Francis J. Haddy

Resistance to blood flow through the vascular bed of the dog forelimb. Local effects of sodium, potassium, calcium, magnesium, acetate, hypertonicity and hypotonicity.

Abstract Evidence is presented which indicates that, in the foreleg of the dog, the local effect of acute slight elevation in the blood concentration of potassium, magnesium or acetate is active arteriolar dilation whereas the local effect of slight elevation of calcium concentration is active arteriolar constriction. Increase or decrease in the concentration of sodium seems to have little effect independent of that due to change of blood tonicity. Increase in blood tonicity produces dilation whereas decrease in tonicity produces constriction. These caliber changes may be passive, due to dehydration or overhydration of the arteriolar wall, or active, due to increase or decrease in the concentration of ions within the smooth muscle cell. These findings may be relevant to the problem of arterial hypertension.

The Influence of Tone upon Responses of Small and Large Vessels to Serotonin

In the dog foreleg, serotonin antagonizes extremes of vascular tone induced by neurogenic means. It produces net dilatation when the bed is constricted and net constriction when the bed is dilated. This bidirectional response derives ultimately from the facts that changes in nervous activity change calibers of small vessels without greatly altering calibers of large vessels, and that serotonin produces small vessel dilatation at the same time that it constricts large vessels. When small vessels are already neurogenically dilated, serotonin cannot dilate them further, but continues to constrict large vessels. Thus, the net effect is constriction. When small vessels are highly constricted, serotonin dilates small vessels more than it constricts large vessels. The net effect is dilatation. The study also indicates why it is more difficult to demonstrate a similar antagonism when tone is varied by humoral means.

The Relation of a Venous-Arteriolar Reflex to Transmural Pressure and Resistance in Small and Large Systemic Vessels

Data are presented which indicate that, even in pressure ranges well above critical closing pressures, transmural pressure is an important factor in determining systemic vascular resistance but that a mechanism is present which actively limits these pressure changes in resistance when transmural pressure is varied on the venous side.

Local Effects of Sodium, Calcium and Magnesium Upon Small and Large Blood Vessels of the Dog Forelimb

Resistance to blood flow through the small vessels of the dog foreleg decreased following local elevation of serum sodium and magnesium concentrations. Small vessel resistance increased following elevation of calcium concentration. Associated with the former changes was decreased responsiveness to levarterenol and methacholine. These changes likely result from effects of the cations upon the smooth muscle cell of the arteriole.

Effect of pH Change upon Systemic Large and Small Vessel Resistance

In the dog foreleg acute increase and decrease of hydrogen ion concentration is associated with active small vessel dilatation and constriction, respectively, through some direct effect upon vascular smooth muscle. These small vessel resistance changes do not affect total resistance in the intact leg because of directionally opposite active changes in artery resistance. The latter response appears to be related to central nervous connections and perhaps to circulating or locally released epinephrine, norepinephrine or unknown vasoactive substances.

Serotonin and the vascular system.

them. Serotonin has other unusual effects. It produces peculiar coloration of the skin. Injection beneath the skin produces edema at the site of injection. Serotonin constricts some vascular beds but has a variable effect upon others. In this paper, the above and some other effects of serotonin will be briefly reviewed and an explanation, based’ upon research published elsewhere, will be proposed for these effects. All of the above gross effects can be explained if one accepts the evidence which indicates that serotonin actively constricts large vessels at the same time that it actively dilates small vessels. The evidence1. 2 as derived from the foreleg vascular bed of the dog, is as follows. When serotonin is administered into the brachial artery in amounts without effect upon systemic arterial and venous pressures, the pressures in small arteries fall and those in small veins rise. The rate

Effect of Elevation of Intraluminal Pressure on Renal Vascular Resistance

Elevation of renal venous pressure in pentobarbitalized laparotomized dogs elicits renal vascular constriction. Part of the vasoconstriction appears to be dependent upon a venous-arteriolar reflex. The reflex pathway is not distributed locally. A portion of the vasoconstriction is dependent upon still unrecognized local factors.

Continuous infusion indicator dilution measurement of limb blood flow and vascular response to magnesium sulfate in normotensive and hypertensive men

A constant infusion, indicator dilution technique for blood flow measurements in the forearm and hand of man was tested and validated in vitro and in vivo. This technique employs jet injection to improve mixing of indicator with arterial blood. The mixing characteristics of the jet injection system were studied in vitro in tubing simulating the brachial artery of man. In addition, actual blood flows in the isolated pump-perfused forelimbs of five dogs were compared with constant infusion, indicator dilution calculated flows. Measurements were also made of mixing and of blood flow in the forearm and hand of man. The technique was used to compare forearm and hand vascular responses with constant intrabrachial arterial infusions of magnesium sulfate in 13 normotensive and 13 essential hypertensive men. In vitro and in vivo the jet injection system significantly improved mixing of indicator with blood, as compared with mixing produced by standard infusion techniques, without causing hemolysis. In 30 measurements in isolated, perfused dog forelimbs the correlation coefficient between actual and calculated blood flow was 0.992. Resting limb vascular resistance in the hypertensive group was significantly higher than in the normotensive group. Limb vascular resistance in all 26 men decreased in response to intrabrachial-arterial infusion of 0.25% magnesium sulfate (8 ml/min). Rate of infusion of Mg(++) was 0.162 mEq/min. There was a significant positive linear correlation between level of initial limb vascular resistance and magnitude of response to magnesium sulfate. Vascular response data adjusted for this source of variation were similar in hypertensives and normotensives.The data suggest that this constant infusion, indicator dilution technique allows accurate calculation of total limb blood flow in man, provided that anomalous bifurcation of the brachial artery is not present. The data also suggest that the jet injection system improves mixing of substances with arterial blood. Thus, use of this system should especially aid reliability of studies of limb vascular responses to vasoactive agents infused into the brachial artery.