The Associations of Abnormal Prolactin Secretion and Metabolic Health in Acyclic Female African elephants (Loxodonta africana)
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Krcmarik, Matthew D
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Abstract
Reproductive success is an increasing concern for captive African elephants (Loxodonta africana) in North America. Low fecundity rates indicate these populations are unsustainable. Chronic hyperprolactinemia (HPRL), elevated prolactin secretion, has been proven to have a strong association with ovarian dysfunction in African female elephants. Previous studies have identified metabolic effects correlated with acyclicity, such as higher concentrations of insulin and leptin and lower glucose-to- insulin (G: I) ratios. However, metabolic effects from chronic elevated prolactin have yet to be investigated. In humans, in addition to amenorrhea, hyperprolactinemic women have shown increased risks for accelerated atherosclerosis, hyperandrogenemia, reduced metabolism, and insulin resistance. The aim for the study was to explore possible associations between abnormal prolactin secretion (high and low) and metabolic disorders in elephants. One year of serum samples, collected biweekly, were obtained from African female elephants (n=36) with varying status of prolactin secretion (high= 12, normal= 12, low= 12). Biomarkers were assessed to compare thyroid function, glucose and lipid metabolism and cardiovascular health amongst the high, normal, and low prolactin state groups. Generalized linear mixed models (GLMs) were performed in R. Results determined that high prolactin secretion is associated with abnormal TSH and thyroid hormone production, elevated cortisol and cholesterol, and reduced fructosamine. Low prolactin individuals were found to have heightened levels of testosterone. Taken together, this study highlights several areas in need of further study to further advance our understanding of African elephant physiology and the etiology of hyperprolactinemia in female elephants. This study suggests that hyperprolactinemic females may have further hormone perturbations with associated changes in thyroid, cortisol and cholesterol levels, while hypoprolactinemic females have increased levels of serum testosterone. More studies are warranted to better understand the effects associated with acyclicity and abnormal prolactin secretion.
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Hyperprolactinemia, Thyroid, Glucose, Elephant, Acyclicity, Lipid