[Labor pain--physiologal basis and regulatory mechanisms]

Clinically, labor (visceral) pain is extremely prevalent in general population, yet its mechanisms have been poorly understood. With development of new electrophysiological techniques and molecular biology technologies, our understanding of physiological bases of labor pain has been markedly improved; in that way possibilities for therapeutic modulation of labor pain are expanded. The aim of this study was to describe the new insight into this topic. In this paper, the theory was exposed that the reason for labor pain had been found in sensitization at the levels of the uterus, dorsal root neurones and phychologic factors. Peripheral sensitization occurs due to cervical inflammatory reaction, associated with cervical ripening and remodeling. Chemical inflammatory mediators (notably prostaglandins, cytokines, granulocytes, enzymes such as metalloproteinases, integrines) activate nociceptive nerve fibers. Nociceptive threshold is reduced (resulting in primary hyperalgesia) and because of that there occurs the total number of action potentials generated and propagated by nociceptive peripheral nerves (visceral hypersensitivity). Central sensitization arises due to phosphorylation of N-methyl-D-aspartate (NMDA) receptors of dorsal root neurones. Numerous receptors, ion channels and signaling molecules, which, together with opioid peptides participate in spinal pain control, represent, at the level of central sensitization, possible therapeutic goals for labor pain modulation. Some of them are: DREAM which constitututively suppresses transcription of mRNA for opioid peptides, oncostatin M, COX-2 inhibitors, cFOS protein, tachykinins, gamma-butyric acid agonist, L-type Ca++ channels. Fear, as one of the most frequent phychologic factors, does (not) provide good control in transmision of pain sensitization by descendent nerve fibers. Some of the candidates for objective pain marker are also described. This article outlines the factors that, based on the contemporary viewpoint, could reduce transmission of pain signals, and thus broaden therapeutic possibilities for modulation of labor pain.