Postnatal Development of Peptidergic Innervation of the Canine Heart

The autonomic innervation of the canine heart develops with considerable regional asymmetry during the early neonatal period. To examine the development of the peptidergic component of the innervation, 28 mongrel puppies 1–6 weeks of age from five litters were studied at weekly intervals. Four of the mothers were also studied as adult and breed controls. Tissue neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP) concentrations were determined by radioimmunoassay in myocardial specimens obtained from several specific sites of the cardiac chambers and from the proximal coronary arteries. Data were analysed according to age, cardiac chamber/vessel, gender and individual litter. In general, NPY concentrations in pg/mg protein were six- to eight-fold higher than those of VIP. Also concentrations for both peptides were about two-fold higher in the coronary arteries than the myocardium and differed among chambers, being higher and similar in the atria and lower in the ventricles, particularly for NPY. No gender differences were identified. Concentrations varied among litters, but the developmental pattern was similar with the highest peptide concentrations identified in the first and fourth week. Whereas the differences among chambers may also reflect differing rates of developmental increase of myocardial mass, the pattern corresponds only in part to previously identified functional changes in sympathetic innervation since, in contrast to previous findings, high NPY concentrations in the first 2 weeks suggest anatomically advanced innervation.