Circulating opioid peptides during water immersion in normal man

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Abstract
This study was designed to evaluate variations in plasma .beta.-endorphin, methionine-enkephalin, adrenocorticotropic hormone and serum prolactin in healthy volunteers during head-out water immersion. Water immersion induced an increase in methionine-enkephalin plasma levels, which was associated with a significant fall in mean arterial pressure and heart rate. Conversely, a suppression of plasma .beta.-endorphin, adrenocorticotropic hormone and serum prolactin was detected during water immersion. We suggest that a dopaminergic inhibitory control mechanism may be involved in regulating circulating levels of .beta.-endorphin, adrenocorticotropic hormone and prolactin in normal subjects undergoing extracellular fluid volume expansion produced by water immersion.