Myointimal hyperplasia and sympathetic reinnervation following local cold injury and rapid rewarming in the rabbit central ear artery

BACKGROUND

Functional and pathological improvements following rapid rewarming in 42 degrees C water was compared with alterations following slow thawing at room temperature (22 degrees C) after frostbite (-9 degrees C, 15 minutes) in vivo of the rabbit central ear artery.

METHODS

Following two to ten weeks of in vivo regeneration, vascular segments were tested in vitro. Maximal and dose-dependent isometric contractions were induced by exogenous noradrenaline. Sympathetic nerves in the vascular wall were stained with glyoxylic acid. Vascular ring segments were stained with haematoxylin and eosin.

RESULTS

Following slow thawing, the total uptake, the K+ evoked and the spontaneous release of [3H]noradrenaline in the sympathetic nervous system were strongly reduced two weeks after freezing, with a subsequent increase to control level within 3-4 weeks. After rapid rewarming the total uptake, the spontaneous release and the K+ evoked release of [3H]noradrenaline commenced earlier such that after ten weeks the level was twice as high as following slow rewarming. The glyoxylic acid induced catecholamine fluorescence in sympathetic nerves, revealed an earlier regeneration after rapid rewarming. Haematoxylin and eosin-stained segments revealed less intimal hyperplasia three to 20 weeks after rapid rewarming than after slow thawing.

CONCLUSION

Rapid rewarming of in vivo frozen arteries in warm water (42 degrees C) did not prevent immediate vasoparalysis and degeneration of sympathetic nerves. However, nerve regeneration occurred earlier and with higher tissue nerve densities as compared to tissue that had been slowly rewarmed. Myointimal hyperplasia was less pronounced after rapid rewarming. Abnormal sympathetic nerve function and myointimal hyperplasia, as observed in this study, may contribute to a greater understanding of sequelae in the human body following frostbite.

Phytoplanktonic and Bacterial Carbon Pools and Productivities in the Gerlache Strait, Antarctica, during Early Austral Spring

Abstract Phytoplankton and bacterial biomass and productivities were investigated at four depths in the upper 500 m of the water column in the Gerlache Strait, Antarctica, during the prebloom period of early austral spring, from October 13 to November 4, 1995. The concentrations of all carbon pools were low, with the total particulate organic carbon (POC) concentration averaging 1.9 +/- 0.9 µM. Bacterial, protozoan, and phytoplankton carbon accounted for 21% of the total POC, indicating that detritus or unenumerated organisms comprised the bulk of the POC during this period. Larger zooplankton or protozoa, such as ciliates, may account for this difference, since microzooplankton can represent a significant fraction of the total microbial biomass. Primary and bacterial secondary production rates were also low, less than 300 and 30 ng C L(-1) h(-1), respectively. However, when production was normalized to either chlorophyll or bacterial cell number, rates were similar to those recorded during the spring bloom periods. This indicates that the cells were metabolically active during the prebloom period. Chlorophyll specific primary production averaged over the upper 80 m of the water column was 1.28 +/- 0.84 µg C µg chl(-1) h(-1), whereas the mean bacterial specific growth rate over the same depth interval was 0.34 +/- 0.24 d(-1). The overall production rates were low only because of the low abundance of cells during the prebloom period. When the site was reoccupied the following year, all measures of biomass and productivity were higher [36], emphasizing the large interannual variability in the Gerlache Strait.http://link.springer-ny.com/link/service/journals/00248/bibs/38n3p296.html</hea

Early and late functional and histopathological perturbations in the rabbit ear-artery following local cold injury

BACKGROUND

These experiments aimed to study the in vivo short and long term neurovascular regeneration after frostbite.

METHODS

The rabbit central ear-artery was used as the experimental model. The effects on the noradrenergic innervation of the artery were measured in isolated vascular ring segments the first day and 2, 3-4, and 8-10 or 10-20 weeks following freezing at -9 degrees C or -18 degrees C for 15 min with slow rewarming for 7 min at room temperature.

RESULTS

Two days after freezing the sympathetic nerves were completely degenerated, as observed with glyoxylic acid-induced fluorescence. The vascular isometric tension responses to exogenous noradrenaline and endogenously released noradrenaline by electrical stimulation in vitro were abolished. A varying degree of necrosis of the vascular wall was observed. Two weeks after freezing at -18 degrees C in vitro responses to exogenous noradrenaline and electrical stimulation were still abolished, then gradually approaching control levels after 10-20 weeks of in vivo regeneration. Eight and 10 weeks after injury at -9 degrees C increased vascular tension responses to exogenous noradrenaline was found. In spite of a long regeneration period the total uptake and the spontaneous and K+ (75 mM) evoked releases of [3H]noradrenaline were persistently decreased after frostbite at -18 degrees C, but they were regenerated to control levels already 10-20 weeks after -9 degrees C. Regeneration of noradrenergic nerve function, expressed as [3H]noradrenaline uptake and release and responsiveness to electrical stimulation, expressed as vascular contraction, was slower than the regeneration of the vascular smooth muscle. Myointimal hyperplasia developed in response to -9 degrees C and -18 degrees C frostbite. The uptake and the K+ evoked release of [3H]noradrenaline were particularly sensitive parameters for autonomic nerve function.

CONCLUSIONS

The present findings may demonstrate important neurovascular reactions to local frostbite and may explain human sequelae following frostbite.

