Assessing impacts of future climate change on extreme fire weather and pyro-regions in Iberian Peninsula

Weather conditions play an important role in wildfire activity. In many regions, future climate could lead to different fire weather, with impacts on the ignition, behaviour, and suppression of wildfires, which may, therefore, force new fire regimes. This study aimed to assess the evolution of fire weather indices and the Number of Extreme Days (NED) in the context of climate change. We estimated the impact of these changes on monthly Normalized Burnt Area (NBA) and in the spatial distribution of Pyro-Regions (PR), using a recently identified relationship between NED and NBA intra-annual patterns. The components of the Canadian Forest Fire Weather Index System (CFFWIS) in the Iberian Peninsula were analysed for present-day conditions and future climate scenarios, using daily data from ERA-Interim (1980-2014) and an ensemble of simulations from 11 EURO-CORDEX high spatial resolution models, for two future periods (2041-2070 and 2071-2100) and scenarios (RCP4.5 and RCP8.5). Results suggest a significant increase in future fire weather risk, especially in late spring and early autumn, and also in southern and eastern Iberian Peninsula. NED is expected to strongly increase in summer months in the four PRs, but also to decrease in March and April in the northwestern and southwestern PR. This could change the spatial distribution of PRs, with a general northwards movement: the northern PR is expected to disappear except north of the Cantabrian Mountains, being replaced by the northwestern PR; the southwestern PR is expected to grow and occupy part of the area currently in the northwestern PR; and a new PR could appear in parts of the current eastern PR. These PR changes follow the projected modifications in the major climate regions. Results suggest different fire regimes in the future, with higher fire weather risk, and a longer and harsher fire season.

Differential impact of a cardiac rehabilitation program in functional parameters according to patient gender

INTRODUCTION

Exercise-based cardiac rehabilitation (EBCR) programs are of paramount importance in the management of acute myocardial infarction (AMI) survivors. Albeit this, female patients tend to be less referred for these programs, while also having a poorer prognosis. We aimed at assessing the impact of a contemporary EBCR program on functional parameters after an AMI, and specifically the impact of gender on its potential benefits.

METHODS

Observational, retrospective cohort study including all patients admitted to a tertiary center due to an AMI who completed a phase II EBCR program after discharge, between November 2012 and April 2017. Functional parameters were assessed by a symptom-limited cardiopulmonary exercise test (CPET). Patients were dichotomized according to gender.

RESULTS

A total of 379 patients were included, 19% of whom were women. After the program, peak oxygen uptake (pVO2) and exercise duration increased significantly (P<0.001). Though female patients presented a lower pVO2 and completed a shorter CPET at both the beginning and end of the study, there were no differences in the magnitude of improvement in these parameters between both groups [pVO2 delta 1.37 ± 3.08 vs 1.31 ± 2.62 mL/kg/min, P=0.876; CPET duration delta 120 (60-167) vs 85 (60-146), P=0.176].

CONCLUSIONS

A contemporary EBCR program was associated with significant improvements in functional parameters, as assessed by CPET. Though female patients had lower levels of pVO2, the benefits of this program were similar among groups. These results highlight the importance of EBCR among this higher risk subset of patients.

Impacts of climate and land use changes on the water quality of a small Mediterranean catchment with intensive viticulture

Studies that address the potential effects of climate and land use changes on surface water quality are scarce in the Mediterranean region. In the present work, the impacts of climate and land use changes on nutrient and copper exports from a humid Mediterranean catchment (São Lourenço) were evaluated using the SWAT model. SWAT reproduced reasonably well total nitrogen (TN), phosphorus (TP) and copper (Cu) exports in São Lourenço, providing an adequate baseline scenario as well as a suitable model parameterization for assessing the impacts of climate and land use changes under the A1B and B1 emission scenarios for the end of the 21st century (2071-2100). Land use changes scenarios were generated along the same storylines as climate change scenarios to assess the combined effects of the two stressors. Climate changes itself led to a decline in annual TN and TP exports under both emission scenarios mostly due to a decrease in runoff and erosion induced by a reduction in rainfall, but it hardly affected Cu exports largely due to its strong immobilization in soils. Land use changes per se resulted in an increase in streamflow, but the changes in water quality varied markedly according to the scenarios. A substantial decrease in TN, TP and Cu exports was observed under scenario A1B, due to a reduction in vineyard areas. Under scenario B1, however, TP exports decreased much less while TN exports hardly changed, reflecting differences in the preferential transport pathways of these compounds. Cu exports also remained the same, as no changes occurred in the vineyard areas. The combination of climate and land use change scenarios revealed additive impacts on the exports of all three contaminants, emphasizing the importance of integrated approaches to define adaptive land management practices that can ensure the future sustainability of Mediterranean water resources.

