Whole-Body Lipids and Fatty Acid Synthetase Activity in Richardson's Ground Squirrels, Spermophilus richardsonii

Abstract

Whole-body lipids andfatty acid synthetase (FAS) activity of liver, white adipose tissue (WAT), and brown adipose tissue (BAT) infield-caught Richardson's ground squirrels were measured to determine the effects of reproduction on fattening. Whole-body lipids increased by 9 g and 8 g/wk, respectively, in males and nonparous females between April 1 and June 5 and by 10 g/wk between May 10 and July 1 inparous females. Males were always heavier than nonparous females, but thepercentage of body mass that was lipid was similar. The lipid mass accumulated by parous females by July 1 had been achieved by nonparousfemales 1 mo earlier. For both liver and WAT, FAS activity in males and nonparous females was similar throughout the active season. FAS activity of liver was depressed in late pregnancy. FAS activity of both liver and WAT was depressed during lactation, being 70 times greater in WAT of nonparous than of parous females. FAS activity in WAT and liver of postlactating females increased, but there was no compensatory increase in rate of fattening or FAS activity above that in males and nonparous females. Apparently, parous females hibernate later than other adults because reproduction causes them to initiate fattening later, and, once initiated, rate offat deposition is similar to that in other members of the population. WAT appears to be the principal tissue of fatty acid synthesis for prehibernation fattening.