Metabolism of [6,7-3H]norethisterone enanthate in rats
Abstract
The absorption, distribution and excretion of [6,7-3H]norethisterone enanthate in female rats are reported. After iv injections, the plasma radioactivity showed an initial rapid drop (t1/2=49 min) and a subsequent slow decline (t1/2=77 h). The average volumes of distribution V1 and V were about 80 and 2014 ml, respectively. The disappearance curve was analyzed on the basis of a biexponential curve representing a model consisting of 2 compartments. The drug was rapidly taken up by various organs. The disappearance curve showed an initial rapid fall followed by a slow decay. After 30 min a high level of radioactivity was present in the liver, while appreciable radioactivities were present in spleen, adrenals, lungs, heart, kidneys, ovaries, pituitary and intestine. The radioactivities were low in muscle, stomach, fat, uteri, oviducts, mammary glands, vagina, brain, bone and hypothalamus.
The uptake of the drug in fat tissues was low. After an iv injection of the drug 50 microCi/kg, the radioactivities were found to be 31% in feces and 11.5% in urine in 24 h and 51% in feces and 19% in urine in 7 d.
After an im injection, its slow release from the injection sites accounted for its prolonged contraceptive action. The radioactivity in the plasma after im injections increased markedly from the 2nd hour on and reached its peak within 48-72 h. This peak level in the plasma declined to one-half in about 12 d. About 8-10% of the peak level persisted after 45 d. After an im injection of 400 microCi/kg, the total radioactivity eliminated in 12 d was 47% in feces and 16% in urine.
Keywords:
The uptake of the drug in fat tissues was low. After an iv injection of the drug 50 microCi/kg, the radioactivities were found to be 31% in feces and 11.5% in urine in 24 h and 51% in feces and 19% in urine in 7 d.
After an im injection, its slow release from the injection sites accounted for its prolonged contraceptive action. The radioactivity in the plasma after im injections increased markedly from the 2nd hour on and reached its peak within 48-72 h. This peak level in the plasma declined to one-half in about 12 d. About 8-10% of the peak level persisted after 45 d. After an im injection of 400 microCi/kg, the total radioactivity eliminated in 12 d was 47% in feces and 16% in urine.