Effect of chlorpromazine on sympathetic neuroeffector transmission in the rabbit isolated pulmonary artery and aorta

Effects and related mechanism of alpha-adrenergic receptor inhibitor phentolamine in a rabbit model of acute pulmonary embolism combined with shock

BACKGROUND

To observe the effect and mechanism of alpha-adrenergic receptor inhibitor phentolamine (PTL) in a rabbit model of acute pulmonary embolism (APE) combined with shock.

METHODS

Twenty-four New Zealand rabbits were randomly divided into sham operation group (S group, n = 8), model group (M group, n = 8) and PTL group (n = 8), the model of APE combined with shock was established. Mean pulmonary arterial pressure (MPAP), peripheral mean arterial pressure (MAP) and pulmonary circulation time were evaluated. The expression levels of α1 receptor, α2 receptor and their downstream molecules in pulmonary embolism (PE) and non-pulmonary embolism (non-PE) regions lung tissues were detected and compared, respectively.

RESULTS

In M group, α receptor-related signaling pathways were significantly activated in both PE and non-PE areas as expressed by up-regulated α1, α2 receptor and phospholipase C (PLC); the expression level of phosphorylated protein kinase A (p-PKA) was significantly down-regulated; myosin light chain kinase (MLCK) and α-smooth muscle actin (α-SMA) levels were up-regulated. PTL treatment significantly improved pulmonary as well as systemic circulation failure: decreased MPAP, restored blood flow in non-PE area, shortened pulmonary circulation time, increased MAP, and restored the circulation failure. PTL induced significantly down-regulated expression of α1 receptor and its downstream molecule PLC in both PE and non-PE area, the expression level of α2 receptor was also down-regulated, the expression level of p-PKA was significantly up-regulated. PTL treatment can inhibit both α1 and α2 receptor-related signaling pathways in whole lung tissues, and inhibit Ca2+ signaling pathways. The expression level of MLCK and α-SMA were significantly down-regulated. Compared with PE area, the changes of expression levels of α receptor and its downstream molecules were more significant in the non-PE region.

CONCLUSION

In this model of APE combined with shock, the sympathetic nerve activity was enhanced in the whole lung, α1 and α2 receptor and their downstream signaling activation might mediate blood flow failure in the whole lung. PTL treatment can effectively restore pulmonary blood flow in non-PE area and improve pulmonary as well as systemic circulation failure possibly through down-regulating α1 and α2 receptor and their downstream signaling pathways.

Chlorpromazine confers neuroprotection against brain ischemia by activating BKCa channel

Chlorpromazine (CPZ) is a well-known antipsychotic drug, still widely being used to treat symptoms of schizophrenia, psychotic depression and organic psychoses. We have previously reported that CPZ activates the BKCa (KCa1.1) channel at whole cell level. In the present study, we demonstrated that CPZ increased the single channel open probability of the BKCa channels without changing its single channel amplitude. As BKCa channel is one of the molecular targets of brain ischemia, we explored a possible new use of this old drug on ischemic brain injury. In middle cerebral artery occlusion (MCAO) focal cerebral ischemia, a single intraperitoneal injection of CPZ at several dosages (5mg/kg, 10mg/kg and 20mg/kg) could exert a significant neuroprotective effect on the brain damage in a dose- and time-dependent manner. Furthermore, blockade of BKCa channels abolished the neuroprotective effect of CPZ on MCAO, suggesting that the effect of CPZ is mediated by activation of the BKCa channel. These results demonstrate that CPZ could reduce focal cerebral ischemic damage through activating BKCa channels and merits exploration as a potential therapeutic agent for treating ischemic stroke.

