bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence that 5‐HT2receptor activation decreases noradrenaline release in rat hippocampusin vivo
Authors: Done C.J.G. , Sharp T. 
Published: July 2012

Recent electrophysiological studies have shown that 5‐HT2/5‐HT1Creceptor agonists inhibit the electrical activity of noradrenergic neurones in the rat locus coeruleus. Here we examine the effect of various agonists and antagonists of 5‐HT2/5‐HT1Creceptors on noradrenaline release in hippocampus of anaesthetized rats using microdialysis.Subcutaneous administration of the 5‐HT2/5‐HT1Creceptor agonist, 1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane (DOI: 0.2 and 0.5 mg kg−1), caused a marked decrease (50% of pre‐drug levels 60 min after injection) of noradrenaline in hippocampal dialysates which was long‐lasting (> 120 min). Noradrenaline output also decreased in response to administration of the structural analogue of DOI, 1‐(2,5‐dimethoxy‐4‐bromophenyl)‐2‐aminopropane (DOB: 1 mg kg−1, s.c.).The effect of DOI on noradrenaline output was prevented by pretreatment with the 5‐HT2/5‐HT1Creceptor antagonist, ritanserin (0.4 mg kg−1, s.c.). Spiperone (0.2 and 1 mg kg−1, s.c.), a 5‐HT2/dopamine D2receptor antagonist which has low affinity for 5‐HT1Creceptors, also antagonized the effect of DOI (0.5 mg kg−1, s.c.). Sulpiride (50 mg kg−1, s.c.), a dopamine D2receptor antagonist did not alter the response to DOI (0.5 mg kg−1, s.c.).Both the non‐selective 5‐HT receptor agonist, quipazine (1 mg kg−1, s.c.), and the 5‐HT‐releasing agent,p‐chloroamphetamine (2 mg kg−1, s.c.), decreased noradrenaline release in hippocampus and these effects were antagonized by pretreatment with ritanserin (0.4 mg kg−1, s.c.).Our data suggest thatin vivo, noradrenaline release in hippocampus is inhibited by 5‐HT2receptor activation. This effect is probably associated with a decrease in noradrenergic neuronal activity.
Adenosine A1‐receptor stimulated increases in intracellular calcium in the smooth muscle cell line, DDT1MF‐2
Authors: Dickenson John M. , Hill Stephen J. 
Published: July 2012

The effect of a range of adenosine receptor agonists on intracellular free calcium concentration ([Ca2+]i) has been studied in the hamster vas deferens smooth muscle cell line DDT1MF‐2.
Adenosine receptor agonists elicited a rapid and maintained increase in [Ca2+]i in fura‐2 loaded DDT1MF‐2 cells. The initial rise could be maintained in the absence of extracellular calcium, whereas the maintained or plateau phase was dependent upon the presence of extracellular calcium and appeared to be associated with calcium influx. The rank order of agonist potencies was N6‐cyclopentyladenosine > 5′‐N‐ethylcarboxamidoadenosine > 2‐chloroadenosine > adenosine.
The response to 2‐chloroadenosine was antagonized by the antagonists 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX, KD 0.14 nm) and 8‐phenyltheophylline (KD 112 nm).
Pretreatment with the 5‐lipoxygenase inhibitor AA861 (20 μm) produced only a small (14 ± 2%) inhibition of the [Ca2+]i response elicted by N6‐cyclopentyladenosine (300 nm), in nominally Ca2+‐free buffer containing 0.1 mm EGTA. The cyclo‐oxygenase inhibitor, indomethacin (2 μm) was without effect.
The Ca2+‐influx associated with the plateau phase required the continued presence of agonist on the receptor. The antagonist DPCPX (100 nm) attenuated the rise in [Ca2+]i observed when extracellular Ca2+ was re‐applied after the cells had been stimulated with N6‐cyclopentyladenosine (CPA;300 nm) in experiments initiated in nominally Ca2+‐free buffer.
Pretreatment with pertussis toxin (200 ng ml−1 for 4 h) inhibited the CPA (100 nm) stimulated intracellular Ca2+ release and Ca2+ influx but was without effect on the response to histamine (100 μm).
These data suggest that adenosine A1‐receptor activation in DDT1MF‐2 cells stimulates release of Ca2+ from intracellular stores and influx of extracellular Ca2+ through Ca2+ entry pathways in the plasma membrane which required the continued presence of agonist on the receptor.
Selective inhibition of agonist‐induced but not shear stress‐dependent release of endothelial autacoids by thapsigargin
Authors: Macarthur Heather , Hecker Markus , Busse Rudi , Vane John R. 
Published: July 2012

