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Biomedical subjects

B Folkow

Publications and source records attributed to B Folkow.

At least 109 records · Page 6Linked to original sources
PubMed1981

Extent of structurally reduced venous distensibility in rats.

1. Venous pressure--volume relations were studied in maximally vasodilated whole-body preparations after cardiac arrest, as well as in fully vasodilated, perfused hindquarter preparations of spontaneously hypertensive rats (SHR) and normotensive controls. Central venous pressures were measured also in the anaesthetized animals before cardiac arrest. 2. Central venous pressure in intact, anaesthetized SHR was 1.9 +/- 0.20 mmHg compared with 0.75 +/- 0.25 in controls (P less than 0.001). 3. In both preparations SHR showed a nearly 20% reduction in venous compliance, whereas calculated 'unstressed' volumes (volumes at zero transmural pressure) were largely equal in SHR and controls. 4. SHR capacitance vessels thus appear to have a structurally reduced wall distensibility of about 10% with no change in overall size. It probably reflects a structural adaptation to a modest increase of average transmural pressure that also affects the low-pressure side.

Animals↗
PubMed1981

Central blood volume in spontaneously hypertensive rats and Wistar-Kyoto normotensive rats.

Central blood volume and blood volume were determined in spontaneously hypertensive rats and Wistar Kyoto rats at two ages, 6 and 12 weeks, representing "borderline' hypertension and early "established' hypertension, respectively. A technique was used where plasma and erythrocyte indicators were injected into conscious rats. Blood volume in the cardiopulmonary compartment, present in the 'resting' awake steady-state, could then be estimated by sudden freezing of the entire rat. 12 week-old spontaneously hypertensive rats showed a decreased total blood volume, while the fraction of blood contained in the cardiopulmonary area was significantly increased compared with that of normotensive Wistar Kyoto rats. In 6-week-old spontaneously hypertensive rats, total blood volume was only marginally decreased but also here a tendency towards centralization of the blood was seen. Thus, alone with the development of hypertension in the spontaneously hypertensive rat their decreasing blood volume tends to become increasingly centralized to the cardiopulmonary area. Both neurohormonal influences and structural wall changes in the low-pressure capacitance side may contribute to this.

Animals↗
PubMed1981

Structurally reduced distensibility of cardiovascular low-pressure' compartments in primary hypertension, as studied in spontaneously hypertensive rats (SHR).

Adult male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) were compared to explore to what extent venous "unstressed" volume, compliance and wall distensibility are structurally altered in primary hypertension. The perfused, maximally vasodilated hindquarters and the entire, completely relaxed cardiovascular system during cardiac arrest were used for comparisons of "initial" volumes and pressure volume characteristics of the respective low-pressure compartments. In both preparations SHR and WKY showed identical "unstressed" venous volumes, computed by extrapolation to zero pressure from initial volumes and the nearly linear pressure-volume relationships, while venous compliance (delta V/delta P) was in each case about 20% reduced iun SHR. Consequently, the structurally determined wall distensibility of the low-pressure compartment, calculated as the square root of volume compliance/unstressed (or initial) volume, was significantly reduced in SHR; about 10%. Such venous "structural resetting" has important hemodynamic consequences, not least because it reinforces increase of venous return and cardiac filling pressure in SHR, caused by given sympathetic activations. Evidently, not only resistance, cardiac and barostat functions but also the venous capacitance function are structurally reset early in primary hypertension, implying a redesign of the entire cardiovascular system to operate at a higher pressure equilibrium.

Animals↗
PubMed1980

Studies on the role of sodium-potassium-activated ATPase as determinant of vascular reactivity in Wistar-Kyoto and spontaneously hypertensive rats.

1. The role of Na+-K+-activated ATPase in the regulation of resistance vessel reactivity to barium chloride and noradrenaline was investigated with a pair-perfused hindquarter technique in spontaneously hypertensive rats and Wistar-Kyoto rats (6 and 12 week old). Ouabain (10(-4) mol/l) was used to inhibit the sodium pump. 2. In all groups studied, dose-response curves to agonists were shifted to the left when ouabain was added to the perfusion medium. This potentiation in vascular reactivity produced by ouabain was expressed as 'index for sodium-pump inhibition' (ISPI = ED 50 of an agonist/ED50 + ouabain). 3. In mature rats index for sodium-pump inhibition calculated for both agonists was significantly greater in spontaneously hypertensive rats in comparison with Wistar-Kyoto rats, but not so in young spontaneously hypertensive rats. There was, however, a trend towards increased noradrenaline sensitivity in spontaneously hypertensive rats although the difference from Wistar-Kyoto rats was not statistically significant. 4. The data may suggest that there is some increase in the activity of the sodium pump in the resistance vessels of mature spontaneously hypertensive rats, perhaps to compensate for an increased passive sodium permeability.

