Plasma β-endorphin during clinical and experimental ischaemic pain

Abstract

P-endorphin during clinical and experimental ischaemic pain. Scand J Clin Lab Invest 1987; 47: 751-758.An improved radio-immunoassay using an antiserum directed towards the N-terminal part of the endogenous opioid peptide f3-endorphin 1-31 (f3-EP) was validated and applied to a study of P-EP in plasma during ischaemic pain. Experimental ischaemic pain induced in seven healthy volunteers by the submaximal effort tourniquet test did not change plasma P-EP or adrenocorticotrophin. Plasma P-EP was determined in 21 patients with acute myocardial infarction (AMI) and in seven patients with unstable angina pectoris. Plasma P-EP was 4.9 fmoVml with 95% confidence limits, 3.2-7.8 fmol/ml in AM1 patients at admittance, and 2.9 (2.G3.4) fmoUml one week later in stable and pain-free condition (p<0.05). The level in 49 healthy persons was 2.8 (2.4-2.9) fmol/ml. Elevated P-EP levels were found in five AM1 patients with cardiogenic shock and in four AM1 patients dying within 24 h after admittance compared to the rest of AM1 patients (p<0.02). P-EP was not elevated during unstable angina pectoris, although pain scores were similar to AMI. The AM1 group revealed a significant, although weak, positive correlation between plasma P-EP and pain score (Spearman r=0.49. p<0.05), while there was no correlation during unstable angina pectoris. P-EP was not correlated to the amount of morphine required within the 48 h after admittance of AM1 patients. We conclude that the increase of p-EP in plasma during AM1 may be due to stressful factors other than ischaemic pain and that it is questionable whether p-EP in plasma is related to antinociception.The 31 amino acid residue peptide, Panalgetic properties when tested in biological endorphin (P-EP), characterized by potent assays [l], is cleaved from the 31 kDa common 75 1 Scand J Clin Lab Invest Downloaded from informahealthcare.com by McMaster University on 11/18/14 For personal use only. Scand J Clin Lab Invest Downloaded from informahealthcare.com by McMaster University on 11/18/14 For personal use only. Scand J Clin Lab Invest Downloaded from informahealthcare.com by McMaster University on 11/18/14 For personal use only.

What do plasma beta‐endorphin levels reveal about endogenous opioid analgesic function?

“…Endogenous opioids are relevant to understanding responses to both acute (Buchsbaum et al., ; Gracely et al., ; Anderson et al., ) and chronic pain (Maixner et al., ; Bruehl et al., ; Bragdon et al., ; Bruehl et al., ). BE is a key analgesic endogenous opioid that has been the focus of numerous studies, often via assessment of plasma levels (Cohen et al., ; Pickar et al., ; Bach et al., ; Leonard et al., ; Guasti et al., ; Bragdon et al., ; Matejec et al., ; al'Absi et al., ; Bruehl et al., ). Surprisingly little is known about what information resting plasma BE levels provide regarding functioning in the endogenous opioid antinociceptive system.…”

“…Previous studies have not directly examined associations between resting plasma BE and functional measures of endogenous opioid antinociceptive activity. Prior work focusing on plasma BE and pain-related outcomes variously suggested these associations might be positive (Cohen et al, 1982;Pickar et al, 1983), negative (Bach et al, 1987;Leonard et al, 1993;Matejec et al, 2003) or non-existent (Sheps et al, 1995;Tordjman et al, 2009). Interpretation of these studies was hindered by frequently small sample sizes [e.g., n = 9 (Cohen et al, 1982); n = 17 (Matejec et al, 2003)].…”

“…Three small studies reporting that higher resting pre‐surgical plasma BE levels predict lower post‐operative opioid analgesic requirements (Cohen et al., ; Pickar et al., ; Nader‐Djalal et al., ) and work noting inverse associations between resting plasma BE and subsequent experimental pain sensitivity (Guasti et al., ) suggested that elevated resting BE levels might be a marker for more effective endogenous opioid analgesia. In contrast, clinical studies indicating that higher resting plasma BE predicts greater subsequent acute pain intensity suggested that higher BE levels might be a marker for reduced endogenous opioid analgesia (Bach et al., ; Leonard et al., ; Matejec et al., ). The current study tested these two alternative hypotheses.…”

“…One is to assay levels of beta‐endorphin (BE), an endogenous mu opioid receptor agonist with significant analgesic properties (Millan, ). Due to ease of acquiring samples, plasma BE levels are often examined as they relate to acute and chronic pain outcomes (Cohen et al., ; Pickar et al., ; Bach et al., ; Falcone et al., ; Leonard et al., ; Guasti et al., ; Matejec et al., ; al'Absi et al., ; Bruehl et al., ). Other studies examine pain‐related influences of BE in the central nervous system (CNS) via sampling of cerebrospinal fluid (Cleeland et al., ; Spaziante et al., ; Matejec et al., ).…”

Do Resting Plasma β-Endorphin Levels Predict Responses to Opioid Analgesics?

“…Plasma BE levels therefore do not necessarily indicate opioid status in the central nervous system, where the primary analgesic effects of BE occur 23–25 . Nonetheless, a number of studies report associations between plasma BE levels and pain responses, although not always in a consistent direction 26–34 .…”