bluuebunny/crossref_metadata_2025 huggingface dataset:
Vascular 5‐HT1‐like receptors mediating vasoconstriction and vasodilatation: their characterization and distribution in the intact canine cardiovascular system
Authors: Cambridge D. , Whiting M.V. , Butterfield L.J. , Marston C.
Published: July 2012

In anaesthetized dogs, intra‐left atrial administration of 5‐hydroxytryptamine (5‐HT) and selected tryptamine analogues (5‐carboxamidotryptamine, 5‐CT; 5‐methyl tryptamine, 5‐MT; α‐methyl 5‐hydroxytryptamine, α‐HT; sumatriptan, Sum) in the presence of ketanserin and MDL72222 (5‐HT2 and 5‐HT3 receptor antagonists, respectively), produced dose‐related changes in carotid, coronary and renal vascular conductance mediated by vascular 5‐HT1‐like receptors.

In the carotid vascular bed, 5‐HT, 5‐MT, α‐HT and Sum were vasoconstrictors with a rank order of potency (comparing ED50 values) of 5‐HT = Sum > 5‐MT > α‐HT. By contrast in this vascular bed, 5‐CT was a potent vasodilator.

In the coronary vascular bed, 5‐HT, 5‐CT, 5‐MT and α‐HT were vasodilators with a rank order of potency (comparing ED50 values) of 5‐CT > 5‐HT > 5‐MT > α‐HT. In this vascular bed, Sum was without effect.

In the renal vascular bed, 5‐HT, 5‐CT, 5‐MT, α‐HT and Sum were vasoconstrictors with a rank order of potency (comparing ED50 values) of 5‐CT > 5‐HT > Sum> 5‐MT > α‐HT.

The coronary (and carotid) vasodilator responses to 5‐CT were antagonized by the 5‐HT1‐like receptor antagonists, spiperone (1 mg kg−1) and methiothepin (0.1 mg kg−1), whereas the renal vasoconstrictor responses to this tryptamine analogue were antagonized only by methiothepin.

It is concluded from these studies that agonist finger‐printing in vivo, using tryptamine analogues, identifies and confirms the functional presence of at least two pharmacologically distinct subtypes of the 5‐HT1‐like receptor in the intact canine cardiovascular system. These two subtypes are located on the vascular smooth muscle and mediate direct vasoconstriction and vasodilatation responses in vivo.

In addition, these studies confirm that the distribution of these subtypes within the major vascular beds, shows a marked heterogeneity. The carotid vascular responses to the tryptamine analogues indicate the presence of both the vasodilator and the vasoconstrictor subtypes. The coronary vascular responses to these analogues are, however, consistent with presence of the vasodilator subtype, only. By contrast, the renal vascular responses to these analogues indicates only the presence of the vasoconstrictor subtype.
Haemostatic mechanism in the endometrium: role of cyclo‐oxygenase products and coagulation factors
Authors: Gelety Timothy J. , Chaudhuri Gautam
Published: July 2012

The primary mechanism of haemostasis in the endometrium of rat was studied and results were compared to that in the mesenteric artery.

The bleeding time of the rat endometrium as assessed by haemoglobin output was significantly decreased after pretreatment of the animals with either indomethacin (5 mg kg−1, i.v.) or meclofenamate (3 mg kg−1, i.v.) whereas the bleeding time was significantly increased in the rat mesenteric artery.

The bleeding time of the rat endometrium was unchanged from control values following treatment with prostacyclin (0.5 μg kg−1 min−1, i.v.) or 1‐benzylimidazole (50 mg kg−1, i.v.) whereas the bleeding times were increased in the rat mesenteric artery.

Administration of heparin (100 units kg−1) increased the bleeding time in the rat mesenteric artery but had no effect on the bleeding time of the endometrium.

Superfusion of the endometrium with 16, 16‐dimethyl PGE2 (1 μg ml−1), a vasodilator, increased the bleeding time of the endometrium but superfusion of PGE2 over the mesenteric artery did not affect the bleeding time from this site.

Histological studies of the mesenteric artery and the endometrium following haemostatis revealed that the haemostatic plug in the mesenteric artery was mainly composed of platelets and fibrin whereas in the endometrium it was mainly composed of fibrin.

These findings suggest that haemostasis in the endometrium may be mediated by the vascular tone and fibrin whereas formation of the platelet plug may be the primary mechanism for haemostasis in the mesenteric artery.
Evidence for lack of modulation of μ‐opioid agonist action by δ‐opioid agonists in the mouse vas deferens and guinea‐pig ileum
Authors: Elliott J. , Traynor J.R.
Published: July 2012

There is evidence from in vivo studies for an interaction of μ‐ and δ‐opioid ligands. In the present work this concept has been investigated using the mouse vas deferens and guinea‐pig ileum myenteric plexus‐longitudinal preparations.

In field stimulated vasa deferentia of the mouse, co‐administration of sub‐effective concentrations of the δ‐opioid agonist [d‐Pen2,d‐Pen5]enkephalin (DPDPE) and [Met5]‐ or [Leu5]enkephalin had no effect on the dose‐response curves of the μ‐agonists [d‐Ala2, MePhe4, Gly‐ol5]enkephalin (DAMGO) and morphine. Similarly, the δ‐opioid agonists did not alter the potency of morphine and DAMGO when added at different times prior to the μ‐opioid agonists, or when EC50 concentrations of δ‐opioid ligands were co‐administered. Compounds with preferred activity for the putative δ1‐(DPDPE) or δ2‐ ([d‐Ala2,Glu4]deltorphin II (Delt II)) opioid receptors were ineffective in this respect.

The guinea‐pig ileum contains δ‐opioid receptors. No function of these receptors in mediating blockage of field‐stimulated contractions was observed with ligands having affinity for the putative δ1 or δ2 subtypes nor were the agonists able to modulate responses to μ‐opioid ligands in this tissue.

