Evidence of receptors for thyrotropin-releasing hormone in human prolactin-secreting adenomas.

Specific receptors for TRH were demonstrated on cellular membranes from 8 out of 10 human PRL-secreting adenomas. One binding site was characterized. The mean (+/- SD) value for the dissociation constant (Kd) from 8 adenomas was 68 +/- 7 nM. The maximal number of binding sites varied from 1 adenoma to another (from 50-1200 fmol/mg protein). In 7 of the 8 patients, there was little or no in vivo plasma PRL response to TRH although receptors for TRH were present on their tumors. It is thus suggested that in vivo absence of stimulatory effect of TRH in human PRL-secreting adenomas is not due to the absence of TRH receptors.