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R Rubio

Publications and source records attributed to R Rubio.

At least 163 records · Page 9Linked to original sources
PubMed1982

Effect of adenosine on calcium uptake by intact and cultured vascular smooth muscle.

The effect of adenosine (ADO), a potent vasodilator, on the cellular calcium uptake by vascular smooth muscle (VSM) was studied. In addition, similar experiments were conducted with other vasoactive agents to ensure the validity of results obtained with the cultured VSM cell model. Primary VSM monolayers from rat aorta were incubated for 30 min in 45Ca-enriched physiological salt solution (PSS) (37 degrees C) and washed with 20 mM Ca-EGTA (4 degrees C) to remove extracellular 45Ca. Calcium uptake with 4.6 mM K+ was 65.3 +/- 2.4 pmol Ca/10(5) cells. Verapamil (10(-6) M) or 4 degrees C incubation decreased this value 27 and 65%, respectively, whereas ADO (10(-7) M) and isoproterenol (10(-6) M) elevated calcium uptake 21 and 9%, respectively. Elevation of extracellular K+ (25 mM) increased calcium uptake to 87.8 +/- 5.0 pmol Ca/10(5) cells. ADO (10(-7) M), isoproterenol (10(-6) M), and 4 degrees C incubation significantly attenuated this K+-induced increase 25, 19, and 64%, respectively. The calcium uptake of nondepolarized cells was not changed by norepinephrine (10(-6) M) in the presence of either alpha- or beta-adrenergic blockade. Experiments were performed in a similar manner with porcine carotid artery strips in the presence of alpha- and beta-adrenergic blockade. Calcium uptake increased from 2.3 +/- 0.2 X 10(-7) to 3.0 +/- 0.1 X 10(-7) mol Ca/g wet wt after elevation of the medium K+ to 25 mM. This increase was inhibited by 10(-6) M ADO. ADO (10(-6) M) was found to have no effect on the 45Ca efflux from cultured VSM. It is concluded that ADO relaxes VSM by reducing the inward movement of calcium during stimulation. The significant ADO-induced elevation of cellular calcium under conditions when cultured cells were not partially depolarized suggests the existence of an enhanced calcium sequestration within these cells.

Adenosine↗
PubMed1982

Adenosine and coronary blood flow in conscious dogs during normal physiological stimuli.

The role of adenosine in matching myocardial oxygen supply to demand by regulating coronary blood flow has been the subject of intensive study. The present experiments were designed to determine the relationship among myocardial oxygen consumption, coronary blood flow, and adenosine production as estimated by pericardial adenosine accumulation under several physiological conditions in the same animal. Conscious chronically instrumented dogs were used to measure changes in coronary blood flow, myocardial oxygen consumption, and pericardial adenosine accumulation during two levels of treadmill exercise, excitement caused by loud noises, and feeding (the presentation and consumption of a meal). The results show significant increases in the adenosine production with all experimental procedures and significant linear correlations between myocardial oxygen consumption and coronary blood flow (r = 0.78), myocardial oxygen consumption and adenosine production (r = 0.73), and adenosine production and coronary blood flow (r = 0.88). These data show that increases in adenosine production by the normally oxygenated myocardium can be the physiological mechanism for matching oxygen supply to increased oxygen demand in the conscious dog.

Adenosine↗
PubMed1981

Growth of aortic vascular smooth muscle cells in lowered oxygen tension.

Primary cultured of vascular smooth muscle cells, isolated from rat aorta, were grown under normoxic (20% O(2)) and mildly hypoxic (5% O(2)) conditions. Cells from both conditions were compared for growth characteristics, morphology, protein synthesis, lysosomal enzyme activity, and oxygen consumption. In no case was a consistently significant difference observed. These observations indicate that these cells can adapt or are adapted to mildly hypoxic conditions. Moreover, these results may indicate that the culture of vascular smooth muscle cells in mild hypoxia represents a closer approximation of in vivo growth conditions for these cells.

