Functional vasoactive intestinal polypeptide (VIP)-system in salt glands of the Pekin duck

Summary In saltwater-acclimated ducks with fully specialized supraorbital salt glands, intracarotid application of acetylcholine (5 nmoles/min/kg b.w.) or porcine vasoactive intestinal polypeptide (pVIP) (240 pmoles/min/kg b.w.) induced secretion from the salt glands at threshold conditions of secretory activity. pVIP-like immunoreactivity could be localized in fibers of the postganglionic secretory nerve ramifying throughout the glandular parenchyma. Both middle-sized arterioles and secretory tubules were innervated, and pVIP-immunoreactive varicose fibers formed peritubular baskets around the basal region of secretory tubules indicating direct innervation of the secretory tissue. pVIP-specific staining could be abolished by preabsorption of the antiserum with peptide extracts of salt-gland tissue. Synthetic pVIP and endogenous VIP from salt glands of the duck co-eluted on the HPLC system, suggesting structural similarity of the peptides. Membrane-binding studies with radioiodinated pVIP revealed the presence of high-affinity binding sites in salt-gland tissue. Affinities of unlabeled pVIP analogues to compete for these binding sites were as follows: pVIP > PHI > pVIP antagonist > secretin > pVIP (10–28) > chicken VIP (16–28). Peptide extracts of salt glands had affinities similar to pVIP. Binding sites could be localized mainly at the apical end of the radially arranged secretory tubules, as demonstrated by receptor autoradiography.It is concluded that, in addition to the classical parasympathetic transmitter acetycholine, VIP serves as neuromodulator/transmitter in cranial parasympathetic control of avian salt-gland secretion by acting on both the arteriolar network and the secretory tubules of the gland.     

Solubilization and characterization of active neuropeptide Y receptors from rabbit kidney

Active neuropeptide Y receptors were solubilized from rabbit kidney membranes using the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid (CHAPS). In membrane fragments and soluble extracts neuropeptide Y binding was time dependent, saturable, reversible, and of high affinity. Scatchard analysis of equilibrium binding data indicated a single class of binding sites with respective KD and Bmax values of 0.09 nM and 530 fmol/mg of protein for the membrane-bound receptors and 0.10 nM and 1585 fmol/mg of protein for the soluble receptors. Neuropeptide Y binding was specifically inhibited by the nonhydrolyzable GTP analog guanosine 5'-O-(3-thiotriphosphate) in a concentration-dependent manner, with IC50 values of 28 and 0.14 microM for membrane-bound and soluble receptors, respectively, suggesting that neuropeptide Y receptors are functionally coupled to GTP-binding regulatory proteins. Cross-linking studies were performed with the heterobifunctional N-hydroxysuccinimidyl-4-azidobenzoate and the monofunctional neuropeptide Y derivative, azidobenzoyl and led to the identification of a 100 kDa peptide that should represent the covalently labeled neuropeptide Y receptor.     

Parthenolide attenuates LPS-induced fever, circulating cytokines and markers of brain inflammation in rats

Parthenolide, a sesquiterpene lactone, has been reported to exhibit a variety of anti-inflammatory and immunomodulatory effects. To test the effect of parthenolide on brain inflammatory responses, brain oxidative stress and fever, we treated rats with parthenolide (1 mg/kg), simultaneously or 1 h prior to a systemic (i.p.) challenge with a moderate dose (100 μg/kg) of lipopolysaccharide (LPS). The initial hypothermia was exaggerated; the second phase of the biphasic LPS-induced fever and circulating interleukin-6 (IL-6) and tumor necrosis factor α (TNFα) were significantly attenuated only in parthenolide-pretreated animals. In the hypothalamus, markers of NFκB/NF-IL6 pathway activation (inhibitor κBα, NF-IL6 and the serin/threonin kinase-like protein mRNA expression) and markers of oxidative stress (including nuclear respiratory factor 1) and NFκB immunoreactivity were significantly reduced while NF-IL6 immunoreactivity and suppressor of cytokine signaling 3 mRNA expression remained unaltered, 8 h after LPS-stimulation with parthenolide-pretreatment. Importantly, this response was accompanied by decreased mRNA expression of the rate limiting enzyme in prostaglandin synthesis, cyclooxygenase 2 (COX2), known for its critical role in fever induction pathways. A direct action of parthenolide on brain cells was also confirmed in a primary neuro-glial cell culture of the vascular organ of the lamina terminalis a pivotal brain structure for fever manifestation with a leaky blood-brain barrier. In summary, pretreatment with parthenolide attenuates the febrile response during LPS-induced systemic inflammation by reducing circulating IL-6 and TNFα and decreasing hypothalamic NFκB/NF-IL6 activation, oxidative stress and expression of COX2. Thus parthenolide appears to have the potential to reduce brain inflammation.     

Localized vs. systemic inflammation in guinea pigs: a role for prostaglandins at distinct points of the fever induction pathways?

