Both oxidative stress and β-MHC expression are associated with pathological
cardiac hypertrophy. β-
adrenergic receptor stimulation plays an important role in
cardiac hypertrophy. Recent studies have reported a negative interplay between
opioid receptors and
adrenoceptors in heart. This study investigated the effect of
U50,488H (a selective κ-
opioid receptor agonist) on myocardial oxidative stress and α- and β-MHC expression in
isoproterenol-induced
cardiac hypertrophy. Male Wistar rats were administered
normal saline (control),
isoproterenol (ISO) (5 mg/kg BW s.c. OD), and
isoproterenol with
U50,488H (0.4 and 0.6 mg/kg BW, i.p. OD) for 14 days. In a separate group,
nor-binaltorphimine (
nor-BNI) (0.5 mg/kg, BW, i.p.) (κ-receptor antagonist) was administered along with ISO and
U50,488H. ISO administration caused significant increase in left ventricular (LV) wall thicknesses, LV mass in echocardiography, heart weight to
body weight ratio, and myocyte size as compared to control. Both the doses of
U50,488H offered significant protection against these changes. The higher dose of
U50,488H significantly prevented ISO-induced increase in myocardial lipid peroxidation and depletion of myocardial
antioxidants (
glutathione,
superoxide dismutase, and
catalase), while a similar trend (although not significant) was observed with the lower dose also. ISO-induced myocardial
fibrosis was also significantly attenuated by both the doses of
U50,488H.
Isoproterenol-induced β-MHC expression in the hypertrophied heart was not altered by either doses of
U50,488H, however, the latter prevented the loss of myocardial α-MHC expression. All these effects of
U50,488H were blocked by
nor-BNI. This study provides the evidence that
U50,488H reduced oxidative stress and preserved expression of α-MHC in
isoproterenol-induced
cardiac hypertrophy.