Theophylline interferes with the modulatory role of endogenous adenosine on cholinergic neurotransmission in guinea pig ileum

The ability of theophylline and other phosphodiesterase inhibitors to alter contractile responses to cholinergic nerve stimulation was investigated in isolated longitudinal muscle of the guinea pig ileum. Theophylline in low concentrations (10-100 microM), having no or little effect on measured phosphodiesterase activity, antagonized inhibitory effects of exogenous adenosine. In higher concentrations (0.1-10 mM), shown to be effective in inhibiting phosphodiesterase, theophylline as well as a "pure" cAMP phosphodiesterase inhibitor, ZK 62, 711, inhibited contractile responses. Dipyridamole and dilazep, inhibitors of adenosine inactivation, and also selective inhibitors of cAMP and cGMP phosphodiesterase, respectively, were found to enhance effects of exogenous adenosine and to cause a marked leftward shift to adenosine threshold dose. When dipyridamole and dilazep by themselves had inhibitory effects these could be antagonized by theophylline, suggesting an action through increased levels of endogenous adenosine. As a further indication of endogenous adenosine modulating neurotransmission low concentrations of theophylline enhanced responses to transmural stimulation. Endogenous purine concentrations in tissues and bath media were measured by HPLC. Because of tissue and microbial adenosine inactivation direct estimates of extracellular adenosine concentration could not be obtained. However, adenosine levels increased during transmural stimulation, and during inhibition of adenosine inactivation were sufficient, even in the bath medium, to interfere with the cholinergic neurotransmission.

Anaphylactic shock in monkeys passively sensitized with human reaginic serum. II. Respiratory mechanics, hematology and metabolism

Seven monkeys were passively sensitized intravenously (i.v.) with human serum containing IgE antibodies specific to dog albumin. I.v. administration of the antigen resulted in an immediate increase in pulmonary resistance (Rpulm) with a concomitant decrease in pulmonary dynamic compliance (Cdyn). Initially these changes in the respiratory system resulted in pronounced effects on venous admixture, arterial oxygen saturation (SaO2) and arterial pH. After 30 min, as Rpulm and Cdyn returned towards control levels, the blood gas changes were mainly due to low cardiac output. There was a transient increase in hematocrit, a decrease in plasma fibrinogen and a transient reduction in the number of circulating leukocytes. The anaphylactic reaction resulted in a 10- to 30-fold increase in plasma adrenaline with time and in a substantial but less marked increase in plasma noradrenaline and dopamine. Probably as a consequence of the increase in plasma catecholamine, there was a rise in plasma cyclic AMP, glucose and glycerol. No increase in plasma histamine levels was found. In two animals sensitized with purified IgE a reaction which was less severe but had the same general pattern was observed. The findings show that IgE-mediated anaphylaxis in the monkey results in a bronchoconstriction leading to a profound respiratory disturbance characterized by decreased SaO2 due to increased venous admixture. After 30 min these variables were normalized and the shock state was dominated by poor tissue perfusion due to a low cardiac output.

Cyclic 3',5'-adenosine monophosphate in umbilical cord blood of the newborn infant: relation to fetal stress and plasma catecholamines

Cyclic 3',5'-adenosine monophosphate (cyclic AMP) was analyzed in the venous blood of the mothers and in the umbilical vein and artery of the infant at birth. In general, higher cyclic AMP levels were found in the umbilical vein than in the artery which were similar to the maternal values. Asphyxia and vacuum extraction were associated with significantly higher cyclic AMP levels, while the concentration was lower after elective cesarean sections than after uncomplicated vertex deliveries. The cyclic AMP concentrations were inversely correlated to pH and directly related to the catecholamine concentrations. The origin and possible significance of cyclic AMP in umbilical cord plasma is discussed.

