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Conversion of Pregnenolone-4¹⁴C to Progesterone-414C by Bovine Luteal Tissue at Selected Stages of the Estrous Cycle¹

Department of Animal Science, University of California, Davis

ABSTRACT

Conversion rates of 3 ß-hydroxy-pregn-5-en-20-one to pregn-4-en-3,20-dione during the estrous cycle were measured in bovine luteal homogenates by incubating 20 mg eq of tissue for five min, using a substrate of 200 mµmoles of 3 ß-hydroxy-pregn-5-en-20-one-4¹⁴C adjusted to a specific activity of 1 µCi/µmole. Conversion rates varied with the age, size, and histological integrity of the corpus luteum, and exhibited a pattern similar to other in vitro methods reported in the literature (1, 12). Pregn-4-en-3,20-dione synthesis was low in the early stages of the cycle, reached a maximum between the 10th and 12th days, decreased slightly between the 14th and 16th days, rose again between the 18th and 20th days, and was minimum during estrus. Under these experimental conditions less than 1% of the pregn-4-en-3,20-dione synthesized in vitro was converted to other metabolites by the luteal tissue of any stage of the cycle.

¹ Data taken from a Ph.D. thesis by R. Garth Sasser, University of California, Davis.

² National Institutes of Health Trainee, Grant no. 5T1 GM646. Present address: Department of Dairy Science, University of Idaho, Moscow.