Oxygen uptake and tissue oxygen tension during adrenergic stimulation in canine subcutaneous adipose tissue

[Is Oxygen Deficiency Always Harmful?]

Is Oxygen Deficiency Always Harmful? Abstract. The role of the cardiovascular circulation is to supply tissue with oxygen and nutrients. Oxygen deficiency (hypoxia) is considered life-threatening, since cells die, either through apoptotic or necrotic processes. Tissue tries to counteract this by means of evolutionary signalling pathways, such as the nuclear hypoxia-inducible factor, which protects the tissue by promoting cell survival strategies and simultaneously intervening in angiogenesis, haematogenesis and metabolic processes. Recent findings indicate that these conserved signalling pathways can also function as therapeutic approaches in wound healing of bones and skin, as well as in the regeneration of tissues, e.g. in the liver, and in the hematopoietic system.

Development of gangrene during sleep

A method for continuous measurement of subcutaneous adipose tissue blood flow in the forefoot over 24 h (SBF) is described. The method is based on the radioisotope wash-out principle using 133-Xenon (133Xe). A portable semiconductor detector is placed just above a local depot of 37-74 kBq 133Xe in 0.1 ml isotonic saline, injected into the subcutaneous adipose tissue in the forefoot. The detector is connected to a memory unit allowing for storage of data. Because of the short distance, the recorded elimination rate constant must be corrected for combined convection and diffusion of the radioactive indicator. Characteristic 24-h blood flow patterns were unveiled in patients with normal peripheral circulation and in patients having ischaemic nocturnal rest pain. In normal subjects, SBF doubled from day to night. This is ascribed to the local veno-arteriolar sympathetic axon reflex, which induces vasoconstriction when the transmural pressure of the veins exceeds approximately 25 mmHg. In patients having ischaemic rest pains SBF was reduced by 37% on the average from day to night. This was caused by nocturnal hypotension, which is reflected proportionally in the foot. As the resistance vessels most probably are fully dilatated in feet with rest pain, the blood pressure drop during sleep causes the perfusion pressure and, therefore, blood flow to drop below a certain critical limit. There was a pronounced correlation between the reduction systemic mean arterial blood pressure and SBF. The patients complaining of intermittent claudication, but no rest pains, demonstrated a variety of changes in SBF compatible with the continuous spectrum of peripheral arteriosclerotic disease. The reduced blood flow during sleep in patients having ischaemic rest pains give rise to the concept of the development of gangrene during sleep.

Concentration of adenine nucleotides and glycolytic intermediates in erythrocytes, liver and muscle tissue in rats after thermal injury

A 40% total body scald burn was produced in mature rats. An immediate decrease of the metabolic rate was followed by a hypermetabolic response similar to that described in human beings following thermal injury. The amounts of adenine nucleotides and hexosemonophosphates were monitored in three types of cells: erythrocytes (which lack mitochondria), skeletal muscle cells (which to a certain extent can rely on an increased glycolysis for their increased energy supply) and liver cells (which are sensitive to hypoxia and have a great need of energy in the post-traumatic period). Only in the liver did the energy charge derived from the individual concentrations of adenine nucleotides change significantly, but remained virtually constant in muscle cells and erythrocytes despite a change in total oxygen consumption, from minus 85% (in the early phase) to plus 30% (in the later phase) of the expected value. Altered energy metabolism in liver and muscle tissues is related to wound healing, whereas the biochemical changes in erythrocytes is related to the degree of haemolysis of younger cells induced by the thermal injury.

Uptake and release of adenosine in isolated rat fat cells

Radioactively labelled adenosine and adenine were rapidly taken up by isolated rat fat cells, and incorporated into nucleotides, of which ATP dominated. The overall process had an apparent Km of 1--5 micrometers. During incubation, especially in the presence of lipolytic agents, there was a reduction in labelled ATP with a compensatory increase in ADP, AMP, cAMP and nucleosides. The build-up of adenosine during incubation was inhibited by theophylline, which inhibits 5'-nucleotidase. Radioactivity released from perifused fat cells consisted mainly of nucleoside material, of which adenosine predominated. Lipolytic stimulation caused no significant increase in nucleoside outflow from perifused cells, whereas oxygenation was capable of reducing this outflow. It is concluded that adenosine is formed by fat cells as a consequence of ATP breakdown. Stimulation of lipolysis during activation of the sympathetic nerves leads to reversible ATP breakdown and adenosine release. Adenosine might therefore act as a modulator of lipolysis in vivo under these conditions, even though it does not serve as a feed back regulator in the proper sense.

