THE EFFECT OF GHRH ON TSH RELEASE IN RATS IN-VIVO AND IN-VITRO

In man, GHRH has been shown to potentiate the TSH-releasing activity o f TRH. To study the way by which GHRH affects TRH-stimulated TSH relea se, we examined the effect of GHRH (1-29)NH2 on basal and stimulated T SH secretion in intact male rats and superfused dispersed rat pituitar y cells. In the intact rats, GHRH(1-29)NH2 potentiated TRH-stimulated TSH release in the evening, but potentiation was not observed in the m orning and in dispersed pituitary cells. Basal TSH levels were not cha nged by GHRH(1-29)NH2. It is concluded that GHRH(1-29)NH2 potentiates the TSH-releasing activity of TRH in the evening in rats possibly thro ugh suprahypophyseal disinhibition.