Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates adenylyl cyclase and phospholipase C activity in rat cerebellar neuroblasts

The presence of receptors for the novel neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has been recently demonstrated in the external granule cell layer of the cerebellum, a germinative matrix that generates the majority of cerebellar interneurons. In the present study, we have taken advantage of the possibility of obtaining a culture preparation that is greatly enriched in immature cerebellar granule cells to investigate the effect of PACAP on the adenylyl cyclase and phospholipase C transduction pathways. The two molecular forms of PACAP, i.e., 27-(PACAP27) and 38-(PACAP38) amino-acid forms of PACAP, induced a dose-dependent stimulation of cyclic AMP production in granule cells. The potencies of PACAP27 and PACAP38 were similar (ED50 = 0.12 +/- 0.01 and 0.23 +/- 0.07 nM, respectively), whereas vasoactive intestinal polypeptide (VIP) was approximately 100 times less potent. PACAP27 and PACAP38 also induced a dose-dependent stimulation of polyphosphoinositide breakdown (ED50 = 19.1 +/- 6.3 and 13.4 +/- 6.0 nM, respectively), whereas VIP had no effect on polyphosphoinositide metabolism. The effect of PACAP38 on inositol phosphate formation was significantly reduced by U-73122 and by pertussis toxin, indicating that activation of PACAP receptors causes stimulation of a phospholipase C through a pertussis toxin-sensitive G protein. In contrast, forskolin and dibutyryl cyclic AMP did not affect PACAP-induced stimulation of inositol phosphates. Taken together, the present results demonstrate that PACAP stimulates independently the adenylyl cyclase and the phospholipase C transduction pathways in immature cerebellar granule cells. These data favor the concept that PACAP may play important roles in the control of proliferation and/or differentiation of cerebellar neuroblasts.

Effects of the ETA/ETB receptor antagonist, bosentan on endothelin-1-induced myocardial ischaemia and oedema in the rat

1. The purpose of this study were to assess the role of ETB receptors in mediating endothelin-1 (ET-1)-induced myocardial ischaemia and oedema in rats and to study the inhibitory action of the novel nonpeptide ETA/ETB receptor antagonist, bosentan on these actions of ET-1. 2. Intravenous bolus injection of ET-1 (1 nmol kg-1) into anaesthetized rats produced marked ST segment elevation of the electrocardiogram without causing arrhythmias. ST segment elevation developed within 30-50 s and persisted for at least 30 min following injection of the peptide. 3. Pretreatment of the animals with bosentan (10 mg kg-1, i.v.) inhibited on average by 96% the ST segment elevation elicited by ET-1 (1 nmol kg-1) compared to the 82% inhibition observed with the ETA receptor-selective antagonist, FR 139317 (2.5 mg kg-1, i.v.). 4. Bolus injection of ET-1 (1 nmol kg-1, i.v.) to conscious chronically catheterized rats evoked a transient depressor response followed by a prolonged pressor effect. Corresponding to changes in blood pressure, a transient tachycardia and a sustained bradycardia were observed. ET-1 (1 nmol kg-1) enhanced albumin extravasation by 119 and 93% in the left ventricle and right atrium, respectively, as measured by the local extravascular accumulation of Evans blue dye. 5. Pretreatment of the animals with bosentan (10 mg kg-1) inhibited by 71 and 90% the depressor and pressor actions of ET-1 (1 nmol kg-1) and the accompanying tachycardia and bradycardia, respectively. FR 139317 (2.5 mg kg-1) attenuated the pressor response to ET-1 and accompanying bradycardia by 75%, without affecting the depressor action and accompanying tachycardia. ET-1-induced albumin extravasation was completely inhibited by bosentan (10 mg kg-1) both in the left ventricle and right atrium, compared to the 86% inhibition observed with FR 139317 (2.5 mg kg-1).6. Like ET-1, the ETB receptor-selective agonist, IRL 1620 (0.3 and 1 nmol kg-1, i.v.) also produced dose-dependent ST segment elevation in anaesthetized rats and enhanced albumin extravasation (up to141% of control) in the left ventricle and right atrium, respectively, in conscious rats. These effects ofIRL 1620 were completely prevented by bosentan (10 mg kg-1).7. These results indicate that ETB receptors, albeit to a lesser extent than ETA receptors, are also involved in mediating ET-1-induced myocardial ischaemia and oedema in the rat, and suggest the therapeutic potential for bosentan in the treatment of ischaemic myocardial diseases.

