Rate of concentration and digestion of radioactive growth hormone preparations injected in rats, as measured by the amount and nature of radioactivity in the tissues

The distribution of radioactivity in the tissues of the rat has been established after the administration of radioactive bovine growth hormone preparations. Bovine growth hormone was used either transformed in to a14C-guanidinated derivative, which was fully active, of labeled with less than 1 mole per mole of125I. The tissue radioactivity distribution curves obtained belong to two different categories: in kidney, liver and spleen there is an early concentration which attains a maximum in 15 minutes after the injection of the hormone, and rapidly declines. In heart, skeletal muscle, pancreas, intestine, bone and fat, the radioactivity increases gradually and a steady-state is reached after 30 to 60 minutes. Kidney is the organ where the highest concentration of radioactivity occurs. However, muscle accumulates more than 60% of the initial doses after 2 hours. Very little radioactivity appears in the urine, in this period. Similar results have been obtained with pharmacological or physiological doses of the labeled hormones. Blood plasma does not degrade the injected hormone but kidney, liver and muscle rapidly produce radioactive fragments soluble in 10% trichloro-acetic acid. © 1977 Dr. W. Junk b.v. Publishers.