initiation of the peristaltic waves. Nitrovasodilators significantly decreased the initial response to acetylcholine. Methylene blue (5 x 10(-5) mol/l), a soluble guanylate cyclase inhibitor, increased the tonic response to acetylcholine and reversed the inhibition caused by nitrovasodilators. The frequency and amplitude of peristaltic waves were decreased by nitrovasodilators. Methylene blue significantly increased both the frequency and amplitude of peristaltic waves, however, it did not reverse the inhibition caused by nitrovasodilators tested. Results suggest that nitrates decrease the acetylcholine-induced contraction and peristaltism of isolated guinea-pig sphincter of Oddi and NO released by acetylcholine may partially suppress its own tonic contractile response.

Cyclosporin A and Cremophor-EL augment renal vascular responses to various agonists and nerve stimulation

The acute actions of cyclosporin A and its solvent Cremophor-EL on the rise of perfusion pressure induced by periarterial stimulation were studied in the rabbit isolated kidney. Thirty-second stimulations were used and the parameters were 1-25 Hz, 5 msec duration, and 15 V. The responses to periarterial stimulation were frequency-dependent. Noradrenaline (0.01-20 microgram) induced similar effects when given into the renal artery. Clonidine (10(-7)M), added to the perfusion medium, inhibited the responses to periarterial stimulation without altering the effect of noradrenaline. Cyclosporin A (10(-7)-4 x 10(-5)M), added to the perfusion medium, potentiated the responses both to periarterial stimulation and exogenously given noradrenaline and restored the responses to clonidine (10(-7)M). The effects of cyclosporin A and Cremophor-EL on the responses to various contractile agonists (potassium chloride, phenylephrine, serotonin and angiotensin II) were also studied in the rabbit isolated renal artery. The results suggest that cyclosporin A may exert a direct action on the vasculature rather than an action on the vascular adrenergic neurotransmission of the rabbit kidney.

Amplification of responses to sumatriptan by various agonists in rabbit isolated iliac artery

Rabbit iliac arteries (IA) were almost unresponsive to the serotonin (5-HT1-like) receptor agonist sumatriptan under control conditions, whereas this agent elicited concentration-dependent contractions in IA rings given a moderate tone by threshold concentrations (EC10-EC20) of prostaglandin F2 alpha (PGF2 alpha), angiotensin II (AII), histamine, norepinephrine (NE), phenylephrine (PE), or potassium chloride. These results suggest that 5-HT1-like receptors are uncovered not only by histamine or thromboxane/prostaglandin receptor agonists, as shown in rabbit renal and femoral arteries, but also by various agonists in rabbit IA as shown in this study.

The effect of indomethacin on cyclosporin A- and its solvent-induced inhibition of endothelium-dependent relaxation and the drug-induced contraction of rabbit isolated arteries

1. In the isolated rabbit arteries, the effects of intravenous cyclosporin A preparation (Sandimmun) and its solvent (Cremophor-EL) on acetylcholine-induced endothelium-dependent relaxation were investigated in the absence and presence of indomethacin (10(-5) M), a cyclooxygenase inhibitor. 2. The effect of indomethacin on the drug- and solvent-induced contraction of superior mesenteric artery was also evaluated. 3. The inhibitory effects of cyclosporin and the solvent on endothelium-dependent relaxations were decreased by indomethacin. The direct contractions produced by the drug and the solvent in rabbit mesenteric artery were inhibited by indomethacin.

The action of amyl nitrite and isosorbide dinitrate on the contractility of sphincter of Oddi of guinea-pigs

1. This study was designed to investigate whether relaxation of isolated guinea-pig sphincter of Oddi preparation by nitrates is mediated by guanylate cyclase activation indirectly by nitric oxide (NO), as in vascular tissues. 2. Sodium nitroprusside, isosorbide dinitrate and amyl nitrite induced dose-dependent relaxations of Oddi's sphincter precontracted by potassium chloride (150 mM). Methylene blue (5 x 10(-5) M), an inhibitor of guanylate cyclase, did not significantly inhibit the relaxations caused by nitrovasodilators. 3. Unlike potassium chloride, acetylcholine (10(-7) - 10(-3) M) induced unsustained contractions which were significantly increased by methylene blue. NG-monomethyl-L-arginine (L-NMMA; 4 x 10(-4) M), an inhibitor of NO biosynthesis, also increased the contractile response to acetylcholine. 4. These results suggest that another mechanism rather than inhibition of guanylate cyclase is involved in the nitrovasodilators-induced relaxations and that acetylcholine releases a relaxing factor, possibly NO, that may modulate its own contraction in this preparation.

