A novel inositol phosphate selectively inhibits vasoconstriction evoked by the sympathetic co-transmitters neuropeptide Y (NPY) and adenosine triphosphate (ATP)

Effect of peripheral axotomy on pain-related behavior and dorsal root ganglion neurons excitability in NPY transgenic rats

In order to clarify the physiologic role of NPY in sensory processing, we obtained intracellular recordings of DRG neurons from wild type (WT) and NPY overexpressing transgenic rats (NPY-TG) before and after injury. We investigated medium and large diameter DRG neurons since upregulation of NPY peptide following the nerve injury occurs primarily in those cells. Neurons were classified as Aalpha/beta and Adelta using conduction velocity and action potential duration. Prior to the injury, Aalpha/beta neurons of NPY-TG rats conducted more slowly and had a more brief AHP than similar cells from the WT group. Adelta neurons at baseline conducted faster in TG animals compared to WT. Ligation of the 5th lumbar spinal nerve (SNL) produced certain changes in Aalpha/beta cells that were evident only in the TG group. These include increased refractory period, increased input resistance, AHP prolongation and a depolarizing shift in threshold for AP initiation. The expected injury-induced CV slowing was not seen in NPY-TG Aalpha/beta cells. In the Adelta cell group, injury produced a depolarizing shift in the resting membrane potential, an increase in AP duration and decrease in AHP and refractory period duration only in WT rats, while NPY-TG cells lacked these injury-induced changes. Behavior tests showed diminished sensory response to nerve injury in NPY-TG rats, i.e., shorter duration of enhanced pain-related behavior and attenuation of contralateral effect. In conclusion, our observations suggest that NPY overexpression leads to reduced neuronal activity following nerve injury in a cell-specific manner.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Effect of neuropeptide Y on inflammatory paw edema in the rat: involvement of peripheral NPY Y1 and Y5 receptors and interaction with dipeptidyl-peptidase IV (CD26)

Several lines of evidence suggest that neuropeptide Y (NPY) may exert regulatory effects in local inflammatory responses. Here, we show that intraplantarly (i.pl.) applied NPY, peptide YY (PYY), and an NPY Y5 receptor-selective agonist dose-dependently potentiate concanavalin A (Con A)-induced paw edema in the rat. The NPY Y1 receptor antagonist BIBO 3304 abolishes the pro-inflammatory action of both NPY and PYY while the dipeptidyl-peptidase IV (CD26) inhibitor Ile-thiazolidide exerted synergistic and potentiating effects in vivo. Taken together, the present data reveal an NPY Y1/Y5 receptor interplay and an involvement of CD26 in the NPY-induced potentiation of paw edema in the rat.

D-myo inositol 1,2,6, triphosphate (alpha-trinositol, pp56): selective antagonist at neuropeptide Y (NPY) Y-receptors or selective inhibitor of phosphatidylinositol cell signaling?

1. D-myo inositol 1,2,6 trisphosphate (alpha-trinositol, pp56), an isomer of the second messenger substance, D-myo inositol 1,4,5 trisphosphate, has an interesting pharmacological profile that includes anti-inflammatory and analgesic effects and antagonism of neuropeptide Y (NPY)-mediated cellular responses. 2. However, not all responses elicited by this neuropeptide are sensitive to antagonism by pp56. Evidence is emerging, at least in certain tissues, that other receptor populations, in addition to those for NPY, are also sensitive to inhibition by pp56. 3. A direct or allosteric interaction of pp56 at receptors for NPY is now considered unlikely and it is more probable that pp56 might interfere at some point in the phosphatidylinositol signaling pathway, possibly at the level of the plasmalemmal inositol 1,3,4,5, tetrakisphosphate receptor. 4. Full realization of the therapeutic potential of this novel compound, however, must await a thorough characterization of the cellular mechanism(s) associated with the various pharmacological effects of pp56.

Effect of alpha-trinositol on swelling and damage of glial cells by lactacidosis and glutamate

The therapeutic efficacy of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate), an isomer of the intracellular messenger IP3, was analyzed for cytotoxic swelling and damage of glial cells in vitro from lactacidosis or glutamate. Lactacidosis and the interstitial accumulation of glutamate are prominent sequelae in ischemic or traumatic brain tissue. C6 glioma cells harvested from culture and suspended in a physiological medium were either exposed to pH 5.0 by administration of lactic acid, or to 1 mM glutamate at normal pH. Cell swelling and viability were quantified by blood flow cytometry. Addition of alpha-trinositol (3 mM) under control conditions at pH 7.4 resulted in transient cell shrinking to 96.5 +/- 1.3% of control within 3 min (p < 0.05). Lactacidosis of pH 5.0 led to an increase in cell volume to 139.7 +/- 1.3% within 20 min, whereas alpha-trinositol reduced the swelling response by approximately 25% (p < 0.01). In addition, cell viability was severely affected at pH 5.0 amounting to only 53.8 +/- 3.1% after 60 min. alpha-Trinositol was found to markedly improve cell viability; at 60 min 70.2 +/- 1.6% of the cells were still viable (p < 0.01). Addition of glutamate (1 mM) led to a steady increase in cell size, reaching 110% of control after 120 min, irrespective of wether alpha-trinositol was present or not. The attenuation of cell swelling may be attributed to an interference with pH-regulatory mechanisms, such as the Na+/H(+)-antiporter, while protection of cell viability might be caused be effects of alpha-trinositol on Ca(2+)-overload. On the other hand, the increase in cell volume by glutamate associated with its intracellular uptake was not influenced by alpha-trinositol.