Regional variation in electrically-evoked contractions of rabbit isolated pulmonary artery

1. Electrically-evoked contractions in different regions of the rabbit isolated pulmonary artery have been investigated using stimulation parameters generally assumed to stimulate nerves selectively. 2. In extrapulmonary artery, trains of stimuli (10 Hz; pulse width 0.1 ms) evoked monophasic contractions. In contrast, a biphasic contraction was evoked in the intrapulmonary artery consisting of an initial fast component followed by a secondary very long-lasting component. 3. The contraction in the extrapulmonary artery was prazosin-sensitive (1 micro M) whereas that in the intrapulmonary artery was prazosin-resistant. 4. alpha,beta-Methylene ATP (1 micro M), atropine (1 micro M), losartan (1 micro M), BIBO3304 (1 nM) or nifedipine (1 micro M) had no effect on the biphasic contraction of the intrapulmonary artery. Bretylium (2 micro M) abolished the contraction of extrapulmonary artery but only partially inhibited the initial component in the intra region with no effect on the second component. 5. Tetrodotoxin (0.3-1 micro M), abolished the contraction of extrapulmonary artery but only partially reduced the electrically-evoked contraction of intrapulmonary artery. 6. Removal of the endothelium and application of sulphisoxazole (0.6-22 micro M) had no effect. 7. Varying the resting tone on the arteries, or applying gadolinium, had no effect on contractions. 8. Using confocal microscopy and calcium imaging, reproducible whole cell calcium transients were evoked in individual smooth muscle cells in intact preparations but only when direct muscle stimulation was used (pulse width of 5-10 ms). No detectable changes in calcium were elicited when brief pulse widths were used (0.1-2 ms). 9. Together, these data suggest that noradrenaline is the neurotransmitter inducing contraction in extrapulmonary artery. Noradrenaline and sympathetic nerves appear to play a less important role in the intrapulmonary artery. The tetrodoxin-resistant component is not mediated by ATP, NPY, acetylcholine, angiotensins, ET-1, stretch-activation or Ca(2+) influx through L-type Ca(2+) channels. Smooth muscle cells do not appear to be damaged by the stimulation protocol. The mechanism underlying the long lasting contraction of intrapulmonary artery evoked by brief electrical stimuli remains to be elucidated.

Inhibition of human alpha1E subunit-mediated ca2+ channels by the antipsychotic agent chlorpromazine

Chlorpromazine is a neuroleptic antipsychotic agent with a long history of clinical use. Its primary mode of action is thought to be through modulation of monoaminergic inter-neuronal communication; however, its side-effect profile indicates substantial activities in other systems. Recent work has begun to uncover actions of this compound on ion channels. In this light we have investigated the actions of chlorpromazine on the recombinant alpha1E subunit-encoded voltage-sensitive Ca2+ channel (VSCC) that is believed to encode drug-resistant R-type currents found in neurones and other cells. Chlorpromazine produced a dose-dependent antagonism of these channels that was reversed on drug removal. The mean IC50 was close to 10 microM. At this concentration, the level of antagonism observed was dependent on the membrane potential, with greater inhibition being observed at more negative test potentials. Furthermore, chlorpromazine induced substantial changes in the steady-state inactivation properties of alpha1Ebeta3-mediated currents, although it was not seen to elicit a corresponding change in inactivation kinetics. These results are discussed with regard to the possible clinical mechanisms of chlorpromazine actions.

Effect of dopexamine hydrochloride on contractions of rabbit isolated aorta evoked by various agonists

