Mammary cell proliferation and catabolism of adipose tissues in nutrition-restricted lactating sows were associated with extracellular high glutamate levels.

Background: Persistent lactation, as the result of mammary cellular anabolism and secreting function, is dependent on substantial mobilization or catabolism of body reserves under nutritional deficiency. However, little is known about the biochemical mechanisms for nutrition-restricted lactating animals to simultaneously maintain the anabolism of mammary cells while catabolism of body reserves. In present study, lactating sows with restricted feed allowance (RFA) ( n  = 6), 24% feed restriction compared with the control (CON) group ( n  = 6), were used as the nutrition-restricted model. Microdialysis and mammary venous cannulas methods were used to monitor postprandial dynamic changes of metabolites in adipose and mammary tissues.

Results: At lactation d 28, the RFA group showed higher ( P  < 0.05) loss of body weight and backfat than the CON group. Compared with the CON group, the adipose tissue of the RFA group had higher ( P  < 0.05) extracellular glutamate and insulin levels, increased ( P  < 0.05) lipolysis related genes ( HSL and ATGL) expression, and decreased ( P  < 0.05) glucose transport and metabolism related genes ( VAMP8 , PKLR and LDHB ) expression. These results indicated that under nutritional restriction, reduced insulin-mediated glucose uptake and metabolism and increased lipolysis in adipose tissues was related to extracellular high glutamate concentration. As for mammary glands, compared with the CON group, the RFA group had up-regulated ( P  < 0.05) expression of Notch signaling ligand ( DLL3 ) and receptors ( NOTCH2 and NOTCH4 ), higher ( P  < 0.05) extracellular glutamate concentration, while expression of cell proliferation related genes and concentrations of most metabolites in mammary veins were not different ( P  > 0.05) between groups. Accordingly, piglet performance and milk yield did not differ ( P  > 0.05) between groups. It would appear that activation of Notch signaling and adequate supply of glutamate might assist mammogenesis.

Conclusions: Mammary cell proliferation and catabolism of adipose tissues in nutrition-restricted lactating sows were associated with extracellular high glutamate levels.