bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced growth-dependent expression of TGFβ1 and hsp70 genes in aortic smooth muscle cells from spontaneously hypertensive rats
Authors: Tremblay Johanne , Hadrava Vratislav , Kruppa Ursula , Hashimoto Toshihiko , Hamet Pavel
Published: April 2011

Enhanced proliferation of vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) as compared with Wistar–Kyoto rats (WKY) persists in long-term culture and is characterized by an accelerated entry of these cells into the synthetic S phase of the cell cycle and a higher specific growth rate, particularly evident at high cell density. In the present study, we investigated by Northern blot experiments the expression of genes putatively involved in the regulation of VSMC growth. One of them is the transforming growth factor β1 gene (TGFβ1), a bifunctional modulator of cell growth whose action is dependent on cell density. The accumulation of TGFβ1 mRNA was enhanced in growing SHR cells at every density studied as early as 24 h after inoculation with a further increase at later times. Protooncogenes c-fos and c-myc, which have been implicated in G1/S phase transition, have also been investigated in VSMC by Northern blot analysis. At low cell density, calf serum stimulated c-fos and c-myc mRNA expression was comparable in WKY and SHR cells whereas at high cell density, c-fos induction was higher in VSMC from SHR. SHR VSMC respond more to mitogenic stimulation and to environmental (e.g., heat) stress, particularly when growing near saturation density. hsp70 constitutes a gene family responsive to environmental stimuli (heat) and to mitogenic stimulation. Our data demonstrated that heat-inducible hsp70 mRNA is expressed at higher levels in SHR as compared with WKY cells, whereas the differential expression of serum responsive hsp70 between the two strains is more evident in growing VSMC with only slight differences in quiescent cells. TGFβ1 and hsp70 proteins autoregulate their own expression. A defect in feedback regulation of TGFβ1 and hsp70 expression may be involved in the hyperproliferation and altered density-dependent inhibition of SHR VSMC.Key words: hypertension, SHR, vascular smooth muscle cells, cell cycle, transforming growth factor β1, oncogenes, hsp70.
Reset of the osmotic threshold for vasopressin in rats fed a low NaCl, K-free diet
Authors: Peterson L. N. , Mathur S. , Borzecki J. S.
Published: April 2011

Activation of the renin-angiotensin system induced by feeding a low NaCl, K-free (LS) diet is associated with polydipsia and a chronic reduction in effective plasma osmolality (efPosm). We have recently shown that converting enzyme inhibition with enalapril (EP) abolishes polydipsia. The present study was designed to test the hypothesis that the osmotic threshold for vasopressin is reset in rats fed the LS diet and to examine the effect of EP on ambient and osmotically stimulated plasma vasopressin levels (PAvp). Animals were fed the LS diet or a control salt diet and treated with vehicle or the lowest dose of EP sufficient to prevent polydipsia (7.5 mg∙kg−1∙day−1) in rats fed the LS diet. PAVP and efPosm were measured under ambient conditions and after osmotic loading. Urine osmolality (Uosm) was measured under ambient conditions and after water loading. The chronic reduction in efPosm in LS rats was associated with the excretion of a Uosm 1–2 times greater than the corresponding Posm, PAVP similar to controls (LS, 2.27 ± 1.08 vs. control, 1.19 ± 0.22 pg/mL) and the ability to excrete a water load. Following osmotic loading, efPosm and PAVP increased significantly and similarly in both LS and control rats. EP administration had no effect on water intake, ambient efPosm and PAVP, and the AVP response to osmotic loading in rats fed the control diet. EP prevented polydipsia in LS rats, however it had no significant effect on ambient or osmotically stimulated PAVP or efPosm. These results provide evidence that the osmotic threshold for AVP is reset in rats fed the LS diet and although converting enzyme inhibition has a profound effect on water intake, angiotensin II does not appear to be the only variable affecting the osmotic threshold for AVP release.Key words: arginine vasopressin, antidiuretic hormone, osmotic threshold, plasma osmolality, rats, converting enzyme inhibition, angiotensin II, thirst.
Comparison of the release of vasoactive factors from venous and arterial bovine cultured endothelial cells
Authors: D'Orleans-Juste Pedro , Mitchell Jane A. , Wood Elizabeth G. , Hecker Markus , Vane John R.
Published: April 2011

The release of endothelium-derived relaxing factor (EDRF), prostacyclin (PGI2), and endothelin-1 (ET-1) was measured from endothelial cells (EC) cultured from either bovine vena cava (BVCEC) or bovine aorta (BAEC). EDRF release was determined by using the superfusion bioassay technique, whereas ET-1 and PGI2 were measured by specific radioimmunoassays. Bradykinin (BK) (0.05–30 pmol) given through columns of venous or arterial EC induced a dose-dependent release of EDRF. BK (0.05 pmol) evoked a release of EDRF from venous EC that was similar to the effect of a dose of 1 pmol from arterial EC. As with BAEC, infusions of NG-monomethyl-L-arginine (30 μM) caused an inhibition of EDRF release from BVCEC that was partially reversed by coinfusions of L-arginine (L-Arg; 100 μM). BK also induced a dose-dependent release of PGI2 from BVCEC. BVCEC and BAEC produced PGI2 in equivalent amounts when arachidonic acid (9.2 and 32 pmol) was added to the Krebs' solution perfusing the cells. BVEC and BAEC released detectable amounts of ET-1 (0.4 ± 0.1 and 0.9 ± 0.3 ng/mL, respectively), over a 4-h period, and the release of ET-1 was increased approximately twofold by coincubations with thrombin (0.05–1 U/mL). These findings demonstrate that venous EC have a similar capacity to arterial EC to release vasoactive factors, thus supporting the hypothesis that veins have a functional endothelium that may modulate venous tone and platelet function.Key words: cultured endothelial cells, vein, artery, endothelium-derived relaxing factor, prostacyclin, endothelin.
Production of tumour necrosis factor by cells exposed to sulphonamide reactive metabolites
Authors: Rieder Michael J. , Mask Monica , Bird Ingrid A.
Published: April 2011

