Kidney stone disease is known to affect bottlenose dolphins and can lead to kidney obstruction, failure, and organ death. Certain populations or collections of dolphins appear to be more at risk than others for kidney stone formation. To better understand the problem, we set out to study kidney health in Sarasota Bay dolphins to determine whether or not this population is afflicted with the disease.
Ultrasound provides a rapid assessment of organ health in humans and animals, including bottlenose dolphins. During 2011-2013, we gathered ultrasound data on Sarasota Bay dolphin kidneys to look for evidence of kidney stones. Thirty-nine dolphins were screened for the disease, and none of the dolphins had evidence of stone formation, which is great news for the population.
Sarasota Bay dolphins now serve as an unaffected, control population for kidney stone disease. Studying their urine physiology can help us determine how they are protecting themselves from stone formation. In 2014, we conducted ultrasound exams to confirm that the dolphins being examined had no evidence of stone disease. We also collected urine from as many of the study dolphins as possible, and then performed sophisticated analyses on the urine samples.
We discovered that Sarasota Bay dolphins have similar urine chemistry to dolphins that form stones, however some key differences exist. First, Sarasota Bay dolphins have higher levels of citrate in their urine, therefore citrate may be playing a role in inhibition of stone formation. Second, Sarasota Bay dolphin urine is supersaturated with ammonium urate, which is the stone type most commonly diagnosed in dolphins. However, the level of supersaturation is greater in a collection of animals with a high prevalence of stone formation. The difference in supersaturation indices may prove critical and is likely related to foraging behavior and prey types. Future studies will focus both on inhibitory factors and the influence of foraging behavior on the risk of stone formation, continuing to utilize Sarasota Bay as a healthy, control population of dolphins. Our collaborators for this project include SDRP, Dolphin Quest, and the University of Florida. We thank the Office of Naval Research for their continued support of this project.
This article was published on page 13-14 in the November 2014 issue of Nicks n Notches