Impacts of climate and land use changes on the hydrological and erosion processes of two contrasting Mediterranean catchments

The impacts of climate and land use changes on streamflow and sediment export were evaluated for a humid (São Lourenço) and a dry (Guadalupe) Mediterranean catchment, using the SWAT model. SWAT was able to produce viable streamflow and sediment export simulations for both catchments, which provided a baseline for investigating climate and land use changes under the A1B and B1 emission scenarios for 2071-2100. Compared to the baseline scenario (1971-2000), climate change scenarios showed a decrease in annual rainfall for both catchments (humid: -12%; dry: -8%), together with strong increases in rainfall during winter. Land use changes were derived from a socio-economic storyline in which traditional agriculture is replaced by more profitable land uses (i.e. corn and commercial forestry at the humid site; sunflower at the dry site). Climate change projections showed a decrease in streamflow for both catchments, whereas sediment export decreased only for the São Lourenço catchment. Land use changes resulted in an increase in streamflow, but the erosive response differed between catchments. The combination of climate and land use change scenarios led to a reduction in streamflow for both catchments, suggesting a domain of the climatic response. As for sediments, contrasting results were observed for the humid (A1B: -29%; B1: -22%) and dry catchment (A1B: +222%; B1: +5%), which is mainly due to differences in the present-day and forecasted vegetation types. The results highlight the importance of climate-induced land-use change impacts, which could be similar to or more severe than the direct impacts of climate change alone.

Using the soil and water assessment tool to estimate dissolved inorganic nitrogen water pollution abatement cost functions in central portugal

Coastal aquatic ecosystems are increasingly affected by diffuse source nutrient water pollution from agricultural activities in coastal catchments, even though these ecosystems are important from a social, environmental and economic perspective. To warrant sustainable economic development of coastal regions, we need to balance marginal costs from coastal catchment water pollution abatement and associated marginal benefits from coastal resource appreciation. Diffuse-source water pollution abatement costs across agricultural sectors are not easily determined given the spatial heterogeneity in biophysical and agro-ecological conditions as well as the available range of best agricultural practices (BAPs) for water quality improvement. We demonstrate how the Soil and Water Assessment Tool (SWAT) can be used to estimate diffuse-source water pollution abatement cost functions across agricultural land use categories based on a stepwise adoption of identified BAPs for water quality improvement and corresponding SWAT-based estimates for agricultural production, agricultural incomes, and water pollution deliveries. Results for the case of dissolved inorganic nitrogen (DIN) surface water pollution by the key agricultural land use categories ("annual crops," "vineyards," and "mixed annual crops & vineyards") in the Vouga catchment in central Portugal show that no win-win agricultural practices are available within the assessed BAPs for DIN water quality improvement. Estimated abatement costs increase quadratically in the rate of water pollution abatement, with largest abatement costs for the "mixed annual crops & vineyards" land use category (between 41,900 and 51,900 € tDIN yr) and fairly similar abatement costs across the "vineyards" and "annual crops" land use categories (between 7300 and 15,200 € tDIN yr).