Hypersensitivity reactions are the most common adverse events associated with therapy with the sulphonamide antibiotics. These reactions have been shown to occur among individuals with pharmacogenetically determined differences in the capacity of their cells to detoxify reactive products of oxidative metabolism of the sulphonamides. These reactions appear to be propagated by an inflammatory response by the immune system. To investigate the role of the cytokine tumour necrosis factor (TNF-α) in these reactions, we studied the production of TNF-α by peripheral blood mononuclear cells (PBMCs) that had been incubated with sulfamethoxazole and murine microsomes in the presence and absence of a microsomal-activating system and TNF-α production by PBMCs in the presence and absence of the hydroxylamine derivative of sulfamethoxazole. The PBMCs showed a time-related increase in the production of TNF-α. There was no increase in TNF-α production seen during incubation with sulphonamide reactive metabolites; rather, there was a decrease in TNF-α elaboration that was most marked when PBMCs were incubated with the hydroxylamine of sulfamethoxazole. There is no evidence from these in vitro studies that TNF-α is involved as a mediator of the inflammatory response in sulphonamide hypersensitivity adverse drug reactions.Key words: sulphonamide, tumour necrosis factor, adverse drug reaction, hydroxylamine.
Digitaloid pregnanes promote potassium-sparing diuresis in the guinea pig
Authors: Smyth D. D. , Templeton J. F. , Kumar V. P. Sashi , Yan Y. , Widajewicz W. , LaBella F. S.
Published: April 2011

The synthesis of 17α-acetoxy-3β-[(β-D-glucopyranosyl)oxy]-6α-methylpregn-4-en-20-one, the glucoside of medroxyprogesterone acetate (MPA-glu), is described. MPA-glu and 14-amino-20β-hydroxy-3β-[(α-L-rhamnopyranosyl)oxy]-5β,14β-pregnane (LND 623), pregnane glycosides that bind to the digitalis receptor, and digoxin, a cardiac glycoside, were infused intravenously into the anesthetized guinea pig. Each of the three steroids significantly enhanced urinary volume and sodium excretion without affecting blood pressure and creatinine clearance. Potassium excretion was markedly enhanced by digoxin but unaffected by MPA-glu or LND 623. These observations conform to previous work that demonstrated, in the rat, potassium-sparing diuresis by the glucoside of 14β-hydroxyprogesterone, a cardiotonic pregnane. There is a dissociation between potency to inhibit [3H]ouabain binding and the extra ATPase actions of the digitaloid pregnanes.Key words: pregnanes, cardiac glycosides, diuretic, LND 623, medroxyprogesterone acetate.
Differential effects of blood insulin levels on microsomal enzyme activities from hepatic and extrahepatic tissues of male rats
Authors: Carnovale Cristina E. , Catania Viviana A. , Monti Juan A. , Carrillo Maria C.
Published: April 2011

Microsomal glutathione S-transferase, UDP-glucuronyl transferase, and aniline hydroxylase activities were determined in liver, renal cortex, and small intestine of control, streptozotocin-diabetic, alloxan-diabetic, and untreated insulin-injected male Wistar rats. Renal microsomal glutathione S-transferase activity showed a direct linear relationship with insulin blood levels, in agreement with our previous report on cytosolic glutathione S-transferase. This result suggests a possible regulatory mechanism of insulin that needs to be further examined. The hepatic microsomal UDP-glucuronyl transferase was only decreased in streptozotocin-diabetic rats and was not restored by insulin treatment. Intestinal UDP-glucuronyl transferase exhibited an opposite response in streptozotocin-treated animals that was not normalized by the administration of insulin. Hepatic aniline hydroxylase showed the same behaviour as intestinal UDP-glucuronyl transferase. These results suggest that streptozotocin and (or) its metabolites have a direct effect on hepatic and intestinal UDP-glucuronyl transferase activity and on hepatic aniline hydroxylase activity. On the other hand, insulin regulation of enzyme activity varies from one organ to another.Key words: insulin, streptozotocin, alloxan, glutathione S-transferase, UDP-glucuronyl transferase, aniline hydroxylase.
Central actions of angiotensin in cardiovascular control: Multiple roles for a single peptide
Authors: Ferguson Alastair V. , Wall Katharine M.
Published: April 2011

Angiotensin II (ANG II) acts peripherally as a hormone, with actions on the vasculature, adrenals, and kidney. In addition, certain actions of ANG II in the central nervous system are directed toward cardiovascular control and fluid volume homeostasis. Dense binding sites for ANG II are found at circumventricular organs, which apparently have the ability to relay information to cardiovascular centers via neural circuitry. Microinjection of ANG II into the subfornical organ (SFO) or area postrema (AP) produces site-specific increases in blood pressure. In addition, electrophysiological studies demonstrate profound effects of ANG II, acting at the SFO, on activity of neurohypophysial neurons and release of oxytocin and vasopressin, which can be antagonized by ANG II blockers or attenuated by SFO lesions. Evidence from microinjection, electrophysiological, and lesion studies indicate a complex interaction between central sites involved in mechanisms of cardiovascular control: the SFO, AP, organum vasculosum of the lamina terminalis, and paraventricular and supraoptic nuclei of the hypothalamus. Not only is ANG II a humoral messenger in this central scenario, but evidence suggests it acts as a neurotransmitter or neuroendocrine substance within specific CNS pathways, suggesting multiple roles for this peptide in central cardiovascular control.Key words: blood pressure regulation, circumventricular organs, vasopressin, area postrema, subfornical organ.
Localization of the reflex pathway responsible for the vasodepressor reaction induced by inferior vena caval occlusion and isoproterenol
Authors: Waxman Menashe B. , Asta John A. , Cameron Douglas A.
Published: April 2011

