Effect of boron on the ultrastructure of parathyrocytes and atrial cardiomyocytes

Abstract

Ultrastructural shifts in parathyrocytes and atrial cardiomyocytes induced by long-term treatment with boron-containing water (250 mg/liter) were found against the background of boron accumulation. These changes are indicative of enhanced secretory activity of these cells. It is hypothesized that boron modulates the effect of parathyroid hormone and atrial natriuretic factor and the rate calcium-sodium exchange. Key Words: boron; parathyrocytes; atrial cardiomyocytes; ultrastructural changesPublished data and our previous studies have demonstrated that boron affects the structure of cell membranes [6] and calcium and magnesium metabolism [15], enhances diuresis [121, and reduces blood pressure [1]. It can be hypothesized that boron affects the functioning of the parathyroid gland and production of parathyroid hormone (PTH) which regulates blood calcium level and reduces blood pressure [4]. Moreover, one can expect structural and functional shifts in atrial cardiomyocytes, since atrial natriuretic factor (ANF) is involved into regulation of sodium-calcium exchange and exerts a pronounced antipressor effect [10].There are no published data on the effect of boron on the ultrastructure of parathyrocytes and atrial cardiomyocytes, therefore, these questions were the focus of our investigation. MATERIALS AND METHODSExperiments were carried out on 20 male albino rats weighing 220-250 g. The animals were given sodium tetraborate dissolved in water (250 mg/liter in a volume of 3 ml, pH 8.0, per os). This concentration naturally occurs in mineral water used for the treatment and rehabilitation. Daily dose of boron was Laboratory-of Morphology, Russian Center of Rehabilitation and Physiotherapy, Ministry of Health of the Russian Federation, Moscow 3.75 mg/kg. Control animals received tap water. The total course consisted of 24 procedures. The animals were decapitated after 15 or 24 procedures, and the boron content in the thyroid-parathyroid complex (the parathyroid glands in rats are submerged into the thyroid tissue) and in the heart was determined spectrophotometrically using H-resorcin [9]. Electron microscopy of the parathyroid gland and left atrium was performed after 15 procedures (the maximum tissue accumulation of boron). To this end, specimens were fixed in 2.5% glutaraldehyde and postfLxed with OsO4, dehydrated in alcohol of ascending concentrations and acetone, and embedded in EponAmldite. Ultrathin sections were examined under JEM-100C and JEM-100CX electron microscopes. Quantitative parameters of parathyrocytes and atrial cardiomyocytes were analyzed stereologically and by automorphometry with an MOP-Videoplan device. The volume portion and number of mitochondria, volume portion of granular endoplasmic reticulum (GER), Golgi apparatus, and the area of secretory granules in atrial cardiomyocytes were calculated. RESULTSMaximum accumulation of boron was noted after 15 procedures: its concentration in the thyroid-parathyroid complex and heart increased 3.4-fold (p< 0.05) and 8-fold (p<0.001), respectively (Table ...