Using an Oral Sugar Test to Biologically Validate the Use of a Commercial Enzyme Immunoassay to Measure Salivary Insulin in Western Lowland Gorillas (Gorilla gorilla gorilla)

Abstract

Noninvasive evaluations of hormones can contribute to the assessment of health and welfare of animals. Variations in insulin levels and sensitivity, for example, have been linked to health concerns in non-human and human primates including insulin resistance, diabetes, and heart disease, the leading cause of death in zoo-housed gorillas. Few published studies have assessed insulin concentrations in western lowland gorillas (Gorilla gorilla gorilla), and all did so using serum. Anesthesia is typically required to collect blood samples from zoo-housed gorillas, limiting sampling frequency and restricting samples to the fasted state. The ability to measure insulin levels in saliva would eliminate these constraints and provide a minimally invasive means for monitoring this hormone. The purpose of this study was to analytically and biologically validate the measurement of insulin in saliva of western lowland gorillas using a commercially available enzyme immunoassay. For validation, an oral sugar test was conducted on five adult gorillas residing at Cleveland Metroparks Zoo. Such assessments are common practice in both human and equine medicine to evaluate the body's insulin response to ingestion of sugars. The test involved measuring salivary insulin at timed intervals before and after gorillas consumed doses of sugar. Salivary insulin levels increased from 15 min post-sugar ingestion and peaked after 90 to 120 min. One female had a high response and peaked at 990.21 mU/L. The other four gorillas had peaks between 49.82 and 167.04 mU/L. The assessment provided a biological validation for the measurement of salivary insulin in western lowland gorillas.