bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms of pulmonary vasoconstriction and bronchoconstriction produced by PAF in the guinea‐pig: role of platelets and cyclo‐oxygenase metabolites
Authors: Argiolas Livio , Fabi Fulvia , del Basso Paola 
Published: July 2012

The mechanisms of action of platelet activating factor (PAF) in the bronchial and cardiovascular systems have not yet been fully elucidated. In order to characterize better and to ascertain whether the effects of PAF in both these systems may be ascribed to the same mechanisms, we examined the actions of PAF in the heart‐lung preparation of guinea‐pig (HLP). The role of platelets and of cyclo‐oxygenase metabolites was investigated.
In HLPs perfused with autologous blood, bolus injections of PAF (4–32 ng) produced major effects at the pulmonary vascular and bronchial levels. Both dose‐related pulmonary vascular hypertension and bronchoconstriction produced by PAF were diminished to the same extent (46% and, respectively, 47%) when HLPs were perfused with a medium consisting of homologous red blood cells suspended in physiological solution containing 3.5% dextran (RBC). This suggests that the effects of PAF partially depend on the presence of formed elements.
When indomethacin (30 μm) was added to the perfusing blood, the dose‐response curve for the pulmonary hypertensive responses produced by PAF was strongly reduced (90%) in comparison to control preparations, whereas the bronchoconstrictor effects of PAF were only partially diminished (23%). These data constitute direct evidence that products of the cyclo‐oxygenase pathway exert a major role in the vascular, rather than in the bronchial actions of PAF.
In HLPs perfused with RBC containing indomethacin (30 μm), the pulmonary vascular hypertensive responses produced by PAF were almost completely abolished, thus indicating that cyclo‐oxygenase products from tissues are involved in these effects. Conversely, PAF administration continued to cause dose‐related bronchoconstrictor responses that were reduced only partially in comparison with HLPs perfused with RBC in the absence of the cyclo‐oxygenase inhibitor. This implies that PAF also has direct action on the bronchoconstriction evoked.
At the cardiac level, administration of PAF in HLPs perfused with blood caused a dose‐related increase in right atrial pressure accompanied by a decrease in left atrial pressure and cardiac output, which were completely suppressed or attenuated by the absence of formed elements and the addition of indomethacin. This suggests that the progressive heart impairment is secondary to the severe pulmonary hypertension induced by PAF.
The results of this study performed in the heart‐lung preparation of the guinea‐pig, which made it possible to simultaneously record cardiovascular and bronchial parameters, indicate that various components are involved in the responses produced by PAF. It is suggested that different mechanisms depending on the relative contribution of these components may account for the PAF‐induced effects at the pulmonary vascular and airway levels.
The effects of calyculin A upon calcium‐, guanine nucleotides‐ and phorbol 12‐myristate 13‐acetate‐stimulated ACTH secretion from AtT‐20 cells
Authors: McFerran B.W. , Guild S.B. 
Published: July 2012