Comparison of the effect of endothelium on the responses to sumatriptan in rabbit isolated iliac, mesenteric and carotid arteries

The contractions induced by the 5-hydroxytryptamine (5-HT) and 5-HT1-like receptor agonist sumatriptan in open ring segments of rabbit iliac, mesenteric and common carotid arteries were studied isometrically in vitro. The alteration of the responses by removal of the endothelium and by inhibitors of nitric oxide synthase and cyclooxygenase was investigated. 5-HT induced concentration-dependent contractions of all these three arterial segments. Sumatriptan did not induce any contraction of quiescent mesenteric and iliac arteries, but when a moderate tone was given with a threshold concentration of prostaglandin F2 alpha, it elicited contractions of both arteries (Emax values for sumatriptan in mesenteric and iliac arteries were 84.7% and 29.7% of the phenylephrine maximal effect and EC50 values were 0.22 +/- 0.14 and 0.33 +/- 0.06 microM, respectively). Sumatriptan had no contractile effect at all in carotid arteries in which 5-HT-induced contractions seemed to be mediated by 5-HT2 receptors only. Removal of the endothelium did not affect the responses to 5-HT in iliac, mesenteric and carotid arteries. The contractions induced by sumatriptan were not influenced by removal of the endothelium in the mesenteric artery, while sumatriptan responses were potentiated in the endothelium-denuded preparations of the iliac artery (Emax = 50.8% of the phenylphrine maximal effect; EC50 = 0.46 microM). L-NG-monomethyl arginine (100 microM), a nitric oxide synthase inhibitor, also potentiated the sumatriptan responses in the endothelium-intact segments of the iliac artery. Indomethacin (0.1 microM), a cyclooxygenase inhibitor, did not affect the sumatriptan responses. These results suggest that sumatriptan-induced contractions of the rabbit iliac, but not mesenteric artery, were depressed by itself through the release of nitric oxide upon stimulation of 5-HT1-like receptors located on the endothelium, whereas neither on vascular smooth muscle nor on endothelium, 5-HT1-like receptors were present in the rabbit carotid artery.

Direct vascular smooth muscle contractile effect of cyclosporin A and its vehicle in rabbit isolated arteries

cyclosporin A is a widely used immunosuppressant agent which has direct vascular effects such as contraction of the arterial smooth muscle and potentiation of other vasoconstrictor agents. In rabbit isolated arterial segments, the contractile effects of a cyclosporin A preparation (Sandimmun; 10(-6) M) and its solvent (Cremophor-EL) were investigated. Both caused an increase in the basal tension of arterial segments after an incubation period of 1 hour. Several substances were tested to antagonize the contractile activity of the cyclosporin A preparation and its solvent. Prednisolone and quinacrine (phospholipase A2 inhibitors), indomethacin (cyclooxygenase inhibitor), verapamil (calcium antagonist), phentolamine (alpha-adrenoceptor blocker), captopril (angiotensin-converting enzyme inhibitor) and prazosin (alpha 1-adrenoceptor-blocking agent) decreased the contractile responses to the cyclosporin A preparation and its solvent in a comparable manner. These findings indicate that the solvent of the cyclosporin A preparation is responsible for the contractile effect of this latter preparation and that this contractile activity cannot be explained by a single mechanism.

Kostmann's syndrome with chronic pneumonia and lymphocytosis: effect of recombinant human G-CSF

Kostmann's syndrome is a congenital disorder characterized by impairment of myeloid differentiation in bone marrow with severe absolute neutropenia. A 17-month-old girl was admitted to the hospital with complaints of recurrent skin infections since birth and severe pneumonia of the right lung which had been resistant to antibiotics since the patient was eight months old. Anemia, severe neutropenia and maturational arrest of granulocytes at the myelocyte stage in bone marrow were detected. At the age of 20 months, a right pneumonectomy was performed because of resistant cystic infection. Postoperatively, she was diagnosed with Kostmann's syndrome. Recombinant human granulocyte-colony-stimulating factor (rhG-CSF) was administered intravenously at a dose of 3 micrograms/kg/day, gradually increasing to 60 micrograms/kg/day in sequential seven-day courses to obtain a neutrophil count of more than 500 cells/mm3. Absolute neutrophil counts increased to greater than 1000 cells/mm3 at a dose of 60 micrograms/kg/day, and at that time bone marrow aspiration revealed an increase in neutrophilic granulocytic precursors beyond the myelocyte stage. In order to maintain the neutrophil response, a dose of 20 micrograms/kg/day rhG-CSF subcutaneously was continued successfully. The patient has tolerated rhG-CSF treatment without complications, and infectious attacks have significantly decreased.

