Morphine inhibits TRH-induced intestinal transit increases.

Area of Science:

• Pharmacology
• Neuroscience
• Gastroenterology

Background:

• Opioid agonists like morphine and endogenous opioids such as beta-endorphin play roles in regulating gastrointestinal function.
• Thyrotropin-releasing hormone (TRH) is known to stimulate intestinal motility.
• Age-related differences in opioid sensitivity and central nervous system development are significant.

Purpose of the Study:

• To investigate the effects of intraperitoneal (IP) and intracisternal (IC) administration of morphine and beta-endorphin on TRH-induced small intestinal transit.
• To determine age-related differences in the efficacy of these opioids in modulating gastrointestinal motility.

Main Methods:

• Anesthetized rats of different age groups (14-day-old and older) were used.
• Morphine and beta-endorphin were administered via IP and IC routes.
• Thyrotropin-releasing hormone (TRH) was used to induce increases in small intestinal transit.
• Charcoal bolus transit was measured to assess intestinal motility.

Main Results:

• Intraperitoneal morphine (2 mg/kg) consistently blocked TRH-induced intestinal transit increases across all age groups.
• Intracisternal administration of 1 microgram of morphine or beta-endorphin failed to block TRH-induced transit in 14-day-old rats.
• However, 1 microgram of IC morphine and beta-endorphin effectively blocked TRH-induced transit in adult rats.
• Dose-response studies indicated that higher IC doses of morphine were necessary to inhibit TRH-induced transit in preweaning rats.

Conclusions:

• The efficacy of central opioid administration in inhibiting TRH-induced intestinal motility is age-dependent.
• Younger rats exhibit reduced sensitivity to intracisternal morphine and beta-endorphin compared to adult rats.
• These findings highlight developmental changes in opioid receptor-mediated regulation of gastrointestinal function.