bluuebunny/crossref_metadata_2025 huggingface dataset:
Origin of 5‐hydroxytryptamine‐induced hyperpolarization of the rat superior cervical ganglion and vagus nerve
Authors: Ireland S.J.
Published: July 2012

5‐Hydroxytryptamine (5‐HT)‐induced membrane potential changes were recorded extracellularly from rat superior cervical ganglia (SCG) and cervical vagus nerves in vitro.

On the SCG, low concentrations of 5‐HT (1 × 10−8‐3 × 10−7 m) induced concentration‐related hyperpolarization responses. Higher concentrations of 5‐HT (1 × 10−6‐1 × 10−4 m) induced complex responses which typically consisted of an initial hyperpolarization, followed by a depolarization and subsequent after‐hyperpolarization. The depolarization, but not the initial hyperpolarization, was blocked by metoclopramide (3 × 10−5 m), quipazine (1 × 10−6 m) or MDL 72222 (1 × 10−5 m).

5‐HT‐induced hyperpolarization of the SCG was potentiated when the amount of calcium chloride added to the superfusion medium was reduced from 2.5 to 0.15 mmol l−1. Hyperpolarization responses recorded from SCG preparations superfused with this low‐calcium medium were unaffected by the substitution of lithium chloride for sodium chloride and were potentiated by the omission of potassium ions. Ouabain (1 × 10−3 m) abolished both the hyperpolarization and the depolarization induced by 5‐HT.

On the vagus nerve, 5‐HT (1 × 10−7‐3 × 10−5 m) did not induce initial hyperpolarization in either normal or low‐calcium Krebs‐Henseleit medium. However, in the latter solution only, depolarization responses induced by 5‐HT at concentrations of 1 × 10−6 m or greater were followed by hyperpolarization. Both the depolarization and the post‐5‐HT hyperpolarization were blocked by metoclopramide (3 × 10−5 m) but were unaffected by spiperone (1 × 10−7 m).

On the vagus nerve, post‐5‐HT hyperpolarization responses were selectively and reversibly inhibited by ouabain, and by superfusion with Krebs‐Henseleit medium that was either potassium‐free or contained lithium chloride in place of sodium chloride.

These results demonstrate the generation in the rat SCG of a 5‐HT‐induced hyperpolarization response that is not mediated through 5‐HT3 receptors and is unlikely to be a consequence of depolarization. In contrast, on the rat vagus nerve, the post‐5‐HT hyperpolarization observed in the present study had the characteristics expected of depolarization‐dependent activation of a sodium ion pump.
An investigation of the actions of diltiazem on rat aorta exposed to acute hypoxia followed by re‐oxygenation
Authors: Marriott J.F.
Published: July 2012

The effects of diltiazem and removal of extracellular Ca2+ were examined on contractions, of the rat isolated aorta, to noradrenaline (NA) and high K+, during exposure to oxygenated conditions and hypoxia followed by re‐oxygenation.

Exposure to hypoxia caused a similar reduction of contractile responses to NA and KCl, while re‐oxygenation restored contractile activity.

Ca2+‐free conditions abolished responses to KCl but a transient response to NA remained which was resistant to hypoxia.

Diltiazem produced similar reductions of responses to NA during both oxygenated conditions and hypoxia, whereas during re‐oxygenation the effects of diltiazem upon responses to NA were enhanced.

Diltiazem produced a more pronounced reduction of responses to KCl than of responses to NA. However, the reduction of responses to KCl by diltiazem was not modified by the changes in Po2 examined in the present study.

The present study indicates that contractions of the rat aorta mediated by intracellular Ca2+ are resistant to the hypoxic conditions studied in the present investigation, whereas those responses mediated by an influx of Ca2+ are reduced. The increase in the contractile response to NA following re‐oxygenation may result from an increased influx of extracellular Ca2+ since such responses show an enhanced sensitivity to diltiazem.
Voltage‐independent catecholamine release mediated by the activation of muscarinic receptors in guinea‐pig adrenal glands
Authors: Nakazato Y. , Ohga A. , Oleshansky M. , Tomita U. , Yamada Y.
Published: July 2012

The differences between the mechanisms of muscarinic and nicotinic receptor‐mediated catecholamine secretion with respect to their dependence on voltage changes and extracellular Ca were examined using perfused adrenal glands of the guinea‐pig.

Acetylcholine (ACh, 10−6 to 10−3 m) caused a dose‐dependent increase in catecholamine secretion. The ED50 value for ACh was 7 × 10−5 m. In the presence of atropine (10−5 m), the dose‐response curve for ACh was shifted to the right. Hexamethonium (5 × 10−4 m) preferentially reduced the responses to higher concentrations of ACh (> 10−5 m). Pilocarpine (5 × 10−4 m) and nicotine (3 × 10−5 m) also stimulated catecholamine release.

During perfusion with isotonic KCl solution, ACh and pilocarpine, but not nicotine, evoked catecholamine secretion. These responses were abolished by atropine (10−6 m). Pilocarpine‐stimulated catecholamine secretion was enhanced during perfusion with isotonic KCl solution. Under these conditions, hexamethonium (10−3 m) significantly augmented ACh‐evoked catecholamine release.

During perfusion with either Ca‐free isotonic KCl or Ca‐free Locke solution, ACh and pilocarpine caused a partial increase in catecholamine secretion whereas nicotine and high K solution (56 mm) did not. The responses to ACh and pilocarpine were completely inhibited by atropine but not by hexamethonium.

When guinea‐pig adrenal glands were perfused with isotonic KCl solution containing 2.2 mm Ca which was subsequently removed and replaced with EGTA, ACh‐induced catecholamine secretion was similar in magnitude to that observed during perfusion with Locke solution.