Use of D-myo inositol 1,2,6 trisphosphate to inhibit contractile activity in rat ventricular cardiomyocytes induced by neuropeptide Y and other cardioactive peptides through phospholipase C

1. D-Myo inositol 1,2,6 trisphosphate (alpha-trinositol, pp56), an isomer of the second messenger substance, inositol 1,4,5 trisphosphate, has an interesting pharmacological profile that includes antagonism of a number of neuropeptide Y (NPY)-mediated cellular processes. The ability of pp56 to inhibit selectively the myocardial contraction mediated by NPY in relation to the responses to other cardioactive peptides, including endothelin-1, calcitonin gene-related peptide (CGRP), secretin and vasoactive intestinal peptide (VIP), was assessed. In order to investigate the possible interaction of pp56 with mechanisms of inositol phosphate signalling generated in heart muscle cells by activation of the beta-isoenzyme of phospholipase C (PLC beta), noradrenaline was used as a positive control, and isoprenaline and forskolin were included as negative controls. 2. Ventricular cardiomyocytes, isolated from the hearts of adult rats, were stimulated to contract at 0.5 Hz in the presence of calcium ion (2 mM). The concentrations of agonists used were in the region of their maximally effective concentrations for myocyte contraction and the concentration of pp56 was in the range of 1-100 microM. Contractile activity was monitored by video microscopy and maximum shortening determined by image analysis. 3. In the absence of agonist, contractile amplitudes following 20 min preincubation with pp56 were not different from that observed in the absence of pp56. Pp56 (1-100 microM) inhibited significantly the positive contractile response to noradrenaline (5 microM) in the presence of propranolol (500 nM), such that the response was almost completely attenuated at the highest concentration of the inhibitor. Pp56 did not inhibit the positive contractile responses to forskolin (40 microM) or isoprenaline (100 nM). 4. NPY alone does not influence the basal level of contraction of cardiomyocytes, but can attenuate isoprenaline-stimulated contraction and can increase contractile amplitude from basal when the transient outward current is blocked with 4-aminopyridine. In the presence of isoprenaline (100 nM), the negative response to NPY (100 nM) was attenuated significantly by pp56 (1-100 microM). With 4-aminopyridine, the positive contractile response to NPY (200 nM) was decreased by pp56, although this was not statistically significant. 5. Pp56 inhibited the positive contractile responses to CGRP (1 nM) and endothelin-1 (20 nM) completely, but did not affect the responses to secretin (20 nM) or VIP (20 nM). 6. In conclusion, these data challenge the previously obtained selectivity of pp56 as an antagonist of NPY-mediated cellular processes, since responses to CGRP and endothelin-1 were at least equally sensitive. Furthermore, as pp56 discriminated clearly in its inhibition of responses to alpha-adrenoceptor by comparison with beta-adrenoceptor/adenylate cyclase stimulation, it appears that pp56 may be a useful pharmacological agent with which to distinguish between PLC beta-dependent and PLC beta-independent coupling mechanisms. On this basis, further evidence has been obtained that, in rat cardiomyocytes, the contractile responses to NPY, CGRP and endothelin-1 are attributable to the activation of PLC beta-dependent pathways, whereas the responses to secretin and VIP are mediated by PLC beta-independent pathways.

Photoaffinity analogue for the anti-inflammatory drug alpha-trinositol: synthesis and identification of putative molecular targets

alpha-Trinositol (alpha T), or Ins(1,2,6)P3, is a semisynthetic inositol trisphosphate produced commercially by the partial degradation of phytic acid with phytase. The molecular targets mediating the mechanism of action of this novel anti-inflammatory, analgesic, and antivasoconstrictive drug are unknown. A new photoaffinity analogue, 4-[3H]BZDC-alpha T, has been prepared in which the [3H]-p-benzoyldihydrocinnamoyl ([3H]BZDC) photophore is tethered through an O-(5-aminopentanoyl) linkage to the 4-OH of alpha T. Photoaffinity labeling experiments with two human tissues, umbilical cord vascular smooth muscle cells and platelet membranes, revealed proteins that were selectively labeled by 4-[3H]BZDC-alpha T. Thus, co-incubation with alpha T but not with Ins(1,3,4,5)P4 during photolysis competitively displaced labeling of a 55 kDa platelet protein. In vascular epithelial cells, alpha T and Ins(1,3,4,5)P4 both displaced labeling of a 55 and 43 kDa proteins. The identification of putative protein targets for alpha T in smooth vascular tissue may have important implications in elucidation of the mechanism of action of this unusual drug.

Swelling and damage of glial cells by lactacidosis and glutamate: effect of alpha-trinositol

The therapeutical efficacy of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate), an isomer of the intracellular messenger IP3, was analyzed on cytotoxic swelling and damage of glial cells in vitro from lactacidosis or glutamate. C6 glioma cells suspended in a physiological medium were either exposed to pH 5.0 by administration of lactic acid, or to 1 mM glutamate. Cell swelling and viability were quantified by flow cytometry. Lactacidosis of pH 5.0 led to an increase in cell volume to 139.7 +/- 1.3% within 20 min whereas alpha-trinositol was reducing the swelling response by approximately 25% (P < 0.01). In addition, at pH 5.0 the fraction of viable cells was lowered from 94.3 +/- 0.2% (control) to only 53.8 +/- 3.1% after 60 min. Alpha-trinositol was found to protect also cell viability; at 60 min of lactacidosis 70.2 +/- 1.6% of the cells still were viable (P < 0.01). The addition of glutamate (1 mM) to the cell suspension led to a steady increase in cell size, reaching 110% of control at 120 min, irrespectively of whether alpha-trinositol was added or not.