Post-fire overland flow generation and inter-rill erosion under simulated rainfall in two eucalypt stands in north-central Portugal

The aim of this study was to improve the existing knowledge of the runoff and inter-rill erosion response of forest stands following wildfire, focusing on commercial eucalypt plantations and employing field rainfall simulation experiments (RSE's). Repeated RSE's were carried out in two adjacent but contrasting eucalypt stands on steep hill slopes in north-central Portugal that suffered a moderate severity fire in July 2005. This was done at six occasions ranging from 3 to 24 months after the fire and using a paired-plot experimental design that comprised two pairs of RSE's at each site and occasion. Of the 46 RSE's: (i) 24 and 22 RSE's involved application rates of 45-50 and 80-85 mm h(-1), respectively; (ii) 22 took place in a stand that had been ploughed in down slope direction several years before the wildfire and 24 in an unploughed stand. The results showed a clear tendency for extreme-intensity RSE's to produce higher runoff amounts and greater soil and organic matter losses than the simultaneous high-intensity RSE's on the neighbouring plots. However, there existed marked exceptions, both in space (for one of the plot pairs) and time (under intermediate soil water repellency conditions). Also, overland flow generation and erosion varied significantly between the various field campaigns. This temporal pattern markedly differed from a straightforward decline with time-after-fire and rather suggested a seasonal component, reflecting broad variations in topsoil water repellency. The ploughed site produced less runoff and erosion than the unploughed site, contrary to what would be expected if the down slope ploughing had occurred after the wildfire instead of several years before it. Finally, sediment losses at both study sites were noticeably lower than those reported by other studies involving repeat RSE's, i.e. in Australia and western Spain. This possibly reflected a history of intensive land use in the study region, including in more recent times after the widespread introduction of eucalypt plantations.

Cardiac troponin I in systemic diseases. A possible role for myocardial strain

Cardiac troponin I levels are frequently above normal values in several disease states in which myocardial necrosis is not a prominent aspect, particularly in pulmonary embolism, heart failure, liver cirrhosis, septic shock, renal failure and arterial hypertension. Sub-clinical myocardial necrosis has been postulated to be the cause of the phenomenon. Studies performed so far have not included pathological data to confirm this hypothesis. Increased troponin I plasma levels may be the result of myocardial strain, especially the type of strain that accompanies some forms of cardiac dilatation or hypertrophy. Troponin I may act as a marker of myocardial strain, either acute (in pulmonary embolism, septic shock and acute heart failure) or chronic (in chronic cardiac, renal and hepatic failure, as well as in arterial hypertension). The apparent paradox of elevated levels of troponin I without elevated levels of creatine kinase in several disease states might be solved if troponin I could be released from myocardial cells without the disruption of myocardial cell plasma membranes. Precise pathological studies are needed to elucidate whether increased troponin I with normal CK is associated with myocyte death, and, if so, with necrosis or with apoptosis.

Wall tension and contraction of the aorta in 6-month-old spontaneously hypertensive rats

1. The present study aimed at comparing the influence of passive tension on the effect exerted by noradrenaline on the thoracic aorta of 6-month-old Wistar and spontaneously hypertensive rats (SHR). 2. Concentration-response curves to noradrenaline were obtained in aorta rings, at two levels of passive tension: 3 and 0.5 g. 3. The maximal responses (in percentage of the maximal response to noradrenaline obtained in the beginning of the experiment at a tension of 2 g) were significantly larger (P < 0.05) at 3 g than at 0.5 g in both kinds of rats: 171 versus 69%, respectively, for SHR; 139 versus 76%, respectively, for Wistar rats. 4. When expressed as mg of active tension per mg of tissue, the maximal contraction at both 3 and 0.5 g was smaller in SHR than in Wistar rats (at 3 g: 64.6 +/- 6.7, n = 6 versus 122.3 +/- 19.1, n = 8, respectively, P < 0.05; at 0.5 g: 24.0 +/- 1.0, n = 6 versus 49.0 +/- 5.9, n = 8, respectively, P < 0.05). 5. Maximal responses to noradrenaline were markedly decreased by cytochalasin B (50 microM) (to 15.2 +/- 6.0%, n = 6, at 3 g and 2.8 +/- 1.9%, n = 6, at 0.5 g in SHR; to 11.8 +/- 2.3%, n = 4, at 3 g and 4.3 +/- 1.3%, n = 4, at 0.5 g in Wistar rats). Cytochalasin B at a lower concentration (4 microM) produced a less marked decrease in responses to noradrenaline in both strains of rats. The presence of cardiovascular structural changes in SHR was confirmed by the fact that the heart weight (mg):body weight (g) was higher in SHR (3.37 +/- 0.06, n = 10) than in Wistar rats (2.40 +/- 0.12, n = 11) (P < 0.05). 6. It is concluded that in 6-month-old SHR the contractile capacity of the aortic tissue is reduced. However, the differential sensitivity of aortic smooth muscle at the two different levels of tension remains present. This difference may depend on filament interaction. Contractions to noradrenaline in the rat aorta are highly dependent on actin polymerization.

