Abstract

Megestrol acetate is a progestin that is sometimes used in male dolphins, and in some cases, the animals are maintained on high levels of the hormone for long periods of time. There have been few, if any, studies of the long term effects on the dolphins, but studies in other species, including humans, suggest that glucocorticoid effects are likely with chronic usage due to inhibition of the hypothalamic-pituitary-adrenal axis. In an attempt to begin to understand the effects of megestrol acetate usage in cetaceans, a population of captive male Atlantic bottlenose dolphins, Tursiops truncatus, of various ages, most of which had been on relatively high levels of megestrol acetate for 2-3 years (80-120 mg SID per dolphin), was gradually reduced and/or withdrawn from the drug to very low to zero levels. Routine complete blood counts and blood chemistries were compared before and after reduction/withdrawal and significant differences were observed. Of particular note were alkaline phosphatase levels that were greatly suppressed by high levels of megestrol acetate and that returned to normal levels with reduction in dosage and cholesterol levels that showed the inverse relationship. The current protocol for use of the megestrol acetate at the facility is to maintain the animals either off the drug or at low levels (10-20 mg per dolphin SID) and to increase the drug level by 10-20 mg per dolphin (usually only 10 mg) for 10-14 days as necessary, at which time the drug dosage is reduced back to the previous level.

Acknowledgments

The author wishes to thank Dr. Michael Renner for his input regarding withdrawal of animals from megestrol acetate and to the entire training and laboratory staff at Dolphin Cay for their assistance.