Intrathecal neuropeptide Y exacerbates nerve injury-induced mechanical hyperalgesia

In normal animals, spinal administration of neuropeptide Y induces analgesia to thermal stimuli, but has no effect on mechanical thresholds. Recent anatomical studies, however, have shown that following nerve injury there is an altered expression of neuropeptide Y and its receptors. The aim of this behavioural study, therefore, is to examine the effect of intrathecal administration of neuropeptide Y, its agonists and an antagonist on mechanical nociceptive thresholds in rats with partial injury to the sciatic nerve. Test agents were administered for 14 days via osmotic pumps (0.5 microliter/day) attached to intrathecal catheters and the nociceptive flexion reflex was quantified using an Ugo Basile Analgesymeter. Partial injury to the sciatic nerve, in animals treated intrathecally with saline, induces a significant decrease in mechanical threshold as compared to the sham operated, contralateral paw. The nerve injury-induced hyperalgesia is exacerbated by 2 microM neuropeptide Y and by 2 microM [Leu31,Pro34]-neuropeptide Y, a Y1 receptor agonist. The Y2 receptor agonist, N-acetyl-[Leu28,Leu31]-neuropeptide Y24-36 (2 microM), had no effect on the nerve injury-induced hyperalgesia. The putative neuropeptide Y antagonist, alpha-trinositol (10 microM), significantly attenuated the nerve injury-induced hyperalgesia. This study suggests that neuropeptide Y may contribute to nerve injury-induced mechanical hyperalgesia via the Y1 receptor and provides further insight into the possible mechanisms underlying nerve injury-induced hyperalgesia to mechanical stimuli.

The effect of alpha-trinositol (D-myo-inositol 1,2,6-trisphosphate) on formalin-evoked spinal amino acid and prostaglandin E2 levels

The effect of the inositol trisphosphate analog alpha-trinositol on noxious-evoked behavior, amino acid and prostaglandin E2 (PGE2) release was examined in unanesthetized rats using intrathecal microdialysis probes. Subcutaneous injection of 50 microliters 5% formalin solution produced two phases of pain-like behavior and significant elevation of glutamate, aspartate, glycine, taurine and serine during phase 1. PGE2 concentrations were increased during both phases 1 and 2. Intraperitoneal delivery of 300 mg/kg alpha-trinositol significantly suppressed both phases 1 and 2 of formalin-induced behavior and the associated elevation of amino acids and PGE2. These data demonstrate that the antinociceptive effect of alpha-trinositol corresponds to suppression of noxious-evoked release of amino acids and PGE2 from the spinal cord.

Does the neuropeptide Y Y1 receptor contribute to blood pressure control in the spontaneously hypertensive rat?

OBJECTIVE

To study the effects of the selective neuropeptide Y (NPY) Y1 receptor antagonist BIBP 3226 in spontaneously hypertensive rats (SHR) in order to elucidate whether NPY function may be altered in the SHR and whether the NPY Y1 receptor plays a specific role in the maintenance of high blood pressure in this genetic form of hypertension.

METHODS

Pithed and conscious SHR were studied after intravenous administration of 0.125-1 mg/kg BIBP 3226. The cardiovascular effects were evaluated under baseline conditions, under acute stress and after exogenous administration of 20 microg/kg NPY. The potentiating effects of NPY on pressor responses to phenylephrine and tyramine were studied in the SHR.

RESULTS

Intravenous administration of 0.125-1 mg/kg BIBP 3226 dose-dependently inhibited the pressor response to exogenous NPY in pithed SHR. At higher doses BIBP 3226 had an effect duration of 20-40 min. In the pithed SHR, a 0.5 mg/kg bolus injection of BIBP 3226 shifted the pressor response curve for exogenous NPY significantly to the right It also inhibited significantly the potentiating effects of NPY on pressor responses to phenylephrine and tyramine. In conscious SHR, 0.125-1 mg/kg BIBP 3226 did not reduce the basal blood pressure. In combination with a hypotensive dose of prazosin, administration of 0.5 mg/kg BIBP 3226 had no added effects lowering the basal blood pressure. A stressful stimulus, namely an air jet, caused a brief increase in blood pressure and heart rate in the conscious SHR. In this model, 0.5 mg/kg BIBP inhibited the heart rate response slightly but had no effect on the blood pressure response.

CONCLUSIONS

Our results demonstrate that, although the selective NPY Y1 receptor antagonist BIBP 3226 may shift the pressor response to exogenous NPY potently, it does not influence basal blood pressure significantly in the SHR.

Antagonistic effect of D-myo-inositol-1,2,6-trisphosphate (PP56) on neuropeptide Y-induced vasoconstriction in the feline dental pulp

Intra-arterial injection of neuropeptide Y (NPY) (1.3-2.0 micrograms/kg) resulted in decreases of pulpal blood flow by 37.7 +/- 5.7% (mean +/- SEM). The intra-arterial injection of D-myo-inositol-1,2,6-trisphosphate (PP56) (0.3 mg/kg) alone changed pulpal blood flow by 1.0%. The effect of NPY in the presence of PP56 resulted in significantly smaller decreases in pulpal blood flow ranging from 27.2 +/- 5.4 to 16.6 +/- 3.5% from control as compared with NPY alone. In effect, PP56 partially blocked the decreases in pulpal blood flow caused by NPY. The electrical stimulation of the sympathetic nerve alone resulted in decreases in pulpal blood flow of 41.7 +/- 6.2%. The electrical stimulation of the sympathetic nerve following the intra-arterial administration of PP56 decreased pulpal blood flow by 23.1 +/- 6.0% from control, significantly less than the sympathetic nerve stimulation alone. PP56 attenuated the decrease in pulpal blood flow caused by the sympathetic nerve stimulation by 44.4 +/- 11.0%. Similarly, the combination of PP56 and phentolamine followed by electrical stimulation of the sympathetic nerve reduced the decrease in pulpal blood flow caused by the sympathetic nerve stimulation alone by 43.0 +/- 8.6%. These results provide evidence that the non-peptide PP56 is capable of antagonizing vasoconstriction caused by NPY in the feline dental pulp. In addition, they show functional evidence that NPY as well as noradrenaline are released from the sympathetic nerve endings during its stimulation and cause vasoconstriction.