The influence of the wall tension on the contractile responses of arteries

The present study aimed at determining the influence of tension on the responses of arterial smooth muscle to noradrenaline, phenylephrine and angiotensin II. Concentration-response curves to these agonists were obtained in the rat aorta, at two levels of tension: 3 g (29.4 mN) and 0.5 g (4.9 mN). The results obtained show that the maximal responses to the agonists used (in percent of the maximal response to noradrenaline) were significantly larger (P < 0.05) at 3 g than at 0.5 g: 113% versus 66%, respectively, for noradrenaline; 95% versus 59%, respectively, for phenylephrine; 60% versus 24%, respectively, for angiotensin II. In the presence of gadolinium (100 mumol/L)--a mechanogated ion channel blocker--the responses to noradrenaline at 3 g were still significantly larger than responses at 0.5 g: 103% versus 67%, respectively. The compound H-7 (20 mumol/L)--a protein kinase C inhibitor--caused a marked decrease in the maximal responses to noradrenaline at both levels of tension, the responses being reduced to 44% at 3 g and to 20% at 0.5 g. Isradipine (1 mumol/L)--a calcium channel blocker--caused a slight decrease in the responses to noradrenaline at both levels of tension, the responses being reduced to 86% (3 g) and to 50% (0.5 g). In endothelium-free arterial rings, the responses to noradrenaline at 3 g and 0.5 g were also significantly different: 118% versus 80%, respectively. It is concluded that the tension of the arterial wall is a major factor influencing the effects of vasoconstrictor agents; however the mechanisms underlying this supersensitivity at higher tension remain unknown.

The role of membrane proximal threonine residues conserved among guanine-nucleotide-binding-protein-coupled receptors in internalization of the m4 muscarinic acetylcholine receptor

Many guanine-nucleotide-binding-protein-coupled receptors contain consensus sequences for phosphorylation by cAMP-dependent protein kinase (PKA), often located in the membrane proximal regions critically important for receptor signalling. In the present study, we have evaluated by site-directed mutagenesis the role of the putative PKA phosphorylation sites in the m4 muscarinic acetylcholine receptor (mAChR), i.e. Thr145 in the second cytoplasmic loop and Thr399 in the third cytoplasmic loop, and the influence of PKA on m4 mAChR function and internalization. Antagonist binding was unaltered by any of the mutations studied, while the agonist-binding affinity was either not affected (Thr145 alanine), increased (Thr399 alanine) or decreased (Thr399 serine or aspartic acid). m4 mAChR-mediated inhibition of adenylyl cyclase was unaltered by the mutations, except for an approximately tenfold reduced agonist potency of the Thr399 aspartic acid mutated receptor. Agonist-induced receptor internalization was unaltered with Thr399 serine or aspartic acid mutations of the receptors, but was strongly decreased in its rate and extent upon replacement of Thr399, Thr145 or both of these residues with alanine. These mutational effects could not be reproduced by treatment of wild-type receptor-expressing cells with the PKA inhibitor H-8. Furthermore, maximal stimulation of cellular PKA neither affected receptor internalization nor signalling measured as receptor-mediated Ca2+ mobilization. We conclude that the membrane proximal threonine residues of the m4 mAChR are not required for receptor signalling, but replacement by alanine residues can significantly affect receptor internalization, independently of PKA phosphorylation. Sequence comparisons suggest that threonine residues at corresponding positions may be relevant to internalization of other guanine-nucleotide-binding-protein-coupled receptors.