Characterization of 5-hydroxytryptamine receptors in rabbit isolated iliac artery

To characterize the 5-hydroxytryptamine (5-HT) receptors, the contractile effects of both 5-HT and the 5-HT1-like receptor agonist sumatriptan were investigated in isolated open ring preparations of the rabbit common iliac artery. 5-HT induced concentration-dependent contractions. Sumatriptan did not induce any contraction of unstimulated preparations, whereas it elicited concentration-dependent contractions in preparations given a moderate tone with a threshold concentration of prostaglandin F2 alpha. In vessel segments precontracted with prostaglandin F2 alpha, Emax values for 5-HT and sumatriptan reached about 85% and 30% of the phenylephrine maximal effect, respectively. The mean EC50 values for sumatriptan and 5-HT were 3.34 microM and 1.5 microM, respectively. Pargyline, cocaine or normetanephrine were without significant effect on the contractions induced by 5-HT or sumatriptan. The 5-HT3 receptor antagonist tropisetron (1 microM) had no effect on 5-HT- and sumatriptan-induced contractions. The 5-HT2 receptor antagonist ketanserin (0.1-1 microM) produced parallel displacements to the right of the 5-HT and phenylephrine concentration-effect curves, without significant reduction in the maximum responses. The pA2 values were 7.85 +/- 0.19 and 7.9 +/- 0.16, respectively. Ketanserin had no effect on the sumatriptan concentration-effect curves. The nonselective 5-HT receptor antagonists methysergide (0.3 microM) and methiothepin (0.01 microM) shifted the concentration-response curve to sumatriptan to the right (mean pKB values of 6.91 and 8.68, respectively). The pA2 value for prazosin against 5-HT (9.98 +/- 0.43) was not significantly different from the value against phenylephrine (9.27 +/- 0.20). These results suggest that the sumatriptan-induced contraction is mediated by a 5-HT1-like receptor, whereas an additional mechanism, probably an alpha 1-adrenoceptor stimulation, plays a role in the contraction induced by 5-HT in the rabbit iliac artery.

Response to the endothelium-dependent vasodilator acetylcholine in perfused kidneys of normotensive and spontaneously hypertensive rats

The possible role of endothelium-derived relaxing factor (EDRF) was investigated in resistance vessels of the kidney obtained from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Kidneys were studied in parallel and perfused with Tyrode's solution at constant optimal flow rates. In the presence of indomethacin, during vasoconstriction (increase in perfusion pressure) produced by prostaglandin F2 alpha, acetylcholine caused a graded dilatation (pressure fall) that was greater in kidneys of WKY than of SHR. Methylene blue and hydroquinone, but not oxyhemoglobin, inhibited the decreases in perfusion pressure induced by acetylcholine, but not those by papaverine. The results suggest that part of the renal vasodilatation induced by acetylcholine is mediated by endothelium-derived relaxing factor, and that the response is impaired in the resistance vessels of the hypertensive rat kidney.

Serotonin releases a vasoconstrictor prostanoid in the kidney of the aging spontaneously hypertensive rat

The isolated and perfused kidney of the spontaneously hypertensive rat (SHR) exhibits an increased vascular reactivity to serotonin when compared to normotensive Wistar-Kyoto (WKY) rats. Experiments were designed to determine the involvement of a prostanoid constricting factor in the augmented response to serotonin in the SHR kidney. Kidneys taken from male (12 months) SHR and WKY rats were studied in parallel and perfused with Tyrode's solution at constant, optimal flow rates. Vasoconstrictor response were recorded as increases in perfusion pressure. The dose-response curves to serotonin obtained in the SHR were shifted to the left compared to the WKY. Indomethacin decreased the responses to the smaller doses of serotonin in the SHR, but increased those to the higher doses of the monoamine in the WKY. The responsiveness to the monoamine was no longer significantly different in the two strains in the presence of the inhibitor of cyclooxygenase. Dazoxiben, an inhibitor of thromboxane synthetase, did not alter the responses to serotonin in either the WKY and SHR kidneys. These experiments suggest that a prostanoid, but not thromboxane A2, may play a role in the augmented response to serotonin in the kidney of aged SHR.