The effects of the Ca2+‐ATPase inhibitor, thapsigargin, on the shear stress‐dependent and on the agonist‐stimulated release of endothelium‐derived relaxing factor, i.e. nitric oxide (NO), and prostacyclin (PGI2) were studied in bovine and human cultured endothelial cells as well as in endothelium‐intact arterial segments of the rabbit.
Preincubation with thapsigargin (1 μm for 10 min) had no effect on the shear stress‐dependent release of NO from bovine aortic endothelial cells grown on beads, but abolished the release of NO induced by ADP, bradykinin, ionomycin or poly‐l‐lysine. Similarly, thapsigargin completely abrogated the agonist‐stimulated PGI2 release from these cells, but had no effect on the shear stress‐dependent release of PGI2.
The acetylcholine‐induced release of NO from the luminally perfused thoracic aorta and femoral artery of the rabbit was suppressed by pretreatment with thapsigargin (1 μm). In contrast, thapsigargin did not affect the shear stress‐dependent release of NO from the femoral artery.
Administration of thapsigargin to these vascular preparations or to cultured endothelial cells alone produced a substantial release of both NO and PGI2. This release declined towards previous values after washout of thapsigargin.
In human and bovine cultured endothelial cells, thapsigargin (1–1000 nm) caused a dose‐dependent sustained rise in [Ca2+]i, an effect that was abolished in the absence of extracellular Ca2+. Stimulation of these cells with bradykinin, histamine, ADP or ionomycin after previous exposure to thapsigargin (30–1000 nm) no longer caused an increase in [Ca2+]i.
These findings demonstrate that by emptying intracellular Ca2+ stores, thapsigargin selectively blocks the agonist‐stimulated release of both NO and PGI2, suggesting a principal difference in the control by [Ca2+]i of the release of these endothelial autacoids caused by shear stress or receptor‐dependent and independent agonists.
α2‐Autoreceptor subclassification in rat isolated kidney by use of short trains of electrical stimulation
Authors: Bohmann C. , Schollmeyer P. , Rump L.C. 
Published: July 2012

Rat kidneys were perfused with Krebs‐Henseleit solution and incubated with [3H]‐noradrenaline. The renal nerves were electrically stimulated at either 1 Hz for 30 s or 100 Hz for 0.06 s. The stimulation induced (S‐I) outflow of radioactivity was taken as an index of endogenous noradrenaline release.
At a frequency of 1 Hz for 30 s the α‐adrenoceptor antagonists BRL 44408 (0.01, 0.1 μm) and imiloxan (0.1, 1.0 μm) enhanced S‐I outflow of radioactivity. However, at a frequency of 100 Hz for 0.06 s the α‐adrenoceptor antagonists, idazoxan (0.1, 1.0 μm), imiloxan (0.1, 1.0 μm), BRL 44408 (0.1, 1.0 μm), BRL 41992 (0.1, 1.0 μm) and prazosin (0.01 μm) failed to enhance S‐I outflow of radioactivity.
Thus, the rat isolated kidney stimulated at 100 Hz for 0.06 s, avoids autoinhibition by endogenous noradrenaline and α‐adrenoceptor antagonist affinities (pKB) at the prejunctional α‐autoreceptor were estimated without disturbance by the endogenous activator.
The α2‐adrenoceptor agonist, clonidine, inhibited the S‐I outflow of radioactivity with a maximum of 90% and an EC50 of 7.2 nm.
All α‐adrenoceptor antagonists used caused parallel shifts of the concentration‐response curve for clonidine to the right. The rank order of potencies was: rauwolscine (α2A/B) > idazoxan (α2A/B) > phentolamine (α2A/B) > WB 4101 (α2A) > BRL 44408 (α2A) > BRL 41992 (α2B) > prazosin (α2B) = imiloxan (α2B).
These data, when compared with binding, molecular and functional data of various other tissues and cell lines, indicate that prejunctional α2‐autoreceptors in rat kidney do not belong to the α2B‐ or α2C‐subtype. The α2‐autoreceptor of rat kidney seems to be of the α2A‐subtype. However, α2‐autoreceptor affinities of the present study correlate also well with binding affinities of the recently described α2D‐ligand binding site in bovine pineal gland.
Ion channel blockade by oximes and recovery of diaphragm muscle from soman poisoning in vitro
Authors: Tattersall John E. H. 
Published: July 2012