Vasodepressor reactions were induced in 27 rats by a combination of inferior vena caval occlusion and an infusion of isoproterenol. A vasodepressor reaction was defined as paradoxical heart rate slowing during inferior vena caval occlusion. The R-R intervals were measured at 5-s intervals before, during, and after 60 s of inferior vena caval occlusion. The purpose of this study was to examine the role of the right and left vagus nerve and the right and left stellate ganglia in this reflex. Under control conditions inferior vena caval occlusion accelerated the rate (R-R, −15.9 ± 0.9 ms). During an infusion of isoproterenol (0.5–1.0 μg∙min−1), inferior vena caval occlusion produced paradoxical rate slowing, i.e., a vasodepressor reaction (R-R, +75.0 ± 2.2 ms). The vasodepressor reaction was examined during inferior vena caval occlusion and isoproterenol under the following additional states: atropine methyl bromide or right vagotomy did not alter the reaction; left vagotomy eliminated the reaction; and right or left stellectomy greatly reduced the vasodepressor reaction. We conclude the following: (1) left vagal afferents mediate the vasodepressor reaction; (2) cardiac sympathetic fibers participate in the vasodepressor reaction by withdrawing efferent tone through the right stellate ganglion, and by generating the afferent signal, which triggers the vasodepressor reaction through the left stellate ganglion.Key words: vasodepressor reaction, reflex localization, isoproterenol.
The effects of sympathetic denervation on spontaneous ventricular defibrillation in the rat
Authors: Waxman Menashe B. , Sharma Arjun D. , Asta John , Endrenyi Laszlo
Published: April 2011

Ventricular tachycardia or ventricular fibrillation was electrically induced in 38 normal rats (group 1) and 24 sympathetically denervated rats (6-hydroxydopamine) (group 2). The time for spontaneous reversion to sinus rhythm was measured during (1) control, (2) isoproterenol, and (3) the combination of isoproterenol and phenylephrine. The time for spontaneous reversion was the same in both groups in the three states. The reversion time was prolonged threefold by isoproterenol, and restored to control values when phenylephrine was added to the infusion of isoproterenol. The tachycardia duration and the refractory period were inversely related: log10 (tachycardia duration) = 3.466 – 0.091 (refractory period). Ventricular tachycardia/fibrillation induction was examined as follows: (i) Ventricular tachycardia/fibrillation was induced in 100% of normal rats (group 1), but only 42% of the denervated rats (group 2, p < 0.001); (ii) during isoproterenol, ventricular tachycardia/fibrillation was induced in 100% of rats of both groups; and (iii) when phenylephrine was added to isoproterenol, ventricular tachycardia/fibrillation was induced in 100% of group 1 rats versus 82% of group 2 rats, (p = NS). These observations suggest (1) the induction of ventricular tachycardia/fibrillation is highly dependent on intact sympathetic innervation, and (2) exogenous adrenergic agonists modulate the duration of ventricular fibrillation through their effects on ventricular refractory period, independent of sympathetic innervation.Key words: spontaneous defibrillation, sympathetic denervation.
A comparison of the effects of acute verses chronic administration of phenoxybenzamine on pressor responses elicited by the selective α1-adrenoceptor agonist cirazoline in the pithed rat preparation
Authors: Tabrizchi Reza , Triggle Christopher R.
Published: April 2011

The effects of nifedipine on the pressor responses to cirazoline were examined in the pithed rat preparation that had received either acute or chronic phenoxybenzamine treatment. Phenoxybenzamine was administered, i.v., to conscious rats, either acutely at 0.01, 0.03, and 0.1 mg/kg, 60 min prior to the commencement of the experiments or chronically at 0.1, 0.3, and 1.0 mg/kg, once daily for 7 days. Nifedipine was administered i.a. (1.0 mg/kg) after the animals had been pithed. The acute or chronic administration of phenoxybenzamine alone displaced the dose–response curve to cirazoline to the right in a dose-dependent manner, while reducing the slope function and maximum response to the agonist. The combined effects of acute phenoxybenzamine and nifedipine produced an additive inhibitory effect on the pressor response elicited by cirazoline, which was most apparent following the removal of receptor reserve by acute phenoxybenzamine. The inhibitory effects of nifedipine and chronically administered phenoxybenzamine were additive at the lower administered doses of the alkylating agent but, in contrast with the effects of acute phenoxybenzamine, the enhanced inhibitory effects of nifedipine were reduced following the removal of receptor reserve. These results indicate that the chronic administration of phenoxybenzamine reduces the additive inhibitory effects of nifedipine and phenoxybenzamine that were observed following the acute administration of phenoxybenzamine.Key words: α1-adrenoceptors, vasoconstriction, subtypes, pithed rat, calcium channel antagonist.
Biotransformation of glyceryl trinitrate by rat brain homogenate
Authors: Marks Gerald S. , McLaughlin Brian E. , Nakatsu Kanji , Brien James F.
Published: April 2011

