Effects of hemorrhage on vasopressin and Met-Enk releases in blood and cerebrospinal fluid in dogs.

To assess whether hemorrhagic shock causes simultaneous release of methionine enkephalin-like substance (MELS) and arginine vasopressin (AVP) both in cerebrospinal fluid (CSF) and circulating blood, continuous bleeding at a rate of 1 ml.kg-1.min-1 was undertaken for 40 min in anesthetized dogs (n = 6) and mean arterial pressure and heart rate were measured. In a time control study (n = 6), hemorrhage was omitted. Plasma AVP and MELS concentrations did not differ from CSF AVP and MELS in the control period in either the hemorrhage or the control groups. In the hemorrhage group, plasma AVP increased at 20 min and thereafter during the hemorrhagic shock, and plasma MELS increased at 30 and 40 min. No changes in AVP and MELS in the CSF occurred during hemorrhage, except a rise in AVP at 40 min. In the control group, AVP and MELS in the plasma and CSF did not change during the study, except for a rise in CSF AVP at 40 min. MELS was found in three forms: its large-molecular-weight form, methionine enkephalin, and metabolite; but the large-molecular-weight form was only observed in the CSF. These results showed that hemorrhage increases circulating MELS and AVP, but not MELS and AVP in the CSF, except for a slight rise in AVP during severe hypotension.