Adenosine and lipolysis

The present review briefly summarizes work from the author's laboratory aiming at the clarification of the role played by adenosine in the regulation of adipose tissue circulation and metabolism. Studies on isolated fat cells demonstrate that adenosine, in mumolar concentrations, can inhibit lipolysis induced by eg noradrenaline. The effect appears to be due to inhibition of cyclic AMP formation. Studies of subcutaneous adipose tissue in situ also demonstrate the effect of exogenous adenosine on lipolysis. Furthermore, adenosine causes vasodilation and inhibition of noradrenaline release from sympathetic nerve endings. The actions of adenosine are antagonized by theophylline and other methylxanthines in concentrations lower than those required to inhibit cyclic AMP breakdown. It is shown that adenosine is normally present in adipose tissue in approximately 0.3 microM concentration and that the level is increased by sympathetic nerve stimulation. From a quantitative comparison of adenosine levels and dose-effect relationships as well as from pharmacological studies it is concluded that adenosine is a physiological regulator of adipose tissue circulation and lipolysis, while the physiological role of adenosine as a transsynaptic modulator of noradrenaline release remains to be established.

The release of adenosine and inosine from canine subcutaneous adipose tissue by nerve stimulation and noradrenaline

1. Plasma and adipose tissue purine nucleosides were assayed by reversed phase high-performance liquid chromatography after purification of the samples on phenylboronate affinity gel. 2. The adenosine content of unstimulated subcutaneous adipose tissue was close to 1 n-mole/g. The concentrations of adenosine and inosine in canine arterial plasma were 0.26 +/- 0.03 and 0.16 +/- 0.03 microM, respectively. In venous plasma from the canine subcutaneous adipose tissue the corresponding values were 0.32 +/- 0.04 and 0.28 +/- 0.06 microM under basal conditions. The arterio-venous concentration difference of adenosine was linearly dependent upon the arterial adenosine concentration. At arterial concentrations below 0.3 microM there was a net production of adenosine; above 0.3 microM there was a net extraction of approximately 77% of the adenosine. Adenosine was extensively eliminated in blood. The major part of this elimination could be accounted for by metabolism to inosine, hypoxanthine and uric acid. 3. Following sympathetic nerve stimulation (4 Hz for 20 min) the rate of adenosine outflow from adipose tissue increased from 0.33 +/- 0.22 to a peak value of 1.2 +/- 0.26 n-mole/min. This corresponds to a net release of 8.7 +/- 3.0 n-mole/100 g tissue. Inosine outflow rose from 0.64 +/- 0.37 to 5.3 +/- 1.4 n-mole/min, corresponding to a net release of 24.6 4/- 8.7 n-mole/100 g. Nerve stimulation also increased the release of [3H]purines from [3H]adenine pre-labelled adipose tissue. The fractional release increased 15-fold after stimulation. The radioactivity was mainly in the form of hypoxanthine, inosine and uric acid while adenosine was a minor component. When metabolism in blood was inhibited by dipyridamole and an adenosine deaminase inhibitor nerve-stimulation-induced release of [3H]purines was mainly in the form of adenosine. 4. Noradrenaline injection also induced a release of radioactive purines and of inosine. On the other hand, the outflow of endogenous adenosine was very small. 5. The present results demonstrate that under basal conditions adenosine is present in arterial and venous canine plasma. The free extracellular tissue level may be similar to the basal arterial adenosine concentration. Sympathetic nerve stimulation and noradrenaline induces a marked release of adenosine which is rapidly metabolized in the tissue and blood stream to inosine, hypoxanthine and uric acid. In adipose tissue the levels of adenosine reached after adrenergic stimulation appear high enough to be of physiological relevance.

Effects of ethanol on human lymphocyte levels of cyclic AMP. In vitro: Potentiation of the response to isoproterenol, prostaglandin E2 or adenosine stimulation

The effects of ethanol, acetone and dimethylsulfoxide (DMSO) were tested on the accumulation of cyclic AMP in human peripheral blood lymphocytes in vitro. Isoproterenol (1.0X10(-8) - 1.0X10(-4)M), PGE2 (3X10(-8)-3X10(-6)M), adenosine (10(-7) - 10(-4)M) and phenylisopropyladenosine (10(-8) - 10(-4)M) caused a dose dependent increase in cyclic AMP accumulation. Over the entire range of concentration of stimulating drugs, ethanol caused an enhanced accumulation of cyclic AMP. At temperatures between 15 degrees and 30 degrees the effect of ethanol rose with increasing concentration from 0.2-6%. At 37 degrees and 40 degrees, 6% ethanol had less stimulatory effect than 2% ethanol. The effect of ethanol was shared by acetone and to a minor extent by DMSO, and was present also when phosphodiesterase was inhibited by isobutylmethylxanthine. It is suggested that ethanol enhances adenylate cyclase activity as a consequence of altered cell membrane fluidity. Since the effects on cyclic AMP accumulation can be observed already at rather low concentration of the solvents they may be of toxicological significance.

