Showing papers by "Ulf Ekelund published in 1995"

Muscle blood flow in cats: comparison of microdialysis ethanol technique with direct measurement

Abstract: A quantitative validation of the microdialysis ethanol technique was performed in cat gastrocnemius muscle. Six to eight microdialysis probes were inserted into the isolated muscle preparation and perfused (0.5-10.0 microliters/min) with Krebs-Henseleit buffer containing between 5 and 1,000 mmol/l ethanol. Skeletal muscle blood flow was held constant in the range of 4-99 ml.100 g-1.min-1 by a servo-controlled roller pump and was determined with the microdialysis ethanol technique as well as by timed collection of venous outflow. The ethanol concentration outflow-to-inflow ratio ([ethanol]collected dialysate/[ethanol]infused perfusion medium) decreased in a nonlinear fashion when microdialysis perfusion flow rates of 0.5 and 1.0 microliter/min were employed. However, a linear decrease was found between 4 and approximately 45 ml.100 g-1.min-1 (r = -0.92 to -0.99). The lower outflow-to-inflow ratio was at 4 ml.100 g-1.min-1 (i.e., due to a low probe perfusion flow rate or a large dialysis membrane), the greater the sensitivity of the method was. It is concluded that this nonradioactive technique provides a simple and valid method for determining nutritive blood flow in skeletal muscle.

A mathematical model for measuring blood flow in skeletal muscle with the microdialysis ethanol technique

Abstract: A theoretical analysis of the microdialysis ethanol technique in skeletal muscle is presented, and a model governing the transport of ethanol from the microdialysis probe to the capillaries in the muscle tissue is proposed. The model is derived under the assumption of a steady-state situation, and an analytical solution is found for the outflow-to-inflow ratio of ethanol in the perfusate. Theoretically calculated results are compared with experiments, and for at least one of the two probe types used good agreement is achieved in a wide range of blood flow and perfusate flow rates. The main uncertainty factor in the theoretical calculations is the diffusivity of ethanol in muscle tissue, and the value for best agreement between theory and experiments has been used. Error estimates show that for a constant relative error in the outflow-to-inflow ratio of ethanol in the perfusate, low perfusate flow rates give better predictions of the blood flow.

In vivo effects of prostacyclin on segmental vascular resistances, on myogenic reactivity, and on capillary fluid exchange in cat skeletal muscle

Abstract: OBJECTIVE: To analyze the local circulatory effects of prostacyclin in skeletal muscle. DESIGN: A prospective experimental study. SETTING: A university laboratory. SUBJECTS: Twelve adult cats. INTERVENTIONS: The study was performed on autoperfused, sympathectomized gastrocnemius muscle. MEASUREMENTS AND MAIN RESULTS: Arterial blood flow, total and segmental vascular resistances (arterial vessels of > 25 microns, arterioles of 25 microns. Hydrostatic capillary pressure increased by 1.9 +/- 0.3 mm Hg, causing fluid filtration. The relative fluid filtration was less than that value shown for some other vasodilator drugs (isoprenaline, calcium-channel blockers, thiopental) in this muscle preparation. Capillary filtration coefficient decreased by 25%. Myogenic reactivity was depressed but to a lesser extent than previously observed for other vasodilator mechanisms (muscle exercise, beta-adrenergic receptor stimulation, thiopental infusion, nifedipine infusion). CONCLUSIONS: Prostacyclin is a vasodilator, both on the arterial and venous side, that restricts the increase in hydrostatic capillary pressure. The decrease in capillary filtration coefficient most likely reflects a decrease in capillary permeability, explaining the smaller relative filtration rate. The relatively well-preserved myogenic reactivity may imply a better preserved microvascular flow distribution and peripheral oxygen uptake.

Effects of the combined ETA and ETB receptor antagonist PD145065 on arteries, arterioles, and veins in the cat hindlimb.

Abstract: The aim of this study was to describe in quantitative terms the effects of ETA and ETB receptor blockade on vascular tone (resistance) in large-bore arterial resistance vessels (> 25 microns), small arterioles (< 25 microns), and veins in the cat gastrocnemius muscle in vivo. In the muscle vascular bed, the combined ETA and ETB receptor antagonist PD145065 (1 mg/kg/min, intra-arterially) abolished the biphasic vascular responses (dilatation followed by constriction) to both ET-1 (0.4 microgram/kg/min, intra-arterially) and to the selective ETB receptor agonist IRL1620 (3.2 micrograms/kg/min, intra-arterially). In the cat femoral artery and vein in vitro, PD145065 competitively inhibited the contractile responses to both ET-1 and IRL1620. The contractile response to the latter agonist could be evoked only after long-term incubation of the vessels (37 degrees C for 5 days). These results indicate that PD145065 is a potent antagonist at both ETA and ETB receptors in vivo and in vitro. Therefore, this antagonist may prove useful for elucidating the possible physiologic and/or pathophysiologic roles of the endothelins. For example, it was shown that PD145065 had no effect on vascular tone in the resting state, indicating no role for the endothelins in the regulation of basal vascular tone in cat skeletal muscle.