Increased permeability of hamster microcirculation to glycosylated albumin

The permeability of the microcirculation to native and glycosylated albumin was tested in 25 non-diabetic Syrian hamsters. The microvasculature of the cheek pouch was studied by a fluorescent video-microscopy technique after the animals had been injected with fluorescent native or glycosylated albumin or with both. Native albumin remained in the cheek pouch microvasculature, whereas glycosylated albumin leaked out of the microvascular bed along the postcapillary and collecting venules. The extravascular leakage of glycosylated albumin, probably due to its electrical or conformational change, may represent the initial event in the development of diabetic microangiopathy.

Microvessel diameter changes during hemorrhagic shock in unanesthetized hamsters

The effects of hypovolemic shock on the time-dependent diameter changes of small arteries and arterioles were studied in the hamster skin fold window preparation. This experimental model permits the visualization of the microvasculature without the effects of acute surgery, anesthesia, and exposure. In these conditions, all the arterial microvessels showed vasomotion, while the venules and small veins, that were also studied, did not show rhythmic diameter changes. Hemorrhage was induced by the withdrawal of blood through a chronically implanted arterial catheter. The mean arterial blood pressure was reduced to 40 mm Hg in 20 min, and was maintained at this value for an additional 30-min period. Reinfusion of the withdrawn blood was made at 50 min. During the shock period, vasomotion disappeared in all arterial vessels. The small arteries and arterioles, A1 (70-100 micron, mean diameter), A2 (40-70 micron, md), and A3 (15-40 micron, md), contracted by 20 +/- 7, 33 +/- 10, and 34 +/- 11% of the control mean diameter, respectively. A4 terminal arterioles (less than 15 micron, md) dilated after the onset of bleeding; their rhythmic diameter changes subsequently stopped and their mean diameter increased by 75 +/- 7% of the original value. V1 small veins (150-200 micron, md) contracted during shock, while V2 (35-55 micron, md), V3 (25-35 micron, md), and V4 (15-25 micron, md) venous vessels did not show any significant change. Reinfusion of shed blood caused the reappearance of vasomotion; control vasomotion patterns recovered after reinfusion. Our results indicate that the microcirculatory responses to hypovolemic shock are dependent on the vessel type; this inhomogeneous reactivity may be due to the different responsiveness of microvessels to the mechanisms elicited by hemorrhage.

Variations of rhythmic diameter changes at the arterial microvascular bifurcations

The variation of the pattern of the rhythmic diameter changes, in the hamster skin fold window preparation, was studied sequentially along the branching network of the arterial vessels, from A1 small arteries (70-100 micron diameter) to A4 terminal arterioles (less than 15 micron diameter). Contraction and dilation waveforms were characterized at all subsequent levels of bifurcation. The frequency of vasomotion was determined by a specialized spectral method called PRONY, which approximates the spectral composition of complex waveforms by the least square criteria and estimates the coefficient of correlation between reconstructed and original data. It was found that the frequency of vasomotion changes abruptly at the branching points, systematically increasing in the downstream direction. The power spectrum showed that the frequencies, which appear to originate at the bifurcations and have maximum amplitude at these points, are also found in the upstream waveforms. The downstream propagation of contractions and dilations causes superposition of waves. Thus the pattern of vasomotion is the composite effect of signals that originate at various branching points and spread downstream and upstream in the microvasculature. It seems likely to suggest that single unit smooth muscle cells, located at the branchings (local pacemakers), control the arterial rhythmic diameter changes. This time dependent phenomenon affects deeply the microvascular blood flow.

The effects of alpha- or beta-adrenergic receptor agonists and antagonists and calcium entry blockers on the spontaneous vasomotion

The effects of systemic injections of vasoactive substances were studied in the micro-circulation of the hamster skin fold window preparation, which can be observed without anesthesia, exposure, and acute surgical procedures. The effects were characterized by the continuous measurement of the diameter of the arterial microvessels ranging from 100 to 8 micron. Power spectrum analysis was utilized to determine the frequency and the amplitude of the fundamental component of spontaneous diameter changes. Epinephrine and norepinephrine increased the frequency of vasomotion and reduced mean diameter at low dosages. Phentolamine reduced the frequency of vasomotion and increased mean diameter. Propranolol increased the frequency of vasomotion and did not significantly change mean diameter. Adenosine and verapamil suppressed vasomotion and increased mean diameter. These results are explained by postulating that low-dosage alpha-adrenergic receptor stimulation facilitates the spontaneous discharge of smooth muscle cells; beta-adrenergic receptor stimulation has the opposite effect, whereas beta-adrenergic receptor inhibition also enhances the vasomotor effect. Calcium entry blockers abolish the rhythmic discharge. This explanation of the activity of the various substances supports the hypothesis that the spontaneous vasomotion of the arterial microvessels is related to the intrinsic property of smooth muscle cells.

Quantitation of rhythmic diameter changes in arterial microcirculation

The diameter of the arterial and arteriolar blood vessels was measured as a function of time in the hamster skin fold window preparation. When the animals recovered from the surgical implantation, the diameters of the arterial microvessels exhibited a continuous rhythmic activity throughout the preparation for a period of 2 wk while the chamber was intact. The amplitude of the diameter changes was directly proportional to the mean vessel size. The frequency of this phenomenon was determined by power spectrum analysis implemented with a Fourier transform method and was found to decrease from a maximum of 9-15 cycles/min in 8- to 15-micron A4 arterioles to 1-3 cycles/min in 70- to 100-micron A1 small arteries. A1 and A4 vessels had relatively well-defined characteristic fundamental frequencies, whereas A2 and A3 vessels showed a power spectrum that included the frequencies present in A1 and A4 vessels. The activity was not synchronized throughout the microvasculature, and frequencies and amplitudes of diameter variations changed at branching points. Anesthesia induced by the intravenous injections of pentobarbital and chloralose-urethan invariably stopped this activity throughout the preparation. The distribution of this time-dependent activity and the nature of the effect of the anesthetics suggests that this phenomenon is due to local pacemaker activity of groups of unitary smooth muscle cells.

[Erythrocyte deformability determined by filtration]

Authors studied red blood cell filtrability by means of an original apparatus. The red blood cells were suspended in 0,9% NaCl and Teitel solutions. Teitel solution was the most usefullness in filtrability studies.

[Erythrocyte deformability dependent on variations in pH]

Authors studied the influence of pH changes on red blood cell deformability by means of filtration technique. In 0,9% NaCl solutions, there was decrease of RBC deformability upon both lowering and increasing of pH. In Teitel solutions, RBC deformability increased on alcalyne pH.

[Oxygen consumption in organs of rats treated with serotonin]

The serotonin injected intraperitoneally in rats (20 mg/Kg of body weight) increases the oxygen utilization of slices of heart, liver and muscle with a maximum value after 60 min from the injection. The serotonin, probably, acts on intracellular metabolism increasing some enzymatic activities or metabolic pathways.