Selenium metabolism in the dairy cow: the influence of the liver and the effect of the form of Se salt

Abstract

1. Six adult Friesian cows were given 75 Se as either 75 SeO 3 2− or 75 SeO 4 2− intravenously. Five of the cows had cannulas in an hepatic vein, the portal vein and one carotid artery to enable the uptake of 75 Se by the liver to be measured. Radioactive balance studies were carried out on two of the cows given 75 SeO 3 2− and two given 75 SeO 4 2− . A seventh cow was given an oral dose of 75 Se-labelled barley and the excretion of 75 Se in faeces, urine and milk was measured for 14 d. 2. After the injection of 75 SeO 3 2− plasma 75 Se concentration decreased during the first 30 min with a mean half-life (t ½ ) of 15.6 min. From 30 to 60 min after dosing the concentration of radioactivity increased to reach approximately 50% of the level present 2 min after dosing. Following the injection of 75 SeO 4 2− the 75 Se was cleared with a mean t ½ of 28.5 min during the first 30 min and plasma radioactivity increased only slightly during the next 30 min. 3. During the phase of rapid clearance of 75 Se after the injection of 75 SeO 3 2− the hepatic venous 75 Se concentration was approximately 5% lower than portal veous 75 Se concentration. During the period when plasma 75 Se activity was increasing the activity in hepatic venous plasma was 3% greater than portal activity. Of the 75 Se cleared from plasma after injecting 75 SeO 3 2− 40% was calculated to be removed by the liver. 4. After intravenous dosing with 75 SeO 3 2− or 75 SeO 4 2− approximately 9.5 and 17.0% respectively of the dose injected was excreted in faeces and 10% in urine within 14 d. Almost three times as much 75 Se was excreted in urine and 3.5 times as much in faeces during the first 24 h after dosing with 75 SeO 4 2− as after 75 SeO 3 2− .