The inhibitory affinity of dopexamine hydrochloride to postsynaptic adrenoceptors, cholinoceptors, 5-hydroxytryptamine and histamine receptors was studied in rabbit isolated aorta. Dopexamine (10(-7)-10(-5) M) antagonized competitively the contractions of rabbit aorta evoked by noradrenaline (pA2: 6.60). Neither cocaine plus corticosterone nor cocaine, corticosterone plus propranolol altered the inhibition (pA2: 6.77 and 6.63, respectively). The antagonism of dopexamine against noradrenaline-evoked contractions was the same after 1 and 4 hr of pretreatment with dopexamine. In the presence of cocaine plus corticosterone, dopexamine antagonized the contractions evoked by phenylephrine (pA2: 6.94). Removal of endothelium did not influence this antagonism (pA2: 7.06). Dopexamine (10(-7)-10(-5) M) did not antagonize the contractions of aorta evoked by histamine (3 x 10(-7)-6 x 10(-5) M) and by 5-hydroxytryptamine (3 x 10(-7)-3 x 10(-4) M). Dopexamine (10(-8 and 10(-7) M) did not alter the contractions of endothelium-free aorta evoked by carbachol. Dopexamine (10(-7)-10(-5) M) slightly enhanced the contractions of aorta evoked by potassium (10(-2)-5.5 x 10(-2) M). These results suggest that dopexamine is an alpha 1-adrenoceptor antagonist. Furthermore, dopexamine has no affinity to cholinoceptors, histamine and 5-hydroxytryptamine (5-HT2) receptors and is apparently not a calcium antagonist.

The problem with autoreceptors

There are numerous problems with the concept that antagonists enhance transmitter release by blockade of feedback. It was shown that antagonist enhancement of transmitter release does not correlate satisfactorily with the intensity of stimulation or with other indices of biophase transmitter concentration. Wide variations were shown to exist between antagonists in the amount of enhancement of release they induce. Also, antagonists enhance transmitter release or the effector response with a single stimulation pulse, a condition under which no feedback is possible. A study of agonist/antagonist relationships indicates different sites of action, and it was determined that the antagonist effect has negligible or minimal latency and that enhancement by antagonists is maximal under minimal condition of stimulation. Antagonists were shown to enhance release by a direct action, not by passive occupancy of agonist sites. Experiments were described in which acetylcholine and cold selectively antagonized antagonist but not agonist effects. Further, experiments with pulse duration shifts and with veratridine pointed to a direct action of antagonists on Na+ (also Ca++?) channel gating mechanisms, which results in a shift in the voltage dependence of activation. If antagonists, in some particular instances, enhance release by blockade of sites involved in negative feedback this is likely lost or mired in their more prominent direct actions on neurosecretion--and these must be sorted out. The acceptance of the fact that antagonists act directly to alter transmitter release (and not only as passive occupiers of presynaptic receptors), as the present study shows, both in the central nervous system and in the periphery, opens a new area for future investigation, and may be exploitable for therapeutic purposes and to gain an enriched understanding of the mechanism of neurosecretion.

Effects of some antipsychotic drugs on cardiovascular catecholamine receptors in the rat

1. Experiments were performed to determine the activity of four antipsychotic drugs on several catecholamine receptors that control the sympathetic cardiovascular responses in rats. 2. Chlorpromazine, thioridazine (0.03 and 0.1 mg kg-1) and haloperidol (0.3 and 1 mg kg-1) inhibited methoxamine-induced diastolic blood pressure increases in the pithed rat, whereas sulpiride (1 and 3 mg kg-1) was without effect. 3. Only sulpiride (3 mg kg-1) antagonized the pressor responses induced by xylazine. 4. Xylazine inhibited the heart rate increase induced by electrical stimulation of the spinal cord (C7-Th1) in the pithed rat. This effect was partially prevented by sulpiride (1 and 3 mg kg-1) and chlorpromazine (0.3 mg kg-1). A higher dose of chlorpromazine (1 mg kg-1) abolished the inhibitory effect of xylazine. 5. Apomorphine infusion inhibited the pressor responses induced by electrical stimulation (Th5-L4) in pithed rats. This effect was reversed by sulpiride (0.01, 0.03 and 0.1 mg kg-1) and partially antagonized by haloperidol (0.1 mg kg-1). 6. The depressor response to fenoldopam in anaesthetized rats was only inhibited by the higher dose of chlorpromazine and thioridazine (3 mg kg-1). 7. Our results suggest that, in the peripheral nervous system of the rat, haloperidol and sulpiride act as antagonists of DA2 receptors while chlorpromazine and thioridazine antagonized DA1 receptors. Furthermore, thioridazine and haloperidol show alpha 1-adrenoreceptor antagonist properties, whereas sulpiride antagonizes alpha 2-adrenoreceptors. Chlorpromazine shows mixed alpha 1/alpha 2-adrenoreceptor antagonism.