Synthesis and characterization of a selective peptide antagonist of neuropeptide Y vascular postsynaptic receptors

1. A cyclic dimeric nonapeptide neuropeptide Y (NPY) receptor antagonist, 1229U91, was synthesized by Fmoc chemistry and dimerised in solution. Its effects were assayed in mesenteric arteries from rats and mice, and in rat vas deferens. 2. Mesenteric arteries were cannulated and pressurised to 55 mmHg and the external diameters continuously measured. NPY, PYY, Leu31Pro34NPY and NPY(13-36) each caused concentration-related contractions with the order of potency PYY > or = Leu31Pro34NPY = NPY > NPY (13-36), consistent with the Y1 receptor subtype. 3. 1229U91 had no agonist activity in the arteries but caused a concentration-related rightward shift of NPY (mouse arteries) or Leu31Pro34NPY (rat) concentration-response curves. The antagonism was competitive with pKBS of 7.69 +/- 0.15 and 7.47 +/- 0.13 in the mouse and rat arteries, respectively. 4. Sympathetic nerves in the vas deferens were stimulated with a single electrical field pulse every 20 s and the twitch responses recorded. NPY, PYY, Leu31Pro34NPY and NPY(13-36) inhibited the twitches with the order of potency PYY > NPY > NPY(13-36) >> Leu31Pro34NPY, consistent with the Y2 receptor subtype. 5. 1229U91 inhibited the vas deferens twitch with a shallow concentration-response curve and a time-course of inhibition distinct from that of NPY. 1229U91 (30 microM) did not cause a rightward shift of the NPY concentration-response curve. 1229U91 is at least 5 orders of magnitude less potent in the vas deferens than in rat brain Y2 binding assays reported by others, suggesting that the brain and vas deferens Y2 receptors are different. 6. It is concluded that 1229U91 is a competitive antagonist of NPY Y1 vascular receptors and has additional properties that inhibit the electrically evoked twitch of the rat vas deferens.

Binding sites for alpha-trinositol (inositol 1,2,6-trisphosphate) in porcine tissues; comparison with Ins(1,4,5)P3 and Ins(1,3,4,5)P4-binding sites

1. The molecular mechanism of action of the inositol trisphosphate isomer, alpha-trinositol (Ins(1,2,6)P3) which has potential therapeutic use in treatment of inflammation and burn oedema, is still unclear. Therefore we have studied binding sites for alpha-trinositol in different tissues. 2. In membranes from pig cerebellum, liver, kidney, heart, and spleen, the density of specific [3]-alpha-trinositol binding sites was maximal at pH 5.0. Cerebellum and spleen showed only one binding site (cerebellum KD = 9.1 microM, spleen KD = 7.3 microM). In the other tissues, there were a high-affinity site (heart KD = 70 nM, liver KD = 790 nM and kidney KD = 1800 nM), besides a low-affinity site with a KD ranging between 32 and 120 microM. In cerebellar membranes, the affinity and density (107 pmol mg-1 protein) of alpha-trinositol binding sites were not affected by phosphate (0 to 25 mM). 3. Binding of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 to membranes from different porcine tissues was also determined. Ins(1,3,4,5)P4, the isomer stereochemically related to alpha-trinositol, binds with an affinity of 1.2 nM in cerebellum, but in the other tissues the binding site density was too low to determine the affinity. With cerebellar membranes heterologous displacement of [3H]-Ins(1,3,4,5)P4 by alpha-trinositol yielded a K1 of 11 microM. The Ins(1,4,5)P3 receptor displayed an affinity of 15 nM in cerebellum and of 5 to 7 nM in the other tissues investigated. 4. The solubilized Ins(1,3,4,5)P4 receptor preparation from cerebellum did not show Ins(1,2,6)P3 binding. Ins(1,2,6)P3 binding was found in the pellet obtained after solubilization of the membranes with the detergent Brij 58. 5. Thus, in different tissues alpha-trinositol binds to proteins with different affinity. They are obviously not related to binding sites for Ins (1,4,5)P3 or for Ins(1,3,4,5)P4. Future experiments have to unravel the identity of the binding protein(s) for alpha-trinositol.

The effect of alpha-trinositol on cholera toxin-induced hypersecretion and morphological changes in pig jejunum

alpha-Trinositol (D-myo-inositol 1,2,6-trisphosphate, PP56) is a novel antiinflammatory drug. This study elucidates the effect of intravenous alpha-trinositol on basal and acute fluid transport and morphological changes following cholera toxin administration in pig jejunum in vivo. Using isolated jejunal tied-off loops, the fluid hypersecretory (accumulation) effect of different doses of cholera toxin was studied in pigs treated intravenously with saline added different doses (0, 4, 8, 16 and 32 mg x kg-1 x hr-1) of alpha-trinositol. Levels of alpha-trinositol, as well as stereomicroscopical, light microscopical and scanning electron microscopical morphological studies were performed. Cholera toxin evoked a dose-dependent fluid hypersecretion. Treatment with alpha-trinositol caused a dose-dependent inhibition of the cholera toxin-induced fluid hypersecretion and did not affect basal fluid absorption. The 16 mg x kg-1 x hr-1 alpha-trinositol dose gave a maximal inhibition of 36%. Morphological studies showed only minor changes following 6 hr of exposure to 20 micrograms x loop-1 cholera toxin. These changes consisted of dilation of the villus capillaries, an increase of apical membrane blebbing and a reduction of the intercellular space. Treatment with 16 mg x kg-1 x hr-1 alpha-trinositol alone did not induce any morphological changes, and did not alter the morphological changes induced by cholera toxin, which caused fluid hypersecretion and only minor acute morphological changes. In conclusion, alpha-trinositol treatment reduced cholera toxin-induced fluid hypersecretion without altering basal fluid absorption, basal morphology, or cholera toxin-induced morphological changes in pig jejunum in vivo.

