Scanning electron microscopic studies of the vasa vasorum of thoracic aortas

Using hot alkaline solution, the elastic laminae were extracted from aortas and observed with scanning electron microscopy. Vascular structures were found in the elastin layers of the tunica media in descending thoracic aortas of sheep, dogs, and pigs, and these tube-like structures were filled with elastomer which was injected through the heart of the animal in vivo. Sub-intimal microvessels were also found to be filled with the elastomer and it is concluded that vasa vasorum can exist close to the internal elastic lamina in these animals.

A morphological comparison of aortic elastin from five species as seen with the scanning electron microscope

The elastic laminae were extracted from thoracic aortas of adult animals including sheep, dogs, rabbits, cats and rats by treating them in hot alkaline solution (0.1 N NaOH at 75 degrees C) and observed with a scanning electron microscope. The elastic laminae are comprised of sheet-like internal elastic lamina, fibrous and membraneous elastin in tunica media, interlamellar fibers and hollow spaces which we presume were formerly filled with smooth muscle cells in the tunica media. These structures are the same in all five species except that the number of layers and the total thickness of the wall differs.

Mechanical anisotropy of purified elastin from the thoracic aorta of dog and sheep

Mechanical anisotropy was found in elastin from the wall of the thoracic aorta by testing digested vessels from seven mature dogs and five pregnant ewes. The elastin was purified by removing the muscle and collagen with 0.1 N NaOH at 75 degrees C for 5 h. Strips oriented circumferentially and longitudinally with respect to the vessel axis were cycled at increasing loads until failure. Combining the results for four dogs and three sheep the ultimate tensile strength was 405 X 10(3) +/- 155 X 10(3) SD N/m2 circumferentially and 189 X 10(3) +/- 85 X 10(3) SD N/m2 longitudinally. The difference is significant at p less than 0.01. The ultimate strain was not significantly different, 1.19 +/- 0.29 SD circumferentially and 1.01 +/- 0.26 SD longitudinally. At 0.4 strain, the Young's modulus for four samples from four dogs was 404 X 10(3) +/- 64 X 10(3) SD N/m2 circumferentially; the modulus for five samples from five dogs was 245 X 10(3) +/- 60 X 10(3) SD N/m2 longitudinally. The difference is significant at p less than 0.05. At 0.7 strain, the Young's modulus for four dogs was 486 X 10(3) +/- 82 X 10(3) SD N/m2 circumferentially and 343 X 10(3) +/- 62 X 10(3) SD N/m2 longitudinally. The difference is significant at p less than 0.05. The reasons for the anisotropy in terms of the structure are not obvious from preliminary studies using the scanning electron microscope with stretched samples.

Quantitative changes in the size of fenestrations of the elastic laminae of sheep thoracic aorta studied with SEM1

The elastic laminae were extracted from thoracic aortas of 6 adult sheep by treating them in 0.1 N NaOH at 75 degrees C, and the surface of internal elastic lamina (IEL) was observed for windows by scanning electron microscopy. The fenestration analysis on IEL showed that mean diameters of the holes ranged from 0.46 microns (+/- 0.013 SEM) to 1.35 microns (+/- 1.019 SEM), which is smaller than those of human cerebral arteries (7.0 +/- 0.34 at the apex of the bifurcation and 2.1 +/- 0.13 SEM microns in the straight sections; [3]), and mean densities ranged from 6,513 to 31,544/mm2. Both size and density of windows are found to increase when the digestion time in the hot alkaline solution is increased form 1 to 3 h. It is concluded that the IEL of the sheep thoracic aorta has smaller windows than human cerebral arteries and because of the wall thickness the thoracic aorta requires longer digestion times than human cerebral arteries.

Pancreatic pseudocyst simulating dilated biliary duct system on computed tomography

A case of pseudocyst simulating the biliary ductal system is reported. Several CT findings indicate that the biliary system was not involved: (a) no dilatation of the more proximal intrahepatic biliary radicles; (b) the gallbladder was not distended; (c) lucency extending to the left at the level of the pancreas; (d) a position more medial and anterior than anatomic for the distal common bile duct.

