bluuebunny/crossref_metadata_2025 huggingface dataset:
The interaction of benzodiazepines with thyrotropin‐releasing hormone receptors on clonal pituitary cells
Authors: Joels Lesley A. , Drummond Alan H.
Published: July 2012

Seven benzodiazepines were investigated for their ability to interact with receptors for thyrotropin‐releasing hormone (TRH) on GH3 and GH4C1 pituitary tumour cells.

Midazolam and chlordiazepoxide were the most potent inhibitors of TRH‐induced [3H]‐inositol phosphate formation with Ki values in the low micromolar range. The antagonism was competitive in nature and was increased in potency at sub‐physiological temperatures.

None of the agents examined antagonized bombesin‐induced [3H]‐inositol phosphate formation in GH4C1 cells.

While the ability of benzodiazepines to interact with the GABA receptor‐chloride channel ionophore is markedly stereospecific, little difference was evident in the ability of (+)− and (−)−4‐methylmidazolam (Ro 21–5656 and Ro 21–5657) to compete with TRH at its receptor.

Recently it has been suggested that, in contrast to phosphatidylinositol hydrolysis, the TRH‐induced breakdown of phosphatidylinositol polyphosphates is transient in clonal pituitary cells. Addition of chlordiazepoxide to TRH‐stimulated GH3 cells up to 60 min after initiating the reaction leads, however, to an immediate decline in the cellular content of inositol trisphosphate. This indicates that TRH‐induced phosphatidylinositol 4,5‐bisphosphate hydrolysis is not transient.
Augmentation by external Mg ions of β‐adrenoceptor‐mediated actions in the longitudinal muscle of rat uterus
Authors: Maruta Keiji , Osa Takuro
Published: July 2012

The longitudinal muscle isolated from the uterus of oestrogen‐treated rats was not spontaneously active in Locke solution, and electrical stimulation evoked phasic contraction. Isoprenaline (3 × 10−11‐10−8m) and dibutyryl cyclic AMP (db cyclic AMP, 0.1–0.8 mm) depressed the phasic contraction; the depression was enhanced in the presence of 0.6 mm Mg.

The contracture generated by 40 mm K was partially relaxed by isoprenaline (10−11‐10−8m) and db cyclic AMP (0.1–0.8 mm). Mg (0.6 mm) enhanced the isoprenaline‐induced relaxation, but not that induced by db cyclic AMP.

The membrane potential of the muscle was −61 mV, and electrical stimulation induced an action potential which consisted of spike and plateau components. Application of isoprenaline and db cyclic AMP mainly reduced the duration of the plateau potential. The effect was potentiated by 0.6 mm Mg.

The membrane was hyperpolarized, accompanied by a decrease in membrane resistance, when 10−8 m isoprenaline or 0.8 mm db cyclic AMP was applied. The effects of isoprenaline were prominently augmented in the presence of 1.2 mm Mg, while those of db cyclic AMP were slightly potentiated.

Forskolin (0.1 μm) or papaverine (10 μm) inhibited the phasic contraction and the K‐contracture. The effect on the phasic contraction was potentiated by 0.6 mm Mg, while that on the K‐contracture was not affected.

Forskolin shortened the action potential at 0.3 μm, and hyperpolarized the membrane with a decrease in membrane resistance at 3.0 μm. The membrane effects were augmented by 0.6 and 1.2 mm Mg, respectively.

It was hypothesized that external Mg ions could affect at least two processes involved in actions at β‐adrenoceptors on rat myometrium; receptor‐agonist interaction and cyclic AMP‐mediated inhibition of membrane excitability.
Tolerance to cromakalim in the rat uterus in vivo
Authors: Downing Sandra J. , Miller M. , Hollingsworth> M.
Published: July 2012

Cromakalim (0.1 and 1 mg kg−1) produced inhibition of uterine contractions and falls in mean blood pressure in ovariectomized, non‐pregnant rats, the durations of which were dose‐dependent. Frequency of contractions was inhibited selectively compared to amplitude.

The durations of the uterine effect of cromakalim (1 mg kg−1), when given at 12 h intervals, were less after the second, third and fourth doses compared to the first dose in non‐pregnant rats. In ovariectomized rats treated from day 18 of pregnancy, using the same experimental design, no uterine relaxant effects were seen to the third and fourth doses. The timing of delivery and foetal viability were unaffected by cromakalim.

The sensitivity of the uterus to cromakalim was tested using small doses before and after three cromakalim doses (1 mg kg−1) given at 8 h intervals in non‐pregnant rats. This regime resulted in a 25 fold decrease in the sensitivity of the uterus to cromakalim.

Cromakalim can produce long‐lasting inhibition of uterine contractions in the rat after bolus i.v. dose but it exhibits little selectivity relative to its vasodepressor action and there appears to be tolerance to the uterine relaxant action of cromakalim in vivo.
Evidence that central 5‐hydroxytryptaminergic neurones are involved in the anxiolytic activity of buspirone
Authors: Carli M. , Prontera C. , Samanin R.
Published: July 2012

A two‐compartment exploratory test was used to assess the role of central 5‐hydroxytryptaminergic neurones in the anxiolytic activity of buspirone in rats.

Buspirone 0.1 mg kg−1, administered subcutaneously 15 min before testing, significantly increased black‐white transitions (BWT) in control rats but had no effect in animals injected intra‐cerebroventricularly one week before with 150 μg 5,7‐dihydroxytryptamine (in 20 μl).

Infusion of buspirone in the median raphe (but not in the dorsal raphe) significantly enhanced BWT, at doses from 1 μg to 10 μg (in 0.5 μl). Buspirone 5 and 10 μg, but not 1 μg, administered in the median raphe, significantly enhanced motor activity of rats during the first 10 min of testing in the activity cages.

The effect on BWT of 5 μg buspirone in the median raphe was completely antagonized in animals which had received either 5,7‐dihydroxytryptamine intraventricularly, 150 μg (in 20 μl), one week before or an infusion of 0.1 μg (in 0.5 μl) (−)‐propranolol in the same area 5 min before. (−)‐Propranolol infused in the median raphe did not modify the effect of buspirone on locomotion.

