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Biomedical subjects

J B Scott

Publications and source records attributed to J B Scott.

At least 55 records · Page 3Linked to original sources
PubMed1975

Coronary vascular and myocardial responses to carotid body stimulation in the dog.

Coronary vascular and myocardial responses to selective hypoxic and/or hypercapnic carotid chemoreceptor stimulation were investigated in constantly ventilated, pentobarbital or urethan-chloralose anesthetized dogs. Bilaterally isolated carotid chemoreceptors were perfused with autologous blood of varying O2 and CO2 tensions via an extracorporeal lung circuit. Systemic gas tensions were unchanged. Effects of carotid chemoreceptor stimulation on coronary vascular resistance, left ventricular dP/dt, and strain-gauge arch output were studied at natural coronary blood flow with the chest closed and during constant-flow perfusion of the left common coronary artery with the chest open. Carotid chemoreceptor stimulation slightly increased left ventricular dP/dt and slightly decreased the strain-gauge arch output, while markedly increasing systemic pressure. Coronary blood flow increased; however, coronary vascular resistance wa.as not affected. These studies show that local carotid body stimulation increases coronary blood flow but has little effect on the myocardium. The increase in coronary blood flow results mainly from an increase in systemic arterial pressure. Thus these data provide little evidence for increased sympathetic activity of the heart during local stimulation of the carotid chemoreceptors with hypoxic and hypercapnic blood.

Animals↗
PubMed1975

Direct effects of hypoosmolality on vascular resistance and myocardial contractile force (38587).

Hemodialysis was used to study the direct effects of acute hypoosmolality upon the resistance to blood flow through the gracilis and coronary vascular beds and upon left ventricular contractile force in the dog. When sodium chloride was removed from the blood perfusing the gracilis vascular bed, resistance increased linearly over the range 300-225 mOsm/kg. A 10% decrease in osmolality produces a 20% increase in resistance. When the removed sodium dhloride was replaced with mannitol such that plasma osmolality did not change, resistance rose slightly but failed to regularly return to the control value. Hypoosmolality also raised coronary vascular resistance and this was associated with an increase in left ventricular force. Thus direct effects of hypoosmolality on peripheral vascular beds and perhaps myocardium may participate in the compensatory mechanisms that tend to stabilize blood pressure during hypoosmotic states such as acute salt depletion.

Animals↗
PubMed1975

Effects of ischemia on forelimb weight and lymph protein concentration.

The aim of this study was to determine if edema develops in the canine forelimb after relief of prolonged ischemia. Two hours of ischemia was induced either by interrupting brachial artery inflow in collateral-free innervated, naturally and constantly perfused preparations or by applying a pressure cuff in intact preparations. Changes in extravascular fluid volume were inferred from changes in limb weight. Relief of ischemia produced a transient 1.7% increase in weight in the collateral-free, naturally perfused preparation but had no effect on weight in the collateral-free, constantly perfused or intact preparations. Skin lymph flow failed to change significantly and total lymph protein concentration increased only slightly. Thus, relief of 2 hr of ischemia does not produce marked edema or a large increase in microvascular permeability to plasma proteins in the dog forelimb.

Albumins↗
PubMed1975

Effects of histamine and acetylcholine on equine digital lymph flow and composition.

We measured the flow rate and protein concentration of lymph collected from a digital lymphatic in eight anesthetized ponies. Additionally, we recorded systemic arterial pressure (Part), and small vein pressure (Psv). Control lymph flow averaged 0.068 ml/min, and contained 3.11 g/100 ml of protein with albumin/globulin ratio of 0.75. Twenty-minute local intra-arterial infusion of acetylcholine (10 mug/min.) elevated Psv but did not increase lymph flow rate or protein concentration. A 60-min local intra-arterial infusion of histamine (10 mug/min) produced a marked sustained increase in Psv and both lymph flow and protein concentration. Edema developed in the digit receiving histamine. These data support the conclusion that in the horse, as in other species, histamine edema is due primarily to a decreased transcapillary colloid osmotic pressure gradient rather than an increased transcapillary hydrostatic pressure gradient.

Acetylcholine↗
PubMed1975

Effects of indomethacin on local blood flow regulation in canine heart and kidney.

In two series of experiments we studied the effects of indomethacin on (a) coronary reactive hyperemia and, (b) renal blood flow, autoregulation, and reactive dilation. Coronary blood flow was measured in closed-chest dogs. Reactive hyperemia was induced by coronary occlusion for 5 and 15 sec. Indomethacin, an inhibitor of prostaglandin synthesis, was infused intra-arterially in doses of 90-200 mg over periods ranging from 30-120 min. Coronary reactive hyperemia was not affected by indomethacin. The canine renal vascular bed was studied under conditions of natural flow, controlled flow, and controlled pressure. Intra-arterial infusion of 90 mg of indomethacin over a 30- to 60- min period caused increased renal vascular resistance and an attenuation of reactive dilation (induced by stopping renal blood flow for 90 sec). Indomethacin slightly attenuated the autoregulatory response to decreasing perfusion pressures, but did not affect the respone to increasing pressures. Thus the study fails to provide evidence for participation of the prostaglandins in regulation of coronary blood flow and suggests only minimal participation of prostaglandings in renal blood flow regulation.

Animals↗
PubMed1975

Vascular responses in the equine digit.

The digital circulation was isolated in 12 ponies under pentobarbital anesthesia. Blood flow was either controlled by a pump or measured under natural perfusion. The responses to rapid changes and stoppages of blood flow indicated no evidence of autoregulation or reactive hyperemia. Local administration of acetylcholine, histamine, and prostaglandins E1 and E2 decreased prevenous resistance, whereas epinephrine and serotonin caused prevenous constriction. Large doses of epinephrine and serotonin decreased venous caliber. The effects of prostaglandins A1 and F2alpha were variable. The equine digital vasculature responds to changes in flow and to vasoactive agents like the canine forelimb skin vasculature.

Acetylcholine↗
PubMed1975

Metabolic factors in peripheral circulatory regulation.

The old and recent literature bearing on the role of metabolic factors in exercise hyperemia has been reviewed. Two general conclusions have gradually emerged over the years. First, no one factor is by itself a sufficient explanation for the hyperemia. Second, the contributions of the various factors appear to change with time of exercise. While additional temporal studies are needed to firmly establish more specific conclusions, those now available suggest that factors related to skeletal muscle cell depolarization initiate the hyperemia while factors related to oxygen consumption in excess of oxygen delivery contribute more to the maintenance of the hyperemia. For example, the potassium that leaves the skeletal muscle cell on depolarization appears to contribute more to the initiation of the hyperemia than to its maintenance. Hydrogen, on the other hand, appears to have little to do with initiation but may contribute to maintenance, at least with grades of exercise that reduce cellular oxygen tension. The picture that emerges from the review seems to be one of multiple factors acting in concert with a changing temporal pattern.

Adenine Nucleotides↗