Actions of cyclosporin A preparation and Cremophor-EL in rabbit mesenteric artery and thoracic aorta in vitro

1. We studied the in vitro and direct effects of intravenous cyclosporin A preparation (Sandimmun) and its solvent (Cremophor-EL) on acetylcholine-induced endothelium-dependent relaxation, phenylephrine-induced contraction and drug-induced contraction of rabbit thoracic aorta and superior mesenteric artery segments. 2. At the lower concentration (5 micrograms/ml), cyclosporin A preparation inhibited endothelium-dependent relaxation of the superior mesenteric artery but not of the thoracic aorta. At this concentration cyclosporin A preparation augmented phenylephrine-induced contraction in both segments but by more in the superior mesenteric artery, and induced a slow increase in the tone of isolated superior mesenteric artery and thoracic aortic rings, which was greater in magnitude in the superior mesenteric artery than in the thoracic aorta. 3. Acetylcholine-induced endothelium-dependent relaxation was inhibited by cyclosporin A preparation (50 micrograms/ml) in both arteries but to a greater extent in the superior mesenteric artery. 4. The solvent of the intravenous cyclosporin A preparation (Cremophor-EL) in concentrations corresponding to those of the drug caused less inhibitory effects than cyclosporin A preparation on acetylcholine-induced endothelium-dependent relaxation, had comparable effects on phenylephrine-induced contraction, and produced similar contractions of both arteries. 5. The results indicate that Cremophor-EL may contribute to the inhibitory action of cyclosporin A preparation on acetylcholine-induced endothelium-dependent relaxation in the superior mesenteric artery, but is fully responsible for the smooth-muscle-contracting effect and the potentiation of phenylephrine-induced contraction in both arteries.

Heterogeneity of 5-HT responsiveness in different segments of rabbit arteries

The variation in sensitivity to serotonin (5-HT) as assessed by pD2 was investigated in isolated 25 arterial segments of different vascular regions obtained from rabbits. The responses of the vascular rings which were opened by a transverse cut to form rectangular strips were recorded isometrically. pD2 values for 5-HT of thoracic and abdominal aortic segments were significantly greater than those of visceral arterial branches. Maximal contractions produced by 5-HT in visceral segments were higher than those of thoracic and abdominal aortic segments. There was a positive correlation between the pD2 values for 5-HT and the radii and the thickness of the tunica media layer (r = 0.62 and r = 0.54, respectively, P less than 0.05). The results indicate that the activity of 5-HT varies regionally in different segments of the rabbit arteries and the sensitivity to 5-HT of the segments decreases as the radii of the vessels diminish.

Role of prostanoids in the increased vascular responsiveness and delayed tachyphylaxis to serotonin in the kidney of spontaneously hypertensive rats

The isolated and perfused kidney of the spontaneously hypertensive rat (SHR) exhibits an increased vascular reactivity and a delayed tachyphylaxis to serotonin (5-hydroxytryptamine) when compared with normotensive Wistar-Kyoto (WKY) rats. Experiments were designed to determine the involvement of products of cyclooxygenase in the augmented response and delayed tachyphylaxis to serotonin in the SHR kidney. Kidneys taken from male, 4-month-old SHR and WKY rats were studied in parallel and perfused with Tyrode's solution at constant, optimal flow rates. Vasoconstrictor responses were recorded as increases in perfusion pressure. The vasoconstrictor responses to serotonin, norepinephrine and angiotensin II were exaggerated in the SHR kidney compared with that of the WKY rat. Indomethacin did not affect the responsiveness to serotonin in the kidney of the SHR but increased the responses to the higher doses of the monoamine in the kidney of the WKY rats. Indomethacin accelerated the tachyphylaxis to serotonin in the SHR but delayed it in the WKY rats. Dazoxiben did not alter the responses to serotonin in the SHR. Responses to norepinephrine in the kidneys from both strains were not affected by indomethacin. The inhibitor of cyclooxygenase reduced the responses to angiotensin II in the kidneys from both hypertensive and normotensive animals. The basal and stimulated (serotonin, norepinephrine and angiotensin II) release of prostaglandins were measured by radioimmunoassay. The basal release of prostacyclin was lower, but that of thromboxane A2 higher, in the kidneys of SHR compared with those of WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Antiplatelet antibodies in childhood idiopathic thrombocytopenic purpura

