Accumulation of Thyrotropin Releasing Hormone by Rat Hypothalamic Slices

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Abstract
TRH may play an active role in synaptic transmission. If such is the case, an inactivation mechanism must exist, in analogy to other neuroactive substances. The possibility that TRH may be taken up by rat hypothalamic slices was considered. In the presence of bacitracin TRH was stable in the medium up to 90 min. Intact [3H]Pro-TRH was associated with the slices as evidenced by TLC and paper electrophoresis; the association was time-dependent up to 60 min, and the maximum tissue-to-medium ratio was 1.3 at this time. At 5 min incubation, 30-50% of the TRH was not extracellular, and the plot of TRH-associated tissue vs. the total amount of tissue was linear up to 2 hypothalami per flask. The association was saturable (Km 1.07 .mu.M) and temperature-dependent, and the saturable part of the accumulation was inhibited by ouabain, dinitrophenol and the absence of glucose. Results suggest that an uptake mechanism for TRH exists in the hypothalamus; its physiological relevance remains to be elucidated.