This is particularly well demonstrated in slow on a restricted diet.Capillary density was higher and CF was lower in both muscles in less wellfed animals up to the age of yr.When fibers became smaller in older animals, this difference disappeared. Some reports show a lack of relationship between CD and biochemical estimates of SDH activity. Al though a greater demand for oxygen was considered as an element in capillary proliferation, other factors, such as insulinstimulated glucose uptake, have been recently considered as important determinants of CD in human muscles.During phylogeny, capillary supply in the heart is related mainly to the heart work and intensity of oxida tive metabolism and less to the size of the heart or myo cytes.In skeletal muscles, capillarization is much more closely related to fiber size, although the oxi dative capacity is perhaps of equal importance.Dots represent individual capillaries.EDL, extensor digitorum longus; TA, tibialis anterior.Ab scissa, CF ratio; ordinate, frequency distribution.However, this may simply reflect the fact that SDH is not a good indicator of tissue oxidative capacity.In con trast, there is a very good correlation between the activ ity of citrate synthase and CD among a variety of mus cles. Studies involving birds and mammals show that the pat tern during embryogenesis is similar to that described in phylogenesis, with lacunary supply at the earliest stage and capillaries appearing gradually, first in the subepicardial and later in subendocardial layers, and contacts with the branches of the aorta appear after the terminal vascular bed has already been formed hearts, capil lary formation starts in the right ventricle and spreads toward the left ventricle as heart weight increases.After days of age in rats, capillary growth stops and CD gradually decreases. Capillary basement mem brane is formed during late fetal development in rats, together with a decreas ing numerical density of plasmalemmal vesicles. Ultrastructural differentiation of capillary endothe lium in rats is completed, days Entecavir hydrate postnatally, but the development of various enzymes characteristic of capil lary endothelium is only completed after wean ing. The development of the vascular bed in human hearts is similar to that described, but the time course is different in that coronary circulation is established in the first quarter of pregnancy compared with postnatal replacement of sinusoids by capillaries in rat hearts. As in rats, most of the capillaries develop postnatally, and there is also a subsequent increased branching of larger vessels.The capillary Dimenhydrinate network on the th day of gesta tion is formed by polygonal loops that gradually stretch under the tension of growing muscle fibers. Capillary sprouts are numerous even after birth, repre senting of the capillary network, and di sappear by days postpartum. As in cardiac muscle, growth of capillaries is fast during early postnatal devel opment. In contrast to cardiac muscle, the terminal vascular bed at birth in rat skeletal muscles consists mainly of capillaries, with arterioles and venules developing later. Capillary growth gradually slows, although fiber growth continues and thus CD decreases while CF in creases in muscles of chickens. Thus many more smaller fibers in a dayold dog are supplied by the same number of capil laries as the relatively few fibers per square millimeter in adult animals.