THE O-METHYLATION OF CATECHOL ESTROGENS BY PIG CONCEPTUSES AND ENDOMETRIUM DURING THE PERIIMPLANTATION PERIOD

Pig conceptuses display a surge in oestrogen and catecholoestrogen synthetic activity during the peri-implantation period. However, the pathways of catecholoestrogen metabolism in pig conceptuses and endometrium are unknown. O-Methylation is an important route of catecholoestrogen metabolism. Therefore, the O-methylations of 2- and 4-hydroxy-oestradiols (2- and 4-OH-oestradiol) by cytosol of pig conceptuses and endometrium during the peri-implantation period were studied. Kinetic studies performed in tissues obtained on day 13 of pregnancy (day 0 = first acceptance of the male) indicated that the O-methylation of 2-OH-oestradiol displayed simple Michaelis-Menten kinetics in both tissues. In blastocysts, the apparent Michaelis constant (K(m)) and maximum velocity (V(max)) for the O-methylation of 2-OH-oestradiol were 1.4 μmol/l and 11.27 pmol/mg protein per min respectively, and when 4-OH-oestradiol was used as substrate, the values were 2.53 μmol/l and 9.86 pmol/mg protein per min respectively. The apparent K(m) and V(max) values for the O-methylation of 2-OH-oestradiol in endometrium were 0.77 μmol/l and 19.6 pmol/mg protein per min respectively, and for the O-methylation of 4-OH-oestradiol were 2.44 μmol/l and 10.38 pmol/mg protein per min respectively. Ontogenesis of catechol-O-methyltransferase (COMT) in conceptuses and endometrium was studied from day 10 to day 19 of pregnancy. Conceptus COMT activity was lowest on day 10 and increased gradually to day 19 of pregnancy. Because a surge of oestradiol-2/4-hydroxylase activity occurs on days 11-13, less COMT activity on these days than on the later days of pregnancy is consistent with a role for catecholoestrogens in conceptus-maternal signalling during pregnancy establishment. Endometrial COMT activity on day 10 was higher than that on later days of pregnancy. Therefore, a role for COMT in modulation of catecholoestrogen and oestrogen function during the peri-implantation period is possible.