Effects Of Exogenous Melatonin Or Leptin On Body Mass And Thermogenesis In Eothenomys Miletus From Kunming And Dali Regions

In the natural environment,the seasonal changes of the morphological,physiological,behavioral and reproductive characteristics of non-hibernating small mammals are important strategies for their adaptation to the environment.The regulation of body mass,energy metabolism and heat production capacity are an important physiological strategy to cope with seasonal changes in environmental conditions such as photoperiod,environmental temperature,food resources（quantity and quality）.In this paper,the rats distributed in the central Yunnan plateau（Kunming）and Hengduan Mountains regions（Dali）were taken as the research objects.The physiological regulatory responses of the Eothenomys miletus in different regions to exogenous melatonin and leptin were studied from the whole,tissues and organs to biochemical levels by measuring the body mass,thermogenic capacity,serum hormones and other energy-related indicators after injection of exogenous melatonin and leptin.The main results and conclusions are as follows:1.Under the condition of exogenous melatonin injection,the body mass and food intake of the E.miletus in Kunming and Dali decreased significantly,while the resting metabolic rate（RMR）and nonshivering thermogenesis（NST）increased significantly;Contents of total protein,mitochondrial protein,the activities of cytochrome C oxidase（COX）andα-glycerophosphate oxidase（α-PGO）in liver and brown adipose tissue（BAT）were enhanced;the activity of thyroxin 5’-deiodinase（T₄5’-DII）and uncoupling protein 1（UCP1）in BAT were also increased.Serum leptin,triiodothyronine（T₃）levels and T₃/T₄ratio were significantly increased,thyroxine（T₄）levels was significantly decreased.Serum T₃is positively correlated with T₄5’II activity and NST,indicating that T₃and T₄5’II may play an important role in melatonin regulating energy metabolism and weight regulation of E.miletus.After the injection of melatonin,the body mass,food intake and thermogenic activity of the E.miletus in Kunming were higher than those in Dali,indicating that the E.miletus in Kunming were more sensitive to melatonin,which may be related to the long-term living environment of the E.miletus in the two regions.The E.miletus in Dali mainly mainly lived in the habitat of small leaf shrubs,while the E.miletus in Kunming lived in the habitat of evergreen broad-leaved forests.2.Under the condition of injection of exogenous leptin,body mass and food intake of E.milletus in Kunming and Dali areas decreased significantly,RMR and NST increased,and the content of mitochondrial protein and COX activity in liver,COX activity and UCP1 content in brown adipose tissue,serum T₃,T₄,T₃/T₄ratio,thyrotropin-releasing hormone（TRH）and adrenal corticotropin-releasing hormone（CRH）concentration increased.After leptin injection,the serum leptin level was negatively correlated with body mass and food intake,and the serum T₃level was positively correlated with the content of NST and UCP1.After exogenous injection of leptin,the body mass of Kunming E.miletus was higher than that of Dali E.milletus,while the changes of food intake,RMR and NST were lower than that of Dali rats.This indicates that the E.miletus in Dali area were more sensitive to the injection of exogenous leptin,which may be related to the lower temperature of the living environment and poor food quality of the E.miletus in this area.In conclusion,exogenous injection of leptin reduced the body mass and food intake of E.milletus in the two regions,increased their thermogenic capacity and energy metabolism,indicating that leptin participated in the regulation of body mass and thermogenesis.3.The physiological characteristics of the two regions also showed regional differences.For example,the body mass and food intake of Kunming E.miletus were higher than that of Dali,while the RMR and NST were lower than that of Dali.Regional differences in environmental factors such as photoperiod,food resources,temperature,etc.among different regions may be the core factor determining the phenotypic differences between biological regions and their adaptability to extreme environments.In conclusion,exogenous melatonin and leptin are involved in the regulation of weight and thermogenesis in the E.miletus.There are significant differences in the physiological characteristics of rats in different regions when facing different hormone injections.Kunming E.miletus are more sensitive to melatonin,while Dali E.miletus are more sensitive to exogenous leptin injection.Adaptation to light,temperature,food resources and other environmental conditions in the habitat may be the main reason for the phenotypic differentiation of the E.miletus in different regions.