Cyclic AMP and metabolic substrates following hemorrhage in awake and anesthetized rats

The levels of several metabolites in plasma were studied during a period of 4 h in awake and barbiturate anesthetized rats after a blood volume loss of approximately 3% of b.w. Blood pressure was 70 mmHg (9.3 kPa) in the awake and 35 mmHg (4.7 kPa) in the anesthetized rats. Resting levels of plasma glucose, blood lactate and pyruvate and plasma cyclic AMP were higher in the awake rats than in the anesthetized rats. Bleeding caused an increase of plasma glucose in both groups. There was a more rapid increase in blood lactate and pyruvate as well as in plasma cyclic AMP levels in the awake rats than in the anesthetized rats. By contrast, plasma glycerol levels were unaltered by bleeding, and plasma FFA levels were decreased in both groups. At the end of the 4-h bleeding period plasma glucose was higher and blood lactate levels were lower in the awake rats. The initial changes in plasma metabolite levels appeared to be directly related to changes in plasma catecholamine levels. There were no differences in the relationship between the adrenaline level and cyclic AMP or glucose increase, suggesting that anesthesia did not alter beta-adrenoceptor sensitivity, but only catecholamine concentrations. The results also indicate that awake rats tolerate long-lasting blood volume loss better than anesthetized rats, because the sympatho-adrenal activation is more short-lasting.

Are the anti-allergic actions of theophylline due to antagonism at the adenosine receptor

Adenosine potentiated anaphylactic histamine release from isolated rat mast cells in a dose-dependent manner between 10(-8) and 10(-5) M. Adenosine was found to be present during a normal incubation of mast cells, but the concentration was low (2 x 10(-8) M). In rat plasma the concentration was 1.5 x 10(-7) M. The effect of 10(-5) M adenosine was dose-dependently inhibited by theophylline. 50% inhibition was found at 3 x 10(-5) M theophylline. Cyclic nucleotide phosphodiesterase inhibition required much higher concentrations (IC50 approximately 10(-3) M). It is suggested that some of the anti-allergic actions of theophylline (clinical concentration range: 10(-5) M) does not involve cyclic nucleotides but may be due to inhibition of the effects of endogenous adenosine.

Efflux of cyclic AMP, prostaglandin E2 and F2 alpha and thromboxane B2 in leg lymph of rabbits after scalding injury

Leg lymph was collected from pentobarbital anaesthetized rabbits before and after scalding injury of the paw (75 degrees C for 20 s), and the contents of cyclic AMP (cAMP), prostaglandin E2 (PGE2) and PGF2 alpha and thromboxane B2 (TXB2) in lymph were determined. After injury lymph flow increased about four times. The maximal rate of flow was found between 30 and 60 min after scalding. The efflux of cAMP and immunoreactive iPGE2, iPGF2 alpha and iTXB2 also increased. The maximum values were detected at approximately 0-30, 30-60, 30-60 and 180-240 min, respectively, after the injury. The output of cAMP, iPGE2 and iPGF2 alpha and iTXB2 in lymph of the contralateral non-scalded paw remained low throughout the experiments. When rabbits were injected with indomethacin (2.5 mg/kg) or diclofenac sodium (2.5 mg/kg) immediately after the scalding injury, the efflux of cAMP, iPGE2 and iPGF2 alpha were low. Lymph flow was markedly reduced after treatment with diclofenac sodium; treatment with indomethacin did not significantly affect lymph flow. The results suggest a prostaglandin-dependent formation of cAMP following scalding injury which may be related to the initial responses to scalding.

