Characterization of a new animal model of chronic hyperprolactinemia.

Animal models of chronic prolactin (PRL) excess have included rats bearing transplantable pituitary tumors that have produced other hypophyseal hormones in addition to PRL. We report characterization of a new model, the Buffalo rat implanted with the MMQ tumor, a line developed from the 7315a line. Rats implanted with the MMQ tumor have serum PRL levels that increase with time and correlate with the estimated volume of the subcutaneous tumor. When rats are killed 4 weeks after implantation, serum PRL levels are strikingly higher in tumor-bearing rats compared with controls (females, 2,723 +/- 266 v 192 +/- 46 ng/mL, P less than .0001; males, 1,637 +/- 213 v 99 +/- 11 ng/mL, P less than .0001). Serum PRL levels measured by the Nb2 lymphoma assay were higher than immunoassay measurements in both tumor-bearing and control Buffalo rats. Sephadex chromatography of serum from tumor-bearing rats showed that most of the PRL immunoreactivity co-eluted with 125I-rPRL. Neither serum growth hormone (GH) nor luteinizing hormone (LH) levels were different from controls in tumor-bearing rats. Female MMQ-bearing rats had lower estradiol levels. At death, the wet weights of adrenal glands, kidneys, and gonads were not affected by the presence of tumor. In contrast, tumor-bearing rats had increased spleen weight and histological evidence of white pulp hyperplasia. The Buffalo rat implanted with the PRL-only MMQ tumor is a promising new tool for the study of chronic hyperprolactinemia.