Development of an experimental ovarian tumor over a year in the rat

Tumor growth, possible malignant transformation or metastatic propagation a nd hormonal patterns were evaluated over a year in luteoma induced by intro ducing an ovary into the spleen of ovariectomized 60 day-old rats. Sham cas trated animals had a piece of muscle inserted into the spleen. Jugular bloo d samples were taken monthly. After a year animals were cycled and decapita ted. Troncal blood was collected, autopsies were performed and luteoma were measured and fixed in 10% buffered formalin. Serum LH, FSH, PRL, estradiol and progesterone were measured. Serum inhibin content was determined in on e month-old tumors-bearing animals and estrous rats as controls. After one year no external changes in tumor-bearing rats were observed, nor differenc es in body weight or mortality rates compared to Sham animals. Metastatic p ropagation was absent. Routine histological examination showed two types of tumors according to either granulosa or luteal cell predomination, tumor t ype did not determine hormonal patterns. However, a clear relationship betw een gonadotropin levels and tumor size was established. Low gonadotropins: Small tumors, 18.7 % of cases and high gonadotropins: Large tumors, 81.3 %. In Sham animals gonadotropins attained castrate levels and remained elevat ed until the end of the experiment. In the Small group no increases in gona dotropins or estradiol were detected, progesterone and PRL fluctuated. In t he Large tumor group LH increased to Sham titers until month 7, then fell t o initial levels, FSH augmented significantly as from month three and remai ned high up to month 5. No variations in either estradiol, progesterone or PRL were observed. Serum inhibin of one month-old tumor-bearing rats was si gnificantly elevated, justifying the lack of FSH increase at this time poin t. We conclude that these luteoma do not suffer malignant transformation or induce metastases. They appear in two histological types. Tumor size depen ds on hormonal patterns. The delay in the initial increase and the sharp de crease observed in FSH in animals bearing Large tumors suggest a possible r ole for inhibin in this regulation.