Altered extracellular magnesium and variations in vascular smooth muscle responses to agonists

Background: There is a paucity of information on the heterogeneity of vascular smooth muscles in their responses to agonists following exposure to varying extracellular magnesium, [Mg2+]0. The present study was designed to examine, comparatively, the influence of variations in [Mg2+]0 on vascular smooth muscles of rabbit aortic, carotid and femoral arteries. Methods: Contractile responses induced by Phenylephrine (PE), Histamine (HIST) and 5-HydroxylTryptamine (5-HT) were examined on 2mm ring segments of the arteries which were suspended in 20 ml organ baths containing physiological salt solution (PSS), for measurement of isometric contractions, at 37oC and pH 7.4. The medium was bubbled with 95% O2, 5% CO2+, and rings were given an initial load of 2g. Cumulative concentration responses to the agonists were studied in normal PSS (control) and following 30 minutes exposure to Mg2+-free or high-Mg2+ (4.8mM) PSS. Contractile responses were expressed as percentage of 80 mM K+ contractions in normal PSS. Results: Maximal contractions (Emax) induced by PE, HIST and 5-HT compared with high K+ contraction in the various preparations were differentially altered (p<0.05) following exposure to varying [Mg2+]o. Conclusion: Based on the sensitivity (EC30) and potency (EC50) values for the dose-response curves of the agonists, we report that vascular smooth muscles of rabbit aortic, carotid and femoral arteries demonstrate considerable variability in their responses to altered [Mg2+]o.Keywords: Vascular smooth muscle, Extracellular magnesium, Phenylephrine, Histamine, 5-Hydroxytryptamin

Review: Vascular Effects of Histamine

Four subtypes of receptors (HFour subtypes of receptors (H1, H2, H3 and H4) mediate the actions of histamine. In the vascular wall, the effects of histamine are mediated via H1 and H2 receptors and the actions are modulated by H3 receptor subtype located on presynaptic neurones. Alterations in vascular responses to histamine are associated with experimental as well as a human form of hypertension, suggesting a role for histanine in cardiovascular regulation.Keywords: Histamine, Vascular smooth muscle, Endothelium

Prevalence Of Visual Disorders In Deaf Children In Benin City

The most developed and most important of the special senses of the body is the sense of sight and hearing, both of which are predisposed to gradual impairment in the absence of the other. It has been shown that the occurrence of either visual impairment and deafness or hearing loss existing independently or co-existinghave potential complications inthephysicalwellbeingof anindividual child. Of the 86 students examined in this research, 34(39.53%) were males while 52(60.47%) were females. However, 63(73.26%) subjects of the total population studied had visual disorders. The Pearson Correlation coefficient result of -0.77 showed a negative association in the distribution between age and visual disorders. It is thus advocated that prompt attention and treatment be paid to visual abnormalities inthe hearing impaired child at an early age

Enhanced Phenylephrine Contractions in Rabbit Carotid Arteries Following Exposure to Haemoglobin from Subjects with Sickle Cell Trait.

We have previously reported raised resting diastolic blood pressure (BP) in subjects with single S-gene inheritance – although the mechanism was unclear. The goal of this study was to characterize, in vitro, the modulatory role of erythrocyte components from subjects with different Hemoglobin (Hb) genotypes on contractile responses induced by phenylephrine (PE) in isolated rabbit carotid arterial smooth muscle. Carotid arteries were isolated from rabbits and cut into 2mm rings, suspended in 20ml organ baths and bubbled with 95% O2, 5% CO2 and isometric contractions examined under an initial load of 1g, at 37oC and pH 7.4. Contractile responses to EC70 (M) PE in arterial rings exposed to various erythrocyte components obtained from subjects of different Hb genotypes (AA, AS and SS) were examined in control rings as well as in rings exposed for 30 minutes to (a) intact washed erythrocytes (b) erythrocyte ghosts and (c) haemoglobin solution. Arterial rings were exposed to 50μl of each of the erythrocyte constituents at an adjusted haematocrit of 0.6. The magnitudes of the PE-induced contractions with intact erythrocytes were: 1180±202, 1700±260 and 900±302 for Hb AA, Hb AS and Hb SS respectively (n=13); these values were significantly increased following exposure to various erythrocyte components in the order: RBC> HB > Ghost (P<0.05, respectively). There were no significant differences in PE contractions following exposure to intact erythrocytes and ghosts from subjects with different Hb genotypes; however, exposure to haemoglobin solution significantly enhanced PE contractions in Hb AS subjects than in Hb AA and Hb SS (P<0.05 respectively). In conclusion, we reason that the haemoglobin content of Hb AS erythrocytes may be responsible for the enhanced contractile responses to PE and may explain in part, why diastolic BP values remain high in Hb AS subjects.Keywords: Phenylephrine, Sickle cell trait, Haemoglobin solution, Erythrocyte

