Search

Sympathetic innervation has no direct effect on the growth of the microvascular system in fetal rat atrial or ventricular tissue grafted into the host rats' anterior eye chamber. The volume percentage of blood vessels, myocytes, extracellular matrix, and other cells in 14- or 35-days-old innervated grafts is similar to that in noninnervated grafts. Sympathetic innervation has no effect on metabolism and perfusion of the graft.

A study of the relationship between thyroid hormones and coronary neovascularization of embryonic rat hearts reveals that embryonic rat hearts that are cultured in oculo are not affected by thyroid hormones and that increased work-related events lead to the thyroid hormone-induced angiogenic effects observed in loaded hearts. Stimulation of hypothyroidism or T4 administration does not influence vascularity or growth of unloaded hearts. Extracellular matrix and volume densities of myocytes and vessels do not exhibit any variations.

A study of the relationship between age and chronic thyroxine (T4)-induced angiogenesis by comparing control and T4-treated rats of different age groups reveals that chronic T4-induced angiogenic effects are not restricted to senescence. The enhancement in heart rate due to T4 is offset by capillary and precapillary growth, enabling a normal myocardial perfusion per unit mass. Capillary proliferation and diameter increase lead to normal capillary volume density in T4-treated rats that have cardiac hypertrophy.

Image analysis and morphometric measurements in the arteriovenous (A-V) shunt in the left and right ventricles of rats show that arteriolar angiogenesis has a linear relationship with the magnitude of volume overload-induced ventricular enlargement and is responsible for 50% of the cardiac hypertrophy. The arteriolar length density is lesser in the left ventricle of the A-V shunt rats while it is the same in the right ventricle of both A-V shunt and control rats. Thus, capillary and arteriolar growth compensate for the overload-induced ventricular enlargement.

Maximal coronary blood flow and reserve in Fischer 344 rats is modulated by factors such as aging and hypertension. The influence of age factor and hypertension on ventricular structure, function and myocardial microvessels is assayed in middle-aged and senescent rats by inducing hypertension in them. The wall-to-lumen ratios of the finest arterioles is enhanced and the capillary numerical density reduces significantly. The wall-to-lumen ratios of small arterioles is proportionate to the age factor in normotensive rats, suggesting that the hypertension in these age groups involves substantial cell loss and endomyocardial fibroses.