Infusion of 5 μg buspirone (in 0.5 μl) in the median raphe significantly enhanced punished responses in a conflict test with no effect on unpunished responding. Buspirone infused in the dorsal raphe had no effect on punished or unpunished responding over a wide dose range.

The results indicate that at the relatively low dose used in the present study buspirone produces an anxiolytic effect by acting on central 5‐hydroxytryptaminergic neurones. It is likely that activation of 5‐hydroxytryptamine1A‐receptors in the median raphe is involved.
Inhibition by glibenclamide of the vasorelaxant action of cromakalim in the rat
Authors: Buckingham Robin E. , Hamilton Thomas C. , Howlett David R. , Mootoo Sheila , Wilson Campbell
Published: July 2012

In rat isolated thoracic aortic rings pre‐contracted with noradrenaline (10−6 m), cromakalim (3 × 10−7‐3 × 10−5 m) produced concentration‐related relaxation. This effect was progressively inhibited by increasing concentrations of the anti‐diabetic sulphonylurea drug, glibenclamide (10−6‐10−5 m).

In rat isolated portal veins, cromakalim (3 × 10−8‐10−6 m) produced concentration‐related inhibition of the spontaneous contractive activity and glibenclamide (3 × 10−7‐3 × 10−6 m) prevented this inhibitory action in a concentration‐dependent manner.

In both rat aortic rings and portal veins, cromakalim (10−5 m) stimulated 86Rb efflux. Prior exposure to glibenclamide (10−7‐10−6 m) produced a concentration‐related inhibition of this response.

In conscious rats, cromakalim, 0.075 mg kg−1 i.v., produced a rapid and sustained fall in arterial blood pressure which was not influenced by pretreatment (2 h) with a large oral dose of glibenclamide (100 mg kg−1).

In conscious rats, the hypotensive action of cromakalim, 0.075 mg kg−1 i.v., was abolished by pretreatment (30 min) with glibenclamide, 20 mg kg−1, given by the intravenous route.

The results suggest that the vasorelaxant and hypotensive actions of cromakalim involve a K+ channel which can be inhibited by glibenclamide, but which may be distinct from the ATP‐sensitive K+ channel of the pancreatic β‐cell.
6‐Cyano‐7‐nitroquinoxaline‐2,3‐dione as an excitatory amino acid antagonist in area CA1 of rat hippocampus
Authors: Blake J.F. , Yates R.G. , Brown M.W. , Collingridge G.L.
Published: July 2012

A quantitative pharmacological investigation of the excitatory amino acid antagonist 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) has been made in area CA1 of rat hippocampal slices bathed in 1 mm Mg2+ containing medium.

At a concentration of 10 μm, CNQX reversibly antagonized responses to α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA), quisqualate and kainate; it produced a parallel shift in their log dose‐response curves. Responses to N‐methyl‐d‐aspartate (NMDA) were not antagonized by 10 μm CNQX (dose‐ratio: 1.04 ± 0.06, n = 3).

Schild plots (constructed over the range 1–100 μm) yielded the following estimated pA2 values, AMPA 5.8, quisqualate 5.9, and kainate 5.9. NMDA was antagonized by 100 μm CNQX, giving an apparent log K of 4.44 ± 0.06.

The slopes (±s.e.mean) of the Schild plots were for AMPA 0.84 + 0.06, quisqualate 0.79 ± 0.04 and kainate 0.68 ± 0.07. These were all significantly less than unity.

Synaptic responses elicited by low frequency activation of the Schaffer collateral‐commissural pathway were blocked completely by CNQX (10 μm) providing that a low stimulus intensity was used. With high intensity stimulation a small component remained that was blocked by the selective NMDA antagonist d‐2‐amino‐5‐phosphonovalerate (APV).

These results suggest that CNQX does not differentially affect the responses of CA1 neurones to AMPA, quisqualate and kainate. It does, however, depress responses to these agonists to a greater degree than it does responses to NMDA and it is a highly effective synaptic antagonist.
Sex‐related differences in central adrenergic function and responsiveness to repeated administration of desipramine or electroconvulsive shock
Authors: Heal D.J. , Bristow L.M. , Hurst E.M. , Elliott J.M. , Buckett W.R.
Published: July 2012

Clonidine induces hypoactivity in rodents. Male rats were found to be markedly more susceptible to the sedative effects of this α2‐adrenoceptor agonist than females. Thus to obtain identical hypoactivity responses for subsequent experiments, clonidine was administered to male and female rats at doses of 0.2 and 0.5 mg kg−1, respectively.

The clonidine‐induced hypoactivity response of female rats was not affected by the oestrous cycle.

Repeated injection of desipramine (DMI; 5 mg kg−1 b.d.) for up to 14 days progressively attenuated clonidine‐induced hypoactivity in both male and female rats. However, in males the attenuation was more rapid in onset and a greater overall reduction was obtained. This α2‐adrenoceptor‐mediated response was also progressively reversed by repeated daily administration of an electroconvulsive shock (ECS; 110 V, 1 s). In this case, although the maximum decrease was greater in males, the time of onset was identical in both sexes.

There were no sex‐related differences in either the number or affinity of α2‐ and β‐adrenoceptors in rat cortex. Cortical α2‐adrenoceptors were decreased by 14 days of DMI injection or 10 days of ECS treatment (ECS × 10) and these effects were identical in both sexes. These receptors were not altered by 2 days administration of DMI or ECS. Cortical β‐adrenoceptors were reduced in male and female rats by 2 and 14 days of DMI injection and by ECS × 10, but not ECS × 2.