Influence of non-steroidal anti-inflammatory drugs on renal function and 24h ambulatory blood pressure-reducing effects of enalapril and nifedipine gastrointestinal therapeutic system in hypertensive patients

OBJECTIVE

To evaluate the influence of non-steroidal anti-inflammatory drugs (NSAIDs; aspirin and indomethacin) on the renal and antihypertensive effects of enalapril and nifedipine gastrointestinal therapeutic system (GITS) in patients with essential hypertension.

DESIGN AND METHODS

In a crossover study, 18 patients on an unrestricted-salt diet were randomly assigned to receive either enalapril (20-40 mg/day) or nifedipine-GITS (30-60 mg/day) for 4-8 weeks, followed by aspirin (100 mg/day for 2 weeks) and then indomethacin (75 mg/day for 1 week). Blood pressure was measured by 24h ambulatory monitoring.

RESULTS

Enalapril and nifedipine-GITS significantly reduced blood pressure compared with placebo. Aspirin did not alter the antihypertensive effect of either drug. Indomethacin attenuated (by 45%) the antihypertensive effect of enalapril throughout the 24h period of evaluation, but did not interfere with the effect of nifedipine. Furthermore, indomethacin significantly reduced the fractional excretion of sodium and plasma levels of prostaglandins in a similar way when added to either the enalapril or the nifedipine regimen.

CONCLUSIONS

Vasodilatory prostaglandins are probably involved in the antihypertensive effects of enalapril but not of nifedipine, and this interaction seems to be independent of any indomethacin-induced decrease in renal sodium excretion. Nifedipine may be an appropriate drug to treat hypertensive patients requiring concomitant therapy with NSAID.

Central alpha 2-adrenoceptors and blood pressure regulation in the rat

The role of alpha 2-adrenoceptors in the central regulation of blood pressure has been questioned, since drugs such as clonidine stimulate both alpha 2-adrenoceptors and imidazoline-preferring receptors. The present work was undertaken to study the influence of alpha 2D-adrenoceptors, encoded by the RG20 gene, on blood pressure in the rat. An antisense phosphodiester oligodeoxynucleotide, directed at nucleotides 4-21 of the RG20 gene, was injected in the right lateral cerebral ventricle, causing an increase in systolic blood pressure, both at 1 and 2 days after the injection, when compared to groups of control rats (injected with the sense oligodeoxynucleotide or a missense oligodeoxynucleotide or distilled water). Antisense oligodeoxynucleotides directed either at nucleotides 65-82 of the RG10 gene (encoding for alpha 2C-adrenoceptors) or at nucleotides 26-43 of the RNG gene (encoding for alpha 2B-adrenoceptors), failed to produce any change in blood pressure after being injected. We conclude that the alpha 2-adrenoceptor encoded by the RG20 gene may play a role in blood pressure regulation in the rat.

24-hour blood pressure profile early after renal transplantation

Renal transplant patients are often found to have high blood pressure. We studied 12 cyclosporine-treated patients 8-10 days after kidney transplantation by 24-hour ambulatory blood pressure monitoring, and once again at 35-40 days after kidney transplantation. The patients were found to have high mean blood pressure values at 8-10 days after transplantation, with a significant (p < 0.05) decrease at 35-40 days after transplantation (154.2 +/- 4.9/94.4 +/- 2.8 and 142.2 +/- 4.0/88.6 +/- 2.7 mmHg, respectively). A significant (p < 0.05) decrease in blood pressure values was also noted in the second series of measurements, when compared to the first series, in the day-time systolic and in the night-time systolic and diastolic blood pressure values, but not in the day-time diastolic blood pressure values. An abnormal day/night pattern of blood pressure ("non-dipper") was found in these patients in both occasions, with a difference between average blood pressure values during day- and night-time of 1.3/3.0 (systolic/diastolic) and 5.7/7.6 mm Hg at 8-10 and 35-40 days after transplantation, respectively. This tendency towards attenuation of the "non-dipper" pattern occurred in association with the decrease in body weight and of the dose of immunosuppressive drugs. As hemodynamic factors may play a role in both the short and the long-term function and viability of kidney transplant grafts, the high blood pressure and the "non-dipper" pattern of blood pressure found early after kidney transplantation may require a special therapeutic approach.

