The Effect Of Ambient Temperature And Lactation Experience On Fat Accumulation During Post-lactation In Striped Hamster

Physiological variations of energy metabolism and body fat accumulation are the main energy budgets in animals to cope with natural environmental changes.Temperature is one of the important environmental factors.Animals usually increase energy intake and metabolic thermogenesis to cope with the cold temperature.Reproduction is an important stage in the lifespan of animals,and lactation is one of the most energetically demanding activities of female mammals.The mothers usually increase food intake and metabolize fat reserves to meet the energy requirement of their offspring.Females usually increase their food intake and energy output with increasing litter size that they are raising during lactation.The mothers would be expected to gradually replenish their fat reserves after lactation,which is important for enhancing its own survival adaptability.However,its energy metabolism characteristics and physiological mechanisms are still unclear.In order to investigate the effects of ambient temperature and lactation experience on fat accumulation during post-lactation in striped hamsters,in this study,we designed three experiments:1)Female hamsters were randomly assigned to one of two groups;a post lactation group(post-lactation,PL)and a virgin control group(virgin,V).When the pups were weaned,females in both groups were randomly divided into two subgroups;low-fat(LFD)and high-fat diet(HFD).We measured the energy budget,serum leptin levels and the expression of several hypothalamic neuropeptide genes in female striped hamsters for 21 days after lactation.2)The female hamsters were randomly divided into 3 groups:large litter size(large,L),medium litter size(medium,M),and small litter size(small,S).On day 5 of lactation,the number of pups of L,M and S groups was adjusted to 8-10,5-6,1-2,respectively.The pups were weaned at the end of day 16 of lactation,after which the females in three groups were fed high-fat food.We measured the energy budget and body composition changes of the females during the peak period of lactation and after lactation.3)The striped hamsters were randomly divided into 3 groups on the day of weaning,fed with high-fat food,and exposed to room temperature(21?),cold temperature(5?)and warm temperature(30?)for 29 days.We measured mitochondrial state 4respiration and cytochrome c oxydase(COX)activity of liver,the gene expression of BAT uncoupling protein 1(UCP₁),serum thyroid hormone(T₃ and T₄)levels,and body fat content of the females after lactation.The results showed that:1)The body mass and GEI of PL females were 20%(P<0.01)and 21.9%(P<0.05)higher than that of virgin females.The masses of subcutaneous,abdominal and mesenteric fat deposits were108.6%,302.5%and 210.8%higher,respectively,in PL females than in the virgin controls.The serum leptin levels of PL females were 77%(P<0.01)higher than those of virgin females.2)The masses of subcutaneous,mesenteric,perirenal and abdominal fat deposits were almost decreased to zero at peak lactation.The litter size raised during lactation had no significant effects on energy intake,digestibility,body fat content and resting metabolic rate in post-lactating females.But the body mass increased by 18.6%,21.0%and 20.0%(P<0.05)in post-lactating females compared with that at weaning.The masses of subcutaneous fat increased were 4.6-,707.5-and 1141.6-fold higher in post-lactating females than that during lactation.The masses of the small intestine,large intestine,caecum,and liver were significantly higher in L group than that in S group.3)Hamsters increased energy intake by 89.2%(P<0.05),but decreased body mass by 14.8%(P<0.05)at the cold compared to the hamsters maintained at room temperature after lactation.The masses of subcutaneous,mesenteric and abdominal fat were decreased by 65.1%,64.4%,and 80.1%(P<0.05)in the cold than that in room temperature.Hypothalamic NPY gene expression was up-regulated by 18.0%(P<0.05),state 4 respiration of liver,BAT UCP₁ gene expression and serum T₃ levels were increased by 31.2%,83.6%and 77.2%(P<0.05)in the cold than that in room temperature.These above results indicate that 1)The negative energy balance during lactation promotes the accumulation of fat after weaning,which may be an adaptive strategy that is beneficial to replenish fat reserves to cope with future food shortages and/or energy needs.2)The females increased energy intake during the peak period of lactation,but it was not enough to meet the energy requirements of the offspring's growth and development.The litter size that the mothers raised during lactation had no effect on the plasticity of tissues,organs and energy budget strategy after lactation.3)The increase of metabolic thermogenesis mediated by serum thyroid hormone at cold temperature plays an important role in inhibiting the accumulation of body fat after lactation.