Viewed overall, the data show differences in α2‐adrenoceptor function between the sexes, as determined by clonidine‐induced hypoactivity and the responsiveness of this paradigm to repeated administration of DMI and ECS. In contrast, no differences were observed in complementary α2‐ and β‐adrenoceptor binding experiments using rat cortical tissue.
Further characterization of the 5‐HT receptor mediating vascular relaxation and elevation of cyclic AMP in porcine isolated vena cava
Authors: Sumner M.J. , Feniuk W. , Humphrey P.P.A.
Published: July 2012

5‐Hydroxytryptamine (5‐HT) and 5‐carboxamidotryptamine (5‐CT) produce both smooth muscle relaxation and elevation of tissue adenosine 3′: 5′‐cyclic monophosphate (cyclic AMP) levels in isolated rings of neonatal porcine vena cava. We now present studies attempting to characterize in more detail the 5‐HT receptor mediating these responses.

Both 5‐HT and 5‐CT relaxed porcine isolated vena cava rings (EC50 values 200 nm and 4 nm respectively) and elevated tissue cyclic AMP levels (EC50 values 1500 nm and 16 nm respectively). For both responses 5‐CT was approximately 50–100 fold more potent than 5‐HT.

Both 5‐CT‐induced smooth muscle relaxation and cyclic AMP elevation were potently and specifically antagonized to a similar extent by methiothepin, methysergide and spiperone.

At concentrations up to 1 μm, 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin, buspirone, ipsapirone, n,n‐dipropyl‐5‐CT, cyanopindolol, RU24969, ketanserin, GR38032 and GR43175 were devoid of both agonist and antagonist activity for both responses.

These findings suggest that the same 5‐HT1‐like receptor mediates both smooth muscle relaxation and elevation of cyclic AMP. This receptor is unlike any known 5‐HT1 ligand binding site or adenylate cyclase‐coupled 5‐HT receptor in brain tissues.
Involvement of the protein kinase C system in calcium‐force relationships in ferret aorta
Authors: Ruzycky A.L. , Morgan Kathleen G.
Published: July 2012

Intracellular Ca2+‐force relationships were investigated in ferret aortic smooth muscle by the simultaneous measurement of aequorin luminescence and isometric force. Complete calcium‐force curves were constructed by plotting calibrated aequorin luminescence versus force, while intracellular [Ca2+] was made to change by increasing degrees of K+ depolarization or decreasing extracellular [Ca2+].

The steady state calcium‐force curve in response to K+ depolarization exhibited maximal force generation at an intracellular [Ca2+] of approximately 4 × 10−7 m. Further increases in intracellular [Ca2+] did not yield additional increments in force.

Protein kinase C activation with the phorbol ester, 12‐deoxyphorbol‐13‐isobutyrate 20 acetate (DPBA) produced contractions accompanied by no detectable increases in aequorin luminescence. DPBA significantly shifted the control [Ca2+]‐force relationship leftward to lower intracellular [Ca2+] with an increase in the magnitude of maximal generated force.

In aorta maximally precontracted by K+ depolarization, the addition of DPBA resulted in a significant increase in force in the absence of further increases in intracellular [Ca2+]. Conversely, in muscles maximally precontracted with DPBA, responses to K+ depolarization resulted in subsequent increases in force in the presence of simultaneous sustained increases in intracellular [Ca2+].

The relatively specific protein kinase C antagonist H‐7 caused a significant decrease in intrinsic myogenic tone in the absence of any statistically significant decrease in intracellular [Ca2+].

These results suggest that protein kinase C may be an important regulator of vascular smooth muscle contractility by: (1) providing a mechanism by which the apparent [Ca2+] sensitivity of the contractile apparatus during agonist‐induced contractions is increased, and (2) maintaining intrinsic myogenic tone by a mechanism the [Ca2+] requirement of which is satisfied by the resting [Ca2+]i.
Secretion of acetylcholinesterase and butyrylcholinesterase from the guinea‐pig isolated ileum
Authors: Appleyard M.E. , Smith A.D.
Published: July 2012

Strips of longitudinal muscle from guinea‐pig ileum, retaining Auerbach's plexus, were superfused with oxygenated Krebs solution. Addition of 50 mm KCl led to a pronounced Ca2+‐dependent increase in the activities of both acetylcholinesterase and non‐specific cholinesterase (butyrylcholinesterase) in the perfusate but with no change in lactate dehydrogenase activity.

No release of acetylcholinesterase, either spontaneous or K+‐evoked was observed in tissue freed of the nerve plexus, although release of butyrylcholinesterase still occurred.

Carbachol induced a marked Ca2+‐dependent increase in the release of acetylcholinesterase but had no effect on the release of butyrylcholinesterase or lactate dehydrogenase. This carbachol‐evoked increase in acetylcholinesterase release was blocked by hexamethonium but not by atropine.

Four readily soluble molecular forms of acetylcholinesterase and three soluble molecular forms of butyrylcholinesterase were present in innervated longitudinal muscle strips, but insignificant amounts of acetylcholinesterase were detected in denervated strips of muscle. Only one of the four molecular forms of acetylcholinesterase was recovered in the perfusates.

It is concluded that acetylcholinesterase is secreted from the nerves of Auerbach's plexus in response to depolarizing stimuli or to nicotinic cholinergic stimulation, while butyrylcholinesterase is secreted from non‐neural elements, possibly the longitudinal muscle cells, of guinea‐pig ileum in response to a depolarizing stimulus.
Effect of pirenzepine and gallamine on cardiac and pulmonary muscarinic receptors in the rabbit
Authors: Maclagan Jennifer , Faulkner David
Published: July 2012

The effect of muscarinic antagonists considered to be selective for M1 receptors (pirenzepine) and for M2 receptors (gallamine) were studied on bronchoconstriction and bradycardia elicited by stimulation of the vagal nerves and by i.v. acetylcholine (ACh) in anaesthetized rabbits.

Pirenzepine was equipotent as an antagonist of ACh‐induced responses at postjunctional muscarinic receptors in the heart, lung and blood vessels, whereas gallamine was at least ten times less potent at pulmonary and vascular muscarinic receptors. Thus, gallamine never caused complete inhibition of bronchoconstrictor or hypotensive responses to i.v. ACh, whereas doses of pirenzepine in excess of 1 μmol kg−1 abolished all muscarinic responses.

