Influence of intake of sweet solutions on the analgesic effect of a low dose of morphine in randomly bred rats.

The time course for the development of morphine tolerance, following prolonged sweet intake, was examined in randomly bred Sabra rats. Exposure to 3% glucose in 6 mM saccharin solution increased drinking by about three times as compared to rats supplied only with water. Suppression of the analgesic effect of morphine was already detectable after 24 h of intake and became progressively more marked within the next 5 weeks. These results support an active interaction between sweet consumption and endogenous opioids in randomly bred rats.