CHARACTERIZATION OF ACYLTRANSFERASE ACTIVITY IN OVINE PLACENTAL TISSUE DURING PREGNANCY AND AT THE TIME OF LABOR

Although it is well established that the formation of eicosanoids by o vine intrauterine tissues increases during pregnancy and at the time o f labour, the biochemical mechanisms involved remain to be clearly est ablished. In this study, we tested the hypothesis that the gestational and labour-associated increases in eicosanoid formation are associate d with a reduction in the activity of the reacylating enzyme, acyl Coe nzyme A lysophosphatide acyltransferase (LAT). To evaluate this propos al, in vitro LAT activity was; quantified in ovine placenta (cotyledon s) obtained during pregnancy (85-147 days of gestation and at the time of labour). Ovine placental LAT increased from 1.81 +/- 0.06 nmol/min per mg protein at 85 days of gestation to 2.34 +/- 0.10 nmol/min per mg protein at 142 days of gestation (P < 0.005, n = 15). The apparent K-m did not vary significantly between the 85- and 142-day groups. V-m ax, however, was significantly greater in the late-gestation group (2. 98 +/- 0.02 nmol/min per mg protein) than in the mid-gestation group ( 2.38 +/- 0.13 nmol/min per mg protein, P < 0.05). In association with labour, placental LAT activity decreased by 16% (1.96 +/- 0.13 nmol/mi n per mg protein) when compared with that observed in tissue obtained from the non-labouring ewe (P < 0.01). The data obtained are consisten t with the hypothesis that changes in LAT activity in ovine placenta d o not contribute to the gestational increase in prostaglandin formatio n, but a contribution to the labour-associated increase in non-esterif ied arachidonic acid availability and eicosanoid formation cannot be n egated.