We conclude that both nicotinic and muscarinic receptors are involved in ACh‐induced catecholamine secretion from guinea‐pig adrenal chromaffin cells. Activation of muscarinic or nicotinic receptors appears to stimulate catecholamine release through different mechanisms with respect to both voltage‐dependence and Ca requirements.
Cardiovascular effects of apamin and BRL 34915 in rats and rabbits
Authors: Cook Nigel S. , Hof Robert P.
Published: July 2012

The cardiovascular effects of apamin, a selective blocker of certain calcium‐activated potassium channels, and BRL 34915, a vasodilator thought to act by opening of potassium channels, have been investigated in vivo in rats and rabbits.

In anaesthetized normotensive rats, apamin (0.05 and 0.15 mg kg−1, i.v.) potentiated angiotensin II pressor responses but did not modify baseline blood pressure or heart rate.

Apamin (0.15 mg kg−1, i.v.) was without cardiovascular effects in rabbits.

BRL 34915 (0.1 and 0.3 mg kg−1, i.v.) lowered blood pressure in rats dose‐dependently and caused reflex tachycardia. The heart rate increase was abolished by prior administration of the β‐adrenoceptor blocker bopindolol (0.1 mg kg−1, i.v.).

In anaesthetized rabbits, regional blood flow measurements (with radioactive tracer microspheres) showed that BRL 34915 (3 to 30 μg kg−1, i.v.) caused marked vasodilatation in the stomach, with increases in flow also to the heart and small intestine. Brain blood flow also tended to increase. Blood flow to the kidneys was reduced by BRL 34915, whereas flow to skeletal muscle was unchanged.

Apamin pretreatment did not modify the blood pressure lowering activity of BRL 34915 in rats. The site at which BRL 34915 acts to cause vasodilatation in vivo thus appears to be apamin‐insensitive.
A study of the renal actions of amlodipine in the normotensive and spontaneously hypertensive rat
Authors: Johns Edward J.
Published: July 2012

Normotensive Sprague‐Dawley and spontaneously hypertensive rats anaesthetized with sodium pentobarbitone were used to determine the systemic and renal actions of amlodipine, a new calcium channel blocking drug.

Amlodipine, 200 μg kg−1 plus 50 μg kg−1 h−1, decreased blood pressure by 12 ± 3 mmHg in normotensive rats, although the fall was not statistically significant in the hypertensive rats; did not change renal haemodynamics and caused significant increases in urine flow, absolute and fractional sodium excretions of 70%, 91% and 113%, respectively, in normotensive rats and 65%, 91% and 96%, respectively in hypertensive rats. Fractional lithium excretion was unchanged in the normotensive rats but increased by 28% in the hypertensive animals while absolute fluid reabsorption in the proximal tubule did not change in either group. Absolute water and sodium reabsorption in the segments beyond the proximal tubule were unchanged in the normotensive rats but increased in the hypertensive animals by 24% and 22%, respectively, while fractional sodium excretion in this portion of the nephron increased by 88% and 51% in the normotensive and hypertensive rats, respectively.

Amlodipine, 400 μ kg−1 plus 100 μg kg−1 h−1, decreased blood pressure by 12 ± 4 mmHg in the normotensive and by 27 ± 5 mmHg in the hypertensive rats. Renal blood flow was not changed in either group of rats and glomerular filtration rate increased by 25% in the spontaneously hypertensive animals. There were significant increases in urine flow, absolute and fractional sodium excretions of 105%, 145% and 142%, respectively, in the normotensive rats and 224%, 421% and 259%, respectively, in the hypertensive rats. Fractional lithium excretion was elevated by 29% and 38%, in the normotensive and hypertensive rats, respectively, but absolute fluid reabsorption at the proximal tubule remained unchanged. At the same time there were significant increases in absolute water and sodium reabsorption beyond the proximal tubule of 26% and 18%, respectively, in the normotensive animals and of 63% and 60%, respectively, in the hypertensive animals. Fractional excretion of water and sodium in the nephron regions after the proximal tubule were increased by 55% and 88%, respectively, in the normotensive rats and by 84% and 121%, respectively, in the hypertensive rats.

These doses of amlodipine caused modest reductions in blood pressure, minimal changes in renal haemodynamics and a natriuresis and diuresis. Proximal sodium and water reabsorption was not affected by the drug and it is suggested that the changes in tubular fluid handling were compatible with depression of reabsorption further along the tubule.
Differential effect of ω‐conotoxin on release of the adrenergic transmitter and the vasoconstrictor response to noradrenaline in the rat isolated kidney
Authors: El‐Din Mahmoud m. Mohy , Malik Kafait U.
Published: July 2012

The effects of the Ca2+ channel blockers ω‐conotoxin (ω‐CgTx), nifedipine and diltiazem, on the increase in tritium overflow and perfusion pressure elicited by renal nerve stimulation (RNS), veratridine (Vt) and potassium chloride (KCl), and on the vasoconstrictor response produced by noradrenaline (NA) were investigated in the isolated kidney of the rat perfused with Tyrode solution and prelabelled with [3H]‐noradrenaline ([3H]‐NA).

RNS (1–4Hz), Vt (15–90 nmol) and KCl (150–500 μmol) produced renal vasoconstriction and enhanced the tritium overflow in a frequency‐ and concentration‐dependent manner, respectively.

Administration of ω‐CgTx (50 nm) inhibited RNS‐, Vt‐ and KCl‐induced overflow of tritium; the associated renal vasoconstriction produced by RNS or Vt but not by KCl was inhibited. In contrast, ω‐CgTx failed to alter the vasoconstrictor response elicited by exogenous NA.

Infusion of nifedipine (10 μm) enhanced the tritium overflow elicited by RNS and KCl but not by Vt; a low dose of nifedipine (1.4 μm) enhanced the tritium overflow elicited by all these stimuli. Low doses of diltiazem (6 μm) failed to alter the tritium overflow produced by these stimuli. However, higher doses of diltiazem (60 μm) reduced the tritium overflow elicted by RNS or Vt but enhanced that caused by KCl. The renal vasoconstriction produced by RNS, Vt and KCl as well as by exogenous NA was inhibited by low and high doses of nifedipine and diltiazem.