The results demonstrate that modulation of μ‐opioid agonists by δ‐opioid agonists does not occur in the isolated peripheral tissues examined. Thus the findings do not support the concept of a functional coupling of opioid receptors, though the results may be explained by differences between opioid systems in the brain and peripheral tissues examined.
Evidence that 5‐hydroxytryptamine release in rat dorsal raphé nucleus is controlled by 5‐HT1A, 5‐HT1B and 5‐HT1D autoreceptors
Authors: Davidson Colin , Stamford Jonathan A.
Published: July 2012

Electrically stimulated 5‐hydroxytryptamine (5‐HT) release was monitored in slices of rat dorsal raphé nucleus (DRN) by fast cylic voltammetry. Pseudo‐single pulse stimulations (5 pulses at 100 Hz) were used to enable the effect of various receptor agonists to be seen without competition from endogenously released transmitter. The selective 5‐HT1A receptor agonist, (+)‐8‐OH‐DPAT (1.0 μm) decreased stimulated 5‐HT release to 31 ± 3% of controls. This decrease was inhibited by the 5‐HT1A receptor antagonists, (+)‐WAY‐100135 (1.0 μm) and WAY‐100635 (0.1 μm) but not by the 5‐HT1D/B antagonist, GR127935 (0.05 μm). The selective 5‐HT1B receptor agonist, CP‐93129 (0.3 μm) decreased stimulated 5‐HT release to 61 ± 4% of control. This effect was antagonized by the 5‐HT1B receptor antagonist, isamoltane (0.5 μm) but not by (+)‐WAY‐100135. The 5‐HT1D agonist, sumatriptan (0.5 μm) decreased stimulated 5‐HT release to 52 ± 2 % of controls. This decrease was blocked by GR‐127935 but not by WAY‐100635. These results suggest that 5‐HT release in the rat DRN is under the control of 5‐HT1A, 5‐HT1B and 5‐HT1D autoreceptors.
Ca2+ entry activated by emptying of intracellular Ca2+ stores in ileal smooth muscle of the rat
Authors: Ohta Toshio , Kawai Kazue , Ito Shigeo , Nakazato Yoshikazu
Published: July 2012

1 The effects of depletion of intracellular Ca2+ stores on muscle tension and the intracellular Ca2+ concentration ([Ca2+])i were studied in fura‐2 loaded longitudinal smooth muscle cells of the rat ileum.

2 After exposure to a Ca2+‐free solution, application of Ca2+ caused a small contraction and a rise in [Ca2+]i, both of which were potentiated when the muscle was challenged with carbachol or caffeine before the addition of Ca2+.

3 Cyclopiazonic acid (CPA), a specific inhibitor of sarcoplasmic reticulum Ca2+‐ATPase, dose‐dependently decreased tension development and the rises in [Ca2+]i induced by carbachol and caffeine in the Ca2+‐free solution, but conversely increased the Ca2+‐induced responses even in the presence of the voltage‐dependent Ca2+ channel blockers, methoxyverapamil and nifedipine.

4 The contraction and rise in [Ca2+]i evoked by Ca2+ gradually declined with time after removal of CPA, while the reverse was the case for the responses to carbachol and caffeine.

5 The Ca2+‐induced contraction and rise in [Ca2+]i in the presence of CPA were inhibited by the replacement of Na+ with K+ or Cs+, and by the addition of Cd2+, Ba2+, Ni2+ or La3+.

6 The influx of Mn2+ was much greater in extent in the presence of CPA than in its absence.

7 These results suggest that the emptying of intracellular Ca2+ stores may activate Ca2+ influx not associated with voltage‐dependent Ca2+ channels in the rat ileal smooth muscle.
Regulation of prostaglandin production by nitric oxide; an in vivo analysis
Authors: Salvemini Daniela , Settle Steven. L. , Masferrer Jaime. L. , Seibert Karen , Currie Mark. G. , Needleman Philip
Published: July 2012

1 Endotoxin E. Coli lipopolysaccharide (LPS)‐treatment in conscious, restrained rats increased plasma and urinary prostaglandin (PG) and nitric oxide (NO) production. Inducible cyclo‐oxygenase (COX‐2) and nitric oxide synthase (iNOS) expression accounted for the LPS‐induced PG and NO release since the glucocorticoid, dexamethasone inhibited both effects. Thus, LPS (4 mg kg−1) increased the plasma levels of nitrite/nitrate from 14 ± 1 to 84 ± 7 μm within 3 h and this rise was inhibited to 35 ± 1 μm by dexamethasone. Levels of 6‐keto PGF1α in the plasma were below the detection limit of the assay (< 0.2 ng ml−1). However, 3 h after the injection of LPS these levels rose to 2.6 ± 0.2 ng ml−1 and to 0.7 ± 0.01 ng ml−1 after LPS in rats that received dexamethasone.

2 The induced enzymes were inhibited in vivo with selective COX and NOS inhibitors. Furthermore, NOS inhibitors, that did not affect COX activity in vitro markedly suppressed PG production in the LPS‐treated animals. For instance, the LPS‐induced increased in plasma nitrite/nitrate and 6‐keto PGF1α at 3 h was decreased to 18 ± 2 μm and 0.5 ± 0.02 ng ml−1, 23 ± 1 μm and 0.7 ± 0.01 ng ml−1, 29 ± 2 μm and 1 ± 0.01 ng ml−1 in rats treated with LPS in the presence of the NOS inhibitors NG‐ monomethyl‐l‐arginine, NG‐nitro arginine methyl ester and aminoguanidine, respectively.

3 The intravenous infusion of the NO donors sodium nitroprusside (SNP) or glyceryl trinitrate (GTN) increased prostaglandin production in normal animals (for instance urinary PGE2 excretion was increased from 96 ± 10 to 576 ± 12 pg min−1 and 400 ± 24 pg min−1 in the presence of GTN or SNP respectively).

4 Proteinuria was measured in order to evaluate the roles of NO and PG in renal damage associated with the in vivo injection of LPS. Interestingly, dexamethasone and the NOS inhibitors attenuated proteinuria in the LPS‐treated rats. The COX inhibitors had no effect. It therefore appears that NO and not PG contributes to the LPS‐induced renal damage; these findings support the potential use of NOS inhibitors in the treatment of renal inflammation.

