Contractile and endothelium-dependent dilatory responses of cerebral arteries at various extracellular magnesium concentrations

To clarify the effect of extracellular magnesium (Mg2+) on the vascular reactivity of feline isolated middle cerebral arteries, the effects of slight alterations in the Mg2+ concentration on the contractile and endothelium-dependent dilatory responses were investigated in vitro. The contractions, induced by 10(-8)-10(-5) M norepinephrine, were significantly potentiated at low Mg2+ (0.8 mM v. the normal, 1.2 mM). High (1.6 and 2.0 mM) Mg2+ exhibited an inhibitory effect on the contractile responses. No significant changes, however, in the EC50 values for norepinephrine were found. The endothelium-dependent relaxations induced by 10(-8)-10(-5) M acetylcholine were inhibited by high (1.6 and 2.0 mM) Mg2+. Lowering of the Mg2+ concentration to 0.8 mM or total withdrawal of this ion from the medium failed to alter the dilatory potency of acetylcholine. The changes in the dilatory responses also shifted the EC50 values for acetylcholine to the right. The present results show that the contractile responses of the cerebral arteries are extremely susceptible to the changes of Mg2+ concentrations. In response to contractile and endothelium-dependent dilatory agonists, Mg2+ probably affects both the calcium influx into the endothelial and smooth muscle cells as well as the binding of acetylcholine to its endothelial receptor. Since Mg2+ deficiency might facilitate the contractile but not the endothelium-dependent relaxant responses, the present study supports a role for Mg2+ deficiency in the development of the cerebral vasospasm.     

Distribution and function of cholinergic receptors in the sheep detrusor muscle

The distribution of cholinergic nerve fibres, as well as the characterization of the muscarinic receptors responsible for the contraction, were determined in the detrusor smooth muscle of the sheep. The results obtained demonstrated a rich presence of acetylcholinesterase (AChE)-positive fibres distributed throughout the bladder body forming dense neuromuscular, subepithelial and perivascular plexuses. Furthermore, intramural ganglia containing AChE-positive cell bodies were identified. However, acetylcholine and carbachol induced a dose-dependent contraction of detrusor smooth muscle. The effect observed with carbachol was competitively antagonized by atropine (pA2: 8.94), pirenzepine (pA2: 7.38), AF-DX 116 (pA2: 7.35), 4-DAMP (pA2: 9.26) and hexahydroxiladifenidol (HHSiD) (pA2: 8.49). The pA2 value for pirenzepine is intermediate between M1- and M2-receptors which suggests that this antagonist does not act on M1- or M2-receptors, but that it does on M3-receptors. The pA2 value for AF-DX 116 is consistent with the presence of M2-receptors in this tissue. Moreover, the pA2 values obtained for both 4-DAMP and HHSiD are in agreement with the presence of M3-receptors, due to the lack of effect of pirenzepine on M1-muscarinic receptors. These results indicate the existence of a rich parasympathetic innervation in the sheep detrusor muscle and suggest that its contraction could be mediated by the stimulation of muscarinic receptors belonging to both M3- and M2-subtypes.     

Skeletal muscle characteristics of sprint cyclists and nonathletes

Muscle fiber distribution and muscle enzyme activity (m. vastus lat.) were investigated in 10 elite sprint cyclists and 12 nonathletes. The ratio of fast to slow muscle fibers was 2:3 in cyclists and 3:2 in nonathletes. The mean diameter of each muscle fiber type was significantly higher in the athletes. The mean enzyme activity values in mu kat X g-1 w.w. for cyclists and nonathletes, respectively, were as follows: triosephosphate dehydrogenase (TPDH), 6.2 and 3.78; lactate dehydrogenase (LDH), 4.4 and 4.59; citrate synthase (CS), 0.154 and 0.13; hydroxyacyl-CoA dehydrogenase (HAD), 0.041 and 0.07. The mean difference between groups in TPDH and in (TPDH + LDH)/(CS + HAD) ratio were statistically significant. Maximum voluntary isometric strength (knee extension) was about 17% greater in cyclists than the mean value for Czechoslovakian men of the same age. A strong positive correlation (r = 0.72) between the percent of fast glycolytic fibers (type II B) and isometric strength was observed in the cyclists. Furthermore, mean weight-compensated maximal oxygen consumption (VO2 max, ml X kg-1 X min-1) for all subjects (n = 22) was significantly related to percent of slow oxidative fibers (type I) (r = 0.75) and to the mean diameter of type II B (r = 0.58), fast oxidative-glycolytic fibers (type II A) (r = 0.68) and type I fibers (r = 0.59).     

Work capacity evaluation in patients after surgery for detached retina

The authors investigated the enlistment into work in patients after operation of detached retina at the Ophthalmological Clinic in Brno in 1985. From the results of the work it is apparent that the risk of relapse in conjunction with unsuitable work after operation is practically nil. Socio-economic aspects of patients who before operation suffered from some predisposing eye disease are more affected. The authors recommend systematic screening and dispensary care, in particular during the period when these people decide on their future occupation, i. e. already in primary school.     

