Plasma Clearance and Plasma Half-Disappearance Time of Exogenous Thyrotropin-Releasing Hormone and Pyroglutamyl-N3im-Methyl-Histidyl Prolineamide*

Abstract

The plasma clearance rate (PCR) and plasma half-disappearance time (t½) of TRH was compared to the PCR and t½ of pyroglutamyl-N^3im-methyl-histidyl prolineamide (methyl-TRH), a more potent analog of TRH in normal subjects. The PCR for TRH was 1500 ± 329 (SD) ml/min, which was significantly greater than the PCR of methyl-TRH (783 ± 96 ml/min). The t½ of TRH was 6.2 min compared to a t½ of 11.5 min for methyl-TRH. The slower clearance of methyl-TRH is probably due to the increased resistance to degradation by serum enzymes of methyl-TRH compared to TRH. (J Clin Endocrinol Metab48: 377, 1979)