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Dietary Fat and the ß-Adrenergic-Mediated Chronotropic Response in the Rat¹

Department of Nutrition, Rutgers University, New Brunswick, NJ 08903

We have investigated the effect of dietary fat on isoproterenol-stimulated and propranolol-inhibited heart rate in the rat. In the first experiment, weanling male Sprague-Dawley rats were fed diets containing 10% butter (10B), 10% corn oil (10C) or 9% butter/1% corn oil (10M) for 4 wk. Heart rate was determined in response to increasing i.v. doses of isoproterenol. The percent stimulation at the highest dose of isoproterenol (100 µM) was found to be significantly higher (P < 0.05) in the 10C-fed group than either the 10B- and 10M-fed groups. A similar study investigated the effect of propranolol inhibition of heart rate in low-fat (10C and 10B) as well as high-fat (25C) corn oil- and high-fat (25B) butter-fed animals. Heart rate was elevated with a constant i.v. infusion of isoproterenol and the inhibitory effect of propranolol was determined. The ED₅₀ was found not to depend on the level of fat, but was found to be significantly lower in the corn oil-fed animals than in those fed butter fat (P < 0.05). Thus, animals appear to be more sensitive to these ß-adrenergic agonists/antagonists when fed a diet containing corn oil rather than butter fat as the lipid source.

KEY WORDS: • dietary fat • heart rate • myocardial ß-adrenergic receptor

¹ A preliminary report of this work was presented at the FASEB meeting in Washington, DC, April 1987. [New Jersey Agricultural Experiment Station Publication No. D-14137-4-87, Fed. Proc. 46(4): 1474 (Abs.)]. This work was supported by State funds, NIH Grant No. HL38223, American Heart Association (New Jersey Affiliate) Grant No. 85-37 and Biomedical Research Support Grant No. RR0705821.

² To whom all correspondence should be addressed.

Manuscript received 29 December 1987. Revision accepted 28 July 1988.