[The vasomotion characteristics in isolated segment of the tail artery under conditions of slow constant increase of the perfusion pressure].

In vitro, the Wistar rat tail artery segments were perfused with the Crebs-Henselite solution. Under the conditions of perfusion pressure increasing from 0 to 110 mm Hg with the velocity of 5 mm Hg/min, the "diameter-pressure" curves were obtained. Changes in the vessel diameter during increase of pressure in the vessel were accompanied by vasomotions. For the first time, a regularity of the vasomotion direction changes as determined by an increase or decrease of the vessel diameter was established. The increase of the vessel diameter was accompanied by a sequence of its spike-formed decreases, whereas decrease of the vessel diameter was accompanied by a sequence of its spike-formed increases.

[Responses of isolated arterial segment to a slow changing of perfusion pressure in it]. / Reaktsii izolirovannogo areterial'nogo segmenta na medlennoe izmenenie v nem perfuzionnogo davleniia.

In in vitro experiments, segments of the Wistar rat tail artery's segments were perfused with the Krebs-Henselite solution. Increase of the perfusion pressure with the velocity of 5 mm Hg/min from 0 to 110 mm Hg with its subsequent drop with the same velocity down to zero showed that, within the limits of the above interval of values of the intravascular pressure, existed a range where two values of the artery diameter corresponded to each established value of the pressure. The data obtained prompt a further deciphering of mechanisms of the mechanogenic regulation of the blood vessels.

[Direct effect of hypoxia on the function of skeletal muscle blood vessels in the cat]. / Priamoi éffekt gipoksii na funktsii sosudov skeletnykh myshts u koshek.

In decentralized skeletal muscles of the cat hindlimbs, pO2 of arterial blood dropped from 105 to 87, 68 and 37 mm Hg in artificial respiration with 18% O2 (slight), 14% O2 (moderate) and 8% O2 (grave hypoxia) mixtures, resp. The slight hypoxia practically did not affect vascular resistance and capacity, distensibility of veins, capillary filtration coefficient and mean capillary hydrostatic pressure. Moderate and grave hypoxia reduced perfusion pressure by 3.5% and 9%, resp., increased the capillary filtration coefficient by 16% and 19%, resp., and did not alter the vascular capacity, distensibility of veins and capillary hydrostatic pressure. Precapillary sphincters and arterioles are most sensitive to hypoxia in skeletal muscles.

[Coefficient of capillary filtration and distensibility of small intestine vessels at various levels of blood flow and venous and perfusion pressure]. / Koeffitsient kapilliarnoi fil'tratsii i rastiazhimost' sosudov tonkogo kishechnika pri raznykh urovniakh krovotoka, venoznogo i perfuzionnogo davleniia.

In the cat decentralized small intestine perfused with a constant blood volume, the capillary filtration coefficient (CFC) increased from 0.02 to 0.22 ml/min/mm Hg/100 g on increase of the venous pressure from 0 to 18 mm Hg. The stretching ability of the intestinal veins was maximal at mean values of the venous pressure (6-18 mm Hg) and decreased at low (0-3 mm Hg) and high (24 mm Hg) values. At 6-24 mm Hg, a vein-arteriolar response occurred consisting of two components: a fast short (20-30 sec) and a slow one (stable). Changes within the large range of blood flow (30-170%) and perfusion pressure (30-170 mm Hg) did not affect the CFC or the stretching ability. In the blood flow decreased by 25, 50 and 75%, the O2 extraction from the blood consistently increased, the O2 consumption was slightly reduced, and the CFC did not change. A hypothesis is advanced that the intestine precapillary sphincters are more sensitive to decrease of the arterial blood pO2 than to decrease of the O2 total transport to the intestine due to reduction of the blood flow.

[Direct effect of hypoxia on the functions of the small intestinal vessels of the cat]. / Priamoi éffekt gipoksii na funktsii sosudov tonkogo kishechnika u koshek.

In anesthetized cats, artificial ventilation with 18, 14 and 8% O2 mixtures decreased the arterial blood pO2 from 104 to 85, 69 and 38 mm Hg, resp. Resistance of the intestine vessels and their capacity decreased in 14 and 8% O2; the capillary filtration coefficient increased at all levels of hypoxia whereas distensibility of veins and mean capillary hydrostatic pressure practically did not alter. A significant diminishing of constrictor responses of the intestine arterial vessels to noradrenaline only occurred in 8% O2. Precapillary sphincters are much more sensitive to O2 deficiency than other portions of the intensive vascular bed but their responsiveness to noradrenaline does not alter even in grave hypoxia.

[Capillary filtration coefficient and the distensibility of the venous vessels of the small intestine in the process of high-altitude adaptation]. / Koéffitsient kapilliarnoi fil'tratsii i rastiazhimost' venoznykh sosudov tonkogo kishechnika v protsesse vysokogornoi adaptasii.