Effect of alpha-trinositol on interstitial fluid pressure, oedema generation and albumin extravasation in experimental frostbite in the rat

1. The anti-inflammatory effect of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate) on oedema formation, microvascular protein leakage and interstitial fluid pressure (Pif) in rat skin after frostbite injury, was investigated. Alpha-trinositol (40 mg kg body weight(-1)) was administered intravenously as a bolus both before and/or in the interval between freezing and thawing of the tissue. 2. Pif was measured in rat paw skin with micropipettes connected to a servo-controlled counterpressure system. Oedema formation was estimated by measuring the increase in total tissue water content (wet weight minus dry weight divided by dry weight). Albumin extravasation (i.e., the difference between the plasma equivalent space for 125I- and 131I-human serum albumin (HSA) circulating for different time intervals) was used to estimate the microvascular leakage. 3. Compared to untreated animals, alpha-trinositol given pre- and/or post-freeze reduced total tissue water and albumin extravasation as well as the fall in Pif in injured tissue significantly (P<0.05). Alpha-trinositol given only post-freeze reduced total tissue water and albumin extravasation from 4.46+/-0.93 and 2.37+/-1.12 to 2.51+/-0.29 and 0.36+/-0.18 ml g dry weight(-1), respectively (P<0.05). 4. Pif fell from -0.8+/-0.2 mmHg pre-freeze to -3.4+/-1.0 mmHg (P<0.05) at 20 min after tissue injury (circulatory arrest) and was attenuated by treatment with alpha-trinositol. 5. We conclude that alpha-trinositol exerts its anti-oedematous effect by acting on the extracellular matrix, attenuating the lowering of Pif as well as on the microvascular wall, thereby decreasing the protein extravasation.

[Frostbite injuries]

Frostbite injuries occur mainly in toes, fingers, ears, nose and cheek. Typically an initial vasoconstriction in the skin will protect from drop in core temperature. Ice crystal development occurs when tissue temperature drops to -2 degrees C, leading to increased osmolality of the extracellular fluid and intracellular dehydration. An additional insult occurs with thawing due to reperfusion of the tissue and thereby release of inflammatory mediators. Symptoms of frostbite injury are: White-cyanotic discoloration, pain and numbness followed by hypoaesthesia. General hypothermia should be prevented and treated before managing the local frostbite injuries. Direct contact with warm skin without rubbing should be used in superficial injuries. More severe and deeper injuries should not be thawed until definite treatment could be given in a hospital. Re-freezing and mechanical influence on the injured parts must be avoided. Thawing should preferably be done in stirred water of 40-42 degrees C with mild soap. Antibiotics may be indicated when the skin barrier is broken. Surgical debridement should be postponed until a clear demarcation occurs.

The effect of water soluble cyanotoxin(s) produced by two species of Anabaena on the release of acetylcholine from the peripheral cholinergic nervous system of the rat airway

A water extract of the lyophilised fresh-water alga Anabaena flos-aquae enhanced substantially the release of [(3)H]acetylcholine ([(3)H]acetylcholine and [(3)H]choline) from cholinergic nerves of rat bronchi. Parallel experiments performed with the related species Anabaena lemmermannii did not demonstrate this effect. The effect on the release of [(3)H]acetylcholine by A. flos-aquae extract was concentration dependent. The A. flos-aquae induced [(3)H]acetylcholine release was not reduced by exposure to a low concentration of Ca(2+), but ω-conotoxin GVIA (1.0 μM), a blocker of N-type Ca(2+) channels reduced the release of [(3)H]acetylcholine induced by the A. flos-aquae extract. Addition of verapamil in a concentration (1.0 μM) specific for inhibition of L-type Ca(2+) channels had no effect on the neurotransmitter release. A reduction in the release was, moreover, observed with the intracellular Ca(2+) chelator BAPTA/AM (30 μM) and with the Na(+) channel blocker tetrodotoxin (3.0 μM). During patch-clamp studies of GH(4)C(1) neuronal cells, which have L- and T-type Ca(2+) channels, but no Na(+) channels, it was shown that a water extract of A. flos-aquae depolarised these cells and reduced, rather than enhanced, the influx of Ca(2+). Such an effect was not seen following exposure of GH(4)C(1) cells to water extracts of A. lemmermannii. In addition to its presynaptic activity, the water extract of A. flos-aquae showed an antimuscarinic effect by displacing [(3)H]QNB binding from muscarinic receptors in homogenates of rat bronchi. A similar but more potent effect was observed during experiments with water extract of A. lemmermannii. None of the respective water extracts showed any effects on cholinesterase activities in rat bronchial smooth muscle. The present observations suggest, therefore, that water extracts of A. flos-aquae may depolarise cells by activation of mono and divalent cation channels in cholinergic nerve cells. These channels are probably Na(+) channels and N-type, but not L- or T-type Ca(2+) channels. L- and T-type Ca(2+) channels were blocked in experiments with GH(4)C(1) cells and high concentrations of Ca(2+) channel blockers were necessary to reduce the effects of A. flos-aquae extract in cholinergic nerves in the airways. Furthermore, A. flos-aquae extract may also mobilise Ca(2+) from intracellular compartments. A. lemmermannii, on the other hand, does not contain components which alter mono and divalent cation-fluxes across cell membranes, but may rather have substances with more potent antagonistic effects on muscarinic cholinergic receptors than what is observed in experiments with A. flos-aquae.