Antiplatelet antibodies were shown by the Handin and Stossel method in the sera of all 103 patients with acute idiopathic thrombocytopenic purpura (ITP) and in 100 cases following recovery from it. These antibodies were also shown in the sera of all 46 patients with chronic ITP and 32 cases after recovery. The decrease in level of antiplatelet antibodies was significant in all these children following recovery (P less than 0.001 for acute ITP, P less than 0.05 for chronic ITP). Antiplatelet antibodies could be determined in 67 acute and 21 chronic ITP cases in thrombocytopenic phase and following recovery, which showed very significant decreases in levels in each case in a later period. Antiplatelet antibody levels corresponding to the thrombocytopenic phase and recovery in acute and chronic ITP were significantly higher than normal and thrombocytopenic control values (P less than 0.001 for each).

Sulphamethoxazole acetylation in fast and slow acetylators

Acetylation of sulphamethoxazole was studied in 22 subjects previously phenotyped with sulphadimidine. Sulphamethoxazole and its acetylated metabolite were measured in 6 h plasma and 0-6 h urine samples. Percentage of plasma acetylated-sulphamethoxazole did not correlate with the percentage of urinary acetylated-sulphamethoxazole. There was also no correlation between the percentage of acetylated-sulphadimidine and percentage of acetylated-sulphamethoxazole in plasma. The finding suggest that the acetylation of sulphamethoxazole has no predictive value in determining acetylator status.

Dopamine receptor agonists, N,N-dipropyl-2-aminotetralin (TL-68) and 2-di-n-propylamino-4,7-dimethoxyindane (RDS-127) antagonize oxotremorine-induced tremors by antimuscarinic action in mice

Central antimuscarinic actions of dopamine receptor agonists: N,N-dipropylaminotetrain (TL-68) and 2-di-n-propylamino-4,7-dimethoxyindane (RDS-127), were evaluated against oxotremorine-induced tremors in mice. Both TL-68 and RDS-127 inhibited the tremor intensity but were less potent than atropine.

N-acetylation phenotyping with sulphadimidine in a Turkish population

The distribution of acetylator phenotypes was studied in 244 unrelated Turkish subjects. Sulphadimidine and its acetylated metabolite were measured in 6 h plasma and 0-6 h urine samples after an oral dose of 10 mg/kg. Subjects with 37.5% or less acetylsulphadimidine in plasma were regarded as slow acetylators and the others as rapid acetylators. The mean plasma concentration of acetylsulphadimidine was about 2.5-times lower in slow acetylators. Urinary excretion of total sulphadimidine (free + acetylated) was also significantly lower in slow acetylators compared to rapid acetylators. The frequency of slow acetylators was 60.7% in the population (95% confidence interval 54.3% to 66.8%). Sulphadimidine acetylation showed no variation due to sex, age, body weight or pre-existing disease.

Influence of temperature on the responses to serotonin (5-HT) in perfused rat lung

The effects of serotonin (5-HT) on the perfusion pressure of the isolated rat lung was investigated at 2 different temperatures (37 degrees C and 15 degrees C). 5-HT (1-30 micrograms) increased the perfusion pressure dose-dependently and a biphasic vasoconstrictor response appeared with the doses of 3-30 micrograms at 37 degrees C. Both phases were only blocked by methysergide (5 X 10(-10) M) among the 5-HT antagonists tested. At 15 degrees C, 5-HT (0.3-30 micrograms) elicited a similar response but the second phase appeared with the higher doses of the agonist compared to that at 37 degrees C. The initial phase, which was significantly higher than that at 37 degrees C, was antagonized by ketanserin, mianserin, pizotifen and methysergide in a noncompetitive manner. The order of potencies of the 4 serotonergic antagonists was compared with their affinity for central 5-HT receptors. The results led us to conclude that receptors mediating the initial phase of the vasoconstrictor response to 5-HT at 15 degrees C are neither of the 5-HT1 nor of the 5-HT2 type, but are 5-HT1 ones at 37 degrees C in the rat pulmonary vascular bed.

