Brita Eklund

Extraction of endogenous plasma triglycerides by the working human forearm muscle in the fasting state.

The extraction of triglycerides (TG) by the working forearm was determined in eight healthy fasting men, both by the measurement of chemical arterial-deep venous (a-dv) TG differences and by the a-dv differences in TG radioactivity after endogenous labeling with tritiated palmitate. Measurements were made before and then during nicotinic acid infusion. Correction for plasma water shift in the forearm vasculature was made by estimating the (125I)albumin activity after an intravenous injection. The overall mean value +/- S.E.M. without and with nicotinic acid was for TG arterial concentration (mumol/1) 713 +/- 153 and 695 +/- 140, TG a-dv concentration difference (mumol/1)-14 +/- 7 and -6 +/- 4, TG arterial radioactivity (cpm/ml) 1650 +/- 469 and 1471 +/- 342, TG a-dv radioactivity difference 12 +/- 24 and -2 +/- 13. The average standard errors for the determinations of triglycerides were 0.85% and 1.5% for the chemical and the isotope methods, respectively. In conclusion, no significant average a-dv difference in TG concentration as determined by either the chemical or the isotope method was detected. With the standard errors achieved, however, a-dv differences of less than around 20 mumol/lcould not be discovered. Such an extraction of endogenous plasma TG could, if oxidized, account for about 25% of the oxygen extraction by the eercising forearm.

The relation between carbohydrate extraction by the forearm and arterial free fatty acid concentration in man: I. Forearm work with nicotinic acid infusion

To see if the magnitude of carbohydrate extraction by working skeletal muscle in man is inversely correlated with the arterial free fatty acid (FFA) concentration as in the heart, eighteen healthy men were studied during dynamic forearm work with and without nicotinic acid. The extraction or release of glucose, lactate and pyruvate was determined by the simultaneous sampling of blood from the brachial artery (a) and a deep vein (dv) of the active forearm. Nicotinic acid decreased the arterial FFA concentration from 498 +/- 53 to 134 +/- 12 mumol per litre plasma and this caused a decrease in calculated extraction of FFA. However, it did not affect the extraction of glucose, which was of a magnitude similar to one third of the oxidative metabolism in both situations. One of the possible reasons of this difference compared to the human heart muscle is that the exercising skeletal muscle may utilize stored substrate to a greater extent, which makes possible shifts in substrate utilized for oxidation without changes in substrate extraction. Another reason may be that FFA utilization covers a far smaller proportion of oxidative metabolism in skeletal than in heart muscle already before nicotinic acid.

Differences in heparin-released lipolytic activity in the superficial and deep veins of the human forearm.

Abstract. Various doses of heparin were given as a single injection into the brachial artery of each of twelve fasting healthy males. Plasma lipolytic activity was measured in samples obtained before and at frequent time intervals after heparin injection, in the artery and the deep and superficial veins of the same forearm.

Haemodynamic Effects of Dihydroergotamine During Spinal Anaesthesia in Man

Cardiac output was determined and arterial and pulmonary artery pressures were recorded during a control period, after spinal anaesthesia (Th I—III) and after administration of 1 mg dihydroergotomine (DHE) i. v. in 10 healthy males.

Blood flow in the resting forearm during prolonged contralateral isometric handgrip at maximal effort

1. In earlier studies we have shown that muscle contraction performed as handgrip at constant force, one third of maximal voluntary contraction (MVC), induces a rapid vasodilation in the resting contralateral forearm which in all probability is neurogenically mediated, followed by a relative increase in resistance.

Circulatory effects in healthy young men of atrial pacing at rest and during isometric handgrip.

1. The influence of a fixed heart rate and cardiac output on the cardiovascular response to isometric handgrip at one third of maximal voluntary contraction has been studied by means of atrial pacing. 2. At rest, atrial pacing with a mean heart rate of 109 beats/min increased cardiac output and forearm blood flow while total systemic and forearm vascular resistance decreased. 3. During handgrip, total systemic resistance increased both with and without pacing. A slow lowering of forearm vascular resistance was noted in the former situation, no change in the latter. 4. It is concluded that atrial pacing per se increases cardiac output in healthy, young volunteers. Handgrip elicits a vasoconstriction on other vascular beds than the resting forearm.

Forearm blood flow after isometric contraction at different loads in relation to potentially vasodilating substances.

Forearm blood flow and some constituents of effluent venous blood were studied after a sustained handgrip at 1/3, 1/4, and 1/8 of maximal voluntary contraction. The peak flow increased with contraction force and the increase was to a certain extent proportional to the increase in venous osmolality and lactate concentration but not to K+ or Po2, and consequently these factors might play a significant role in the regulation of exercise hyperemia although, in agreement with the often proposed contention, other factors seem to contribute.

The Effect of Noradrenaline and of Increased Sympathetic Activity on the Hyperemia following Short and Prolonged Forearm Work

Forearm blood flow was measured plethysmographically after 5- and 55-min forearm work. While the post-exercise peak flow was essentially the same in both situations, venous PCO2, H+, lactate, K+, and osmolality were lower during and after prolonged work. It was concluded that they could not have acted as major flow-increasing factors unless the sensitivity to vasoactive stimulation was changed. The sensitivity to adrenergic stimuli was then tested by noradrenaline infusion and lower body low pressure, which evoked almost the same flow reduction after long and short term work. The infusion after prolonged work was, however, followed by a marked flow increase which could be blocked by propranolol, indicating a qualitative change in sensitivity. However, the change in adrenergic sensitivity seems not to be great enough to be the factor maintaining flow during prolonged work.

Insulin and substrate exchange in the forearm during prolonged forearm work

Forearm exchange of insulin and uptake of oxygen, glucose and free fatty acids (FFA) were studied during 120 min forearm work in six healthy male volunteers. At rest the arterial-deep venous difference of insulin was zero. At the onset of work release of insulin occurred, which continued at constant rate throughout the work despite unaltered arterial insulin concentration. Extractions of oxygen, glucose and FFA were of similar magnitudes at 120 as at 15 min work, while lactate release decreased with time. It is concluded that (1) a significant insulin release from muscle tissue or its vascular bed occurs and continues at undiminished rate during prolonged work, (2) a substantial amount must be bound in the tissue, unless local synthesis takes place and (3) despite this loss of insulin from the forearm no major change in glucose and FFA extraction occurs with duration of work.

Effects of withdrawal and reinfusion of blood on limb circulation at rest and during contralateral isometric handgrip.

An isometric handgrip induces a rapid decrease in vascular resistance in the resting contralateral forearm presumably mainly mediated by β-adrenergic effects. This response was used to elucidate if a moderate blood loss provokes an altered peripheral vascular reactivity. Thus, heart rate, arterial pressures and forearm and calf blood flow were studied in eight healthy males at rest, and during contralateral isometric handgrip (CIH) before and after withdrawal of about 16% of the blood volume and again after reinfusion. Resting values of cardiac output, right atrial and pulmonary arterial pressures were also measured. Blood withdrawal reduced stroke volume and cardiac output by one fifth and slightly decreased arterial pressure compared to control state, thus total systemic resistance was increased. Mean forearm and calf blood flows were not significantly changed although forearm vascular resistance increased moderately. The response to CIH of heart rate and arterial mean pressure was similar in the normov...