Intrahypothalamic localization and onset of production of thyrotrophin releasing factor (TRF) in the albino rat.

Thyrotrophin Releasing Factor (TRF) activity ofacidic extracts of the hypothalamus was investigated following lesions of different hypothalamic areas by the use of the intracarotid pituitary trophic hormone depletion technique of David et al. [1965]. TRF was almost completely absent following lesions of the suprachiasmatic, the paraventricular and of the arcuate-ventromedial hypothalamic areas. These three regions correspond to the hypophysiotrophic area (HTA) of Halasz et al. [1962, 1965]. No significant decrease in hypothalamic TRF activity was observed after lesions outside the HTA but still within hypothalamus (the dorsomedial, mamillary and antero-lateral areas). The destruction of the stalk-median eminence (SME) region led to an increased TRF concentration of the hypothalamic extract. This latter effect might be due to an accumulation of TRF in the SME, caused by the inhibition of TRF-output as a consequence of the interruption of the pituitary stalk and of the portal vessels. TRF production starts at the 6th postnatal day and reaches the adult level at about the 17th day after birth. The onset of TRF production corresponds with the time of the final development of the pituitary portal circulation.