Calcium channel blockers and prevention of migraine]

Calcium antagonists have been proposed for the prophylactic treatment of migraine because of their putative vasodilating antispasmodic effect and of their action against the cellular consequences of brain hypoxia. Published reports of controlled double-blind studies of calcium antagonists for the prophylactic treatment of migraine are reviewed herein. The effectiveness of verapamil, diltiazem, and nifedipine in this indication cannot be considered as firmly demonstrated, when problems with trial design and the amount of available data are taken into account. Nimodipine failed to demonstrate significant effectiveness in migraine with or without an aura. In contrast, the ability of a diphenylpiperazine, flunarizine, to decrease the incidence of migraine attacks in patients with common or classical migraine has been firmly demonstrated, although there is less evidence of this agent's effectiveness on the duration and severity of attacks. The percentage of patients who respond to flunarizine seems comparable to the percentages of propranolol or pizotifen responders. However, flunarizine is associated with unpleasant (weight gain) or severe (extrapyramidal or depressive symptoms) adverse effects which limit its place to that of a second-line drug. Lastly, the analysis of these studies failed to disclose a correlation between calcium movements across the cell membrane and effectiveness for the prevention of migraine attacks. Flunarizine's effect in migraine probably involves monoamine mechanisms which bear no relation to calcium.     

神经降压素在大鼠应激性胃溃疡中的作用

选健康雄性Ｗｉｓｔａｒ大鼠１２２只，用脑室微量注射和放射免疫等分析方法，观察了中枢内、外源性神经降压素（ＮＴ）在大鼠束缚加水浸诱导的应激性胃溃疡中的作用。结果表明：（１）在大鼠应激性胃溃疡产生的同时，其血浆内神经降压素样免疫活性物（ＮＴＬＩ）的含量明显减少（Ｐ〈０．０５），而下丘脑、中脑、脑桥、延脑和垂体中ＮＴ－ＩＲ含量则明显升高（Ｐ〈０．０１）；（２）侧脑室注射抗ＮＴ血清中，大鼠应激性胃溃疡的产     

Calcium flow-independent actions of calcium channel blockers in toad urinary bladder

A role for transmembrane calcium movement in vasopressin stimulation of its target cell has been postulated based on studies with calcium entry blockers such as verapamil. We examined the effect of three sets of structurally different calcium blockers--D600 (an analogue of verapamil), diltiazem, and nifedipine--on water flow in toad bladder. D600 (200 microM), diltiazem (200 microM), and nifedipine (60 microM) inhibited vasopressin-induced water flow but enhanced adenosine 3',5'-cyclic monophosphate (cAMP)-induced water flow, suggesting that the drugs inhibit cAMP generation in response to vasopressin but enhance the response to exogenous cAMP by inhibiting phosphodiesterase activity. In the case of vasopressin stimulation, inhibition of cAMP generation appears to be the overriding effect. This was confirmed by measurements of cAMP content and the protein kinase ratio (-cAMP/+cAMP), which were significantly lower in bladders receiving both D600 and vasopressin than in those receiving vasopressin alone. Furthermore the drugs inhibited activation of adenylate cyclase by vasopressin in cell homogenates and inhibited phosphodiesterase in both homogenates and membrane-free supernatants. Thus these "calcium channel blockers" can directly alter cAMP metabolism in settings where movement of calcium should be irrelevant. The close correlation between the biochemical and transport effects of these agents suggests that their effect on water flow may occur by a direct effect on cellular enzymes or the membranes in which they reside and not by altering local calcium concentrations.     

Calcium channel effectors are potent non-competitive blockers of acetylcholine receptors

Nicardipine and other calcium channel effectors (CCEs) were studied for their effects on nicotinic acetylcholine receptor (nAChR) activity. While CCEs had no effect on frog (Rana pipiens) skeletal muscle contractions resulting from nerve stimulation or direct stimulation of the muscle, nicotinic agonist-induced contractures were blocked. Nicardipine did not affect nAChR single-channel open time or amplitude, corroborating data from endplate currents (EPCs); EPC amplitudes and decays were unaffected. All the CCEs tested, however, non-competitively blocked nAChRs. The block of nAChRs resulted in a shortened agonist-induced depolarization and thus a diminished contracture response. An increase in cultured mouse skeletal muscle (C-2) cell single-channel closed times was observed with the intracellular addition of nicardipine, verifying a direct block of nAChRs. Using single-channel analysis, nicardipine's site of action, or at least access to its site of action, was determined to be at the intracellular side of the receptor. A direct action of the CCEs on the nAChR was also shown by their ability to block phencyclidine (PCP) binding to Torpedo nobiliana membranes. All the CCEs blocked specific binding of [³H]-PCP to its binding site on the nAChR-channel complex, with bepridil and nicardipine being the most potent. These data are compatible with a model in which nicardipine and other CCEs, at concentrations which do not alter nAChR channel open time or conductance, block the effects of superfused nicotinic agonist on nAChRs either by stabilizing the formation of the nAChR desensitized state or by effecting a slow channel block.     

