Abstract
Summary
Genetically obese Zucker rats (fa/fa) and their nonobese littermates (Fa/?) were studied during the active phase of obesity onset to characterize serum levels of immunoreactive growth hormone, prolac-tin, thyroid-stimulating hormone, and corti-costerone. The effect of fasting on serum hormone levels in lean and obese rats was also investigated. Fasting reduced insulin levels in both lean and obese rats but the fasted levels in the obese rat were still 9 to 10 times higher than the lean littermates. Growth hormone levels were lower in the obese and were reduced by fasting. In the lean rat serum growth-hormone levels increased with age (25 to 480 ng/ml); however, the obese rat showed only marginal increases (25 to 65 ng/ml) during the same period. Corticosterone levels decreased with age and were higher in the obese rat at 11 weeks of age only. Thyroid-stimulating hormone increased with age and was lower in the obese rat at 9 weeks of age. During 5 and 7 weeks of age, serum prolactin was decreased in the obese rat but was similar by 11 weeks of age. These changes are discussed in relationship to their potential role in excessive lipid deposition in genetically induced obesity.
The radioimmunoassay kits for rat growth hormone, prolactin, and TSH were supplied through the generosity of the Hormone Distribution Office, NIAMD, NIH, Bethesda, Maryland.
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