Beta-adrenoceptor stimulating effects of phenylephrine and noradrenaline in the rat pulmonary vascular bed

The effects of phenylephrine and noradrenaline have been investigated on the perfusion pressure of the rat isolated lung. Both drugs (0.3-30 micrograms) produced a dose-dependent decrease in perfusion pressure elevated by 20 mM KCl, which was reversed to a dose-dependent increase after addition of propranolol (1 x 10(-7) M) to the perfusion fluid. Increments due to both agonists in the presence of propranolol were antagonized by prazosin (1 x 10(-6) M). Propranolol, but not prazosin, elevated the basal perfusion pressure. The results indicate that phenylephrine and noradrenaline are more effective in stimulating beta-adrenoceptors than alpha-adrenoceptors in the rat pulmonary vascular bed and that beta-adrenoceptors may regulate the vascular tone of the rat pulmonary circulation.

Are there any presynaptic 5-HT receptors in frog atria?

The effect of 5-hydroxytryptamine (5-HT) on the stimulation-induced inotropic responses was investigated in the isolated frog atria and ventricles. 5-HT (1 X 10(-5)-2 X 10(-4) M) inhibited the contractile responses elicited by intramural nerve stimulation (INS) in atria. The inhibitory action of 5-HT was antagonized by raising the external Ca++ concentration. Pizotifen and methysergide (1 X 10(-6) M) antagonized the inhibitory action of 5-HT on high frequency INS responses. Higher concentrations of methysergide by itself depressed the responses to low frequency INS. Ketanserin, metoclopramide and phentolamine (1 X 10(-6) M) failed to antagonize the inhibitory action of 5-HT. The results suggest that the inhibitory effect of 5-HT in frog atria is mediated through a subtype of 5-HT receptors which is neither of 5-HT2 nor of "M" type but may correspond to the 5-HT1 subtype of serotoninergic receptors. In contrast with atria, 5-HT-induced inhibition of INS responses was not observed in frog ventricles.

Receptor mechanisms for 5-hydroxytryptamine in isolated human umbilical artery and vein

In order to characterize the 5-hydroxytryptamine (5-HT) receptors, the contractile effects of both 5-HT and alpha-adrenoceptor agonists were studied in helically-cut human umbilical artery and vein in the presence of different antagonists. Noradrenaline, phenylephrine and clonidine caused maximum contractions in vein amounting to only 9%, 14% and 11% of the maximum effect of 5-HT, respectively. The maximum effects of noradrenaline and phenylephrine in artery were only 18% and 29% of that of 5-HT. Clonidine failed to induce contractions in the artery. The alpha 1-adrenoceptor blocker, prazosin (1 X 10(-6) and 1 X 10(-5)M) did not antagonize 5-HT-induced contractions in the tissues studied. However, yohimbine, an alpha 2-adrenoceptor blocker, shifted the concentration-effect curves of the 5-HT to the right without any reduction in the maximum responses in both tissues. The pA2 values for yohimbine against 5-HT (6.46 and 6.72 in artery and vein, respectively) were different from the values for yohimbine against alpha 2-adrenoceptor agonists (8.2 and 8.6 against clonidine and M-7, respectively) in dog saphenous vein which contains postsynaptic alpha 2-adrenoceptors. 5-HT2 receptor antagonists, ketanserin (1 X 10(-7)-1 X 10(-6)M) and mianserin (1 X 10(-7)-1 X 10(-6)M) competitively antagonized 5-HT-induced contractions in both tissues. The pA2 values for ketanserin (7.89 and 7.86 in artery and vein, respectively) and mianserin (8.06 and 7.73 in artery and vein, respectively) were significantly lower than those obtained in other tissues which were shown to contain 5-HT2 receptors by the other authors. The results suggest that alpha-adrenoceptors play a minor role in 5-HT-induced contractions in both tissues. Yohimbine antagonized 5-HT action competitively, by blocking probably 5-HT receptors. The results also indicate that 5-HT receptors in human umbilical vessels are less sensitive to certain 5-HT2 antagonists than those of other tissues. A third subtype of 5-HT receptors different from the 5-HT1 and 5-HT2 receptors may be present in the human umbilical artery and vein.