These data suggest that (a) RNS, Vt and KCl enhance the release of adrenergic transmitter by promoting the influx of Ca2+ into the nerve terminal through specific Ca2+ channels, probably N‐type Ca2+ channels that are distinct from those located in the vascular smooth muscle and (b) ω‐CgTx could be a useful tool to differentiate between Ca2+ channels at the adrenergic nerve terminal and vascular smooth muscle.
Regional differences in the mechanical properties of rabbit airway smooth muscle
Authors: Fujiwara Takashi , Itoh Takeo , Kuriyama Hirosi
Published: July 2012

In studies of rabbit airway smooth muscle, differences in mechanical responses to acetylcholine, histamine and high K+ in intact muscles, and in Ca2+ sensitivity in skinned muscles, have been examined in tissue taken from 5 different regions of the airway. Interactions between prostaglandin F2aL and epithio‐thromboxane A2 and the above spasmogenic agencies were also studied.

Mechanical responses to histamine (10 μm) and to 128 mM K+ were smallest in trachea and were largest in 3rd and 4th order bronchi. In all regions, spasm evoked by 10 μm acetylcholine was greater than that evoked by 10 μm histamine or 128 mM K+.

In the third and fourth branches of the rabbit right middle bronchus, contractions evoked by 10 μm acetylcholine, 10 μm histamine and 128 mM K+ showed similar amplitudes of phasic response. In Ca2+‐free solution containing 2 mM EGTA, the phasic components of the acetylcholine‐ or histamine‐induced contraction remained unchanged in comparison with that observed in Krebs solution, but the phasic and tonic components of the K+‐induced contraction and the tonic changes induced by acetylcholine and histamine were abolished.

Two subtypes of the histamine receptor, excitatory H1‐ and inhibitory H2‐ receptors were detected on the bronchial smooth muscle. The H1‐induced contraction was mediated by release of stored Ca2+ together with activation of Ca2+ influx relatively insensitive to Ca2+ antagonists.

The ‐log(EC50) values for acetylcholine and histamine (in the presence of cimetidine and atropine) were 6.11 ± 0.11 and 5.33 ± 0.08, respectively, in the third branch of right middle bronchus. These values were similar to those observed for trachea.

Prostaglandin F2α (10 μm) and 9,11‐epithio‐11,12‐methano‐thromboxane A2 (0.1 μm) neither provoked nor enhanced the contractions evoked by any stimulants.

No difference was observed between the Ca2+ sensitivity of chemically skinned muscle from the trachea and that of muscle from the third branch of the right middle bronchus.

Regional differences in the response to histamine and acetylcholine observed in airway smooth muscles are discussed and it is concluded that these may be due to differences in receptor numbers.
Pharmacological properties of GR38032F, a novel antagonist at 5‐HT3 receptors
Authors: Butler A. , Hill J.M. , Ireland S.J. , Jordan C.C. , Tyers M.B.
Published: July 2012

This paper describes the pharmacology of the novel 5‐hydroxytryptamine3 (5‐HT3) receptor antagonist GR38032F.

On the isolated vagus nerve and superior cervical ganglion of the rat, R,S‐GR38032F behaved as a reversible competitive antagonist of 5‐HT‐induced depolarization with pKB values of 8.61 ± 0.08 (n = 19) and 8.13 ± 0.07 (n = 16), respectively. The resolved R‐ and S‐isomers of GR38032F were approximately equipotent as 5‐HT antagonists on the rat vagus nerve: the pKB values were 8.95 ± 0.05 (n = 16) and 8.63 ± 0.08 (n = 17), respectively. R,S‐GR38032F was also an effective antagonist of 5‐HT on the rabbit isolated vagus nerve: in this case the pKB value was 9.40 ±0.14 (n = 4).

On the rabbit isolated heart, low concentrations of R,S‐GR38032F (3 × −1011 −1 × 10‐9 m) antagonized the positive chronotropic effect of 5‐HT and 2‐methyl‐5‐hydroxytryptamine (2‐methyl‐5‐HT). However, the effects of the compound did not appear consistent with simple reversible competition.

On the longitudinal smooth muscle of the guinea‐pig ileum, R,S‐GR38032F caused concentration‐dependent parallel rightward displacement of the 2‐methyl‐5‐HT concentration‐contraction response curve; in contrast, a portion of the response to 5‐HT appeared resistant to R,S‐GR38032F. pKB values estimated from the effects of the compound against 2‐methyl‐5‐HT or the inhibitable portion of the response to 5‐HT were 7.31 ± 0.06 (n = 8) and 7.33 ± 0.13 (n = 8), respectively. Against 2‐methyl‐5‐HT, R‐GR38032F seemed more potent (pKB 7.20 ± 0.10; n = 6) than S‐GR38032F (pKB 6.30 ± 0.05; n = 6).

R,S‐GR38032F is highly selective for 5‐HT3 receptors, and at concentrations of 3 × 10−6‐3 × 10−5m, had negligible agonist or antagonist activity on other 5‐HT or non‐5‐HT receptor‐containing tissues on which it was tested.

The potency and duration of action of R,S‐GR38032F in blocking 5‐HT3 receptors in vivo were assessed by measuring its ability to antagonize the bradycardic response to 5‐HT or 2‐methyl‐5‐HT administered intravenously (i.v.) to anaesthetized animals. For i.v. administration to the rat, the ED50 for R,S‐GR38032F against 2‐methyl‐5‐HT (100 μg kg−1) was 0.4 (95% confidence limits 0.18–0.87) μg kg−1 (n = 10); the corresponding value for oral administration to this species was 7.0 (3.0–22.0) μg kg−1 (n = 8–10 per dose level). R,S‐GR38032F was similarly effective in the anaesthetized cat.