Enhancement of acetylcholine release by homoanatoxin-a from Oscillatoria formosa

The strain NIVA-CYA 92 of Oscillatoria formosa Bory ex Gormont produces phycotoxins with neurotoxic properties. Chemical analysis by gas chromatography/mass spectrometry of a water extract of lyophilized material of the organism showed the presence of only homoanatoxin-a. The mechanism of action of homoanatoxin-a on peripheral cholinergic nerves is so far not known. The neurotoxicity of O. formosa containing homoanatoxin-a was investigated in rat bronchi, rat brain synaptosomes and in GH(4)C(1) cells. The water extract of lyophilized material of the organism produced a concentration-dependent reversible increase in the release of [(3)H]acetylcholine from both K(+) (51 mM) depolarised and non-depolarised cholinergic nerves of the rat bronchial smooth muscle. The K(+)-evoked release of [(3)H]acetylcholine was enhanced by about 75% by a water extract from 15-20 mg/ml of lyophilized algal material. The enhanced release of [(3)H]acetylcholine was substantially reduced by the L-type Ca(2+)-channel blocker verapamil (100 μM) and not by the N-type Ca(2+)-channel blocker ω-conotoxin GVIA (1.0 μM) or the P-type Ca(2+)-channel blocker ω-agatoxin IV-A (0.2 μM). Chelation of intra-cellular Ca(2+) by 1,2-bis-(aminofenoxi)etan-N,N,N',N'-tetraacidic acid/acetoxymethyl (BAPTA/AM) (30 μM) had no effect on the phycotoxin-induced release of [(3)H]acetylcholine, indicating that an extracellular pool of Ca(2+) was important for the action of the phycotoxin on the release of [(3)H]acetylcholine from peripheral cholinergic nerves. In rat brain synaptosomes the algal extract enhanced the influx of (45)Ca(2+) in a tetrodotoxin (1.0 μM) and ω-conotoxin MVIIC (blocker of N-, P- and Q-type Ca(2+) channels) (1.0 μM) insensitive manner. Patch-clamp studies showed that the phycotoxin opened endogenous voltage dependent L-type Ca(2+) channels in neuronal GH(4)C(1) cells. These Ca(2+) channels and the effect of the toxin on the channels were blocked by the L-type Ca(2+)-channel antagonist gallopamil (200 μM). The present results suggest, therefore, that the investigated strain of O. formosa contains homoanatoxin-a, which enhances the release of acetylcholine from peripheral cholinergic nerves through opening of endogenous voltage dependent neuronal L-type Ca(2-) channels.

The effect of trimethyltin on acetylcholine release in the guinea-pig trachea

The purpose of the present work was to characterise the effects of trimethyltin on the release of acetylcholine from parasympathetic nerves and its effect on the postjunctional cholinergic stimulation of a smooth muscle. The guinea-pig trachea has been used as a model. Prejunctionally, trimethyltin (3.0 × 10(-3) M) significantly enhanced in a reversible manner the high K(+) (75 mM) evoked release of endogenous acetylcholine and [(3)H]acetylcholine. The evoked release of endogenous acetylcholine and [(3)H]acetylcholine was released from a pool of acetylcholine being independent of extraneuronal Ca(2+) in the presence, but not in the absence of trimethyltin. The effect of trimethyltin on the release was not inhibited by low Ca(2+) (0 mM and 1.0 × 10(-4) M) or by Ca(2+) channel blockers (verapamil, 1.0 × 10(-4) M, flunarizine, 1.0 × 10(-4) M, ω-conotoxin GVIA, 2.0 × 10(-7) M and ω-agatoxin, 2.0 × 10(-7) M). The present results also demonstrate that trimethyltin induce emptying of a non-vesicular, probably a cytoplasmic storage pool of acetylcholine, since AH5183 (2.0 × 10(-5) M), an inhibitor of the translocation of acetylcholine into synaptic vesicles, and α-latrotoxin (1.0 × 10(-8) M), a toxin from black widow spider venom inducing vesicle depletion, had no inhibitory effects on the release of [(3)H]acetylcholine evoked by trimethyltin (3.0 × 10(-3) M). The release of [(3)H]acetylcholine was moreover enhanced by trimethyltin when the vesicular uptake of [(3)H]acetylcholine was inhibited by AH5183, probably as a result of a higher cytoplasmic concentration of [(3)H]acetylcholine. Trimethyltin also reduced the neuronal uptake of [(3)H]choline and this was probably due to a depolarising effect of trimethyltin on the cholinergic nerve terminals. A similar depolarisation induced by trimethyltin was observed during patch clamping of GH(4) C(1) neuronal cells. Postjunctionally, trimethyltin had no effect by itself or on the carbachol-induced smooth muscle contraction, indicating that trimethyltin did not have a general depolarising effect on smooth muscle cells or an effect on muscarinic receptors. Furthermore, the reduced electrical field-induced contraction and the subsequent increase in the basal smooth muscle tension that was observed by addition of trimethyltin was activity-dependent, and was most probably due to emptying of a nervous non-vesicular storage pool of acetylcholine, followed by rapid hydrolysis of acetylcholine by acetyl- and pseudocholinesterases.

In vitro effects of toxogonin, HI-6 and HLö-7 on the release of [3H]acetylcholine from peripheral cholinergic nerves in rat airway smooth muscle

The purpose of this work was to evaluate the possible non-reactivating effects of toxogonin (1,1'[oxybis(methylene)]bis[4-[hydroxyimino) methyl]pyridinium]-dichloride), HI-6 (1-[[[(4-aminocarbonyl)pyridinio] methoxy]methyl]-2-[(hydroxyimino)methyl]pyridinium-dichloride) and HLö-7 (pyridinium, 1-[[[4-(aminocarbonyl)pyridino]methoxy] methyl]-2,4-bis-[(hydroxyimino)methyl]diiodide) on the release of acetylcholine from cholinergic nerves. The oximes have been tested in our rat bronchial smooth muscle model, with respect to the effects of oximes on the K+ (51 mM)-evoked release of [3H]acetylcholine in the presence and absence of soman (1.0 microM). Toxogonin (100 microM) had no effect on the K(+)-evoked release of [3H]acetylcholine in the presence or absence of soman (1.0 microM). Similar results were found for HI-6 (100 microM). In contrast, HLö-7 (100 microM) enhanced the K(+)-evoked release of [3H]acetylcholine in the absence of soman. In the presence of soman HLö-7 did not alter the release of [3H]acetylcholine induced by K+ stimulation. The potentiating effect of HLö-7 on the release of [3H]acetylcholine could be blocked by the L-, N- and P-Ca2+ channel blockers verapamil (0.1 and 1.0 microM), omega-conotoxin GVIA (1.0 microM) and omega-agatoxin IV-A (0.2 microM), respectively. Muscarinic receptor antagonists (atropine (10 microM), pirenzepine (M1) (1.0 microM) and methoctramine (M2) (1.0 microM) had no effects on the HLö-7 (100 microM)-enhanced release of [3H]acetylcholine. Protein kinase inhibitors (H-7 (20 microM), calphostin C (1.0 microM) and KN-62 (10 microM) inhibited the HLö-7 (100 microM)-enhanced K(+)-evoked release of [3H]acetylcholine. The results showed that only HLö-7 had a direct enhancing effect on the release of acetylcholine through activation or opening of Ca2+ channels and a subsequent protein phosphorylation in the nerve terminal.

