Cryptic Met-enkephalin in adrenal and portal vein during splanchnic artery occlusion shock in cats

Adrenal vein (AD), portal vein (PV), and femoral artery (FA) plasma levels of immunoreactive (IR) Met-enkephalin pentapeptide (ME) and extended ME-IR forms, obtained after sequential incubation of plasma with trypsin and carboxypeptidase B, were examined in 4 cats during splanchnic artery occlusion shock at baseline (S1), during early shock (S2), late shock (S3), and after naloxone (1 mg/kg, i.v.) administration (S4). Early shock (S2) led to a significant increase in levels of extended and fully processed Met-enkephalin IR at all 3 collection sites (AD, PV, FA) without a change in proportional levels of extended Met-enkephalin IR to the pentapeptide IR (ME). Naloxone administration during late shock (S4), however, resulted in a disproportionate increase (150-fold from baseline) in adrenal vein plasma levels of extended Met-enkephalin IR forms, as compared to ME IR (23-fold). In contrast, no changes in plasma levels occurred in PV and FA.