RATIONALE: Several investigators have shown that male rodents are more sensitive than females to morphine's antinociceptive effects. OBJECTIVE: The present study was conducted to determine whether this sex difference is stable after chronic morphine treatment. RESULTS: Acutely administered morphine produced significantly greater hotplate and tail withdrawal antinociception in males than in females. In contrast, there were no sex differences in morphine's hotplate or tail withdrawal effects under repeated (1-week interval) dosing conditions. In a separate group of rats, after 2 weeks of twice-daily morphine treatment (10-20 mg/kg per injection), the ED50 for morphine's antinociceptive effects increased approximately 6.9-fold in males versus only 3.7-fold in females; chronic morphine treatment also disrupted the estrous cycle of females. In a separate group of rats treated with 10 mg/kg morphine twice daily for 5 days, treatment with naloxone (1.0 mg/kg) on day 6 produced greater withdrawal scores in males than in females. CONCLUSIONS: These experiments demonstrate sex differences in development of tolerance to and dependence on morphine in the rat.
RATIONALE: Several investigators have shown that male rodents are more sensitive than females to morphine's antinociceptive effects. OBJECTIVE: The present study was conducted to determine whether this sex difference is stable after chronic morphine treatment. RESULTS: Acutely administered morphine produced significantly greater hotplate and tail withdrawal antinociception in males than in females. In contrast, there were no sex differences in morphine's hotplate or tail withdrawal effects under repeated (1-week interval) dosing conditions. In a separate group of rats, after 2 weeks of twice-daily morphine treatment (10-20 mg/kg per injection), the ED50 for morphine's antinociceptive effects increased approximately 6.9-fold in males versus only 3.7-fold in females; chronic morphine treatment also disrupted the estrous cycle of females. In a separate group of rats treated with 10 mg/kg morphine twice daily for 5 days, treatment with naloxone (1.0 mg/kg) on day 6 produced greater withdrawal scores in males than in females. CONCLUSIONS: These experiments demonstrate sex differences in development of tolerance to and dependence on morphine in the rat.
Authors: Laura Gioiosa; Xuqi Chen; Rebecca Watkins; Nicole Klanfer; Camron D Bryant; Christopher J Evans; Arthur P Arnold Journal: Horm Behav Date: 2007-09-14 Impact factor: 3.587
Authors: Monica Rodriguez; M Angeles Carlos; Ignacio Ortega; Elena Suarez; Rosario Calvo; John C Lukas Journal: Pharm Res Date: 2002-06 Impact factor: 4.200