Seasonal changes in absolute and relative organ weight in 3-month male Wistar rats

BACKGROUND: To correctly interpret preclinical studies and basic research, it is necessary to accurately assess the biometric parameters of normal status and their limits. Biometric parameters of animals of genetically pure lines are known to vary according to factors such as sex and age, but little attention is paid to a seasonal factor. Therefore, it seems relevant for physiology and pathophysiology to develop reference values of normal status and their limits for working with genetically pure animals during certain periods of ontogenesis and different seasons. AIM: The aim of the study was to determine the absolute body and organ weights and the relative organ weights of adult male Wistar rats at three months of age during different seasons of the year. MATERIALS AND METHODS: The experiment involved 160 male Wistar rats. The animals were divided into four groups so that the rats reached the age of three months in one of the seasons: spring, summer, fall, or winter. In each group, absolute and relative body and organ weights were measured for the brain, spleen, thymus, liver, kidneys, adrenal glands, heart, lungs, and testes. RESULTS: The most significant seasonal differences were found in the absolute weights of all organs, while the relative weight coefficients of the organs differed in only 50% of the cases. Synchronous seasonal differences in kidney and adrenal gland weights were observed. The heart was found to have the most significant seasonal variability in both weight parameters studied. CONCLUSIONS: The absolute organ weight is one of the most sensitive parameters in determining reference values, but changes in the relative weight coefficient should also be considered. This study established reference ranges for the weight of major organs in a population of healthy, genetically homogeneous Wistar rats at three months of age and showed seasonal variations in these reference ranges. Further research is needed to understand changes in organ weights combined with pathological data.