5 This study demonstrates the regulatory contribution of NO on the in vivo production of prostanoids and suggests that in inflammatory diseases that are driven by both NO and the prostaglandins, NOS inhibitors may act to reduce inflammation by the dual inhibition of cytotoxic NO and pro‐inflammatory PG.
Effects of the tachykinin NK1 receptor antagonist, RP 67580, on central cardiovascular and behavioural effects of substance P, neurokinin A and neurokinin B
Authors: Culman Juraj , Wiegand Brigitte , Spitznagel Heidi , Klee Sabine , Unger Thomas
Published: July 2012

1 We have investigated the effects of the non‐peptide NK1 tachykinin receptor antagonist, RP 67580, and its inactive enantiomer, RP 68651, on the cardiovascular and behavioural responses to substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) injected intracerebroventricularly (i.c.v.) in conscious rats.

2 The SP and NKA (25 pmol)‐induced increases in blood pressure (BP) and heart rate (HR) were of the same magnitude. The cardiovascular responses to both peptides were associated with excessive grooming behaviour and wet dog shakes (WDS). Relative to SP, NKA was weaker in inducing hindquarter grooming (HG), but more effective in eliciting WDS. The cardiovascular response to NKB (50 pmol) comprised an increase in BP and HR, while the behavioural response was weak.

3 RP 67580 (100 pmol), injected 10 or 30 min prior to SP, effectively inhibited the cardiovascular and behavioural responses to the peptide whereas lower doses were ineffective. Pretreatment with 500 pmol of RP 67580, 10 or 30 min prior to SP, reduced the BP response. Of the behavioural manifestations, only face washing was attenuated when the antagonist was injected 10 min before SP. At 2500 pmol, the antagonist exaggerated the BP response to the peptide without affecting the behavioural response. RP 68651 (100 or 2500 pmol) did not modify the central responses to SP.

4 Neither RP 67580 nor RP 68651 (100 pmol), affected the cardiovascular and behavioural responses to NKA or NKB.

5 Our results indicate that RP 67580 is a selective and high affinity antagonist at central NK1 tachykinin receptors in the rat.
Influence of chronic treatment with a nitric oxide donor on fatty streak development and reactivity of the rabbit aorta
Authors: Bult Hidde , De Meyer Guido R.Y. , Herman Arnold G.
Published: July 2012

1 The influence of chronic treatment with molsidomine, pro‐drug of the nitric oxide (NO) donor, 3‐morphohno‐sydnonimine (SIN‐1), on fatty streak development and release of NO and prostacyclin (PGI2) was studied in the aorta of normal and cholesterol‐fed rabbits.

2 Groups of 10 rabbits received standard diet (150 g day−1), or diets with 0.3% cholesterol, with 0.02% molsidomine or with the combination of cholesterol and molsidomine for 16 weeks. Lesion area and thickness, maximum change in isometric force (Emax and sensitivity (‐logEC50 or pD2) to constricting and relaxing agonists were assessed in segments of arch, thoracic and abdominal aorta. Bioassay was used to assess NO release.

3 Cholesterol‐induced fatty streaks tapered off towards the abdominal aorta. Area, thickness, weight and cholesterylester content of the lesions were augmented by the NO donor, whereas the hypercholesterolaemia remained unchanged. The exacerbation was attributed to co‐release of superoxide anion from the sydnonimine.

4 As fatty streaks progressed, amplitude and pD2 of acetylcholine (ACh)‐induced relaxations decreased, whereas cyclic GMP and cyclic AMP second messenger systems were not influenced, since Emax and sensitivity to SIN‐1 and forskolin remained unchanged. However, extensive lesions apparently trapped some NO, as the pD2 of authentic NO decreased.

5 The fatty streaks curtailed the biosynthesis of PGI2 and the overflow of NO from the perfused thoracic aorta. The latter defect was not restored by L‐arginine and appears to be consistent with a functional change of the endothelial muscarinic receptors.

6 The NO donor desensitized the aorta to cyclic GMP‐mediated relaxations (ACh, SIN‐1 and NO), without affecting cyclic AMP‐mediated relaxation to forskolin or constrictor responses to phenylephrine and 5‐hydroxytryptamine.

7 The drug also suppressed the ACh‐induced overflow of NO, without changing PGI2 release. This selective reduction of endothelial NO release and the desensitization of cyclic GMP‐mediated relaxations occurred independently of fatty streak formation.

8 The results indicate that chronic exposure to exogenous NO downregulates endothelial NO release and cyclic GMP‐mediated relaxations, and provide evidence for the existence of negative feedback regulations of the L‐arginine NO pathway under in vivo conditions.
Increase of meningeal blood flow after electrical stimulation of rat dura mater encephali: mediation by calcitonin gene‐related peptide
Authors: Kurosawa Mieko , Messlinger Karl , Pawlak Matthias , Schmidt Robert F.
Published: July 2012

1 The dura mater encephali of the rat was exposed and the blood flow around branches of the medial meningeal artery was monitored with a laser Doppler flowmeter. Changes in the meningeal blood flow (MBF) following electrical stimulation of the dura mater at a parasagittal site were registered. The effects of human calcitonin gene‐related peptide (h‐αCGRP) and the CGRP antagonist (h‐αCGRP8–37) on the MBF were tested.

2 Electrical stimulation with rectangular pulses of 0.5 ms, 10–20 V, 5–10 Hz and a duration of 30 s caused an increase of the MBF in 14 out of 16 rats tested. The increases were dependent on stimulus strength and frequency.

3 The increase in MBF was inhibited in a dose‐dependent manner by topical application of 0.1 ml of h‐αCGRP8–37 at concentrations of 10−7‐10−5M. The highest dose abolished the increase in MBF.

4 Topical administration of 0.1 ml of h‐αCGRP at a concentration of 10−4 M increased the basal MBF by 15% on average.

5 It is suggested that the increase in MBF following electrical stimulation of the dura mater is mediated by the release of CGRP. The contribution of the dural afferent and sympathetic and parasympathetic efferent nerve fibres to this response are discussed.
5‐HT2‐mediated bronchial responses after syngeneic lung transplantation in the rat
Authors: Tavakoli Reza , Frossard Nelly
Published: July 2012

1 The effect of lung transplantation was assessed on the subsequent bronchial responses to 5hydroxytryptamine (5‐HT) in the rat in vitro.

