Thyrotropin releasing hormone receptor and the adrenal gland

Abstract

Thyrotropin releasing hormone (TRH) is a hormone which is made in the hypothalamus and attaches to the thyrotropin releasing hormone receptor (TRHR) in the pituitary gland. By binding it stimulates the secretion of TSH which stimulates the secretion of T4 and T3. In horses with Cushing disease it also stimulates the ACTH secretion and subsequently the cortisol secretion. This fact is used in the TRH stimulation test to diagnose the horses with Cushing. In dogs TRH administration has a different result. After administrating TRH the cortisol concentration rises without an increasing in the ACTH concentration, in both healthy and Cushing dogs. These results can be explained when there would be expression of TRHR in the adrenal gland. This is the object of this research. In six adrenal gland samples and two pituitary gland samples the expression of TRHR is examined. After RNA isolation and cDNA synthesis, PCR is performed. In several samples of the adrenal glands and in both pituitary gland samples the TRHR is found. To evaluate the quantity of the TRHR in the adrenal gland, qPCR is used. Several gradients are performed but all did not succeed due to the lack of purity and quality of the products. Therefore no information about the quantity of the TRHR is available. Immunohistochemistry of the eight different adrenal gland sections revealed the presence of the receptor in the cortex and medulla of the adrenal glands. More research has to be done to measure the exact amount of the TRHR in the adrenal gland, to evaluate the difference between male and female, between cortex and medulla and between the different zones of the cortex. Also the whole receptor should be sequenced to examine the variation between different dogs and to compare the TRHR with the canine TRHR gene.