The mouse AtT‐20/D16‐16 anterior pituitary tumour cell line was used as a model system for the study of protein phosphatase involvement in the late stages of the secretory pathway for adrenocorticotrophin (ACTH) secretion. The effects of the type 1 and 2 phosphatase inhibitor calyculin A upon calcium‐, guanine nucleotide‐ and phorbol 12‐myristate 13‐acetate (PMA)‐stimulated ACTH secretion from electrically‐permeabilized AtT‐20 cells were studied.
Calyculin A (1 nM‐1 μm) inhibited both calcium (10 jam)‐ and guanosine 5′‐0‐(3‐thiotriphosphate) (GTP‐γ‐S) (100 μm)‐evoked ACTH secretion from permeabilized cells in a concentration‐dependent manner. These effects were maximal with 100 nM calyculin A.
ACTH secretion was stimulated from electrically‐permeabilized cells when the cytosolic free calcium ion concentration, controlled by calcium‐EGTA buffers, was raised over the concentration range of 100 nM to 10 μm. This calcium‐stimulated ACTH secretion was inhibited by co‐incubation with calyculin A (100 nM).
GTP‐γ‐S (10nM‐100μm) stimulated ACTH secretion from permeabilized cells at concentrations greater than 1 μm GTP‐γ‐S. Co‐incubation with calyculin A (100 nM) inhibited this stimulation of ACTH secretion observed at these concentrations of GTP‐γ‐S.
PMA (100 nM) significantly stimulated ACTH secretion from permeabilized cells in the absence of either calcium and guanine nucleotides and this action was enhanced by calyculin A (100 nM). Furthermore, an inhibition of GTP‐γ‐S (100 μm)‐stimulated ACTH secretion observed in the presence of calyculin A (100 nM) was not observed in the presence of PMA (100 nM).
The results of the present study indicate that dephosphorylation by phosphatases plays an important role in stimulus‐secretion coupling in AtT‐20 cells and is involved in mediating the effects of GE upon the secretory apparatus in these cells. Furthermore, the point of regulation of the secretory response by PKC which underlies the ability of PKC to amplify the calcium/GE system may lie distal to both GE and these phosphatases.
Heparin‐insensitive calcium release from intracellular stores triggered by the recombinant human parathyroid hormone receptor
Authors: Seuwen Klaus , Boddeke Hendrikus G.W.M. 
Published: July 2012

In the present study we have characterized the parathyroid hormone (PTH)‐induced calcium signalling in 293 cells stably transfected with the human PTH receptor cDNA. In these cells, human PTH‐l(l‐38) strongly stimulates adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) formation (EC50 = 0.39 nM) but fails to activate phosphoinositide (PI) turnover. The latter pathway is strongly activated, however, by carbachol (CCh) acting through endogenous M3‐muscarinic receptors.
Despite the lack of detectable inositol phosphate (IP) formation, hPTH‐(l‐38) elicited calcium transients (EC50 =11.2 nM) which were comparable to the signals evoked by CCh. These signals are independent of cyclic AMP generation as cyclic AMP elevating agents did not mimic or modify the PTH response.
The PTH‐stimulated calcium signal still occurred in calcium‐free medium but was absent in cells pretreated with thapsigargin, an inhibitor of the calcium pump of the endoplasmic reticulum (ER). hPTH‐(l‐38) did not accelerate Mn2+‐influx through the plasma membrane. These data indicate that PTH releases calcium from intracellular stores.
Using heparin, an inhibitor of the IP3‐activated calcium release channel of the ER, we tested whether the formation of a low amount of IP3, escaping detection by our biochemical assay, might be the origin of the PTH‐induced calcium response. However, intracellular infusion of heparin through patch pipettes in voltage clamp experiments failed to block hPTH‐(l‐38)‐induced calcium signals, whereas it abolished the CCh response.
The PTH response, like the CCh response, was insensitive to micromolar concentrations of ryanodine and ruthenium red, eliminating the possibility that hPTH‐(l‐38) stimulates calcium‐induced calcium release through ryanodine receptors.
We conclude that the recombinant human PTH receptor stimulates calcium release from intracellular stores through a novel pathway not involving IP3‐ or ryanodine receptors.
Protein kinase A and nicotinic activation of bovine adrenal tyrosine hydroxylase
Authors: Marley Philip D. , Thomson Kerrie A. , Bralow Roger A. 
Published: July 2012