In acute experiments on cats, the increase of capillary filtration coefficient and venous distensibility in small intestine was revealed after 3-5, 14-16 and 29-31 days of high altitude adaptation (The Pamirs, 3370 m above sea level), the changes being more obvious (by 78% and 45%, resp.) after 3-5 days in comparison with low altitude control. The effects of noradrenaline on the small intestine precapillary sphincters and venous distensibility were preserved at high altitude, whereas regional blockade of alpha- or beta-adrenoreceptors exerted no effect on the results. The increased capillary filtration coefficient seems to be of great importance in "struggle for oxygen" at high altitude hypoxia, and this obviously depends on the opening of preexisting capillaries.

[Adrenoreactivity of the vessels of the small intestine during adaptation to high altitude in the cat]. / Adrenoreaktivnost' sosudov tonkogo kishechnika u koshek v protsesse vysokogornoi adaptatsii.

Responses of the resistance and capacitance vessels of small intestine to adrenergic stimulation and blockade were studied in acute experiments on cats after 3-30 days of high altitude adaptation (the Pamirs, 3370 m). In comparison to control (Dushanbe, 830 m) constrictor responses of the resistance vessels to noradrenaline and adrenaline were significantly increases at high altitude, whereas the dilator responses to beta-stimulator propranolol were obviously reduced. Changes of venous blood outflow from small intestine in response to catecholamines at high altitude exceeded the control values. Pharmacological analysis suggests that the reactivity of alpha-adrenoreceptors of the small intestine resistance and capacitance vessels at high altitude was increased, whereas the beta-reactivity of the resistance vessels was reduced. Crucial shifts of the adrenoreactivity occurred after 3-5 and 14-16 days of the adaptation.

[Effect of adrenoreceptor blockade and stimulation on the resistance and capacitance of intestinal vessels]. / Vliianie blokady i stimuliatsii adrenoretseptorov na soprotivlenie i emkost' sosudov kishechnika.

Resistography and extracorporeal venous flow in cats revealed that i. a. administration of noradrenaline (NA) increased the intestine vascular resistance, adrenaline (A) decreased it and novodrine (N) sharply decreased it in all the experiments. After the alpha-adrenoreceptors blockade with dihydroergotoxin, NA as well as A decreased the vascular resistance whereas N exerted just the same dilator response as before blockade. Blockade of B-adrenoreceptors with obsidan augmented the NA constriction of the arterial vessels, sharply decreased their N dilatation and induced obvious constrictor responses to A. The vascular resistance after the alpha-blockade decreased by 7% whereas after the beta-blockade it increased by 26%. The venous outflow from the intestine increased after A and N disregarding the alpha-blockade but being prevented with the beta-blockade. Irregular changes of the venous outflow in response to NA preserved after the blockade of both types of adrenoreceptors.

[Changes in transcapillary fluid exchange and the distensibility of small intestinal blood vessels upon adrenergic stimulation]. / Izmeneniia transkapilliarnogo obmena zhidkosti i rastiazhimosti venoznykh sosudov tonkogo kishechnika pri adrenergicheskoi stimuliatsii.

In acute experiments on cats, the mean coefficient of capillary filtration (CFC) in denervated small intestine was 0.10 ml/min/mm Hg/100 g and the stretching ability of the intestinal venous vessels was 0.21 ml/mm Hg/100 g. Infusion of noradrenaline (5 micrograms/min) reduced the CFC by 33% and the stretching ability by 24%. Blockade of vascular alpha-adrenoreceptors abolished and beta-adrenoreceptors augmented the noradrenaline effect on CFC and stretching ability. The data obtained indicate presence of both alpha- and beta-adrenoreceptors in precapillary sphincters and venous vessels of small intestine. Stimulation of the alpha-adrenoreceptors entails constriction of precapillary sphincters and decreases venous stretching ability whereas stimulation of beta-adrenoreceptors leads to opposite effects. Noradrenaline exerts main effect on alpha-adrenoreceptors of precapillary sphincters and venous vessels in the denervate intestine; alpha-blockade is followed by an obvious beta-effect in the form of relaxation of precapillary sphincters and increase of the venous stretching ability.

[Comparative characteristics of the reactions of small intestine vessels to neurogenic influences and catecholamine application]. / Sravnitel'naia kharakteristika reaktsii sosudov tonkogo kishechnika pri neirogennykh vliianiiakh i primenenii katekholaminov.

In acute experiments on cats using resistography and extracorporeal venous reservoir, responses of the small intestine's arterial and venous vessels were studied by means of successive pressor reflexes, electrical stimulation of the splanchnic nerve (1-80/sec) and i.a. administration of different doses of adrenaline (A) and noradrenaline (NA). The maximal constrictor responses of the vessels occurred mainly on the 10/sec stimulation; A induced mainly an increase in the perfusion pressure and venous outflow whereas NA induced chiefly an increase in the perfusion pressure and diminishing of the venous outflow. In pressor reflexes, low-frequency stimulation of the splanchnic nerve (2-5/sec) and i.a. administration of A, the venous vessels actualise a considerably greater part of the possible neurogenic constriction as compared to the arteries. The constrictor responses of the arteries in the pressor reflexes under study are equal to those on either left splanchnic nerve stimulation (1-2.5/sec) or i.a. administration of A or NA in doses lower than 0.5-1.0 mcg. The constrictor responses of the venous vessels in these conditions are equal to those on either left splanchnic nerve stimulation (3-8/sec) or i.a. administration of A in doses 0.5-1.0 mcg.