Skin temperature in lower hind limb subjected to distal vein arterialization in rats.

Vascular surgery for distal vein arterialization (DVA) has been adopted clinically as a strategy for saving arteriosclerotic lower limbs from amputation. To gain more detailed information on DVA, the present study investigated the procedure in hind limbs of rats under isoflurane anesthesia. Since successful DVA requires destruction of venous valves, a coronary angioplasty catheter guidewire was used to destroy valves either solely in the femoral vein or in both femoral and popliteal veins. The femoral artery was then anastomosed to the femoral vein with sutures under binocular microsopic control. Changes in the distribution of skin blood flow in the hind limbs were studied with a thermal camera. Skin temperature increased in the thigh and knee after femoral venous valve destruction, but hyperthermia was observed in the distal leg and foot only when the valves in the popliteal vein were also disrupted. These results showed that increased arterial blood flow could be established by DVA surgery in both the proximal and distal regions of the hind limbs.

Venular valves and retrograde perfusion.

Forced retrograde perfusion through the venous system with arterial blood can provide adequate oxygen to peripheral tissues at rest through veno-capillary networks which is the basis for surgical restoration of blood flow by distal vein arterialization (DVA). To be successful such surgery requires disruption of valve leaflets in the veins, which can be accomplished easily in the larger vessels. However, the smallest veins (venules) of less than 100 µm in diameter, also possess valves, are distributed widely throughout all tissues and are too fine for any effective surgical interference. Thus venular valves cannot be disrupted or dissected with presently available technology. Nevertheless, clinical observations suggest that retrograde peripheral blood flow is rapidly established after DVA surgery. There is as yet no rational explanation for this phenomenon. In the present study, using Laplace's law, we attempt to elucidate the mechanical properties of venules and their valves. We speculate that the remarkably thin venular walls (and especially those of the smaller vessels which have the thinnest walls), are capable of considerable, rapid distension when subjected to increased hemostatic pressure. The increase in diameter of venules in response to the increased blood pressure renders their valve leaflets incompetent, so that the valves themselves cannot close the vessel lumen. In addition, the thin bicuspid leaflets may also be forced open retrogradely by the increased blood pressure.

Biological maintenance of distal vein arterialization.

Eleven weeks after surgery, a fine microvessel network was seen in the feet of patients with arteriosclerosis obliterans treated by distal vein arterialization. A possible mechanism for establishment of blood flow to, and biological maintenance of, the graft in the foot, in relation to oxygen consumption rate during walking was investigated, using Krogh's tissue cylinder model. Our calculations showed that the increase in oxygen consumption rate of the muscle when patients walked would reduce the size of the oxygen front in the tissue cylinder, thus producing small, transient hypoxic regions in skeletal foot muscle. Such muscle hypoxia, although localized, could stimulate synthesis of vascular endothelial growth factor and facilitate angiogenesis in the grafted tissue. The architecture of fine microvessel networks observed in the foot by angiography seems consistent with this supposition and, moreover, suggests that the reinstatement of blood vessel networks in the foot tissues after grafting is supported by "normal" biological mechanisms.

Micropores in the vitteline layer of the eggs of the dragonfly Oligoaeshna pryeri: a preliminary observation from the viewpoint of oxygen uptake.

In dragonfly eggs, oxygen diffusing in, and carbon dioxide diffusing out, encounter barriers in the shell.According to Tullett and Board, in avian eggs the most important of these barriers results from the geometry of the pores through the shells. As in birds, dragonfly egg shells consist of three layers: the exochorion, endochorion and the innermost vitelline membrane. Trueman has described pores and fine anchorlike structures in the endochorion but the vitelline membrane does not seem to have been studied. In the present work we have used scanning electron microscopy to examine the vitelline membrane in hatching eggs of Oligoaeschna pryeri. We have assumed that the numerous openings seen on the micrographs are pores through the membrane.Results are expressed as means ± SD. The pore diameter, pore area and number per µm2 of the vitelline membrane were 74.7 ± 61.3 nm, 4380 ± 3555 nm2 and 4.16 ±1.3 pores/µm2 (4.16 x108 pores/cm2), respectively. The total pore area was calculated to be 18,222 nm2/ µm(2). In avian egg shells pore density depends on the weight of the egg. Results given by Tullett and Board suggest that an egg weighing 1 g may have a pore density of 300 pores/cm2, which is much lower than the present result for dragonflies. It seems likely that the difference reflects the fact that in Oligoaeshna pryeri the eggs are immersed in water.

Sufficient oxygen can be transported to resting skeletal muscle via arterialization of the vein: theoretical considerations in a rat model.

