How does finasteride affect time-dependent modulatory effect of morphine-induced analgesia?

Finasteride inhibits 5?-reductase which converts testosterone to dihydrotestosterone. The aim of this study is to evaluate how finasteride affects the analgesic effect of morphine time-dependently.Local bred albino male mice (25-40 gram) synchronized with a standard light-dark regimen (12hours:12hours Light:Dark, lights on 08:00) were used. All experiment groups include 10-12 mice and were tested at six time points of the day as 1, 5, 9, 13, 17 and 21 hours after lights on. All drugs were administered subcutaneously. Basal pain sensitivity (saline; 10 mg/kg) and morphine-induced analgesia (10 mg/kg) were determined 30 minutes before hot-plate test (55 ± 0.5ºC). To test the administration time-dependent interaction, a third group of animals were injected with a predetermined dose of finasteride (15 mg/kg) 20 minutes before morphine and response latencies were tested. Response latencies shorter than 3 seconds were regarded as spontaneous and excluded. To avoid heat injury, animals not responding within 45 seconds were removed from the hot-plate. To avoid the seasonal variations all experiments were performed in June and July. Data analyzed by ANOVA or Kruskal Wallis and student t-test where necessary.The results of this study indicate that there is time-dependent interaction between finasteride and morphine-induced analgesia. In the dark period, especially 13 and 21 hours after lights on, finasteride enhanced morphine-induced analgesia.