Effect of Estrogen-Promoted Bacterial Infections of the Rat Uterus on Bioassay of Mammalian Cell Growth Factor Activities in Uterine Luminal Fluid

Abstract

Exogenous estradiol treatment of intact or ovariectomized rats causes accumulation of significant volumes of fluid in the uterine horns. In this report, evidence is presented showing the presence of mammalian cell growth factor(s) in uterine luminal fluid (ULF), along with other data showing that the exogenous estradiol treatment needed to cause significant accumulation of the fluid also facilitates the movement of vaginal origin bacteria into the uterine horns. It is shown that microorganisms infect the uteri of 80% or more of rats administered exogenous estradiol, and that the microorganisms are most probably of vaginal origin; procedures such as ligation of the uterine body above the cervix or antibiotic treatment did not suppress the infections. Administration of different doses of exogenous estrogen by either implantation of a single 25-mg estradiol/cholesterol pellet which causes a 20- to 50-fold elevation of estradiol levels above physiological plasma concentrations, or instead, by a Silastic tube delivery method that elevates levels only 2- to 3-fold above the normal range, resulted in equal frequency of uterine infections and in the appearance of infection at the same time after starting treatment. A number of bacterial species are present in the contaminated ULF, and these are the origins of intracellular products which are potent inhibitors of mammalian cell growth; the presence of these bacterial origin inhibitors interferes with the bioassay of the ULF growth factor activity, and hence, impedes the characterization of the growth factor(s) present in luminal fluid. Characterization of the origins of the growth-inhibiting activities showed that Pseudomonas aeruginosa and Proteus mirabilis are the predominant species present in infected uteri and that both produce exotoxin activities which inhibit growth of mammalian cells in culture; Pseudomonas appears to be the greater producer of cytotoxic activity. Evidence is presented that suggests that the well-known Exotoxin A produced by Pseudomonas may be responsible, in part, for the toxic effects of this organism. Other, as yet unidentified, cell growth inhibitors also may be produced by the bacteria found in ULF. Surgical separation of the uterine body from the cervix allows preparation of ULF which contains no bacteria and substantially reduced levels of growth inhibitors to mammalian cell lines.