Response of beagle mammary dysplasias to various hormone supplements in vitro.

The canine mammary tumor system is receiving increas ing attention as a model system for drug testing and for experimental study of basic mammary biology. In order to contribute to this model system, the hormone sensitivity of three types of canine preneoplastic lesions was identified morphologically on the basis of in vitro responses of organcultured expiants to various hormone supplements. Dysplastic tissues were selected in vivo on the basis of their difference in hormone responsiveness. Differential hor mone sensitivity of dysplastic from normal tissues persisted in vitro. Three types of tissues were studied: ductal connec tive tissue dysplasias, hyperplastic alveolar lobular dysplasias, and expiants of an adenoma. All maintained their structure in vitro, independent of the hormone supplement provided. Secretion in alveolar lesions was hormone-inde pendent. Secretion in the adenofibroma was hormone re sponsive, both to supplements that promote secretion in normal tissues of beagles (cortisol, mammotropin, and in sulin; and estradiol, progesterone, cortisol, mammotropin, somatotropin, and insulin) and to two hormone combina tions to which normal tissues are unresponsive (mammotro pin, somatotropin, and insulin; and estradiol, progesterone, cortisol, and insulin). Exploitation of in vitro techniques promises to be a valua ble tool for exploring the progression from normal to neoplastic in canine mammary tissues.