Timing of sympathetic innervation affects growth of myocardium in oculo

The effects of sympathetic innervation on myocardial growth during the proliferative and hypertrophic phases of cardiac growth were examined with the use of embryonic day 12 whole hearts or ventricles cultured in the anterior eye chamber of adult rats for 8 wk. Sympathetic innervation of whole heart and ventricular grafts was prevented by removing the superior cervical ganglion 1 wk before grafting or was limited to the cellular proliferation phase of growth by superior cervical ganglionectomy after grafts had been in oculo for 4 wk. Grafts in sympathetically innervated eye chambers were significantly larger than grafts in eye chambers denervated at 4 wk and grafts in eye chambers sympathectomized 1 wk before grafting. Innervation of grafts was delayed until 5-6 wk in oculo by crushing the internal carotid nerve. Delayed innervation produced grafts that were as large as those in innervated eye chambers. Together, these experiments suggest that the effects of sympathetic innervation on myocardial growth in oculo are most apparent during the second 4 wk in oculo (i.e., during the cellular enlargement phase of growth.