In the lung, both antagonists inhibited bronchoconstriction caused by vagal stimulation and ACh‐induced bronchoconstriction to the same extent (pirenzepine, mean ED50 65 ± 22 and 130 ± 28 nmol kg−1 respectively; gallamine, ED50 > 10,000 nmol kg−1 for both responses). Enhancement of vagally‐induced bronchoconstriction was never observed.

In the heart, however, both pirenzepine and gallamine were ten times less potent as antagonists of vagally‐induced bradycardia than of ACh‐induced bradycardia. This differential blockade was unaltered by propranolol (1 mg kg−1) pretreatment.

It is concluded that there is no evidence for M1 or M2 muscarinic receptors in the pulmonary innervation of the rabbit and the potency of the antagonists in abolishing vagally‐induced bronchoconstriction was consistent with blockade of M3 muscarinic receptors on airway smooth muscle.

The results suggest that M2 muscarinic receptors may exert an inhibitory effect on transmission in the parasympathetic nerves innervating the heart in the rabbit. Blockade of such neuronal receptors would increase transmitter output to the atrial cells and explain the low potency of both antagonists in abolishing vagally‐induced bradycardia in the rabbit.
Generation of histamine‐releasing activity from serum albumin by medium derived from stimulated neutrophils of rat
Authors: Cochrane David E. , Boucher William , Carraway Robert E.
Published: July 2012

Medium conditioned by rat neutrophils stimulated by N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP) has been found to generate mast cell histamine‐releasing activity (HRA) when incubated with bovine serum albumin (BSA).

Histamine release increased as the concentration of BSA used to generate HRA was increased from 0.25 to 10 mg ml−1, as the concentration of neurotrophil conditioned medium was increased and as the concentration of FMLP used to stimulate the neutrophils was increased. Histamine release was non‐cytotoxic as it was inhibited by energy deprivation or by removal of calcium and it was accompanied by degranulation.

HRA was detectable after 30 min of incubation with BSA and its generation continued to increase over the 18 h of our measurements.

Generation of HRA was dependent upon the presence of medium from stimulated neutrophils and on the presence of BSA, although plasma could substitute for BSA. Likewise, HRA could be generated from γ‐globulin although to a lesser extent than with albumin.

Generation was optimum at acid pH and was inhibited by prior boiling of the neutrophil conditioned medium or by the addition of pepstatin.

It is suggested that an enzyme(s) released from the neutrophil during stimulation acts on an albumin‐like substrate to generate HRA. It is proposed that HRA is peptide in nature and may be generated during an inflammatory response.
Inhibition of histamine‐stimulated inositol phospholipid hydrolysis by agents which increase cyclic AMP levels in bovine tracheal smooth muscle
Authors: Hall I.P. , Donaldsona J. , Hill S.J.
Published: July 2012

The effect on histamine‐stimulated [3H]‐inositol phosphate accumulation of a range of agents which increase the accumulation, or mimic the actions, of cyclic AMP has been investigated in bovine tracheal smooth muscle.

Salbutamol (1 μm), forskolin (1 μm) and vasoactive intestinal peptide (VIP, 1 μm) inhibited the inositol phosphate response to 0.1 mm histamine and increased the accumulation of [3H]‐cyclic AMP in [3H]‐adenine‐labelled slices of bovine tracheal smooth muscle. The effect on inositol phospholipid hydrolysis was mimicked by the membrane permeant analogues of cyclic AMP, dibutryl‐cyclic AMP (1 mm) and 8‐bromo‐cyclic AMP (1 mm).

In contrast to salbutamol, which was equally effective at producing the two effects, forskolin produced large increases in [3H]‐cyclic AMP accumulation (EC50 = 1.2 μm) at much higher concentrations than those required for inhibition of histamine‐stimulated [3H]‐inositol phosphate accumulation (EC50 = 0.09 μm). However, significant increases in [3H]‐cyclic AMP accumulation, of similar magnitude to those obtained with salbutamol and VIP, were observed over the concentration range appropriate for inhibition of the inositol phosphate response to histamine.

In the presence of histamine (0.1 mm), isobutylmethylxanthine (IBMX, 1 mm) and rolipram (0.1 mm) both significantly (P < 0.05) elevated tissue [3H]‐cyclic AMP levels. IBMX, rolipram and (to a lesser extent) SKF 94120 significantly (P < 0.05) reduced histamine‐stimulated [3H]‐inositol phosphate accumulation by 81%, 68% and 20%, respectively. M&B 22948 was without a significant effect on either [3H]‐cyclic AMP or histamine‐induced [3H]‐inositol phosphate accumulation.

Both rolipram and forskolin reduced the increase in incorporation of [3H]‐inositol into membrane phospholipids which followed stimulation with histamine. However, a significant inhibition of [3H]‐inositol phosphate accumulation could be demonstrated under conditions in which there was no change in the level of [3H]‐inositol incorporation.
Alterations of coronary vascular responses to noradrenaline, acetylcholine and isoprenaline during acute myocardinal ischaemia in dogs
Authors: Sun Jian‐Zhong , Li Zhi‐Yuan , Zang Yi‐Min , Wang Fu‐Zhou
Published: July 2012

The reactivity of coronary arteries to noradrenaline (NA), acetylcholine (ACh) and isoprenaline (Iso) during acute myocardial ischaemia was studied in anaesthetized, open‐chest dogs.

The left anterior descending coronary artery (LAD) was cannulated and perfused via an extracorporal circuit at constant flow. Ischaemia was produced by decreasing the perfusion blood flow of the LAD to 50% (moderate ischaemia) and 27% (severe ischemia) of normal. A dose of each agent which had no significant myocardial effects was chosen. Heart rate was held constant by ventricular pacing during ACh administration.

Under normal conditions, the infusion of NA, ACh and Iso into the LAD produced significant decreases in coronary vascular resistance (P < 0.01). However, under either moderate or severe ischaemic conditions intracoronary NA resulted in a marked increase in coronary vascular resistance (P < 0.01), which was completely blocked by phentolamine, an α‐adrenoceptor blocker; intracoronary ACh and Iso did not have a significant effect on coronary vascular resistance (P > 0.05).

