Quantitative immunohistochemical assessment of bovine myocardial innervation before and after cryosurgical cardiac denervation.

OBJECTIVE

The aim was to determine the relative distribution and possible origins of peptide containing nerves in the bovine heart before and after functional extrinsic denervation established by cryosurgery.

METHODS

A quantitative immunohistochemical technique was used.

RESULTS

In the intact heart, myocardial nerve fibres and fascicles displaying immunoreactivity for the general neural marker protein gene product 9.5 had an atrial to ventricular gradient in density. The right atrium was the most densely innervated region and a major proportion of the total myocardial innervation, visualised by protein gene product 9.5 immunoreactive nerves, showed neuropeptide tyrosine (45%) and tyrosine hydroxylase (20%) immunofluorescence staining, while nerves immunoreactive for vasoactive intestinal polypeptide and calcitonin gene related peptide formed relatively minor subpopulations (representing less than 2% and 0.5%, respectively, of the total fluorescent myocardial innervation). Following cryoablation there was a significant reduction in the percentage fluorescent area of protein gene product 9.5 immunoreactive nerves throughout the heart, of greater than 90% of the control values. There were highly significant reductions in the percentage fluorescent area of nerves showing immunoreactivity to neuropeptide tyrosine, tyrosine hydroxylase, and calcitonin gene related peptide, to 1.01, 0.92, and 0.05%, respectively, of the intact myocardial innervation. The distribution of vasoactive intestinal polypeptide immunoreactive nerves was more variable and displayed an equivocal response to cardiac cryoablation.

CONCLUSIONS

The majority of nerves showing immunoreactivity to neuropeptide tyrosine, tyrosine hydroxylase, and calcitonin gene related peptide are of extrinsic origin, while vasoactive intestinal polypeptide immunoreactive nerves may have intrinsic as well as extrinsic origins. The distribution and apparent origins of immunohistochemically defined nerves in the bovine heart are similar to those observed in the human heart which suggests that the calf may be an appropriate model for comparative studies.