Incubation of glyceryl trinitrate (GTN) with 5% (w/v) rat brain homogenate (RBH) resulted in biotransformation of the organic nitrate vasodilator drug to a mixture of glyceryl-1,2-dinitrate (1,2-GDN) and glyceryl-1,3-dinitrate (1,3-GDN). Heating of the RBH at 100 °C for 5 min and (or) pretreatment with 5 mM N-ethylmaleimide at 37 °C for 10 min demonstrated that about two-thirds of the GTN biotransformation activity was due to a sulfhydryl-dependent enzymatic process resulting in the predominant formation of 1,2-GDN, and that the remaining biotransformation activity was due to a sulfhydryl-dependent nonenzymatic process resulting in the selective formation of 1,3-GDN. In a preliminary experiment, nitric oxide formation was observed during the incubation of GTN with RBH under anaerobic conditions. These data support the idea that some of the therapeutic and adverse effects of GTN are mediated through its action in the central nervous system.Key words: glyceryl trinitrate, biotransformation, rat brain homogenate, sulfhydryl-dependent enzyme, nitric oxide formation.
Relationship of postprandial motilin, gastrin, and pancreatic polypeptide release to intestinal motility during vagal interruption
Authors: Chung S. A. , Greenberg G. R. , Diamant N. E.
Published: April 2011

Experiments were performed to determine how postprandial motilin, gastrin, and pancreatic polypeptide plasma concentrations measured during vagal blockade relate to coincident small intestinal motility patterns. Feeding produced a postprandial pattern of intestinal motility coincident with a sustained increase in gastrin and pancreatic polypeptide and a decline in motilin plasma concentrations. Vagal blockade replaced the fed pattern with one similar to migrating motor complex (MMC) activity. Highest motilin plasma concentrations were observed during phase III of this MMC-like activity, as occurs in the fasted state. Vagal blockade reduced but did not abolish the postprandial increase in plasma gastrin and pancreatic polypeptide concentrations. Termination of vagal cooling produced a decline in motilin and an elevation in gastrin and pancreatic polypeptide concentrations, coincident with the return of the fed pattern. In conclusion, during vagal blockade in the fed state (i) motilin, but not gastrin or pancreatic polypeptide plasma concentrations, fluctuate with the MMC-like activity, and any measurement of motilin concentrations under these circumstances must be interpreted on the basis of gut motility patterns, and (ii) gastrin and pancreatic polypeptide concentrations are marginally elevated, but these changes are not enough to disrupt the MMC or have any motor effect. Lastly, the fed pattern and the postprandial changes in motilin, gastrin, and pancreatic polypeptide concentrations are in part dependent upon intact vagal pathways.Key words: gastrointestinal motility, vagus, motilin, gastrin, pancreatic polypeptide.
The effect of neonatal treatment of rats with nerve growth factor on the blood pressure and structure of the mesenteric arteries
Authors: Lee Robert M. K. W. , Coughlin Michael , Tsoporis Jim , Kwan Chiu-Yin , Guan Yong-Yuan , Leenen Frans H. H.
Published: April 2011

Newborn male Wistar rats were treated with nerve growth factor daily by subcutaneous injection for 2 weeks, and control rats were treated with either cytochrome c or buffered saline. Average body weight of the treated animals was lower than that of the controls during the 2 weeks of treatment, but became similar to that of the controls thereafter. Tissue levels of norepinephrine were elevated in the brain, adrenal glands, mesenteric arteries, and vas deferens of the treated animals immediately after the treatment, but became similar in the three groups 2 weeks after the termination of the treatment. Blood pressure and heart rate were measured beginning at 4 weeks of age until 28 weeks, when the rats were sacrificed and the mesenteric arteries sampled for morphometric measurements of vessel wall dimensions. Pretreatment with nerve growth factor did not affect blood pressure, nor heart rate. Structural alteration of the three types of mesenteric arteries was also absent in the treated animals. We conclude that even though neonatal treatment of normal Wistar rats with nerve growth factor for 2 weeks induced an elevation of the norepinephrine levels in several tissues at the end of the treatment period, it was not sufficient to produce hypertension and structural alterations in the blood vessels.Key words: nerve growth factor, sympathetic nerve, hypertension, vascular changes, morphometry.
Specific endothelin binding sites in renal medullary collecting duct cells: lack of interaction with ANP binding and cGMP signalling
Authors: Cernacek Peter , Legault Louis , Stewart Duncan J. , Levy Mortimer
Published: April 2011

