Hyperprolactinemia is not associated with hyperestrogenism in noncycling African elephants (Loxodonta africana)

African elephants in US zoos are not reproducing at replacement levels. This is in part due to physiological problems, one of which is abnormal ovarian cyclicity that has been linked to increased prolactin secretion (hyperprolactinemia). A relationship between increased estrogen production (hyperestrogenism) and hyperprolactinemia has been found in other species. Therefore, the objective of this study was to determine if elevated prolactin was associated with increased estrogen concentrations in non-cycling African elephants. In cycling elephants (n = 12), prolactin secretion followed a normal cyclic pattern, with higher concentrations observed during the follicular phase; overall mean concentration was ∼18 ng/ml and baseline prolactin was ∼6 ng/ml. Non-cycling females (n = 18) were categorized into three groups: (1) low prolactin (<15 ng/ml; n = 3); (2) moderate hyperprolactinemia (16-30 ng/ml; n = 7); and marked hyperprolactinemia (>31 ng/ml; n = 8). Mean urinary estrogen conjugate concentrations ranged from 5.4 to 41.4 ng/mg Crt, and were similar between normal cycling (15.4 ± 1.5 ng/mg Crt) and non-cycling, low prolactin elephants (18.4 ± 7.3 ng/mg Crt), but were lower in moderate (9.4 ± 1.3 ng/mg Crt) and marked hyperprolactinemic (9.8 ± 1.1 ng/mg Crt) groups (P < 0.05). In conclusion, African elephants appear to be sensitive to alterations in prolactin production, with both low (e.g., a non-cycling pattern) and high prolactin secretion being associated with abnormal ovarian activity. However, hyperestrogenism was not related to hyperprolactinemia in the non-cycling females.