ASGSB 1999 Annual Meeting Abstracts

LEPTIN RESPONSE TO FASTING IS ATTENUATED IN 2G. L.E. Warren, B.A. Horwitz and C.A. Fuller. Section of Neurobiology, Physiology and Behavior, Univ. of California, Davis, CA.

Changes in the ambient force environment alter the regulation of food intake and body fatness. Since fat regulation underlies human survival capacity, an understanding of the related regulatory pathways and their responsiveness to the ambient force environment may be critical to long duration spaceflight. Leptin, a hormone secreted by adipocytes in proportion to body fat, acts centrally in a negative feedback loop to modify food intake and energy expenditure. We have studied the effects of 2G on plasma leptin in lean (Fa/Fa) male Zucker rats. Rats were individually housed in metabolism cages with food and water provided ad libitum. Control rats were similarly maintained at 1G. Following a 2-week baseline period at 1G, the 2G group was subjected to centrifugation on a 3-m diameter centrifuge for 8 weeks. Animals were sacrificed immediately post-centrifugation, and trunk blood was collected for analysis. A subset of rats was fasted for 48-hrs prior to sacrifice in order to test the responsiveness of leptin regulation. Plasma leptin is normally depressed by fasting, presumably in an effort to maintain energy balance. Plasma leptin levels (ng/ml) in non-fasted rats exposed to 2G (1.8 ± 0.2; n=7) were significantly lower than those in rats at 1G (9.7 ± 2; n=6) (p=0.003). At 1G, the 48-hr fast significantly reduced leptin levels to 1.3 ± 0.5 (n=8; p=0.001) while at At 2G, the 48-hr fast reduced plasma leptin to 0.3 ± 0.05 ( n=9; p<0.0001). Thus, despite lower leptin levels in 2G rats, the response to fasting remains, indicating that this portion of the feedback system is intact. (Supported by NASA: NAG5-3959 to BAH and GSRP to LEW).

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