Effect of centrally administered neuropeptide Y on hypothalamic and hypophyseal proopiomelanocortin-derived peptides in the rat

In a previous study, we have shown that neuropeptide Y inhibits the release of alpha-melanocyte-stimulating hormone from the rat hypothalamus in vitro. The aim of the present study was to investigate the possible effect of neuropeptide Y on the regulation of proopiomelanocortin-derived peptides in vivo. Rats received acute or chronic administration of neuropeptide Y in the lateral ventricle and the amount of alpha-melanocyte-stimulating hormone was measured in the hypothalamus and in the neurointermediate lobe of the pituitary. In the same experiments, the amounts of corticotropin-releasing factor and corticotropin were quantified in the hypothalamus and anterior pituitary, respectively. Acute treatment with synthetic neuropeptide Y (0.1 to 10 micrograms/rat) did not modify the amount of alpha-melanocyte-stimulating hormone in the hypothalamus. In contrast, chronic infusion of neuropeptide Y (1.25 micrograms/h) over a seven day period significantly decreased the hypothalamic content of alpha-melanocyte-stimulating hormone, suggesting that neuropeptide Y regulates the synthesis and/or the processing of proopiomelanocortin. Concurrently, we found that both acute and chronic infusion of neuropeptide Y induced a significant reduction in corticotropin-releasing factor in the hypothalamus as well as a significant decrease in alpha-melanocyte-stimulating hormone and corticotropin in the neurointermediate and anterior lobes, respectively. Quantitative in situ hybridization histochemistry showed that chronic administration of neuropeptide Y also caused a reduction of proopiomelanocortin messenger RNA levels both in the intermediate and anterior lobes of the pituitary. Administration of neuropeptide Y (10(-6) M) on perifused rat hypothalamic slices caused a significant increase in corticotropin-releasing factor release.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunization trial of cats with a replication-defective adenovirus type 5 expressing the ENV gene of feline immunodeficiency virus

Our aim was to develop a recombinant replication-defective adenovirus suitable for the vaccination of cats against feline immunodeficiency virus. We first demonstrated that this vector was able to transfer a marker gene (E. coli beta-galactosidase) in feline cells in vitro. We then constructed an adenovirus type 5 expressing the Feline Immunodeficiency Virus (FIV) envelope (ENV) gene of the Wo isolate in the absence of the rev gene (Ad-ENV-Wo). Ad-ENV-Wo was then tested in four cats in a 3 injections scheme (at day 0, day 30 and day 210). Four other control cats received Ad-gp50, a similar recombinant adenovirus expressing gp50 (Ad-gp50) of pseudorabies virus (PRV). Viruses were formulated in two different kind of oil adjuvants (water/oil and water/oil/water), a protocol previously shown to enhance the immune response against the virus-induced protein. The control cats developed neutralizing antibodies against PRV, demonstrating the potency of recombinant human adenovirus 5 (Ad5) as a vector in cats. Antibody responses appeared after the first injection and were higher with the water/oil/water formulation than with the water/oil controls. However, none of the four cats vaccinated with Ad-ENV-Wo developed antibodies against two peptides of the envelope protein. Animals were challenged with 20 infectious doses 50% of the strain Wo. All of them developed antibodies against FIV within 4 to 5 weeks, and FIV virus could be isolated from all.

Structure of human calcitonin gene-related peptide (hCGRP) and of its antagonist hCGRP 8-37 as determined by NMR and molecular modeling

The solution structures of human calcitonin gene-related peptide (hCGRP, 37 residues) and of its antagonistic fragment hCGRP 8-37 have been determined by two-dimensional 1H nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. Analysis of the double quantum filtered correlation spectroscopy, total correlation spectroscopy and nuclear Overhauser enhancement spectroscopy spectra led to a complete assignment and to the identification of more than 350 intra- and interresidue connectivities for each peptide. Molecular models were calculated by molecular dynamics and energy minimization using distance constraints. The structure of hCGRP is characterized by a rigid N-terminal disulfide-bonded loop followed by helix segments (Val8-Leu16), a gamma-turn (Ser19-Gly21) and several local hydrogen-bonded patterns. The structure of hCGRP 8-37 is less defined than the structure of hCGRP and no helix structure is present. Molecular models of both peptides are consistent with the NH temperature coefficients and secondary chemical shifts of the alpha-protons. Hydrogen bonding with the disulfide-bonded ring appears to be critical for helix formation, both structural elements being essential for agonistic activity.

