An in oculo model for quantitation of vascular growth in the rat heart

The aim was to describe, both qualitatively and quantitatively, vascularisation in an in oculo model that may prove useful for studying neovascularisation in the myocardium.

Whole hearts from 13-14 d rat fetuses were implanted into the anterior chamber of host Sprague Dawley rats. Implant growth was monitored and at 3 months postimplantation grafts were recovered.

Fixed tissue sections were histologically characterised with light and electron microscopy and morphometrically analysed using image analysis.

At two weeks, 92% of implanted hearts were beating. At 1 month, well vascularised implants that were beating were slightly larger than those not beating, at 16.0(SD 1.0) v. 12.3(2.0)mm2. By 2 months, beating implants were significantly (p less than 0.05) larger than non-beating implants, at 23.5(3.0) v. 12.4(1.7)mm2. In non-beating implants, the larger the extent of vascularisation, the larger the implant size. Histologically, well vascularised beating implants showed normal adult cardiac myocyte structure, with normal appearing sarcomeres and intercalated discs, but no preferential fibre orientation. The amount of area occupied by muscle and connective tissue varied between implants. Implant vasculature, including arterioles and capillaries, appeared normal. The percentage of vascular area was consistent between grafts. A small percentage of total area was occupied by lymphocytes.

This investigation indicates that sufficient vascularisation is important for growth of grafts, provides for the first time quantitative morphometric data characterising the in oculo cardiac implant model, and reports baseline data that will be useful for comparison to myocardium treated with putative angiogenic factors in the future.