The diverse biological actions of endothelins (ET) appear to be mediated by specific cell-surface receptors. Autoradiography and membrane binding studies have shown abundant ET binding sites in the kidney. However, their expression in specific types of renal cells is unclear. We studied the binding of 125I-labelled endothelin-1 in freshly isolated cell suspensions from canine inner medullary collecting duct. Competition binding experiments revealed the presence of specific high-affinity binding sites: unlabelled ET-1 and ET-2 competed with the radioligand with an IC50 of 135 and 83 pM, respectively, while the IC50 of ET-3 and big ET-1 were 2 and 4 orders of magnitude higher, indicating the presence of ETA-type receptor. Angiotensin II, vasopressin, and atrial natriuretic peptide (ANP) did not compete for ET binding even at a concentration of 10−6 M. Saturation binding experiments showed a single class of binding sites of high density (Bmax = 56.7 ± 10.3 fmol/106 cells) and high affinity (Kd = 69.8 ± 10 pM). In contrast, ANP receptors in the same cell preparations appeared as two classes of binding sites with widely different affinity and density. The high-affinity ANP site (Kd = 311 ± 48 pM) was compatible with ANP-B (guanylate cyclase-coupled) receptor. ET-1 did not compete for this receptor. ET-1 (10−7 M) did not alter ANP-induced cGMP generation in these cells (3.8-fold increase at 10−7 M ANP), nor basal levels of cGMP. The expression by the distal tubular epithelium of specific ET-1 binding sites strongly suggests the presence of a functional receptor, which may mediate the inhibition of Na+ transport in these cells. The mechanism and the transduction pathway of this effect appear to be different and independent from those of ANP.Key words: endothelin receptor, distal collecting duct, atrial natriuretic peptide receptor, cGMP generation.
Differential sensitivities of the sphincter of Oddi and gallbladder to cholecystokinin in the guinea pig: their role in transsphincteric bile flow
Authors: Harrington Karen , Bomzon Arieh , Sharkey Keith A. , Davison Joseph S. , Shaffer Eldon A.
Published: April 2011

Cholecystokinin (CCK) is considered to simply contract the gallbladder and relax the sphincter of Oddi with meals. In this study, we examined this hypothesis by investigating the action of CCK on the sphincter of Oddi and gallbladder of the guinea pig. The experimental design used an in vitro preparation of the sphincter of Oddi to measure contraction of the circular muscle. CCK increased tone in both the gallbladder and the sphincter of Oddi in a concentration-dependent manner. The normalized concentration–response curves for CCK, however, revealed that the gallbladder had a greater sensitivity to CCK (ED50 7 nM) than the sphincter of Oddi (ED50 22 nM; p < 0.01). Conversely, the sphincter was more sensitive to bethanechol than was the gallbladder. When the sphincter of Oddi was stimulated maximally with CCK in the presence of atropine (10−6 M) or tetrodotoxin (10−6 M), the contractile response was significantly reduced (p < 0.05) although not abolished. Conversely, atropine completely abolished the responses to bethanechol (10−3 M) and transmural field stimulation (70 V, 10 Hz, 1 ms, for 20 s). Transmural field stimulation of the sphincter that had been precontracted with CCK (26 nM) caused a transient, initial relaxation followed by contraction. Pretreatment with atropine augmented the duration of this relaxation, which could be completely abolished by tetrodotoxin. Thus, CCK contracts the sphincter of Oddi in the guinea pig by a direct (myogenic) and a neural (likely cholinergic) mechanism. Relaxation of the sphincter of Oddi also occurs in the guinea pig via noncholinergic inhibitory nerves. Duodenal delivery of bile is expedited by CCK, which induces gallbladder contraction at low, near-physiological levels without stimulating the sphincter. Under other conditions, sphincter of Oddi relaxation may facilitate transsphincteric flow. In contrast, increased cholinergic tone may help prevent duodenal reflux into the biliary system.Key words: cholecystokinin, bethanechol, enteric nervous system, gallbladder function, sphincter of Oddi.
Effects of restricting uteroplacental blood flow on concentrations of corticotrophin-releasing hormone, adrenocorticotrophin, cortisol, and prostaglandin E2 in the sheep fetus during late pregnancy
Authors: Sue-Tang Alicia , Booking Alan D. , Brooks A. Nigel , Hooper Stuart , White Susan E. , Jacobs Ross A. , Fraher Laurence J. , Challis John R. G.
Published: April 2011

We have examined the effects of reduced uterine blood flow and prolonged fetal hypoxemia on the temporal relationship between changes in hormones associated with the activity of the pituitary–adrenal axis (corticotrophin-releasing hormone (CRH), adrenocorticotrophin (ACTH), cortisol, and prostaglandin E2 (PGE2)) in the ovine fetus at 120–125 days of pregnancy, and we sought evidence for placental secretion of CRH and ACTH during prolonged hypoxemia. Uterine blood flow was reduced by placing an adjustable Teflon clamp around the maternal common internal iliac artery to decrease fetal arterial oxygen saturation from mean values of 59.1 ± 3.3 to 25.7 ± 4.6% (±SEM, n = 10). There was a transient peak in immunoreactive (IR-) CRH at 1–2 h after reducing uterine blood flow. IR-ACTH rose to peak values at +2 h, then gradually decreased to control level by +12 h. Fetal plasma cortisol and PGE2 concentrations were elevated significantly by +2 and +4 h, respectively, and at 20–24 h. The identity of IR-CRH in fetal plasma and in ovine placental extracts was confirmed by HPLC, but there was no consistent umbilical vein – femoral arterial concentration difference for either IR-CRH or IR-ACTH during normoxemia or hypoxemia. We conclude that a sequence of endocrine changes involving CRH, ACTH, PGE2, and cortisol occurs in the fetus during a prolonged reduction in uterine blood flow. However, we did not obtain evidence, for placental secretion of either CRH or ACTH in response to this manipulation.Key words: fetus, adrenocorticotrophin, corticotrophin-releasing hormone, prostaglandin E2, placenta.
Portal venous infusions of L-glutamine in anaesthetized dogs do not influence renal function
Authors: Levy Mortimer
Published: April 2011

