Diminished neuropeptide Y and dopamine beta-hydroxylase immunoreactivity in a guinea pig model of left ventricular hypertrophy.

Abstract

The aims of the study were to determine the effect of chronic pressure overload of the left ventricle on the density and distribution of neuropeptide-Y-like immunoreactive (NPY-LI) nerve fibres in heart and to compare any changes to those observed in adrenergic nerve fibres, identified by dopamine beta-hydroxylase immunoreactivity. Pressure overload was produced in female adult guinea pigs by constriction of the abdominal aorta, using a modified Weck haemoclip. The same operation was performed on a separate group of animals except that no clip was placed around the aorta. Five weeks after surgery, animals were anaesthetised, and the hearts were fixed by perfusion for immunohistochemistry. Cryostat sections were stained, using an indirect peroxidase/antiperoxidase method, for NPY or dopamine beta-hydroxylase. Aortic stenosis caused a 45% increase in left ventricular weight and a 58% increase in left atrial weight at 5 weeks postsurgery. Pulmonary oedema, a sign of cardiac failure, was evident in most of the animals with aortic stenosis. Immunohistochemical studies showed that in atria and right ventricles from animals with abdominal aortic stenosis the distribution and density of NPY-LI nerve fibres were similar to those in the sham operated guinea pigs. However, the left ventricles obtained from the animals with aortic stenosis were nearly devoid of NPY-LI nerve fibres. The density of dopamine beta-hydroxylase-LI nerve fibres was also substantially reduced in the hypertrophied left ventricles. Aortic stenosis resulting in left ventricular hypertrophy caused a nearly complete loss of NPY-LI and dopamine beta-hydroxylase-LI nerve fibres from the left ventricle. The parallel reduction in both neuropeptide Y and dopamine beta-hydroxylase is in accordance with the association of neuropeptide Y with sympathetic (adrenergic) nerve fibres in the left ventricle and suggests that chronic left ventricular hypertrophy causes a severe degeneration of sympathetic axons supplying this chamber and/or reduces the ability of these sympathetic neurones to maintain normal levels of neurotransmitter related enzymes and neuropeptides.