Stimulation of nicotinic cholinoceptors on bovine chromaffin cells increases phosphorylation of three serine residues in tyrosine hydroxylase (TOH) and activates TOH. One of the serines is a target for protein kinase A phosphorylation, and phosphorylation of this serine is adequate alone to cause TOH activation. The role of protein kinase A in nicotinic activation of TOH was therefore investigated.
TOH activity was studied in situ in intact, cultured, bovine adrenal chromaffin cells, by measuring 14C02 evolved following the hydroxylation and rapid decarboxylation of [14C]‐tyrosine offered to the cells.
Nicotine (5 μm), forskolin (1 μm) and 8‐bromo‐cyclic AMP (8‐Br‐cyclic AMP, 1 mM) each increased TOH activity by up to 200% over 10 min. The effect of nicotine was completely abolished by removal of extracellular Ca2+.
TOH activation by all three drugs was blocked by H89 (3–20 4mUm), which inhibits protein kinase A by competing for the ATP binding site on the kinase. Adenosine 3′:5′‐cyclic monophosphorothioate Rp‐diastereomer (Rp‐cAMPS) (1 mM), an inhibitor of protein kinase A that competes with cyclic AMP for the regulatory subunit of the kinase, abolished the activation of TOH by nicotine, and reduced that by forskolin and 8‐Br‐cyclic AMP. Both H89 and Rp‐cAMPS inhibited basal TOH activity by 50–80%.
A structural analogue of H89, H85 (3–20 μm), which lacks activity as a protein kinase A inhibitor, did not inhibit either the activation of TOH by nicotine (5 μm) or basal TOH activity. Neither sodium nitroprusside (0.3–10 μm) nor 8‐Br‐cyclic GMP (1 mM) increased TOH activity.
In digitonin‐permeabilized chromaffin cells, forskolin (3 μm), cyclic AMP (10 μm) and Ca2+ (approx. 2 μm free Ca2+) each increased TOH activity. The response to all three drugs was blocked by H89 (10 μm), which also reduced basal TOH activity in the permeabilized cells.
Maximal activation of TOH by forskolin was achieved with 10 μm forskolin. This concentration was less than the EC50 for forskolin‐induced cyclic AMP accumulation in these cells. The activations of TOH by forskolin (10 μm) and nicotine (5 μm) were additive.
The results indicate that both basal TOH activity and nicotinic activation of TOH in bovine chromaffin cells require protein kinase A activity. However, it is unlikely that nicotinic activation of TOH is directly mediated by an activation of protein kinase A in response to elevated cyclic AMP levels. It is possible that protein kinase A plays a permissive role in allowing nicotinic cholinoceptors to activate TOH by another signalling pathway.
Contribution of P2‐purinoceptors to neurogenic contraction of rat urinary bladder smooth muscle
Authors: Hashimoto Minori , Kokubun Shinichiro 
Published: July 2012

The contribution of P2‐purinoceptors to neurogenic contraction was investigated in rat urinary bladder smooth muscle by measurement of isotonic tension.
Contraction of rat urinary bladder smooth muscle induced by electrical stimulation was decreased to 84.19±3.90% of the control (n= 16) in the presence of atropine (1 μm), which was further decreased to 38.80 ±2.75% of the control (n = 49) in the presence of both atropine and 10 μm α,β‐methylene adenosine 5′‐triphosphate (α,β‐Me ATP).
The contractile response induced by electrical stimulation in the presence of atropine and α,β‐Me ATP was decreased to 27.81 ±4.07% (n = 23) and 26.63 ±5.01% (n = 15) of the control, by the addition of 100 μm cibacron blue 3GA and 100 μm suramin, respectively. The application of 100 μm adenosine 5′‐0–2‐thiodiphosphate (ADPβS) in the presence of atropine and α,β‐Me ATP decreased the contractile response induced by electrical stimulations to 17.15 ±3.71% (n=15) of the control.
Pretreatment of muscle strips with 100 μm ADPβS significantly reduced the response to either 200 μm α,β‐methylene adenosine 5′‐diphosphate or 200 μm ADPβS.
Uridine 5′‐triphosphate (100 μm to 1 mM) concentration‐dependently contracted muscle strips, and this contraction was significantly antagonized by desensitization of P2‐receptors with α,β‐Me ATP (10 μm), and completely antagonized by pretreatment of muscle strips with both α,β‐Me ATP and ADPβS (100 μm).
Di(adenosine‐5′) tetraphosphate (30 and 100 μm) contracted muscle strips, whereas it failed to contract after desensitization of P2‐receptors.
It is suggested that about 20% of the neurogenic contraction of rat urinary bladder smooth muscle is mediated via ADPβS‐sensitive purinoceptors.
Contribution of P1 (A2b subtype) and P2‐purinoceptors to the control of vascular tone in the rat isolated mesenteric arterial bed
Authors: Rubino Annalisa , Ralevic Vera , Burnstock Geoffrey 
Published: July 2012

