A novel effect of salmon calcitonin on in vitro Ca-uptake by rat brain hypothalamus: the regional and hormonal specificities

Calcium inflow in cells transfected with cloned rat and porcine calcitonin receptors

Ca2+ fluxes were examined in HEK 293 cells stably expressing the rat or porcine calcitonin receptors (CTRs). Calcitonin (CT) rapidly increased cytosolic Ca2+ ([Ca2+]i) concentrations in these cells in a manner which was sustained in the presence of extracellular Ca2+ ([Ca2+]e). In cells pretreated with CT, elevation of the [Ca2+]e concentration resulted in a further increase in [Ca2+]i which was concentration-dependent with respect to both the concentration of CT and the increment of [Ca2+]e. Untransfected cells, cells transfected with vector alone, and CTR-transfected cells not treated with CT, were unresponsive to [Ca2+]e. The microsomal Ca(2+)-ATPase inhibitor thapsigargin was able to mimic both the acute [Ca2+]i fluxes and responsiveness to [Ca2+]e mediated by CT in these cells. The CT-induced responsiveness to [Ca2+]e was neither mimicked by, nor affected by, activators of the cAMP or protein kinase C pathways. Treatment of cells with pertussis toxin influenced neither the primary Ca2+ fluxes in response to CT or thapsigargin nor the agonist-induced [Ca2+]e influx. Nifedipine failed to block responses to either CT or thapsigargin. These results lead to the important conclusion that the CTR participates in receptor-activated Ca2+ inflow, in which depletion of intracellular Ca2+ pools leads secondarily to influx of extracellular Ca2+.

Pharmacodynamics of salmon calcitonin in humans: new markers of pharmacological activity

In order to define the pharmacodynamic profile of salmon calcitonin (sCT) in humans, several markers of the biological activity of the drug have been studied, namely cAMP, adenosine and pO2 in venous blood, and the cytosolic free calcium level in circulating cells. Different dosages and routes of administration (1.5 IU.kg-1 and 0.75 IU kg-1 IM, and 1.5 IU.kg-1 via nasal spray) were compared. sCT caused an increase in cAMP, adenosine and pO2, and a decrease in cytosolic free calcium in neutrophils, lymphocytes and platelets. The peak times of all these parameters ranged between 109 and 182 min, and 101 and 168 min after IM and nasal spray administration respectively. There was greater variability in the values after IM than nasal spray of administration of sCT. It is concluded that adenosine and pO2 in venous blood, and cytosolic free calcium in circulating cells are valuable markers of the activity of sCT and that sCT decreases the cytosolic free calcium level in neutrophils, lymphocytes and platelets. Pharmacodynamic analysis of the biological effects of the drug is highly reliable and valuable in predicting its pharmacological profile. sCT administration via a nasal spray is able to produce significant biological effects, although they are less marked than after IM dosing.

Salmon calcitonin-induced modulation of free intracellular calcium

Salmon calcitonin (sCT), a hormone shown to modulate calcium in the periphery modulated free, intracellular calcium, ([Ca++]i), in mouse brain synaptosomes as measured by changes in fura-2-mediated fluorescence. A 5-min incubation of synaptosomes with sCT produced an increase in the basal levels of [Ca++]i and an increase in KCl-stimulated levels of [Ca++]i. A 5-min pretreatment of mice with intraventricularly administered sCT antagonized morphine-induced antinociception in the tail-flick test, and facilitated naloxone antagonism of morphine. Conversely, pretreatment of synaptosomes for 1 h with salmon CT produced a decrease in depolarization-stimulated levels of [Ca++]i. The sCT-induced decrease in the stimulated rise in [Ca++]i at 1 h correlated temporally to sCT-induced antinociception in vivo. The effects of sCT in the electrically stimulated guinea pig ileum bioassay appeared to correlate to sCT effects in vivo. The data indicate that calcitonin may function as a neuromodulator via modulation of Ca++ within the central nervous system.

Calcitonin stimulates adenylate cyclase activity, the accumulation of cyclic adenosine 3',5' monophosphate and the release of prostaglandin E2 in rat intestinal mucosa

Calcitonin stimulates intestinal fluid and electrolyte secretion by an unclear mechanism. The present results show that synthetic salmon calcitonin significantly stimulates adenylate cyclase activity in the membranes of rat intestinal mucosal cells. The effect of the hormone was in a dose-dependent manner for a dose range of 10(-9)-10(-7) M. The stimulated enzyme activity was followed by a progressive accumulation of cyclic adenosine 3',5' monophosphate and release of prostaglandin E2 in these cells during a 20 min experimental period of time. These results are discussed, and suggest that the formation of cyclic adenosine 3',5' monophosphate possibly mediates the action of calcitonin on intestinal cell functions.

