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Postulated Physiological and Pathophysiological Roles on Motility
Published in Edwin E. Daniel, Neuropeptide Function in the Gastrointestinal Tract, 2019
Hans-Dieter Allescher, Sultan Ahmad
In the cat excitatory effects of opioids administered into the celiac arterial supply were demonstrated in the stomach534 and the pylorus.534–536 However, only inhibitory actions could be found in the canine stomach8 and canine pylorus10 when opioids were given close intra-arterially. When given intravenously, Met-enkephalin,537 morphine,538 and a κ-selective agonist, U-50488,539 were shown to increase gastric contractions and motor activity. However, in these studies a central action or an action outside the gastrointestinal tract could not be excluded or was probable.
CNS Receptors for Opioids
Published in Edythe D. London, Imaging Drug Action in the Brain, 2017
Richard J. Knopp, Mary Hunt, James K. Wamsley, Henry I. Yamamura
These observations of opioid receptor modulation of gastrointestinal transit differ from studies of the antidiarrheal properties of opioids. The antidiarrheal effect of opioids probably results as much from their antisecretory activity in the gastrointestinal tract as from their antitransit effects since: (1) all opioids studied are significantly more potent as antidiarrheal agents than as antitransit agents and (2) the pharmacological profile of opioid-induced antidiarrheal activity is different from that of antitransit activity (Shook et al., 1989). U-50,488, which has little activity against gastrointestinal transit, is a potent inhibitor of castor oil-induced diarrhea in mice after S.C., but not i.c.v., administration while DPDPE, which fails to affect gastrointestinal transit after s.c. or i.c.v. injection, inhibits diarrhea following administration at both sites. Thus, the population of opioid receptors mediating opioid antidiarrheal activity includes all three receptor types and involves actions at peripheral and CNS sites.
Use and knowledge of novel synthetic opioids: An Italian survey
Published in Journal of Ethnicity in Substance Abuse, 2022
Gianfranco Stigliano, Andrea Miuli, Alessandra Vizziello, Arianna Ida Altomare, Aliseo Lalli, Maria Chiara Alessi, Antonella Sociali, Annarita Rucco, Chiara Vannini, Giovanni Martinotti, Massimo di Giannantonio
Novel synthetic opioids (NSOs) are a large family of analgesics and anesthetics, mainly synthesized in the 1970s (Tabarra et al., 2019) and belonging to the family of new psychoactive substances (NPS), that are defined as “[s]ubstances of abuse, either in a pure form or a preparation, that are not controlled by the 1961 Single Convention on Narcotic Drugs or the 1971 Convention on Psychotropic Substances, but which may pose a public health threat” (Arillotta et al., 2020; Van Hout et al., 2018). On a pharmacodynamic level, these drugs work by binding mu (μ), delta (δ), and kappa (κ) opioid receptors (Baumann et al., 2018). The inhibition of gamma-aminobutyric acid (GABA) release mediated by μ1-opioid receptor activation results in a subsequent increase in release of dopamine in the nucleus accumbens (Horsfall & Sprague, 2017), a fundamental stage of the reward system (Carelli, 2002). One of the most used NSOs for analgesic purpose is fentanyl, a high-potency opioid, 80 times more powerful than morphine (Raffa et al., 2018) and 40 times more than heroin (Fairbairn et al., 2017). It was synthesized in the 1950s, and the US Food and Drug Administration approved it as an analgesic agent for persistent moderate to severe chronic pain and also for general and regional anesthesia (Nair, 2017). Fentanyl was only the first of the NSOs, and it was followed by a series of related substances (the so-called fentanyls) which share a similar chemical structure and therapeutic efficacy but also similar addiction power (Carelli, 2002; Nair, 2017). To obtain substances similar to fentanyl, the propionyl chain (e.g., acetylfentanyl) or the ethyl-phenyl moiety (e.g., isofentanyl) could be modified (Misailidi et al., 2018). Some of these substances, such as falfentanil or sufentanil, have become widely used as anesthetics and for pain management, while carfentanil and thiafentanil are used in veterinary medicine to immobilize large animals (Evans-Brown et al., 2018; Ujváry et al., 2017). Beside fentanyls, there are also structurally distinct non-fentanyl opioid receptor agonists, divided into benzamides (such as AH-7921, U-47700, U-77891, U-48800, and U-49900), acetamides (such as U-51754 and U-50488), and piperazines (MT-45, W-18, and AD-1211; Solimini et al., 2018).