Calcium channel blockers in psychiatry: Potential for a growing role in pharmacotherapy

Calcium channel blockers have an established role in the treatment of various cardiovascular disorders and potential applications in psychiatry. Preliminary reports based on limited numbers of patients indicate that they are promising for mania, of uncertain utility for depression or schizophrenia, and deserving of further investigation for a number of other psychiatric disorders. The authors conclude their review with guidelines for clinical use and precautions to preclude possible undesirable drug interactions.     

Calcium channel blockers and risk of AD: the Baltimore Longitudinal Study of Aging

OBJECTIVE: To investigate the association between use of calcium channel blockers (CCB), dihydropyridine (DHP) or nondihydropyridine (nonDHP) type CCB and risk of developing Alzheimer's Disease (AD) or mortality. There is evidence suggesting that calcium plays a key role in changes in the brain leading to AD. Previous reports suggest a possible role for CCB in the treatment of AD. However, there are some indications that CCB increase mortality in patients with cardiac disease. METHODS: Subjects were 1092 participants in the Baltimore Longitudinal Study of Aging (BLSA) older than 60 years of age. Data on CCB use was collected prospectively for up to 19 years. Cox proportional hazards regression was used to estimate relative risks (RR) and confidence intervals (CI) of AD and mortality associated with use of CCB or use of only DHP or nonDHP-CCB. Analyses were adjusted for gender, education, smoking, blood pressure and history of heart problems. RESULTS: Use of DHP-CCB was not associated with a significantly reduced risk of AD compared to non-users, although the estimate of the RR was low with DHP-CCB (RR = 0.30, 95% CI = 0.07-1.25, P = 0.10). Use of nonDHP-CCB was not associated with reduced risk of AD and the estimate of the RR risk was close to one (RR = 0.82, 95% CI = 0.37-1.83, P = 0.63). In addition, there was no increase in mortality among users of DHP-CCB (RR = 0.64, 95% CI = 0.32-1.29, P = 0.21) or nonDHP-CCB (RR = 1.10, 95% CI = 0.65-1.87, P = 0.72). CONCLUSION: Users of DHP-CCB and nonDHP-CCB in this study did not have a significantly reduced risk of AD.     

Electroconvulsive stimulations prevent chronic stress-induced increases in L-type calcium channel mRNAs in the hippocampus and basolateral amygdala

Although affective disorders have high prevalence, morbidity and mortality, we do not fully understand disease etiopathology, nor have we determined the exact mechanisms by which treatment works. Recent research indicates that intracellular calcium ion dysfunction might be involved. Here we use the chronic restraint stress model of affective disorder (6 h restraint per day for 21 days) in combination with electroconvulsive stimulations to examine the effects of stress and an effective antidepressive treatment modality on L-type voltage gated calcium channel subunit mRNA expression patterns in the brain. We find that stress tended to upregulate Ca_v1.2 and Ca_v1.3 channels in a brain region specific manner, while ECS tended to normalise this effect. This was more pronounced for Ca_v1.2 channels, where stress clearly increased expression in both the basolateral amygdala, dentate gyrus and CA3, while stress only upregulated Ca_v1.3 channel expression significantly in the dentate gyrus. ECS effects on Ca_v1.2 channel expression were generally specific to stressed animals. Our findings are consistent with and extent previous studies on the involvement of intracellular calcium ion dysfunction in affective disorders. Selective modulation of neuronal L-type voltage gated calcium channels appears to be a promising target for the development of novel antidepressive treatment modalities.     

Calcium channel blockers protect against ethylene glycol monomethyl ether (2-methoxyethanol)-induced testicular toxicity

Disruption of normal calcium homeostasis has been implicated in the development of cell injury by certain chemicals. Furthermore, calcium channel blockers, which may prevent such a disruption, were shown to protect against this type of cellular damage in some excitable and nonexcitable tissues. Therefore, the present work was designed to address the role of calcium in the pachytene cell death caused by ethylene glycol monomethyl ether (EGME) by investigating the effect of the calcium channel blockers, verapamil and diltiazem, on the pathogenesis of such lesions. Male F344 rats were treated with a single gavage dose of 200 or 300 mg EGME/kg. Other groups of rats were treated with the same doses of EGME in combination with one, two, three, or four doses of verapamil or diltiazem. Twenty-four hours after administration of EGME, the animals were sacrificed, and the left testis and epididymis were excised, fixed in Bouin's solution, embedded in paraffin, sectioned, and stained with PAS-H. The sections were evaluated "blind" and scored for the number of lesioned stage XIV tubules. At 200 mg/kg, EGME produced a moderately severe lesion as characterized by pachytene spermatocyte cell death in stage XIV semniferous tubules. Verapamil was protective against this lesion with the protection being directly proportional to the number of verapamil doses administered and was maximum in rats treated with three doses. At 300 mg/kg, EGME caused a severe lesion in the testis, and verapamil was not as effective in protecting against this lesion as against the low dose of EGME. In contrast, diltiazem was not as effective as verapamil at either dose of EGME. These studies show, for the first time, that verapamil protects rats against EGME-induced testicular toxicity.     

