Placenta ingestion by rats enhances delta- and kappa-opioid antinociception, but suppresses mu-opioid antinociception.
Ingestion of placenta or amniotic fluid produces a dramatic enhancement of centrally mediated opioid antinociception in the rat. The present experiments investigated the role of each opioid receptor type (mu, delta, kappa) in the antinociception-modulating effects of Placental Opioid-Enhancing Factor (POEF-presumably the active substance). Antinociception was measured on a 52 degrees C hotplate in adult, female rats after they ingested placenta or control substance (1.0 g) and after they received an intracerebroventricular injection of a delta-specific ([D-Pen2,D-Pen5]enkephalin (DPDPE); 0, 30, 50, 62, or 70 nmol), mu-specific ([D-Ala2,N-MePhe4,Gly5-ol]enkephalin (DAMGO); 0, 0.21, 0.29, or 0.39 nmol), or kappa-specific (U-62066; spiradoline; 0, 100, 150, or 200 nmol) opioid receptor agonist. The results showed that ingestion of placenta potentiated delta- and kappa-opioid antinociception, but attenuated mu-opioid antinociception. This finding of POEF action as both opioid receptor-specific and complex provides an important basis for understanding the intrinsic pain-suppression mechanisms that are activated during parturition and modified by placentophagia, and important information for the possible use of POEF as an adjunct to opioids in pain management.
DiPirro
Jean M
JM
Behavioral Neuroscience Program, Department of Psychology, University at Buffalo, Buffalo, NY 14260, USA. dipirrjm@buffalostate.edu
Kristal
Mark B
MB
D000700:Analgesics / Q000008:administration & dosage; D000818:Animals; D001522:Behavior, Animal; D004056:Differential Threshold; D004305:Dose-Response Relationship, Drug; D005247:Feeding Behavior; D005260:Female; D007276:Injections, Intraventricular; D009043:Motor Activity; D017288:Pain Threshold / Q000187:drug effects; D010920:Placenta; D011247:Pregnancy; D011759:Pyrrolidines / Q000008:administration & dosage; D051381:Rats; D020318:Rats, Long-Evans; D011930:Reaction Time / Q000187:drug effects; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000378:metabolism*; D017473:Receptors, Opioid, kappa / Q000819:agonists / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000378:metabolism*; D012726:Sexual Behavior, Animal
D000700:Analgesics; D011759:Pyrrolidines; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; C051272:spiradoline