The direct vascular effects of adenosine and ATP were compared in the isolated and perfused mesenteric arterial bed of the rat. The actions of analogues of adenosine and ATP were also examined.
In preparations at basal tone, adenosine lacked vasoconstrictor actions, while ATP elicited dose‐dependent vasoconstrictor responses. When the tone of preparations was raised by adding methoxamine to the perfusate, adenosine and its stable analogue, 2‐chloroadenosine (2‐CADO) elicited dose‐dependent vasodilatation. The A2 adenosine receptor agonist, 5′‐N‐ethylcarboxamidoadenosine (NECA) was active at lower doses than adenosine, while the A2a‐selective agonist, CGS 21680 and the selective A1 agonist, N6‐cyclopentyladenosine (CPA) failed to induce vasodilatation. ATP and its analogue, 2‐methylthio ATP, elicited dose‐dependent vasodilatation at doses 400 fold lower than adenosine.
Vasodilator responses to adenosine and 2‐CADO were sensitive to antagonism by 1 μm 8‐sulphophenyltheophylline (8‐SPT) and were unaffected by inhibition of nitric oxide synthase by Nω‐nitro‐L‐arginine methyl ester (L‐NAME). In contrast, vasodilator responses to ATP were not sensitive to antagonism by 8‐SPT and were almost abolished by L‐NAME treatment.
These results indicate that in the rat mesenteric arterial bed, while both adenosine and ATP participate in the purinergic control of vascular tone, adenosine appears to be a weaker vasodilator than ATP and lacks vasoconstrictor action. A2b adenosine receptors account for the adenosine‐induced vasodilatation which is independent of the production of nitric oxide.
Actions of endothelins and sarafotoxin 6c in the rat isolated perfused lung
Authors: Lal H. , Woodward B. , Williams K.I. 
Published: July 2012

Endothelin (ET) receptors within the vasculature and airways were studied in a rat perfused lung model in which pulmonary perfusion pressure (PPP), pulmonary inflation pressure (PIP) and lung weight were continuously monitored.
The vascular potencies of ETs (ET‐l>ET‐2>ET‐3) suggest an action via ETA receptors. This was confirmed by use of the antagonist, BQ123 (2 μm). The vasoconstrictor effects of sarafotoxin 6c (SX6C) also indicated the presence of ETB receptors.
Lung weight increases induced by ETs appeared to be a consequence of their vasoconstrictor potencies. The mixed ET receptor antagonist, bosentan (5 μm), markedly attenuated the responses of ET‐1 and SX6C on PPP and lung weight, further implicating activation of both ETA and ETB receptors in these responses.
Endothelin‐1 (ET‐1) induced an accumulation of albumin‐bound Evans blue dye in orthogradely perfused lungs. Retrograde perfusion attenuated the extravasation and increase in lung weight due to ET‐1 but significantly augmented those induced by SX6C.
The bronchoconstrictor actions of ETs (ET‐l = ET‐2 = ET‐3) and SX6C suggest this is an ETB‐mediated response. However SX6C was more potent than ETs and the dose‐response curve was significantly steeper and achieved a higher maximum.
Indomethacin did not affect the vascular or bronchial responses to ET‐1 or SX6C.
These findings indicate that rat pulmonary vasculature contains both ETA and ETB receptors. Retrograde perfusion suggests that ETB receptors are located arterially whereas ETA receptors are predominantly venous in distribution. Differences in the bronchoconstrictor potency of SX6C (compared to ETs) and the antagonism by bosentan may indicate ETB receptor heterogeneity in the airways.
Functional characterization of the adenosine receptor mediating inhibition of peristalsis in the rat jejunum
Authors: Hancock Debra L. , Coupar Ian M. 
Published: July 2012

