Thyrotrophin receptor protein expression in normal and adenomatous human pituitary

Thyrotrophin (TSH) synthesis and secretion is under the positive control of thyrotrophin releasing hormone and under the negative control of the thyro id hormones. However, it is hypothesised that TSH has a direct effect on th e regulation of its own synthesis through an intrapituitary loop mediated b y pituitary TSH receptors (TSH-R), The aim of this investigation was to stu dy the expression of TSH-R in normal human pituitary at mRNA and protein le vels, and to compare the pattern of protein expression between different pi tuitary adenomas. Using RT-PCR we were able to detect TSH-R mRNA in the nor mal pituitary, and immunohistochemical studies showed TSH-R protein express ion in distinct areas of the anterior pituitary. Double immunostaining with antibodies against each of the intrapituitary hormones and S100 revealed t hat TSH-R protein is present in thyrotrophs and folliculostellate cells. Ex amination of 58 pituitary adenomas, including two clinically active and two clinically inactive thyrotroph adenomas, revealed TSH-R immunopositivity i n only the two clinically inactive thyrotroph adenomas. This study shows, for the first time, the presence of TSH-R protein in the normal anterior pituitary and in a subset of thyrotroph adenomas. The expre ssion of TSH-R in the thyrotroph and folliculostellate cell subpopulations provides preliminary evidence of a role for TSH in autocrine and paracrine regulatory pathways within the anterior pituitary gland.