Growth and Obesity Following Ventromedial Hypothalamic Lesions Placed in Female Rats at Four Different Ages

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Abstract
Female Holtzman rats received bilateral electrolytic lesions in the ventromedial hypothalamic area at the age of 27, 59, 75, and 140 days, respectively. Intact rats of corresponding ages served as controls. The animals were observed for 6 weeks and then sacrificed. Linear growth was reduced most in lesioned weanling rats and progressively less in rats operated on when older. The difference in body weight between lesioned and unlesioned rats was least in the weanling rats and greatest in the 140-day-old rats. According to the obesity index, however, the lesioned weanling animals were as obese as the lesioned older rats. Food intake was similar in lesioned and unlesioned weanling rats but lesioned older rats ate more than their respective controls. Relative organ weights were reduced in all groups of lesioned rats. Pituitary, thyroid and adrenal weights were reduced most in rats lesioned at 59 days of age, ovarian weight was reduced most in animals lesioned at 75 days of age. Mean pituitary acidophils were greatly reduced in number in lesioned weanling rats and in those operated on when 140 days old. Thyroid histology revealed no apparent difference between lesioned and unlesioned rats. The data show that the greatest reduction of growth following placement of ventromedial lesions occurred in weanling rats. It is suggested that this is due to their greater requirement for hypothalamic factor(s) necessary for the release of growth hormone and other hypophyseal hormone(s) affecting growth.