Evidence that chloroethylclonidine can contract the dog saphenous vein via a protein kinase C-dependent mechanism

Chloroethylclonidine has recently been shown to produce concentration-dependent contractions in the dog saphenous vein. These contractions are very sensitive to cooling, yohimbine and rauwolscine, and moderately sensitive to prazosin. The effects of compound H-7 (a protein kinase inhibitor) and isradipine (a calcium channel blocker) on the contractions to chloroethylclonidine, UK14304 and phenylephrine were studied in the dog saphenous vein. Compound H-7 (20 mumol/l) produced a very marked (85%) inhibition of chloroethylclonidine-induced contractions, a moderate (48%) inhibition of UK14304-induced contractions and a slight (19%) inhibition of phenylephrine-induced contractions. Isradipine (1 mumol/l) produced a moderate (49%) inhibition of chlorethylclonidine-induced clonidine-induced contractions and a slight (15%) inhibition of phenylephrine-induced contractions. Phorbol 12,13-dibutyrate (1 mumol/l) produced a contraction that reached 61.1 +/- 3.2% of the maximum and was inhibited moderately (46%) by compound H-7. It is suggested that, in the dog saphenous vein, the receptor activated by chloroethylclonidine may be coupled to protein kinase C.

Chloroethylclonidine irreversibly activates postjunctional alpha 2-adrenoceptors in the dog saphenous vein

This study was aimed at analysing the contractile response of the dog saphenous vein to chloroethylclonidine. At 37 degrees C, chloroethylclonidine (0.1-100 mumol.l-1) caused a long-lasting contraction in both proximal and distal segments of the dog saphenous vein, reaching 77.6 and 52.6% of the maximal response to phenylephrine, respectively. At 18 degrees C, and in both segments, the maximal response to chloroethylclonidine was markedly reduced, whereas that to phenylephrine was not changed and that to UK-14,304 was enhanced. The response to chloroethylclonidine was unaffected by pretreatment with cocaine. Warming to 37 degrees C caused contraction of strips which at 18 degrees C had remained unresponsive to chloroethylclonidine, even if these strips were repeatedly washed before warming. At 18 degrees C, chloroethylclonidine (100 mumol.l-1) did not alter the responses to UK-14,304 and phenylephrine. At 37 degrees C, the contractile response to chloroethylclonidine was antagonized by yohimbine, rauwolscine and prazosin, with the potency rank yohimbine = rauwolscine > prazosin. Phenoxybenzamine (30 nmol.l-1) displaced the concentration-response curve to chloroethylclonidine to the right and depressed its maximum. After phenoxybenzamine, yohimbine continued to be more effective than prazosin, which remained very potent.(ABSTRACT TRUNCATED AT 250 WORDS)

Severe acute form of adult dermatomyositis treated with cyclosporine

The classical treatment of severe forms of dermatomyositis includes high doses of steroids and/or cytotoxic agents. Acute forms are frequently life threatening. Because cyclosporine is a fast-acting immunosuppressive drug, it appears to be a good candidate for the treatment of refractory forms of acute dermatomyositis. We report a dramatic improvement of a severe, acute, steroid-resistant adult form after cyclosporine administration. A rapid clinical and biochemical improvement is reported, and the reversibility of immunologic abnormalities is emphasized.

