Induction of cyclooxygenase and prostaglandin E2 production by the bovine pre-embryo

Abstract

A study was conducted to determine the induction of cyclooxygenase production in the cleaved and non-cleaved oocyte and to measure the secretion of prostaglandin E2 (PGE2), PGF2 alpha and tumour necrosis factor-alpha (TNF alpha) in the conditioned medium of non-mature oocytes (denuded), mature oocytes (oocyte-cumulus complex), cleaved oocytes, and non-cleaved oocytes (mature oocytes incubated in the absence of sperm). Cyclooxygenase was readily detectable in 48-h cleaved oocytes whereas the signal for the enzyme in the non-cleaved oocytes was weak or undetectable. Cyclooxygenase expression in the cleaved oocytes was transient and enzyme concentrations at the early morula stage (72 h) were low. Measurable amounts of both PGE2 and TNF alpha were secreted during the first 24 h of maturation and 6 h after fertilization, whereas PGF2 alpha was undetectable at these times. There was a dramatic enhancement in PGE2, PGF2 alpha and TNF alpha secretion 48 h after fertilization. At 72 h after fertilization, PGE2 concentrations were much lower and PGF2 alpha was again undetectable which corresponded to a low concentration of cyclooxygenase. In contrast, high TNF alpha activity continued to be detected even 72 h after fertilization. It is possible that the induction of the production of cyclooxygenase and the secretion of PGs and TNF alpha by fertilized oocytes at specific times after fertilization plays a role in the regulation of embryonic development, maternal immunological recognition of pregnancy, and the maintenance of a suitable hormonal environment for embryonic viability.