CORTICOTROPH, SOMATOTROPH AND MAMMOTROPH CELL-KINETICS IN THE POSTNATAL INFANT FEMALE RAT

The aim of this work was to detect if hypothalamic-pituitary maturatio n was accompanied by significant proliferation changes in differentiat ed pituitary cell pools. For this purpose, pituitary corticotroph (Ct) , mammotroph (Mt) and somatotroph (St) proliferation activities were s canned in intact female rats during the postnatal (P) period (1-35 pos tnatal days). The techniques of tritiated thymidine labelling, immunos taining and autoradiography were combined to visualize DNA synthesis o f hormone containing cells. Immunoreactive cell densities were measure d using image analysis, and double labelled cells were counted. Cortic otroph proliferation activity increased significantly on day P12, foll owed by an increase in the Ct proportion on days P13-14. This is the f irst observation of a spontaneous change of corticotroph proliferation at the end of the stress nonresponsive period. The mammotroph density and proliferation rate increased gradually during postnatal maturatio n, until the Mt pool overran other cell types of the female hypophysis on day 35. The somatotroph pool was the most numerous until day P20; the proliferation rate remained constant while St proportions increase d reaching a plateau between days P13 and 20, then decreased to the ad ult level. Each cell type examined showed a characteristic, individual density and proliferation pattern.