On the mechanism of relaxation of tracheal muscle by theophylline and other cyclic nucleotide phosphodiesterase inhibitors

The mechamism of action of theophylline was studied by investigating the relationship between relaxant effect and inhibition of cyclic nucleotide phosphodiesterase (PDE) and by studying interactions with adenosine actions. Guinea pig tracheal smooth muscle cyclic AMP PDE had two apparent KmS': 0.4 and 70 microM for cyclic AMP. Theophylline and papaverine competetively inhibited the low Km form. Hydrolysis of 2.0 microM cyclic AMP and cyclic GMP was inhibited by several drugs. Some agents (e.g. ZK 62 711, ICI 63,197, Ro 20--1724, dipyridamol) were considerably more potent as inhibitors of cyclic AMP than of cyclic GMP hydrolysis, while other agents (M & B 22.948 and dilazep) selectively inhibited cyclic GMP breakdown, and some (theophylline, papaverine, IBMX and SQ 20,006) showed little selectivity. There was a weak but significant correlation between inhibition of cyclic AMP phosphodiesterase and relaxation of tracheal smooth muscle in vitro. There was also a correlation between the ratio of IC25 cyclic AMP/IC25 cyclic GMP and the smooth muscle relaxation, indicating that inhibition of cyclic AMP rather than cyclic GMP hydrolysis determined relaxation. However, there was a marked tachyphylaxis to the relaxant effect of the cyclic AMP selective PDE-inhibitors, while the nonselective methylxanthines did not show tachyphylaxis. The effect of theophylline was antagonized by low concentrations of adenosine, which by itself caused a weak tracheal contraction. The effect of PDI-inhibitors can be partly explained by decreased cyclic AMP breakdown but other mechanisms, such as antagonism of endogenous adenosine, may contribute to the observed relaxant action.

Release of radioactive purines from cat nictitating membrane labeled with 3H-adenine

Cat nictitating membranes were incubated with 1-2 x 10(-7) M 3H-adenine or 3H-adenosine for 1 h. A tissuebath ratio of about 15 was found for both compounds in intact and denervated membranes. In intact nictitating membranes sympathetic nerve stimulation (4 Hz, 5 min) caused a net release of purines (0.66 +/- 17% of the tissue content), which was reduced by alpha-blockade. Noradrenaline (1-3 microM) or tyramine 60 microM), which produced the same contractile response as did nerve stimulation, increased purine release to the same extent as did nerve stimulation. The effect of either agent was reduced or abolished by phentolamine. Purine release could also be induced by acetylcholine and ATP. This release was not altered after surgical denervation. There was an excellent correlation between the contractile response and the purine release induced by nerve stimulation, noradrenaline, tyramine and acetylcholine. However, ATP caused a larger release of 3H-purines than expected from the contractile responses, possibly indicating displacement. The results indicate that most if not all of the 3H-purines released by nerve stimulation in the cat nictitating membrane are derived from postjunctional elements.

Effect of sensitization on spontaneous and phosphatidylserine-induced histamine release and on cyclic AMP and GMP levels in isolated rat mast cells

Sprague Dawley rats were sensitized with 20 microgram or 100 mg egg albumin (using pertussis vaccine as adjuvant). Mast cells isolated from the former group of animals showed a higher degree of histamine release upon challenge in vitro with egg albumin than those from the latter group. Using the lower amount of antigen for immunization mast cells from Hooded Lister rats showed an even higher degree of histamine release induced by antigen. An increased antigen-induced histamine release was associated with an increased spontaneous and phosphatidylserine-induced histamine release. Histamine release induced by phosphatidylserine was found to be specific in so far as it was calcium dependent and theophylline-inhibited. The basal level of cyclic AMP in mast cells was significantly depressed by sensitization. There was a relationship between the cyclic AMP/cyclic GMP ratio and the degree of spontaneous, phosphatidylserine-induced and anaphylactic histamine release. The results suggest that sensitization induces an increased release of histamine not only to the specific antigenic stimulus but also to more unspecific stimuli. Concomitantly there is a fall in the cyclic AMP/cyclic GMP ratio. The relationship between these two phenomena is discussed.