These results indicate that coronary arterial responsiveness to some intrinsic vasoactive substances, such as NA and ACh, is altered during acute myocardial ischaemia. This may be important in the pathophysiology of myocardial ischaemia.
Endothelium‐derived relaxing factor is an endogenous vasodilator in man
Authors: Collier Joe , Vallance Patrick
Published: July 2012

Removal of venous endothelium in man leads to vasoconstriction and loss of dilator response to acetylcholine but not to glyceryl trinitrate. This pattern of responses can be accounted for by loss of endotheliumderived relaxing factor (EDRF), but not by loss of prostacyclin. This provides the first direct evidence for endothelium‐dependent dilatation in man in vivo, and suggests that basal release of EDRF is a determinant of resting venous tone.
The action of dopamine and vascular dopamine (DA1) receptor agonists on human isolated subcutaneous and omental small arteries
Authors: Hughes A.D. , Sever P.S.
Published: July 2012

Human small arteries were obtained from surgical specimens and studied in vitro by use of a myograph technique. Following induction of tone with a potassium depolarizing solution, dopamine in the presence of β‐adrenoceptor and catecholamine uptake blockade relaxed isolated omental and subcutaneous arteries. Preincubation of tissues with phentolamine increased the maximum relaxation in response to dopamine.

The selective vascular dopamine receptor agonists, fenoldopam and SKF 38393 also relaxed isolated subcutaneous and omental arteries in a concentration‐dependent manner. The order of potency for agonists was dopamine > fenoldopam > SKF 38393.

Dopamine‐induced relaxation was competitively antagonized by SCH 23390, (R)− and (S)‐sulpiride, and fenoldopam induced relaxation by SCH 23390 and (+)− but not (−)‐butaclamol.

These results indicate the presence of vascular dopamine receptors (DA1 subtype) on human isolated resistance arteries from omental and subcutaneous sites.
Endothelin‐ and neuropeptide Y‐induced vasoconstriction of human epicardial coronary arteries in vitro
Authors: Franco‐Cereceda Anders
Published: July 2012

The effects of the recently discovered peptide endothelin and neuropeptide Y (NPY) on human epicardial coronary arteries were studied in vitro.

Endothelin induced a concentration‐dependent, endothelium‐independent, long‐lasting vasoconstriction regardless of vessel size. NPY evoked contractions of small coronary arteries with a similar potency to that of endothelin, although to a significantly lower degree. Large coronary arteries did not respond to NPY. Endothelin did not relax coronary arteries precontracted with potassium.

The effect of endothelin was dependent on extracellular Ca2+ and, like NPY, significantly reduced by the Ca2+‐antagonist nifiedipine.

In conclusion, endothelin is a potent human vasoconstrictor in vitro. It is suggested that endothelin may be involved in the regulation of coronary blood flow.
Actions of guanine nucleotides and cyclic nucleotides on calcium stores in single patch‐clamped smooth muscle cells from rabbit portal vein
Authors: Komori S. , Bolton T.B.
Published: July 2012

Single smooth muscle cells were obtained from the rabbit portal vein by enzymic digestion and membrane currents under voltage clamp measured by whole‐cell patch clamp technique.

When held at depolarized potentials, spontaneous outward currents (STOCs) were discharged; it is likely that these represent the cyclical storage and release within the cell of calcium in relation to Ca‐activated K‐channels.

Application of lower concentrations of carbachol (10−5m) or caffeine (10−3m) accelerated STOC discharge. Higher concentrations of caffeine (10−2m) or carbachol (10−4m), or noradrenaline (10−5m), produced an outward current of 1–5 nA which disappeared within 5–15 s and which was considered to result from the discharge of calcium stores; STOC discharge was abolished for a period.

Ryanodine (10−5‐10−4m) or a non‐hydrolysable GTP analogue, GTPγS (10−5‐10−3m) introduced into the cell abolished STOC discharge within 2–5 min. STOCs were large in cells filled with GDPβS (10−3m) and the action of GTPγS introduced at various concentrations was antagonized.

GTPγS (10−4‐10−3m) in the cell reduced or abolished outward current to caffeine (10−2m) noradrenaline (10−5m) or carbachol (10−4m); the effect on caffeine outward current was antagonized by GDPβS (10−3m) introduced into the cell. GDPβS reduced noradrenaline outward current but not caffeine outward current implying the existence of a G‐protein step in noradrenaline‐evoked Ca‐store release, possibly regulating phospholipase C enzyme activity and D‐myo inositol 1,4,5 trisphosphate formation.

If cyclic AMP (10−3m) or cyclic GMP (10−3m) was introduced into the cell, or 8‐bromo cyclic AMP (0.5 × 10−3m) or 8‐bromo cyclic GMP (0.5 × 10−3m) applied to the cell in the bathing solution, STOC discharge was only slightly affected. However, the outward current to caffeine applied after noradrenaline was much enhanced.

The results could be explained if cyclic GMP and cyclic AMP enhance calcium storage whereas GTPγS depletes calcium stores, an action antagonized by GDPβS.
Effects of experimental diabetes on the responsiveness of rat aorta
Authors: Mulhern Mark , Docherty James R.
Published: July 2012

Vascular responsiveness was examined in aortic ring preparations, with or without endothelium, from rats with experimental diabetes induced by streptozotocin and from vehicle‐treated (control) rats.

There were no significant differences between diabetic tissues and control tissues in the responsiveness to the vasoconstrictors noradrenaline, 5‐hydroxytryptamine and KCl, and to the vasodilators sodium nitroprusside, isoprenaline and acetylcholine.

When maximum contractions to vasoconstrictors was expressed relative to tissue weight, maximum contractions were significantly greater in diabetic tissues.

When expressed in terms of the KCl contraction, there were no significant differences between diabetic and control tissues in the maximum contraction to vasoconstrictors.