Frog vasoactive intestinal polypeptide and galanin: primary structures and effects on pituitary adenylate cyclase

Vasoactive intestinal polypeptide (VIP) and galanin were isolated in pure form from the stomach of the European green frog, Rana ridibunda. Frog VIP is identical to the previously characterized VIP from chicken and alligator. The primary structure of frog galanin contains only two amino acid substitutions (asparagine for histidine at position 23 and histidine for tyrosine at position 26) compared with porcine galanin. The data indicate that evolutionary pressure to conserve the amino acid sequence of both peptides during the evolution of amphibia to mammals has been strong. Synthetic frog VIP produced a dose-dependent increase in cAMP concentration in frog anterior pituitary fragments. The potency of the peptide (ED50 = 1.2 x 10(-6) M; mean +/- SE; n = 8) was comparable to that of porcine VIP (EC50 = 1.3 x 10(-6) M), but was approximately 10-fold less than that of frog pituitary adenylate cyclase-activating polypeptide [PACAP-(1-38); ED50 = 1.1 x 10(-7) M] in the same system. The increases in cAMP concentrations produced by maximal doses of PACAP (10(-5) M) and VIP (10(-5) M) were not additive. The data suggest that the effects of both peptides are mediated through a common PACAP-preferring receptor that is pharmacologically different from the mammalian PACAP type I receptor. Synthetic frog galanin also produced a dose-dependent increase in the concentration of cAMP in isolated frog anterior pituitary fragments (ED50 = 9.3 x 10(-8) M) consistent with a possible role for the peptide as a hypophysiotropic factor in amphibians.

Neuropeptide tyrosine in the brain of the African lungfish, Protopterus annectens: immunohistochemical localization and biochemical characterization

Lungfishes, which share similarities with both fishes and amphibians, represent an interesting group in which to investigate the evolutionary transition from fishes to tetrapods. In the present study, we have investigated the localization and biochemical characteristics of neuropeptide Y (NPY)-immunoreactive material in the central nervous system of the African lungfish, Protopterus annectens. NPY-immunoreactive cell bodies were found in various regions of the brain, most notably in the telencephalon (septal area, ventral striatum, and nucleus accumbens), in the diencephalon (preoptic nucleus, periventricular region of the hypothalamus, and ventral thalamus), and in the tegmentum of the mesencephalon. A strong immunoreaction was also detected in cell bodies of the nervus terminalis. Immunoreactive nerve fibers were particularly abundant in the ventral striatum, the nucleus accumbens, the diagonal band of Broca, the hypothalamus, and the mesencephalic tegmentum. Positive fibers were also seen in the median eminence and in the neural lobe of the pituitary. The NPY-immunoreactive material localized in the brain and pituitary was characterized by combining high-performance liquid chromatography (HPLC) analysis and radioimmunological quantitation. The displacement curves obtained with synthetic porcine and frog NPY and serial dilutions of brain and pituitary extracts were parallel. Reversed-phase HPLC analysis of telencephalon, diencephalon, and pituitary extracts resolved a major NPY-immunoreactive peak that coeluted with frog NPY. The similarity between the distribution of NPY-containing neurons and the biochemical characteristics of the immunoreactive peptide in the brain of lungfish and frog strongly favors a close phylogenetic relationship between dipnoans and amphibians.

Involvement of the Y2 receptor subtype in the regulation of prolactin gene expression by neuropeptide Y in the male rat

In order to determine the influence of neuropeptide Y (NPY) on the biosynthesis of prolactin (PRL), we have studied the effects of NPY and some NPY analogs on PRL gene expression in the male rat anterior pituitary gland. The following peptides (4 micrograms/100 g body wt): NPY, peptide YY (PYY), NPY13-36 (a Y2 receptor agonist) and [Leu31,Pro34]NPY (a Y1 receptor agonist) were injected into the left lateral ventricle of adult male rats. Control animals received only the vehicle (0.9% NaCl). All the animals were perfused with 4% paraformaldehyde 4 h after injection and processed for in situ hybridization. The intracerebroventricular injection of NPY, PYY, and NPY13-36 induced a significant increase in the hybridization signal (22-40% over control). On the other hand, the Y1 receptor agonist [Leu31,Pro34]NPY did not influence PRL mRNA levels. These data then suggest that activation of the Y2 NPY receptor subtype at the central level can positively regulate PRL gene expression.

