PROLACTIN AND GROWTH-HORMONE MESSENGER-RNA AND PROTEIN CHARACTERIZATION IN SMTTW RAT PITUITARY-TUMORS

We have combined different techniques to analyse passages of five diff erent rat spontaneous pituitary tumours (SMtTW) that were transplanted under the kidney capsule. These tumours were secreting prolactin (PRL ), GH or both hormones. RIA, immunocytochemistry (ICC) and Western blo t analysis were applied to characterize the hormone(s) stored (ICC and Western blot) and secreted (RIA). mRNA content was analysed by PCR, N orthern blot analysis and in situ hybridization.The data point not onl y to the reliability of the techniques used at both protein and RNA le vels for each tumour studied but also to the complementarity of some t echniques. For example, whereas Northern blot analysis demonstrates th e presence and size of hormone mRNA, in situ hybridization indicates t he percentage of cells expressing a given hormone mRNA and allows the presence of one population (or more) of cells in a given tumour to be identified. Moreover, the tumours were compared with normal rat pituit ary. Although the PRL and GH mRNAs were identical in size, the amount of mRNA was lower in the tumours. At the protein level, the PRL and GH variants exhibited a different pattern of expression in tumours compa red with the normal rat pituitary. The biological significance of thes e differences is discussed.