The linear regression of body weight and age in intact, ovariecotomised, and estrogen treated rats: some applications and implications.
Many variables, including rat body weight (BWt), are sequentially measured in individuals yet the information obtained is often poorly utilised. Many advantages result if a linear relationship is established, on the original or transformed scales, between the variable and time. For individual rats log BWt, which is normally distributed, is linearly related to the reciprocal of age. Slopes (rates of BWt gain) and constants (ultimate BWts) then serve as data. Linearity extended from 4 weeks onwards in ovariectomised (OvX) and intact rats, implying that puberty does not affect BWt and that BWt increases before puberty following pre-pubertal OvX; the ovary inhibiting growth before puberty. For individual rats weaning BWt was correlated with rate of BWt gain but not with ultimate BWt, indicating postweaning compensatory growth which continues to maturity. Pre-treatment and post-treatment measurements were made on individuals, allowing within-animal comparisons and regression. Thus the BWt response to OvX or estrogen treatment depended on the pre-treatment rate of BWt gain and ultimate BWt, implying that the BWt response entails a form of compensatory growth. OvX at three ages (day 2, week 4, and week 7) produced different rates of BWt gain but similar ultimate BWts. These results support the hypothesis that ultimate BWt is predetermined, but can be modified by treatment.
D000375:Aging / Q000187:drug effects; D000818:Animals; D001835:Body Weight / Q000187:drug effects*; D002369:Castration; D004958:Estradiol / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D051381:Rats; D012741:Sexual Maturation / Q000187:drug effects
D004967:Estrogens; D004958:Estradiol