Antifertility effect of calcium channel blockers on male rats: association with oxidative stress

PurposeCalcium ions are vital in many biologic processes including a variety of enzymatic reactions, activation of excitable cells, coupling of electrical activation to cellular secretion, haemostasis, bone metabolism and sperm functions. Calcium channel blockers (CCB) appear to have a reversible anti-fertility effect on male rats which does not occur through inhibition of the pituitary-gonadal axis. While the effects of CCB on male reproductive function have been investigated, less information is available regarding other reproductive indices and the underlying mechanism in the pathogenesis of male reproductive dysfunction. Therefore, the involvement of oxidative mechanisms in the adverse manifestation induced by CCB on male reproductive functions is investigated in this study.MethodsFor this purpose, lipid peroxidation; enzymatic antioxidants such as superoxide dismutase, catalase and glutathione reduced; epididymal sperm count, motility; histopathology of the testes, epididymis, seminal vesicle, prostate glands; and reproductive performance were determined.ResultsCCB administration in rats causes significant oxidative stress in the male reproductive milieu in term of increase in malondialdehyde (MDA) level and a concomitant decrease in catalase, superoxide dismutase and reduced glutathione enzyme activities in the testes. In addition, CCB treatment significantly decreased the sperm count, sperm motility, fertility index, implantation count, and litter size in this study.ConclusionThere is substantial evidence that CCB induces significant oxidative stress in the testes, which appears to be responsible for the adverse effects of decreased sperm count and motility ultimately leading to reduced fertility in rats.     

Calcium channel blockers increase the amount of nitrite production in rabbits without decreasing the responsiveness of platelets to collagen

By virtue of their ability to increase nitric oxide (NO) production, it is thought that calcium channel blockers (CCBs) may be involved in the inhibition of platelet aggregation. In an attempt to compare the abilities of different groups of calcium antagonists to affect NO generation and platelet aggregation, single doses of the calcium antagonists verapamil, nicardipine and diltiazem were administered to rabbits. It was found that each of these drugs increased the levels of nitrite significantly. It was also found that these drugs had different time courses of action. Of the CCBs used in this study, verapamil was found to induce the greatest increase in nitrite production (about a 4-fold increase over basal levels), peaking at 90 min (P<0.001). Diltiazem and nicardipine (3.5-fold and 2.5-fold increase over basal levels, respectively) were both found to induce increases in NO which peaked at 150 min (P<0.001 and P<0.01 respectively). Each of the drugs was then given at double the original dose; however, nicardipine was the only drug that was seen to further increase nitrite production (P<0.001). Blood samples taken from the animals were analysed using whole-blood aggregometry in order to assess the amount of collagen-induced platelet aggregation. At the time point when NO release was expected to be maximal (150 min), it was found that the collagen-induced platelet responses were not significantly altered in platelets from rabbits that had been treated with either verapamil or nicardipine. In contrast, at the 150-min time point, diltiazem treatment made the platelets hypersensitive to collagen stimulation. The results of this study demonstrate that treatment with calcium channel antagonists increases the levels of NO produced in rabbits, however, this increase in NO production is not accompanied by a decrease in the reactivity of platelets to collagen.     

T-type calcium channel blockers as neuroprotective agents

T-type calcium channels are expressed in many diverse tissues, including neuronal, cardiovascular, and endocrine. T-type calcium channels are known to play roles in the development, maintenance, and repair of these tissues but have also been implicated in disease when not properly regulated. Calcium channel blockers have been developed to treat various diseases and their use clinically is widespread due to both their efficacy as well as their safety. Aside from their established clinical applications, recent studies have suggested neuroprotective effects of T-type calcium channel blockers. Many of the current T-type calcium channel blockers could act on other molecular targets besides T-type calcium channels making it uncertain whether their neuroprotective effects are solely due to blocking of T-type calcium channels. In this review, we discuss these drugs as well as newly developed chemical compounds that are designed to be more selective for T-type calcium channels. We review in vitro and in vivo evidence of neuroprotective effects by these T-type calcium channel blockers. We conclude by discussing possible molecular mechanisms underlying the neuroprotective effects by T-type calcium channel blockers.     

