Distribution of progesterone and its metabolites in cattle tissues following administration of progesterone-4-14C1,2,3,4.

Abstract

Four choice grade Angus steers weighing 454 to 544 kg and six lactating, non-pregnant Guernsey cows were given twice daily progesterone injections (50 μg/kg/day) for 13 to 21 days in which progesterone-4-14C was included in the last 2 to 5 days. Blood, urine and feces of all animals and milk from the cows were collected and sampled during the treatment period. At slaughter, two to three hr after the last injection, radioactivity was slightly higher in muscle than in plasma, and was two to seven times higher in fat, three times higher in kidney and 13 times higher in liver than in muscle. The concentration of radioactivity exceeded the level in plasma by four times in milk, 30 times in urine and 500 to 1,300 times in the bile. The excretion of radioactivity during the treatment period was 50 and 12% in feces and 2.0 and 1.2% in urine for cows and steers, respectively. An additional .25% was removed with the milk by the cows. After extraction and defatting, the percentage of total radioactivity in the non-conjugated (free) fraction was 99, 98 and 65 in milk, muscle and fat, respectively. Approximately 50% of the radioactivity of muscle and milk extracts behaved chromatographically like progesterone, 20 to 30% like monohydroxy metabolites, 6 to 10% like multihydroxy metabolites and 5 to 10% like pregnanediones. In both the free and glucuronide fractions of fat extracts, 67 to 78% of the radioactivity chro-matographed like progesterone with 15 to 20% like the monohydroxy metabolites. Cooking or frozen storage for 9 months did not appear to have any effect on the nature or quantity of metabolites found.