Receptivity in Mongolian gerbils: dose and temporal parameters of ovarian hormone administration

The dose and temporal effects of oestrogen and progesterone treatment on the induction of receptivity in female Mongolian gerbils were investigated. One group of animals was primed with 10 micrograms oestradiol benzoate (OB) 48 and 24 h prior to testing and received 500 micrograms progesterone (Pr) 0, 1, 2, 3, 6, 9, 12, 15, 18, 21 or 24 h prior to testing. These subjects were found to exhibit high levels of receptivity from hour 2 to hour 18. This is similar to the reported duration of heat during natural oestrus. A second group of animals were primed with 10 micrograms OB and were then given either 0, 10, 50, 100, 250 or 500 micrograms Pr 3 h prior to testing. Results indicated that the administration of 100 micrograms Pr could elicit high levels of receptivity. A final group of animals were given either 0.5, 1.0, 5.0 or 10.0 micrograms OB 48 and 24 h before testing and then 100 micrograms Pr 3 h prior to testing. It was found that only the 10 micrograms dose of OB elicited high levels of receptivity in these animals.