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

Abstract

The activity of the enzyme 20IX-hydroxysteroid dehydrogenase present in erythrocytes of foetal and new-born ruminants has been determined by incubating 0·1 ml blood with 0·16,umol [4_'4C]_ progesterone for 15 min at 39°C in a final volume of 2 ml buffered saline. It was found that the activity, measured as ,umol 20IX-hydroxypregn-4-en-3-one produced from progesterone per millilitre of erythrocytes per hour, declined from levels at birth as high as 1'50,umol for sheep, 0'50,umol for goats and O' 43 ,umol for cattle to levels of around 0'11, O' 08 and O' 04 ,umol respectively by 30-60 days of age. This decline in activity was also apparent in blood taken from sheep foetuses in which longitudinal studies were possible and appeared to have begun prior to 35 days before term. The highest activity obtained was 2· 59 ,umol for foetal sheep blood taken at 115 days of gestation. It is suggested that the observed decline in 20IX-hydroxysteroid dehydrogenase activity is a function of the replacement of foetal erythrocytes with adult-type erythrocytes which begins around 120 days of gestational age and that the role of the enzyme is to maintain an appropriate progestational environment within the foetoplacental unit.