Extract of the marine alga Prymnesium patelliferum induces release of acetylcholine from cholinergic nerves in the rat bronchial smooth muscle

An extract of the marine algal flagellate Prymnesium patelliferum enhanced the spontaneous as well as the K+ evoked (51 mM K+) release of [3H]acetylcholine and endogenous acetylcholine from autonomic cholinergic nerves of rat bronchial smooth muscle. The effects were concentration-dependent and reversible. The enhancement of the K+ evoked release by the algal extract was partly dependent on extracellular Ca2+ and was significantly suppressed by the organic Ca2+ blockers omega-conotoxin GVIA (1 microM), diltiazem (100 microM), nifedipine (100 microM) and flunarizine (100 microM). The enhancement of the spontaneous release seemed Ca2+ independent and not sensitive to the Na+ channel blocker tetrodotoxin. Sphingosine (20 microM), a protein kinase C inhibitor, strongly potentiated the enhancement of spontaneous release of [3H]acetylcholine induced by the algal extract whereas another protein kinase C inhibitor. 1-(5-quinolinesulphonyl)-2-methylpiperazine (H-7) (20 microM), was without effect. A similar potentiation as seen with sphingosine was observed with procaine (100 microM) and flunarizine (100 microM). The results indicate that the enhancement of the K+ evoked release of [3H]acetylcholine by the toxic extract of P. patelliferum was partly caused by activation of voltage-dependent Ca2+ channels. The increase in the spontaneous release of [3H]acetylcholine and endogenous acetylcholine induced by the algal extract alone may be caused by an ionophore-like property of the algal extract. This effect of the algal extract may be enhanced by compounds that facilitate the interaction of the algal toxin with the plasma membrane such as the lipophilic compounds flunarizine, procaine and sphingosine.

Responses of noradrenergic nerves in rabbit ear-artery before and after experimental frost-bite

Experiments were designed to determine the effects of sub-zero temperatures on the function of the noradrenergic innervation of a peripheral blood-vessel. The central ear-artery of the rabbit was used for this purpose. The ear was exposed to temperatures of -6, -9 or -18 degrees C in vivo for 15 min. After 1 day (24 h) or 6 days in vivo, the central ear-artery was dissected free, incubated in [3H]-noradrenaline (NA) and stimulated in vitro with high potassium (75 mM) for 5 min to evoke release of [3H]-NA. The release of [3H]-NA was Ca(2+)-dependent. One day after exposure to -6, -9 or -18 degrees C, increases of 45-57 and 44-72% and a reduction of 12-35% were observed, respectively, in three successive potassium-evoked NA-releases. After 6 days in vivo an increase of 30-34% was observed following exposure to -6 degrees C, while no alteration was observed after exposure to -9 degrees C. A reduction of 84-89% was recorded after exposure to -18 degrees C. Following this exposure to -18 degrees C, there was also a great reduction in the evoked release of [3H]-NA compared with the spontaneous release, whereas this correlation did not change after exposure to -6 and -9 degrees C. The total uptake of [3H]-NA was unchanged after freezing the tissue at -6 degrees C, but was substantially reduced after exposure to -9 and -18 degrees C. A short period of in vivo restoration (6 days, enhanced the uptake of [3H]-NA.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of experimental frost-bite on the responses of the rabbit ear-artery to adrenergic and electrical stimulation

The aim of the present investigation was to study the effect of sub-zero temperatures on the adrenergic activated, smooth muscle-contraction of a peripheral blood-vessel. The central ear-artery of the rabbit was used for this purpose. The artery was stimulated to contract in vitro by activation of phentolamine sensitive, post-junctional, alpha-adrenoceptors by use of noradrenaline, or by noradrenaline released from noradrenergic nerves in the blood-vessel following electrical field stimulation. The effect of freezing the tissue in vivo for 15 min at sub-zero temperatures (-4, -6 and -9 degrees C) was studied in vitro. Exposure to -4 and -6 degrees C did not alter the apparent affinity (ED50) of noradrenaline significantly, when measured immediately, or 2 or 6 days after exposure. The maximal response to noradrenaline was reduced by approximately 54, 74 and 100% following exposure to -4, -6 and -9 degrees C, respectively. The response was completely restored after 2 and 6 days of regeneration in vivo following exposure to -6 degrees C, whereas the response after exposure to -9 degrees C was restored by only about 8 and 30% after 2 and 6 days regeneration, respectively. The maximal response to electrical field stimulation, which was completely inhibited by tetrodotoxin and phentolamine, was reduced by approximately 92% after exposure for 15 min to -4 and -6 degrees C, while it was completely inhibited after exposure to -9 degrees C. The response was restored by only 15-20% following 2 and 6 days in vivo after exposure to -6 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of pyridostigmine pretreatment, HI-6 and Toxogonin treatment on rat tracheal smooth muscle response to cholinergic stimulation after organophosphorus inhalation exposure

