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(M658) LIFESTYLE AND HORMONE DYNAMIC INDICES: FREE TESTOSTERONE DYNAMIC INDEX INCREASES ON A HIGH FAT DIET AND DECREASES WITH AEROBIC EXERCISE.

Wynne-Edwards, Katherine¹, Hicks, Kristin¹, Lazier, Joanna¹, ¹ Queen's University, Kingston, ON, Canada

ABSTRACT- For the first time, repeated hormone sampling within individual small mammals has been used to calculate a dynamic index for free testosterone (unbound/bio-available fraction in plasma). The free testosterone dynamic index was highly variable, with individual indices in this outbred laboratory hamster population ranging from 80% to 243% and was independent of free testosterone concentration. Each adult male hamster (Phodopus sungorus) had two weeks of acclimation, four weeks including 12 blood samples, and then crossed-over to the other treatment for two weeks of acclimation and four weeks of sampling. Free testosterone was quantified with the Diagnostic Products Corp. free testosterone radioimmunoassay. Intra-assay variability contributing to the dynamic index was less than 8%. Free testosterone results were reduced to a mean and a dynamic index for each individual under each treatment and analyzed by paired comparisons. Free testosterone concentration was not affected by the lifestyle alteration. However, the dynamic index for free testosterone within individual male hamsters was reversibly increased by consumption of a high animal fat diet (calorie/ protein/ fibre-matched with 25%, rather than 12% of calories from lard) and decreased by access to an exercise wheel. The hormone dynamic index is a novel endocrine parameter with biologically plausible links to the differential activation of cellular response pathways and might have relevance to behavior-hormone and behavior-disease interactions.

KEY WORDS: diet, activity, testosterone, bioavailable