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Clinical pharmacology: opioids
Published in Pamela E Macintyre, Suellen M Walker, David J Rowbotham, Clinical Pain Management, 2008
David J Rowbotham, Alcira Serrano-Gomez, Anne Heffernan
Martin and colleagues4 were the first to classify opioid receptors. In 1976, they described the mu (μ), kappa (κ), and sigma receptors (σ). This was based on the specificity of three agents acting at these receptors, i.e. morphine, ketazocine (ketocyclazocine), and SKF10047, respectively. The delta (δ) and epsilon (ε) receptors were identified shortly after this, based on their responses to enkephalins and β-endorphins (but not morphine), respectively.5, 6 However, data from later studies demonstrated conclusively that sigma and epsilon receptors were not opioid receptors.7, 8 It has taken a long time for these findings to be appreciated by some, particularly with respect to the sigma receptor. From the 1980s, only three opioid receptors (μ, κ, and δ) were recognized.
The sigma-2 (σ-2) receptor: a review of recent patent applications: 2013–2018
Published in Expert Opinion on Therapeutic Patents, 2018
Benjamin E. Blass, John Patrick Rogers
The sigma-2 receptor and the analogous sigma-1 receptor have been an enigma since their original discovery in 1976. In their key paper, Martin and his colleagues described their efforts to classify opioids based on responses observed in chronic spinal dogs. The authors described that morphine (1), ketocyclazocine (2, aka ketazocine), and SKF-100047 (3, aka N-allylnormetazocine, NANM) (Figure 1) produced different responses in this model. On that basis, they postulated that there were three opiate receptors. These receptors were designated the µ-opioid receptor (morphine type, MOR), the κ-opioid receptor (ketocyclazocine type, KOR), and the σ-opioid receptor (SKF-100047 like) [1]. The aforementioned studies were conducted with racemic material, and while they were critical to the development of the modern understanding of MOR and KOR, the use of racemic SKF-100047 produced an erroneous conclusion with regard to the sigma receptor. It has since been determined by Su et al. [2] and Khazan et al. [3] that (–)-SKF-100047 elicits opioid-mediated physiological responses through MOR and KOR. In addition, the activity of (+)-SKF-100047 is mediated by a nonopioid receptor, the sigma receptor.