Relaxant effects of alpha-human atrial natriuretic peptide on venous smooth muscle

1 The present study has examined the relaxant effects of alpha-human atrial natriuretic peptide (alpha-hANP) and sodium nitroprusside on dog saphenous vein ring preparations; responses were tested on a background of tone corresponding to 30% and 80% of maximal contraction. Also tested on the lower background of tone were the responses to carbachol, M&B 22,948, forskolin and 3-isobutyl-1-methylxanthine (IBMX). The vascular responses to alpha-hANP and carbachol were also examined in dog splenic artery ring preparations. 2 On a background of tone corresponding to 30% of maximal contraction, both alpha-hANP and sodium nitroprusside were found to relax venous ring preparations with IC50 values of 6 x 10(-8) and 2 x 10(-7) M, respectively. When the background of tone was raised to 80% of maximal contraction, the relaxant effect of sodium nitroprusside was significantly reduced and that of alpha-hANP became almost completely abolished; the IC50 value for sodium nitroprusside in these experimental conditions was 2 x 10(-6) M. 3 The cGMP phosphodiesterase inhibitor M&B 22,948 was found to produce a concentration-dependent relaxation, with an IC50 value of 2 x 10(-6)M in saphenous vein rings with a background of tone corresponding to 30% of maximal contraction. By contrast, saphenous vein rings were found to be insensitive to carbachol. Forskolin and IBMX were also found to produce concentration-dependent relaxing responses of venous preparations, with IC50 values of 2 x 10(-7) and 7 x 10(-7) M, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Postsynaptic alpha-adrenoceptors in the perfused canine saphenous vein in vitro

To study the relative localization of alpha 1 and alpha 2-adrenoceptors in relation to the intima and the adventitia of canine saphenous vein, a comparison was made of the potency of alpha 1- and alpha 2-adrenoceptor agonists applied by intraluminal and extraluminal route of perfused segments of that vessel. Noradrenaline was the most potent of the agonists used and was approximately as potent by intraluminal as by extraluminal route. Cocaine (12 mumol/l) caused supersensitivity to noradrenaline which was of about the same magnitude (threefold) irrespective of the route of administration of noradrenaline. The selective alpha 1-agonist phenylephrine was about 10 times less potent than noradrenaline and was also equieffective by both routes. The selective alpha 2-agonist UK-14,304, at concentrations lower than 0.3 mumol/l, caused very small responses and only in 3 out of 14 experiments. In all cases it caused responses at concentrations higher than 0.3 mumol/l. Cocaine did not change the sensitivity to either phenylephrine or UK-14,304. Thus, it is concluded that the results obtained with cocaine agreed with expectations for a homogeneously innervated tissue. Furthermore, alpha 1-adrenoceptors seem to predominate and to be evenly distributed throughout the media. The lack of responses to the low concentrations of UK-14,304--those selectively acting on alpha 2-adrenoceptors--was ascribed to the very low efficacy of this agonist on the distal part of the canine saphenous vein and to the tone created by the perfusion pressure which might be high enough to mask this small response.

Alpha 1- and alpha 2-adrenoceptors at different levels of the canine saphenous vein

Presynaptic alpha2- and postsynaptic alpha1-adrenoceptors were compared at the distal and proximal parts of the dog saphenous vein. The results obtained show that: (1) yohimbine is more effective against postsynaptic responses to phenylephrine distally than proximally. On the contrary, WB-4101 is more effective proximally; (2) phenylephrine increases inositol monophosphate production at both levels, but the increase is more pronounced distally; (3) UK-14, 304 and adrenaline reduce and yohimbine and phentolamine increase the release of 3H-noradrenaline caused by electrical stimulation at both levels. However, while adrenaline as well as the antagonists are equipotent at the two levels, UK-14,304 is more potent distally than proximally. In conclusion, we suggest that: more alpha 1A-adrenoceptors exist distally than proximally; imidazoline sites can exist at the distal level which contribute to the higher potency of UK-14,304 distally.

