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Biomedical subjects

B Folkow

Publications and source records attributed to B Folkow.

At least 127 records · Page 7Linked to original sources
PubMed1978

Plasma volume, blood volume and transcapillary escape rate (TER) of albumin in young spontaneously hypertensive rats (SHR) as compared with normotensive controls (NCR).

A detailed comparison of blood and plasma volumes and of the transcapillary escape rate (TER) of albumin was performed in SHR and matched NCR, particularly during the phase of rapid pressure rise in SHR. Throughout this early phase of life, the relative plasma and blood volumes tend to be lower, and TER higher in SHR, as would be expected when neurogenic mechanisms dominate the initiation of hypertension. Only in late established SHR hypertension, with increasing signs of cardiovascular complications, blood volume tends to be higher in SHR than in NCR. These results are in general agreement with most observations in early essential hypertension in man. They are of interest in contrast to recent findings in another variant of primary hypertension in rats, MHS. Also the apparently quite different initiating mechanisms in SHR and MHS primary hypertension are discussed.

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PubMed1977

Oxygen consumption and contractile force during vibrations of cat soleus muscle.

The influence of longitudinal vibrations (50 Hz, 0.4 mm) on isometric twitch force development (4 Hz), blood flow and oxygen consumption was studied in the acutely denervated soleus muscle of the anesthetized cat. It was found that the sinusoidal vibrations reduced the twitch amplitude by 60 per cent whereas oxygen consumption and blood flow were lowered by 15 per cent only. Similar reduction in twitch force was also obtained by lowering the nerve stimulation intensity (4 Hz). This was associated with a diminution in oxygen consumption, the degree of which was linearly related to the attenuation of active force, i.e. the number of activated motor units. The results are in agreement with previous observations as to the mechanical effect of vibrations on active force in smooth and striated muscle. They demonstrate that vibrations prevent the contractile response with maintained high oxygen consumption which adds further support to the hypothesis forwarded by Joyce et al. (1969) that vibrations cause increased rate of detachment of actin-myosin cross-links. In addition it appears possible that vibrations to some extent prevent formation of such cross-links.

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PubMed1977

Capillary permeability to albumin in normotensive and spontaneously hypertensive rats.

Transcapillary passage of plasma proteins is enhanced in man's primary hypertension and it is debated whether this reflects increased permeability or merely a raised capillary pressure. To elucidate this problem, maximally vasodilated hindquarters of spontaneously hypertensive rats (SHR) and normotensive controls (NCR) were perfused in parallel at constant flow with dextran, horse serum or mixtures of the two, using labelled albumin as indicator of capillary permeability to macromolecules. By equal increases of venous pressure modest filtration was maintained during one hour, after which the edema and its albumin content were determined.--There was less edema in SHR, reflectin a slightly lower postcapillary resistance and a much higher precapillary resistance compared with NCR, which here resulted in a lower capillary pressure in SHR. In both SHR and NCR the presence of dextran slightly enhanced the capillary filtration coefficient but increased albumin permeability up to tenfold, also after antihistamine drugs. However, for each perfusate the SHR capillaries were, if anything, slightly less permeable to albumin than the NCR ones.--The results suggest that the enhanced transcapillary passage of plasma proteins in primary hypertension reflects an increased capillary pressure in some circuit(s), probably mainly skeletal muscle, resulting from the functional balance in vivo between the pre- and postcapillary resistances.

Animals↗
PubMed1977

Dependence on external calcium for the noradrenaline contractility of the resistance vessels in spontaneously hypertensive and renal hypertensive rats, as compared with normotensive controls.

Isolated hindquarters of rats were perfused at constant flow with a plasma substitute so that pressor responses to various concentrations of noradrenaline (NA) could be measured in consective sections of the vascular bed with normal (greater than 1.5 mM) or low (0.2 mM) Ca2+ in the perfusate. The animals used were 6-week-old spontaneously hypertensive rats of the Okamoto strin (SHRy), normotensive controls of the same age NCRy); 6--7-month-old SHR (SHRA) and NCR (NCRA); and rats made hypertensive by clipping of one renal artery (RHR) plus matched normotensive controls (NCRR). Concentration-response curves to NA showed that constrictor responses to NA become more dependent on external calcium as one proceeds peripherally in the vascular system in both SHRA and NCRA, with responses in proximal vessels being least and small pre- and postcapillary vessels being most dependent in both cases. In low calcium SHRA retained their responses better than NCRA, whereas RHR retained their responses to NA poorer than did NCRR. No significant differences in responses in low calcium were observed in SHRY compared to NCRY though a trend in the same direction as in SHRA could be traced. It is concluded that there is no evidence that altered handling of calcium initiates vascular hyperreactivity in SHR, but that the handling of vascular calcium in SHR differs from RHR and both differ from NCR.

Animals↗
PubMed1977

Contractile responses to noradrenaline: varying dependence on external calcium of consecutive vascular segments of perfused rat hindquarters.

To study the dependency of vascular smooth muscle contractions, produced by noradrenaline, on the concentration of extracellular calcium, experiments were performed on adult male Wistar rats. The hemodynamic characteristics of the isolated, perfused hindquarters were investigated from maximal dilatation up to maximal, noradrenaline-induced constriction under constant flow conditions. Pressor responses to noradrenaline in the consecutive segments of the vascular bed ("proximal" and "distal" precapillary resistance vessels and postcapillary resistance vessels) were determined at low (0.2mM) and at normal (1.5-2.0 mM) Ca++ concentrations in the perfusate. Dependence on external calcium is much greater peripherally. The smallest pre- and postcapillary resistance vessels are the most dependent while the larger, "proximal" resistance vessels are the least dependent on the availability of external calcium. The results illustrate the considerable differentiation of smooth muscle, depending on its location along the vascular circuit. They further indicate that it is likely that the hemodynamically so important microvessels are highly dependent on extrinsic Ca++ sources not only concerning their involvement of remote adrenergic control, but also in their maintenance of normally pronounced "myogenic" tone.