The ex vivo contraction response of the rat tracheal smooth muscle was examined after 10 min in vivo inhalation of soman and/or pretreatment with pyridostigmine and/or post-exposure treatment with HI-6 ([[[(4-aminocarbonyl)pyridinio]methoxy]methyl]-2[(hydroxy imino) methyl]pyridinium dichloride) or Toxogonin (1,1'-[oxybis-(methylene)]bis[4-[(hydroxyimino)methyl]-py rid inium] dichloride). In vivo pretreatment with pyridostigmine was achieved by subcutaneous (s.c.) implantation of an osmotic pump that delivered pyridostigmine continuously (0.01 mg/h) in the neck region of the rat 18 h before soman exposure. The ex vivo cholinergic tracheal smooth muscle response increased during the first 60 min after soman exposure in animals pretreated with pyridostigmine. The amplitude of the contraction response in pyridostigmine pretreated animals was about 60% of control, compared to 15% of control without pyridostigmine pretreatment. Pyridostigmine pretreatment also produced significant recovery of the total cholinesterase (ChE) activity in plasma, but not in trachea and lung. Intraperitoneal (i.p.) injection of HI-6 or Toxogonin (50 mg/kg), immediately after 10 min inhalation exposure to soman, also significantly improved the ex vivo cholinergic contraction response of the trachea (decapitation 15 min after oxime administration). The recovery of the physiological response with Toxogonin was, however, not stable. HI-6 was superior to Toxogonin with respect to the initial airway contraction response, and the response increased up to a stable level not significantly different from control. There was no significant reactivation of the ChE activity after treatment with the oximes. Combination of pyridostigmine pretreatment and oxime treatment enhanced the recovery of the tracheal contraction response and the ChE activity in the trachea compared to treatment with oximes alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of calcium antagonists (omega-conotoxin GVIA, verapamil, gallopamil, diltiazem) on bronchial smooth muscle contractions induced by soman

The effect of the calcium antagonists omega-conotoxin GVIA, verapamil, gallopamil and diltiazem was investigated on in vitro bronchial smooth muscle contraction in the rat induced by the nerve agent soman. Soman inhibits the acetylcholinesterase activity irreversibly. The effect of the calcium channel antagonists on contractions induced by electrical field stimulation and carbachol was also investigated, in order to elucidate the mechanism by which calcium antagonists inhibit the soman induced contraction. omega-Conotoxin GVIA reduced the bronchial smooth muscle contraction induced by electrical field stimulation with an almost complete inhibition at approximately 1.0 x 10(-6) M. The soman induced contraction was only inhibited by 15% at a concentration of 3.0 x 10(-6) M omega-conotoxin GVIA. The organic calcium antagonists verapamil, gallopamil and diltiazem reduced both electrically and soman induced smooth muscle contraction. Complete inhibition of the contractions induced by soman was achieved at 1.4 x 10(-4) M for verapamil and gallopamil, while diltiazem inhibited the contraction to 7% of control at 1.4 x 10(-4) M. Verapamil, gallopamil and diltiazem increased the EC50 for carbachol significantly, while omega-conotoxin GVIA had no effect. None of the calcium antagonists had any effect on the maximal contraction induced by carbachol. Verapamil, gallopamil and diltiazem blocked, however, sub-maximal contractions induced by carbachol (10(-7)-10(-5) M) resulting in a right-shift of the dose response curve. The results show that omega-conotoxin GVIA inhibits the calcium-dependent release of acetylcholine which causes contraction of airway smooth muscle, while it has no effect on smooth muscle contraction induced by soman.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of AH5183 (vesamicol) on cholinergic transmission in intact airway smooth muscle

The effect of the vesicular acetylcholine (ACh) transport blocker trans-2-(4- phenyl-piperidino)-cyclohexanol (AH5183) was studied in bronchial smooth muscle during activation of the vagus nerve. AH5183 inhibited in a dose-dependent manner the Ca(2+)-sensitive electrically induced smooth muscle contractions in vitro with a half-inhibitory concentration (IC50) of 1.6 +/- 0.4 microM. The inhibition was complete within 68 +/- 1 min (n = 8) at approximately 20 microM AH5183 and was partly reversible after washing of the preparations. AH5183 (20 microM) reduced the level of endogenous ACh by 47.4 +/- 7.6% (n = 4) during this time period. The effect of AH5183 is most likely prejunctional, since the contractions induced post-junctionally by carbachol were not altered by AH5183. The irreversible anticholinesterase, soman, increased the tonus of airway smooth muscle as a result of accumulation of spontaneously released ACh from prejunctional leakage. AH5183 had no effect on this increase of muscle contraction. The present results show that the nerve-evoked release of ACh comes from an AH5183-sensitive pool, probably a vesicular pool, whereas leakage of ACh presumably comes from the cytoplasmic pool in airway smooth muscle.

Prejunctional stimulation of cholinergic nerves in rat airway smooth muscle by an adenosine analogue

The effect of 5'-N-ethylcarboxamidoadenosine (NECA) on rat bronchial smooth muscle was examined in vitro. Both the nerve mediated muscle contraction induced by electrical stimulation and the potassium evoked release of [3H]ACh were enhanced by NECA. The apparent affinity (EC50) of NECA in the contraction experiments was 0.30 +/- 0.06 microM. The adenosine (ADO) receptor antagonist, 8-phenyltheophylline (8-PT), inhibited the NECA induced potentiation of both the electrical induced contraction and the potassium evoked release of [3H]ACh. The EC50 and intrinsic activity of exogenous ACh were not altered in the presence of NECA (1 microM) in experiments where smooth muscle contraction were measured, indicating that NECA has a prejunctional effect and not a postjunctional effect on muscarinic receptors. The new A2 specific ADO receptor agonist 2-p-(2-carboxyethyl)-phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680) and ADO also enhanced the nerve-mediated contraction (EC50 = 35 +/- 8 microM and 69 +/- 20 microM, respectively). 8-PT (10 microM) and enprofylline (ENPF) (10 microM) inhibited the electrically induced contraction by 55 +/- 16% and 45 +/- 5% respectively. The potassium evoked release, however, was stimulated 56 +/- 6% and 39 +/- 7% by 50 microM 8-PT and ENPF respectively. The results provide evidence for a NECA specific ADO receptor in rat bronchi that is most likely prejunctional. Stimulation of this receptor, which may be of an A2 receptor subtype, enhances the nerve mediated release of ACh and thereby induce contraction of the bronchial smooth muscle.