Animals↗
PubMed1980

Central blood volume in spontaneously hypertensive rats and Wistar-Kyoto normotensive rats.

1. Central blood volume and total blood volume were determined in spontaneously hypertensive rats and Wistar-Kyoto rats at two ages (6 and 12 weeks), representing 'borderline' hypertension and early 'established' hypertension. 2. A technique was used where plasma and erythrocyte indicators were injected into conscious rats. Blood volume in the cardiopulmonary compartment, present in the 'resting' awake steady state, could then be estimated by sudden freezing of the entire rat. 3. Twelve week-old spontaneously hypertensive rats showed a decreased total blood volume, and the fraction of blood contained in the cardiopulmonary area was significantly increased compared with that of normotensive Wistar-Kyoto rats. 4. In 6 week-old spontaneously hypertensive rats, total blood volume was only marginally decreased but here also a tendency towards centralization of the blood was seen. 5. Thus, along with the development of spontaneously hypertensive rat hypertension, a decreasing blood volume tends to become increasingly centralized to the cardiopulmonary area. Both neuro-hormonal influences and structural wall changes in the low-pressure capacitance side may contribute to this.

Aging↗
PubMed1980

Simultaneous measurements of capillary filtration and diffusion capacities during graded infusions of noradrenaline (NA) and 5-hydroxytryptamine (5-HT) into the rat hindquarter vascular bed.

The relationships between capillary diffusion capacity (PS) for Cr-EDTA respective capillary filtration capacity (CFC) and vascular resistance during graded intraarterial infusions of NA and 5-HT into the artificially constant flow perfused rat hindquarter vascular bed were investigated. During maximal vasodilatation PS for Cr-EDTA was some 5.5--5.7 ml/min x 100 g, CFC some 0.04 ml/min x mmHg x 100 g, while vascular resistance was 2.8 mmHg x ml-1 x min x 100 g (PRU100) and isogravimetric capillary pressure 12.8 mmHg on an average. Setting out from maximal vasodilatation, increasing doses of NA and 5-HT produced graded reductions in capillary surface area as reflected by progressive decreases in both PS for Cr-EDTA and CFC. These changes occurred simultaneously with progressive increases in both pre- and postcapillary resistances, causing elevations in both arterial and capillary hydrostatic pressures and hance in capillary fluid filtration at constant flow. Capillary hydrostatic pressure increased maximally to 45 mmHg (calculated for NA) and vascular resistance to some 21 mmHg x ml-1 x min x 100 g on an average. PS for Cr-EDTA decreased maximally to some 0.7--1 ml/min x 100 g for both NA and 5-HT and furthermore, the relationships between PS for Cr-EDTA and PRU100 for NA respective 5-HT were almost identical. This was taken to indicate that capillary surface area for nutritional exchange is affected similarly by both drugs. However, the CFU-PRU100 relationship was shifted towards some 30--50% higher CFC values for 5-HT than for NA at almost every level of vasoconstriction. This might suggest that 5-HT besides reducing capillary surface area also induced moderate increases in capillary permeability though increases in number and/or radius of large pores (gaps) (cf. Rippe, Kamiya & Folkow 1978). Even during NA-induced vasoconstriction, when virtually no changes in capillary permeability occurred, PS for Cr-EDTA was reduced to a relatively greater extent than CFC, the discrepancy being most pronounced during marked vasoconstriction. The significance of this finding is discussed.

Animals↗
PubMed1979

Transcapillary passage of albumin, effects of tissue cooling and of increases in filtration and plasma colloid osmotic pressure.

'Initial' clearance of radiolabelled serum albumin was measured in the perfused, maximally vasodilated muscle vascular bed of rat hindquarters during tissue cooling, during increases in filtration and during changes in serum colloid osmotic pressure. Albumin clearance during ordinary serum perfusion at isogravimetry amounted to 0.03 ml/min times 100 g, increasing linearly with filtration rate to some 0.07 ml/min times 100 g at 0.5 ml/min times 100 g of filtration. During cooling from 36 degrees C to 14 degrees C both CFC and initial albumin clearance at isogravimetry decreased some 40%, in due proportion to the increased viscosity of the fluid. Increases of the colloid osmotic pressure of the perfusate correspondingly increased both the isogravimetric capillary pressure and 'initial' albumin clearance during isogravimetry.--It is concluded that even during isogravimetry the transmicrovascular albumin passage is to about 70 per cent due to filtration, and only some 30 per cent of transport at ordinary serum colloid osmotic pressure takes place by diffusion, both events presumably via 'large pores'. There was no evidence that transendothelial vesicular transport should to any significant extent contribute to the passage of albumin from vessels to tissue.