Acute pro-inflammatory actions of endothelin-1 in the guinea-pig lung: involvement of ETA and ETB receptors

1. Although recent observations suggest that endothelin-1 (ET-1) may play a role in the pathogenesis of asthma, to date little is known about the effects of ET-1 on parameters other than bronchoconstriction. The objectives of the present experiments were to study whether intravenously administered ET-1 could exert pro-inflammatory actions in the guinea-pig lung and to assess the involvement of endothelin ETA and ETB receptors in these events by using the ETA receptor-selective antagonist, FR 139317, the novel ETA/ETB receptor antagonist, bosentan and the ETB receptor-selective agonist, IRL 1620. 2. Bolus i.v. injection of ET-1 (0.1-1 nmol kg-1) to anaesthetized guinea-pigs evoked dose-dependent increases in mean arterial blood pressure which lasted for 6-12 min. This was accompanied by a dose-dependent haemoconcentration (8-15% plasma volume losses) and increases (up to 546%) in albumin extravasation in the trachea, upper and lower bronchi, but not in the pulmonary parenchyma. Qualitatively similar changes were observed following i.v. injection of the ETB receptor agonist, IRL 1620 (0.3 and 1 nmol kg-1), although IRL 1620 appeared to be about 3 times less potent than ET-1. The ETA receptor-selective antagonist, FR 139317 (2.5 mg kg-1) inhibited the ET-1 (1 nmol kg-1)-induced pressor response, haemoconcentration and albumin extravasation by 75, 77 and 60-70%, respectively, whereas it did not attenuate IRL 1620 (1 nmol kg-1)-induced changes. The ETA/ETB receptor antagonist, bosentan (10 mg kg-1) almost completely inhibited the pressor, haemoconcentration and permeability effects of both ET-1 and IRL 1620. 3. ET-1, but not IRL 1620 (0.1-1 nmol kg-1), produced a dose-dependent neutropenia with relative lymphocytosis and monocytosis, but did not induce influx of neutrophil granulocytes into pulmonary tissues or the bronchoalveolar space. ET-1 (1 nmol kg-1)-induced neutropenia was prevented by pretreatment of the animals with FR 139317 (2.5 mg kg-1), bosentan (10 mg kg-1) or adrenaline (90 nmol kg-1), indicating that ET-1 caused intravascular sequestration of neutrophil granulocytes. 4. ET-1 or IRL 1620 (10(-10)-10(-6) M) alone did not activate alveolar macrophages in vitro, whereas at a concentration of 10(-8) M, ET-1, but not IRL 1620, markedly potentiated superoxide production in response to f-Met-Leu-Phe (10(-9)-10(-7) M) and platelet-activating factor (PAF, 10(-9)-10(-7) M), but not to phorbol 12-myristate 13-acetate (10(-9) M). ET-1 did not affect f-Met-Leu-Phe- or PAF-induced increases in intracellular free calcium concentration. This potentiating effect of ET-1 was abolished by FR 139317(1.5 X 10-7 M).5. We conclude that, in addition to evoking airway contractions, ET-1 exerts pro-inflammatory actions via activation of the ETA and to a lesser extent the ETB receptors, and therefore, might contribute to the airway inflammation present in asthma. These findings also suggest the therapeutic potential of ETA/ETB receptor and perhaps ETA receptor-selective antagonists in this disease.

Contractile activity of endothelin precursors in the isolated gallbladder of the guinea-pig: presence of an endothelin-converting enzyme

