Luteinizing hormone surge in adult female rats after androgen priming

The effects of androgens alone and in combination with oestrogens on luteinizing hormone secretion in adult female rats were studied after 1, 2 and 4 months of priming. Each adult female rat was implanted with a Silastic capsule filled with testosterone or dihydrotestosterone alone or together with another similar capsule of oestradiol. An oestrogen challenge test was carried out in each rat after priming. Blood samples were collected before androgen priming. During the oestrogen challenge test, blood samples were collected before (0 h or day 0) and at 12, 24, 36 and 48 h after the intramuscular injection of 50 μg oestradiol vaierate for rats primed for 1 month, or daily for 5 days (days 1 to 5) for other rats. An oestrogen challenge test was also performed in two groups of untreated male and female rats which served as controls. The results indicated that long-term androgen priming had resulted in the attenuation or total blockade of the luteinizing hormone surge which normally occurs during an oestrogen challenge test in adult female rats. This suggests that androgens may be important modulators of the luteinizing hormone surge mechanism in rats. Furthermore, the fact that the luteinizing hormone surge can be blocked by androgen priming in adult female rats suggests that the sexual dimorphic response to oestrogen feedback is not immutably imprinted in the hypothalamic-pituitary axis as was originally proposed.