Female rats of Wistar strain were injected SC, starting at Day 5 after ovariectomy, with estradiol dipropionate (ED) at weekly intervals. Forty-eight hours after each injection they were subjected to standardized mating tests. A 6 μg ED dose showed to be insufficient to maintain estrous behavior. Both precopulatory and lordosis behavior disappeared in the course of eight weeks. On the other hand, the behavioral effectiveness of 10 and 30 μg ED increased with the number of injected doses. Under these circumstances, estradiol proved to be sufficient to induce not only full copulatory readiness but also all the degree of precopulatory behavior of pattern (Presenting, Hopping ending in Presenting, and Darting ending in Presenting). Although there are large individual differences in behavioral effectiveness of ED, the estradiol thresholds for inducing Presenting, Hopping, and Darting were found to increase in the given order. However, prolonged (up to Week 12) treatment with 30 μg ED resulted in the disappearance all estrous behaviors. This decline of estradiol effectiveness was reversed by increasing the estradiol dose to 100 μg. © 1981.
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