Degradation of thyrotropin releasing hormone and a related compound by rat liver and kidney homogenate.

The inactivation of the hypothalamic hormone by rat liver and kidney homogenates was studied, using specific radioimmunoassays for the measurement of thyrotropin releasing hormone, pGlu-His-Pro-NH2 (TRH), and for an analogous peptide, pGlu-His-Pro-OH(TRH-OH), which has been proposed as a major metabolite of TRH [NAIR et al., 1971]. The inactivation of TRH and the free acid was found to be rapid. Heat lability and saturation kinetics suggest the involvement of enzymatic processes. In liver homogenate, TRH-OH production from TRH was observed. The accumulation of TRH-OH was substantial in experiments employing near-saturation concentrations of TRH. The liver and kidney are ascribed as major sites for breakdown of TRH in vivo.