2 Bronchial ring segments from syngeneic lung transplant recipients, from sham‐operated and from non‐operated control animals were studied in organ baths one month after unilateral left lung transplantation.

3 Responses of the bronchial smooth muscle to 5‐HT (10−8 to 10−4M) significantly increased after lung transplantation (80.6 ± 7.6% of the maximal contractile response to acetylcholine) compared with the responses of all other controls (ca. 40% of the maximal contractile response to acetylcholine, P<0.01). pD2 values were similar for the left transplanted (5.70 ±0.11) and all other control bronchi (ranging from 5.53 to 5.82).

4 Contraction to 5‐HT was blocked by the selective 5‐HT2 antagonist, ketanserin. Responses to the selective 5‐HT2 agonist, α‐methyl‐5‐HT, were similar to those to 5‐HT; pD2 values were similar in all groups (ranging from 5.41 to 5.74).

5 The selective 5‐HT3 agonist, 1‐m‐chlorophenyl biguanide, had no contractile effect on rat bronchus, whether transplanted or not.

6 Atropine, a muscarinic cholinoceptor blocking agent, had no effect on 5‐HT‐induced bronchial contraction. Hence, acetylcholine released from nerve terminals does not play any role in the observed bronchial hyperresponsiveness to 5‐HT.

7 These results show bronchial hyperresponsiveness to 5‐HT in vitro one month after lung transplantation in the rat, mediated through 5‐HT2 receptor activation. This might be caused by upregulation of 5‐HT2 receptors in the lung after transplantation.
Characterization of kinin receptors modulating neurogenic contractions of the mouse isolated vas deferens
Authors: Maas Jonny , Rae Giles A. , Huidobro‐Toro Juan P. , Calixto João B.
Published: July 2012

1 This study analyses the receptors mediating the effects of bradykinin (BK) and analogues on neurogenic twitch contractions of the mouse isolated vas deferens evoked, in the presence of captopril (3 μm), by electrical field stimulation with trains of 4 rectangular 0.5 ms pulses of supramaximal strength, delivered at a frequency of 10 Hz every 20 s.

2 BK (0.1–300 nM) induced a graded potentiation of twitches, with an EC50 (geometric mean and 95% confidence limits) of 4.5 nM (1.7–11.6) and an Emax of 315 ± 19 mg per 10 mg of wet tissue (n = 6). Similar results were obtained in tissues challenged with Lys‐BK, [Hyp3]‐BK, Met, Lys‐BK and the selective B2 receptor agonist [Tyr(Me)8]‐BK (0.1–300 nM).

3 The selective B2 receptor antagonists, Hoe 140 (1–10 nM) and NPC 17731 (3–30 nM), caused graded rightward shifts of the curve to BK‐induced twitch potentiation, yielding apparent pA2 values of 9.65 ± 0.09 and 9.08 ±0.13, respectively, and Schild plot slopes not different from 1. Both antagonists (100 nM) failed to modify similar twitch potentiations induced by substance P (3 nM) or endothelin‐1 (1 nM). Preincubation with the selective B1 receptor antagonist, [Leu8des‐Arg9‐BK (1 μm), increased the potentiating effect of BK on twitches at 30–300 nM.

4 In contrast to BK, the selective B1 receptor agonist, [des‐Arg9‐BK (0.3–1000 nM) reduced the amplitude of twitches in a graded fashion, with an IC50 of 13.7 nM (10.4–16.1) and an Imax of 175 ± 11 mg (n = 4). The twitch depression induced by [des‐Arg9]‐BK (300 nM) was not affected by Hoe 140 (30 nM) or NPC 17731 (100 nM), but was abolished by the selective B1 receptor antagonist, [Leu8des‐Arg9‐BK (1 μm), which did not modify the twitch inhibitory effect of clonidine (1 nM) or morphine (300 nM).

5 In non‐stimulated preparations, BK (100 nM) also potentiated, in a Hoe 140‐sensitive (10 nM) manner, the contractions induced by ATP (100 μm), but not by noradrenaline (10 μm), whereas [des‐Arg9]‐BK (300 nM) did not modify the contractions induced by either agonist.

6 It is concluded that the mouse vas deferens expresses both B1 and B2 receptors, which modulate sympathetic neurotransmission in opposing ways. Neurogenic contractions are inhibited by stimulation of possibly prejunctional B1 receptors, whereas activation of B2 receptors increases twitch contractions, in part by amplifying the responsiveness of the smooth muscle cells to the sympathetic co‐transmitter ATP.
G‐protein involvement in muscarinic receptor‐stimulation of inositol phosphates in longitudinal smooth muscle from the small intestine of the guinea‐pig
Authors: Prestwich S.A. , Bolton T.B.
Published: July 2012

Aluminium fluoride (AlF), pertussis toxin (PTX) and cholera toxin (ChTX) have been used to examine the involvement of G‐proteins during muscarinic acetylcholine receptor (AChR) stimulation of inositol phospholipid hydrolysis in fragments of longitudinal smooth muscle from the small intestine of the guinea‐pig.

Carbachol (CCh) induced time‐ and concentration‐dependent increases in [3H]‐inositol monophosphates, [3H]‐inositol (1,4) bisphosphate, [3H]‐inositol (1,3,4) trisphosphate, [3H]‐inositol (1,4,5) trisphosphate ([3H]‐Ins (1,4,5)P3) and [3H]‐inositol tetrakisphosphates measured by h.p.l.c. These increases were inhibited >95% in the presence of the muscarinic AChR antagonist atropine (0.5 μm).

AlF transiently increased the basal levels of [3H]‐Ins (1,4,5)P3 but increases in the levels of the other [3H]‐inositol phosphates occurred more slowly. CCh‐induced increases in the levels of all the [3H]‐inositol phosphates were strongly inhibited in the presence of AlF.