The cholinergic innervation of the rat fascia dentata: identification of target structures on granule cells by combining choline acetyltransferase immunocytochemistry and Golgi impregnation

A monoclonal antibody against choline acetyltransferase (ChAT), the acetylcholine-synthesizing enzyme, was used to study cholinergic synapses on identified (Golgi stained) granule cells in the rat fascia dentata. Choline acetyltransferase immunocytochemistry was applied to 40-microns Vibratome sections cut perpendicular to the longitudinal axis of the hippocampus. Light microscopy revealed fine varicose ChAT-immunoreactive axons in all layers of the fascia dentata, i.e., in the stratum moleculare, the stratum granulosum, and the subgranular polymorph zone. Most fibers were observed in the vicinity of granule cell bodies where they ran mainly parallel to the granular layer. Next, the immunostained Vibratome sections were sandwiched between small pieces of Parafilm and piled to form a block that was covered with agar and Golgi stained. After that, the sections were separated by cutting away the agar and removing the Parafilm. Sections containing well-impregnated granule cells were gold-toned (Fairén et al., '77), embedded in Araldite, and subjected to ultrathin sectioning for electron microscopy. A total of 14 gold-toned granule cells were examined in the electron microscope for synaptic contacts with cholinergic afferents. Choline acetyltransferase-immunoreactive axon terminals were observed that established symmetric synaptic contacts with the cell bodies and dendritic shafts of the gold-toned identified granule cells. Two types of contact were observed on spines arising from gold-toned granule cell dendrites. Immunoreactive terminals established asymmetric synaptic contacts with the head of small spines and symmetric contacts with the stalk of large, complex spines. The boutons forming asymmetric synaptic contacts with the cup-shaped spine head of the complex spines were not found to be immunoreactive. Our results demonstrate that cholinergic fibers to the rat fascia dentata establish characteristic types of synaptic contact with different postsynaptic elements of granule cells, suggesting a complex function of this afferent system.     

Relationship between oxidative stress and essential hypertension.

This study investigated the association of blood pressure with blood oxidative stress-related parameters in normotensive and hypertensive subjects. A cross-sectional design was applied to 31 hypertensive patients and 35 healthy normotensive subjects. All subjects were men between the ages of 35 and 60 years. Exclusion criteria were obesity, dyslipidemia, diabetes mellitus, smoking and current use of any medication. All patients underwent 24-h ambulatory blood pressure monitoring and sampling of blood and urine. Antioxidant enzymes activity, reduced/oxidized glutathione ratio (GSH/GSSG), and lipid peroxidation (malondialdehyde) were determined in erythrocytes. Parameters measured in the plasma of test subjects were plasma antioxidant status, lipid peroxidation (8-isoprostane), plasma vitamin C and E, and the blood pressure modulators renin, aldosterone, endothelin-1 and homocysteine. Daytime systolic and diastolic blood pressures of hypertensives were negatively correlated with plasma antioxidant capacity (r=-0.46, p<0.009 and r=-0.48, p<0.007), plasma vitamin C levels (r=-0.53, p<0.003 and r=-0.44, p<0.02), erythrocyte activity of antioxidant enzymes, and erythrocyte GSH/GSSG ratio, with hypertensives showing higher levels of oxidative stress. Blood pressures showed a positive correlation with both plasma and urine 8-isoprostane. Neither plasma vitamin E nor the assessed blood pressure modulator levels showed significant differences between the groups or correlation with blood pressures. These findings demonstrate a strong association between blood pressure and some oxidative stress-related parameters and suggest a possible role of oxidative stress in the pathophysiology of essential hypertension.     

Enhanced dispersion of atrial refractoriness as an electrophysiological substrate for vulnerability to atrial fibrillation in patients with paroxysmal atrial fibrillation.

Atrial electrical remodeling plays a part in recurrence of atrial fibrillation (AF). It has been related to an increase in heterogeneity of atrial refractoriness that facilitates the occurrence of multiple reentry wavelets and vulnerability to AF. AIM: To examine the relationship between dispersion of atrial refractoriness (Disp_A) and vulnerability to AF induction (A_Vuln) in patients with clinical paroxysmal AF (PAF). METHODS: Thirty-six patients (22 male; age 55+/-13 years) with > or =1 year of history of PAF (no underlying structural heart disease--n=20, systemic hypertension--n=14, mitral valve prolapse--n=1, surgically corrected pulmonary stenosis--n=1), underwent electrophysiological study (EPS) while off medication. The atrial effective refractory period (AERP) was assessed at five different sites--high (HRA) and low (LRA) lateral right atrium, high interatrial septum (IAS), proximal (pCS) and distal (dCS) coronary sinus--during a cycle length of 600 ms. AERP was taken as the longest S1-S2 interval that failed to initiate a propagation response. Disp_A was calculated as the difference between the longest and shortest AERP. A_Vuln was defined as the ability to induce AF with 1-2 extrastimuli or with incremental atrial pacing (600-300 ms) from the HRA or dCS. The EPS included analysis of focal electrical activity based on the presence of supraventricular ectopic beats (spontaneous or with provocative maneuvers). The patients were divided into group A--AF inducible (n=25) and group B--AF not inducible (n=11). Disp_A was analyzed to determine any association with A_Vuln. Disp_A and A_Vuln were also examined in those patients with documented repetitive focal activity. Logistic regression was used to determine any association of the following variables with A_Vuln: age, systemic hypertension, left ventricular hypertrophy, left atrial size, left ventricular function, duration of PAF, documented atrial flutter/tachycardia and Disp_A. RESULTS: There were no significant differences between the groups with regard to clinical characteristics and echocardiographic data. AF was inducible in 71% of the patients and noninducible in 29%. Group A had greater Disp_A compared to group B (105+/-78 ms vs. 49+/-20 ms; p=0.01). Disp_A was >40 ms in 50% of the patients without A_Vuln and in 91% of those with A_Vuln (p=0.05). Focal activity was demonstrated in 14 cases (39%), 57% of them with A_Vuln. Disp_A was 56+/-23 ms in this group and 92+/-78 ms in the others (p=0.07). Using logistic regression, the only predictor of A_Vuln was Disp_A (p=0.05). CONCLUSION: In patients with paroxysmal AF, Disp_A is a major determinant of A_Vuln. Nevertheless, the degree of nonuniformity of AERP appears to be less important as an electrophysiological substrate for AF due to focal activation.