The present results are discussed with reference to the postulated existence of subtypes of the 5‐HT3 receptor.
Heterogeneous vasomotor responses of anatomically distinct feline cerebral arteries
Authors: Hamel Edith , Edvinsson Lars , MacKenzie Eric T.
Published: July 2012

The vasomotor reactivity to a number of neurotransmitters and blood‐borne substances was evaluated in several anatomically distinct arteries of the cat cerebral circulation. Few regional differences were observed in their vasoconstrictor responses to noradrenaline, dopamine, 5‐hydroxytryptamine and prostaglandin F2α. Only the anterior cerebral artery reacted strongly to all vasoconstrictor agents.

Adenosine, acetylcholine and histamine induced pronounced relaxation in the vast majority of the major cerebral arteries. The relaxation elicited by adenosine showed a slight degree of heterogeneity between the arteries and the overall response accounted for 81 ± 6% of the pharmacologically‐induced tone. On the other hand, the dilatation induced by acetylcholine and histamine varied as a function of the anatomical localization of the cerebral arteries. The acetylcholine‐induced vasodilatation was significantly more pronounced in the middle cerebral, anterior communicating and anterior cerebellar arteries, with respective responses of 72, 66 and 83% of the induced tone as compared to 43% in the other vessels. However, all arteries were equally sensitive to acetylcholine with an overall mean pD2 value of 7.47 ± 0.06. The most heterogeneous results were obtained with histamine and applied both to the magnitude of the maximal response and the sensitivity of the various arteries to this amine. The intensity of the relaxation varied from 20% (anterior communicating artery) to 118% (posterior cerebellar artery).

Among the neuropeptides studied, substance P and bradykinin were considerably less potent than vasoactive intestinal peptide on all the cerebral arteries. The least responsive vessel to bradykinin was the anterior cerebral artery with a maximal response of 22 ± 5% of the induced‐tone and a pD2 value of 7.56 ± 0.24. All vessels responded weakly to substance P and those from the vertebrobasilar circulation were significantly less sensitive to this neuropeptide with pD2 values around 8.07 as compared to 9.82 in the more rostral arteries. Although all vessels were equally sensitive to vasoactive intestinal peptide, the dilator responses were significantly less pronounced in the middle cerebral and basilar arteries (maximal response of 86 ± 5% and 69 ± 6% of the induced‐tone, respectively, as compared to 110 ± 9% in the other vessels).

The vertebrobasilar arteries were as reactive, if not more reactive, to vasoconstrictors than the vessels originating from the carotid circulation. In contrast, the dilator responses were less marked in most caudal arteries. Such dichotomies may be important in the regulation of local cerebral blood flow.

The results emphasize the considerable heterogeneity in the vasomotor responses to a given substance among the various cerebral arteries. Further, they suggest the presence of multiple receptor populations which mediate opposite effects and which are distributed in different proportions among the cephalic arteries.
Impairment of endothelium‐dependent relaxation in aortae from spontaneously diabetic rats
Authors: Durante William , Sen Amar K. , Sunahara Fred A.
Published: July 2012

Diabetes mellitus is known to produce alterations in vascular reactivity. The present study examined the effects of endothelium‐dependent and endothelium‐independent relaxing substances on thoracic aorta from control and spontaneously diabetic rats.

Endothelium‐dependent relaxation produced by acetylcholine or the calcium ionophore, A23817, in aortic rings precontracted with phenylephrine was significantly attenuated in diabetic vessels.

Relaxations produced by sodium nitroprusside or adenosine in diabetic preparations were comparable to those in control vessels.

The results show that diabetes leads to a specific impairment of endothelial‐dependent relaxation.
Evidence for excitatory 5‐HT2‐receptors on rat brainstem neurones
Authors: Davies Michael , Wilkinson Lawrence S. , Roberts Malcolm H.T.
Published: July 2012

The technique of microiontophoresis was used to investigate the identity of the receptor mediating the excitatory effects of 5‐hydroxytryptamine (5‐HT) upon neurones in the midline of the medullary brainstem of the rat in vivo.

The 5‐HT1‐like receptor agonists 5‐carboxamidotryptamine (5‐CT) and 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OH‐DPAT) failed to excite the majority of neurones excited by 5‐HT. The mobilities of 5‐CT and 8‐OH‐DPAT when tested in vitro were found not to differ significantly from that of 5‐HT, suggesting that the lack of effect of these agonists was not due to a lower rate of release from the microelectrodes.

The excitatory responses to 5‐HT were attenuated by the 5‐HT2‐receptor antagonists ketanserin and methysergide when applied microiontophoretically or administered intravenously (0.3 and 1 mg kg−1 respectively). Excitatory responses to glutamate and noradrenaline were not reduced.

The 5‐HT3‐receptor antagonist MDL 72222 failed to attenuate selectively the excitatory response to 5‐HT when applied either by microiontophoresis or administered intravenously (1 mg kg−1).

Microiontophoretic application of the α1‐adrenoceptor antagonist prazosin did not attenuate excitatory responses to either 5‐HT or noradrenaline. Intravenously administered prazosin (0.8 mg kg−1) also failed to attenuate excitatory responses to 5‐HT, but did block excitatory responses to noradrenaline.

These results suggest that 5‐HT2‐receptors, but not 5‐HT1‐like receptors, 5‐HT3‐receptors or α1‐adrenoceptors, are involved in the excitatory response of midline medullary neurones to 5‐HT.
Adrenoceptor‐mediated changes of action potential and force of contraction in human isolated ventricular heart muscle
Authors: Jakob Helga , Nawrath Hermann , Rupp Johanna
Published: July 2012

The effects of α‐adrenoceptor stimulation on the action potential and force of contraction were investigated in human isolated ventricular heart muscle and compared with those of β‐adrenoceptor Stimulation.

The maximal stimulation by isoprenaline of β‐adrenoceptors produced large changes in the force of contraction, which were accompanied by moderate increases in the height of the action potential. The maximal inotropic effect produced by stimulation of α‐adrenoceptors with phenylephrine, in the presence of propranolol (1 μmol l−1) was much smaller (about 10% of that seen in response to β‐adrenoceptor stimulation), and no significant changes of the action potential configuration were observed.