It has been reported that the intraportal infusion of glutamine in Munich–Wistar rats will cause depression of renal perfusion and the urinary excretion of salt and water. We have attempted to reproduce these findings in anaesthetized dogs. L-Glutamine was infused at doses between 120 and 150 μmol/min into the portal vein and femoral vein of anaesthetized dogs. No effect was observed on portal venous pressure, blood pressure, or kidney function. Similar data were obtained with D-glutamine. Liver biopsy revealed no abnormalities. When 1.5–3 μg histamine (free base) was infused into the portal system, portal venous pressure rose from 15.2 ± 0.33 to 24.8 ± 0.40 cmH2O (p < 0.05) (1 cmH2O = 98.1 Pa). Glutamine infusions do not appear to initiate hepatorenal reflexes in dogs as they have been reported to do in rats.Key words: liver, portal hypertension, hepatorenal reflex.
Motilin and the postprandial motility of the antrum
Authors: Boivin M. , Riberdy M. , Raymond M. -C. , Trudel L. , Poitras P.
Published: April 2011

This study was designed to establish whether the rise in plasma motilin observed after a meal in humans can influence the postprandial motor activity of the antrum. Antroduodenal postprandial motility profiles and indices obtained from 5 controls and 5 subjects infused with exogenous synthetic motilin (0.1 μg∙kg−1) or with the motilin receptor agonist erythromycin lactobionate (200 mg) were compared. Motilin infusion increased plasma motilin concentrations about 5 times above the physiological range but failed to modify the normal postprandial contractile response. On the other hand, in 4 of the 5 subjects, erythromycin induced an intense motor response that mimicked phase III of the migrating motor complex. Our study demonstrates that, during the postprandial period, motilin antral receptors can be stimulated only with doses of motilin exceeding the physiological plasma concentrations, and that the motor effect obtained did not mimic the usual postprandial motility pattern. Our results, therefore, do not support the proposal that the postprandial motility of the antrum is regulated by the plasma levels of motilin.Key words: antral motility, gastrointestinal hormone, gastrointestinal motility, motilin, regulatory peptide, smooth muscle function.
The integrative role of synaptic cotransmission in the bullfrog vasomotor C system: evidence for a synaptic gain hypothesis
Authors: Horn John P.
Published: April 2011

Understanding the integrative significance of synaptic cotransmission is a central problem in autonomic physiology. What are the functional roles of slow synaptic potentials in autonomic ganglia? This paper reviews the problem and its historical roots by focusing on work in the amphibian paravertebral sympathetic system. The phenotypic properties that distinguish the sympathetic B and C cell systems are summarized. Then, a synaptic gain hypothesis is proposed for the integrative function of muscarinic and peptidergic synapses in the vasomotor C system. The model states that the peripheral output of the vasomotor system is subject to synaptic amplification by two gain stages in series. The first gain stage is postulated to arise in ganglia from interactions between two slow postsynaptic potentials; the excitatory response mediated by luteinizing hormone releasing hormone, and the inhibitory response mediated by the muscarinic action of acetylcholine. The second gain stage is postulated to arise in arteries from interactions between two postganglionic cotransmitters: epinephrine and neuropeptide Y. A circuit with these properties would enable preganglionic patterns of electrical activity to regulate the system's output over a wider dynamic range than possible without cotransmitters.Key words: vasomotor sympathetic neurons, muscarinic synapses, luteinizing hormone releasing hormone, neuropeptide Y, neuronal model.
Preganglionic axons from the third thoracic spinal segment fail to induce long-term potentiation in the superior cervical ganglion of the cat
Authors: Bachoo M. , Polosa C.
Published: April 2011

A stimulus train to preganglionic axons produces long-term potentiation (LTP) of population responses of sympathetic ganglion cells evoked by the same or by other converging axons. The present study shows that preganglionic axons emerging from the spinal cord in different thoracic rami, and converging onto a common pool of ganglion cells that innervate a single target, differ in their ability to induce LTP. In anesthetized cats under partial nicotinic block with hexamethonium, the nictitating-membrane (NM) contraction evoked by stimulation of the first (T1) and third (T3) thoracic white rami (WR) was recorded. Each ramus produced a contraction of similar amplitude. In contrast, the homosynaptic potentiation produced by a 40-Hz 10-s train differed markedly. T1WR produced a potentiation of duration comparable to that produced by stimulation of the cervical sympathetic trunk, while T3WR produced either no potentiation or a potentiation of much shorter duration. The NM response evoked by T3WR, however, was potentiated by similar extent and duration as was the response evoked by T1WR when the train was applied to T1WR (heterosynaptic LTP). This suggests that the ganglionic synapses made by T3WR possess the mechanism for expressing LTP. Conversely, T3WR was ineffective at potentiating heterosynaptically the NM response evoked by T1WR. These results suggest that the ability to produce or release the LTP inducer varies markedly among sympathetic preganglionic neurons.Key words: preganglionic neuron heterogeneity, long-term potentiation induction, synaptic transmission, neuropeptides.
Intracellular transduction mechanisms for the slow synaptic events
Authors: Kobayashi Haruo , Mochida Sumiko , Takahashi Susumu Y.
Published: April 2011

Electrical activities of the postganglionic neurons in the superior cervical ganglia of rabbits are modulated in various ways following activation of the subtypes of muscarinic acetylcholine receptors, (i) M1 receptors mediate a slow depolarization consisting of at least three types of ionic conductance changes, and one of these is possibly mediated by cyclic GMP. (ii) M2 receptors mediate a slow hyperpolarization that seems to be generated by inositol triphosphate derived from phosphatidylinositol breakdown. (iii) M2 receptors also cause, through an activation of C kinase, a suppression of Ca entry during action potentials that results in a characteristic change in the action potentials and thereby modulates excitability of superior cervical ganglion neurons. Each subtype of muscarinic receptors thus regulates different pathways of intracellular transduction and modulates the electrical signaling of sympathetic neurons.Key words: superior cervical ganglion, electrical signals, muscarinic responses, muscarinic receptor subtypes, second messengers.
Separation and modulation of calcium currents in bullfrog sympathetic neurons
Authors: Jones Stephen W. , Elmslie Keith S.
Published: April 2011

