Salmon calcitonin potentiates the analgesia induced by antidepressants.

Antidepressants are used in the treatment of a variety of pain syndromes. Most of them act by blocking noradrenaline (NA) and serotonin (5-HT) reuptake. It is also well known that the serotonergic system is also involved in calcitonin (CT) analgesia. Taking these two evidences into account, the modification of the analgesic effect of nortriptyline, amitriptyline, and paroxetine in the presence of salmon CT (s-CT) was examined in mice. The forced-swimming test was carried out in order to choose doses of each drug that did not induce an antidepressant effect under our experimental conditions (nortriptyline: 0.2-5 mg/kg ip, amitriptyline: 2.5-20 mg/kg ip, and paroxetine: 5-30 mg/kg ip). The analgesic effect of each antidepressant was then evaluated using the acetic acid test. At the doses tested, the antidepressants induced a dose-dependent analgesic effect. When mice were pre-treated with a subanalgesic dose of s-CT (2.5 IU/kg), the analgesic effect of amitriptyline and paroxetine was significantly increased though no modification was found for nortriptyline. In summary, s-CT was able to increase the analgesic effect of the antidepressant drugs that reduce the uptake of 5-HT, suggesting that the joint administration of antidepressants and CT may be an interesting alternative in pain management.

Study of mechanisms of calcitonin analgesia in mice. Involvement of 5-HT3 receptors.

The analgesic effect of calcitonin when serotonin (5-HT) concentration is increased and the involvement of some 5-HT receptors were studied using the writhing test in mice. 5-hydroxytryptophan (5-HTP) administration increased both 5-HT levels in the central nervous system (CNS) and calcitonin analgesia. The 5-HT(1A) agonist (+/-)-8-hydroxy-2-dipropylaminotetralin hydrobromide (8-OH-DPAT) diminished calcitonin analgesia, this effect being antagonised by the 5-HT(1A) antagonist (WAY 100, 135). As the stimulation of 5-HT(1A) autoreceptors reduces the turnover of 5-HT, the effect of 8-OH-DPAT on calcitonin analgesia may be attributed to this decrease. The 5-HT(2A-2C) agonist (+/-)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride (DOI) diminished calcitonin analgesia. A sub-analgesic dose of the 5-HT(2A) antagonist ketanserin failed to prevent this effect. The 5-HT(3) agonist (+/-)-2-methyl-5-hydroxytryptamine maleate (2-methyl-5-HT) potentiated calcitonin analgesia, whereas it was significantly reduced by the 5-HT(3) antagonist tropisetron. The effect of 2-methyl-5-HT on calcitonin analgesia was also reversed by tropisetron, This result suggests that the 5-HT(3) receptor may play an important role in the relationship between calcitonin and the serotonergic system. Tropisetron also reversed the analgesia induced by calcitonin plus 5-HTP corroborating importance of the 5-HT(3) receptors.

Calcitonin reverts pertussis toxin blockade of the opioid analgesia in mice.

The aim of this paper is to study the influence of salmon calcitonin (SCT) on opioid analgesia when opioid transduction pathways are functionally uncoupled from Gi/o proteins by treatment with pertussis toxin (PTX). The antinociceptive effect of morphine and three selective opioid agonists, [D-Ala2,N-Me-Phe2,Gly5-ol]enkephalin (DAMGO) (OP(3-mu receptor agonist), [D-Pen2.5]-enkephalin (OP-1-delta receptor agonist) and trans-( +/- )-3,4-dichloro-N-methyl-N-[2-1(-pyrrolidinyl)-cyclohexyl]-benzene-acetam ide methane sulfonate (U-50, 488H) (OP1-kappareceptor agonist) was evaluated, using the tail flick test, in mice treated with PTX or with PTX and SCT. PTX blocked the antinociceptive effect of the opioids, being the antinociception similar in control animals and in mice treated with PTX and SCT. Thus, SCT prevents the effect of the blockade of Gi/o-proteins. From this it could be suggested that calcitonin activates alternative antinociceptive mechanisms that are not dependent on Gi/o-proteins.

Effect of salmon-calcitonin on the analgesic effect of selective mu, delta and kappa opioid agonists in mice.