Animals↗
PubMed1981

Brain adenosine concentration during hypoxia in rats.

We analyzed brain tissue for adenosine and its metabolites, inosine and hypoxanthine, in rats during acute (30 s) hypoxia and during sustained (5 min) hypoxia and hypocarbia. Within 30 s of the onset of hypoxia, adenosine levels were increased from 0.34 +/- 0.08 (SE) to 1.65 +/- 0.33 nmol/g (P less than 0.005), paralleling temporally the changes in cerebral blood flow. During sustained hypoxia and hypocarbia, brain tissue was sampled by a fast (freeze-blow) or slow (in situ) freezing method. With the freeze-blow technique, adenosine concentrations remained stable between arterial partial pressure of O2 (PaO2) greater than 200 and 100 mmHg, doubled at PaO2 = 50 mmHg, and increased sevenfold (P less than 0.005) when PaO2 reached 30 mmHg. No increases in adenosine or its metabolites were noted with the in situ technique. During hypocarbia (arterial CO2 partial pressure less than 20 mmHg), adenosine concentrations increased with both sampling techniques. Freezing times in brain were measured during in situ freezing and were increased during hypoxia and decreased during hypocarbia. In conclusion, 1) adenosine concentrations in brain are increased during hypoxia, and 2) the in situ technique in rat does not appear to be optimal for sampling brain tissue for subsequent measurement of adenosine under conditions where cerebral blood flow is increased.

Acute Disease↗
PubMed1981

Adenosine and the acid-base state of vascular smooth muscle.

Hog carotid artery media was incubated under conditions of normocapnia (95% O2-5% CO2) and hypercapnia (nominally 75% O2-25%CO2). The intracellular pH (pHi) was determined from the distribution of 14C-labeled 5,5-dimethyloxazoladine-2,4-dione, alpha- and beta-receptor antagonists were used to block the effects of endogenous catecholamines. With 5% CO2, adenosine had no effect on the pHi. High K+ (25mM) and dipyridamole (DPM) induced a cellular metabolic acidosis that was reversed by adenosine and not affected by 0.5 mM ca2+ or ouabain. Hypercapnia decreased the resting pHi from 7.30 to 6.79. Adenosine significantly attenuated this decrease. With high K+ or DPM, a similar degree of hypercapnia only depressed the pHi to 6.91 and 6.90, respectively. The alkalinizing effect of high K+ and DPM was not altered by 0.5 mM Ca2+, was partically reversed by ouabain, and was completely reversed by adenosine. These results suggest that, under normocapnic conditions, although adenosine relaxes the contraction associated with K+-depolarization, it does not do so by elevating cellular proton levels. However, adenosine may decrease a tissue's ability to attenuate a local respiratory acidosis characteristic of increased O2 demand, resulting in relaxation under hypercapnic conditions. In any case, this demonstrates an interaction, with respect to the acid-base state of the vascular smooth muscle cells, among adenosine, K+, and H+, all suggested components of the metabolic theory of blood flow autoregulation.

Acid-Base Equilibrium↗
PubMed1980

Adenosine release during early and sustained exercise of canine skeletal muscle.

During contraction of skeletal muscle in the isolated dog hindlimb under constant-flow perfusion, the specific activity of infused [8- 14C]adenosine (nonvasoactive concn) in venous effluents decreased to 7% of the resting level in 1.25 min and was associated with a concomitant decrease in vascular resistance to 39% of the resting value. Since this decrease in specific activity of labeled adenosine could have been due to 1) an enhanced adenosine release by parenchymal tissue, 2) an exercise-induced increase in the number of open capillaries (greater surface area) in the absence of increased adenosine production 3) some degree of tissue hypoxia, or 4) a combination of these factors, experiments with maximally dilated vessels were performed. Acetylcholine and a nonvasoactive concentration of [8- 14C]adenosine were continuously infused into an isolated dog hindlimb which was perfused at constant flow during periods of rest, contraction, and recovery while arterial oxygenation was maintained at normoxic levels. Approximately 2.75 min after the onset of contraction with the vascular bed maximally dilated, the specific activity of [8- 14C]adenosine in venous effluents decreased to 38% of the resting level while the venous Po2 decreased from 78 to 42 mmHg; the value of 42 mmHg indicates apparent absence of hypoxia in the muscle. These observations are consistent with the concept that adenosine release is involved in the vasodilation observed in contraction of skeletal muscle.

