[Biological titration of antidiuretic activity of ovine plasma].

We studied a relationship of the antidiuretic hormone to the level of urea in the ovine blood. An antidiuretic activity of the ovine blood plasma before and after 36-hour fasting was determined by biological titration on 22-day-old rats. Optimum control doses were calculated as follows: 1.0 muU for pitressin, 2.5 muU for lysine-vasopressin and 0.1 muU for arginine-vasopressin, these doses securing 80-85% antidiuretic activity. The antidiuretic activity of the ovine blood plasma reached 90, 70, 46% before fasting and 58, 59, 46% after 36-hour fasting, in comparison with the control doses. It can be concluded from the results that there is no relationship between the antidiuretic activity of the ovine plasma and an increased urea concentration in the blood during the first days of fasting (36 hours).