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The study investigated effects of dexamethasone (Dexa), a synthetic analogue of cortisol, on cycle intervals and the periods for the stages of the oestrous cycle in the Wistar rat. Vaginal smears were taken every morning and evening from cycling rats for 30 consecutive days each, before and after Dexa treatments. Microscopic examination of smears for cellular characteristics was used to determine the cycle intervals and the period of each stage within an interval. Average cycle length and number of cycles in each 30 days, and average periods obtained for each cycle stage in 30 days were compared between those recorded before and after Dexa treatment, and values obtained in the treatment and control groups. Treatment with Dexa significantly (P < 0.05) increased oestrous cycle length and reduced the number of cycles within a given length of time in the Wistar rat. The increase obtained in oestrus cycle length in Wistar rats treated with Dexa was, apparently, due to a significant (P < 0.05) increase in the period of the dioestrus stage of the cycle. The present study confirmed that Dexa administration in cycling animals increases oestrous cycle length by prolonging the dioestrus period. In conclusion, Dexa causes infertility and its administration should be done with caution in animals of reproductive importance.
Keywords: Dexamethasone, Vagina, Cytology, Oestrus, Cycle, Period, Dioestrus, Infertility, Wistar, Rats