Effects of hypergravity on mammary metabolic function: gravity acts as a continuum

1 University of Vermont, Burlington, Vermont 05405; and 2 National Aeronautics and Space Administration-Ames Research Center, Moffett Field, California 94035 Submitted 19 March 2003 ; accepted in final form 6 August 2003 Mammary metabolic activity in pregnant rats is significantly increased in response to spaceflight. To determine whether changes in mammary metabolism are related to gravity load, we exposed pregnant rats to hypergravity and measured mammary metabolic activity. From days 11–20 of gestation (G), animals were centrifuged (20 rpm; 1.5, 1.75, or 2.0 x gravity) or were maintained at 1 G. On G20, five rats from each group were removed from the centrifuge and euthanized. The remaining dams ( n = 5/treatment) were housed at 1 G until parturition. After 2 h of nursing by the pups, the postpartum dams were euthanized (G22). Glucose oxidation to CO 2 and incorporation into lipids was measured. Mammary glands from dams euthanized on G20 revealed a strong negative correlation between metabolic rate and increased G load. Approximately 98% of the variation in glucose oxidation and 94% of the variation in glucose incorporation into lipids can be accounted for by differences in G load. Differences in metabolic activity disappeared in the postpartum dams. When we combined previous data from the microgravity with hypergravity environments and plotted the ratio of mammary metabolic rate vs. G load, there was a significant exponential relationship ( r 2 = 0.99). These data demonstrate a remarkable continuum of response across the microgravity and hypergravity environments and support the concept that gravitational load influences mammary tissue metabolism. gravity; mammary gland; rat Address for reprint requests and other correspondence: K. Plaut, Univ. of Vermont, 570 Main St., Burlington, VT 05405 (E-mail: kplaut{at}zoo.uvm.edu ).