Effects of glibenclamide on the regional haemodynamic actions of alpha-trinositol and its influence on responses to vasodilators in conscious rats

1. In conscious rats, alpha-trinositol (D-myo-inositol-1, 2, 6 triphosphate; 5-80 mg kg-1 h-1 infusion) caused dose-dependent hypotension, tachycardia and hyperaemic dilatation in renal, mesenteric and hindquarters vascular beds. These effects were accompanied by inhibition of the renal vasodilator effects of acetylcholine (ACh), and of the mesenteric vasodilator effects of sodium nitroprusside (SNP) and, particularly, of levcromakalim (LCK). 2. In the light of the latter finding, in a second experiment, we assessed the influence of the KATP channel inhibitor, glibenclamide (20 mg kg-1), on resting haemodynamics, on responses to ACh, bradykinin (BK), SNP and LCK, on the haemodynamic action of alpha-trinositol, and on the effects of the latter on responses to the vasodilators, over a period of 3 days. 3. In the presence of saline, glibenclamide caused a reproducible pressor effect, accompanied by renal, mesenteric, and hindquarters vasoconstrictions on all 3 experimental days; these effects were unrelated to changes in blood glucose. In the presence of glibenclamide, only the hindquarters vasodilator response to BK, and all the cardiovascular actions of LCK were inhibited. 4. On the first experimental day, the hindquarters vasodilator effect of alpha-trinositol was substantially inhibited by glibenclamide, the renal vasodilatation less so, and the mesenteric vasodilatation not at all. However, over the subsequent two days, the mesenteric vasodilator effect of alpha-trinositol became increasingly sensitive to glibenclamide. 5. In the presence of alpha-trinositol and glibenclamide, on the first experimental day, the inhibition of the renal vasodilator effect of ACh was no greater than with alpha-trinositol alone in the first experiment. Moreover, on the third experimental day, both before and after glibenclamide, the inhibition by alpha-trinositol of the renal vasodilator response to ACh was less than on the first experimental day. Similarly, the alpha-trinositol-induced inhibition of the mesenteric vasodilator effect of SNP, and of the hindquarters vasodilator action of BK, waned over the 3 experimental days. The inhibition of the cardiovascular effects of LCK were similar on all 3 experimental days, but no greater in the presence of alpha-trinositol and glibenclamide than with glibenclamide alone. 6. These results indicate that KATP channels are involved in the maintenance of resting vasodilator tone in renal, mesenteric and hindquarters vascular beds. However, although additional activation of KATP channels is responsible for all the haemodynamic effects of LCK, it contributes only to the hindquarters vasodilator action of BK and is not involved in any of the responses to ACh or SNP. The hindquarters, renal and mesenteric vasodilator effects of alpha-trinositol may involve (in the same rank order) activation of KATP channels, probably through an indirect mechanism. However, it is unlikely that direct or indirect interaction of alpha-trinositol with KATP channels explains the ability of the drug to inhibit the renal vasodilator action of ACh, or the mesenteric vasodilator effects of SNP or LCK.

Antinociceptive effect of alpha-trinositol, a novel D-myo-inositol phosphate derivative, in the formalin test in rats

The antinociceptive effect of alpha-trinositol was examined in rats using the formalin test following systemic, spinal and local subcutaneous administration. Injection of formalin into the paw evoked two phases (phase 1: 0-9 min; phase 2: 10-60 min) of flinching behavior of the injected paw. Intrathecal administration of alpha-trinositol resulted in a dose-dependent suppression of the first (ED50: 8 microg) and second (ED50: 9 microg) phase of formalin-evoked behavioral response. Similarly, intraperitoneal delivery showed a dose-dependent reduction of the first (ED50: 83 mg/kg) and second (ED50: 56 mg/kg) phase of the formalin test. Subcutaneous injection of 100 microg, but not 10 mu g, alpha-trinositol into the rat paw together with the formalin solution, had no effect on the first phase, but reduced by 20% the second phase of behavior. These data show that alpha-trinositol produces a suppression of acute and prolonged nociceptive behaviors with a central mechanism of action, although some peripheral component may contribute to the reduction of the late phase following systemic administration.

Peptides as neurotransmitters in vascular autonomic neurons

1. Neuropeptides are present in the majority of autonomic neurons projecting to blood vessels, where they are co-localized with non-peptide transmitters and sometimes with other peptides. 2. Neuropeptides are released from vasoconstrictor and vasodilator nerve terminals after high frequency stimulation ( > 2-5Hz) with trains of impulses. 3. Neuropeptides can have potent post-synaptic effects on vascular tone, but often these effects are restricted to selected regions of the vasculature. 4. Post-synaptic effects of neuropeptides tend to be more slowly-developing and more long-lasting than those of non-peptide transmitters. 5. Autonomic vasoconstrictor and vasodilator responses often have multiple phases, with the faster phases being mediated by non-peptide transmitters and the slower phases medicated predominantly by one or more neuropeptides. 6. Some neuropeptides do not seem to have post-synaptic effects in a particular vascular bed, but can have presynaptic actions on neurotransmitter release. 7. Neuropeptides form an important component of the repertoire of neurotransmitters used by vascular autonomic neurons to regulate regional blood flow in response to a range of physiological stimuli.

