Thyrotropin-releasing hormone (TRH): Measurements in human spinal fluid

Levels of thyrotropin-releasing hormone (TRH) were quantitated in human lumbar spinal fluid (CSF) utilizing a sensitive and specific TRH radioimmunoassay. Endogenous TRH was sufficiently stable in CSF to permit 85% recovery of intact TRH after 48 h storage at 4 C. TRH levels in AM or PM samples obtained from 15 women and 12 men were easily detected in all CSF specimens. No significant difference between the TRH concentration in CSF of men and women was observed (44.2+/-6.8 and 38.1+/-6.5 pg/ml (mean+/-SE) respectively). TRH concentrations were 40.2+/-6.9 pg/ml (mean+/-SEM) in AM and 41.4+/-8.0 pg/ml in PM samples. By contrast, CSF cortisol levels obtained concurrently were twofold higher in AM than PM (0.68+/-0.08 vs 0.38+/-0.02 mug/100 ml (mean+/-SEM) respectively, P less than 0.001). These data are consistent with the possibility that a portion of the TRH in CSF can be derived from the central nervous system (CNS) and unrelated to the hypo-physiotropic control of thyrotropin (TSH) synthesis and secretion.