The effects of noradrenaline and adrenaline on the force of contraction were not affected by prazosin.

It is concluded that the adrenoceptor‐mediated changes of the force of contraction (in the presence of either noradrenaline or adrenaline) in the human ventricle are due virtually exclusively to the stimulation of β‐adrenoceptors.
Modulation of divalent cation‐activated chloride ion currents
Authors: Scott R.H. , McGuirk S.M. , Dolphin A.C.
Published: July 2012

Voltage‐sensitive calcium channel currents carried by Ca2+ (ICa) or Ba2+ (IBa) were followed by tail currents carried by Cl− ions in approximately 45% of cultured dorsal root ganglion neurones.

Extracellular application of (−)‐baclofen (100 μm) inhibited IBa and ICl(Ba) BaY K 8644 (5 μm) potentiated both currents.

Intracellular GTP‐γ‐S increased the proportion of neurones in which ICl(Ba) was recorded. In addition, the activation by GTP‐γ‐S of a pertussis toxin‐sensitive GTP binding (G)‐protein resulted in a steady increase in the Cl− tail current with time, despite a concurrent reduction in IBa.

Extracellular application of 10 mM caffeine selectively reduced ICl(Ba) without significant change in IBa. When Ca2+ was the charge carrier, caffeine had little effect on ICl(Ca), and increased the inactivation of ICa.

We conclude that, in addition to being regulated by divalent cation entry through Ca2+ channels, the Cl− current is also regulated by G‐protein activation. The mechanism of activation of ICl(Ba) may involve Ca2+ release from intracellular stores.
Selective regulation of β1‐and β2‐adrenoceptors in the human heart by chronic β‐adrenoceptor antagonist treatment
Authors: Michel M.C. , Pingsmann A. , Beckeringh J.J. , Zerkowski H.‐R. , Doetsch N. , Brodde O.‐E.
Published: July 2012

In 44 patients undergoing coronary artery bypass grafting, the effect of chronic administration of the β‐adrenoceptor antagonists sotalol, propranolol, pindolol, metoprolol and atenolol on β‐adrenoceptor density in right atria (containing 70% β1‐ and 30% β2‐adrenoceptors) and in lymphocytes (having only β2‐adrenoceptors) was studied.

β‐Adrenoceptor density in right atrial membranes and in intact lymphocytes was assessed by (−)−[125I]‐iodocyanopindolol (ICYP) binding; the relative amount of right atrial β‐ and β2‐adrenoceptors was determined by inhibition of ICYP binding by the selective β2‐adrenoceptor antagonist ICI 118,551 and analysis of the resulting competition curves by the iterative curve fitting programme LIGAND.

With the exception of pindolol, all β‐adrenoceptor antagonists increased right atrial β‐adrenoceptor density compared to that observed in atria from patients not treated with β‐adrenoceptor antagonists.

All β‐adrenoceptor antagonists increased right atrial β1‐adrenoceptor density; on the other hand, only sotalol and propranolol also increased right atrial β2‐adrenoceptor density, whereas metoprolol and atenolol did not affect it and pindolol decreased it.

Similarly, in corresponding lymphocytes, only sotalol or propranolol increased β2‐adrenoceptor density, while metoprolol and atenolol did not affect it and pindolol decreased it.

It is concluded that β‐adrenoceptor antagonists subtype‐selectively regulate cardiac and lymphocyte β‐adrenoceptor subtypes. The selective increase in cardiac β1‐adrenoceptor density evoked by metoprolol and atenolol may be one of the reasons for the beneficial effects observed in patients with end‐stage congestive cardiomyopathy following intermittent treatment with low doses of selective β1‐adrenoceptor antagonists.
Peripheral sympatho‐inhibitory cardiovascular effects of opioid peptides in anaesthetized rabbits
Authors: Szabo Bela , Hedler Liselotte , Schurr Claudia , Starke Klaus
Published: July 2012

Opioid agonists influence isolated cardiovascular tissues from rabbits, as well as the cardiovascular system of pithed rabbits, through presynaptic receptors on postganglionic sympathetic nerve fibres. The present experiments were carried out in order to study effects which result from activation of these receptors in anaesthetized rabbits.

In pithed rabbits with electrically stimulated sympathetic outflow, infusion of [D‐Ala2‐D‐Leu5]‐enkephalin (DADLE) 10 μg kg−1 min−1 and dynorphin‐(1–13) (dynorphin) 1 μg kg−1 min−1 decreased the plasma noradrenaline concentration, mean arterial pressure (MAP) and heart rate. The effects of dynorphin and, less completely, those of DADLE were antagonized by the peripherally selective opioid antagonists N‐methyl naloxone bromide (NMN) 1.3 mg kg−1 and N‐methyl levallorphan methanesulphonate (NML) 1–3 mg kg−1.

In pentobarbitone‐anaesthetized rabbits, DADLE 3–30 μg kg−1 min−1 and dynorphin 0.3–3 μg kg−1 min−1 decreased the plasma noradrenaline concentration and MAP. The highest dose of dynorphin also decreased heart rate, whereas DADLE 10 μg kg−1 min−1 caused slight cardioacceleration. The effects of DADLE but not those of dynorphin decreased upon repeated administration.

The effects of dynorphin 10 μg kg−1 min−1 were abolished or greatly attenuated by NMN 1.3 mg kg−1 and NML 3 mg kg−1. In contrast, the antagonists reduced only slightly the blood pressure‐lowering effect of DADLE 10 μg kg−1 min−1 and did not reduce significantly the effects of DADLE on the plasma noradrenaline level and heart rate.