The analgesic effect of three different opioid agonists, DAMGO ([D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin), U-50,488H (trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidynyl)cyclohexyl] benzene-aceramide methane sulphonate), and [D,Pen2-D,Pen5]-enkephalin, which act upon mu, delta and kappa opioid receptors, respectively, was compared in the presence and absence of salmon-calcitonin (s-CT). The analgesic test used was the writhing test in mice. The analgesic effect of the opioids was significantly enhanced by pretreatment of the animals with s-CT intraperitoneally (i.p.) administered. This effect was more evident for the delta and kappa-agonists. The present result suggests that the joint administration of s-CT and opioids may be a useful and interesting alternative in the treatment of painful diseases resistant to other treatments.

Age-related changes in nociception, behavior, and monoamine levels in rats.

1. Pain threshold, behavioral parameters, and monoamine levels were compared in two groups of rats: adult (12 months old) and old rats (25 months old). 2. No differences in nociception were found between the two groups using the tail-shock test. 3. Behavioral experiments with the holeboard test showed that locomotor activity and exploration activity were lower in aged animals, whereas no significant differences were found in emotivity. 4. Using high-performance liquid chromatography (HPLC) techniques, we found that serotonin and dopamine showed lower levels in the old group.

Serotonergic mechanisms involved in calcitonin potentiation of kappa-opioid receptor-mediated effects on adrenal secretion.

Calcitonin can selectively modulate the effects of opioids on the rat hypothalamic-pituitary-adrenal axis and increase the release of corticosterone induced by a kappa-opioid receptor agonist. Considerable evidence supports the involvement of opioid and serotonergic systems in the analgesic effect of calcitonin. In this study, the involvement of hypothalamic serotonergic pathways in the calcitonin potentiation of the effect of (trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]-benzeneacetamide methane sulphonate (U-50,488H) on the secretion of corticosterone was examined. The correlation between the calcitonin-induced potentiation of the pituitary adrenal response to U-50,488H and changes in serotonin turnover was evaluated. Our results show that the increase in the release of corticosterone induced by treatment with calcitonin + U-50,488H was not evident when the turnover of serotonin was decreased by inhibition of its synthesis with m-hydroxybenzylhydrazine (NSD 1015) or by blockade of its metabolism with trans-2-phenylcyclopropylamine (tranylcypromine). Although other factors can not be discarded, from the present data it can be suggested that the serotonergic system plays an important role in the interaction calcitonin-kappa-opioid receptor agonist in the hypothalamic-pituitary-adrenal axis.

Influence of pertussis toxin on the calcitonin-opioid interaction in isolated tissues.

1. In order to clarify one of the mechanisms involved in the analgesic effect of calcitonin, we have tested the in vitro modifications induced by calcitonin on the effect of opioids. 2. The inhibition of the contractions induced by opioids or clonidine, in guinea-pig ileum or in mouse vas deferens, were significantly reduced in tissues incubated with pertussis toxin (PTX). When tissues were incubated with PTX and calcitonin, the inhibitory effect was restored. 3. These results suggest that calcitonin is able to potentiate a non-PTX-sensitive mechanism of transduction and support the possibility of involvement of similar G-proteins in the effects of opioid and alpha 2-adrenoceptor agonists.

Effects of nimodipine and nifedipine upon behavior and regional brain monoamines in the rat.

The effects of single and repeated (9 times) administration of two dihydropyridines (DHPs), nimodipine (NIM) and nifedipine (NIF) (5 mg/kg per 12 h and 2.5 mg/kg per 12 h, IP), on the behavior of male adult rats in the holeboard and in the plus-maze, were investigated. Besides, the effects of repeated administration of the drugs on the levels of dopamine (DA), serotonin (5-HT), and their respective major metabolites in several regions of the central nervous system (CNS) were also assessed. The effects of single and repeated administration of the drugs were similar. Both DHPs caused a significant decrease in general motor activity which was evident in both tests and more marked, with the higher doses. The two exploratory parameters measured in the holeboard, i.e. head-dipping frequency and duration, were dissociated under pharmacological treatment. The drug-treated animals did not show an increased emotionality in the holeboard. However, in the plus-maze, NIF (5 mg/kg) and to a lesser extent NIM, appeared to induce some anxiety-related responses which may be secondary, at least in part, to the depressing effect on activity and exploration. Repeated administration of NIM and NIF caused an increase in striatal DA and DOPAC levels, whilst no effects were found on serotonergic system in any of the regions of the CNS analyzed.