Transient Refractive Changes In A Newly Diagnosed Diabetic-ACase Report

Hyperglycemia is the most frequently observed sign of diabetes and is considered the etiologic source of diabetes complication both in the body and in the eye. Changes in refraction are very common in diabetic patients and sometimes, it could be the first sign to the existence of the condition. Transient hyperopic changes are highly dependent on the magnitude of plasma glucose concentrations and rapid correction of hyperglycemia is strictly correlated with complete recovery of refraction. To account for this phenomenon, the sorbitol production via the polyol pathway with over hydrationof the lens has beenconsidered, aswell asachange inthe refractive index of the lens. Refractive corrections or alterations are to be discouraged until plasma glucose levels have normalized

Influence of endothelium on the membrane-stabilizing effect of calcium

Background: A decrease in membrane permeability to calcium ions, caused by increased extracellular calcium concentration is referred to as membrane-stabilization. There is a paucity of information on the role of vascular endothelium in the membrane-stabilizing effect of Ca2+ ions. The goal of the present study was to examine the influence of the endothelium on the membrane-stabilizing effect of Ca2+ ions in rabbit aortic smooth muscle. Methods: Isometric contractions of 2mm ring segments of rabbit aorta, placed in 20ml organ baths containing physiological salt solution (PSS) and bubbled with 95% O2, 5% CO2 gas mixture at 37oC and pH 7.4 were examined. The magnitude of the relaxation responses induced by increasing extracellular Ca2+ concentration from 5.0 to 25mM in phenylephrine pre-contracted rings was taken as an indirect indicator of the membrane-stabilizing effect of Ca2+. The relaxation responses induced by 25mM Ca2+ were estimated in endothelium-intact, endothelium-denuded rings as well as following exposure to 10-6M methylene blue. Results: In all experiments, an increase in [Ca2+]o (low bicarbonate PSS) from 5.0 to 25.0mM in rings with intact endothelium resulted in relaxation responses. These relaxation responses were attenuated in endothelium-denuded rings as well as following exposure to methylene blue. Conclusion: The results show that relaxation responses induced by high Ca2+ due to membrane stabilization is endothelium-dependent.Keywords: Calcium, rabbit aorta, Vascular smooth muscle, Membrane stabilization,Endothelium, methylene blue, Guanylate cyclas

Blood pressure variations in Subjects with different Haemoglobin Genotypes

Previous studies on low blood pressure in patients with homozygous sickle cell disease (SCD) have sought various hypotheses on the mechanism of their low blood pressure. However, these studies have not compared the role of the single inheritance of the s-gene in the variations in blood pressures as well as relating the blood pressures in different haemoglobin (HB) genotypes to each other. Blood pressures in 20 steady and crisis states SCD patients respectively with 40 apparently healthy heterozygous HB AS and HB AA genotype (age and sex –matched). They were aged between 20 and 40 years. Results showed a significantly (p<0.05) lower blood pressure (systolic and diastolic) in SCD in stable (but not in crisis) state compared with the normal controls. The systolic blood pressures in control (HB AA) and SCD patients were 125.33 ± 2.25 versus 115.25 ± 2.9 (stable state); 125.33 ± 2.25 versus 124.83 ± 2.88 (crisis state, p>0.05), 82.33 ± 1.2 versus 72.25 ± 1.81 (stable state, p<0.05) and 82.33 ± 1.2 versus 99.5 ± 5.81 (crisis state, p<0.05). Also, HB AS subjects exhibited significantly higher diastolic pressure than HB AA and HB SS subjects during crisis. In conclusion, this study shows that systolic and diastolic blood pressures are lower in SCA patients in stable state (compared with control, HB AA subjects) but are relatively higher during crisis while diastolic blood pressure is significantly higher in HB AS than HB AA and HB SS subjects in crisis. Further work needs to be done to determine the mechanism for this variation.Keywords: Blood pressure, Hemoglobin, Genotypes Sickle cell anemi

