Kriván M, Szabó G, Sarnyai Z, Kovács G L, Telegdy G
Department of Pathophysiology, Albert Szent-Györgyi, Medical University, Szeged, Hungary.
Pharmacol Biochem Behav. 1995 Nov;52(3):591-4. doi: 10.1016/0091-3057(95)00145-m.
The development of cross-tolerance to an analgesic effect was observed between two mu-receptor agonists, heroin and fentanyl. Repeated treatments with heroin twice a day for 4 days resulted in a decreased nociceptive effect to fentanyl on day 5. The fentanyl dose-response line shifted to the right, and was considered to be a sign of the development of cross-tolerance. Peripheral treatment with oxytocin did not block the development of heroin-fentanyl cross-tolerance. However, intracerebroventricular administration of oxytocin blocked the development of tolerance, causing a leftward shift in the dose-response curve and supporting the assumption that oxytocin blocks the development of heroin-fentanyl cross-tolerance via CNS mechanisms.
