Relationship of corticotroph proliferation answer and survival time after adrenalectomy was examined. Corticotroph proliferation rates were detected by short-term 3H-thymidine radiolabeling, then ACTH immunostaining and autoradiography. Effect of adrenalectomy on corticotroph proliferation rate was examined in vivo and an elevation was demonstrated first on the second postoperative day, increasing on the third-fourth day postoperatively and then decreasing. Effects of different secretagogues on corticotroph proliferation were examined in short-term pituitary monolayer cultures taken from ADX rats. CRF and Forskolin treatment potentiated corticotroph proliferation in cultures taken from adrenalectomized rats, but not in the controls. We suggest that croticotroph proliferation is stimulated via the cAMP-proteinkinase A pathway, while adrenalectomy plays a permissive role.
The aim of this work was to detect if hypothalamic-pituitary maturation was accompanied by significant proliferation changes in differentiated pituitary cell pools. For this purpose, pituitary corticotroph (Ct), mammotroph (Mt) and somatotroph (St) proliferation activities were scanned in intact female rats during the postnatal (P) period (1-35 postnatal days). The techniques of tritiated thymidine labelling, immunostaining and autoradiography were combined to visualize DNA synthesis of hormone containing cells. Immunoreactive cell densities were measured using image analysis, and double labelled cells were counted. Corticotroph proliferation activity increased significantly on day P12, followed by an increase in the Ct proportion on days P13-14. This is the first 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 maturation, 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 increased reaching a plateau between days P13 and 20, then decreased to the adult level. Each cell type examined showed a characteristic, individual density and proliferation pattern.
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