Evidence for prejunctional M2 muscarinic receptors in pulmonary cholinergic nerves in the rat

1. The effects of muscarinic antagonists considered to be selective for M1 receptors (pirenzepine) and for M2 receptors (gallamine and methoctramine) were used to investigate the existence of prejunctional muscarinic receptors on cholinergic nerves in the rat lung. The tracheal tube preparation was used in vitro, and contraction of the trachealis muscle was induced by electrical field stimulation (EFS) and by application of an exogenous muscarinic agonist (pilocarpine), and measured as an increase in intraluminal pressure in the tube. 2. The muscarinic antagonists, gallamine and methoctramine, enhanced the contractions induced by nerve stimulation, while contractions elicited by exogenous application of pilocarpine were inhibited by the antagonists. 3. In contrast, pirenzepine blocked contractions induced by both EFS and pilocarpine in a dose-dependent manner (EC50 0.1 microM) due to blockade of the postjunctional muscarinic receptors on airway smooth muscle. Potentiation of the response to EFS was never seen with this antagonist. 4. The muscarinic agonist, pilocarpine, caused a slow maintained increase in tone of the tracheal tube and at the same time reduced the contractions induced by EFS. This inhibitory effect was blocked by gallamine and methoctramine. 5. The results suggest that prejunctional inhibitory muscarinic receptors may be localised on the parasympathetic cholinergic nerve terminals innervating tracheal smooth muscle in the rat. This confirms previous findings obtained by measuring transmitter release in this species. The present results suggest that these receptors are of the M2 subtype. Blockade of these autoreceptors with gallamine or methoctramine would increase the output of acetylcholine (ACh) and thereby enhance the nerve-induced contraction of tracheal smooth muscle.

Amino acids as modulators of cholinergic nerves in airways

The bronchial smooth muscle of rat was examined for contractile responses to excitatory amino acids. The electrical field stimulation (EFS) which induces release of ACh, induced contraction which was enhanced by exogenous L-glutamate (L-glu). The ED50 of L-glu was 3.5 +/- 0.1 mM. Inhibition of the release by TTX or by HC-3 completely abolished the potentiation of the EFS-induced contraction by L-glu. The effect of L-glu is therefore probably a prejunctional effect. Concentrations of L-glu higher than 22 mM inhibited the EFS evoked contractions, and enhanced the tonus of the muscle by a postjunctional stimulation. The ED50 of ACh was not altered by L-glu. In contrast, an increase of the intrinsic activity (alpha) of ACh was seen, providing evidence for a postjunctional potentiation of ACh induced contraction. L-glu did not inhibit AChE-activity at concentrations up to 50 mM, indicating that the effect is not due to an accumulation of ACh. A relaxation of the EFS-induced bronchial smooth muscle contraction was seen with high concentrations of D-glu, L-asp, L-alpha-amino adipate and ibotenate. Neither L-GDEE nor DL-APV had any inhibitory effect on L-glu and L-asp induced alteration of EFS-evoked contraction or on the L-glu enhanced tonus of the bronchial smooth muscle. Kainate, NMDA and quisqualate had only minor transient potentiating effects on the EFS-induced contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of peripheral cholinergic nerves by glutamate indicates a new peripheral glutamate receptor

The bronchial smooth muscle of the rat was examined for contractile responses to excitatory amino acids. The nerve-mediated contraction induced by electrical field stimulation was enhanced by exogenous L-glutamate (L-Glu). The apparent affinity (ED50) of L-Glu was 3.5 +/- 0.1 mM. Both tetrodotoxin and hemicholinium-3 completely abolished the electrical field-induced contraction and therefore the potentiation by L-Glu, which indicates that L-Glu has a prejunctional effect. Concentrations of L-Glu higher than 22 mM inhibited the electrical field-induced contractions and enhanced the tonus of the smooth muscle by postjunctional stimulation. The ED50 of exogenous ACh was not altered by L-Glu. High concentrations (62 mM) of L-Glu increased the intrinsic activity (alpha) of ACh, indicating a postjunctional potentiation of ACh-induced contractions. L-Glu did not inhibit the activity of acetylcholinesterase, therefore the postjunctional potentiation was not due to ACh accumulation. Inhibition of the electrical field-induced contraction was seen with high concentrations of D-Glu, L-aspartate (L-Asp), L-alpha-amino adipate and ibotenate. Neither glutamate diethyl ester nor 2-amino-5-phosphonovalerate had any inhibitory effects on the L-Glu- and L-Asp-induced alterations of the electrical field-stimulated contraction or on the L-Glu-enhanced tonus of the bronchial smooth muscle. Kainate, N-methyl-D-aspartate, quisqualate and N-acetyl-aspartyl-glutamate had only minor transient potentiating effects on the electrical field-induced contraction. The results provide evidence for a L-Glu receptor in rat bronchi that has a different specificity for glutamate agonists and antagonists than the L-Glu receptor described in the CNS. The receptor seems to be located prejunctionally and enhances nerve-mediated responses and thereby stimulates the bronchial smooth muscle to contract. The possible involvement of this type of receptor in the 'Chinese restaurant syndrome' is discussed.