The actions of oximes and related compounds on the nicotinic acetylcholine receptor ion channel at the adult mouse muscle endplate were investigated by use of single‐channel recording techniques. The aim of the study was to determine whether the channel‐blocking properties of the compounds could contribute to their therapeutic effectiveness against soman poisoning in vitro.
Therapeutic effectiveness was assessed in guinea‐pig phrenic nerve‐hemidiaphragm preparations by measuring the degree of recovery of neuromuscular function produced by the compounds following poisoning by soman. A number of the compounds, including some which lacked the oxime group, produced a significant recovery of neuromuscular function which was unrelated to acetylcholinesterase (AChE) reactivation; this was reversed by washing off the compound, and was therefore attributed to a direct pharmacological action on the muscle.
Single channel recordings showed that some of the compounds blocked open nicotinic receptor ion channels in preparations of mouse muscle fibres. The compounds which showed the greatest direct pharmacological actions in diaphragms produce a very fast, flickering blockade of the channels. Several quantitative measures of channel‐blocking activity correlated very well with the direct pharmacological action. Furthermore, for two compounds studied in greater detail, the direct action and channel‐blocking showed similar concentration‐response relationships.
The results of this study indicate that the direct pharmacological action of oximes and their analogues against neuromuscular blockade by soman in vitro is due to their channel‐blocking activity. The direct action does not correlate well with protection against soman poisoning in vivo, however, which suggests that additional non‐reactivating properties of these compounds, at sites other than the neuromuscular junction, may also be important for their therapeutic effectiveness.
Enhancement of airway reactivity to histamine by isoprenaline and related β‐adrenoceptor agonists in the guinea‐pig
Authors: Galland Barbara C. , Blackman J.G. 
Published: July 2012

The effect of isoprenaline, adrenaline and salbutamol on airway reactivity to histamine was observed in anaesthetized, ventilated guinea‐pigs. Airway reactivity was determined before and 20 min and 90 min after a 30‐min i.v. infusion of each agonist by constructing cumulative dose‐response curves from breath‐by‐breath measurements of the effect of different rates of i.v. infusion of histamine on lung resistance (RL) and dynamic compliance (Cdyn).(±)‐Isoprenaline infused i.v. for 30 min at a rate of 0.4 μmol h−1kg−1caused bronchodilatation and a fall in blood pressure. Recovery to starting values of RLand Cdynoccurred within 20 min of stopping the infusion.Reactivity to histamine was greatly enhanced when measured 20 min and 90 min after stopping the infusion of (±)‐isoprenaline. This was not an effect of the prior infusion of histamine or of the dissolving solution.Infusion of (−)‐isoprenaline for 30 min at a rate of 0.2 μmol h−1kg−1also enhanced reactivity to histamine. However, enhancement of reactivity to histamine was not demonstrable after infusion of (+)‐isoprenaline at equal or higher dose rates.Infusions of bronchodilator concentrations of adrenaline and salbutamol also enhanced airway reactivity to histamine, but the bronchodilator effect of salbutamol lasted longer than that of isoprenaline or adrenaline and the development of hyperreactivity was delayed.After acute bilateral vagotomy, infusion of (±)‐isoprenaline enhanced airway reactivity but only at the highest dose of histamine.(±)‐Isoprenaline did not enhance contractile responses to histamine in isolated preparations of first branch bronchi.We conclude that the bronchodilator effect of activating β‐adrenoceptors in the airways of guinea‐pigs is followed by a more persistent state of hyperreactivity to histamine.
Evidence for a nucleotide receptor on adrenal medullary endothelial cells linked to phospholipase C and phospholipase D
Authors: Purkiss John R. , Wilkinson Graeme F. , Boarder Michael R. 
Published: July 2012