The calcium current of frog sympathetic neurons has relatively rapid activation kinetics (τ < 3 ms) in response to changes in voltage. Pharmacologically, the current is blocked ~90% by ω-conotoxin, but < 10% by dihydropyridine antagonists. This suggests that nearly all of the current is N type. However, inactivation is slow and incomplete even for depolarizations lasting > 1 s, consistent with recent evidence that N-type channels do not always inactivate rapidly. The calcium current is partially inhibited via receptors for acetylcholine, luteinizing hormone releasing hormone, substance P, ATP, and norepinephrine. These effects are mimicked by internal dialysis with GTP-γ-S, suggesting involvement of a G protein. The transmitters affect the activation kinetics of the calcium current in a voltage-dependent manner, which can be modeled as a reversible shift of some channels to "reluctant" states in which strong depolarization is needed to produce channel opening. The effects of transmitters develop and recover with t½ ~ 1–2 s, so if a second messenger is involved in receptor – calcium channel coupling, it must act rapidly.Key words: norepinephrine, ω-conotoxin, dihydropyridine, inactivation, G protein.
Intracellular Ca2+ dynamics in response to Ca2+ influx and Ca2+ release in autonomic neurones
Authors: Kuba Kenji , Nohmi Mitsuo , Hua Shao-Ying
Published: April 2011

Spatial and temporal changes in the intracellular free Ca2+ concentration in response to Ca2+ influx at the cell membrane and to Ca2+ release from intracellular organelles were studied by recording fluorescence of Ca2+-sensitive probes, fura 2 or indo 1, with conventional epifluorescence or confocal laser-scanning microscopy combined with recordings of Ca2+-dependent membrane responses in bullfrog sympathetic ganglion cells. It was found that an increase in the intracellular Ca2+ induced by (an) action potential(s) in freshly isolated ganglion cells bathed in Ringer's solution was solely a result of Ca2+ influx, while a rise in the intracellular Ca2+ by Ca2+ current in voltage-clamped cultured neurones was caused by not only Ca2+ influx but also Ca2+ release. This Ca2+ release was suggested to occur by a voltage-dependent (and graded) mode of activation of a Ca2+-induced Ca2+ release mechanism, explaining the lack of Ca2+ release by action potentials (because of their short-lasting depolarization) in freshly isolated neurones. In both cases, there was an inward spread of an increase in intracellular Ca2+. On the other hand, all or nothing activation of Ca2+-induced Ca2+ release occurred in the presence of caffeine, leading to the oscillation of Ca2+ in the cells. Characteristics of this mode of Ca2+ release and unique properties of drugs to block Ca2+ release were described. Finally, the physiological significance of different types of Ca2+ release was discussed.Key words: Ca2+ current, Ca2+-induced Ca2+ release, Ca2+ transient, confocal microscope, bullfrog sympathetic ganglion cells.
The calyx-type synapse of the chick ciliary ganglion as a model of fast cholinergic transmission
Authors: Stanley E. F.
Published: April 2011

The calyx-type synapse of the embryonic chick ciliary ganglion is reviewed as a model of transmitter release from a vertebrate presynaptic nerve terminal. This nerve terminal is extensive in area, enabling the penetration with microelectrodes and the application of patch-clamp techniques. In other respects the calyx synapse is a typical fast-transmitting cholinergic nerve terminal. This synapse has been used to obtain the first recordings of action potentials and calcium currents in a vertebrate presynaptic nerve terminal and is the only preparation in which it has proved possible to record single calcium channels directly from the transmitter release sites. The calyx remains a powerful experimental preparation for the further analysis of the mechanism and control of neurotransmitter release in fast-transmitting nerve terminals.Key words: synaptic transmission, presynaptic, transmitter release, acetylcholine release, calcium channels.
Ions, water, and energy in brain cells: A synopsis of interrelations
Authors: Hertz Leif , Code William E. , Sykova Eva
Published: April 2011

A brief summary is given of some of the key points of the individual contributions at this International Brain Research Organization satellite meeting, presenting up-to-date, expert knowledge of energy metabolism, ionic turnover, and cell swelling at the cellular level of the mammalian central nervous system. On the basis of this material, we are also suggesting a unified concept of reciprocal interactions between metabolism, ion carriers, and ion channels, which are of crucial importance for the function of the central nervous system.Key words: energy metabolism, ion transport, neurons, swelling, pH regulation, astrocytes.
Coupling of metabolism and electrical activity in cortical astrocytes
Authors: Walz Wolfgang
Published: April 2011

