Concentrations of oxytocin in corpora lutea from pregnant and non-pregnant sheep rose during luteinization to peak between days 5 and 9 after oestrus before falling to low levels on days 12 and 14. Concentrations of the 608-base mRNA encoding the oxytocin-neurophysin prohormone, measured by Northern blotting using a cRNA probe, were highest before day 5, and fell to low levels by day 9. The decline in oxytocin during the second half of the oestrous cycle and in pregnancy could therefore be accounted for by reduced luteal concentrations of oxytocin-neurophysin mRNA. The rate of decline in prohormone mRNA concentration between days 3 and 16 followed first order kinetics, suggesting that gene expression ceased early in the cycle. The lag between peak oxytocin-neurophysin mRNA and peak oxytocin concentrations may represent the time taken for post-translational processing of the prohormone.
J. Endocr. (1988) 117, 409–414