We have investigated whether the ‘atypical’ P2‐purinoceptor previously described on adrenal microvasculature endothelial cells is a nucleotide receptor (responds to pyrimidines and purines) and is linked to phospholipase D as well as phospholipase C.
Cultured bovine adrenal medullary endothelial (BAME) cells responded to the pyrimidine UTP, as well as the purines. The total [3H]‐inositol phosphate responses were with a rank order of UTP > ATP‐ = adenosine 5′‐O‐(3‐thio‐triphosphate) (ATPγS) >> 2MeSATP. The selective P2x agonist β, γ‐methylene ATP was inactive.
Construction of dose‐response curves to ATP, ATPγS and UTP in the presence and absence of additional agonists showed that responses to ATPγS and UTP were not additive, nor were those to UTP and ATP. This suggests that purines and pyrimidines acted via a common nucleotide receptor.
32P‐labelled BAME cells, in the presence of butanol, produced [32P]‐phosphatidylbutanol (PBut) when stimulated with ATPγS or the protein kinase C activator, tetradecanoyl phorbol acetate (TPA).
Cells labelled with [3H]‐palmitate and stimulated in the presence of butanol generated [3H]‐PBut with the same order of agonist potencies seen for inositol phosphate responses.
The protein kinase C inhibitor, Ro 31–8220, abolished TPA and agonist stimulation of [3H]‐PBut production.
These observations, and our related studies on bovine aortic endothelial cells, provide the first demonstration of a phospholipase C linked nucleotide receptor on vascular endothelial cells. It is concluded that BAME cells express a nucleotide receptor linked to phospholipase C and phospholipase D, but that activation of phospholipase D is probably down‐stream of phospholipase C.
Ap4A and ADP‐β‐S binding to P2 purinoceptors present on rat brain synaptic terminals
Authors: Pintor Jesús , Díaz‐Rey M. Angel , Miras‐Portugal M. Teresa 
Published: July 2012

