Effects of a large dose of oestradiol on antithrombin III metabolism in male and female dogs

Abstract

Abstract. Canine antithrombin III (AT) metabolism was studied in twenty healthy dogs of both sexes first under control conditions, using 125I‐AT as a tracer, then, in the same dogs after 20 mg oestradiol intramuscularly and another 20 mg 7 days later. Under control conditions the plasma AT concentration and the amount of plasma AT (x̄) were greater in males than females. The plasma half‐lives of 125I‐AT averaged 2.14 ± 0.09(SD) days in males and 1.97 ± 0.05(SD) days in females and were significantly different. The fractional catabolic rate of plasma AT (j3p) was lower in males than in females, but the amount of plasma AT catabolized (j3pX̄) (synthesis rate) was not significantly different (averaging 20 ± 3.7 (SD) in males and 18 ± 2.2(SD) mg/kg/day in females). The total body AT (x̄+ȳ) was greater in males than in females; average values 55 ± 7.5(SD) and 46 ± 5.2(SD) mg/kg, respectively. Under the influence of oestradiol, the plasma AT concentration and AT(x̄) decreased in both sexes, but the plasma half‐lives of 125I‐AT showed no appreciable changes. The values of AT(j3p) and AT(j3pX̄) were significantly decreased in both sexes; average values of the latter being 14 ± 1.5(SD) in males and 12 ± 2.2(SD) mg/kg/day in females. AT(x̄+ȳ) averaged 43 ± 3.8(SD) in males and 33 ± 6.3(SD) mg/kg in females and were significantly decreased. These results indicate that the decreased values in plasma AT concentration, x̄ and x̄+ȳ following oestradiol administration are due to the decreased synthesis rate of AT and not to an increased catabolic rate.