A single addition of 3 x I0-7 M ET-1, ET-2 or ET-3 produced contractions that reached a steady state in 28.2 +/- 4.2, 21.1 +/- 1.3 and 24.0 +/- 3.8 min, respectively and took 2.7 +/- 0.4, 2.1 + 0.1 and 1.6 +/- 0.1 min to reach half of this steady-state response.4. Contractions induced by 3 x I0-7 M big ET-11-38 or big ET-11- 39 reached a plateau in 38.5 +/- 3.6 and 35.6 +/- 3.3 min, respectively, and half of these responses were attained in 12.0 +/- 2.5 and 7.1 +/- 1.1 min.Thus, these contractions developed more slowly than those induced by ET-1. Contractions induced by 3 x 10-7 M big ET-21-38 were also much slower to develop than those to ET-2, for these took 49 +/- 2 min to reach plateau and 19.4 +/- 2.1 min to attain half that response. Contractions induced by 3 x 10-7 M big ET-31-41 amide took 50.2 +/- 3.7 min to reach a plateau and 27.3 +/- 3.0 min to reach half of this response.5. Phosphoramidon (0.1, 1 and 3 x 10-4 M) inhibited contractions induced by big ET-11.39. For instance,the contractions induced by 3 x 10-7 M big ET-11-39 were inhibited by 10-4 M or 3 x 10-4 M of phosphoramidon by 62.8 +/- 6.7% or 74.5 +/- 4.6%, respectively. Similarly, contractions induced by ET-21-38 were inhibited by 91.3 +/- 5.4% and the small response induced by big ET-3l-4l amide was abolished by 3 x 10-4M phosphoramidon. Conversely, the neutral endopeptidase (EC 24.11) inhibitor DL-thiorphan(3 x 10-4 M) had no effect. Captopril (10-5 M), pepstatin A (10-5 M), phenylmethylsulphonylfluoride(PMSF, 10-3 M), aprotinin (10-5 M), E-64 (10-5 M), cystatin (10-6 M), leupeptin (10-4 M),chymostatin (10-4 M), or bestatin (10-5 M) did not inhibit but rather increased to a similar, but small degree the contractions induced by 3 to 30 x 10-9 M big ET-11-39. Only captopril (10-5 M) or leupeptin(10-4 M) increased the contraction induced by 3 x 10-7 M big ET-11-39. Phosphoramidon (10-4 M),pepstatin (10-5 M) or PMSF (10-3 M) did not affect contractions induced by ET-1.6. Removal of the epithelium increased by 70% the size of the contraction induced by 5 microM histamine(1.08 +/- 0.05 g; n = 160 to 1.84 +/- 0.14 g; n = 12) but did not affect, in absolute terms, the contraction induced by ET-1 (as a % of the response to histamine, these responses were, of course, apparently depressed). Epithelium removal did, however, increase the size of the contractions induced by 3 to 30 x 10-9 M big ET-1 -39 which was very similar to the effect of the protease inhibitors.7. In competition binding studies on membranes prepared from the guinea-pig gallbladder, 10-11 MET-1 inhibited by 76.9 +/- 3.1% the binding of [125]-ET-I while porcine big ET-11-39 caused no inhibition(0.7 +/- 3.0; n = 3). ET-1 (10-6 M) inhibited binding by 95.7 =/- 1.1% (n = 3) while at this much higher concentration, big ET-11-39 inhibited binding by only 16.8 +/- 4.2% (n = 3). This clearly suggests that big ET-11-39 does not bind directly to ET receptors.8. Thus, a phosphoramidon-sensitive endothelin-converting enzyme (ECE), different from neutral endopeptidase (NEP; EC 24.11) and not located on the epithelium, converts big ET-1 into ET-1 in the gallbladder of the guinea-pig. This ECE appears to act preferentially on big ET-1 or big ET-2 over bigET-3.

Regulation of proopiomelanocortin gene expression by neuropeptide Y in the rat arcuate nucleus

In the arcuate nucleus which is richly innervated by both proopiomelanocortin (POMC) and neuropeptide Y (NPY) neurons, it has been shown that NPY fibers are in synaptic contact with POMC cell bodies. In order to determine whether NPY could influence POMC neuronal activity, we have studied the effects of NPY and some NPY analogs on POMC gene expression using quantitative in situ hybridization. The following peptides NPY, [Leu31,Pro34]-NPY (a Y1 receptor agonist), and NPY13-36 (a Y2 receptor agonist) were injected into the left lateral cerebral ventricle of adult male rats 4 h before being perfused for histological procedures. The intracerebroventricular injection of NPY and NPY13-36 induced a significant decrease in the number of grains overlying the labelled neurons. On the other hand, the Y1 receptor agonist [Leu31,Pro34]-NPY did not modify POMC mRNA levels. These data then strongly suggest that NPY negatively regulates the genetic expression of POMC neurons via the Y2 NPY receptor subtype.

Influence of the phospholipid content in docosahexaenoic acid on electrophysiology and contraction of rat heart muscle cells

The cardiovascular beneficial effects of fish oils are currently attributed to docosahexaenoic (C22:6 n-3) and eicosapentaenoic (C20:5 n-3) acids, although most investigations have focused on eicosapentaenoic acid. This study was devoted to the specific effect of docosahexaenoic acid, as compared to eicosapentaenoic acid, on the basal electrophysiological and mechanical characteristics of cultured rat myocardial cells. The myocyte cultures were prepared from newborn rat heart ventricles. The cells were grown for 24 hours in a conventional seric medium, and then incubated in a medium enriched with either docosahexaenoic acid or eicosapentaenoic acid for 96 hours. This treatment resulted in docosahexaenoic acid-rich cells (16% of the phospholipid fatty acids) and docosahexaenoic acid-poor cells (1.5%), both displaying the same phospholipid n-6/n-3 polyunsaturated fatty acid ratio. The transmembrane potentials were recorded with glass microelectrodes. Contractions were monitored photometrically. The action potential amplitude was slightly smaller in docosahexaenoic acid-rich cells (-4 mv), due to a lower plateau phase. There was no difference in action potential duration and spontaneous rate. The contraction measurements were not significantly different between the two groups of cells. We conclude that increasing the docosahexaenoic acid content in cardiomyocyte membrane phospholipids may have modulated the calcium ionic channels governing the plateau phase of the action potential, whereas the other physiological activities remained unaffected.