Diadenosine tetraphosphate (Ap4A) a dinucleotide stored and released from rat brain synaptic terminals presents two types of affinity binding sites in synaptosomes. When [3H]‐Ap4A was used for binding studies a Kd> value of 0.10 ± 0.014 nm and a Bmax value of 16.6 ± 1.2 fmol mg−1 protein were obtained for the high affinity binding site from the Scatchard analysis. The second binding site, obtained by displacement studies, showed a Ki value of 0.57 ± 0.09 μm.
Displacement of [3H]‐Ap4A by non‐labelled Ap4A and P2‐purinoceptor ligands showed a displacement order of Ap4A > adenosine 5′‐O‐(2‐thiodiphosphate) (ADP‐β‐S) > 5′‐adenylyl‐imidodiphosphate (AMP‐PNP) > α,β‐methylene adenosine 5′‐triphosphate (α,β‐MeATP) in both sites revealed by the Ki values of 0.017 nm, 0.030 nm, 0.058 nm and 0.147 nm respectively for the high affinity binding site and values of 0.57 μm, 0.87 μm, 2.20 μm and 4.28 μm respectively for the second binding site.
Studies of the P2‐purinoceptors present in synaptosomes were also performed with [35S]‐ADP‐β‐S. This radioligand showed two binding sites the first with Kd and Bmax values of 0.11 ± 0.022 nm and 3.9 ± 2.1 fmol mg−1 of protein respectively for the high affinity binding site obtained from the Scatchard plot. The second binding site showed a Ki of 0.018 ± 0.0035 μm obtained from displacement curves.
Competition studies with diadenosine polyphosphates of [35S]‐ADP‐β‐S binding showed a displacement order of Ap4A > Ap5A > Ap6A in the high affinity binding site and Ki values of 0.023 nm, 0.081 nm and 5.72 nm respectively. The second binding site potency order was Ap5A > Ap4A > Ap6A, with Ki values of 0.28 μm, 0.53 μm and 5.32 μm respectively.
Displacement studies of [35S]‐ADP‐β‐S with P2‐purinoceptor agonists showed the following potency pattern: ADP‐β‐S > AMP‐PNP > α,β‐MeATP with Ki values of 0.021 nm, 0.029 nm 0.215 nm respectively in the high affinity binding site. 2‐Methylthio‐adenosine 5′‐triphosphate (2MeSATP) was unable to displace [35S]‐ADP‐β‐S in this binding site. The second binding site showed a profile of ADP‐β‐S > α,β‐MeATP> AMP‐PNP > 2MeSATP and Ki values of 0.018 μm, 0.212 μm, 0.481 μm and 18.04 μm respectively.
These studies suggest the presence of a new P2‐purinoceptor in rat brain synaptosomes with high affinity for diadenosine polyphosphates which we tentatively designate as P2d.
Inhibition by recombinant SLPI and half‐SLPI (Asn55‐Ala107) of elastase and cathepsin G activities: consequence for neutrophil‐platelet cooperation
Authors: Renesto Patricia , Balloy Viviane , Kamimura Takashi , Masuda Ken‐ichi , Imaizumi Atsushi , Chignard Michel 
Published: July 2012

The capacity of recombinant human secretory leukocyte proteinase inhibitor (SLPI) to inhibit human leukocyte elastase (HLE) and cathespin G (Cat G) was investigated and compared with a recombinant truncated form (carboxyl‐terminal domain, Asn55‐Ala107) called 1/2 SLPI.
Both compounds were efficient when tested against enzymatic activities of purified HLE and Cat G indicating that the HLE‐ and Cat G‐inhibitory sites were preserved in the truncated form. SLPI and 1/2 SLPI also affected platelet activation induced by 0.2 μm Cat G (IC50 = 112 ± 13 nm for SLPI and 280 ± 12 nm for 1/2 SLPI).
The effects of SLPI and 1/2 SLPI were then tested against polymorphonuclear neutrophil (PMN)‐mediated platelet activation, a cell‐to‐cell interaction mediated by HLE and Cat G released from PMN. In this experimental system, addition of SLPI or 1/2 SLPI before N‐formyl‐Met‐Leu‐Phe (fMLP) led to the inhibition of the resulting platelet activation. As was the case for Cat G enzymatic activity and Cat G‐induced platelet activation, SLPI was more efficient than 1/2 SLPI (IC50 = 676 ± 69 nm vs 1121 ± 150 nm).
The ratio of the IC50 against PMN‐mediated platelet activation compared to purified Cat G‐mediated platelet activation was 6.03 for SLPI and 4.32 for 1/2 SLPI. This difference may be due to the smaller size of the truncated form which could allow this molecule to diffuse more easily between PMN and platelets.
In conclusion, 1/2 SLPI could be a promising candidate in the treatment of pathological states linked to inflammation in which participation of HLE and Cat G has been evoked.
Inhibition of spinal opioid antinociception by intrathecal β‐endorphin1–27 in the rat
Authors: Hong M. , Sutak M. , Jhamandas K. 
Published: July 2012