The effect of acetylcholinesterase-inhibition on the tonus of guinea-pig bronchial smooth muscle

The irreversible acetylcholinesterase inhibitor soman (O-[1,2,2-trimethylpropyl]-methyl-phosphonofluoridate) induced contraction of guinea-pig primary bronchial smooth muscle. The apparent affinity (ED50) of acetylcholine (ACh) was altered from control value of 12 microM to 0.3 microM following exposure of the bronchial smooth muscle to 14 microM soman for 15 min in vitro. The ED50 of the cholinergic agonist carbachol was not changed even when the acetylcholinesterase (AChE) activity was inhibited completely. The intrinsic activity (alpha) of ACh and carbachol was not significantly changed after exposure to soman for 15 min. The results demonstrate that the effect of soman is only due to its anticholinesterase activity. Furthermore, the contraction induced by histamine was not altered by concentrations of soman which increase the cholinergic stimulation. This indicates that histamine does not induce contraction of bronchial smooth muscle in guinea pig through the release of ACh or by modulation of muscarinic receptors. Furthermore, soman also inhibited the carboxylesterase activity in the primary bronchi. In respiratory tissue this group of enzymes may have a major protective function, due to their ability to bind several organophosphorus compounds. Compared to studies performed on other species, this study shows that guinea-pig bronchi are very sensitive to the AChE-inhibitor soman. Therefore, exposure to very low concentrations of AChE-inhibitors may induce contraction of bronchial smooth muscle.

The toxic effect of an AChE-inhibitor on the cholinergic nervous system in airway smooth muscle

Excessive cholinergic stimulation of presynaptic muscarinic cholinergic receptors, due to complete inhibition of acetylcholinesterase (AChE) by O-(1,2,2-trimethylpropyl)-methyl-phosphonofluoridate (soman), reduced the release of acetylcholine (ACh) from cholinergic nerves in rat bronchi by almost 25%. Furthermore, long-term (40 h) exposure by inhalation of soman (0.45-0.63 mg/m3) reduced the contraction of bronchi induced by ACh by approximately 70%. This is probably due to reduction of the number of muscarinic cholinergic receptors, since there was a reduction in the binding capacity (Bmax) of [3H]QNB by 40%, without any changes in the dissociation constant (Kd).

Automated method for the determination of angiotensin-converting enzyme in serum

A method for the determination of angiotensin-converting enzyme in serum (S-ACE; EC 3.4.15.1.) with use of 3-(2-furylacryloyl)-L-phenylalanyl-glycyl-glycine (FAPGG) as substrate has been adapted for the Cobas Bio microcentrifugal analyser. The method allows 24 determinations per hour in a sample volume of 28 microliters with a within run precision of less than 3% and a between run precision of less than 5%. The reaction is linear up to at least 470 U/l. The reference interval in 92 blood donors has been determined to 14-110 U/l. The method correlates well with the manual method of Hurst & Lovell-Smith (r = 0.982). We have found the method excellently suited for routine assay.

Acute and sub-acute inhalation of an organophosphate induce alteration of cholinergic muscarinic receptors

Acute and sub-acute inhalation exposure of rats to the organophosphorus compound soman (O-[1,2,2-trimethylpropyl]-methylphosphonofluoridate) reduced the contraction of the bronchial smooth muscle induced by cholinergic stimulation. Acute exposure to 8.51 mg/m3 of soman for 45 min (total dose of 383 mg X min/m3) inhibited the acetylcholinesterase (AChE) activity of the bronchial smooth muscle by 85% and reduced the contraction induced by ACh and carbachol by 70% and 80% respectively. In spite of the extensive inhibition of AChE and reduction in the contraction following cholinergic stimulation, there was no alteration of the binding capacity (Bmax) or the equilibrium dissociation constant (Kd) to [3H]-quinuclidinyl benzilate ([3H]-QNB) in the rat bronchi following such an acute exposure. After sub-acute exposure (40 hr) to 0.45-0.63 mg/m3 of soman (total dose of 1080-1519 mg X min/m3) there was a reduction in AChE-activity of 94% and in the contraction of the bronchial smooth muscle induced by ACh and carbachol of 70%. Furthermore, also a reduction of the binding capacity to [3H]-QNB of approximately 40% was observed. Following exposure to soman by both acute and sub-acute inhalation exposure there was an increase in the apparent affinity (pD2) to ACh in the bronchial smooth muscle, due to the extensive inhibition of the AChE-activity. Inhalation of soman also induced a substantial inhibition of the AChE-activity in the lung (86%), but somewhat smaller inhibition in the hippocampus (70%) and almost no inhibition in the neostriatum (19%). Moreover, it was only in the lung where sub-acute exposure to soman produced a reduction of the binding capacity to [3H]-QNB and the reduction was approximately 50%. The results therefore show that after sub-acute inhalation of a relatively low concentration of the AChE-inhibitor soman, alterations in the number of cholinergic receptors are only observed in the peripheral cholinergic nervous system.

The effect of soman on potassium evoked 3H-acetylcholine release in the isolated rat bronchi

The in vitro exposure of rat bronchial smooth muscle to the acetylcholinesterase inhibitor soman (0-[1,1,2-trimethylpropyl]-methylphosphonofluoridate) reduced the potassium (51 mM) evoked release of 3H-acetylcholine (3H-ACh). Exposure to 1.0 and 100 microM soman for 15 min inhibited the acetylcholinesterase (AChE) activity completely and reduced the potassium evoked release by 23.1% and 34.4% respectively. In the presence of scopolamine (0.3 microM), however, there was a large enhancement (87.0%) of potassium evoked release during soman inhibited (100%) AChE-activity. Furthermore, soman (1.0 microM) did not reduce the spontaneous release of 3H-ACh. The results indicate that the presynaptic effect of soman is due to the enhanced concentration of ACh following AChE-activity inhibition in the synaptic region. This induces a stimulation of presynaptic muscarinic receptors and thereby modulation of the ACh release only during evoked release.

