Opioids

Modulation of Peripheral Sensory Neurons by the Immune System: Implications for Pain Therapy

“…These peptides and their derivatives exhibit different affinity and selectivity for the -(END, Metenkephalin), ␦-(enkephalins, END), and -(dynorphin) receptors (Table 1). (for review, see Zöllner and Stein, 2007). Two additional endogenous opioid peptides have been isolated from bovine brain: endomorphin-1 and endomorphin-2.…”

“…Tolerance to Opioid Analgesics. Long-term opioid treatment can result in loss of opioid receptor function (desensitization, tolerance) (for review, see Zöllner and Stein, 2007). Previous concepts of opioid tolerance have been revised extensively in view of recent findings on the regulation of intracellular receptor trafficking (Waldhoer et al, 2004;Moore et al, 2007).…”

“…Additional pharmacological subtypes may result from alternative splicing, posttranslational modifications, or receptor oligomerization (Waldhoer et al, 2004; for review, see Kieffer and Evans, 2009;van Rijn et al, 2010). Opioid receptors are expressed by central and peripheral neurons, by neuroendocrine (pituitary, adrenals), immune, and ectodermal cells (for review, see Zöllner and Stein, 2007).…”

Opioid mediated activity and expression of mu and delta opioid receptors in isolated human term non-labouring myometrium

“…The mechanism by which opioid receptor activation alters the contractile response of myometrium is not known but can be postulated through several mechanisms. Opioid receptors interact with various ion channels in the membrane through inhibitory G proteins (Gi) including calcium and potassium channels, leading to suppression of calcium influx and membrane hyperpolarisation respectively (Zollner, 2006). Opioid receptor activation in the myometrium could also lead to increased contractile activity through cAMP accumulation by the inhibition of adenyl cyclase and by stimulating phospholipase C, increasing intracellular calcium (Zollner, 2006).…”

“…Opioid receptors are coupled to inhibitory G proteins. Opioid receptor activation leads to decreased cyclic adenosine monophosphate (cAMP) formation and modification of ion channel activities resulting in reduced calcium influx and stimulation of potassium efflux (Zollner, 2006). These mechanisms suggest that opioids could directly affect the contractile response of human myometrium through the modulation of myocyte calcium fluxes and in decreasing cAMP generation, which at term promotes uterine contractility (Lopez-Bernal, 2003) and decreased progesterone responsiveness (Smith, 2007).…”