These results demonstrate that diabetic‐induced changes in vascular responsiveness, if any, do not occur at the receptor level.
Effects of pinacidil on the sympatho‐adrenal system in dogs
Authors: Damase‐Michel C. , Tran M.A. , Montastruc J.L. , Moatti J.P. , Montastruc P.
Published: July 2012

The aim of the present work was to study the antihypertensive effect of pinacidil, a potassium channel opener, in sinoaortic denervated (SAD) conscious dogs and to investigate whether the involvement of the sympathetic nervous system induced by this vasodilator compound is only of baroceptor reflex origin.

Pinacidil (0.1, 0.2, 0.4 mg kg−1 i.v.) induced a dose‐dependent decrease in blood pressure in normal as well as in SAD dogs. In contrast, the induced‐tachycardia observed in normal dogs was not found in SAD animals.

Since pinacidil induced an increase in plasma catecholamines, free fatty acids, glucose, plasma renin activity and aldosterone in SAD dogs, it is suggested that this sympathetic activation is independent of the baroreceptor reflex pathways.

The sympathetic activation is mainly of peripheral origin, since pinacidil (0.7 mg kg−1 i.v.) induced an increase in adrenaline release from the adrenal gland after section of the great splanchnic nerve in anaesthetized dogs. This increase is probably due to an effect that does not involve K+ channel opening. However, this effect of pinacidil was not observed during splanchnic nerve stimulation (in this case, the involvement of K+ channel opening is suggested).
Electrophysiological abnormalities and enhanced reperfusion arrhythmias in the isolated hearts of hyperthyroid rats
Authors: Miyazawa Katsuhiko , Hashimoto Hisakuni , Uematsu Toshihiko , Nakashima Mitsuyoshi
Published: July 2012

The influence of hyperthyroidism on electrophysiological characteristics and on reperfusion arrhythmias was examined in rat hearts.

Electrophysiological studies were performed with glass microelectrodes, and the experiments on reperfusion arrhythmias were done in isolated perfused hearts.

Ventricular muscle from hyperthyroid rats was more prone than that from euthyroid rats to develop triggered activity under conditions believed to cause myoplasmic Ca2+ overload.

The severity of reperfusion arrhythmias was significantly enhanced in hyperthyroid preparations as compared with euthyroid ones.

The enhanced reperfusion arrhythmias in hyperthyroid rats were significantly reduced by propranolol (3 × 10−7m), lignocaine (1 × 10−5m) and verapamil (3 × 10−8m), but not by nadolol (3 × 10−7m) or prazosin (3 × 10−7m).

These results suggest that increased heart rate due to hyperthyroidism and responses mediated via either α‐ or β‐adrenoceptors were not dominant causes of enhanced reperfusion arrhythmias in hyperthyroid hearts.

The increased tendency to develop triggered activity which was observed in the electrophysiological study, may be one possible explanation of enhanced reperfusion arrhythmias in hyperthyroid hearts.
Functional role of cholinoceptors and purinoceptors in human isolated atrial and ventricular heart muscle
Authors: Jakob Helga , Oelert Hellmut , Rupp Johanna , Nawrath Hermann
Published: July 2012

The effects of cholinergic and purinergic stimulation on action potential, force of contraction and 86Rb efflux were investigated in human atrial and ventricular heart muscle.

In atrial heart muscle, carbachol and (−)‐N6‐(R‐phenyl‐isopropyl)‐adenosine (R‐PIA) and 5′‐(N‐ethyl)‐carboxamido‐adenosine (NECA) evoked transient decreases of action potential duration and force of contraction; the steady‐state effects on force of contraction were virtually identical to control values. In the presence of propranolol, steady‐state values after carbachol, R‐PIA or NECA amounted to about 50% of control values.

In ventricular heart muscle, carbachol, NECA and R‐PIA did not significantly affect the action potential configuration or force of contraction.

Carbachol, NECA and R‐PIA induced a maintained depression of the positive inotropic response to isoprenaline in both atrial and ventricular heart muscle.

The rate constant of 86Rb efflux was slightly increased by carbachol, NECA and R‐PIA in atrial (10–20%) but not in ventricular heart muscle.

In the presence of isoprenaline, carbachol, NECA and R‐PIA did not significantly affect the rate constant of 86Rb efflux in both atrial and ventricular heart muscle. Isoprenaline alone increased the rate constant of 86Rb by about 25% in both tissues.
NK‐1 receptor mediation of neurogenic plasma extravasation in rat skin
Authors: Andrews Paul V. , Helme Robert D. , Thomas Karen L.
Published: July 2012

Plasma extravasation was induced by electrical nerve stimulation and by perfusion of tachykinins over a vacuum‐induced blister base on rat footpad.

Stimulation of the sciatic nerve (18 V, 15 Hz, 0.5 ms) for 20 min produced a significant increase in the protein content of the perfusate. The response in capsaicin pretreated rats was only 4% of the control response. This indicates that the electrically‐induced plasma extravasation response was mediated by capsaicin‐sensitive sensory fibres.

Exogenous perfusion of the mammalian tachykinins substance P, neurokinin A and neurokinin B and the non‐mammalian tachykinins physalaemin, kassinin and eledoisin was used to determine the tachykinin receptor type mediating the plasma extravasation response. Dose‐response curves of the tachykinins (10−9m−10−4m) gave a rank order of potency of substance P = physalaemin > eledoisin ≥ kassinin > neurokinin B = neurokinin A.

In addition, specific agonists of neurokinin receptors were perfused. Perfusion of [Glp6, D‐Pro9] SP6–11 and [Glp6, L‐Pro9]SP6–11 demonstrated that the L‐Pro isomer was much more potent than the D‐Pro isomer.

The rank order of potency and the greater potency of [Glp6, L‐Pro9]SP6–11 over its D‐isomer indicate an NK‐1 neurokinin receptor mediates plasma extravasation in rat footpad skin.
The binding of (+)‐isradipine by guinea‐pig intact atria
Authors: Herzig Stefan , Lüllmann Heinz
Published: July 2012

The accumulation of [3H]‐(+)‐isradipine (PN 200‐110) was measured in quiescent guinea‐pig left atria with normal (K+ 2.7 mm) or lowered (K+ 40 mm) membrane potential.