Influence of ambient temperature on the effects of NPY on body temperature and food intake

Because thermoregulation and food consumption are interrelated, and because thermoregulation processes are influenced by ambient temperature, we examined the effects of neuropeptide Y (NPY) on both body temperature and food intake in various thermal environments after intracerebroventricular administration of 20 micrograms. Results reveal that the prominent effects of NPY on body temperature and food intake in relatively thermoneutral environments are drastically altered at more extreme ambient temperatures. NPY produced hypothermia in animals placed at 4, 12, and 21 degrees C, and actually increased body temperature in animals subjected to 30 and 38 degrees C temperature. On the other hand, in comparison with ambient temperatures of 12 and 21 degrees C, ambient temperatures of 4 and 30 degrees C significantly reduced the stimulatory effect of NPY on food consumption. Moreover, at 38 degrees C the effect of NPY on food intake was totally abolished. These data demonstrate that ambient temperature has a critical influence on central actions of NPY.

Rapid degradation of endothelin-1 by an enzyme released by the rat isolated perfused mesentery

1. In vivo the effects of endothelin-1 (ET-1) are limited by its rapid removal from the circulation and possibly by its metabolism by enzymes such as neutral endopeptidase 24.11, deamidase or carboxypeptidase A. Here, using as a model the isolated perfused mesenteric arterial bed of the rat, we have examined the involvements of these enzymatic activities in the vascular responses to ET-1. 2. Samples of Krebs buffer which had been recirculated through the mesenteric arterial bed for 30 min rapidly destroyed the activity of ET-1 as assessed either by bioassay on rings of rat thoracic aorta or by high performance liquid chromatography (h.p.l.c.). For instance, after 15 min incubation with the recirculated-Krebs solution (recirc-K) the contraction induced by 3 x 10(-9) M ET-1 was reduced by more than 90%. Contractions induced by sarafotoxin 6b (3 x 10(-9) M) were similarly suppressed by preincubation with recirc-K whereas those to Arg-vasopressin (3 x 10(-9) M) were unaffected. 3. The degradation of ET-1 by recirc-K was prevented by 1,10-phenanthroline (10(-3) M), abolished by heating the recirc-K solution to 90 degrees C for 15 min, and reduced by EGTA (5 x 10(-3) M) or ET-1(16-21) (10(-5) M). For instance, in the presence of ET-1(16-21) (n = 6) the contraction induced by ET-1 was reduced by only 40% after 15 min incubation with recirc-K buffer. Leupeptin (3 x 10-4 M), dichloroisocoumarin(5 x 10-5 M), phenylmethyl-sulphonyl fluoride (10-3 M), a combination of bacitracin (300 mg ml-1),bestatin (10-5 M), captopril (10-5 M), phosphoramidon (10-4 M) and thiorphan (10-4 M) or Polypep (aproprietary protein digest) did not inhibit the degradation of ET-1 by recirc-K.4. In experiments examining directly the vascular responses of the isolated perfused mesentery of the rat, the addition of cumulative concentrations of ET-1 to the recirculating Krebs solution caused small concentration-dependent increases in perfusion pressure. The inclusion of ET-1(16-2l), ET-1(17-21), or ET-1(18-21) (10-5M) greatly potentiated these responses, but not those to Arg-vasopressin or methoxamine.The effects of 1,10-phenanthroline or EGTA could not be examined in this system because these agents both depressed non-specifically the vasoconstrictor responses of the mesenteric vascular bed.5. Thus, the rat mesentery releases an enzyme that very rapidly destroys ET-1 or the very closely related peptide, sarafotoxin 6b but not Arg-vasopressin. This enzyme is most probably a metallopeptidase because of its sensitivity to inhibition by 1,10-phenanthroline or EGTA. It is particularly interesting that a simple vascular bed such as the mesentery produces such a powerful endothelin metabolising enzyme. It is tempting, therefore, to speculate that the endothelin degrading enzyme active at neutral pH that- we have found is important in the metabolism of ET-1 throughout the vasculature.

