Objective       To study the distribution and excretion of synthetic thymosin α1 (sTα1) in mice and rats after intravenous (i.v.) injection.      Methods       The sTα1 concentrations in tissues at different time points and cumulative amounts of sTα1 in urine over different periods after i.v. injection of sTα1 into mice were measured by competitive ELISA. The cumulative amounts of sTα1 in bile over different periods after i.v. injection of sTα1 into rats were also measured by competitive ELISA.      Results       The concentration of sTα1 in the thymus gland was the highest (1 533.4±712.4 ng/g) at 15 min after i.v. injection of sTα1 (1 mg/kg) into mice

followed by those in the liver

spleen

and kidney

while sTα1 concentration in the brain was relatively low. At 30 min after i.v. injection of sTα1 into mice

sTα1 concentration in the thymus gland was still the highest (25 583.4±6 244.7 ng/g)

followed by those in the spleen

kidney

and liver. At 1 h after i.v. injection of sTα1 into mice

sTα1 concentration in the kidney was the highest (6 164.1±4 821.8 ng/g)

and that in the thymus gland was (5 665.8±3 881.9) ng/g. At 2 h after i.v. injection of sTα1 into mice

sTα1 concentration in the kidney was the highest (1 408.0±1 252.7 ng/g)

and that in the thymus gland was (306.4±268.6) ng/g

with trace amounts of sTα1 in the other tissues. The concentration of sTα1 in the brain was similar to that in blood plasma

indicating that sTα1 could pass through the blood-brain barrier. After i.v. injection of sTα1 (1 mg/kg) into mice

the cumulative amount of sTα1 in urine over 12 h was 26.35% of administration dosage. There was no sTα1 excretion in bile after i.v. injection of sTα1 (0.5 mg/kg) into rats.      Conclusion       After i.v. injection of sTα1 into mice

sTα1 is mainly distributed in the thymus gland and spleen and primarily excreted through the kidney

and can pass through the blood-brain barrier.