Cortical mouse astrocytes in culture were impaled with two-channel microelectrodes. These mouse astrocytes have the same responses to different K+ concentrations, ouabain, and glutamate as cultured rat astrocytes, with the exception that a large barium-sensitive K+ conductance clamps the membrane potential at the K+ equilibrium potential. Glycolytic and mitochondrial inhibitors have little effect on the mouse astrocytes. Total blockade of energy metabolism leads to an irreversible, calcium-dependent depolarization, but only if applied for longer than 45 min. Increasing the extracellular K+ concentration to 60 mM increases the intracellular K+ concentration by 43 mM and the bicarbonate concentration by 22 mM and leads to a concomitant fast swelling. Together with the 20 mM increse in Cl− concentration reported in the literature this is a good indication for a Boyle- and Conway-mediated K+–anion influx with water. This influx is accomplished by the depolarization-induced opening of Cl− channels as reported in the literature. In conclusion, ischemia-like conditions have little direct, immediate impact on astrocytes. In contrast, ischemia-induced release of substances from neurones, such as K+, produces an immediate and fast response.Key words: astrocytes, energy metabolism, glial cells, ischemia, potassium channels, swelling.
Ca2+ and filopodial responses to glutamate in cultured astrocytes and neurons
Authors: Cornell-Bell A. H. , Thomas P. G. , Caffrey J. M.
Published: April 2011

Neurons and glia exhibit complex homeostatic interactions via shared extracellular space which can involve metabolites, inorganic ions, and neurotransmitters. Focal application of glutamate to both human and rat central nervous system astrocytes in primary culture produced a rapid, transient increase in both cytoplasmic and nuclear Ca2+. These Ca2+ waves can propagate at up to 15–20 μm/s for long distances (millimetres) through the astrocyte syncitium. Oscillatory Ca2+ signals were frequently observed under control conditions and were enhanced by glutamate application. These Ca2+ signals were paralleled by rapid extensions of filopodia from the astrocyte cell margin and apical surface near the point of glutamate application. Focal application of glutamate to rat hippocampal neurons also elicited rapid, transient increases in intracellular Ca2+. Levels of Ca2+ signals were consistently two- to three-fold greater in pyramidal neurons cultured from CA1 than in those from CA3. Filopodial extension was extensive in CA1 neurons, but rare in CA3 neurons, and in either case observable only during the first few days of primary culture. Diversity of glial and neuronal responses to binding the glutamate receptors may reflect their roles in homeostatic interactions.Key words: glutamate, astrocytes, hippocampal neurons, Ca2+ signals, filopodia.
Mechanisms of spreading depression: a review of recent findings and a hypothesis
Authors: Somjen G. G. , Aitken P. G. , Czéh G. L. , Herrearas O. , Jing J. , Young J. N.
Published: April 2011

Spreading depression of Leão (SD) can be provoked by numerous nonspecific mechanical, electrical, and chemical stimuli. A similar, if not identical, phenomenon can be provoked by hypoxia. SD is characterized by drastic depolarization of neurons, severe reduction of membrane resistance, and redistribution of ions across cell membranes. Glial cells also depolarize but retain membrane resistance. Tetraethylammonium hastens the onset of hypoxic SD but reduces the sustained potential shift and K+ outflow from cells; 4-aminopyridine also accelerates SD but has no effect on the voltage shift. N-Methyl-D-aspartate receptor antagonists delay the onset of SD, while nickel and cobalt reduce the amplitude of SD-related redistribution of Ca2+. Yet, no specific blocker of SD has been found. Microdialysis of high-K+ solution in hippocampal CA1 region induces recurrent waves of SD propagating semi-independently in adjacent tissue layers, and a prolonged unstable depressed state that has not previously been described. Neither the release of K+ ions nor of glutamate is the unique agent of SD propagation. On the basis of recent findings we propose a hypothetical sequence of events that reconcile many of the previously seemingly paradoxical observations.Key words: spreading depression, membrane resistance, membrane ion currents, extracellular potassium, extracellular calcium.
The regulation of pH in the central nervous system
Authors: Schlue W.-R. , Dörner R.
Published: April 2011

The pHi regulation from intracellular acidosis in the central nervous system appears to be mediated by mechanisms driven by the large inwardly directed Na+ gradient. The involvement of these mechanisms in pHi regulation of neurones and glial cells has been investigated in the leech central nervous system using ion-selective microelectrodes. For recovery from acidification, there appear to be three separate mechanisms: Na+/H+ exchange, Na+-dependent Cl−/HCO3− exchange, and Na+–HCO3− cotransport. All three mechanisms have a profound effect on the maintenance of pHi homeostasis in glial ceils; whereas in leech neurones, as in other neuronal cells studied previously, the predominant mechanisms are Na+/H+ and Na+-dependent Cl−/HCO3− exchange. In addition to acid extrusion mechanisms we also found evidence for Na+-independent Cl−/HCO3− exchange. At alkaline pHi this exchanger may mediate some of the pHi recovery from intracellular alkalinization.Key words: central nervous system, pH regulation, neurotransmitter.
The regulation of intracellular pH in cultured astrocytes and neuroblastoma cells, and its dependence on extracellular pH in a HCO3-free solution
Authors: Mellergård Pekka E. , Ouyang Yi-Bing , Siesjö Bo K.
Published: April 2011

Microspectrofluorometry was used to study the regulation of intracellular pH (pHi) in 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)-loaded astrocytes and the neuroblastoma–glioma cells of the NG 108-15 line. The cells rapidly regulated pHi during an acid transient induced by an NH4+ prepulse. This regulation was blocked by removal of Na+, or by addition of 1 mM amiloride. The back regulation was also inhibited when extracellular pH (pHe) was lowered. Furthermore, when cells were exposed to buffer with reduced or increased pHe, pHi changed in parallel. Thus, although these cells possess at least one efficient H+ extrusion mechanism, which is likely to be the ubiquitous Na+/H+ antiporter, they fail to regulate pHi, to a normal value unless pHe is held constant. The implications of these findings are discussed.Key words: astrocyte, NG 108-15 cell line, extracellular pH, intracellular pH, Na+/H+ antiporter.