THE EFFECT OF AN INTRAVENOUS INFUSION OF ALDOSTERONE UPON MAGNESIUM METABOLISM IN THE SHEEP

¹ Department of Agricultural Biochemistry and Nutrition, Faculty of Agriculture, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU

The concentration of Mg, Na and K in the rumen and plasma of each of four sheep has been studied while test solutions were infused into their jugular veins for 8 h. The experiment was designed as a 4 x 4 Latin square with: treatment 1: diet only; treatment 2: diet +5% dextrose infusion; treatment 3: diet +5% dextrose infusion containing aldosterone; treatment 4: diet +5% dextrose infusion containing aldosterone and potassium canrenoate (a specific inhibitor of the action of aldosterone). Rumen and blood samples were collected every hour during the 8 h treatment period and for the subsequent 4 h. Rumen volume and outflow rate were estimated using an intra-ruminal infusion of [¹⁴C]Cr-EDTA throughout the collection period. The aldosterone infusion significantly (P 0·001) increased the concentration of Mg in the rumen while rumen volume and outflow rate remained unchanged. Plasma concentrations of Mg and K were significantly (P 0·001 and P 0·05, respectively) lower during the aldosterone infusion while plasma Na concentrations did not vary significantly. The results are discussed in relation to hypomagnesaemic tetany.