The blood supply to the lower limbs is often interrupted in patients suffering from arteriosclerosis obliterans (AO). In this condition, it is necessary to establish an oxygen supply via an alternative route. In the present theoretical study on rats, the possibility that adequate oxygen could be supplied through the venous system has been considered using simple calculations. The study was undertaken in the light of a report of a successful surgical approach in which the capillary bed is bypassed [1].The total lengths of the collecting venules and of the arcade venules per mm3 are reported to be 2.32 and 2.11 mm, respectively [2]. If these vessels were stretched out and connected to form a single, narrow venular tube, the total density would be 4.43 mm/mm(3). From the reciprocal of this value, the tissue cylinder surrounding the venule would have a radius of 268 µm. Taking an oxygen consumption rate for resting skeletal muscle of 0.16 ml/100g/min, and pO2 value of 40 mmHg, the one-dimensional diffusion equation gives a maximal diffusion distance of 328 µm. This is larger than the radius of the tissue cylinder surrounding the venular tube. A calculation for Krogh's tissue cylinder gives an oxygen partial pressure gradient of 54 mmHg between the inflow and the outflow terminals. These calculations suggest the oxygen content of the venous blood is adequate to supply sufficient oxygen to resting skeletal muscle. This is consistent with the successful outcome in patients with direct A-V anastomoses and implies that the capillary network is not essential for oxygen transport to resting skeletal muscle.

Renal vasoconstriction in rats causes a decrease in capillary density and an increase in alkaline phosphatase expression in cardiac capillary nets.

In the rat, experimental renal vasoconstriction induced by the use of a Goldblatt clamp caused arterial hypertension, cardiomyocyte hypertrophy and an increased capillary to cardiomyocyte ratio, the latter indicating the formation of new cardiac capillaries. Total capillary density decreased, but capillary portions expressing alkaline phosphatase increased. This suggested a greater arterialization of capillaries which would increase the flow of arterial blood to the myocardial capillary nets. However, the observed increase in the area of the capillary domains means the extra arterialization was not sufficient to compensate for the lengthening of the oxygen diffusion pathway caused by the hypertrophy. Since the effects of renal vasoconstriction were not seen in rats treated with an inhibitor of angiotensin converting enzyme (ACE) it is suggested they are induced by angiotensin II via activation of the renin-angiotensin system (RAS).

Myocardial capillary net and blood constituents in streptozotocin (STZ)-induced diabetic rats.

Type 1 diabetes was induced in Wistar rats by injection of streptozotocin (STZ). Changes in the myocardial capillary network were examined using the double-staining enzymatic method for alkaline phosphatase (AP) and dipeptidylpeptidase IV (DPPIV) This method allows the identification of the arteriolar (AP-containing) and the venular (DPPIV-containing) portions of the capillary network. In addition, blood plasma was analysed. The AP- and AP/DPPIV-containing capillary portions increased significantly, accompanied by a decrease in the DPPIV-containing portions in 60 days. A significant increase in AP was observed in the plasma. The capillary domain areas of each capillary portion were larger in the STZ-injected group than in the controls. It appears that oxygen transport to the subendocardial myocardial tissues may be decreased in the STZ group. In rats fed with Saji-supplemented chow there was a decrease in plasma AP, with increases in hemoglobin, hematocrit and vitamin C, suggesting a partial improvement of metabolic function and oxygen supply in these diabetic Wistar rats.

Effects of a herbal medicine, Hippophae rhamnoides, on cardiovascular functions and coronary microvessels in the spontaneously hypertensive stroke-prone rat.

The dry fruits of Hippophae rhamnoides (so-called "Saji" or "Sea buckthorn") are used in China as a herbal medicine. The present work studied the effects on microvessels in the left ventricular wall, hematological parameters, cardiovascular performance and plasma constituents in spontaneously hypertensive stroke-prone rats (SHRSP/EZO) treated with Hippophae for 60 days. Analyses showed that the powder made of dry Hippophae fruits contains the vitamins C, B1, B2 and E, provitamin A, rutin, serotonin, cytosterol, selenium and zinc, among other constituents. The experimental rats were fed ad libitum with blocks of rat chow supplemented with Hippophae powder at a concentration of 0.7 g/kg in rat powder chow, while control rats were unsupplemented chow. The mean arterial blood pressure, heart rate, total plasma cholesterol, triglycerides, and glycated hemoglobin were significantly decreased by the Hippophae treatment. The arteriolar capillary portions of microvessels expressing alkaline phosphatase decreased, but there was a trend for an increase in the total capillary density. It was concluded that Hippophae fruits improved the metabolic processes accompanied by reduction of hypertensive stress on the ventricular microvessels.

Cardiovascular effects produced by a traditional fungal medicine, Fuscoporia obliqua extract, and microvessels in the left ventricular wall of stroke-prone spontaneously hypertensive rat (SHRSP).

Studies were carried out on stroke-prone spontaneously hypertensive rats (SHRSP) to determine the cardiovascular effects of a traditional medicine extracted from the fungus Fuscoporia obliqua. The rats received either a hot-water extract of Fuscoporia or tap water for 60 days. Heart rate and blood pressure were measured in the tail and venous blood was analyzed for glycated hemoglobin (HbA1c) and leukocyte number. Sections of the left ventricular wall were stained for alkaline phosphatase and dipeptidylpeptidase IV to distinguish the arteriolar from the venular portions of the capillaries. Capillary to myocyte ratio (C:M ratio) was also measured. Treated rats showed a significant decrease in arterial pressure, a mild increase in leukocyte and a trend towards a decrease in HbA1c. There was a trend towards an increase in total capillary density in the subendomyocardium accompanied by a decrease in the arteriolar capillary portions. C:M ratio showed no clear change. It is concluded that the hot-water extract of Fuscoporia has beneficial effects on cardiovascular function, hematological status and probably immunological function in SHRSP.