Metabolic effects of blood flow restriction in adipose tissue

The metabolic effects of blood flow restriction were studied in isolated blood-perfused canine subcutaneous adipose tissue. Blood flow restriction (on the average to 20 per cent of control flow) was caused by either mechanical clamping of the arterial inflow or by i.a. injections of methoxamine or angiotensin. Glucose uptake in the adipose tissue was reduced during blood flow restriction. This was partially compensated for by a period of increased glucose uptake following restoration of flow. Blood flow restriction also caused an increase in the venous lactate/pyruvate ratio. The basal lipolytic rate was decreased during blood flow restriction. Lipolysis induced by brief (5 min) sympathetic nerve stimulation (4 Hz) was not inhibited by blood flow restriction as the total amount of glycerol released from the tissue was unaffected. The outflow rate was reduced during blood flow restriction, but glycerol trapped within the tissue was apparently not reutilized by the fat cells as it was released upon flow restroation. FFA outflow following nerve stimulation was, however, inhibited suggesting increased reutilization of FFA within the tissue. This increased reutilization may ultimately be caused by the observed change in red./ox.-balance and/or by the limited carrier capacity (albumin) available during blood flow restriction. Three main conclusions may be drawn from the present results. Firstly, plasma levels of glycerol and FFA do not necessarily reflect adipose tissue lipolysis at a given moment. Secondly, the decreased adipose tissue blood flow seems to be a major cause of the lowered FFA-levels during hemorrhage. Thirdly, in contrast to hemorrhage, even severe reduction of adipose tissue blood flow is insufficient to cause irreversible ischemic damage.

Changes in ATP and cyclic nucleotide levels during sympathetic nerve stimulation in canine subcutaneous adipose tissue in situ

Subcutaneous adipose tissue in fed, female dogs was isolated. Biopsies of the tissue (30-150 mg) were taken and rapidly frozen in liquid nitrogen before, during and after nerve stimulation (3-4 Hz). In unstimulated adipose tissue the levels of ATP1 were 74+/-7 nmol/g, of cyclic AMP 90 +/- 12 pmol/g and of cyclic PGMP 18 +/- 3 pmol/g (mean+/-S.E.). During sympathetic nerve stimulation the levels of ATP and cyclic GMP fell by 30 and 50% respectively (p less than 0.01), while the cyclic AMP content increased by 50% (p less than 0.05). After nerve stimulation there was a marked increase in glycerol release, and the levels of all three nucleotides returned to control. The fall in ATP during nerve stimulation was essentially eliminated by prior adrenergic alpha-receptor blockade. It is concluded that 1) sympathetic nerve stimulaton induces a rapid, reversible fall in tissue ATP content, which may be related to hypoxia secondary to the vasoconstriction, and 2) lipolytic responses to sympathetic nerve stimulation in vivo are preceeded by small increases in the tissue cyclic AMP level, and a 3-fold increase in the cyclic AMP/cyclic GMP ratio.

Increased survival of experimental skin flaps in rats following treatment with antiadrenergic drugs

The effect upon the survival of skin flaps of several drugs which affect the adrenergic system was studied in rats. In control animals 41% of the skin flaps had survived seven days after the operation. Reserpine (1 mg/kg) injected intraperitoneally (i.p.) three days and one day before the flap operation increased the surviving flap area by 75% (p less than 0.001) as compared to control rats injected with saline. I.p. injection of guanethidine (5 mg/kg) or bretylium (10 mg/kg) every 12 hours, starting 24 hours before surgery and continued for 5 consecutive days, also increased the surviving flap area (19 and 33% respectively p less than 0.001). The surviving flap area was unchanged when desipramine (5 mg/kg) was injected in the same way and was decreased by 15% (p less than 0.05) following i.p. injection of the MAO inhibitor pheniprazine (5 mg/kg). Treatment with alpha-methyl-p-tyrosine (75 mg/kg), i.p. 30 min before surgery or 6-hydroxydopamine (50 mg/kg) i.v. 24 hours prior to surgery also increased the flap survival (56 and 49% increase in surviving flap area, respectively, p less than 0.001). The results demonstrated that the survival of skin flaps increased when the function of the adrenergic nervous system was inhibited. Enhanced sympathetic nervous activity slightly reduced or did not affect skin flap survival.