The effectiveness of alpha 2-adrenoceptor activation increases from the distal to the proximal part of the veins of canine limbs

1. The effectiveness of alpha 1- and alpha 2-adrenoceptor activation was compared at different levels of the saphenous and cephalic vein of the dog in vitro. 2. Helically cut strips were used to determine concentration-response curves to phenylephrine, noradrenaline, UK-14,304 (5-bromo-6-(imidazoline-2-ylamino)-quinoxaline) and B-HT 920 (2-amino-6-allyl-5,6,7,8-tetra-hydro-4H-(thiazo)-4,5-d-azepine). The effect of prazosin and yohimbine on these curves was also studied. 3. At the distal level, the maximum response to UK-14,304 amounted to 33 and 50% of those to noradrenaline in the saphenous and cephalic vein, respectively, while at the proximal level the maximum response to UK-14,304 amounted to 72 and 78% of those to noradrenaline, in the saphenous and cephalic vein, respectively. 4. In both vessels, the results obtained with B-HT 920 were very similar to those for UK-14,304. 5. The pD2 values for UK-14,304 - which were identical at the three levels of both vessels - and the pA2 values for the antagonism exerted by either prazosin or yohimbine against the responses to UK-14,304 indicate that the alpha 2-adrenoceptors are identical at the different levels of both vessels. 6. These results show that the effectiveness of alpha 2-adrenoceptor stimulation increases from the distal to the proximal regions of canine limb veins. Apparently, this is due to a greater density of alpha 2-adrenoceptors in the proximal regions. 7. Yohimbine is much more potent against phenylephrine distally than proximally in both vessels. However, after 30 nm phenoxybenzamine - a concentration which eliminates the vast majority of alpha,-adrenoceptors without affecting alpha 2-adrenoceptors - yohimbine became equally potent at both levels, suggesting that the difference existing before phenoxybenzamine depended on alpha,-adrenoceptors. Hence it is concluded that alpha,-adrenoceptors in distal and proximal portions may differ.

Loss of selectivity of so-called selective alpha 1-adrenoceptor agonists after phenoxybenzamine

This study examined the nature of alpha-adrenoceptor subtype involved in pressor responses to so-called selective alpha 1-adrenoceptor agonists after treatment with phenoxybenzamine in vivo. The influence of prazosin (0.1 mg/kg) and of yohimbine (1 mg/kg) on the dose-response curves for cirazoline in the pithed rat, and for phenylephrine in the anaesthetized dog were compared, after various doses of phenoxybenzamine. In the pithed rat, after 0.05 mg/kg phenoxybenzamine, prazosin caused a displacement of the dose-response curve of cirazoline to the right which was much larger than that caused by yohimbine; after 0.3 mg/kg phenoxybenzamine, prazosin and yohimbine caused about equal displacements; after 1 mg/kg phenoxybenzamine, yohimbine caused a marked displacement, while prazosin was without effect. In the anaesthetized dog, after 1 mg/kg phenoxybenzamine, prazosin and yohimbine produced about equal rightward shifts of the dose-response curve for phenylephrine. However, after 3 mg/kg phenoxybenzamine the rightward shift of the dose-response curve for phenylephrine was much larger after yohimbine than after prazosin. In the anaesthetized dog, verapamil (1 mg/kg) caused a small and parallel rightward shift of the dose-response curve for phenylephrine before phenoxybenzmine and a large and nonparallel one after phenoxybenzamine (3 mg/kg); the effect of verapamil on responses to the selective alpha 2-adrenoceptor agonist UK-14,304 (before and after phenoxybenzamine) were similar to those on responses to phenylephrine after phenoxybenzamine.(ABSTRACT TRUNCATED AT 250 WORDS)

An unusually important role of O-methylation in the disposition of noradrenaline and adrenaline by the dog renal artery

Using the oil immersion technique, the role of neuronal uptake, monoamine oxidase and COMT in the inactivation of 2 concentrations (0.23 and 2.3 mumol/l) of noradrenaline and adrenaline was determined by the prolongation of the inactivation time caused by cocaine (12 mumol/l), pargyline (1 mmol/l) and U-0521 (50 mumol/l), respectively. The results obtained allow us to conclude that: 1) as previously shown, for the saphenous vein and mesenteric artery, noradrenaline is inactivated more rapidly than adrenaline; 2) in all tissues and for both concentrations of noradrenaline and adrenaline, neuronal uptake is more important for the inactivation of noradrenaline than for that of adrenaline, while O-methylation is more important for the inactivation of adrenaline than for that of noradrenaline. The only exception is that in the renal artery, O-methylation is very clearly the most important pathway of inactivation for both concentrations of both amines.