Differential regulation of phospholipase A2 activity and prostaglandin E2 synthesis in activated and non-activated corpora lutea of lactation by the presence and absence of suckling stimulus in rats

We investigated content of prostaglandin (PG) E2, a luteotropic eicosanoid, and phospholipase A2 (PLA2) activity in two distinct states of rat corpora lutea of lactation (LCL). Rats subjected to forced weaning on day 0 postpartum (PP0) had a significant attenuation of progesterone synthesis and LCL weight on PP6 and/or PP3 compared with normally lactating rats. Repeated administration of prolactin (10 IU, twice daily) to weaned rats reversed impaired LCL function and structural development beyond the normal level of lactating animals. From PP3 to PP6, PGE2 level in lactating LCL was increased while it was not altered in non-lactating LCL. In contrast, PLA2 activity in the cytosol plus microsome fractions was decreased in lactating LCL and was up-regulated in non-lactating LCL as early as on PP3. This study provides the first evidence for differential regulation of PLA2 activity and PGE2 synthesis in activation and activation failure of postpartum CL in rats.