Decline with Age in the Rate of Reduction of Progesterone to 20a-Hydroxypregn-4-en-3-one in the Blood of Perinatal Ruminants

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Abstract
The activity of the enzyme 20.alpha.-hydroxysteroid dehydrogenase present in erythrocytes of fetal and newborn ruminants was determined by incubating 0.1 blood with 0.16 .mu.mol [4-14C]progesterone for 15 min at 39.degree. C in a final volume of 2 ml buffered saline. The activity, measured as .mu.mol 20.alpha.-hydroxypregn-4-en-3-one produced from progesterone/ml of erythrocytes per hour, declined from levels at birth as high as 1.50 .mu.mol for sheep, 0.50 .mu.mol for goats and 0.43 .mu.mol for cattle to levels of .apprx. 0.11, 0.08 and 0.04 .mu.mol, respectively, by 30-60 days of age. This decline in activity was also apparent in blood taken from sheep fetuses in which longitudinal studies were possible and apparently began prior to 35 days before term. The highest activity obtained was 2.59 .mu.mol for fetal sheep blood taken at 115 days of gestation. The observed decline in 20.alpha.-hydroxysteroid dehydrogenase activity is a function of the replacement of fetal erythrocytes with adult-type erythrocytes which begins around 120 days of gestational age, and the role of the enzyme is to maintain an appropriate progestational environment within the fetoplacental unit.