Multiple effects of cocaine upon evoked secretion in bovine adrenal medullary chromaffin cells. Additional insight into the mechanism of action of cardiac glycosides

Experiments to determine the effects of the catecholamine neuronal uptake blockers cocaine and desipramine, and of the cardiac glycoside, ouabain, upon 3H-(noradrenaline) efflux have been performed with bovine adrenal medullary chromaffin cells in tissue culture. Both cocaine and desipramine reduced 3H-noradrenaline uptake into chromaffin cells. Inhibitable uptake was 80% of total accumulation over 60 min; this degree of inhibition was produced by cocaine (30 mumol/l) or desipramine (1 mumol/l). Cocaine (30 mumol/l) had no effect upon spontaneous 3H-efflux measured over 60 min, but reduced that evoked over the same period by carbachol (EC50), veratridine (EC50) and by ouabain (100 mumol/l). Cocaine did not reduce that efflux evoked by raised levels of K+ (28 mmol/l; EC50). Desipramine (1 mumol/l), like cocaine, had no effect upon spontaneous efflux of 3H, but reduced that efflux evoked by carbachol, veratridine and ouabain. Tetrodotoxin (TTX) inhibited veratridine-evoked 3H efflux (IC50 0.2 mumol/l). The degree of inhibition caused by TTX (0.2 mumol/l) was not increased by cocaine (30 mumol/l). TTX also inhibited ouabain-evoked 3H efflux: this was reduced by 55% by a concentration of TTX (1 mumol/l) sufficient to virtually abolish veratridine-evoked efflux. Cocaine (30 mumol/l) in the presence of TTX (1 mumol/l) did not further inhibit ouabain-evoked efflux. Cocaine (30 mumol/l) did not alter 86Rb+ uptake into chromaffin cells, nor did it alter that inhibition of 86Rb+ uptake produced by ouabain (100 mumol/l) indicating that cocaine has no effect upon Na,K-ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Frequency-dependence of 3H-noradrenaline release from rabbit pulmonary artery: effect of alpha-adrenoceptor antagonists and inhibitors of transmitter inactivation

The aim of this study was to examine the modulating role of presynaptic alpha 2-adrenoceptors on transmitter release from vascular sympathetic neurones. This was done by examining the influence of removal of inactivation pathways on the effect of alpha-adrenoceptor antagonists on the release of transmitter from noradrenergic neurones. The rabbit main pulmonary artery preloaded with 3H-noradrenaline (3H-NA) was used. The artery was stimulated with 300 pulses at various frequencies (1, 3, 10 and 30 Hz). Pargyline (3 x 10(-4) M) increased the stimulation-evoked 3H-overflow at 1 and 3 Hz and decreased it at 30 Hz. U-0521 (3',4'-dihydroxy-2-methylpropiophenone; 3 x 10(-6) M) enhanced the overflow at 1 Hz and had no effect at 3-30 Hz. Corticosterone (4 x 10(-5) M) did not alter the stimulation-evoked 3H-overflow at 1-30 Hz. Cocaine (3 x 10(-6) M) enhanced the 3H-overflow slightly at 1-30 Hz. At 3 x 10(-5) M, cocaine enhanced 3H-overflow at 1 Hz and reduced it at 30 Hz. Neither corticosterone (4 x 10(-5) M) nor propranolol (10(-7) M) modified this effect of cocaine. Propranolol (10(-7) M) alone decreased the 3H-overflow at 30 Hz and had no effect at 1-10 Hz. Phenoxybenzamine (10(-6) M) and chlorpromazine (3 x 10(-6) M) potentiated the stimulation-evoked 3H-overflow at 1-30 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)