Release of immunoreactive thyroid stimulating hormone from the rat hypothalamus in vitro

Thyroid stimulating hormone (TSH) has been identified in the hypothalamus and other brain areas of the rat. However, the alteration of the release of brain TSH has not been demonstrated. Therefore, we examined the release of immunoreactive TSH (IR-TSH) in vitro from hypothalamic tissue obtained from hypophysectomized, thyroidectomized and intact control rats. Whereas TRH (10(-5) M) and PGE2 (10(-4) M) did not alter hypothalamic IR-TSH release, depolarizing concentrations of potassium (60 mM) or veratridine (5 mM) stimulated the release of IR-TSH from hypothalamic tissue from all groups. These data suggest that IR-TSH synthesized in the hypothalamus is stored in a releasable form.