The non‐selective adenosine agonist, 5′‐N‐ethylcarboxamidoadenosine (NECA), is a potent inhibitor of morphine withdrawal diarrhoea in rats. More recently we found that NECA exerts its antidiarrhoeal effect by inhibiting secretion in both the jejunum and ileum and also by inhibiting peristalsis in the ileum. The specific aim of this study was to characterize the receptor in the rat jejunum mediating inhibition of peristalsis via functional studies using a range of metabolically stable adenosine analogues based on the pharmacological criteria of relative agonist and antagonist potencies.
Peristalsis in the rat isolated jejunum was achieved by raising the pressure to between 7–11 cmH2O for 3 min followed by a 3 min rest period (pressure at zero). The mean rate of peristalsis during inflation was 7.3 ± 0.1 peristaltic waves per 3 min and this rate remained consistent for up to 30 min, in 5 separate tissues. The inhibitory effects of the adenosine analogues were quantified by expressing their effects as a % reduction in the mean number of peristaltic contractions derived from the control tissues.
The rank order of agonist potency to reduce the rate of peristalsis was: N6‐cyclopentyladenosine (CPA) > NECA > R(−)−N6‐(2‐phenylisopropyl)adenosine (R‐PIA) > chloroadenosine (2‐CADO) > S‐PIA > 2‐phenylaminoadenosine (CV‐1808). This order complies well with the rank order of agonist potency that represents the activation of the A1 receptor subtype (CPA > R‐PIA = CHA = > NECA > 2‐CADO > S‐PIA > CV‐1808).
The selective A1 adenosine antagonist 1,3‐dipropyl‐8‐cyclopentylxanthine (DPCPX) and the nonselective adenosine antagonist 8‐phenyltheophylline (8‐PT) at their respective concentrations of 10 nM and 2 μm caused parallel rightward shifts in the concentration‐response curve to the non‐selective Al/A2 agonist NECA. DPCPX was significantly more potent at inhibiting NECA than 8‐PT as revealed by their apparent pA2 values; DPCPX (9.5) and 8‐PT (7.26). The high affinity of DPCPX relative to that of 8‐PT suggests the presence of an A1 and not an A2B receptor. In addition, the high affinity of DPCPX (pA2:9.37) against the selective A2 agonist CPA, further confirms the presence of the A1 receptor subtype.
In this study we found that the A1 adenosine receptor is involved in regulating in vitro peristalsis which is different from the adenosine receptor regulating inhibition of secretion (A2B) in the same region of intestine of the same species. We propose that A2B adenosine agonists could be of clinical value in the management of diarrhoea that is due to microbiological organisms where antimotility effects are not desired.
Mechanisms of angiotensin II chronotropic effect in anaesthetized dogs
Authors: Lambert C. 
Published: July 2012

The chronotropic effect of angiotensin II (5 μg in 1 ml of Tyrode solution), injected directly into the sinus node artery of 24 anaesthestized and vagotomized dogs pretreated with a β‐adrenoceptor antagonist, was evaluated before and after the administration of: (a) an angiotensin II AT1 receptor antagonist (losartan, 50 μg kg−1 min−1 infused i.v. for 120 min), (b) an α‐adrenoceptor antagonist (prazosin, 1 mg kg−1 i.v. bolus injected), (c) a Ca2+ channel blocker (nifedipine 50, 100 and 200 μg kg−1 i.v. bolus injected) and (d) a protein kinase inhibitor (staurosporine, 800 nM infused via the sinus node artery at 0.6 ml min−1 for 15 min).
Losartan and staurosporine by themselves had no effect on basal systemic arterial pressure and heart rate, whereas prazosin and nifedipine caused significant diminutions of both parameters.
Angiotensin II induced significant increases in heart rate, the mean augmentations being 29 ±2 beats min−1. Losartan, nifedipine and staurosporine significantly decreased the chronotropic effect of angiotensin II, the mean respective diminutions being 65 ±8, 40 ±9 and 64 ±10%, whereas prazosin had no effect.
This work has demonstrated that angiotensin II exerts in vivo a significant positive chronotropic effect that is mediated via AT1 receptors located in the region of the sinoatrial node. This effect is independent of the adrenergic system. It is decreased by the inhibition of the production of protein kinases, most probably of protein kinase C, and by the blockade of the voltage‐sensitive L‐type Ca2+ channels. Other studies are obviously needed to ascertain the role of angiotensin II in the control of heart rate and/or the genesis of arrhythmias.
BaCl2‐ and 4‐aminopyridine‐evoked phasic contractions in the rat vas deferens
Authors: Huang Yu 
Published: July 2012

