The alterations in arterial, venous and adrenal vein levels of immunoreactive Met-enkephalins following endotoxin administration have been investigated in dogs by direct measurement and gel filtration chromatography. Animals were anaesthetized with α-chloralose and allowed to breath spontaneously. The left lumbar adrenal vein, limb vein and femoral artery were cannulated for blood sampling. Severe shock was produced by the administration of a large bolus of E. coli endotoxin followed by a continuous infusion. The production of endotoxin shock was associated with significant increases in adrenal vein and systemic venous plasma immunoreactive Met-enkephalin levels. Forty-five minutes after induction of endotoxin shock arterial immunoreactive Met-enkephalin levels were generally higher than baseline values. In resting anaesthetized animals a large 31 000 molecular weight form of Met-enkephalin, presumably proenkephalin, was found in plasma obtained from the adrenal vein, systemic and pulmonary circulations. Following endotoxin this enkephalin-containing peptide still predominated in arterial and venous plasma, whereas in the adrenal vein the proportion of Met-enkephalin immunoreactivity attributable to this large peptide fell. This was associated with the appearance of increasing amounts of smaller molecular forms (18 000, 8000, 3–5000 molecular weight and the pentapeptide itself). In this model enkephalin-containing peptides were not biochemically modified by their passage through the lungs.

J. Endocr. (1986) 111, 329–334