LOCALIZATION AND CONTENT OF THYROTROPHIN RELEASING FACTOR (TRF) IN MEDIAN EMINENCE OF THE HYPOTHALAMUS

An in vitro assay for thyrotrophin releasing factor (TRF) is described which is based upon release of TSH from hemi-pituitary glands of normal rats. Pre-incubation of the pituitary gland in rat plasma results in considerable increase in sensitivity to approximately 35 pg of TRF. The content of TRF in median eminence of the hypothalamus of normal rats is estimated to be in the range of 102–140 pg. When median eminence is incubated in vitro with 3H-TRF or when radiolabelled hormone is infused intraventricularly, autoradiographic evidence indicates that the hormone is present in specialized ependyma (tanycytes) of the median eminence.