Diet-Hormone Interrelationships in the Rat

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Abstract
Twenty-eight-day old male rats were fed, either ad libitum or in restricted amounts, isoenergetic diets containing 2, 5, 10, 15, 25, or 50% lactalbumin and 5, 11.9, or 21.1% fat for 8 weeks. They were then killed and the plasma levels of triiodothyronine (T3), thyroxine (T4), insulin, glucagon, corticosterone, norepinephrine (NE), and epinephrine (E) were measured. Dietary changes explained most of the variation in the plasma concentrations of T3, T4, insulin, and glucagon but less than 20% of the variation in the plasma concentrations of the adrenal hormones. Dietary protein level was directly related to plasma T4, insulin, and corticosterone and inversely related to plasma T3, glucagon, NE, and E. Dietary fat level had its most significant effect on the plasma glucagon concentration to which it was inversely related whereas the most noteworthy effect of a low energy intake was to reduce plasma E and thereby to increase the NE/E ratio. A refeeding study confirmed the effects of dietary protein level on plasma hormone concentrations and showed that the changes in plasma T3, T4, insulin, and glucagon were reversible. Equations to describe diet-hormone interrelationships in 12-week old male rats have been derived by multiple regression analyses of the data.