Using intravascular autoradiography for an estimation of proliferative activity of rat mesenteric microvessel endothelial cells during the first month of postnatal development.

BACKGROUND/METHODS: We applied a novel method for studying endothelial cells (EC) by using autoradiography of cells labeled by 3H-thymidine: photo emulsion was administered into the vascular bed. In the flat transparent organ, this method allows to compare the mitotic activity of endothelium (MAE) depending on vessel diameter and animal age. RESULTS: The number of the labeled ECs in animals was found to be almost equal in all vessels at the same age. The amount of labeled vessels and the density of the labeled nuclei increase towards near-capillary vessels of a diameter < or =10 microm. With age, MAE decreases in all categories of vessels. However, in 12-day-old animals, MAE temporarily increases. It was noted that high MAE in the bed of these rats precedes or coincides with the period of accelerated weight gain of the digestive system supplied by an increase in organ blood flow. CONCLUSIONS: By using the endothelial autoradiography method that we developed, we obtained the following evidence: (1) the number of ECs in the synthetic phase of the mitotic cycle in mesenterial vessels is approximately identical in animals of the same age, and (2) this number decreases with age, except during the period of accelerated organ growth, when MAE increases.

Mitochondria and blood supply of chicken skeletal muscle fibers in ontogenesis.

Skeletal muscles have been studied during ontogenesis to reveal morphological and functional parameters that at most influence the formation of muscles with different levels of oxygen consumption. Development of oxidative red gastrocnemius muscle (RGM) and glycolytic white pectoralis muscle (WPM) has been studied at a period from being 10-day-old chicken embryos until they become 6-month-old chickens. By morphometry, we measured diameter, length, and numerical density of capillaries; muscle fibers diameter; as well as mitochondria's size, density, and volume fraction in muscle fibers. During the post-embryonic period, the blood flow was estimated by hydrogen clearance method. The data obtained were compared to previously published data on O2 consumption rate in fibers being at the same stages of ontogenesis [Microvasc. Res. 60 (2000) 168]. As shown, relationships between the parameters in the muscles studied appear at different ages. They are described by exponential equations with varying slopes. Beginning with the middle stages of embryogenesis, the clear dependency is seen in both types of muscles between O2 consumption rate in a fiber and summarized perimeter of mitochondria at a fiber section. Capillary bed during embryonal period is superfluous. The clear dependency between capillary-to-fiber number ratio and oxygen consumption in fibers becomes apparent in chickens only 10 days after birth, when the fiber diameter amounts to 20 microm. Since that period, redistribution of mitochondria toward the periphery of a fiber takes place, being especially pronounced in RGM. The regularities found between oxygen delivery and consumption systems enable to search for the leading factors of specialization of skeletal muscles in accordance with the level of oxidative metabolism. These factors may be used for calculation and numerical simulation of the parameters of oxygen transport in skeletal muscles.

Oxygen diffusion coefficient in isolated chicken red and white skeletal muscle fibers in ontogenesis.

Oxygen diffusion from medium to cultured isolated muscle fibers from red gastrocnemius muscle (deep part) (RGM) and white pectoralis muscle (WPM) of embryonic and postnatal chickens (about 6 months) was explored. The intracellular effective O(2) diffusion coefficient (D(i)) in muscle fiber was calculated from a model of a cylindrical fiber with a uniform distribution of an oxygen sink based on these experimentally measured parameters: critical tension of O(2) (PO(2)) on the surface of a fiber, specific rate of O(2) consumption by a weight unit of muscle fibers (;VO(2)), and average diameter of muscle fibers. The results document the rapid hypertrophic growth of RGM fibers when compared to WPM fibers in the second half of the embryonic period and the higher values of;VO(2) and critical PO(2) during the ontogenetic period under study. The oxygen D(i) in RGM fibers of embryos and 1-day chickens was two to three times higher than observed for WPM fibers. For senior chickens, the oxygen D(i) value in RGM and WPM fibers does not differ. The D(i) of O(2) in both RGM and WPM fibers increased from 1.4-2.7 x 10(-8) to 90-95 x 10(-8) cm(2)/s with an ontogenetic increase in fiber diameter from 7. 5 to 67.0 microm. At all stages the oxygen D(i) values in RGM and WPM fibers are significantly lower than the O(2) diffusion coefficient in water: for 11-day embryos they are 889 and 1714 times lower and for adult individuals 25 and 27 times lower, respectively. Why oxygen D(i) values in RGM and WPM fibers are so low and why they are gradually increasing during the course of hypertrophic ontogenetic growth are still unclear.