Formation and degradation of deamido-TRH (pyroglutamyl-histidyl-proline) in rat brain after intraventricular injection of TRH.

Thyrotropin-releasing hormone (TRH) injected into the lateral ventricle of the rat's brain was rapidly metabolized to deamido-TRH (DA-TRH). Brain levels of TRH decreased with a half-life of 7 min, while the DA-TRH formed from its disappeared with a half-life of 2.5 min. To prevent the post-mortem degradation of DA-TRH it was necessary to sacrifice rats by directing focused microwave irradiation towards the brain. The short half-lives determined for TRH and DA-TRH in vivo were much shorter than those obtained using in vitro techniques. The in vivo formation and accumulation of DA-TRH was inhibited by bacitracin and unaffected by probenicid.