EFFECTS OF TRH, PROLACTIN AND TSH ON CELL-PROLIFERATION IN THE INTERMEDIATE LOBE OF THE RAT PITUITARY-GLAND

The effect of TRH on cell proliferation in the anterior lobe of the pi tuitary is well known and documented. On the other hand, there are no data on the effects of TRH on the intermediate lobe of the pituitary g land. The aim of this study was to investigate the effect of TRH and i ts analogues (pGlu-His-Gly, pGlu-His-Gly-NH2) on cell proliferation in the intermediate pituitary lobe. The bromodeoxyuridine technique was used to detect the proliferating cells. It was found that TRH stimulat ed cell proliferation 24 h after a single injection at a dose of 100 m u g/kg body weight. The TRH analogues did not exert any significant st imulatory effect either 12 h or 24 h after the injection. The second e xperiment was carried out to distinguish the probable mechanism of the action of TRH. The effects of TSH and prolactin (PRL) on intermediate lobe cell proliferation were examined. It was found that both PRL and TSH exerted a significant stimulatory effect 24 h after a single s.c. injection of PRL at a dose of 150 IU/kg body weight or TSH at a dose 20 IU/kg body weight. It therefore appears that the stimulatory effect of TRH on intermediate pituitary lobe cell proliferation is mediated by PRL and TSH.