Selective tissue accumulation of manganese and its effect on regional blood flow and haemodynamics after intravenous infusion of its chloride salt in the rat.

• Manganese chloride (MnCl2), with or without the addition of trace amounts of 54Mn2+, was administered as a 7-min i.v. infusion in rats. Tissue accumulation of 54Mn2+ was determined 0-15 min after the infusion, and cardiac output, regional blood flows and vascular resistances were measured 5 and 60 min after the infusion by the microsphere technique. The plasma half-life of 54Mn2+ was found to be 4.7 min. Mn2+ accumulated in several organs, the highest relative concentrations being seen in the liver, duodenum, jejunum, kidney and heart, and intermediate concentrations in the ileum, colon, stomach and spleen. There was no uptake in the lung, skeletal muscle or brain. During the infusion of 180 mumol/kg b.w. of Mn2+, the arterial blood pressure fell from a mean of 123 +/- 5 mm Hg to a minimum of 85 +/- 7 mm Hg, and thereafter returned to normal. Five minutes after termination of the infusion, there was a decrease in cardiac output and minute work but not in total peripheral resistance, a finding interpreted as a negative inotropic effect of Mn2+. At this time blood flow was decreased in the stomach, ileum, colon, spleen and skin, and increased in duodenum, jejunum and liver. The blood flows were normalized 60 min after termination of the infusion in all organs except the liver and heart. The effects are probably due to the calcium-antagonistic properties of Mn2+ and the tissue accumulation is most probably a result of intracellular accumulation through calcium channels. The relation between tissue accumulation and tissue selectivity of blood-flow alterations is unexplained.

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