Characterization of neuropeptide Y binding sites in rat brain membrane preparations using [125I][Leu31,Pro34]peptide YY and [125I]peptide YY3-36 as selective Y1 and Y2 radioligands

The peptide YY (PYY)-derivatives [Leu31,Pro34]PYY and PYY3-36 were respectively developed as selective Y1 and Y2 radioligands devoid of affinity for the Y3 receptor subtype. Each analog was iodinated by the chloramine T method after a purification by reverse-phase high-performance liquid chromatography. Both radioligands bind with high affinity, low capacity and in a time-dependent and saturable manner to specific sites present in rat frontoparietal cortical or hippocampal membrane preparations. [125I][Leu31,Pro34]PYY demonstrated apparent affinities (Kd) of 0.42 +/- 0.07 and 0.22 +/- 0.08 nM and maximal capacities (Bmax) of 185 +/- 14 and 33 +/- 4 fmol/mg of protein to a single class of sites in cortical and hippocampal membrane homogenates, respectively. Conversely, [125I]PYY3-36 apparently bound to a greater amount of sites in hippocampal (Bmax of 109 +/- 13 fmol/mg of protein; Kd of 0.13 +/- 0.03 mM) compared with cortical (Bmax of 33 +/- 5 fmol/mg of protein; Kd of 0.37 +/- 0.06 nM) membrane preparations, which suggests the differential enrichment of these two brain regions with a given neuropeptide Y (NPY) receptor subtype. The comparative ligand selectivity profile of these two radiolabeled PYY derivatives confirmed this hypothesis and revealed that, although the rat frontoparietal cortex is enriched with Y1 sites, Y2, receptor binding sites are most abundant in the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of conformational and binding characteristics of various natriuretic peptides and related analogs

The conformational properties of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), and various analogs and homologs were studied by circular dichroism (CD) spectroscopy in solvent mixtures inducing secondary structures. The CD spectra obtained for rat ANF(99-126), porcine BNP32, and their related analogs indicated that these peptides exhibited mainly a random-coil conformation in pure water. However, the addition of increasing concentrations of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) gave rise for all peptides to a more ordered secondary structure. The analysis of the far-ultraviolet CD spectra suggested that the peptides exist under two conformational states, beta-turn and beta-sheet, in the presence of 20-60% HFIP/water solutions. Moreover, the characterizations of rANF(99-126) and the analog pBNP1, which combines the cyclic core of bBNP32 with the carboxy- and amino-terminal segments of rANF-(99-126), have been carried out by Fourier transform infrared spectroscopy (FTIR) in 40% HFIP/D2O. The FTIR results indicated that these peptides exist predominantly under a beta-turn and beta-sheet mixed conformation. In addition, the amount of organized secondary structure obtained for human BNP32, bovine aldosterone secretion inhibitory factor, also known as ASIF(69-103) and beta-rANF(92-126), in the presence of a 40% HFIP/phosphate buffer mixture, was similar to that of porcine BNP32, whereas rat BNP32 was found to be more structured. In the same solvent mixture, the CD spectra of Met(O)110-human ANF(99-126) and chicken ANF(99-126) indicated that these peptides possess conformational features different to those of rANF(99-126) and hANF(99-126). Porcine CNP22, C-type natriuretic peptide, and the fragment C-ANF exhibited undefined secondary structure in the presence of 40% HFIP/phosphate buffer. These results suggest that the amino acid residues, not common to the various natriuretic peptides, would be involved in the stabilization of either beta-turn and/or beta-sheet conformations. Moreover, these secondary structures appear as particularly important for the recognition of the ANF-R1A receptor subtype found in bovine adrenal cortex.

Structural characterizations of neuropeptide tyrosine (NPY) and its agonist analog [Ahx5-17]NPY by NMR and molecular modeling

The structures of human NPY and of its centrally truncated agonist analog [Ahx5-17]NPY have been investigated in DMSO-d6 by two-dimensional NMR and by molecular modeling. For both peptides, a complete resonance assignment was achieved and a large number (more than 200) of inter-residue NOE connectivities were observed, including long-range connectivities between the N- and C-terminal ends of the chain. Molecular models were calculated using NOE constraints by distance geometry, simulated annealing and conjugate gradient energy minimization. The results indicate that both peptides are folded in the center of their chain, NPY adopting the hairpin shape, whereas the central portion of [Ahx5-17]NPY is characterized by relatively large loops. In contrast to previous models, practically no alpha-helical structure exists for these peptides under our conditions, but two beta-turns are found in NPY and one in [Ahx5-17]NPY. The proximity of the terminal ends could be the determinant factor for their activity.