Anatomical mapping of the rat hypothalamus for calcitonin-induced anorexia

The primary physiological function of calcitonin, a peptide hormone secreted by the thyroid gland, is to modulate plasma calcium concentrations. Calcitonin also has several effects on the central nervous system including an inhibition of feeding behavior. In the present study synthetic salmon calcitonin (15 ng in 0.3 microliter) was found to produce a marked suppression of eating when infused in several hypothalamic areas. The greatest inhibition was produced by infusions into the paraventricular nucleus of the hypothalamus, the perifornical area and several areas on the floor of the hypothalamus. A less marked inhibition of eating was produced by infusions in the nucleus accumbens. Infusions in the olfactory tubercule, the ventrolateral hypothalamus, the medial forebrain bundle and the posterior nucleus of the hypothalamus had no effect. It is concluded that the anorectic effects of calcitonin on the central nervous system are mediated by several hypothalamic and extrahypothalamic sites.

Calcitonin as a feeding suppressant: localization of central action to the cerebral III ventricle

Calcitonin suppresses food and water intake. To further study this effect of calcitonin, rats were subjected to various intra-cerebroventricular (ICV) applications of calcitonin. The results show: (1) Intra-third ventricular (III-ICV) infusion of calcitonin dose-dependently decreased food intake with short- and long-term effects; (2) Potency was decreased by using non-siliconized materials; (3) Potency decreased with age of rats; (4) Infusion into the aqueduct and cisterna magna decreased short- and long-term food intake less than III-ICV administration; (5) Aqueduct obstruction did not affect feeding suppression by III-ICV calcitonin. Aqueduct obstruction did not affect dipsogenic response to III-ICV infusion of angiotensin II; (6) Results of water intake and food to water intake ratios suggest a greater calcitonin effect on food intake than on water intake. The evidence suggests that the hypothalamus is a main locus for suppression of food intake by ICV administered calcitonin.

Inhibitory effects of calcitonin on adenylate cyclase activity in different rat brain areas

We have investigated the effect of calcitonin (CT) on adenylate cyclase in membranes from different rat brain areas. Salmon calcitonin (sCT) dose-dependently inhibited the enzyme activity in midbrain, hypothalamus, medulla, pons and caudate nucleus, but was ineffective in adenohypophysis. The inhibitory effect was enhanced by GTP. Comparison of calcitonins of different origin indicated that sCT was the most potent in inhibiting the enzyme in hypothalamic membranes, eel CT (eCT) was slightly less potent, and human CT (hCT) was ineffective. Chronic I.C.V. pretreatment with sCT did not modify the subsequent in vitro sensitivity of adenylate cyclase to sCT. It is concluded that some of CNS actions of CT might involve modulation of intracellular cAMP levels.

Lithium mechanisms in bipolar illness and altered intracellular calcium functions

Calcium functions as an intracellular second messenger, transducing a variety of hormonal, electrical, and mechanical stimuli by activating a wide range of enzymes. There is evidence, ranging from definitive to strongly presumptive in quality, that lithium can alter many calcium-dependent processes. The list of enzyme systems dependent on calcium and altered by lithium includes adenylate cyclase, glycogen synthase, inositol-1-phosphatase, and calcium adenosine triphosphatase (ATPase). Lithium also interferes with calcium regulation of receptor sensitivity, parathyroid hormone release, microtubule structure, and other systems. All of the neural mechanisms that are hypothesized to explain various psychopharmacological treatments of bipolar illness involve functions that are critically controlled by calcium. Moreover, in every instance, a known action of lithium on calcium function could account for lithium's therapeutic or prophylactic results. From these considerations the dual hypotheses emerge that bipolar illnesses arise from disorders in calcium-regulated functions and that lithium acts by reversing or counterbalancing the effects of these calcium dysfunctions.

Calcitonin receptors in the rat mesencephalon mediate its analgesic actions: autoradiographic and behavioral analyses

Autoradiographic analyses of salmon calcitonin (sCT) binding in the rat mesencephalon revealed an exceptionally high concentration of receptors in the ventral and ventrolateral segments of the periaqueductal gray matter (PAG) extending along the entire rostral-caudal axis. Relatively heavy labeling was also seen along a band extending ventrolaterally through the mesencephalic reticular formation. Other receptor-rich areas include the nucleus linearis, pars compacta and lateralis of the substantia nigra, locus coeruleus, parabrachial nuclei and nucleus raphe pontis of the pontine reticular formation. Injections of sCT into the PAG induced a dose-dependent increase in hot-plate latencies. All rostral-caudal levels of these brain regions appeared to be equally responsive. Injections into the midline pontine reticular formation were also effective in increasing response latencies. Unilateral injections into the hypothalamus, medial thalamus, ventral thalamus and mesencephalic reticular formation proved to be ineffective. Human calcitonin (hCT) was considerably less potent. These biological effects are consistent with the potencies of both peptides in displacing 125I-sCT from slide-mounted sections of rat PAG. Naloxone failed to antagonize sCT-induced analgesia, suggesting an opiate independent mechanism for this peptide in eliciting analgesia.