It was concluded that systemically administered dynorphin produces sympatho‐inhibition and an ensuing fall in blood pressure by an action at peripheral receptors, in all probability presynaptic κ‐receptors on postganglionic sympathetic nerve fibres. The effects of DADLE are more complex and may involve both central and peripheral components.
Temperature‐dependence of the kinetics of the binding of [3H]‐(+)‐N‐methyl‐4‐methyldiphenhydramine to the histamine H1‐receptor: comparison with the kinetics of [3H]‐mepyramine
Authors: Treherne J.M. , Young J.M.
Published: July 2012

The dissociation of [3H]‐(+)‐N‐methyl‐4‐methyldiphenhydramine ([3H]‐QMDP) from the histamine H1‐receptor was markedly temperature‐dependent. The t1/2 was 4 min at 37°C and 16 h at 6°C. The association rate constant, k1, was also temperature‐dependent, but not to the same extent as k‐1.

Plots of the observed rate constant for [3H]‐QMDP‐receptor complex formation, kon, versus [3H‐QMDP] were linear at both 30°C and 10°C, consistent with the interaction of [3H]‐QMDP with the H1‐receptor being a simple, one‐step equilibrium.

The ratio of the kinetic constants, k1/k‐1, indicated that the affinity constant of [3H]‐QMDP for the H1‐receptor should increase with decreasing temperature. Measurement of (+)‐QMDP antagonism of the contraction of longitudinal muscle strips from guinea‐pig small intestine induced by histamine at 37°C, 30°C and 25°C provided some evidence that the affinity of (+)‐QMDP is greater at 25°C than 37°C. However, the flattening of the concentration‐response curves for histamine at low concentrations of (+)‐QMDP at 30°C and 25°C is consistent with a slow dissociation of the (+)‐QMDP‐receptor complex and hence an incomplete equilibration with the agonist.

Arrhenius plots for k1 and k‐1 for [3H]‐QMDP were linear between 37°C and 6°C. The activation energies, Ea, for complex formation and dissociation were 77 ± 4 and 129 ± 3 kJ mol−1, respectively.

An Arrhenius plot for k‐1 for the dissociation of [3H]‐mepyramine from the H1‐receptor was also linear between 37°C and 6°C. The activation energy was 140 ± 2 kJ mol−1.

Activation energies for complex formation with the H1‐receptor, Eaf, and complex dissociation, Ead, were similar for [3H]‐QMDP and [3H]‐mepyramine. The energy difference, Eaf — Ead, equivalent to the enthalpy change, did not differ significantly for the two ligands (‐52 and −48 kJ mol−1, respectively). The larger values of k1 and k‐1 for [3H]‐mepyramine compared to [3H]‐QMDP imply the presence of an entropic component in the interaction.

The simplest explanation for these observations is that transfer from the aqueous phase into a hydrophobic region is a significant factor in antagonist‐H1‐receptor interaction. This would be entropically more favourable for [3H]‐mepyramine, a tertiary amine, than for [3H]‐QMDP, a quaternary amine.
Endothelium‐dependent effects of acetylcholine in rat aorta: a comparison with sodium nitroprusside and cromakalim
Authors: Taylor S.G. , Southerton J.S. , Weston A.H. , Baker J.R.J.
Published: July 2012

The mechanisms involved in the mechano‐inhibitory effects of acetylcholine (ACh) have been compared with those of sodium nitroprusside (SNP) and cromakalim on the rat isolated thoracic aorta.

Relaxations produced by ACh were endothelium‐dependent, whereas those produced by SNP or cromakalim were endothelium‐independent.

ACh, cromakalim and SNP relaxed established contractions produced by noradrenaline (NA) and KCl (20 mm) and these relaxations were well‐maintained.

SNP was a relatively effective inhibitor of contractions produced by KCl (80 mm). ACh was relatively ineffective and cromakalim was without effect against such contractions.

Membrane potential and cyclic GMP concentrations were higher in tissues with an intact endothelium whereas rubbed tissues had a higher 86Rb efflux rate coefficient.

ACh and cromakalim produced a transient and long‐lasting hyperpolarization, respectively. These changes were accompanied by increases in the 86Rb efflux rate coefficient with a time course comparable to that of the electrical changes.

Tissue cyclic GMP concentrations were significantly increased in the presence of ACh or SNP, whereas cromakalim had no effect.

Transmission electron microscopy showed the presence of endothelial cells on intact tissues. On rubbed preparations, such cells were absent and some damage to the underlying smooth muscle cells was detected.

It is concluded that at least two inhibitory substances are released from the endothelial cells by ACh. One of these increases tissue cyclic GMP concentrations and produces an electrically‐silent relaxation. The other produces a transient hyperpolarization associated with the opening of 86Rb‐permeable K‐channels. This event may serve to initiate relaxation processes and to close any open voltage‐dependent Ca‐channels.
Human liver morphine UDP‐glucuronyl transferase enantioselectivity and inhibition by opioid congeners and oxazepam
Authors: Wahlström Agneta , Pacifici Gian Maria , Lindström Björn , Hammar Lena , Rane Anders
Published: July 2012

Morphine uridine diphosphate glucuronyl transferase (UDP‐GT) was studied in human liver microsomes. The (−)− and (+)‐morphine enantiomers were used as substrates and inhibitors, such as oxazepam and various opioid congeners were employed to characterize the different glucuronidation pathways. The kinetics of the oxazepam inhibition were studied in the rat liver.

The overall glucuronidation of (+)‐morphine was higher than that of (−)‐morphine. The morphine congeners tested, potently inhibited the formation of (−)‐morphine‐3‐glucuronide ((−)‐M3G), except for normorphine and codeine. The formation of (+)‐morphine‐6‐glucuronide ((+)‐M6G) was potently inhibited by only dextromethorphan and (+)‐naloxone. All drugs except normorphine inhibited the formation of (+)‐M3G by 18–50%.

The metabolism of (−)‐morphine to (−)‐M3G was more sensitive to oxazepam inhibition than the formation of (+)‐M3G from (+)‐morphine in the rat liver.