Vascular effects of 3-carbomethoxypyridine on rabbit aortic smooth muscle

Background: 3-Carbomethoxypyridine (3-CMP) is a methyl nicotinate that has been isolated and characterized from one of the alkaloidal fractions of Pyrenacantha staudtii. No literature is available on its vascular action. The goal of this study was to characterize the mechanism of action of 3-CMP on rabbit aortic smooth muscle. Methods: Isometric contractions of ring segments of rabbit aorta (under an initial load of 2g) suspended in 20ml organ baths containing physiological salt solution (PSS) and bubbled with 95% O2, 5% CO2, were examined at 37oC and pH 7.4. The protocols examined are: Dose response of tissues to phenylephrine (PE), effect of 3-CMP on baseline tension, dose response of tissues to 3-CMP following phenylephrine (PE, 10-7M) or high K+ (40mM) pre-contraction as well as relaxation responses to 3-CMP and Ach in endothelium-intact and endothelium-denuded rings.Results: The results show that 3-CMP dose-dependently attenuated the contractile responses to PE and High K+. The respective maximum relaxation responses to 3-CMP following pre-contractions with PE (n=8) or high K+ (n=9) were 50.06±2.94 and 18.59±2.88 (p<0.05). Ach-induced relaxation was observed only in rings with intact endothelium. Also 3-CMP-induced relaxation responses were significantly attenuated in endothelium-denuded rings. Conclusion: The results suggest that 3-CMP elicits relaxation of rabbit aortic smooth muscle activated by depolarizationdependent (high-K+) or –independent (PE) agents. The greater effect on PE contraction suggests interference with mechanisms involving agonist-receptor interaction. 3-CMP relaxation is also endothelium-dependent.Keywords: 3-Carbomethoxypyridine, Rabbit Aorta,Vascular smooth muscle, Endotheliu

Variations in Responses of Vascular Smooth Muscles to Na-K Pump Inhibition

There is a paucity of information concerning the variability of Na+-K+-ATPase activity in various vascular preparations. In this study, we have investigated, comparatively, K+-induced relaxation in different vascular tissues, to establish the heterogeneity of the activity of this enzyme. Isometric contractions of ring preparations of porcine tail artery and rat aorta as well as longitudinal strips of rat portal vein, mounted in 20ml organ baths were studied, under an initial load of 1g, at 37oCand pH of 7.4. The protocols examined were: Contractile responses to phenylephrine, 80mM K+ and K+-free exposure as well as relaxation responses to K+ following exposure to K+-free PSS. Phenylephrine, 80mM K+ and K+-free exposure elicited contractile responses in all tissue preparations. Following 30 minutes exposure to K+-free PSS and pre-contraction induced by EC70 (M) concentration of phenylephrine, addition of 5mM K+ elicited relaxation responses only in rat aortic rings and rat portal vein strips. Rings from Porcine tail artery failed to relax to K+ in all experiments. The magnitude of K+-induced relaxation was in the order: Rat Portal Vein > Rat Aorta. The times-to-peak of K+-free-induced contractile responses were 2.0 ± 0.0, 3.5 ± 0.5 and 6.25 ± 3.13 minutes for rat portal vein (n=6), rat aorta (n=6) and porcine tail artery (n=6), respectively. The magnitudes of relaxation in response to 5mM K+ for rat portal vein and rat aorta were 86.5 ± 16.75 and 60.00 ± 10.0%, respectively while the respective durations of K+-induced relaxation were: 30 ± 0 and 180 ± 22 seconds (n=6). The results suggest considerable heterogeneity in the activity of Na+-K+-ATPase enzyme in vascular smooth muscles from the rat portal vein, rat aorta and porcine tail artery.Keywords: Na+-K+-ATPase; Vascular Smooth Muscle; Rat aorta; Rat Portal Vein; Porcine Tail Arter