Acetylcholine↗
PubMed1980

Incorporation of adenosine and its metabolites into brain nucleotides.

Dogs were subjected to cerebrospinal fluid (CSF) convesity-cisternal perfusion with [U-14C]adenosine, [U-14C]inosine, or [U-14C]hypoxanthine to determine the mechanism of incorporation of these purines into brain adenine nucleotides. After craniotomy, brain tissue was frozen in situ, and the adenine nucleotides were separated by chromatography. A portion of the nucleotide fraction from the brain and [U-14C]purine from CSF were hydrolyzed enzymatically to nucleosides and bases and the specific activities (SA) measured. The pathway of incorporation of adenosine and inosine was determined by comparing the ratio of SA nucleoside to SA base obtained from degraded brain to that obtained from degraded CSF. Adenosine was directly phosphorylated to AMP, but inosine was degraded before incorporation into brain nucleotides. By comparing the SA of the brain nucleotides to that of the purine precursor in the cerebral spinal perfusion fluid, the incorporation of adenosine was found to be sevenfold greater than that of inosine or hypoxanthine. Measurement of the radioactivity in sagittal venous blood during convexity-cisternal perfusion yielded a larger percentage of counts after perfusion with [U-14C]inosine than with adenosine or hypoxanthine. In comparison to other tissues, a unique salvage system thus exists in the brain for adenosine that serves to conserve the adenine nucleotide pool.

Adenosine↗
PubMed1980

Brain adenosine production in rat during sustained alteration in systemic blood pressure.

Brain production of adenosine and its metabolites, inosine and hypoxanthine was determined in 46 rats during sustained (5 min) reduction in mean arterial blood pressure (MABP) caused by hemorrhage. Also measured were ATP, ADP, AMP, phosphocreatine (PCr), and lactate. Brain tissue was obtained by the freeze-blowing technique. Ventilation was controlled to maintain constant arterial O2 tension, CO2 tension, and pH. When MABP was decreased from 135 + 3 (SE) mmHg to 72 +/- 2 mmHg, within the range of cerebral autoregulation, brain adenosine concentration doubled from 0.55 +/- 0.12 to 1.16 +/- 0.13 nmol/g (P < 0.015). Unlike the changes in adenosine concentrations, adenine nucleotides and PCr remained stable. Lactate varied inversely with MABP. With moderate to severe hypotension (MABP = 45 +/- 3 mmHg), adenosine levels increased almost sixfold. The increment in brain adenosine concentration within the autoregulatory range supports a role for this potent dilator of pial vessels in the regulation of cerebral blood flow.

Adenine Nucleotides↗
PubMed1980

Localization of purine and pyrimidine nucleoside phosphorylases in heart, kidney, and liver.

In isolated livers and kidneys perfused with Krebs-Henseleit solution, the relationship of the concentration of adenosine (Ado) to that of its degradation products inosine (Ino) and hypoxanthine (Hyp) in biliary, urinary, and venous effluents were determined. They revealed ratios of Hyp:Ado:Ino, 1.9:1:0.9, 0.7:1:0.6, and 1.3:1:0.5 for guinea pig biliary, guinea pig urinary, and rat urinary effluents, respectively, and their respective venous effluent were 58:1:29, 8.6:1:5.4, and 7.4:1:3.2. The greater proportion of Ino and Hyp in the venous effluents suggests active production in Ino and Hyp at the vessel wall. Purine nucleoside phosphorylase localization was determined histochemically and found most active in the cytoplasm of capillary endothelium and Kupffer cells. Thus, there is agreement between purine analysis and histochemical findings. The reliability of the histochemical technique was also tested by comparing activities of purine nucleoside phosphorylase (a cytoplasmic enzyme) and pyrmidine nucleoside phosphorylase (a nuclear enzyme) that catalyze similar reactions (nucleoside + inorganic phosphate in equilibrium base + ribose-1-phosphate) but with different base specificites and cellular localization, as indicated by cell fractionation studies. The histochemical results show that in contrast to the purine nucleoside phosphorylase, the pyrmidine specific enzyme was most active in the nuclei of endothelial and Kupffer cells. Thus, the technique discriminates between the two enzymes.