Cardiovascular and renal effects of alpha-trinositol in ischemic heart failure rats

Previous studies have demonstrated that alpha-trinositol (D-myo-inositol-1.2.6-trisphosphate; PP56) may act as a functional neuropeptide Y (NPY) inhibitor. Because NPY is known to be a potent vasoconstrictor, the effects of alpha-trinositol on renal function, vascular responses and the potentiating effects of NPY were investigated in rats with congestive heart failure (CHF) induced by ligation of the left coronary artery. Incremental doses of alpha-trinositol were given to conscious rats (bolus 2, 4 or 10 mg/kg i.v. followed by a 15-minute infusion 20, 40 and 100 mg/kg/h, respectively). Urinary volume, sodium and potassium excretions were significantly increased in both CHF and sham-operated control animals after alpha-trinositol administration compared with saline. Diuresis and natriuresis were observed also during co-administration of alpha-trinositol with NPY but not with norepinephrine (NE). In the pithed CHF rats, threshold doses of NPY potentiated the pressor effects of endothelin-1 (ET-1) and angiotensin II (AII), but not preganglionic nerve stimulation or phenylephrine administration. Alpha-trinositol antagonized both the pressor response to NPY and the potentiation by NPY of pressor responses to effects of ET-1 and AII. Our data show that alpha-trinositol exhibis diuretic and natriuretic effects as well as vascular antagonistic effects on NPY in normal and CHF rats. These effects of alpha-trinositol may be due to an interaction with NPY mediated antidiuresis and antinatriuresis.

Central nervous system pharmacology of neuropeptide Y

Neuropeptide Y (NPY) is a 36-amino acid peptide belonging to the pancreatic polypeptide family that has marked and diverse biological activity across species. NPY originally was isolated from mammalian brain tissue somewhat more than 10 years ago and, since that time, has been the subject of numerous scientific publications. NPY and its proposed three receptors (Y1, Y2 and Y3) are relatively abundant in and uniquely distributed throughout the brain and spinal cord. This review will highlight the results from a number of research-oriented studies that have examined how NPY is involved in CNS function and behavior, and how these studies may relate to the possible development of medicines, either NPY-like agonists or antagonists, directed towards the treatment of disorders such as anxiety, pain, hypertension, schizophrenia, memory dysfunction, abnormal eating behavior and depression.

Peripheral hyperalgesia in experimental neuropathy: exacerbation by neuropeptide Y

Injury of peripheral nerves often results in hyperalgesia (an increased sensitivity to painful stimuli). This hyperalgesia is mediated in part by sympathetic neurotransmitters. We examined the effect of neuropeptide Y (NPY), specific Y1 and Y2 agonists, and an NPY antagonist on peripheral hyperalgesia in rats whose sciatic nerves had been partially transected. NPY and the Y2 agonist, N-acetyl [Leu28,Leu31] NPY 24-36 exacerbated both mechanical and thermal hyperalgesia, while the Y1 agonist, [Leu31, Pro34]NPY relieved thermal hyperalgesia. Mechanical and thermal hyperalgesia were both relieved by alpha-trinositol (PP56), a non-competitive antagonist of the actions of neuropeptide Y. Hyperalgesia was also relieved by surgical sympathectomy, which eliminated the effects of NPY and its agonists. These results suggest that neuropeptide Y contributes to peripheral hyperalgesia by actions at Y2 receptors, which may be located on postganglionic sympathetic terminals.

Intrathecal alpha-trinositol facilitates the flexor reflex but does not block the depressive effect of neuropeptide Y

We have studied the effects of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate, PP56), a putative antagonist of neuropeptide Y receptors, on the nociceptive flexor reflex in decerebrate, spinalized rats after intrathecal and intravenous administration. Intrathecal alpha-trinositol caused strong and prolonged facilitation of the flexor reflex, which was usually associated with an increase in spontaneous motoneuron activity. The reflex depressive effect of intrathecal neuropeptide Y was neither blocked nor reversed by alpha-trinositol. Intravenous alpha-trinositol at low doses had no effect on the flexor reflex and at high dose, reflex facilitation was sometimes observed. It is concluded that alpha-trinositol acts as a spinal excitant and is not an antagonist of the neuropeptide Y receptor in the rat spinal cord.

Hypotensive effects of [D-Tyr27,36, D-Thr32]Neuropeptide Y (27-36)

An analogue of the 10 C-terminal amino acids of neuropeptide Y (NPY) containing three D-isomeric substitutions (27-36-D) has been synthesized and its cardiovascular activity studied in Sprague-Dawley (SD) and spontaneously hypertensive (SHR) rats. Intravenous administration of 1000 nmol/kg 27-36-D decreases MAP in SHR (-59.9 +/- 5.0 mmHg) and SD rats (-44.4 +/- 4.7 mmHg). The hypotension produced by 1000 nmol/kg 27-36-D diminished by 71.2% following pretreatment with the histamine receptor antagonist diphenhydramine, although histamine depletion with compound 48/80 does not significantly alter this hypotension. These data suggest that NPY (27-36)-D produces a profound and sustained hypotension in two strains of rat which is partially attributable to activity at histamine receptors.