Altered Vascular Reactivity Induced By Malaria Parasites

Objective: In this study, we have examined the possibility that there is altered vascular reactivity due to the direct interaction between parasitized erythrocytes and vascular endothelial cells. Method: Ring preparations of rat aorta were studied using standard in vitro techniques, the rings were mounted in 20 ml organ baths containing PSS under an initial load of 1g, maintained at 37°C at pH 7.4 and isometric contractions were recorded electronically. Rings were allowed 90 minutes to equilibrate before the commencement of the various protocols: *Dose responses to phenylephrine (PE) and other vasoactive agents (high-K+) *Acetylcholine (Ach) – induced relaxation in phenylephrine-contracted rings (pre-contraction was induced by EC70 concentration of phenylephrine) *Ach-induced relaxation in PE-precontracted, endothelium-denuded rings *Also, relaxation responses to acetylcholine was investigated through application of a single (EC70) concentration of acetylcholine in rings exposed to blood with varying concentrations and dilutions of parasitized blood and varying durations of exposure. Results: Incubation with parasitized blood resulted in a significant increase in maximum contractile response to phenylephrine in the rat aortic rings (p < 0.05) but no effect to the base line. Analysis of the whole dose-response curve (using paired t-test) showed a significant left-ward shift following the addition of parasitized blood (p < 0.05), EC70 (M) values increasing from 7 x 10-7 to 5 x 10-6 M. Follow-ing exposure to parasitized blood, the magnitude of Ach-induced relaxation responses reduced signi-ficantly from 73 ± 3.6 to 24.75 ± 7.25% in rat aortic rings (p < 0.05). Ach relaxations were significantly enhanced (p < 0.05) at 5-minute exposure; however at longer durations, Ach-relaxations were variable and inconsistent. The lesser the dilution, due to increased volume of parasitized blood, the lesser the relaxation response. Following endothelium removal, there was a marked impairment in endothelium-dependent relaxation responses to ACh in both the control and incubated vessels. Exposure to para-sitized blood did not significantly alter contractile responses induced by potassium depolarization. Conclusions: This gives evidence in support of an endothelium-dependent action of malaria parasites as vascular effects of malaria parasites are mediated, at least in part, via endothelium-dependent mechanism(s). Keywords: Malaria, vascular, reactivity, tissue specificity Reactividad Vascular Alterada Inducida por los Parásitos de la Malaria RESUMEN Objetivo: En este estudio, hemos examinado la posibilidad de que exista una reactividad vascular alterada debido a la interacción directa entre los eritrocitos parasitados y las células endoteliales vasculares. Método: Se estudiaron preparaciones de anillo de aorta de rata usando técnicas in vitro estándar. Los anillos fueron montados en baños de órgano de 20 ml que contenían solución salina fisiológica (SSF) con una carga inicial de 1g, mantenida a 37°C con un pH de 7.4, y las contracciones isométricas fueron registradas electrónicamente. A los anillos se les dio un tiempo de 90 minutos para permitir que se equilibraran, antes del comienzo de los varios protocolos. *Respuestas a la dosis de fenilefrina (FE) y otros agentes vasoactivos (K+ alto) *Relajación inducida mediante acetilcolina (Ac) en los anillos contraídos con fenilefrina (la pre-contracción fue inducida mediante una concentración EC70 de fenilefrina) *Relajación inducida mediante Ac en anillos despojados de endotelio. Pre-contraídos con FE. *También, se investigaron las respuestas de relajación a la acetilcolina a través de la aplicación de una sola concentración (EC70) de acetilcolina en anillos expuestos a la sangre con diversas concentraciones y diluciones de sangre parasitada y distintas duraciones de exposición. Resultados: La incubación con sangre parasitada tuvo como resultado un aumento significativo en la respuesta contráctil máxima a la fenilefrina en los anillos aórticos de las ratas (p < 0.05) pero ningún efecto a la línea de base. El análisis de toda la curva de respuesta a la dosis (usando la prueba t pareada) mostró un desplazamiento significativo hacia la izquierda tras la adición de sangre parasitada (p < 0.05), EC70 (M), aumentado los valores de 7 x 10-7 a 5 x 10-6 M. Tras la exposición a la sangre parasitada, la magnitud de las respuestas a la relajación inducida por Ac se redujo significativamente de 73 ± 3.6 a 24.75 ± 7.25% en los anillos aórticos de ratas (p < 0.05). Las relajaciones por Ac mejoraron significativamente (p < 0.05) a los 5 minutos de exposición. Sin embargo, a duraciones más largas, las relajaciones por Ac fueron variables e inconstantes. Mientras menor era la dilución, debido al aumento de volumen de la sangre parasitada, menor era la respuesta de relajación. Una vez retirado el endotelio, se producía un marcado deterioro en las respuestas de relajación dependiente del endotelio, ante el Ac, tanto en los recipientes de control como en los encubados. La exposición a la sangre parasitada no alteró de manera significativa las respuestas contráctiles inducidas por la despolarización del potasio. Conclusiones: Esto provee evidencias en apoyo a una acción dependiente del epitelio, por parte de los parásitos de la malaria, por cuanto los efectos vasculares de los parásitos de la malaria se hallan mediados, al menos en parte, por los mecanismos dependientes del endotelio. Palabras claves: Malaria, vascular, reactividad, especificidad del tejid