International journal of microcirculation, clinical and experimental最新文献

To evaluate whether the microsphere method, including the necessary surgical procedures, for blood flow determination creates hemodynamic stress and a secondary reduction in small intestinal perfusion, we monitored the small intestinal perfusion with laser Doppler (LD) fluxmetry in 3 groups of Sprague-Dawley rats. Group I was studied during two microsphere injections without manipulation, group II was subjected to mesenterial-root occlusion during the second injection, and for group III, vasodilatation with papaverine preceded the second injection. While cardiac output and kidney blood flow were constant at the two microsphere injections, mean blood pressure (p < 0.05) and hematocrit (p < 0.01) significantly decreased in all 3 groups. Blood glucose increased significantly (p < 0.01). LD values also declined significantly (p < 0.05) between the start and end of experiments. In group I, the initial values of 9.5 perfusion units (PU) (5-23) decreased to 6.5 PU (3-12), in group II, 10.5 PU (5-24) decreased to 7.0 PU (4-15) and in group III, 9.0 PU (5-13) decreased to 5.5 PU (4-12). In conclusion, these findings suggest that the microsphere technique with two injections of spheres and reference sample withdrawals may affect the perfusion of the small intestine in the Sprague-Dawley rat.

The role of leukocytes (WBCs) and platelets (PLTs) in the pulmonary circulation may be important in the development of monocrotaline (MCT)-induced pulmonary hypertension in rats. We investigated the changes in WBCs and PLTs in the pulmonary microvasculature during the development of chronic pulmonary hypertension in MCT rats by real-time confocal scanning laser microscopy. The number of WBCs sequestered in the pulmonary microvasculature increased significantly from day 7 after MCT injection, but no further increase occurred from days 14-28. The number of PLTs sequestered in the pulmonary microvasculature increased significantly from day 7 after MCT injection, and reached a peak on day 14. However, the number of PLTs sequestered on days 21 and 28 after MCT injection was significantly lower than on day 14. These findings suggest that PLTs mainly contribute to the initial and middle stages of the development of MCT-induced pulmonary hypertension in rats, while WBCs mainly contribute to the middle and late stages.

Due to its strategic anatomical position, the endothelium is constantly exposed to the different risk factors for atherosclerosis. During the last decade it has become clear that hypertension profoundly affects endothelial function. Depending on the form of hypertension, endothelium-dependent relaxation is impaired in most vascular beds. In spontaneous hypertension, the production of nitric oxide, which in endothelial cells is formed from L-arginine via the constitutively expressed enzyme endothelial nitric oxide synthase, represents the main mediator of endothelium-dependent vasodilation and seems to be enhanced. On the other hand, the release of endothelium-dependent contracting factors such as prostaglandin H2 and thromboxane A2 have been demonstrated in this model of hypertension. Similar results have been obtained in the forearm circulation of patients with essential hypertension. In contrast, in models of salt-sensitive hypertension no release of vasoconstrictor prostanoids can be found indicating a decreased production of nitric oxide. Thus, in spontaneous hypertension an increased production of nitric oxide seems to occur, which is ineffective due to either the simultaneous release of endothelium-dependent vasoconstrictors and/or inactivation of nitric oxide, or due to anatomical changes such as hypertension-induced intimal thickness which inhibits its action on vascular smooth muscle cells. In summary, in hypertension, endothelium-dependent vasodilation is blunted and the endothelial L-arginine nitric oxide pathway is altered. These changes seem to represent a consequence rather than a cause of hypertension.

Dilation is the most commonly observed diameter change in blood vessels when intraluminal flow increases. However, at very high and low levels of vascular tone the response is constriction. This complex response seems designed to ensure that time-averaged vascular tone levels are restricted to an intermediate range. Flow dilation is initiated predominantly at the surface of the endothelium, probably by conformational change in macromolecules of the extracellular matrix such as glycosaminoglycans. This is associated with changes in ion binding--flow is exquisitely sodium sensitive, and subsequent alteration in cellular function. In the rabbit basilar artery the inward rectifying potassium channel of the endothelium cell is opened by shear stress increase leading to dilation and the voltage-dependent calcium channel of the smooth muscle cells with constriction. In this blood vessel, at any rate, the final response to flow change seems to be predominantly the consequence of the interaction between these two processes.

In inflammation, cells interact with extracellular matrices or neighboring cells by a spatio-temporal intervention pattern of specific cell surface receptors and adhesion molecules. Resident cells of the injured tissue communicate with circulating effector cells by cytokines and direct cell-cell contact. These cytokines stimulate expression of the adhesion molecules ICAM-1, VCAM-1, and E- and P-selectin on endothelial cell surfaces and upregulate beta 2-integrins and ICAM-1 on luminal leukocytes. White blood cells then adhere to the activated endothelial cells, migrate through the vessel wall, and penetrate areas of infection or tissue damage. The basis for a cellular immune response is formed by the interaction between T lymphocytes and antigen-presenting cells amplified by adhesion molecule LFA-1,2,3 to ICAM-1 binding.

Despite many theories, the initiating circumstances for the development of atherosclerosis remain obscure. The development of animal models of atherosclerosis was based upon the different theories of the origins of atherosclerosis which suggested that it originates at the intimal surface of the vessel. A more recent model of atherosclerosis involves perivascular manipulation of the vessel by positioning of a hollow silastic collar around the artery. In this model, several of the features seen in early human atherosclerosis are generated within a period of 7 days. It is hypothesized that arterial wall hypoxia following occlusion of the vasa vasorum may be the initial lesion of atherosclerosis, and hence that in some cases atherosclerosis is a disease of the outer layers of the arterial wall.