PTX had no effect on basal levels of any of the [3H]‐inositol phosphates but reduced the effects of CCh on these; ChTX had no effects on either basal or CCh‐stimulated levels.

It was concluded that muscarinic AChR‐stimulated increases in the levels of [3H]‐inositol phosphates occur via both a PTX‐sensitive G‐protein and a PTX‐insensitive mechanism. The actions of AlF may suggest the involvement of an inhibitory G‐protein in the regulation of muscarinic AChR‐stimulated inositol phospholipid turnover.
Increase in tone and intracellular Ca2+ in rabbit isolated ear artery by platelet‐derived growth factor
Authors: Hughes A.D.
Published: July 2012

The effect of platelet‐derived growth factor (PDGF‐AB) on tone and intracellular Ca2+ ([Ca2+]i) was examined in rabbit isolated ear arteries. Arteries were mounted in a myograph and loaded with the Ca2+‐sensitive fluorescent indicator, fura‐2, for concurrent measurements of isometric force and [Ca2+]i.

PDGF‐AB contracted rabbit ear artery in a concentration‐dependent manner. PDGF‐AB induced tone was associated with a rise in [Ca2+]i. In the presence of noradrenaline, PDGF‐AB induced a similar rise in [Ca2+]i but contraction in response to PDGF‐AB in the presence of noradrenaline was increased compared with PDGF‐AB alone.

PDGF‐AB‐induced rise in [Ca2+]i and tone were abolished by removal of extracellular Ca2+ (with addition of BAPTA, a Ca2+ chelator), and by preincubation with a dihydropyridine calcium channel blocker, (−)−202 791. Bistyrphostin, a selective inhibitor of tyrosine kinases, also inhibited PDGF‐AB‐induced tone, but had no effect on noradrenaline‐ or potassium‐induced tone.

PDGF‐AB contracts rabbit ear artery by increasing Ca2+ entry through voltage‐operated calcium channels. This effect involves activation of a tyrosine kinase.
Vascular pharmacology of methylene blue in vitro and in vivo: a comparison with NG‐nitro‐l‐arginine and diphenyleneiodonium
Authors: Wang Yong‐Xiang , Cheng Xing , Pang Catherine C.Y.
Published: July 2012

The vascular effects of the soluble guanylyl cyclase inhibitor, methylene blue as well as the nitric oxide (NO) synthase inhibitors, NG‐nitro‐l‐arginine (l‐NOARG) and diphenyleneiodonium (DPI) were studied in rat isolated aortic rings and conscious, unrestrained rats.

Acetylcholine (ACh) and sodium nitroprusside (SNP) caused concentration‐dependent relaxation of preconstricted aortic rings. Both methylene blue (1 × 10−5m) and l‐NOARG (3 × 10−5m) abolished ACh‐induced relaxation; however, methylene blue but not l‐NOARG shifted the concentration‐response curve of SNP to the right.

In conscious rats, i.v. infusion of methylene blue (1.1 × 10−5mol kg−1 min−1), at a concentration which reduced the aortic tissue level of cyclic GMP by 50%, did not significantly alter mean arterial pressure (MAP) and heart rate (HR). In contrast, i.v. bolus injection of l‐NOARG (1.5 × 10−4 mol kg−1) markedly increased MAP and decreased HR.

Both ACh and SNP dose‐dependently decreased MAP in conscious rats. Methylene blue did not alter the magnitude or duration of ACh‐ or SNP‐induced depressor responses. l‐NOARG, on the other hand, significantly though incompletely, reduced the magnitude and duration of the depressor response to ACh but not SNP. The depressor response to ACh or SNP was not altered by pretreatment with indomethacin (1.4 × 10−5 mol kg−1) or capsaicin (3.3 × 10−4 mol kg−1).

NG‐nitro‐l‐arginine methyl ester (l‐NAME) also caused dose‐dependent increases in MAP in conscious rats. Both methylene blue and DPI (1 × 10−5 mol kg−1) selectively shifted the dose‐pressor response curve of l‐NAME to the right.

These results suggest that: (1) the inhibition of endogenous NO biosynthesis does not necessarily lead to pressor response in vivo, (2) l‐NOARG may not produce pressor response solely via the inhibition of endogenous endothelial NO biosynthesis, and (3) the depressor responses to ACh and SNP may not involve the release of NO or prostanoids or afferent nerve transmitters.
Inotropic changes induced by fluoroaluminates in rabbit left atrial muscles: possible involvement of G proteins
Authors: Hattori Yuichi , Imamura Michialki , Akaishi Yasuhiro , Kanno Morio
Published: July 2012

The effects of fluoroaluminate complexes (NaF plus AlCl3) on force of contraction, cyclic AMP accumulation and phosphoinositide hydrolysis were examined in rabbit left atrial muscles.

Fluoroaluminates (1–10 mm NaF + 10 μm AlCl3) produced a biphasic inotropic response which was composed of an early small decline and subsequent increase in force of contraction. In the presence of the Al3+ chelator, deferoxamine (100 μm), the positive inotropic response was completely abolished and a sustained negative inotropic response appeared, suggesting that only the positive inotropic response is due to the action of fluoroaluminates.

The positive inotropic effect of fluoroaluminates was associated with a significant increase in the total duration of a single contraction; the time to peak tension and relaxation time were prolonged. In contrast, these parameters were substantially abbreviated by isoprenaline or histamine.

When force of contraction was increased by isoprenaline or histamine, the addition of fluoroaluminates caused a marked negative inotropic effect, which was eliminated by pretreatment with pertussis toxin.

Fluoroaluminates did not cause a significant increase in cyclic AMP content at concentrations of NaF in the range of 1–10 mm. However, the content of cyclic AMP was greatly elevated by fluoroaluminates when the atrial muscles were pretreated with pertussis toxin.

Accumulation of [3H]‐inositol monophosphate in atrial muscle strips prelabelled with myo‐[3H]‐inositol was significantly increased by fluoroaluminates at concentrations of NaF over 1 mm. The phosphoinositide response to fluoroaluminates remained unchanged with pertussis toxin pretreatment.

