Abstract
Objectives : To determine the effects of β -adrenoceptor and
muscarinic agonists on the contractile rate of isolated right atria of
rats fed a high fructose diet with or without rosiglitazone (RSG).
Materials and Methods : Male Sprague Dawley rats were assigned to four
groups and given ad libitum access to one of the following diets:
standard chow, standard chow supplemented with 4 mg/kg/day RSG, a high
fructose diet and a high fructose diet with 4 mg/kg/day RSG. All the
groups were maintained on these regimens for three weeks with weekly
measurements of systolic blood pressure and body weight. At the end of
the three weeks, the rats were exsanguinated and the hearts were
rapidly removed following which blood glucose, insulin and lipid
profiles were estimated. The right atria were isolated from the heart
and their responsiveness to sympathetic and parasympathetic agonists
was studied. Results : Basal, spontaneous, isolated atrial pacemaker
rate was diminished in fructose-fed rats. The maximum pacemaker rate to
isoproterenol or norepinephrine was unchanged in fructose-fed rats.
Further, the increase in atrial rate and half maximal effective
concentration values for each agent were also unaffected. The
sensitivity to negative chronotropic action of acetylcholine was
enhanced in fructose fed rats, whereas the response to carbachol was
unchanged. The increased sensitivity to acetylcholine was restored by
RSG treatment. Conclusion : High fructose diet induced insulin
resistance and hypertension with alterations in basal spontaneous
pacemaker, enhanced sensitivity to cholinergic agonist without any
changes in the response to adrenergic and cholinergic receptor
activation. Treatment with insulin sensitizer rosiglitazone was able to
prevent all these changes. The present study suggests that
rosiglitazone may have effect on the cardiovascular system in addition
to the insulin sensitising action.