Histamine-independent modulation of the neuropeptide Y-induced pressor response by alpha-trinositol in the pithed rat

The modulatory effects of alpha-trinositol (D-myo-inositol-1.2.6- trisphosphate; PP 56) on the systemic arterial blood pressor responses induced by neuropeptide Y, preganglionic nerve stimulation, phenylephrine and vasopressin were studied in pithed rats. Intravenous administration (within 2 min.) of alpha-trinositol reduced the neuropeptide Y-induced increase in mean arterial pressure within a defined dose range without altering the heart rate. The influence of alpha-trinositol on the neuropeptide Y-induced pressor response in the presence of non-selective as well as H1- and H2-selective histamine antagonists (diphenhydramine, mepyramine and cimetidine respectively) were investigated. The maximal increase in mean arterial pressure induced by neuropeptide Y as well as the duration of the pressor response was enhanced after nonselective (diphenhydramine) or H1-selective (mepyramine) histamine blockade. The enhancement of the neuropeptide Y-induced pressor response by the H1 specific antagonist mepyramine was significantly more pronounced compared to the H2-selective agent. The exaggerated increase in mean arterial pressure in response to neuropeptide Y after histamine blockade was inhibited by alpha-trinositol to a similar extent as without such pretreatment. We conclude that neuropeptide Y interacts with histamine in the pithed rat and that this action may partially offset the pressor actions of the peptide. The neuropeptide Y-induced pressor responses may be inhibited by alpha-trinositol within a defined dose range indicating that this non-peptide agent may act as a functional inhibitor to neuropeptide Y in vascular tissue.

Alpha-trinositol blocks the inhibitory effects of NPY on dilatation to forskolin but not the adenylyl cyclase activity induced by NPY or forskolin in guinea-pig cerebral vessels

There is much data showing correlation between forskolin-induced relaxation and production of cyclic AMP. But are these processes coupled or two phenomena occurring in parallel? This question was studied in guinea-pig cerebral vessels by using NPY as a strong inhibitor and alpha-trinositol as its antagonist. The basal cyclic AMP content of cerebral vessel segments in the control group was 670 +/- 53 fmol/mg wet weight (w.w.). Forskolin (10(-7), 3 x 10(-7) and 10(-6) M) increased the formation of cyclic AMP to 738 +/- 86 (ns), 699 +/- 81 (ns) and 1158 +/- 132 fmol/mg w.w. (p < 0.05), respectively. alpha-trinositol (10(-8)-10(-6) M) neither reduced the formation of cyclic AMP compared to basal cyclic AMP levels nor affected the forskolin-stimulated increase of cyclic AMP (p > 0.05). On the other hand, NPY (10(-7) M) not only decreased basal formation of cyclic AMP (p < 0.05) but also attenuated the forskolin-stimulated increase of cyclic AMP (p < 0.005). The inhibitory effects of NPY on both basal levels of cyclic AMP and forskolin-induced increase of cyclic AMP were not reversed by the application of alpha-trinositol (10(-8)-10(-6) M). In studies on vasomotor responses, forskolin (10(-9)-10(-5) M) induced a concentration-dependent relaxation of precontracted guinea-pig basilar arteries. NPY (10(-7) M) shifted the forskolin-induced relaxation of the basilar arteries towards higher forskolin concentrations. This inhibitory effect of NPY was reversed by alpha-trinositol (10(-6) M). We conclude that 1) NPY decreases basal and forskolin-stimulated cyclic AMP levels; 2) alpha-trinositol neither reverses the inhibitory effect of NPY on nor modulates basal or forskolin-stimulated cyclic AMP levels; 3) However, the antagonistic effect of NPY on forskolin-induced relaxation is significantly reversed by administration of alpha-trinositol. This demonstrates a dissociation of the dilator effects of forskolin and its generation of cyclic AMP.

Effects of chronic infusions of alpha-trinositol on regional and cardiac haemodynamics in conscious rats

1. Male, Long Evans rats (350-450 g) were chronically instrumented for the measurement of renal, mesenteric and hindquarters haemodynamics, and were given three consecutive, 24 h infusions of vehicle (sterile saline at 0.3 ml h-1, n = 8) or alpha-trinositol (D-myo-inositol-1,2,6-triphosphate) at 5, 20 and 80 mg kg-1 h-1 (0.3 ml h-1; n = 9). During infusion of alpha-trinositol at 5 or 20 mg kg-1 h-1, cardiovascular changes were little different from those seen during saline infusion. However, during infusion of alpha-trinositol at 80 mg kg-1 h-1 there were increases in hindquarters vascular conductance, renal flow and vascular conductance, that were all significantly different from the changes seen in the saline group. Infusion of alpha-trinositol at the high dose in naive rats (n = 8) had even more marked vasodilator effects. 2. Two groups of rats (n = 8 in each), chronically instrumented for the measurement of cardiac haemodynamics, were given 48 h infusions of saline (0.3 ml h-1) or alpha-trinositol (2 mg kg-1 bolus, 80 mg kg-1 h-1 infusion at 0.3 ml h-1). During the infusion of saline, there were slight reductions in heart rate, cardiac index, peak aortic flow, dF/dtmax and central venous pressure. In the animals receiving alpha-trinositol, with the exception of central venous pressure, all the above variables, together with total peripheral conductance, increased. 3. These results, collectively, indicate that incremental infusions of alpha-trinositol do not reveal its full vasodilator potential, possibly due to concurrent activation of counter-regulatory vasoconstrictor mechanisms. However, infusion of alpha-trinositol at a high dose causes substantial increases in renal,mesenteric and hindquarters flows and vascular conductances, supported by significant increases in indices of cardiac inotropism. Such effects, in the absence of significant hypotension, tachycardia or signs of desensitization, give alpha-trinositol a unique cardiovascular profile.