These results indicate that, in rabbit left atrial muscles, fluoroaluminates produce a positive inotropic effect which may be mediated by Gq but not by Gs proteins; they produce a negative inotropic effect possibly through Gi only when Gs is activated with other agents.
The biphasic response of rat vesical smooth muscle to ATP
Authors: Bolego Chiara , Pinna Christian , Abbracchoi Maria P. , Cattabeni Flaminio , Puglisi Lina
Published: July 2012

Adenosine‐5′‐triphosphate (ATP) is known to exert a variety of biological effects via the activation of either ionotropic P2X‐ or G‐protein coupled P2Y‐purinoceptor subtypes. In this study the effects induced by ATP and ATP analogues on rat bladder strips were characterized at resting tone and in carbachol‐prestimulated tissues.

ATP exerted a clear concentration‐dependent biphasic response, which was maximal at 1 mM concentration and was characterized by an immediate and transient contraction, followed by a slower sustained relaxation. The receptor mediating contraction was susceptible to desensitization by ATP and by the ATP analogue, α,β‐methyleneATP (α,β‐meATP) showing the typical features of the P2X‐purinoceptor; conversely, ATP‐evoked relaxation did not undergo tachyphylaxis following either ATP or α,β‐meATP.

The slower and sustained relaxant phase seemed to be due to activation of P2Y‐purinoceptors, based on responses obtained with the P2Y agonist, 2‐methyl‐thioATP (2‐meSATP) and, more importantly, based on the clear involvement of the G‐proteins. In fact, the G‐protein activator, guanosine 5′‐O‐(3‐thiotriphosphate) (GTPγS) significantly potentiated and the G‐protein blocking agent, guanosine 5′‐O‐(2‐thio‐diphosphate) (GDPβS) completely abolished the ATP‐induced relaxation. No effects were exerted by these two G‐protein modulators on the ATP‐induced contraction.

The relaxant component of the ATP response of bladder tissue was not significantly influenced by nitro‐benzyl‐thioinosine (NBTI) or by 8‐phenyltheophylline (8‐PT), suggesting that the contribution of the ATP metabolite adenosine to this response was negligible. Moreover, relaxation evoked by ATP and by the adenosine analogue, 5′‐N‐ethylcarboxamidoadenosine (NECA) was additive.

Suramin was unable to modify either the relaxant or the contractile responses of bladder strips to ATP. However, when tested on the concentration‐response curve to the slowly hydrolysable P2x‐agonist α,β‐meATP, a rightward shift was detected, suggesting that ATP contractile responses are mediated by suramine‐sensitive P2x‐purinoceptors.

Uridine‐5′‐triphosphate (UTP) only induced a rapid and concentration‐dependent contraction of the rat bladder preparation, which was not desensitized by pre‐exposure to α,β‐meATP, suggesting that UTP responses were not mediated by the ‘classical’ P2X‐purinoceptor.

It is therefore concluded that both P2X‐ and P2Y‐purinoceptors, which mediate ATP‐induced contraction and relaxation, respectively, are present in rat bladder. Moreover, removal of epithelium did not affect ATP‐elicited contraction, whereas ATP‐induced relaxation was significantly augmented. These data suggest that P2x‐ and P2y‐ purinoceptors are localized in smooth muscle cells and that the relaxant response is probably modulated by excitatory factor(s) released by epithelial cells.
Vascular actions of thrombin receptor‐derived polypeptides: structure‐activity profiles for contractile and relaxant effects in rat aorta
Authors: Laniyonu Adebayo A. , Hollenberg Morely D.
Published: July 2012

Using endothelium‐denuded and intact rat aortic rings, we have determined the contractile and relaxant structure‐activity profile for a series of thrombin receptor‐derived polypeptides (TRPs) based on the human and rat receptor sequences: SFLLR (P5), SFLLR‐NH2 (P5‐NH2) SFFLR (Rat P5), SFFLR‐ NH2 (Rat P5‐NH2), SFLLRNP (P7), SFLLRNP‐NH2 (P7‐NH2), SFFLRNP (Rat P7), SFFLRNP‐NH2 (Rat P7‐NH2), and SFLLRNPNDKYEPF (P14).

A contractile response to thrombin and the TRPs in the endothelium‐denuded aortic tissue was minimal or absent in preparations obtained from animals weighing less than 180 g (<6 weeks of age), but increased with animal size, plateauing in tissues derived from animals weighing between 320 and 420 g (about 9 to 14 weeks of age). In contrast, the contractile responses to KC1 and noradrenaline did not differ in the tissues and relaxant responses to the TRPs in endothelium‐intact aortic preparations were comparable for tissues obtained from either young (≤ 180 g) or older (≤ 320 g) animals.

The contractile response of the endothelium‐denuded preparation to thrombin and the TRPs showed marked cross‐desensitization: the relaxation response of the intact rings did not desensitize to the TRPs.

The relative potencies for the TRPs in the aortic contraction assay were comparable to those for the relaxation assay, but were distinct from the relative potencies we measured previously in a rat gastric longitudinal muscle contraction assay. Further, P5 behaved as a partial agonist in the aortic contraction assay, whereas it had been observed to be a full agonist in the gastric contraction assay.

The contractile activity of P5‐NH2 in endothelium intact aortic rings was low or absent, but in the presence of the nitric oxide synthase inhibitor, Nω‐nitro‐L‐arginine‐methyl ester (L‐NAME), the contractions in the intact preparation were equivalent to the response of the endothelium‐denuded preparation in the absence of L‐NAME.

The contractile response of the endothelium‐denuded aortic preparation to P5‐NH2 was inhibited by nifedipine and the kinase C antagonist, chelerythrine, but was resistant to the action of indomethacin, tetrodotoxin and the tyrosine kinase inhibitor, genistein.

We conclude that the receptor system for the TRPs in the aortic smooth muscle elements, responsible for the contractile response, is similar to the aortic endothelial cell receptor responsible for the relaxation response, but is distinct from the receptor that we have previously characterized in gastric longitudinal smooth muscle, results pointing to the presence of receptor subtypes in the vascular and gastric smooth muscle elements.
Prejunctional facilitatory α1‐adrenoceptors in the rat urinary bladder
Authors: Somogyi G.T. , Tanowitz M. , de Groat W.C.
Published: July 2012

The effect of activation of α1‐adrenoceptors on acetylcholine (ACh) release and neurally evoked contractile responses induced by electrical field stimulation was investigated in smooth muscle strips from the rat urinary bladder.