Is inert gas washout from the tissues limited by diffusion?

To determine the extent to which diffusion may limit the exchange of gases stored in the tissues, nine dogs were allowed to breathe an O2-N2-Ar mixture until saturation was achieved; the inspired gas was then changed to one containing neither N2 nor Ar, and the level of these two species in the arterial and in the mixed venous blood was monitored during the washout. A theoretical analysis shows that in a situation where peripheral gas transport is limited entirely by perfusion, the washout curves should be identical, provided concentrations are expressed as a fraction of the initial value. When the process is restricted by diffusion through the tissues, Ar is expected to lag because of its higher molecular weight. In all animals, the rate of elimination of the two tracers was the same, indicating that the time course of storage or release of inert gas from body stores is governed (mainly or entirely) by perfusion.

Studies on splenic megakaryocytes. I. Recovery of megakaryocytes from the splenic venous outflow

Spleens from 14 healthy adult cats were isolated and perfused with cell-free Ringer's solution. Histological studies on the splenic megakaryocytes, as well as a search for splenic megakaryocytes in samples of the splenic venous outflow, were performed. The samples of the splenic venous outflow contained a lower cellular concentration when perfusion was prolonged, but the number of megakaryocytes appearing in the venous samples increased. At least five different forms of megakaryocytes were observed from smears of the venous outflow: (i) unipolar, (ii) multipolar, (iii) foamy, (iv) mobile and (v) nuclear types. These types were also found in splenic venous outflow of dogs, kittens and bled cats. It is suggested that not only platelets but also the larger megakaryocytes can pass out of the splenic circulation. This may imply that megakaryocytes can be culled, matured in the splenic red pulp, and ultimately released into peripheral blood.

Endocardial surface structures of the feline heart observed with a scanning electron microscope

Internal surface structures of the auricular and ventricular chambers were studied with scanning electron microscopy. We observed vascular connections between the ventricular chamber and the coronary vessels, including cords and papillary muscles covering the lining of the endocardium. The endothelial cells covering the inner surface of the endocardium appeared to be functionally active with many microvilli similar to pinocytic microprojections of other endothelial cells. The pinocytic microprojections ranged between approximately 100 and 300 A in diameter. The epicardium contained mainly bundles of collagenous fibers.

Release of red cells from the slowly-exchanging splenic pool after noradrenaline administration

Isolated, denervated, cat spleens were perfused at constant flow with modified Ringer solution. Perfusion, pressure, outflow rate, and outflow red cell concentration were measured against time. After splenic perfusion by 500 ml solution the cell washout curve became a single exponential function, indicating that only cells from the most slowly exchanging red cell compartment remained (these are immature and abnormal cells which adhere to the fine structures of the red pulp). Splenic contraction was induced by injection of 5 mug noradrenaline into the inflow after perfusion by 600 and 1000 ml of fluid, respectively; outflow cell concentration rose 17-fold before returning to baseline value and 32% of red cells in the spleen were expelled. The time course of changes in cell concentration was similar in shape but delayed with respect to that of outflow rate. The transit time of the cells from the site of release to the splenic vein must have exceeded 40 s, which is consistent only with release from the red pulp. Furthermore, at the peak of the cell concentration curve the mean reticulocyte count was 37.8%. Thus immature and abnormal red cells, which comprise the slowly-exchanging compartment, are indeed released from the spleen during contraction.

Effects of acetate on myocardial contractility and epicardial ECG of isolated and perfused feline hearts

In isolated, perfused hearts, the effects of acetate on epicardial ECG and ventricular pressure were observed during various times of perfusion. Anions-Cl-and acetate-caused changes of ECG configuration, especially in the ST segments. These were different in Phase I (fast compartment) and Phase II (slow compartment).

