If 5HT3 stimulation causes increased GI motility why do we want to block them in Vomiting by giving 5ht3 antag?

NEET PG
#1

If 5HT3 stimulation causes increased GI motility why do we want to block them in Vomiting by giving 5ht3 antag?

While it’s true that 5-HT3 receptor stimulation can indeed increase gastrointestinal (GI) motility, blocking these receptors with 5-HT3 antagonists is an effective strategy for managing vomiting and nausea. Here’s why:

  1. Central and Peripheral Effects: The 5-HT3 receptors are present both centrally (in the brain) and peripherally (in the GI tract). In the brain, 5-HT3 receptors play a role in regulating vomiting reflex pathways, particularly in the chemoreceptor trigger zone (CTZ) and the vomiting center. By blocking these receptors centrally, 5-HT3 antagonists can help reduce the sensation of nausea and the urge to vomit.
  2. Control of Vomiting Reflex: Vomiting is a complex reflex involving multiple neurotransmitters and receptors. While 5-HT3 receptor stimulation in the GI tract may increase motility, it’s important to note that vomiting is not solely driven by increased motility. Rather, it involves coordinated contractions of GI muscles, relaxation of the lower esophageal sphincter, and retrograde peristalsis, among other factors. By blocking 5-HT3 receptors centrally, 5-HT3 antagonists can help interrupt the vomiting reflex at its origin in the brain, regardless of their effects on GI motility.
  3. Chemotherapy-Induced Nausea and Vomiting (CINV): One of the primary indications for 5-HT3 antagonists is the prevention and treatment of chemotherapy-induced nausea and vomiting (CINV). Chemotherapeutic agents can trigger the release of serotonin (5-HT) from enterochromaffin cells in the GI tract, leading to stimulation of 5-HT3 receptors in the CTZ and vomiting center. By blocking these receptors, 5-HT3 antagonists can help prevent or alleviate CINV.
  4. Postoperative Nausea and Vomiting (PONV): 5-HT3 antagonists are also commonly used to prevent postoperative nausea and vomiting (PONV), which can occur as a result of anesthesia and surgical procedures. Similar to CINV, PONV involves activation of 5-HT3 receptors in the CTZ and vomiting center. By blocking these receptors, 5-HT3 antagonists can reduce the incidence and severity of PONV.

In summary, while 5-HT3 receptor stimulation may increase GI motility, blocking these receptors centrally with 5-HT3 antagonists is an effective strategy for managing vomiting and nausea by interrupting the vomiting reflex at its origin in the brain, particularly in conditions such as CINV and PONV.