Studies on the surgical induction of endometriosis in the rat

As a model to examine the pathophysiologic attributes of endometriosis, attempts were made to surgically induce the disease in the rat by autotransplanting endometrial or uterine tissue to the peritoneum. Rats (n = 46) were randomly assigned to one of four surgical techniques: (1) four uterine squares sutured to the peritoneal cavity; (2) uterine luminal lavages instilled into the peritoneal cavity; (3) endometrial scrapings flushed into the peritoneal cavity; and (4) sham-operated controls. Rats were examined at various days after surgery for the presence of endometrial implants. The autotransplantation of uterine squares to the peritoneal cavity was the only treatment that yielded healthy endometriotic implants. These implants grew into ellipsoidal cystic structures that were composed of both endometrial glands and stroma and were found to contain prostaglandin F (202 ng/mg) at concentrations similar to those measured in uterine tissue (205 ng/mg). To examine the effect of surgically induced endometriosis upon fecundity, rats (n = 40) were autotransplanted with uterine squares or were sham operated and mated. The presence of ectopic endometrial tissue reduced the number of pups at term by 48% and the number of day 14 embryos by 28% (P less than 0.05). Peritoneal adhesions were greater in rats with induced endometriosis than in sham-operated controls (P less than 0.05); however, in rats with induced endometriosis, no differences were noted in the severity of adhesions between pregnant and nonpregnant rats. Endometriotic implants underwent complete regression in the day 14 pregnant rat but had doubled in size in the nonpregnant rat. At term, the endometriotic implants were larger than in the day 14 pregnant rat (P less than 0.05) and similar to their original size. The successful growth and development of surgically transplanted endometrial tissue in the rat offers a research model that can be used to study those aspects of endometriosis that cannot be adequately investigated in women.