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 (t1/2) of TRH was compared to the PCR and t1/2 of pyroglutamyl-N3im-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 t1/2 of TRH was 6.2 min compared to a t1/2 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.