Release of 3H-nucleosides from 3H-adenine labelled hypothalamic synaptosomes

[3H]adenine was taken up by a crude hypothalamic synaptosomal fraction and incorporated into mainly nucleotides. The synaptosomes were superfused and after the initial washout a steady fractional release rate of 0.5-1% of the content/min was found. Electrical pulses (2 ms, 50 Hz, 10-20 mA, 4 min) and veratridine (10 microM, 4 min) induced a Ca++-dependent increase in purine release rate. K+ (30 mM, 4 min) caused a largely Ca++-independent increase. Most of the released material co-chromatographed with adenosine, inosine and hypoxanthine, while little or no nucleotide material was detected. Release of endogenous adenosine, inosine and hypoxanthine was detected by high performance liquid chromatography. However, following hypo-osmotic shock most of the released material was in nucleotides. The removal of glucose from the medium increased the fractional release rate 2-3 fold. Histamine, acetylcholine and glutamate were without effect. High amounts of noradrenaline caused an EGTA-inhibited release of purines, which was un-affected by propranolol or phentolamine. It is suggested that purines are released from neuronal structures and that the release reflects increased energy consumption and/or decreased energy production.

Plasma catecholamines, cyclic AMP and metabolic substrates in hemorrhagic shock of the rat. The effect of adrenal demedullation and 6-OH-dopamine treatment

Plasma catecholamines, cyclic AMP and metabolic substrates in hemorrhagic shock of rats was studied in 4 groups of animals: 1) Control rats, 2) rats with adrenal demedullation, 3) rats with 6-OH-dopamine induced chemical sympathectomy, and 4) rats with combined demedullation and sympathectomy. The rats were bled to a systemic blood pressure of 35 mmHg. The basal plasma level of noradrenaline (NA), adrenaline (A) and dopamine (DA) in control animals was each about 1 nmol/1. After hemorrhage for 1 h the A levels had reached 50 nmol/l and there was little further rise after 4 h. The rise was eliminated by demedullation but unaffected by sympathectomy. NA levels rose continuously in the control and in the sympathectomized rats. At 1 h the level was about 4 nmol/l and at 4 h about 20 nmol/l. The demedullated rats showed a 3-fold increase in circulating NA, while little or no change was seen in the combined demedullated and sympathectomized rats. DA levels did not change in any of the groups during the first hour, but were markedly elevated after 4 h of hypotension. Cyclic AMP and glucose levels in plasma showed a rapid increase 1 h after hemorrhage and thereafter returned to or below basal values. Demedullation largely prevented the increase, while sympathectomy had no effect. The increase in lactate and pyruvate levels were diminished but not eliminated by either sympathectomy or demedullation. Glycerol levels were unchanged and FFA decreased in all groups of rats. The results show that the adrenal medulla is the dominating source of plasma catecholamines in hemorrhagic shock in rats. The initial increase in plasma glucose and cyclic AMP appear to be largely mediated by adrenal A. The subsequent fall in these parameters and derangement of circulatory homeostasis are not, in the present shock model, primarily due to a failure of catecholamine secretion, but rather to a decreased responsiveness of peripheral tissues to catecholamine stimulation.

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.

Circulatory and metabolic effects of acute beta 1-blockade in severe pre-eclampsia

Five mg of a beta 1-adrenoceptor antagonist (atenolol) was given i.v. to 5 women with severe pre-eclampsia in the 3rd trimester of pregnancy. There was a significant decrease of both mean systolic blood pressure, from 171 to 155 mm Hg, and mean diastolic blood pressure, from 116 to 107 mm Hg. The mean maternal heart rate decreased significantly from 90 to 74 and mean fetal heart rate significantly from 145 to 138 beats per min. There were no significant changes in the plasma levels of cyclic AMP, insulin, glucose, free fatty acids, 3-hydroxy-butyrate or glycerol.

Acute metabolic and circulatory effects of cigarette smoking in late pregnancy

The acute metabolic and circulatory effects of cigarette smoking (two cigarettes of a standard brand) in the last trimester of pregnancy were studied. 12 subjects, all of whom where hospitalized because of pregnancy complications, volunteered to participate in the investigation. A statistically significant immediate increment in the maternal heart rate, systolic and diastolic blood pressure, fetal heart rate, plasma glucose and plasma cyclic AMP was noted. Plasma glycerol, plasma insulin and blood lactate did not change significantly. 30 min after smoking there was a small but significant increase in plasma nonesterified fatty acids, plasma beta-hydroxybutyrate and plasma C-peptide.