Neurogenic contractions were facilitated by the α1adrenoceptor agonists, phenylephrine (PE) (2–128 μm) and methoxamine (2–128 μm) in a dose‐dependent manner. These agents also increased small amplitude spontaneous contractions of bladder strips and in 10% of strips increased basal tone. However, contractions elicited by exogenous ACh (1–10 μm) were not affected by α1agonists.

The magnitude of the PE facilitation was higher at lower frequencies (1–5 Hz) or at submaximal intensities of stimulation and at lower Ca2+ concentrations (0.5‐1 mM). The selective α1adrenoceptor antagonist, terazosin (TRZ) (0.05‐1 μm), competitively inhibited (pA2 value: 8.6) the PE facilitation of the neurally evoked contractions but not the PE induced increase of spontaneous contractions.

[3H]‐noradrenaline (NA) and [14C]‐ACh release evoked by electrical field stimulation were increased (140% and 173%, respectively) by 2μm PE. TRZ (0.05‐0.1 μm) blocked the PE facilitation of ACh release but not the facilitation of NA release. TRZ alone did not alter the release of ACh or NA nor the amplitude of the neurogenic contractions.

PE (2 μ) did not alter the basal release of ACh but did increase (by 180%) the basal release of NA. Desipramine (2 μm) blocked this effect of PE and also the PE‐facilitation of evoked ACh and NA release.

It is concluded that cholinergic terminals in the rat urinary bladder exhibit α1‐adrenoceptors which can facilitate the release of transmitter. However, under the conditions of our experiments it appears that cholinergic transmission is not modulated by α1 adrenergic mechanisms. Further studies are necessary to determine whether these receptors can be activated by endogenous noradrenaline released within the bladder.
SPECIAL REPORT Regulation of muscle glycogen metabolism by CGRP and amylin: CGRP receptors not involved
Authors: Beaumont Kevin , Pittner Richard A. , Moore Candace X. , Wolfe‐Lopez Deborah , Prickett Kathryn S. , Young Andrew A. , Rink Timothy J.
Published: July 2012

The aim of the present study was to determine whether amylin and calcitonin gene‐related peptide (CGRP) act through shared or distinct receptors to inhibit insulin‐stimulated incorporation of [14C]‐glucose into glycogen. Rat amylin was 3 fold more potent than either rat αCGRP or rat βCGRP at reducing glycogen synthesis from [14C]‐glucose in insulin‐treated rat soleus muscle. This action was blocked by peptide antagonists, with the rank order of potency being AC187> salmon calcitonin 8–32 (sCT8.32) > h‐αCGRP8–37 for antagonism of either amylin or CGRP. The antagonist potency order correlated with affinity for amylin receptors measured in rat nucleus accumbens but not CGRP receptors measured in rat L6 muscle cells. Inhibition of glucose incorporation into glycogen by amylin and CGRP appears to be mediated by shared receptors that have the pharmacological characteristics of amylin receptors, and are distinct from previously described CGRP receptors.
Release of endothelium‐derived hyperpolarizing factor (EDHF) by M3 receptor stimulation in guinea‐pig coronary artery
Authors: Hammarström Anna K.M. , Parkington Helena C. , Coleman Harold A.
Published: July 2012

The muscarinic receptor subtype(s) involved in the release of endothelium‐derived hyperpolarizing factor (EDHF) were studied in the guinea‐pig coronary artery by recording the membrane potential in the smooth muscle cells with intracellular microelectrodes.

Acetylcholine (ACh, pD2 6.68) was 10 times more potent than the M2 agonist, oxotremorine (pD2 5.65) and 500 fold more potent than the M1 agonist, McN‐A‐343 (pD2 3.95) in evoking the EDHF hyperpolarization.

The M3 muscarinic antagonist, 4‐diphenylacetoxy‐N‐methylpiperidine methiodide (4‐DAMP) was the most potent (pA2 9.5) in inhibiting the release of EDHF evoked by ACh, being more potent than pirenzepine (pA2 6.7), and AFDX‐116 (pA2 6.1) which preferentially block M1 and M2 receptors, respectively.

These results suggest that EDHF is released from the endothelium of the guinea‐pig coronary artery upon the activation of the muscarinic M3 receptor subtype.
Extended concentration‐response curves used to reflect full agonist efficacies and receptor occupancy‐response coupling ranges
Authors: Lew Michael J.
Published: July 2012

An approach is described for generating extended agonist concentration‐response curves where the responses are unconstrained by the normal tissue maximum response. Functional antagonism is employed to hold the tissue state in the range where any change in stimulus can be translated into a measurable response.

The maximum response of these extended concentration‐response curves provides an index of intrinsic activity reflecting the agonist efficacy and the receptor occupancy‐response coupling range.

The use of this approach is illustrated with extended concentration‐response curves for noradrenaline (NA), vasopressin, acetylcholine (ACh), and 5‐methylfurmethide in the small mesenteric and tail arteries of the rat. Both NA and vasopressin can maximally activate the arteries, but the new protocol shows that NA can produce more cellular activation than vasopressin in the tail artery. Both ACh and 5‐methylfurmethide are full agonists but ACh has a higher intrinsic activity than 5‐methylfurmethide. The ACh muscarinic receptors in the mesenteric artery have a larger occupancy‐response range than the ACh muscarinic‐receptors in the tail artery, and the α‐adrenoceptors in the tail artery appear to have a larger occupancy‐response coupling range than those in the mesenteric artery.

