Metabolism of selenium-75 in the erythrocytes of sheep and growing calves

Four mature wethers and four Holstein-Hereford steers were dosed with a single intrajugular injection of ⁷⁵Se as selenious acid in order to determine red blood cell life spans. Blood samples collected in heparin were taken at two and eight hours, daily for 10 days, weekly for 12 weeks, and biweekly until the end of the experiment. One ml of each sample was washed in buffered saline, corrected to 100% with the packed cell volume, and used to determine the amount of ⁷⁵Se present in one ml of washed cells. One ml of plasma was collected in order to determine the selenium activity. The remainder of the blood sample was used in ⁷⁵Se chromatographic analysis and ⁷⁵Se incorporation studies. The red blood cell life span of the sheep averaged 123 days, while that of the younger and older calves averaged 114 and 141 days respec-tively. Analysis of the selenoprotein by Dowex 50-8X ion exchange chromatography failed to reveal either selenomethionine or selenocystine. 75 Other short-term incorporation studies suggested that ⁷⁵Se was bound to the sulfur of amino acids and not actually incorporated into the protein molecule. ⁷⁵Se proved to be adequate in determining the red cell life span of calves and sheep. Although studies on the manner of selenium incorporation into protein were not conclusive, methodologies evolved will be useful in continued studies on the metabolism of selenium in sheep.