Cytoprotective effect of centrally administered neurotensin on stress-induced gastric ulcers

Neurotensin, a peptide common to brain and gastrointestinal tissue, has been reported common to brain and gastrointestinal tissue, has been reported to inhibit both gastric acid secretion and gastric mucosal blood flow after central nervous system administration in rats. Therefore, the effect of intracisternal neurotensin on the development of gastric ulcers induced by cold-plus-restraint stress in the rat was studied. Following intracisternal injection, neurotensin (20-30 micrograms) significantly inhibited the development of gastric ulcers in this model. This effect was shown to be both dose related and route specific, inasmuch as neither lower doses of intracisternal neurotensin nor intravenous neurotensin were cytoprotective. In addition, potential actions of central neurotensin that may have mediated this beneficial effect were tested by administering somatostatin or oxotremorine intracisternally and cimetidine or haloperidol intraperitoneally. In contrast to intracisternal neurotensin, none of these substances reduced the incidence of gastric ulcers in this model. This was true despite the fact that cimetidine, but not neurotensin, significantly increased gastric pH. Finally, when cold-plus-restraint-stressed rats were pretreated with indomethacin, an inhibitor of prostaglandin synthesis, the cytoprotective effect of neurotensin was completely abolished. These results suggest that intracisternal neurotensin exerts a significant cytoprotective effect for stress-induced gastric ulcers in rats. This effect, which is mediated by the central nervous system, does not appear to be related to changes in body temperature, neuroleptic-like properties, or gastric acid secretion but requires an intact prostaglandin synthetic pathway.     

Regulation of stress-induced reduced myelopoiesis in rats

In this work we demonstrate that the stress-induced reduction in bone marrow granulocyte-macrophage colonies, reported previously from our laboratory, is prevented by both the inhibition of the hypothalamic-pituitary-adrenal axis (HPAA) and the blockage of opioid receptors. The inhibition of the HPAA was obtained through the administration of dexamethasone (1 mg/kg). The blockage of opioid receptors was done in two ways, by the administration of naltrexone (8 mg/kg) and induction of tolerance to morphine. On the other hand, no protection was observed in metyrapone treated rats. We suggest that the two physiological systems, opioid and HPAA, mediate the stress-induced myelosuppression and that these systems may function independently in this particular situation.     

Olanzapine counteracts stress-induced anxiety-like behavior in rats

Atypical antipsychotics, such as olanzapine, have been reported to display anxiolytic properties as shown in several preclinical and clinical studies. Furthermore, several experimental evidences have shown that olanzapine reduces fear and anxiety in activated anxiety-like behavior test such as Geller-Seifter test, ultrasonic vocalization test and stress-induced EtOH consumption. Here, we hypothesized that the anxiolytic action of olanzapine might be due to via an indirect activation of the γ-amino butyric acid (GABA)-ergic system through 3α-hydroxy-5α-pregnan-20-one [allopregnanolone (ALLO)], a potent neuroactive steroid that positively modulates the benzodiazepine-γ-aminobutyric acid type A (GABA_A)/benzodiazepine receptors complex. To address this question, we used a preclinical animal test to screen for novel anxiolytic compounds – the elevated plus-maze (EPM) – in basal condition and after 45 min restrain stress after acute or repeated (21 days) administration of olanzapine (0.5 mg/kg, i.p.). In this condition, we therefore study the effect of the 5-alpha-reductase inhibitor finasteride (FIN) (50 mg/kg) after co-administration with olanzapine. FIN is an inhibitor of steroidogenic enzymes which acts by inhibiting type II 5-alpha reductase, the enzyme that converts into 5-alpha-reduced metabolites like the GABA_A positive neuroactive steroid ALLO. Results showed an anxiolytic effect of the acute, but not of the chronic, treatment with olanzapine only in stressed rats. This anxiolytic effect was counteracted by the co-administration with FIN. These evidences suggest that the anxiolytic effects of olanzapine might be due to possible action of olanzapine on steroid function via activation of GABA system.     

Alarm pheromone enhances stress-induced hyperthermia in rats

Behavioral and physiological effects of alarm pheromones emanating from stressed conspecific animals were investigated. Experimentally naive male Wistar rats were exposed to the test chambers containing alarm pheromones, which had been released by other rats receiving foot shocks in the same chamber beforehand. Along with behavioral analysis, the heart rate (HR) and core body temperature (cBT) were measured simultaneously using a biotelemetory system. Exposure to the alarm pheromones increased freezing, sniffing and walking and decreased resting as compared with rats exposed to control odors. In addition, these pheromone-exposed animals showed consistent increases in body temperature, i.e., stress-induced hyperthermia. After exposure to the alarm substances, immunoreactivity to nuclear Fos protein in the mitral cell layer in the accessory olfactory bulb (AOB) also increased compared with the reaction to control odors. These results suggest that an alarm pheromone enhances stress responses of conspecific animals both behaviorally and physiologically, and that these effects are mediated via activation of the AOB.