Kinetics of the red cell washout from coronary vessels of isolated feline hearts

Twenty seven isolated feline hearts were perfused with cell-free oxygenated Ringer-Locke solutions. The concentration of red blood cells in samples of venous outflow collected from the coronary sinuses was determined by means of a Celloscope counter. Cellular concentrations decreased gradually as the perfusion time increased, and from 10(9) to 10(5) cells per millilitre after 300 ml perfusion. When the ventricular lumens were filled with residual blood (group I, 15 cats), several red cell peaks were superimposed on the smooth exponential decay curve of red cell washout. It is suggested that the peaks were caused by ejection of red cells from the ventricular lumens into communicating branches between the ventricular lumens and coronary capillaries. In cases of blood-emptied hearts (group II, 12 cats) these peaks did not occur, and mathematical analysis showed that summing three exponential functions could approximate the whole washout curve of red cells. This suggests that the coronary circulation may be described by three red cell compartments. The functional implication of this analysis for the microcirculation in the coronary vessels was discussed.

Sequestration and possible maturation of reticulocytes in the normal spleen

The presence, in the feline spleen, of a slowly exchanging red cell 'compartment' ([Formula: see text] 54 min) has been demonstrated previously. These red cells adhere to reticulum cells and sinus walls in the red pulp and have been shown to be larger in cellular volume and lighter in cellular density than the rest. This suggested that they might be younger cells and we have reported briefly that they contain a high proportion of reticulocytes. Using supravital stains we have measured the percentage of reticulocytes in the outflow from isolated spleens of cats and dogs, perfused with oxygenated Ringer solution. Reticulocyte counts increased from 0.4% to 99% as the perfusion progressed. The results show that the slow compartment consists entirely of reticulocytes. The ratio of reticulocytes to rubricytes in the spleen was found to be 75:1. Therefore the reticulocytes were not produced in the spleen but were accumulated from the circulating blood. The total number of reticulocytes so stored is 1.2 × 1010 cells, equivalent to 1.5 times the daily production in the whole animal. From these data we conclude that reticulocytes released from the bone marrow under physiological conditions are sequestered and matured in the spleen.

Physical characteristics of red cells collected from the spleen

Kinetics of cell washout, when isolated cat spleens are perfused with Ringer solution, have shown previously that the red cells stored in the spleen correspond to a system of three compartments (fast, intermediate, and slow); morphological studies, at different stages of the washout, have already identified these compartments as free cells in vascular channels, free cells within sinuses, and cells adhering to sinus walls, respectively. By collecting the venous outflow at three particular stages of the washout fairly pure samples (>85%) of the cells from each compartment have now been obtained. We have measured the density (phthalate method), volume, and osmotic changes (Celloscope) of these cells. Cells from the fast and intermediate compartments were not significantly different from those of arterial blood, but cells from the slow compartment were lighter (specific gravity difference was 0.0064; p < 0.01), larger in volume (5.0%; p < 0.01), and swelled 14% less in 200 mOsmol/l (p < 0.01). These differences indicated that cells from the slow compartment might be predominantly younger cells and this has been confirmed by finding reticulocyte counts of 58.0 ± 3.8 (S.E.) %. It is suggested that immature red cells, released from the bone marrow, may be sequestered in the spleen and matured.

The distribution of red cells in the spleen

Kinetics of red cell washout, when isolated cat spleens are perfused with Ringer solution, show that the spleen corresponds to a three-compartment system. To determine whether or not there exist morphological counterparts to these compartments we examined microscopic sections from 16 spleens perfused by different volumes of Ringer solution. Red cells could be divided into three groups: (1) free cells in vascular channels and sinuses, (2) cells adhering to reticulum cells or sinus endothelium, and (3) cells in the cytoplasm of macrophages. When 50 ml were perfused no free cells were seen in vascular channels. After 600 ml few free cells remained in the sinuses. Thereafter the number of cells adhering to the sinus wall decreased gradually and cell counts agreed with predictions from the washout curve. We conclude that the compartments of our model (fast, intermediate, and slow) represent, respectively, free cells in vascular channels, free cells within sinuses, and cells adhering to sinus walls. The only cells trapped irreversibly are the very few found in the cytoplasm of macrophages. It is suggested that the slow compartment represents red cells in a pre-phagocytosed stage, e.g. aged cells, abnormal cells containing inclusion bodies, and possibly, reticulocytes in the process of maturation.