Hypothalamic Releasing Hormone Tests

Publisher Summary This chapter describes hypothalamic releasing hormone tests. Two hypothalamic releasing hormone preparations are available for routine diagnostic use: (1) thyrotropin releasing hormone (TRH), also called thyroliberin, and (2) gonadotropin releasing hormone (GnRH), also known as luteinizing releasing hormone or luliberin. The TRH test is used most frequently to assess pituitary thyroid stimulating hormone (TSH) responsiveness; this requires measurement of TSH by radioimmunoassay prior to and following TRH administration. In normal subjects, serum prolactin (Prl) also increases and the test may, therefore, be used in the evaluation of prolactin secretion. The GnRH test is used to assess pituitary gonadotropin reserve, and measurements are, therefore, made of both follicle stimulating hormone and luteinizing hormone by radioimmunoassay prior to and following GnRH administration. The diagnostic indications for releasing hormone tests vary; in some circumstances, a comprehensive evaluation of anterior and posterior pituitary function is required and under such circumstances, the TRH and GnRH stimuli may be applied simultaneously with insulin hypoglycemia, the latter being used to evaluate growth hormone, ACTH, and Prl reserve.