Smooth muscle opioid effects

Loperamide, 4 mg initially, then 2 mg after each loose stool, not to exceed 8 mg daily Imodium A-D, various generic Loperamide, a synthetic opioid, acts on intestinal smooth muscle to decrease motility allowing for absorption of water and electrolytes. Poorly penetrates the CNS and has a lower risk of side effects compared with diphenoxylate or opiates. Not considered a controlled substance. 

Opioids induce an inhibitory effect on gastrointestinal motility and fluid secretion (Kromer, 1990). The effect is peripherally and centrally mediated. The peripheral component is related to p- and K-receptors in intestinal organs, which are densely equipped with opioid receptors. They are located at parasympathic ganglia and inhibit the release of acetylcholine, which stimulates the contraction of smooth muscles. Inhibition of the intestinal fluid secretion is mediated via inhibition of adenylate cyclase. The intestinal effects of opioids extend to all parts of the gut and results in inhibition of stomach emptying and inhibition of secretion and motility of duodenum, jejunum, colon and rectum. 

Esophageal motility is decreased by opioid agonists in both the proximal striated and distal smooth muscle portions. This effect appears to be mediated by mu opioid receptors in rats [70] or kappa opioid receptors in guinea pigs [71],... 

OFQ/N and the ORLl receptor are also involved in a number of other physiological effects (see Refs. 87,891. One of the most significant effects is the anxiolytic activity of OFQ/N (1013), which has been postulated to be one of OFQ/N s most fundamental actions, and may help explain the effects of OFQ/N on other phenomena [e.g., locomotion, reward, and feeding (87)]. A small molecule ORLl agonist has also demonstrated anxiolytic activity (1014), demonstrating an important potential therapeutic application of these compounds. Like opioids, OFQ/N inhibits electrically induced contractions in the GPI and MVD smooth muscle preparations these effects are... 

Paton and Zar (1968) described the dissection of the MP-LMP of the guinea-pig small intestine. This preparation has been invaluable in the study of neurotransmission from the myenteric plexus to the longitudinal smooth muscle, particularly by opioids and cannabinoids, without the confounding effects of the peristaltic reflex. A similar preparation has been used to study neuromuscular transmission to the circular smooth muscle (Izzo et al. 1998). Contractions of MP-LMP induced by electrical field stimulation (EES) were potently inhibited in a concentration-dependent fashion by the cannabinoid receptor agonists CP 55,940, CP 50,556, WIN 55,212-2, nabilone, CP 56,667, A -THC and cannabinol (Coutts and Pertwee 1997 Pertwee 2001). This inhibition was competitively and reversibly antagonised by SR141716A, without any effect on the inhibitory responses to normorphine... 

Kappa receptor activation does not appear to be responsible for dependence, euphoria, or effects on smooth muscle. Increases in cerebral blood flow and (possibly) increased intracranial pressure result from the respiratory depressant actions of opioid analgesics. The latter effects are due to increased arterial PrOj, which results from mu receptor inhibition of the medullary respiratory center. However, the activation of kappa receptors contributes to analgesia at the spinal level and is probably responsible for sedative actions of the opioids. The answer is (D). Codeine and possibly nalbuphine could decrease gastrointestinal peristalsis but not without marked side effects (and a prescription). Dextromethorphan is a cough suppressant. The other two drugs listed are opioids with antidiarrheal actions. Diphenoxylate is not available over-the-counter since it is a constituent of a proprietary combination that includes atropine sulfate (Lomotil). Loperamide is available over-the-counter. The answer is (D). 

The second most common alkaloid in opium is codeine, at 0.5-1% of total mass. Codeine is a weak opioid, and is commonly used as an analgesic, sometimes in combination with acetaminophen. The third most common alkaloid is thebaine, at 0.3-1%. Thebaine has similar chemistry but very different biological effects than morphine or codeine, causing dysphoria and agitation in low doses and seizures in high doses. Thebaine is commonly used as a precursor for synthetic opioids. Papaverine is also about 1% of opium, and is a smooth muscle relaxant with little CNS effect. It should be noted that many specialty varieties of P. somniferum have... 

It is absorbed both neuraxially and systemically. DepoDur has a principal effect on opioid receptors in the dorsal horn of the spinal cord as well as in other regions of the central nervous system (CNS). Additionally, it works in the gastrointestinal (GI) tract and other smooth muscles. However, it does not have a major effect on the cardiovascular system at therapeutic doses. 

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