The glucuronidation of natural morphine is subject to in vitro interaction with oxazepam and several opiate drugs. Our study supports the theory of more than one type of UDP‐GT being involved in morphine glucuronidation.
Effect of phenobarbitone pretreatment upon endothelium‐dependent relaxation to acetylcholine in rat superior mesenteric arterial bed
Authors: Randall Michael D. , Hiley C. Robin
Published: July 2012

Pretreatment of rats for 5 days with phenobarbitone (80 mg kg−1 day−1) enhanced the potency of acetylcholine in opposing noradrenaline‐induced vasoconstriction in the isolated perfused superior mesenteric arterial bed; in 10 saline‐pretreated control animals the ED50 was 14.0 ± 3.9 ng whereas it was 3.23 ± 1.00 ng in 10 phenobarbitone‐pretreated animals.

In both saline‐ and phenobarbitone‐pretreated rats acetylcholine was ineffective at opposing noradrenaline vasoconstriction after the mesentery had been perfused for 90s with a 0.3% solution of the detergent CHAPS in distilled water (to remove the endothelium), but pressor responses to noradrenaline were unaffected.

Pretreatment with phenobarbitone had no effect on the opposition by sodium nitroprusside of noradrenaline pressor responses. Also, the effects of nitroprusside were not affected by perfusion with CHAPS in either control or barbiturate‐pretreated groups.

Inclusion of indomethacin (10 μm) in the perfusion fluid had no effect on the enhancement by phenobarbitone pretreatment of the endothelium‐dependent opposition by acetylcholine of noradrenaline pressor responses; the ED50 values in the absence and presence of indomethacin were, respectively, 2.40 ± 0.31 ng and 1.87 ± 0.27 ng (n = 6).

The concentration of cytochrome P450 in the microsomal fraction obtained from the mesenteric preparation was increased from 204 ± 32 (saline‐pretreated; n = 7) to 784 ± 249 pmol g−1 wet wt (n = 7) by the phenobarbitone pretreatment.

It is concluded that the increase in potency of acetylcholine as an endothelium‐dependent vasodilator by phenobarbitone pretreatment is most probably at the level of the endothelium rather than the vascular smooth muscle.
Effects of furosemide on renal haemodynamics and proximal tubular sodium reabsorption in conscious rats
Authors: Christensen Sten , Petersen Jørgen S.
Published: July 2012

The effects of furosemide given as constant i.v. infusion (7.5 mg kg−1 h−1) or bolus injections (0.5, 7.5 and 120 mg kg−1) on renal haemodynamics and proximal tubular Na reabsorption were studied in conscious water diuretic rats. The clearance of Li (CLi) was used as marker for Na delivery from the proximal tubules, and clearance of [14C]‐tetraethylammonium (CTEA) and [3H]‐inulin (CIn) as markers for renal plasma flow (RPF) and glomerular filtration rate (GFR), respectively.

Furosemide caused a transient increase of RPF and GFR followed by a secondary decrease below baseline levels; the latter could in part be counteracted by volume replacement. The filtration fraction (FF = GFR/RPF) was not significantly changed by furosemide. Fractional proximal Na excretion (CLi/CIn) was significantly increased by all doses of furosemide independent of changes in RPF, GFR and FF.

The peak diuretic/natriuretic effect of furosemide was markedly potentiated by volume replacement, probably due to prevention of antinatriuretic mechanisms triggered by volume depletion.

It is concluded that following i.v. furosemide administration there is a biphasic change in renal haemodynamics in conscious, restrained rats, and that the inhibition of proximal Na reabsorption, as manifested by changes in fractional Li excretion, is not likely to be due to changes in total renal haemodynamics.
An examination of the postjunctional α‐adrenoceptor subtypes for (−)‐noradrenaline in several isolated blood vessels from the rabbit
Authors: Daly C.J. , McGrath J.C. , Wilson V.G.
Published: July 2012

Postjunctional α‐adrenoceptors in several isolated blood vessels from the rabbit have been characterized on the basis of the relative potency of the agonists noradrenaline (NA, non‐selective), phenylephrine (α1‐selective) and UK‐14304 (α2‐selective), and the potency of antagonists rauwolscine (α2‐selective) and corynanthine (α1‐selective) against contractions elicited by NA. In addition, the potency of prazosin against NA was also assessed in the venous preparations.

The thoracic aorta, ear artery and left renal vein appear to possess α1‐adrenoceptors since the agonist potency order was NA > phenylephrine > UK‐14304, while corynanthine was 3–10 fold more potent than rauwolscine.

The ear vein appears to possess α2‐adrenoceptors. The rank order of agonist potency was UK‐14304 > NA > phenylephrine and all three agonists elicited responses of similar magnitude. Furthermore, rauwolscine was 30 fold more potent than corynanthine while prazosin failed to produce a concentration‐dependent inhibition.

The saphenous vein and the plantaris vein appear to possess a mixture of both subtypes since the rank order of agonist potency was UK‐14304 > NA ≫ phenylephrine, while responses elicited by UK‐14304 were smaller than those to the other agonists. However, although rauwolscine was 20 to 100 fold more potent than corynanthine in both preparations, suggestive of predominantly α2‐adrenoceptors, prazosin was either potent (saphenous vein) or relatively inactive (plantaris vein).

The characteristics of postjunctional α1‐ and α2‐adrenoceptors on isolated blood vessels from the rabbit are discussed in relation to the value of both the agonists, particularly NA, and the antagonists used in this study.
An attempt at selective protection from phenoxybenzamine of postjunctional α‐adrenoceptor subtypes mediating contractions to noradrenaline in the rabbit isolated saphenous vein
Authors: Daly C.J. , Dunn W.R. , McGrath J.C. , Wilson V.G.
Published: July 2012

An attempt has been made, with the irreversible α‐adrenoceptor antagonist phenoxybenzamine, to find the conditions under which postjunctional α1‐adrenoceptors in the rabbit isolated saphenous vein can be inactivated, such that postjunctional α2‐adrenoceptors can be studied in isolation.