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PubMed1977

Cardiovascular control in the Milan strain of spontaneously hypertensive rat (MHS) at "rest" and during acute mental "stress".

The cardiovascular responses to acute mental "stress" were compared in the Milan strain of spontaneously hypertensive rats (MHS) and in normotensive control rats (NR). Blood pressure and heart rate were followed in pairs of awake MHS and NR, while defence reactions were provoked by alerting stimuli (noise, vibration). No differences were noted between the two groups in response to "stress" although resting heart rate in MHS was lower than in NR. Administration of atropine or propranolol to MHS and NR showed the MHS to have a higher resting vagal tone and lower sympathetic tone than the NR. Subsequent (at least two weeks later) hemodynamic investigation, under nembutal anesthesia, showed no difference in cardiac output between MHS and NR but a higher stroke volume, presumably related to the lower heart rate in MHS. Thus, total peripheral resistance was increased in MHS as was the ratio left ventricular weight/body weight, and in good proportion to the blood pressure rise. Thus MHS differ substantially in both their responses to "stress" and also hemodynamically from the Okamoto strain of spontaneously hypertensive rat (SHR), being the so far most studied and best known model of essential hypertension in man. In MHS the hypertension is more of a systolic type and is of primarily renal origin. As such, MHS provide another model for investigating the polygenic nature of hypertension in man.

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PubMed1977

Role of the vascular factor in hypertension.

A survey is given of experimental results in both man and hypertensive rats, suggesting a rapid and hemodynamically important structural 'resetting' of the systemic precapillary resistance vessels, of the renal 'long-term' and carotid-aortic 'short-term barostats', as well as of the left heart, which together greatly affect both the initiation and maintenance of hypertension. Particularly the adaptation in design of the precapillary resistance vessels, being a per se normal, local response to more sustained changes in transmural pressure ('structural autoregulation'), implies the introduction of a potential vicious circuit once it affects the entire vascular bed. The reason is that this type of altered vessel design leads to a systemic precapillary hyperreactivity that forms a positive feedback interaction with functional excitatory influences as far as their long range, hemodynamic effect on the arterial pressure level is concerned. It is further discussed how various types of structural and functional vascular changes may often coexist, then mutually interacting with each other, and how they may be experimentally separated for detailed analysis.

Animals↗
PubMed1976

Effects of noradrenaline on consecutive vascular segments at low or normal calcium concentrations in control and spontaneously hypertensive rats.

1. An 'isogravimetric' technique, plus measurement of pressure in a small artery, was used to investigate the responses of upstream and downstream precapillary and postcapillary resistance vessels in the hindquarters of spontaneously hypertensive rats (SHR) and normal control rats perfused at constant flow. 2. Dose-response curves to noradrenaline were constructed under conditions of low or normal calcium. 3. In both control rats and SHR the dependence on external calcium during contraction increased peripherally, with the smaller pre- and post-capillary resistance vessels being most dependent and larger arteries least dependent. 4. There may be differences between SHR and control rats in regard to the handling of calcium, particularly in the small pre- and post-capillary resistance vessels.

Animals↗
PubMed1976

Cardiac receptors in ducks--a link between vasoconstruction and bradycardia during diving.

It has been demonstrated that cardiac receptors, most likely of the left ventricular type, are present also in the duck's heart. These receptors and their reflex responses (i.e. bradycardia and hypotension) could be blocked by intrapericardial administration of lidocaine. Initially, usch receptor blockade did not affect efferent vagal control of heart rate, as revealed by undiminished bradycardia in response to a standardized vagal stimulation. After cardiac receptor blockade, however, the duck's normal bradycardia response to head immersion was greatly reduced. The cardiovascular response to submersion was now instead characterized by a marked rise in arterial pressure, with superimposed bouts of intensified bradycardia and pressure reduction, evidently induced reflexly from the arterial baroreceptors. Meanwhile, the bradycardia response to standarized efferent vagal stimulation was still the same as before intrapericardial lidocaine injection. These results suggest that the marked rise in cardiac filling pressure following the intense shemo-receptor-induced constriction of both resistance and capacitance vessels, activates ventricular stretch receptors signalling in vagal afferents. Apparently, the activation of these receptors contributes crucially to the bradycardia and reduction of cardial output, which balance off the greatly increased peripheral resistance in the diving duck.

Animals↗
PubMed1976

Hemodynamic consequences of resistance vessel rarification and of changes in smooth muscle sensitivity.

Alterations in resistance vessel design in form of an increased wall/lumen ratio appears to markedly influence the resistance control in primary hypertension (Folkow et al. 1973). The raised resistance has also been suggested to be a consequence of a rarification of resistence vessels or/and to an increased vascular smooth muscle sensitivity. Thus two series paired experiments were performed on matched normotensive rats, utilizing the responses of their hindquarter vascular beds during constant flow perfusion. In the first series, the precapillary resistance vessels section was first "rarified" by graded microplugging, thereby raising resistance at maximal dilatation about 50 per cent. Then the vascular responses to noradrenaline were studied to characterize the dose-response or "resistance curves". In the second series the vascular smooth muscle sensitivity to noradrenaline of one of the hindquarters was changed by infusion of phentolamine. The resistance responses were then recorded and the ensuing "resistance curves" compared. --These changes of resistance vascular architecture and vascular smooth muscle sensitivity, respectively, led to mutually different characters of the "resistance curves". Both of these differ, however, in virtually all important respects from those curves characterizing vascular beds of spontaneously or renal hypertensive rats.

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