This approach extends our ability to compare the efficacies of full agonists, and to compare the occupancy‐response coupling ranges of receptors that can normally maximally activate the assay tissue. This is achieved without the use of an irreversible antagonist and should be applicable to many receptors and pharmacological assay systems where responses are stable and functional antagonists are available.
Effects of the two enantiomers, S‐16257‐2 and S‐16260‐2, of a new bradycardic agent on guinea‐pig isolated cardiac preparations
Authors: Pérez Onésima , Gay Pilar , Franqueza Laura , Carron Rosalia , Valenzuela Carmen , Delpon Eva , Tamargo Juan
Published: July 2012

The electromechanical effects of two enantiomers, S‐16257‐2 (S57) and S‐16260‐2 (R60), were studied and compared in guinea‐pig isolated atria and ventricular papillary muscles. The possible stereoselectivity of the interaction on the cardiac Na+ channel was analysed by comparing the effects of the two enantiomers on the onset and recovery kinetics of the frequency‐dependent Vmax block.

In spontaneously beating right atria, S57 and R60 (10−8 m‐10−4 m) exerted a negative chronotropic effect (pIC50 = 5.07 ±0.19 and 4.76 ±0.18, respectively) and prolonged the sinus node recovery time, this effect being more marked with S57. In electrically driven left atria, S57 decreased (P<0.05) contractile force only at 10−4 m and R60 at concentrations ≤5 × 10−5m, whereas in papillary muscles the negative inotropic effect appeared at concentrations > 10−5 m.

In papillary muscles driven at 1 Hz, S57 and R60 at concentrations higher than 5 × 10−6 m produced a concentration‐dependent decrease in the maximum upstroke velocity (Vmax) and amplitude of the cardiac action potential without altering the resting membrane potential or the action potential duration. S57 and R60 had no effect on the characteristics of the slow action potentials elicited by isoprenaline in ventricular muscle fibres depolarized in high K+ (27 mM) solution.

At 5 × 10−5 m, S57 and R60 produced a small tonic Vmax block. However, in muscles driven at rates between 0.5 and 3 Hz both enantiomers produced an exponential decline in Vmax (frequency‐dependent Vmax block) which augmented at higher rates of stimulation. The onset and offset rates of the frequency‐dependent Vmax block were similar for both drugs. Both S57 and R60 prolonged the recovery time constant from the frequency‐dependent block from 20.1 ±2.9 ms to 2–3 s.

At 5 × 10−5m, S57 and R60 shifted the membrane responsiveness curve in a hyperpolarizing direction.

It can be concluded that S57 and R60, the two enantiomers of the new bradycardic agent, produced a similar frequency‐dependent Vmax block which indicated that the interaction with the Na+ channel was not stereospecific. The analysis of the onset and offset kinetics of the frequency‐dependent Vmax block suggested that both enantiomers can be considered as Na+ channel blockers with intermediate kinetics, e.g., class IA antiarrhythmic drugs.
The roles of spinal adenosine receptors in the control of acute and more persistent nociceptive responses of dorsal horn neurones in the anaesthetized rat
Authors: Reeve Alison J. , Dickenson Anthony H.
Published: July 2012

We describe here the effects of intrathecal selective adenosine receptor agonists on acute and more persistent evoked responses of dorsal horn nociceptive neurones recorded in intact rats anaesthetized with halothane.

The effects of the A1 receptor agaonist, N6‐cyclopentyladenosine and the non‐selective agonist 2‐chloroadenosine as well as the A2a receptor agonist, 2‐p‐(2‐carboxyethyl) phenethylamino‐5″‐N‐ethylcarboxamidoadenosine hydrochloride were gauged on the C‐, Aδ‐, Aβ‐fibre, post‐discharge and wind‐up responses produced by peripheral tanscutaneous stimulation. The antagonists, theophylline and 8(p‐sulphophenyl) theophylline were also tested alone and to reverse the agonist effects.

Subcutaneous formalin (5%) was used to produce a more prolonged nociceptive response initiated by peripheral inflammation.

Both N6‐cyclopentyladenosine and 2‐chloroadenosine produced inhibitions of the C‐fibre evoked responses, wind‐up and post‐discharge of the neurones with no significant effects on the AP responses. By contrast, the Aδ evoked responses were facilitated over the same time course and dose‐range as the inhibitions. N6‐cyclopentyladenosine was more potent and effective than 2‐chloroadenosine. In marked contrast to these agonists, the A2a agonist produced only weak non‐specific inhibitions. Theophylline and 8(p‐sulphophenyl) theophylline alone had no effect on the acute responses but prevented or reversed inhibitory effects of N6‐cyclopentyladenosine.

The formalin response was markedly inhibited by spinal N6‐cyclopentyladenosine with both the acute first phase and more prolonged second phase being dose‐dependently inhibited. N6‐cyclopentyladenosine was considerably more potent on the formalin response than on the other neuronal measures.

The results suggest a role of adenosine A1 receptors in the modulation of both acute and inflammatory nociception in the spinal cord.
Effects of pinacidil on arterial and venous resistances and mean circulatory filling pressure in rats
Authors: Waite Robert P. , Lim Su Lin , Pang Catherine C.Y.
Published: July 2012

The effects of the potassium channel opener, pinacidil, on mean arterial pressure (MAP), mean circulatory filling pressure (MCFP), total peripheral resistance (TPR), cardiac output (CO) and resistance to venous return (Rv) were studied in rats.

In pentobarbitone‐anaesthetized rats given mecamylamine (ganglionic blocker, 3.7 μg kg−1) and noradrenaline (1.5 μg kg−1 min−) to suppress autonomic reflexes, pinacidil (60 and 180 μg kg−1 min−1), relative to the vehicle, reduced MAP and TPR in a dose‐dependent manner but did not significantly alter CO, MCFP or Rv.

Pinacidil (10–300 μg kg−1 min−1) caused similar increases in MCFP, an inverse index of venous compliance, and similar dose‐dependent reductions in mean arterial pressure (MAP) in conscious, intact rats and rats infused with the ganglionic blocker, hexamethonium (150 μg kg−1 min−1). In rats with vasomotor tone elevated by the infusion of noradrenaline (1.5 μg kg−1 min−1), pinacidil caused markedly greater depressor responses but did not significantly alter MCFP.

Our results show that pinacidil is an efficacious vasodilator of arterial resistance blood vessels but has little venodilator activity.