Skeletal muscle capillary densities during reactive hyperemia

Summary Reactive hyperemia was induced in hindlimbs of rats by occlusion of the femoral artery. Using fluorescein dye as a peripheral vascular marker, we observed that there was an increase in the number of flowing capillaries supplying the muscle fibres following release of the occlusion. The results indicate that the number of flowing capillaries is not dependent on the duration of occlusion (2–10 min).     

Microsphere measurement of myocardial capillary bed in hypoxic rats

Summary Rats exposed to hypobaric hypoxia for 24 h showed a significant increase in the number of perfused capillaries and in the number of radioactive microspheres trapped in the coronary circulation.     

Effect of vasoactive amines on Weibel-Palade bodies in capillary endothelial cells

The presence and distribution of Weibel-Palade bodies in stomach and colonic mucosal microvessels after the administration of vasoactive amines (serotonin and histamine), the serotonin depletor reserpine, and the von Willebrand factor secretagogue thrombin, was studied by transmission electron microscopy. These agents elevated the number of Weibel-Palade bodies in all microvascular endothelial cells and especially in capillaries. It is concluded that vasoactive amines enhance the synthesis and secretion of large von Willebrand protein multimers by endothelial cells.     

Effect of vasoactive amines on Weibel-Palade bodies in capillary endothelial cells

The presence and distribution of Weibel-Palade bodies in stomach and colonic mucosal microvessels after the administration of vasoactive amines (serotonin and histamine), the serotonin depletor reserpine, and the von Willebrand factor secretagogue thrombin, was studied by transmission electron microscopy. These agents elevated the number of Weibel-Palade bodies in all microvascular endothelial cells and especially in capillaries. It is concluded that vasoactive amines enhance the synthesis and secretion of large von Willebrand protein multimers by endothelial cells.     

A simple method for observation of capillary nets in rat brain cortex

Summary By the authors' technic, the profiles of capillaries in rat brain cortex were clearly demonstrated. The capillaries formed complicated nets by sprouting of their finer branches and anastomosing with each other. Further, a kind of perivascular cells with yellow autofluorescent granules was distributed close to capillaries, arterioles or venules. They seemed to be a special form of macrophage in the brain cortex.     

A simple method for observation of capillary nets in rat brain cortex.

By the authors' technic, the profiles of capillaries in rat brain cortex were clearly demonstrated. The capillaries formed complicated nets by sprouting of their finer branches and anastomosing with each other. Further, a kind of perivascular cells with yellow autofluorescent granules was distributed close to capillaries, arterioles or venules. The seemed to be a special form of macrophage in the brain cortex.     

Fluid and protein clearance in the rat endometrium. Part I: Ultrastructural proof of the absence of an intrinsic lymphatic system from the rat endometrium

An integrated histological and ultrastructural study of the endometrial microcirculation in rats reveals that lymphatic capillaries are absent from the superficial uterine mucosa. Blood capillaries are fenestrated, and their basement membrane may be poorly developed.     

Penetration barrier to sodium fluorescein and fluorescein-labelled dextrans of various molecular sizes in brain capillaries.

The permeability of the blood-brain barrier to sodium fluorescein, or fluorescein-labelled dextrans of various molecular weights, was investigated. Unlike the capillaries in both the area postrema and the eminentia mediana, the capillaries of the cerebral cortex were impermeable to all the intravenous tracer substances used.     

The relation between capillaries and neurons in the caudal neurosecretory system of Pomatomus saltatrix.

The caudal neurosecretory system of Pomatomus saltatrix was examined. Particular interest was devoted to the perikarya of the neurosecretory cells. The majority of these cells were characterized by a close association with the capillary network. The cells appeared to ensheath the capillaries thus bringing the nucleus and perinuclear cytoplasm into close association with the capillaries.     

Fenestrated capillaries in ‘venous patch’ adventitia

Summary Fenestrated capillaries in venous patch adventitia are seen during the 2nd week after microsurgery. The fenestrae contain diaphragms. These capillaries are possibly transitory structures which appear during injury cicatrization. The importance of these capillaries during transcappillary exchange in injuried tissue is discussed.The technical assistance of M. Guerricabeitia is gratefully acknowledged.     

Fluid and protein clearance in the rat endometrium. Part I: Ultrastructural proof of the absence of an intrinsic lymphatic system from the rat endometrium

Summary An integrated histological and ultrastructural study of the endometrial microcirculation in rats reveals that lymphatic capillaries are absent from the superficial uterine mucosa. Blood capillaries are fenestrated, and their basement membrane may be poorly developed.Supported by a grant from the Nationaal Fonds voor Wetenschappelijk Onderzoek-Fonds voor Geneeskundig Wetenschappelijk Onderzoek (Belgium).     

Berechnung von Konzentrationsprofilen in Blutkapillaren und Nierentubuli unter Verwendung derGrätz-Nusseltschen Differentialgleichung

Summary Concentration profiles are computed in blood capillaries and in the artificial perfused proximal tubulus: maximal difference of oxygen partial pressure between wall and centre in lung capillaries 40–60 Torr, in capillaries of the myocard 4–6 Torr. Maximal concentration difference of THO in the proximal tubulus: 8% of the maximum value.     