1-alpha-Hydroxyvitamin D3 derivatives in the treatment of renal bone diseases: justification and optimal modalities of administration

The use of 1 alpha-hydroxyvitamin D3 [1 alpha(OH)D3] derivatives in a uremic patient is justified only in the treatment of hyperparathyroidism (i.e. when plasma intact parathyroid hormone - PTH - levels are above five or three times the upper limit of normal according to whether the patient is on continuous ambulatory peritoneal dialysis or on hemodialysis and between 0.5-1.5, 1-2 and 2-3 times the upper limit of normal for a creatinine clearance of, respectively, 30, between 30 and 10, or below 10 ml/min/1.73 m2). The following prerequisites have however to be satisfied: (1) a good vitamin D3 repletion should be secured by plasma 25(OH(D) levels of 20-30 ng/ml (if necessary by administration of native vitamin D or 25(OH)D3), and (2) phosphate retention (which is aggravated by the increased phosphate intestinal absorption induced by the 1 alpha (OH)D derivatives) and the consequent possible hyperphosphatemia should be prevented or corrected by the oral administration of alkaline salts of calcium given before the meals as phosphate binders without inducing hypercalcemia. These prerequisites explain the narrow therapeutical margin of 1 alpha (OH)D3 derivatives in uremic patients before dialysis (more so in the adult than in the child) and the possible broadening of this margin in the patients on dialysis by the use of low dialysate calcium concentrations (1.25-1.00 mmol/l) in order to prevent hypercalcemia by inducing a negative perdialytic calcium balance. Once hyperphosphatemia is prevented by oral calcium, 1 alpha (OH)D3 derivatives have the advantage to suppress the transcription of the prepro PTH gene by a mechanism independent of an increase in plasma calcium. Controlled randomized trials have not confirmed the claimed advantage in efficacy and safety of the parenteral versus the oral route nor of the intermittent versus the daily mode of their administration. The advantages of using the so called 'nonhypercalcemic hyperphosphatemic' vitamin D3 derivatives in combination with oral calcium over 1 alpha(OH)D3 derivatives in the treatment of uremic hyperparathyroidism are still waiting for clinical demonstration. Vitamin D derivatives have no place in the treatment of aluminic bone diseases which necessitate long term deferoxamine treatment and prevention of aluminum exposure by the dialysate and the phosphate binders. They are not indicated in the treatment of 'idiopathic' adynamic bone disease which is due to uremia per se combined with an excessive PTH suppression for the degree of renal failure. This low bone turnover pattern is associated with an increased risk of hypercalcemia and hyperphosphatemia and necessitates only a stimulation of PTH secretion by inducing a negative calcium balance with a lower dialysate calcium concentration or simply by discontinuing the oral calcium supplement in the uremic patient not yet dialyzed. In rare cases this pattern is due to a granulomatosis and is corrected by prednisone.

[Bone involvement in idiopathic calcium lithiasis]

Bone involvement in idiopathic calcium nephrolithiasis is characterized by the following abnormalities: a) the bone density is decreased, the severity of bone loss being dependent upon the existence of hypercalciuria and upon the pathophysiology of this latter: it is inconsistent in the absence of hypercalciuria or when hypercalciuria is of the absorptive type I or II, whereas it is almost constant in fasting hypercalciuria without secondary hyperparathyroidism and constant and severe in the rare true renal hypercalciuria. b) The bone histology (which has been evaluated only in idiopathic hypercalciuric patients) mainly shows a defect in bone formation at the exception of the rare renal hypercalciuria. Osteoclastic hyperresorption is only seen in this latter type of hypercalciuria whereas in the other types of hypercalciuria only an increase of the total or inactive resorption surface is observed. This phenomenon is possibly explained only by a delayed refilling of the resorption lacunae secondary to the decreased bone formation. The osteoid thickness is either normal or decreased despite decrease in mineralization apposition rate which seems therefore to be secondary to the decreased bone formation. c) Symptomatic bone disease in hypercalciuric stone formers is exceptional and always related to a severe long term calcium restriction. d) The biochemical markers of bone resorption tend to be increased in idiopathic hypercalciuria. Hydroxyprolinuria is more often elevated than pyridinolinuria. However pyridinolinuria is negatively correlated to bone density. The contrast between the increase of these bone resorption markers and the usual normality of plasma PTH and of the osteoclastic resorptive surfaces, suggest the role of meat induced acid load which may favor inactive resorption by dissolution of bone buffers. A disturbed profile synthesis of cytokines which induce differentiation and proliferation of the osteoclasts and which modulate the osteoblastic proliferation and function (IL-1, IL-6, TNF-alpha, GM-CSF...) may play a role in the bone loss of calcium stone formers but further studies are necessary to precise its transient or permanent involvement in their bone disease. e) The decrease of bone formation may be explained by the suppressed PTH secretion which may be explained by hypercalcitriolemia. This excess of calcitriol synthesis may be secondary either to monocyte increased synthesis of IL-1 which stimulates the renal 1 alpha-hydroxylase by the mean of an increased PGE2 synthesis or to the relative hypophosphatemia of the calcium stone formers comparatively to healthy controls. Hypercalcitriolemia may originate from the activated monocyte itself. The decrease in bone formation may also be secondary to the action of monokines on the osteoblast differentiation and/or function.