AN INVESTIGATION INTO THE ROLE OF NEUTROPHILS IN DECIDUALIZATION AND EARLY-PREGNANCY IN THE RAT

Possible roles for neutrophils in the response of sensitized rat uteri to a deciduogenic stimulus were investigated. Ovariectomized rats wer e sensitized for the decidual cell reaction by the administration of e stradiol and progesterone. Sesame oil was injected into one uterine ho rn as a deciduogenic stimulus on the equivalent of Day 5 of pseudopreg nancy. Neutrophil numbers in the endometrium, as determined by microsc opy after application of the stimulus, were dependent on time and stim ulation. Very few neutrophils were found in the endometrium before sti mulation. To determine whether neutrophils were involved in the uterin e responses to a deciduogenic stimulus, rats were depleted of circulat ing neutrophils by prior treatment with either methotrexate (MET) or a ntineutrophil serum (ANS). The increase in endometrial vascular permea bility, as quantified with [I-125]-BSA 10 h after stimulation, was not significantly affected by MET or ANS treatment, nor was the extent of decidualization, as indicated by the weight of the uteri 5 days after stimulation. Endometrial neutrophil numbers were significantly lower in the MET- and ANS-treated animals compared to their respective contr ols. In the uterus, activity of mycloperoxidase, an enzyme found mainl y in neutrophils, was significantly reduced in MET-treated animals. To investigate the role of neutrophils in blastocyst implantation, we tr eated rats with ANS early on Day 5 of pregnancy. On Day 6, neither the numbers of implantation sites nor their weights were affected by ANS treatment. ANS treatment on Day 5 of pregnancy did not attenuate the n umbers and weights of placentae and fetuses on Days 19 and 20 of pregn ancy. These results indicate that treatments that substantially reduce endometrial neutrophil numbers for at least 30 h around the time of t he initiation of implantation/decidualization did not affect the proce ss of implantation/decidualization.