Plasma levels of corticotroph-type pro-opiomelanocortin derivatives such as beta-lipotropin, beta-endorphin(1-31), or adrenocorticotropic hormone are correlated with severity of postoperative pain.
BACKGROUND
In the pituitary of lower species, pro-opiomelanocortin is expressed in corticotroph cells of the anterior and in melanotroph cells of the neurointermediate lobe; enzymatic processing in the corticotrophs results in the release of adrenocorticotropic hormone, beta-lipotropin, or beta-endorphin. In the melanotrophs, these fragments are further modified, eg, by N-terminal acetylation. In the human pituitary, these enzyme systems are located within the same cells in the anterior lobe. We studied the reactions of the pro-opiomelanocortin system under preoperative conditions as well as under postoperative pain.


METHODS
In 17 patients undergoing hip or knee arthroplasty, we determined plasma concentrations of N-acetyl-beta-endorphin immunoreactive material, authentic beta-endorphin [beta-endorphin(1-31)], adrenocorticotropic hormone, beta-lipotropin immunoreactive material, and cortisol, as well as pain severity rated by the patients using a visual analogue scale before surgery, after surgery but still under spinal anesthesia, under postoperative pain, and 1 day after surgery.


RESULTS
Only low levels of N-acetyl-beta-endorphin immunoreactive material were measured in 16 out of 17 patients. High concentrations (1st quartile/median/3rd quartile; pmol/L) of adrenocorticotropic hormone (22.5/55.8/124) and beta-lipotropin immunoreactive material (6.6/34.6/142) were observed under postoperative pain, accompanied by a small increase of beta-endorphin(1-31) concentrations (0.0/6.1/10.9). Preoperatively small but significantly elevated levels of corticotroph-type and melanotroph-type pro-opiomelanocortin derivatives were observed; in contrast, spinal anesthesia suppressed all pro-opiomelanocortin fragment release. Postoperative pain severity correlated with postoperative adrenocorticotropic hormone, beta-lipotropin immunoreactive material, and beta-endorphin(1-31) concentrations.


CONCLUSIONS
We conclude that the melanotroph-type pro-opiomelanocortin system is not activated under postoperative pain; the increase of corticotroph-type pro-opiomelanocortin fragment levels is different in quantity and proportion under preoperative conditions or postoperative pain, respectively.
Matejec
Reginald
R
Department of Anaesthesiology, Intensive Care Medicine and Pain Therapy, Justus-Liebig-University, Giessen, Germany. reginald.matejec@chiru.med.uni-giessen.de
Harbach
Heinz-W
HW
Bödeker
Rolf-H
RH
Hempelmann
Gunter
G
Teschemacher
Hansjörg
H
D000324:Adrenocorticotropic Hormone / Q000097:blood* / Q000378:metabolism*; D000368:Aged; D000775:Anesthesia, Spinal; D019644:Arthroplasty, Replacement, Hip; D019645:Arthroplasty, Replacement, Knee; D001800:Blood Specimen Collection; D002021:Buffers; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007202:Indicators and Reagents; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement / Q000187:drug effects; D010149:Postoperative Pain / Q000097:blood*; D010446:Peptide Fragments / Q000097:blood*; D010902:Pituitary Gland / Q000378:metabolism; D011333:Pro-Opiomelanocortin / Q000097:blood*; D011446:Prospective Studies; D001615:beta-Endorphin / Q000097:blood*; D008083:beta-Lipotropin / Q000097:blood*
D002021:Buffers; D007202:Indicators and Reagents; D010446:Peptide Fragments; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone; D008083:beta-Lipotropin; D006854:Hydrocortisone