The acute effects of oestradiol-17beta and synthetic LH-RH on plasma LH levels in freemartin heifers.

The effects of a single injection of estradiol-17beta and of synthetic luteinizing hormone-releasing hormone (LH-RH) on plasma LH levels in freemartin heifers were studied. Only 7 of 12 animals showed a surge in plasma LH levels within 24 hours of injection with estradiol-17beta. The increases were less than those reported for normal noncyclic heifers though some of the freemartins showed a delayed or more prolonged LH response. The LH response to estradiol was not related to the degree of chimerism or to plasma androstenedione levels. The same treatment 4 months later evoked a similar response even though plasma androstenedione levels had doubled within this period. Injection of LH-RH produced a greater release of LH in freemartins who responded to estradiol treatment than in nonresponders. It is suggested that this difference may involve pituitary dysfunction.