Under control conditions (2.7 mM K+) a high affinity binding of (+)‐isradipine could not be detected. If, however, the atria were partially depolarized to about −30 mV by 40 mM K+, high affinity binding became evident displaying a dissociation constant of 4.2 × 10−11m and a capacity of 9.7 nmol kg−1 wet wt.

The depolarization‐induced binding was reversible upon repolarization of the atria although isradipine was still present in the medium. This indicates that the high affinity binding sites disappear as soon as the cell membranes become polarized.

Isradipine belongs to the less hydrophobic dihydropyridines, but nevertheless the unsaturable binding led to an accumulation of about 84 fold. At a concentration of 2 × 10−8m (+)‐isradipine, which reduces the contractile force by 50%, the cellular concentration will rise to more than 10−6m.
Dual effects of 5‐hydroxytryptamine on the release of γ‐aminobutyric acid from myenteric neurones of the guinea‐pig ileum
Authors: Shirakawa Junji , Takeda Koichiro , Taniyama Kohtaro , Tanaka Chikako
Published: July 2012

The effects of 5‐hydroxytryptamine (5‐HT) on the release of γ‐aminobutyric acid (GABA) were examined in the longitudinal muscle‐myenteric plexus (LM‐MP) preparation of guinea‐pig ileum. 5‐HT increased the spontaneous release and inhibited the electrically‐evoked release of [3H]‐GABA. The 5‐HT‐evoked release was Ca2+‐dependent and tetrodotoxin‐sensitive, and was antagonized by (3α‐tropanyl)‐1H‐indole‐3‐carboxylic acid ester (ICS 205–930), but not by methysergide and ketanserin. The inhibitory effect of 5‐HT was antagonized by methysergide, but not by ketanserin and ICS 205–930. 8‐Hydroxy‐2‐(di‐n‐propylamino)tetralin mimicked the inhibitory effect of 5‐HT. Thus, 5‐HT may exert an excitatory effect on the enteric GABAergic neurone via the 5‐HT3 receptor and an inhibitory effect via the 5‐HT1A receptor.
The mode of action of caffeine on catecholamine release from perfused adrenal glands of cat
Authors: Yamada Yutaka , Nakazato Yoshikazu , Ohga Akira
Published: July 2012

Adrenaline and noradrenaline secretion induced by caffeine was investigated in the perfused cat adrenal glands.

Caffeine (10–80 mm) caused a dose‐dependent increase in both adrenaline and noradrenaline secretion when applied for 1 min and 10 min after replacing Ca2+ with 10−5m EGTA in the perfusion solution. The ratio of adrenaline to noradrenaline was about 1:1. Mg2+ and/or Ca2+ inhibited the response to caffeine.

When caffeine (40 mm) was repeatedly applied in the absence of extracellular Ca2+, the secretory response almost disappeared but only at the second challenge with caffeine. However, the response was partially restored after readmission of Ca2+ (2.2 mm) and was augmented after the readmission of Ca2+ with ouabain (10−5m).

Caffeine‐induced secretion of adrenaline and noradrenaline increased with the increase in the preloaded concentration of Ca2+ and attained a maximum at 16 mM Ca2+.

During perfusion with Ca2+‐free Locke solution containing hexamethonium (10−3m), acetylcholine (10−4m) caused increases in both adrenaline and noradrenaline secretions with a ratio of about 1:2. The secretory responses were partially inhibited by preceding stimulation with exposure to caffeine (80 mm).

These results suggest that caffeine mobilizes Ca2+ from an intracellular storage site that may not be entirely the same as that linked to muscarinic receptors, and causes an increase in both adrenaline and noradrenaline secretion from cat adrenal chromaffin cells.
Effect of bile acid on electrophysiological properties of rabbit sino‐atrial node in vitro
Authors: Kotake Hiroshi , Itoh Toshihiko , Watanabe Masashi , Hisatome Ichiro , Hasegawa Junichi , Mashiba Hiroto
Published: July 2012

In order to examine the action of bile acid on cardiac pace‐maker activity, the effect of sodium taurocholate (NTC) was studied on the membrane potential and current of rabbit sino‐atrial node preparations by means of a double microelectrode voltage clamp technique.

In spontaneously beating sino‐atrial node preparations, NTC (above 30 μm) decreased the maximum rate of rise of the action potential. Above 100 μm, the compound also exerted a brady‐cardiac effect and decreased the rate of diastolic depolarization significantly.

On the current systems, NTC produced dose‐related decreases in the slow inward Ca2+ current and the time‐dependent outward K+ current.

It is concluded that NTC depresses the spontaneous discharge of the sino‐atrial node through decreases in both inward and outward current systems.
Purinoceptors in the pulmonary circulation of the rat and their role in hypoxic vasoconstriction
Authors: McCormack D.G. , Barnes P.J. , Evans T.W.
Published: July 2012

P2‐purinoceptors have been characterized in the systemic circulation of a variety of species but little is known about their nature in the pulmonary vasculature.

In the isolated, blood perfused and ventilated lung of the rat the P2x selective analogues α,β‐methylene ATP(α,β‐meATP) (25 μg) and β,γ‐methylene ATP (400 μg) caused a rise in pulmonary artery pressure (127 ± 32% and 110 ± 23% increase respectively, n = 6), demonstrating the existence of vasoconstrictor P2 receptors in the pulmonary circulation.

Repeated boluses of α,β‐meATP resulted in complete desensitization of the constrictor response to β,γ‐meATP, but a small vasodilator response remained indicating unopposed stimulation of P2y receptors. The desensitization by α,β‐meATP had no effect on angiotensin II‐induced vasoconstriction.