The actions of BaCl2 and 4‐aminopyridine, blockers of K+ channels, on the mechanical activity of the epididymal half of the rat vas deferens were investigated.
Both BaCl2 and 4‐aminopyridine dose‐dependently evoked phasic contractions. High extracellular potassium (35–40 mM) caused a tonic contraction but abolished the BaCl2‐ and 4‐aminopyridine‐induced phasic activity and reduced the BaCl2‐induced sustained component of contraction, but increased the 4‐aminopyridine‐induced tonic contraction.
Omission of calcium from the extracellular medium totally abolished the 4‐aminopyridine‐induced response but only reduced the mean amplitude of phasic contractions induced by BaCl.
Procaine (10 mM), an inhibitor of internal calcium release, completely abolished the phasic activity and reduced the sustained contraction induced by BaCl2. The remaining tone was abolished by nifedipine (1 μm).
Tetraethylammonium (1 mM) suppressed the amplitude of the BaCl2‐induced phasic contractions, and induced a biphasic increase in tonic tension.
The BaCl2‐induced responses were resistant to prazosin (1 μm), yohimbine (3 μm), propranolol (3 μm) or atropine (3 μm); in contrast, the 4‐aminopyridine‐induced activity was effectively inhibited by prazosin (Éμm) attenuated by yohimbine (Éμm) and atropine (Éμm) but not by propranolol (3μm). The 4‐aminopyridine‐induced response was abolished by pretreatment of the vas deferens with 6‐hydroxydopamine (0.5 mM).
The results indicate that the BaCl2‐evoked activity in the vas deferens was mainly due to blockade of Ba2+‐sensitive K+ channels on the smooth muscle plasma membrane. Subsequent calcium entry through the depolarized plasma membrane was needed to trigger generation of phasic contractions. 4‐Aminopyridine‐induced action, however, was largely mediated by neurotransmitters released from the depolarized nerve terminals as a result of blockade of K+ channels.
Potent block of potassium currents in rat isolated sympathetic neurones by the uncharged form of amitriptyline and related tricyclic compounds
Authors: Wooltorton Julian R.A. , Mathie Alistair 
Published: July 2012

The block of K+currents by amitriptyline and the related tricyclic compounds cyproheptadine and dizocilpine was studied in dissociated rat sympathetic neurones by whole‐cell voltage‐clamp recording.Cyproheptadine (30 μm) inhibited the delayed‐rectifier current (Kv) by 92% and the transient current (KA) by 43%. For inhibition of KV, cyproheptadine had a KDof 2.2 μm. Dizocilpine (30 μm) inhibited KVby 26% and KAby 22%. The stereoisomers of dizocilpine were equally potent at blocking KVand KA.Amitriptyline, a weak base, was significantly more effective in blocking KVat pH 9.4 (KD=0.46 μm) where the ratio of charged to uncharged drug was 50:50 compared with pH 7.4 (KD=11.9 μm) where the ratio was 99:1.N‐methylamitriptyline (10 μm), the permanently charged analogue of amitriptyline, inhibited Kvby only 2% whereas in the same cells amitriptyline (10 μm) inhibited Kvby 36%.Neither amitriptyline nor N‐methylamitriptyline had a detectable effect on Kvwhen added to the intracellular solution.It is concluded that the uncharged form of amitriptyline is approximately one hundred times more potent in blocking Kvthan the charged form. However, this does not seem to be due to uncharged amitriptyline having better access to an intracellular binding site.