Calcitonin inhibits the phosphorylation of various proteins in rat brain synaptic membranes

The present report examines the effect of different calcitonins and analogs on the in vitro phosphorylation of brain synaptic membrane proteins. The findings demonstrate that calcitonin is a potent inhibitor of several brain synaptic proteins and that salmon and eel calcitonins are considerably more potent than thyrocalcitonin in eliciting this effect. Deletion of leucine from position 16 in salmon calcitonin sequence resulted in a drastic loss of inhibitory activity, indicating the importance for a hydrophobic residue at position 16 in the intact calcitonin molecule. The mechanism of calcitonin inhibition of protein phosphorylation was likely due to the blockade of stimulation of protein kinases by calmodulin.

Central control of intestinal motility by prostaglandins: a mediator of the actions of several peptides in rats and dogs

The effect of intracerebroventricular and intravenous administrations of prostaglandin E2 on gastrointestinal motility were investigated in conscious rats and dogs using electrodes and strain gauges, respectively. Injections were performed during the fed state and the motor changes were compared with those after intracerebroventricular administration of calcitonin, neurotensin, and (D-Ala2, Met5) enkephalinamide. Intracerebroventricular administration of prostaglandin E2 (0.5 micrograms) to fed rats restored the migrating myoelectric complex for 67 +/- 16 min. A migrating myoelectric complex-restoring effect was also observed after intracerebroventricular administration of calcitonin (0.02 U) and neurotensin (80 ng). This effect was blocked by previous intracerebroventricular administration of indomethacin (0.25 mg). Administered centrally to dogs but not intravenously at a 10-fold greater dose, prostaglandin E2 (0.1 microgram/kg) reduced (52.8%) the duration of the jejunal postprandial motor state similarly to that observed after intracerebroventricular administration of calcitonin (0.1 U/kg), neurotensin (0.1 microgram/kg), and (D-Ala2, Met5) enkephalinamide (0.1 microgram/kg). These effects of calcitonin and neurotensin were abolished 4 h after an intramuscular injection of indomethacin (2 mg/kg), whereas those of (D-Ala2, Met5) enkephalinamide persisted. These results suggest that (a) prostaglandins act centrally to control the pattern of intestinal motility in both rats and dogs and (b) calcitonin and neurotensin when injected intracerebroventricularly affect the intestinal motor profile probably by stimulating prostaglandin release within the brain.

Relationships between hypocalcaemic and anorectic effect of calcitonin in the rat

Salmon calcitonin (sCT, 2 and 20 U/kg), porcine calcitonin (pCT, 20 and 40 U/kg) and human calcitonin (hCT, 20 and 40 U/kg) were injected subcutaneously to rats trained to eat their food during two hours each day. Food intake and serum Ca++ concentrations were determined at the end of 2h-feeding period. A long lasting anorectic effect was observed for 20 U/kg of sCT with a parallelism between hypocalcaemia and anorexia in the first 8 hours after treatment; on the contrary, rats continued to eat less than controls in the following hours when their serum Ca++ concentrations had risen to normal or even higher levels. As regards pCT and hCT, it was shown that these peptides reduced significantly meal size only for 1-2 hours when serum Ca++ levels were at their lowest levels for these peptides.

Intracerebroventricular injection of 125I-salmon calcitonin in rats: fate, anorexia and hypocalcemia

Intracerebroventricular (i.c.v.) injection of 19 pmol/rat or more of salmon calcitonin (sCT) or iodinated sCT suppressed spontaneous intake of food and water in a dose-dependent manner. Tail-whipping was a peculiar behavior which concomitantly developed, but no analgesia ensued from the doses tested (up to 62 pmol/rat). It was examined how the rise and fall pattern of these behavioral effects would correlate with the dispositional pattern of 125I-sCT. When the radioactive peptide was injected in anorectic doses via the i.c.v. route, the radioactivity was found to distribute throughout the brain, but not uniformly. In rats which showed a marked anorexia and tail-whipping behavior, distribution occurred in such a manner that it could be interpreted to reflect the regional and subcellular distribution pattern of sCT-specific binding sites. Even 3 hr after injection, the hypothalamus, the smallest region, retained the highest radioactivity corresponding to about 1% of the dose and at least one half of which was identified as the intact iodo-sCT. To be noted is the finding that sCT injected centrally will quickly enter the systemic circulation and peripherally induced long-lasting hypocalcemia, since the anorectic dose of sCT is considerably higher than the dose needed for the peripheral effect. It is concluded that most of the sCT after i.c.v. injection leaks into the systemic circulation, but the rest is retained rather selectively around the receptor in hypothalamic nuclei for a long time, leading to day-long suppression of feeding and drinking behavior.

In vitro interaction between calcitonin and calmodulin

The effects of salmon calcitonin and human calcitonin on the fluorescence spectra of a fluorescent conjugate of calmodulin with dansyl-chloride and on the calmodulin mediated activation of phosphodiesterase have been studied. We showed that salmon calcitonin provoked calcium-dependent modifications of the spectra of dansyl-calmodulin and completely inhibited the calmodulin mediated activation of phosphodiesterase with a maximum effect at the dose of 5.8 X 10(-7)M and 10(-7) M respectively. No appreciable effect of human calcitonin was observed in either system. This interaction of salmon calcitonin with calmodulin is similar to the interaction of certain neuropeptides and antipsychotic drugs to calmodulin and may explain certain of the peptide's pharmacological effects.