Mechanical forces in lymphatic vascular development and disease

The lymphatic vasculature is essential for fluid homeostasis and transport of immune cells, inflammatory molecules, and dietary lipids. It is composed of a hierarchical network of blind-ended lymphatic capillaries and collecting lymphatic vessels, both lined by lymphatic endothelial cells (LECs). The low hydrostatic pressure in lymphatic capillaries, their loose intercellular junctions, and attachment to the surrounding extracellular matrix (ECM) permit passage of extravasated blood plasma from the interstitium into the lumen of the lymphatic capillaries. It is generally thought that interstitial fluid accumulation leads to a swelling of the ECM, to which the LECs of lymphatic capillaries adhere, for example via anchoring filaments. As a result, LECs are pulled away from the vascular lumen, the junctions open, and fluid enters the lymphatic vasculature. The collecting lymphatic vessels then gather the plasma fluid from the capillaries and carry it through the lymph nodes to the blood circulation. The collecting vessels contain intraluminal bicuspid valves that prevent fluid backflow, and are embraced by smooth muscle cells that contribute to fluid transport. Although the lymphatic vessels are regular subject to mechanical strain, our knowledge of its influence on lymphatic development and pathologies is scarce. Here, we discuss the mechanical forces and molecular mechanisms regulating lymphatic vascular growth and maturation in the developing mouse embryo. We also consider how the lymphatic vasculature might be affected by similar mechanomechanisms in two pathological processes, namely cancer cell dissemination and secondary lymphedema.     

Presence of neurons synthesizing LH-RH in the anterior hypothalamus of the duck (Anas platyrhynchos)]

Using histochemical techniques with LH-RH anti-serum, a large number of LH-RH producing neurons were identified in the Duck hypothalamus, under different physiological conditions. The LH-RH pericaryas were localized in a well delimited area of the anterior hypothalamus, including the dorsal part of the periventricular preoptic nucleus. The LH-RH containing axons were directed downwards towards the infundibulum, and terminated within the external layer of the rostral and caudal median eminence, in close vicinity to the capillaries of the pituitary portal system.     

Penetration barrier to sodium fluorescein and fluorescein-labelled dextrans of various molecular sizes in brain capillaries

Summary The permeability of the blood-brain barrier to sodium fluorescein, or fluorescein-labelled dextrans of various molecular weights, was investigated. Unlike the capillaries in both the area postrema and the eminentia mediana, the capillaries of the cerebral cortex were impermeable to all the intravenous tracer substances used.Part of the experimental work was carried out when F.J. worked at the Department of Anatomy, University of Helsinki on a fellowship from the Finnish-Hungarian Exchange Programme. The authors are grateful to Miss Irma Hiltunen for excellent technical assistance.     

The relation between capillaries and neurons in the caudal neurosecretory system ofPomatomus saltatrix

Summary The caudal neurosecretory system ofPomatomus saltatrix was examined. Particular interest was devoted to the perikarya of the neurosecretory cells. The majority of these cells were characterized by a close association with the capillary network. The cells appeared to ensheath the capillaries thus bringing the nucleus and perinuclear cytoplasm into close association with the capillaries.Supported byA. D. Williams No. 3558 (505), Medical College of Virginia. The authors are grateful to Dr.H. R. Seibel for reading this report.     

La barrière capillaire enzymatique pour la DOPA au niveau de quelques noyaux du tronc cérébral du rat

Summary An enzymatic barrier for Dopa exists at the level of the cerebral capillaries which changes Dopa into Dopamine by means of endothelial decarboxylase. It is abolished by a decarboxylase inhibitor. Its intensity is weaker in structures containing Dopamine (Striatum, Locus Niger). Neurones of the Raphé containing serotonin can be charged with catecholamines. There are close contacts between neurones and capillaries.     

A scanning electron microscopic study of the air and blood capillaries of the lung of the domestic fowl (Gallus domesticus)

Summary Air and blood capillaries of the lung of the domestic fowl constitute the functional gas exchange units. They anastomose profusely and interlace with each other in 3 dimensions. Air capillaries are not blind-ending tubules as has occasionally been suggested. I am most grateful to: Mr K. Veltkamp for aid with SEM, Dr M.A. Abdalla for help with injections, Prof. A.S. King for critical suggestions, Mr J. Geary for aid with photography.     

Choroidal and iris angioarchitecture of the newt: A scanning electron-microscopic study of vascular corrosion casts

The corrosion cast technique provided for the first time an excellent three-dimensional visualization of the vascular pattern of the choroid and iris in the newt eye. The results show the presence of a single arterial afference to the choroidal and iris capillaries: the ophthalmic artery is the origin fo both ciliary arteries and the long posterior ciliary artery. Slightly behind the equatorial circumference of the eyeball the venous drainage consists of a single vessel on the dorsal side and two distinct vessels on the ventral one. It receives blood from both iris and choroid. The surface of the plastic endocasts shows some details of fine luminal structures of the endothelial cells. Shallow depressions may be regarded as imprints of endothelial cell nuclei, and they are distinctly different for arteries and capillaries. The angioarchitecture of the newt eye differs from that of brain in that hairpin-shaped capillary loops are not observed at all.     

Some extracellular matrix elements as markers of 'capillary tunnels' in hypertrophied rat heart.

We studied the distribution of the extracellular matrix proteins fibronectin (FN) and laminin (LM) in the hypertrophied hearts of spontaneously hypertensive rats (SHR), using an immunofluorescence method with specific antibodies. The immunohistochemical reaction was positive in the cytoplasm of some hypertrophied cardiomyocytes. The results showed that FN and LM can be used as markers for tunnels, i.e. intracardiocytic invaginations of the sarcolemma. The tunnels observed contained capillaries.