Adenosine↗
PubMed1980

Changes in brain adenosine during bicuculline-induced seizures in rats. Effects of hypoxia and altered systemic blood pressure.

We analyzed brain tissue in 139 rats for adenosine and its metabolites, inosine and hypoxanthine, during the initial 120 seconds of seizures induced by bicuculline. We also measured ATP, ADP, AMP, phosphocreatine (PCr), and lactate. We divided the rats into four groups by adjustment of their preictal arterial oxygen tension: group I, PaO2 > 200 mm Hg; group II PaO2 = 50 mm Hg; and group III: PaO2 = 100 mm Hg. We treated a fourth group whose PaO2 = 100 mm Hg with phentolamine to block the 44% rise in blood pressure which occurred with the onset of seizures. PaCO2 was maintained between 30 anf 40 mm Hg in all groups. Brain tissue was sampled rapidly after 0, 10, 20, 30, 60, and 120 seconds of seizures by the freeze-blow technique. With normoxia (PaO2 = 100 mm Hg) or hyperoxia (PaO2 > 200 mm Hg), adenosine increased within ten seconds of the onset of seizures and remained elevated even after 120 seconds. Elevations in inosine and hypoxanthine were delayed compared to the increases in adenosine. A reduction in PaO2 (50 mm Hg) or systemic blood pressure during seizures caused a further augmentation in the increase in brain adenosine levels. During the seizure period, transient changes in adenine nucleotides and energy charge were observed, but PCr remained depressed and lactate continued to rise. The rapid and sustained increase in cerebral adenosine levels, temporally paralleling the changes in cerebral blood flow, supports the role for adenosine in the regulation of cerebral blood flow.

Adenosine↗
PubMed1980

Atrioventricular conduction disturbances during hypoxia. Possible role of adenosine in rabbit and guinea pig heart.

Adenosine and related compounds can produce atrioventricular (A-V) conduction block. Similar conduction disturbances are observed in myocardial hypoxia. To investigate the possibility that adenosine might be causally involved in hypoxic conduction disturbances, we measured A-V conduction times, subdivided into atrial-to-His bundle (A-H) and His bundle-to-ventricular (H-V) intervals, with extracellular electrodes in isolated rabbit and guinea pig hearts perfused with modified Krebs-Henseleit solution. Adenosine produced dose-dependent prolongation of A-V conduction time in both species, although guinea pig hearts responded to lower doses (10(-7) M) and showed a steeper dose-response relationship than rabbit hearts. Higher adenosine doses produced second-degree heart block in both species. Conduction delay was confined to the A-H interval, implicating action on A-V node cells. Further investigation of guinea pig hearts revealed a specific antagonism towards adenosine's effects by 10(-5) M aminophylline. Conduction disturbances produced by acetylcholine or MnCl2 were unaffected by aminophylline as were adenosine's effects by atropine. Perfusion with hypoxic perfusate caused A-V conduction delays and second-degree block in guinea pigs hearts. This effect was dramatically attenuated by aminophylline. We conclude that endogenously released adenosine may cause at least some of the A-V conduction disturbances associated with acute myocardial hypoxia. Furthermore, methylxanthines may prove to be of therapeutic value in combatting such disturbances in a clinical setting.

Adenosine↗