Following exposure to various concentrations of phenoxybenzamine, no evidence was found for a selective inactivation of the postjunctional population of α1‐adrenoceptors: the ‘rauwolscine‐resistant’ (α1‐) and the ‘rauwolscine‐sensitive’ (α2‐) responses to (—)‐noradrenaline were similarly affected.

However, in ‘receptor protection’ experiments following exposure to a combination of phenoxybenzamine and the selective α2‐adrenoceptor antagonist rauwolscine, the remaining response to (—)‐noradrenaline appeared to be mediated by a single population of postjunctional α2‐adrenoceptors: the response was insensitive to prazosin and rauwolscine was more potent than corynanthine.

Partial isolation of the α1‐adrenoceptor population was attempted by pre‐exposure of the preparation to a combination of phenoxybenzamine and a selective α1‐adrenoceptor antagonist, i.e. prazosin or YM‐12617. Following receptor protection, the inhibition produced by ‘selective’ concentrations of either of these α1‐adrenoceptor antagonists were not significantly different from that observed in control preparations (no phenoxybenzamine). However, the selective α2‐adrenoceptor antagonists rauwolscine and CH‐38083 were still able to inhibit part of the remaining responses to NA. This is interpreted as indicating that, in addition to protecting the putative postjunctional α1‐adrenoceptors, these procedures fail to produce complete inactivation of postjunctional α2‐adrenoceptors.

It is concluded that, although phenoxybenzamine appeared to be non‐selective for the two populations of postjunctional α‐adrenoceptors in the rabbit isolated saphenous vein, inclusion of a ‘selective’ concentration of a competitive antagonist during the inactivation period results in differing degrees of functional protection of each subtype. Pharmacological isolation was possible for α2‐adrenoceptors but not convincingly for α1‐adrenoceptors.
The contractile activities of lipoxin A4 and lipoxin B4 for guinea‐pig airway tissues
Authors: Jacques Crawford A.J. , Spur Bernd W. , Crea Attilio E.G. , Lee Tak H.
Published: July 2012

The isometric contractile activities of lipoxin A4 (LxA4) and lipoxin B4 (LxB4) were evaluated on guinea‐pig lung tissue over the concentration range, 10−8 to 10−5 m.

LxA4 contracted guinea‐pig lung parenchymal strips; the concentration eliciting 50% maximum histamine response was 3 × 10−6 m. LxA4 did not contract tracheal spirals.

The LxA4 dose‐response curve was parallel to that of leukotriene D4 (LTD4) with LxA4 being approximately 10,000 fold less potent than LTD4.

The time course of the contraction elicited by LxA4 was similar to that of LTD4 and it was slow in onset and did not plateau for 20 min.

Pre‐incubation of parenchymal strips with leukotriene receptor antagonists at a concentration of 1 × 10−6 m to 3 × 10−5 m FPL 55712 or 3 × 10−5 m L 649923 inhibited LxA4 activity.

Pre‐incubation of tissues with 1 × 10−5 m L 651392, a 5‐lipoxygenase inhibitor, or 1 × 10−5 m indomethacin, a cyclo‐oxygenase inhibitor, did not affect the contractile activity of LxA4.

LxB4 did not constrict parenchymal strips or tracheal spirals.
Effects of magnesium, ouabain and bumetanide on 86rubidium uptake in a human atrial cell line
Authors: Borchgrevink P.C. , Ryan M.P.
Published: July 2012

The effects of extracellular magnesium concentrations (0, 0.6, 1.2 mm) on 86Rb (used as an analogue of potassium) uptake were investigated in the Girardi human atrial cell line in the presence and absence of drugs.

Increasing extracellular magnesium resulted in significantly higher 86Rb uptake. Compared to uptake in 0.6 mm (the physiological extracellular magnesium concentration), uptake of 86Rb was significantly higher in the 1.2 mm magnesium medium and significantly lower in the magnesium‐free medium.

Ouabain (10−3 m) and bumetanide (10−4 m) were added to inhibit, respectively, the Na‐K‐ATPase and the Na‐K‐Cl co‐transport system in the media containing the three magnesium concentrations. The ouabain‐sensitive, bumetanide‐sensitive and residual transport were found to be 58%, 29% and 13% of the total uptake in the medium containing 0.6 mm magnesium.

The oubain‐sensitive 86Rb uptake was inhibited significantly by reducing the magnesium concentrations to zero whereas the bumetanide‐sensitive and residual uptake were not significantly affected by different magnesium concentrations.

At three different ouabain concentrations (10−7 m, 10−5 m, 10−3 m) studied there was significantly greater uptake of 86Rb in 1.2 mm magnesium compared to uptake in 0 mm magnesium.

The present findings indicate that extracellular magnesium is important for 86Rb (potassium) transport in cardiac cells, and suggest that the main effect is on the Na‐K‐ATPase component of transport.
Vascular smooth muscle sensitivity to endothelium‐derived relaxing factor is different in different arteries
Authors: Christie M.I. , Lewis M.J.
Published: July 2012

The relaxation responses of pre‐constricted pig coronary artery (PCA) and rabbit aorta (RA) without endothelium, to endothelium‐derived relaxing factor (EDRF) released from either a PCA or RA with intact endothelium have been studied by use of a bioassay cascade system. Effects of EDRF have been compared with sodium nitroprusside (NaNP) and 8‐bromo‐cyclic GMP.

The time course of changes in cyclic GMP levels in response to EDRF in PCA and RA have also been studied.

EDRF (released from a PCA or RA) caused significantly greater relaxation in the PCA than the RA, whether 5‐hydroxytryptamine or high extracellular potassium was used as the constrictor agonist.

These differences in sensitivity to EDRF were paralleled by NaNP but not 8‐bromo‐cyclic GMP.

Cyclic GMP levels peaked earlier in the RA (30 s) than in the PCA (180 s) but the peak levels were significantly greater in the PCA (2.45 fold) than the RA (1.48 fold).

These data show that the previously described differences in EDRF activity between different artery types can be explained in part by differences in the responsiveness of the smooth muscle to EDRF.