Cholesterol-fed rabbits: study of the response of the vas deferens to adrenergic and non-adrenergic stimulus and to a kappa-opioid agonist.

The aim of the present study was to analyse the contractility of the isolated vas deferens from hypercholesterolaemic rabbits; for this purpose we evaluated the contractile response induced by noradrenaline and by electrical stimulation. A significant increase in the amplitude of adrenergic and non-adrenergic responses was observed in vas deferens from hypercholesterolaemic rabbits. These data suggest an increase in the contractility of the smooth muscle in these animals.

Effect of the intraperitoneal administration of salmon-calcitonin on the "in vitro" actions of opioid agonists.

1. The interaction of intraperitoneal administration of salmon-calcitonin with opioids was studied. The study was carried out using guinea pig ileum (mu and kappa-opioid receptors), rabbit vas deferens (kappa-opioid receptors) and mouse vas deferens (delta-opioid receptors), and selective mu, delta and kappa agonists were used in the pertinent tissues. 2. The treatment with salmon-calcitonin increased, in a dose-dependent manner, the effect of U-50,488H in guinea pig ileum and rabbit vas deferens and the effects of [D-Pen2, D-Pen5] enkephalin in mouse vas deferens. 3. The treatment with analgesic doses of salmon-calcitonin enhances the in vitro effects of kappa- and delta-opioid agonists. The increase of the effectiveness of the opioid agonists may be one of the mechanisms involved on the analgesia induced by salmon-calcitonin.

Analgesic effect of two calcitonins and in vitro interaction with opioids.

1. When the analgesic effect of salmon-calcitonin (S-CT) and of eel-calcitonin (E-CT), as well as their influence on the morphine-analgesia were compared, no significant differences were found. 2. While on isolated tissues, E-CT induced a significant increase on the effect of bremazocine, [D-Pen2,D-Pen5]enkephalin and [Met5]enkephalin and no changes were observed on the effect of DAMGO, suggesting that E-CT increases the effects of opioids acting on delta or kappa receptors but not on mu receptors. 3. These findings corroborate the possibility of interactions between calcitonin and the opioid system.

Involvement of central serotonergic pathways in analgesia elicited by salmon calcitonin in the mouse.

The contribution of central serotonergic pathways to the analgesic activity induced by salmon calcitonin in the writhing test was investigated. Salmon calcitonin was administered to mice after lesioning of the ascending and descending serotonergic pathways by means of i.p. administration of p-chloroamphetamine (40 mg/kg, for 2 days) or p-chlorophenylalanine (300 mg/kg, for 3 days). The analgesic effect induced by salmon calcitonin at the doses of 10 and 20 IU/kg was not evident in mice previously treated with p-chloroamphetamine or p-chlorophenylalanine. However, the analgesic effect of salmon calcitonin 40 IU/kg was not significantly modified by p-chloroamphetamine or p-chlorophenylalanine pretreatment. Salmon calcitonin did not alter the depletion of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid after p-chloroamphetamine or p-chlorophenylalanine administration. Similarly, this hormone did not change the NSD 1015-induced accumulation of 5-hydroxytryptophan or the tranylcypromine-induced accumulation of 5-HT. These results indicate that although salmon calcitonin does not influence the synthesis and metabolism of 5-HT, it does require the integrity of the serotonergic system in order to cause analgesia.

Effect of Bay K 8644 on the synthesis and metabolism of dopamine and 5-hydroxytryptamine in various brain areas of the rat.

The effects of Bay K 8644 (1, 2 and 4 mg kg-1, i.p.) on the synthesis and metabolism of dopamine and 5-hydroxytryptamine (5-HT) in rat brain after m-hydroxybenzylhydrazine administration were studied. Bay K 8644 (2 and 4 mg kg-1, i.p.) caused an increase in the synthesis of both dopamine in the striatum and 5-HT in the midbrain and striatum, measured as the accumulation of 3,4-dihydroxyphenylalanine (dopa) and 5-hydroxytryptophan, respectively. Moreover, Bay K 8644 at the dose of 4 mg kg-1 increased the turnover of dopamine in the striatum and of 5-HT in midbrain and striatum. These neurochemical changes were antagonized by the calcium channel antagonist nimodipine (10 mg kg-1, i.p.). It is concluded that dihydropyridine receptors may mediate the brain region-specific changes in the dopaminergic and 5-HT-ergic neurotransmission which occur following activation of neuronal calcium channels.