Hypophysectomy and regulation of body weight in the genetically obese Zucker rat.

Genetically obese Zucker "fatty" rats (fa/fa) and nonobese siblings were weighed regularly from 7 to 150 days of age to determine the onset and time course of the excessive weight gain that characterized the fatty rat. At 150 days of age, male and female fatties and their lean littermates were sham operated or hypophysectomized to examine the role of the pituitary in the fatty obesity. The operated animals were then weighed until sacrifice at 220 days of age, when adrenal weights, gonadal weights, uterine weights, and the Lee Index were determined. Fatty rats were significantly heavier than their nonobese littermates even in the 2nd wk of life (day 7-13). Complete hypophysectomy blocked the continued development of the fatty obesity but did not eliminate the adiposity established prior to hypophysectomy. It is concluded that the pituitary and the major endocrine pathways it controls are not the locus of the primary genetic lesion responsible for maintaining the Zucker fatty rat obesity.