The biological half-life of synthetic, radiochemically pure, biologically active [3H]8-arginine-vasopressin ([3H]AVP), the distribution of radioactivity among the organs and the in-vivo metabolism of the hormone were studied in the rat. The half-life calculated from the [3H]AVP radioactivities isolated from the blood was found to be 1.74 +/- 0.22 (S.D.) min in the fast phase, and 16.98 +/- 1.01 min in the slow phase. The half-lives of total radioactivity were longer in both phases. The radioactivity accumulated to the greatest extents in the adenohypophysis and small intestine. The radioactive substance was accumulated more by the kidney than by the liver, but the hormone underwent inactivation more quickly in the liver.

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SUMMARY[ 22,23-3H2]-Dihydroavermectin Bla of 2.13 TBq/mmol (57.7 ci/mmol) specific activity was derived from avermectin Bla by selective tritiation using Wilkinson*s homogeneous catalyst. Data on binding affinity and nematotoxic activity of the title compound are reported.