Animals↗
PubMed1979

Apparent and true vascular resistances to flow in SHR and NCR kidneys as related to the pre/postglomerular resistance ratio.

In maximally vasodilated SHR and NCR kidneys, perfused with filtrable and non-filtrable perfusates, analyses have been performed concerning the extent of average renal tissue pressure (Pt) elevation which occurs upon glomerular filtration and causes passive autoregulation of flow. The results illustrate the great importance of distinguishing between 'apparent' (PA--PV/flow) and 'true' (PA--Pt/flow) renal resistance to flow. This is particularly so when the compared SHR and NCR renal vascular beds differ not only in true total renal resistance but also concerning the structurally determined ratio between the pre- and post-glomerular resistances. The combined results show that this ratio is considerably elevated in adults SHT kidneys because of structural vascular changes, which is perhaps the most efficient way of resetting the 'long term barostat function' of the kidneys in hypertension. It is also illustrated how the altered pre-/post-glomerular ratio in SHR in combination with Pt rises can so markedly distort the results of apparently precise in vitro comparisons of SHR and NCR renal vascular beds as to give entirely misleading results, with underestimations of the structurally based vascular hyperreactivity of the preglomerular section in SHR.

Animals↗
PubMed1979

Cardiovascular 'reactivity' to graded splanchnic nerve stimulation in spontaneously hypertensive and normotensive control rats.

Cardiovascular 'reactivity' to graded splanchnic nerve stimulation was compared in adult spontaneously hypertensive rats (SHR) and normotensive controls (NCR), during abolished adrenal medullary secretion and neurogenic cardiac control and depressed reflex vascular adjustments. Arterial pressure, heart rate and cardiac output were measured, and total peripheral resistance (TPR) and stroke volume (SV) computed before, during and after nerve stimulation. The neurogenic resistance increases in the major gastrointestinal-renal-hepatic circuits expressed themselves as TPR elevations, which were much accentuated in SHR. This reflects an increased w/ri of SHR resistance vessels rather than any altered effector sensitivity, since the responses were particularly accentuated at high discharge rates when noradrenaline junction concentrations approach maximal levels. The splanchnic capacitance responses expressed themselves as SV increases, being the most relevant aspect of capacitance control. SV increased less in SHR, mainly reflecting the reduced diastolic compliance of the hypertrophied SHR left ventricle and the consequent rightward shift of its Frank-Starling curve. The results indicate that an elevated resistance may well be maintained by a normal sympathetic discharge in established SHR hypertension. There seems, however, to be an increasing need for accentuated discharge to the capacitance side to maintain proper cardiac filling of the hypertrophied left ventricle.

Animals↗
PubMed1978

Simultaneous measurements of capillary diffusion and filtration exchange during shifts in filtration-absorption and at graded alterations in the capillary permeability surface area products (PS).

The diffusion exchange of Cr-EDTA, using the single injection indicator diffusion method, was followed simultaneously with estimations of the capillary filtration capacity (CFC) in an "isogravimetric" rat hindquarter preparation during artificial perfusion and maximal dilatation. Measurements were performed at constant flow and during 1) shifts in filtration-absorbtion, 2) alterations of perfused capillary wall area (graded rarification of capillary network by microsphere injection) and 3) during alterations of permeability (i.a. infusion of histamine). At maximal vasodilatation CFC was 0.037 +/- 0.001 ml/min X mmHg X 100 g and PS for Cr-EDTA 5.67 +/- 0.13 ml/min X 100 g. During filtration or absorbtion, Cr-EDTA transfer from vessels to interstitium changed only slightly but the situation may well be different for solute transfer from interstitium to vessels. Alterations in capillary wall area resulted in proportional changes in PS for Cr-EDTA while the CFC changes were always relatively smaller. Histamine increased CFC some threefold with a marked increase in protein transfer, while PS for Cr-EDTA increased only marginally. This histamine effect could be ascribed mainly to an increase in the number of large pores which, because of their relative paucity, are of little importance for small molecular diffusion exchange but highly important for convective and macromolecular exchange.

Absorption↗