Endothelial and epithelial cells are both barriers and bridges between different compartments. This contribution discusses the general principles of paracellular, transcellular, and transmembrane transport with special emphasis on the relation between asymmetry and net movement of small solutes. Asymmetry of cell membrane transport properties is found in both epithelial and endothelial cell layers and provides the basis for transcellular transport. Furthermore, the asymmetry of membrane transporters such as the blood-brain barrier GLUT1 and the renal sodium-glutamate cotransporter is discussed with regard to their different properties at the extra- and intracellular face. These molecular asymmetries play an important role in the efficiency, direction, and regulation of transport processes across the plasma membranes in endothelial and epithelial cells.

This manuscript presents a brief overview of the physiology and cell biology of the endothelium, which is the basis for understanding the role of endothelial cells in pathological processes as diverse as atherosclerosis, tumour intravasation and multiple organ failure. Following consideration of general aspects of endothelial function in regulating haemostasis, vascular tone and growth, special emphasis will be placed on endothelial regulation of the inflammatory response, which centres on the microcirculation. A particular role in inflammation is played by cell adhesion molecules (CAM), expressed both on endothelial and blood cells. Cell and molecular biological methods to investigate the expression of CAM in endothelial cells in vitro will be presented, as well as novel data, indicating that cytokine-induced up-regulation of CAM in the endothelium may involve signal transduction pathways other than those culminating in the activation of NF-kappa B. Finally, the phenomenon of angiogenesis will be briefly reviewed as a characteristic of endothelial cell activity of central importance to both physiology and pathology and new experimental data presented from an in vitro model to study the ability of individual endothelial cells to form vessel-like structures. In comparative studies to investigate the roles of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor, the dominant role of VEGF in the formation of capillary networks could be unequivocally demonstrated.

The fluid pathway between plasma and lymph comprises 3 matrices of biopolymer chains arranged in series (endothelial glycocalyx, basement membrane, interstitial matrix), each of differing area, thickness, density and biochemical composition. Fluid exchange obeys the Starling principle but the 'balance' of pressures commonly favours filtration even 'downstream', and not venular reabsorption as still widely mistaught. At tissue level the maintenance of fluid balance remains controversial. The 3-pore theory is reviewed and updated following aquaporin characterisation. The permeability of the endothelial layer can be altered by both intracellular (Ca2+i and cyclic nucleotides) and extracellular mechanisms (albumin, orosomucoid), leading to gross 'hole' formation through as well as between cells (inflammatory stimuli) or more subtle changes (e.g. atrial natriuretic peptide). This is currently a fertile zone of interaction between classical physiology and molecular studies.

Intravital microscopy of the hamster cheek pouch microvasculature was used for in vivo studies of the effects of diltiazem (calcium antagonist, group I), prazosin (alpha 1-adrenergic receptor antagonist, group III), rauwolscine (alpha 2-adrenergic receptor antagonist, group V), phenylephrine (alpha-adrenergic receptor agonist, group VII) and isoproterenol (beta-adrenergic receptor agonist, group IX) in a concentration range of 10(-9)-10(-5) M and their combination with 10(-7) M of buflomedil (groups II, IV, VI, VIII and X) on mean arteriolar internal diameter and spontaneous vasomotion. All drugs were applied topically. Vasomotor activity was studied in 270 arterioles (internal diameter range 20.0-75.0 microns) of 60 preparations. Diltiazem dose dependently increased the microvascular diameter and reduced and ultimately abolished the vasomotion frequency and amplitude. Addition of buflomedil did not significantly change the vasodilation evoked by diltiazem and potentiated its depressive effect on vasomotion frequency and amplitude. Prazosin dose-dependently increased the arteriolar diameter and reduced the vasomotion frequency and amplitude. Addition of buflomedil potentiated both the vasodilation elicited by prazosin and the reduction in vasomotion frequency and amplitude. Rauwolscine tended to elicit vasoconstriction at lower concentrations (10(-9) and 10(-8) M) and vasodilation at higher concentrations (10(-5) M) and significantly reduced the vasomotion frequency and amplitude. Addition of buflomedil potentiated both the vasodilation and the reduction in vasomotion frequency, but tended to increase the vasomotion amplitude. Phenylephrine significantly decreased the mean arteriolar internal diameter, moderately decreased the vasomotion frequency and did not significantly change the vasomotion amplitude. Addition of buflomedil totally blocked the vasoconstriction elicited by phenylephrine, potentiated the reduction in vasomotion frequency and amplitude when combined with lower concentrations of phenylephrine (10(-9)-10(-7) M) and restored the vasomotion frequency and amplitude when combined with higher concentrations of phenylephrine (10(-6) and 10(-5) M). Isoproterenol significantly increased the mean arteriolar diameter and reduced the vasomotion frequency and amplitude. Addition of buflomedil did not significantly change either the vasodilation or the reduction in vasomotion frequency and amplitude. The effects observed with buflomedil on the hamster cheek pouch microcirculation further support its properties as a competitive inhibitor of alpha-adrenergic receptors, not selective for either the alpha 1- or alpha 2-adrenergic receptor subtype, and as a weak calcium antagonist.