Inhibition of neuropeptide Y-induced augmentation of noradrenaline-induced vasoconstriction by D-myo-inositol 1,2,6-trisphosphate in the rat mesenteric arterial bed

The effect of the neuropeptide Y antagonist D-myo-inositol-1,2, 6-trisphosphate (alpha-trinositol) was tested against modulatory actions mediated by neuropeptide Y in the isolated rat mesenteric arterial bed. Neuropeptide Y (1 and 10 nM) had no direct postjunctional effects, but augmented vasoconstrictor responses to noradrenaline and to sympathetic nerve stimulation to an extent which was greater with the higher concentration of neuropeptide Y. The augmenting effect of neuropeptide Y at 1 nM on vasoconstriction induced by lower doses of noradrenaline was antagonized by alpha-trinositol (1 microM), producing a shift to the right of the dose-response curve. A lower concentration of alpha-trinositol (0.1 microM) had no inhibitory effect on responses to noradrenaline. Augmentation by the higher concentration of neuropeptide Y (10 nM) of noradrenaline-induced vasoconstriction was not affected by alpha-trinositol at concentrations of up to 10 microM. alpha-Trinositol did not significantly antagonize neuropeptide Y-induced augmentation of vasoconstrictor responses to sympathetic nerve stimulation. alpha-Trinositol alone did not affect vasoconstrictor responses to noradrenaline, potassium, or to sympathetic nerve stimulation. In the raised-tone preparation (tone raised with methoxamine) in the presence of guanethidine (5 microM) to block sympathetic neuro-transmission, perivascular nerve stimulation caused vasodilatation due to activation of sensory-motor nerves. Neuropeptide Y inhibited sensory-motor nerve induced vasodilatation in a concentration-dependent manner but this was not affected by alpha-trinositol (1 microM). These results suggest that alpha-trinositol can be a useful functional antagonist of neuropeptide Y-induced augmentation of vasoconstrictor responses to noradrenaline in the rat mesenteric arterial bed.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of specific binding sites for alpha-trinositol (D-myo-inositol 1,2,6-trisphosphate) in rat tissues

Alfa-trinositol (or D-myo-inositol 1,2,6-trisphosphate) was recently found to, e.g., inhibit agonist-induced vasoconstriction and display antiinflammatory properties. However, its mechanism of action is unknown, although effects on Ca2+ fluxes, perhaps by interfering with endogenous inositol phosphate(s), have been suggested. Here we describe the existence of specific [3H]alpha-trinositol binding sites and compare these with binding sites for naturally occurring inositol phosphates. For this purpose we developed a tritiated analog of alpha-trinositol and used it in a centrifugation binding assay on extensively washed membranes from rat tissues. The degree of specific [3H] alpha-trinositol binding was markedly increased as a result of the many wash steps, indicating the existence of endogenous binding inhibitor(s). A single population of [3H] alpha-trinositol binding sites, displaying a KD of 159 nM and a Bmax of 71 pmol/mg protein, was present in cardiac membranes assayed at pH 7.4. Similar binding site densities were detected also in liver > lung > brain. The relative density of [3H] alpha-trinositol sites in cardiac membranes was 8-fold higher than [3H]Ins(1,4,5)P3 but 2-fold and 4-fold lower than [3H]Ins(1,3,4,5)P4 and [3H]InsP6 binding sites, respectively. Competition binding studies indicated the ability of Ins(1,3,4,5)P4 and InsP6, but not Ins(1,4,5)P3, to potently displace [3H] alpha-trinositol binding. Conversely, unlabelled alpha-trinositol showed relatively low potency vs. [3H]InsP6, but the novel inositol phosphate was virtually equipotent with Ins(1,3,4,5)P4 in inhibiting [3H]Ins(1,3,4,5)P4 binding. Finally, analyses of binding at different pH and ionic conditions revealed differences between alpha-trinositol and the three other previously studied inositol phosphates, although distinct similarities between alpha-trinositol and Ins(1,3,4,5)P4 were again observed.

Neuropeptide Y in sympathetic co-transmission: recent advances in the search for neuropeptide Y antagonists

Since the discovery of neuropeptide Y which is co-stored and co-operate with noradrenaline (NA) in sympathetic nerve fibers, several scientific groups have searched for structures with neuropeptide Y antagonistic properties. Research has mainly focused on various peptide fragments which originate from or are related to the neuropeptide Y sequence. Some non-peptide antagonists have been proposed but they are mostly of low potency and non-selective. Our recent observations that alpha-trinositol (D-myo-inositol 1.2.6-trisphosphate) is an inhibitor of neuropeptide Y effects will hopefully lead to the development of useful non-peptide neuropeptide Y inhibitors. As a novel approach the highly selective approach of down-regulating neuropeptide Y receptors with antisense oligodeoxynucleotides is also discussed. Neuropeptide Y antagonistic agents would help us to understand the physiological role of neuropeptide Y and may serve as useful medication in circulation disorders.

Sympathetic thyroidal vasoconstriction is not blocked by a neuropeptide Y antagonist or antiserum

Sympathetic nerve fibers to thyroid blood vessels contain both norepinephrine (NE) and neuropeptide Y (NPY). To assess the involvement of endogenous NPY in the sympathetic neural control of thyroid blood flow, appropriate doses of a selective NPY antagonist, alpha-trinositol, and an NPY antiserum (NPY-AS) were used during cervical sympathetic trunk stimulation in anesthetized rats. During all experiments, thyroid blood flow was continuously monitored by laser Doppler blood flowmetry. Neither alpha-trinositol nor NPY-AS blocked the thyroidal vasoconstriction evoked by either the first or second stimulation of the cervical sympathetic trunks. Our results suggest that NPY is not involved either directly or indirectly during acute sympathetic vasoconstriction in the rat thyroid gland.