Serotonin-induced contraction of canine saphenous vein: mediation by 5-HT1 receptors

The action of serotonin (5-HT) on alpha 1- and alpha 2-adrenoceptors was investigated on the isolated dog saphenous vein strip. Prazosin (1 X 10(-6) and 1 X 10(-5) M), an alpha 1-adrenoceptor blocker, did not alter 5-HT-induced contractions. However, yohimbine (1 X 10(-6) and 1 X 10(-5) M), an alpha 2-adrenoceptor blocker, shifted the concentration-response curve of 5-HT to the right without any reduction in the maximum response. The pA2 value for yohimbine against 5-HT (7.61 +/- 0.28, mean +/- S.E.M.) is different from the value for yohimbine against clonidine (8.35 +/- 0.08) or M-7 (8.58 +/- 0.07), a substance which stimulates postsynaptic alpha 2-adrenoceptors. Mianserin (1 X 10(-8)-1 X 10(-6) M) and ketanserin (1 X 10(-7)-1 X 10(-5) M) antagonized 5-HT-induced contractions noncompetitively. The results suggest that yohimbine competitively antagonizes 5-HT action by blocking probably 5-HT1 receptors, independently from its alpha 2-adrenoceptor blocking effect.

Acute leukemia in two patients with hemophilia

A 10-year-old classic hemophiliac and 1.5-year-old child with hemophilia B who developed acute lymphocytic and acute myelomonocytic leukemia respectively are presented. No changes in coagulation status of the patients were observed. It is suggested that hemophiliacs should be regarded as "population at risk" for the development of leukemia.

The interaction between metoclopramide and dopaminergic agonists at the level of sympathetic ganglion

The interaction of metoclopramide and two dopaminergic agonists, dopamine and apomorphine, was investigated on ganglionic transmission at the superior cervical ganglion of the anaesthetized cat. Dopamine (100 micrograms, i.a.) and apomorphine (100 micrograms, i.a.) decreased the height of action potential induced by supramaximal preganglionic stimulation. Metoclopramide (3 mg/kg, i.v.) antagonized the inhibition caused by dopamine and apomorphine. But it did not alter the transmission block caused by hexamethonium (100 micrograms, i.a.) or noradrenaline (100 micrograms, i.a.). The results suggest that dopamine-induced inhibition of the ganglionic transmission is related to the activation of dopaminergic receptors of the ganglion cells.

Effects of pyridine and some of its derivatives on prostaglandin synthesis

Effects of pyridine and some of its derivatives namely, nicotinic acid, nicotinyl alcohol, pyridinol carbamate, pyridoxine hydrochloride and pyridostigmine bromide were investigated on the release of a prostaglandin E2-like substance (PGE2-LS) from the isolated perfused rat heart. Furthermore, the effect of neostigmine bromide was also studied as a non-pyridine control compound. At 2 X 10(-5) M concentration, only pyridoxine hydrochloride stimulated the release of PGE2-LS significantly. At 2 X 10(-4) M concentration, pyridine, nicotinic acid and pyridinol carbamate were also found to be active in addition to pyridoxine hydrochloride. At 1 X 10(-3) M concentration, pyridine and all of its derivatives studied increased the release of PGE2-LS significantly. However, neostigmine bromide (1 X 10(-3) M) failed to exert any effect. Indomethacin, a prostaglandin synthetase inhibitor, reduced both the basal release (28%) and the release stimulated by pyridine and its derivatives at 1 X 10(-3) M concentration (more than 50%). These findings suggest that the active substance released is a prostaglandin. It is concluded that the PGE2-LS releasing effect of pyridine and its derivatives from isolated rat heart may be due to the action of the pyridine moiety of the molecules of the compounds studied.

The reversal by metoclopramide of apomorphine-induced inhibition of responses to stimulation of the cardioaccelerator nerves in the cat

The effect of metoclopramide on presynaptic dopamine receptors was investigated in the cat cardioaccelerator nerve preparation. Metoclopramide, a substituted benzamide derivative, antagonized inhibitory action of apomorphine on positive chronotropic responses induced by sympathetic nerve stimulation in cat hearts, in vivo. Neither phentolamine, an alpha-adrenergic blocking agent, nor indomethacin a prostaglandin synthesis inhibitor, antagonized the effect of apomorphine. Apomorphine did not alter the positive chronotropic effects of intravenously administered noradrenaline. Metoclopramide potentiated stimulation-induced positive chronotropic responses. These results suggest that metoclopramide blocks the presynaptic dopamine receptors at the cat heart.