Plasma levels of thyrotropin-releasing-hormone in various splanchnic, renal, suprarenal, and cerebral veins.

Endogenous TRH levels were determined in plasma obtained selectively via percutaneous transhepatic and femoral catheterization. TRH was measured using a very sensitive RIA method. In the pancreatic veins, internal jugular vein, left testicular vein, and other described veins, normal peripheral levels were found. An involvement of the TRH degrading enzyme (TDE) or a rapid intravasal dilution leading to normal peripheral TRH levels in the veins leaving the brain or pancreas, respectively, is discussed.