After desensitization of the vasoconstrictor P2 receptors with α,β‐meATP, hypoxic pulmonary vasoconstriction remained intact, indicating that these receptors are not involved in this response.
Caffeine‐induced inhibition of calcium channel current in cultured smooth muscle cells from pregnant rat myometrium
Authors: Martin C. , Dacquet C. , Mironneau C. , Mironneau J.
Published: July 2012

The inhibitory effect of caffeine on the calcium channel current was investigated in cultured myometrial cells isolated from pregnant rats.

Caffeine inhibited the calcium channel current elicited from a holding potential of — 70 mV in a concentration‐dependent manner. The IC50 was estimated to be 35 mM.

The caffeine inhibition was not enhanced when calcium channels were opened by a conditioning depolarizing pulse sequence or when the number of inactivated calcium channels was increased at depolarized holding potentials.

Caffeine antagonized the specific binding of (+)‐[3H]‐isradipine to myometrial membranes. The IC50 value found in binding experiments was similar to the IC50 value for half‐maximal inhibition of calcium channel current. Caffeine decreased the maximal binding capacity of (+)‐[3H]‐isradipine to myometrial membranes without any significant change in the dissociation constant.

The results indicate that caffeine interacts with a site closely associated with the voltage‐dependent calcium channels in myometrial cells and, in turn, inhibits calcium influx.
Modulation of neurotransmission in the guinea‐pig vas deferens by capsaicin: involvement of calcitonin gene‐related peptide and substance P
Authors: Ellis James L. , Burnstock Geoffrey
Published: July 2012

The effects of capsaicin, calcitonin gene‐related peptide and substance P were studied via three parameters in the guinea‐pig vas deferens: the overflow of ATP and of tritiated noradrenaline, the mechanical responses to field stimulation and the mechanical responses to exogenous noradrenaline and α,β‐methylene ATP.

At 2 Hz, capsaicin inhibited the stimulus‐evoked release of ATP, whereas it was without effect on the release of noradrenaline. At 20 Hz capsaicin did not affect the release of either of the co‐transmitters. Capsaicin enhanced responses to α,β‐methylene ATP, but not to exogenous noradrenaline.

Calcitonin gene‐related peptide, like capsaicin, inhibited the release of ATP, but not noradrenaline at 2 Hz and was without effect on release at 20 Hz. However, calcitonin gene‐related peptide inhibited responses to α,β‐methylene ATP and was without effect on responses to exogenous noradrenaline.

Substance P had no effect on the release of either noradrenaline or ATP at either frequency. However, like capsaicin it enhanced responses to α,β‐methylene ATP and was without effect on exogenous noradrenaline.

These results suggest that the actions of capsaicin on the guinea‐pig isolated vas deferens are mediated via the release of both calcitonin gene‐related peptide and substance P. Furthermore, as capsaicin and calcitonin gene‐related peptide prejunctionally modulate purinergic, but not noradrenergic transmission, this suggests that the mechanisms for the storage and release of the sympathetic co‐transmitters noradrenaline and ATP may not be the same.
Increase in gastric secretion induced by 2‐deoxy‐D‐glucose is impaired in capsaicin pretreated rats
Authors: Evangelista S. , Santicioli P. , Maggi C.A. , Meli A.
Published: July 2012

Gastric acid secretion was determined following intravenous administration of 2‐deoxy‐D‐glucose (2‐DG; 60 mg kg−1) or electrical stimulation of the vagus nerve in urethane‐anaesthetized rats pretreated when newborn with either capsaicin or the vehicle. The secretory response to 2‐DG was substantially reduced in the capsaicin pretreated rats, while that induced by electrical vagal stimulation (1 mA, 1 ms, 3 Hz) was unaffected.

These results suggest that capsaicin‐sensitive fibres are involved in the afferent branch of the reflex response activated by 2‐DG to stimulate gastric acid secretion.
Prostacyclin mediates antiaggregatory and hypotensive actions of endothelin in anaesthetized beagle dogs
Authors: Hermán Ferenc , Magyar Kálmán , Chabrier Pierre‐Etienne , Braquet Pierre , Filep János
Published: July 2012

The effects of endothelin on blood pressure and in vivo aggregation of platelets were studied in anaesthetized beagle dogs. Intravenous administration of endothelin (0.03‐0.3 nmol kg−1) resulted in a dose‐dependent transient hypotension followed by a long‐lasting hypertension and inhibition of platelet aggregation. These changes were accompanied by dose‐dependent elevation of plasma 6‐keto prostaglandin F1α levels. Pretreatment of the animals with acetylsalicylic acid significantly attenuated both the vascular and antiaggregatory responses to endothelin. These data provide evidence for in vivo release of prostacyclin by endothelin in anaesthetized dogs.
Ventricular fibrillation is reduced in hypothyroid rats with enhanced myocardial α‐adrenoceptor responsiveness
Authors: Chess‐Williams R. , Coker S.J.
Published: July 2012

The severity of ventricular arrhythmias induced by coronary artery occlusion and reperfusion has been examined in control rats and animals made hypothyroid by pretreatment with 6‐propylthiouracil (PTU). The maximal driving frequency and sensitivity of isolated left atria and papillary muscles to isoprenaline and to phenylephrine in the presence of propranolol, were also examined in tissues from control and hypothyroid animals.

Pretreatment with PTU resulted in a potentiation of responses to the α‐adrenoceptor agonist phenylephrine in both left atria and papillary muscles, while responses to isoprenaline were depressed in left atria but unaltered in papillary muscles from hypothyroid animals.

In rats subject to coronary artery occlusion, PTU pretreatment reduced the incidence of ventricular fibrillation during acute myocardial ischaemia and abolished reperfusion‐induced ventricular fibrillation. Mortality during myocardial ischaemia and reperfusion was also abolished. Diastolic blood pressure was similar in hypothyroid and control animals, but there was a small reduction in systolic blood pressure and a marked decrease in heart rate in PTU pretreated animals.

These results demonstrate that PTU‐induced hypothyroidism represents a condition where cardiac α‐adrenoceptor‐mediated responses are enhanced but the severity of ischaemia‐ and reperfusion‐induced arrhythmias is reduced.