Presynaptic inhibition of acetylcholine release

High potassium (51 mM) has been shown to evoke release of acetylcholine ([3H]ACh and endogenous ACh) from cholinergic nerves in rat bronchial smooth muscle. The release of [3H]ACh was reduced by 85% when the Ca2+ concentration was changed from 2 to 0.1 mM. The veratridine-induced release was completely inhibited by tetrodotoxin, but tetrodotoxin did not reduce the potassium-evoked release. The muscarinic agonist, oxotremorine, reduced the potassium stimulated release of [3H]ACh, without affecting the basal release. In contrast, scopolamine substantially potentiated the potassium-evoked release. Adenosine had a dual effect in the rat bronchi. Adenosine inhibited the potassium-evoked release of [3H]ACh and this presynaptic effect of adenosine was antagonized by 8-phenyltheophylline. Adenosine also induced contraction of the bronchial smooth muscle and there was potentiation by adenosine of the ACh-induced contraction. The results indicate that cholinergic nerve terminals in the rat bronchi possess muscarinic receptors which inhibit the release of ACh. Adenosine may have analogous effects, e.g. presynaptic inhibition of transmitter release in addition to postsynaptic enhancement of bronchial smooth muscle contraction.

In vitro effects of soman on bronchial smooth muscle

The in vitro exposure of rat bronchial smooth muscle to the cholinesterase inhibitor soman (O-[1,2,2-trimethylpropyl]-methyl-phosphonofluoridate) potentiated the rapid and concentration dependent increase in the contraction induced by acetylcholine (ACh). There was a substantial increase in the response to ACh when soman was present in concentrations from 10 nM to 1 microM which correspond to a 65-100% inhibition of acetylcholinesterase (AChE). The apparent affinity (pD2) to ACh increased from 3.7 to 6.7 without any change in intrinsic activity (alpha) in this concentration interval. In contrast, soman did not alter the apparent affinity or intrinsic activity of carbachol, which supports the suggestion that the effect of soman is entirely due to its anticholinesterase activity. Soman by itself induced contraction which begun at 1-10 nM. This may be explained from its anticholinesterase activity and the subsequent increase in the synaptic concentration of spontaneously released ACh. The effect of soman on inhibition of cholinesterase and carboxylesterases have also been examined. The results demonstrate that low concentrations of soman induces contraction of the airway smooth muscle.

Carboxylesterases, importance for detoxification of organophosphorus anticholinesterases and trichothecenes

Several different types of experiments, including the use of inhibitors, have shown that carboxylesterases are a major factor in the metabolism and therefore detoxification of organophosphorus compounds such as soman and trichothecene toxins. The development of a new assay method for the enzyme has allowed us to separate the carboxylesterases into two major groups. The carboxylesterases can, however, be further separated by gel filtration, affinity chromatography, isoelectric focusing, and chromatofocusing into several isoenzymes. Liver microsomal carboxylesterases can be separated into five or six isoenzymes whereas guinea-pig plasma contains two isoenzymes. The isoenzymes differ in molecular weights, isoelectric points, substrate specificities, and affinity for inhibitors. Intravenous administration of a carboxylesterase preparation lowered the toxicity of soman in young rats. Carboxylesterases from rat and guinea-pig plasma inhibited by soman could be reactivated by DAM, whereas enzymes from porcine liver were not reactivated. Only one of the isoenzymes from rat liver microsomal preparation was responsible for the metabolism of T-2 toxin to HT-2. The further metabolism of HT-2 was performed by esterases from rat liver cytoplasma. Long-term exposure of the bronchial muscle to low concentration of soman modulate the bronchial contraction.

A method for generating toxic vapors of soman: toxicity of soman by inhalation in rats

A method for administration of highly toxic chemicals by inhalation was developed. The model has three features of special interest: (1) a diffusion cell for producing a constant gas concentration, if necessary for several hours and days, (2) a small rapidly equilibrated inhalation chamber (1100 ml), and (3) complete isolation of the toxic chemicals from the atmosphere. The LCt50 of the anticholinesterase soman [o-(1,2,2 trimethylpropyl)-methyl-phosphonofluoridate] was 400 mg min/m3, registered 24 hr after the end of exposure. The lethal concentration X time of soman was 520 +/- 60 mg min/m3 when exposing the animals until death in the inhalation chamber. The exposure was less than 30 min and the concentration of soman was 21 mg/m3. The inhibition of acetylcholinesterase, cholinesterase, and carboxylesterase activities in different tissues was analyzed to study the possible barrier mechanisms that might exist in the body to soman. There was a large inhibition of the carboxylesterase and cholinesterase activities in bronchi and lungs as well as in blood. Carboxylesterases were important as detoxifying enzymes, as shown by 70% enhancement in toxicity of soman following sc pretreatment with TOCP (tri-ortho-cresyl-phosphate), a carboxylesterase inhibitor.

Neurotensin receptors in the rat bronchi

The isolated, circular preparations of the left and right bronchi of the rat were examined for mechanical responses to neurotensin (NT) and other vasoactive peptides. NT caused concentration-dependent increases in the isometric tension of the unstimulated preparations, with an apparent affinity higher than for the cholinergic agonists but with considerably lower intrinsic activity. Pronounced tachyphylaxis to NT was observed. NT potentiated the atropine-sensitive increase in tension resulting from electrical field stimulation. Neither atropine nor methysergide abolished the response to NT in the unstimulated preparations. Bradykinin and to a lesser extent angiotensin II contracted the unstimulated preparations and both systemic peptides enhanced the cholinergic output in response to field stimulation. Substance P and VIP on the other hand were without effects in the stimulated and unstimulated bronchi. The results are consistent with the presence of receptors for NT on the presynaptic cholinergic terminals as well as on the post-synaptic smooth muscles of the rat bronchi.