The effects of intrathecal (i.t.) administration of β‐endorphin and two shorter fragments, human and ovine β‐endorphin1–27, were examined for antinociceptive activity in the tail‐flick and paw‐pressure tests in the rat. Additionally, the ability of ovine β‐endorphin1–27 to influence the action of i.t. β‐endorphin, morphine and [d‐Pen2‐d‐Pen5]enkephalin (DPDPE) was also examined in these tests.
After i.t. injection, β‐endorphin produced potent dose‐related antinociception in the tail‐flick and paw‐pressure tests. Shorter endorphins produced much weaker effects. The order of antinociceptive efficacy was β‐endorphin > human β‐endorphin1_27 > ovine β‐endorphin1–27.
Administration of ovine β‐endorphin1–27 (0.72, 1.44 nmol, i.t.) significantly attenuated the antinociceptive effect of β‐endorphin (2.88 nmol, i.t.) in the tail‐flick and paw‐pressure tests.
Both i.t. morphine and DPDPE produced dose‐related antinociception in the tail‐flick and paw‐pressure tests. The potency of DPDPE was lower than that of morphine in both tests; however, the effect of DPDPE was weaker in the paw‐pressure test.
Administration of ovine β‐endorphin1–27 (1.44 nmol, i.t.) significantly attenuated the antinociceptive effect of morphine (14.9 nmol, i.t.) in both tests and the effect of DPDPE (38.7 nmol) in the tail‐flick test.
The results show that β‐endorphin1–27 acts as an opioid antagonist at the spinal level in the rat. Its ability to inhibit the action of morphine and DPDPE suggests that it may attenuate β‐endorphin action by an interaction with μ‐ and/or δ‐opioid receptors.
Pharmacological characterization of the contractile responses to angiotensin analogues in guinea‐pig isolated longitudinal muscle of small intestine
Authors: Hawcock A.B. , Barnes J.C. 
Published: July 2012

The contractile responses to angiotensin II, angiotensin III and two synthetic analogues, [Lys2] angiotensin II and [Sar1]angiotensin II, in the guinea‐pig isolated longitudinal muscle preparation of small intestine have been characterized in vitro.
Tachyphylaxis to the angiotensin analogues was reduced by use of a Krebs‐Henseleit solution containing a raised (sub‐contractile) concentration of potassium (11.2 mm). Under these conditions, reproducible cumulative concentration‐response curves to all agonists were established. The pD2 estimates for angiotensin II, [Lys2]angiotensin II, angiotensin III and [Sar1]angiotensin II were 9.15 ± 0.14, 7.42 ± 0.06, 7.69 ± 0.18 and 9.50 ± 0.15 respectively and the maximum responses achieved were not significantly different.
The contractile responses to angiotensin II, angiotensin III and [Sar1]angiotensin II were reduced by greater than 80% by tetrodotoxin (TTX; 0.1 μm). However, the responses to [Lys2]angiotensin II were reduced by only 63 ± 5%. Atropine (0.1 μm) also reduced the responses to angiotensin II, angiotensin III and [Lys2]angiotensin II, although its effect was less than that produced by TTX. Furthermore, while responses to these agonists were not significantly modified by the NK1 receptor antagonist (±)‐CP‐96,345 (30 nm) alone, the combined pre‐incubation with both atropine and (±)‐CP‐96,345 reduced maximum agonist responses to a level not significantly different from those produced by TTX.
Indirect and direct contractile responses to angiotensin II and [Lys2]angiotensin II (in the presence of TTX) respectively were characterized by use of the selective AT1 receptor antagonist, losartan and the AT2 receptor antagonist, PD123177. Losartan produced parallel rightward displacement of the concentration‐response curve to angiotensin II and [Lys2]angiotensin II, with an estimated pKB of 8.56 (8.42–8.68) and 9.18 (8.63–9.50) respectively. The AT2 receptor antagonist, PD123177 (3 μm) failed to modify the contractile responses to either angiotensin II or [Lys2]angiotensin II.
We conclude that two populations of angiotensin II receptors exist in the guinea‐pig longitudinal muscle of small intestine, one located neuronally mediating the release of both acetylcholine and substance P and the other located on the smooth muscle mediating direct contractile responses. The neuronal component provides the major contribution to the agonist responses. Both receptor populations are of the AT1 receptor subtype.