Modification of catecholamine-induced changes in heart function by food

restriction in rats.

McKnight KA, Rupp H, Beamish RE, Dhalla NS

Division of Cardiovascular Sciences, St. Boniface General Hospital Research
Centre, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.

In view of the common practice of dieting for weight reduction, the influence
of severe food restriction (about 25% of ad libitum intake) on adrenergic
mechanisms was studied. Cardiac norepinephrine and epinephrine concentrations
as well as plasma norepinephrine levels, were increased upon feeding a
restricted diet to rats for 14 days in comparison with control rats that
ingested about 30 g food/ day. Bradycardia as well as characteristic
electrocardiographic abnormalities, including prolongation of the QRS and QT
intervals, were observed in food-restricted rats. Diet-restricted rats did not
develop ventricular arrhythmias in response to epinephrine injections as
readily as control rats. Depression in both + dP/dt and -dP/dt of the heart in
situ as well as reductions in the inotropic responses to epinephrine were
evident in diet-restricted rats. Beta-adrenergic binding studies revealed a
significant decrease in receptor density, but the dissociation constant for
binding was also depressed in the food-restricted rat heart. Downregulation of
the beta-adrenergic receptors in the heart may explain the lack of an
epinephrine-induced increase in contractile force development as well as
arrhythmias in food-restricted rats. These data demonstrate that severe food
restriction has marked effects on adrenergic mechanisms and heart function, and
thus some caution should be exercised at early periods of this therapy for
weight reduction.