In guinea pigs, dose-dependent febrile responses were induced by injection of a high (100 microg/kg) or a low (10 microg/kg) dose of bacterial lipopolysaccharide (LPS) into artificial subcutaneously implanted Teflon chambers. Both LPS doses further induced a pronounced formation of prostaglandin E(2) (PGE(2)) at the site of localized subcutaneous inflammation. Administration of diclofenac, a nonselective cyclooxygenase (COX) inhibitor, at different doses (5, 50, 500, or 5,000 microg/kg) attenuated or abrogated LPS-induced fever and inhibited LPS-induced local PGE(2) formation (5 or 500 microg/kg diclofenac). Even the lowest dose of diclofenac (5 microg/kg) attenuated fever in response to 10 microg/kg LPS, but only when administered directly into the subcutaneous chamber, and not into the site contralateral to the chamber. This observation indicated that a localized formation of PGE(2) at the site of inflammation mediated a portion of the febrile response, which was induced by injection of 10 microg/kg LPS into the subcutaneous chamber. Further support for this hypothesis derived from the observation that we failed to detect elevated amounts of COX-2 mRNA in the brain of guinea pigs injected subcutaneously with 10 microg/kg LPS, whereas subcutaneous injections of 100 microg/kg LPS, as well as systemic injections of LPS (intra-arterial or intraperitoneal routes), readily caused expression of the COX-2 gene in the guinea pig brain, as demonstrated by in situ hybridization. Therefore, fever in response to subcutaneous injection of 10 microg/kg LPS may, in part, have been evoked by a neural, rather than a humoral, pathway from the local site of inflammation to the brain.     

The TIA1 RNA-Binding Protein Family Regulates EIF2AK2-Mediated Stress Response and Cell Cycle Progression

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Effects of changes in intravascular oncotic pressure on renal responses to volume loading in the saltwater-acclimated Pekin duck (Anas platyrhynchos)

Summary The relative contributions of the intra-and extravascular compartments of the extracellular fluid (ECF) to the control of osmoregulatory renal functions were examined in saltwater-acclimated Pekin ducks. Having established steady-state diuresis and salt gland secretion by continuous infusion of 1 ml·min^-1 isotonic Krebs-Ringer-Bicarbonate (KRB) solution, 5% dextran-70 was added to the infusate for 30 min thereby confining volume expansion to the intravascular compartment. General volume expansion by isotonic KRB caused a drop in plasma osmolality by 23 mOsm·kg^-1, due to NaCl elimination by the salt glands, and decreases in hematocrit (het) and radioimmunologically measured plasma levels of Arg⁸-vasotocin (AVT) and Val⁵-angiotensin II (ANG II), whereas immunoreactivity associated with atrial natriuretic factor (ir-ANF) was increased. Adding 5% dextran-70 to the infusate left plasma osmolality and electrolytes unchanged but was followed by a further decrease in hct and a 36% increase in the plasma colloidosmotic pressure (COP) facilitating fluid shifts from the extra-to the intravascular compartment of the ECF. Plasma levels of AVT and ANG II remained unchanged, but ir-ANF rose three-fold, its increase being three times as great relative to the decrease in hct, as during general volume expansion by isotonic KRB solution. Arterial and central venous pressure measurements did not indicate changes in cardiovascular function. Hyperoncotic infusion initially induced marked antidiuresis with decreased osmolal excretion, despite a slightly elevated urine osmolality. This effects, however, was trasient and not proportional to the rise in COP, but rather seemed to be related to fluid shifts resulting from hyperoncotic loading. With tracer dilution techniques, reductions in both renal plasma flow and glomerular filtration rate were found to contribute to antidiuresis which was associated with reduced fractional water excretion. Salt gland secretion rate did not increase during hyperoncotic intravascular volume expansion but rather tended to decrease. The results of this study are in line with the idea that contributions of the interstitial fluid compartment (IFC) to volume-dependent control of osmoregulatory functions have to be considered. In the present study on saltwater-acclimated ducks, AVT, ANG II, and ir-ANF could be excluded as mediators of the adjustments in renal water and salt handling following fluid shifts due to hyperoncotic intravascular volume expansion.Abbreviations ANF atrial natriuretic factor - ir-ANF ANF-like immunoreactivity - ANG II angiotensin II - AVT arginine vasotocin - BF breathing frequency - b. w. body weight - COP colloid osmotic pressure - CVP central venous pressure - ECF extracellular fluid - ERPF effective renal plasma flow - FF filtration fraction - GFR glomerular filtration rate - IFC interstitial fluid compartment - i.v. intravenous(ly) - hct hematocrit - HR heart rate - KRB Krebs-Ringer Bicarbonate solution - MABP mean arterial blood pressure - PAH paraaminohippuric acid - SEM standard error of mean     

Learning the language of post-transcriptional gene regulation

A large-scale RNA in vitro selection study systematically identified RNA recognition elements for 205 RNA-binding proteins belonging to families conserved in most eukaryotes.