Reduction of litter size during lactation in rats greatly influences fatty acid profiles in dams.

This study aimed to determine in lactating rats how fatty acid profiles are affected by litter size. On day 2 after parturition, litters of lactating rats were adjusted to a normal litter size of 9 pups/dam (NL) or to a small litter of 4 pups/dam (SL), and dams were studied at day 21 of lactation. Plasma glucose, insulin, and docosahexaenoic acid (DHA) concentrations were higher in SL than in NL dams, whereas the concentrations of most other fatty acids, triacylglycerols (TAG), and non-esterified fatty acids were lower in the SL dams. In the liver, the concentration of TAG was lower in SL than in NL dams as was the concentration of most fatty acids, with the exception of stearic acid (STA), arachidonic acid (ARA), and DHA concentrations that were higher in SL. Both plasma and liver Δ9 desaturase indices were lower in SL than in NL dams, whereas both Δ5 and Δ6 desaturase indices were higher in SL dams. In the liver, the expression of acetyl CoA carboxylase was lower in SL than in NL dams, and among the different adipose tissue depots, only mesenteric adipose tissue showed a higher concentration of most fatty acids in SL than in NL dams. It is proposed that reduction of litter size during lactation decreases liver lipogenesis de novo, although the synthesis of long-chain polyunsaturated fatty acids from their corresponding precursors increases, and lipolytic activity in mesenteric adipose tissue decreases probably as result of increased insulin responsiveness.