Effect of irradiation on enzymes of the capillary bed in rat ventricles.

The effect of localized irradiation on the enzyme activity in rat cardiac capillaries was examined in experiments in which the arteriolar and venular portions of the capillary bed were distinguished by the double-staining method. This method shows that the endothelial cells of the former contain alkaline phosphatase (AP) and those of the latter, dipeptidylpeptidase IV (DPP). At both 1 week and 3 weeks after irradiation with 20 Gy, staining for AP was reduced but staining for DPP was unchanged. The loss of enzyme from the arteriolar portions may be a consequence of the greater radiosensitivity of tissues exposed to high oxygen tension, or it may indicate that AP is less stable than DPP when exposed to irradiation.

Expression of proliferating cell nuclear antigen in rat hearts subjected to transient ischemia followed by reperfusion.

Early mechanisms involved in improving capillarity and oxygen transport to cardiac tissue exposed to transient coronary ischemia followed by reperfusion were studied in rats. Under ether anaesthesia, the left coronary artery was mechanically occluded for 3 min after which it was released, and the rats allowed to recover. After 2, 24 or 48 h the rats were sacrificed and the hearts frozen in liquid nitrogen. Frozen cross-sections were stained immunohistochemically for proliferating cell nuclear antigen (PCNA) and for the growth factors, VEGF and bFGF. No reaction for PCNA was seen in sections of sham-operated hearts but an inhomogeneous reaction occurred in annular structures in the occluded hearts at 48 h reperfusion. The stain appeared to be located in proliferating nuclei, and in the cytosol of endothelial cells. It is suggested that PCNA is stimulated by the increase in growth factors that is known to occur within 2 h after the end of the coronary occlusion. It is concluded that the increase in capillarity, indicated by the nuclear proliferation of endothelial cells, will improve the transport of oxygen to the cardiac tissues.

Coronary capillary network remodeling and hypofibrinolysis in aged obese diabetic rats: implications for increased myocardial vulnerability to ischemia.

Despite the known abnormalities of cardiac function in patients with overt non-insulin dependent diabetes mellitus (NIDDM) the temporal changes of coronary capillary network remodeling leading to potential microcirculatory dysfunction have not been elucidated. To this end, left ventricular subendocardial capillary network of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, characterized by hypertension, obesity, hyperglycemia, hyperinsulinemia and mild NIDDM, and control Long-Evans Tokushima (LETO) rats were investigated. Total capillary density in OLETF was significantly higher than that in LETO at 20 weeks, suggesting compensatory improvement of O2 transport at early stages of NIDDM. The increase in capillary density in OLETF was lost at 40 and 60 weeks due to the decreases of intermediate capillary portions and venular capillary portions. Although capillary domain area (area innervated by single capillary) in OLETF was lower than that in LETO at 20 weeks, the values were similar between OLETF and LETO at 40 and 60 weeks, suggesting that adaptive improvement in the capacity for 02 transport with a high perfusion was lost in late stages of NIDDM. Activity of plasma plasminogen activator inhibitor-1 (PAI-1), the major physiologic inhibitor of proteo(fibrino)lysis, in OLETF was higher than that in LETO at 40 and 60 weeks, suggesting that increase of PAI-1 may downregulate compensatory adaptive capillary network remodeling by inhibiting proteolysis and angiogenesis in the cardiac interstitium. Loss of adaptive myocardial microcirculation may therefore contribute to increased vulnerability in ischemic injury and to cardiac dysfunction in NIDDM.

Coronary ischemia/reperfusion increases proliferating cell nuclear antigen in vascular endothelial cells in rat hearts.

To elucidate the sequence of early events in the increase in capillarity caused by reperfusion following transient coronary occlusion, the time course of expression of proliferating cell nuclear antigen (PCNA) was studied immunohistochemically in rat hearts subjected to different periods of reperfusion after a 3 minute occlusion. Twenty-one male Wistar rats were killed after different periods of reperfusion following occlusion of the coronary artery for 3 minutes. The left ventricles were removed and paired serial sections were treated immunohistochemically for PCNA or stained to show the enzymes characteristic of the arteriolar, intermediate and venular portions of the capillary bed. The time course of PCNA expression, and its distribution in relation to the different portions, was examined. An increase in PCNA-expressing nuclei was found at 24 hours after the start of reperfusion; numbers reached a maximum between 72 and 96 hours, and at 168 hours had decreased again. The majority of PCNA-expressing elements were localized to the dipeptidylpeptidase IV-reactive (i.e. venular) capillary portions, with some in the intermediate and alkaline phosphatase-reactive (i.e. arteriolar) portions. The distribution of PCNA in the early reperfusion period suggests that angiogenesis after transient ischemia occurs mainly from the venular side of the capillary bed, with some contribution from intermediate and arteriolar capillary portions.