cyclic-gmp and Brain-Injuries

Outcome of traumatic brain injury (TBI) is impaired by hyperglycemia, hypotension, and glutamate, and improved by insulin. Insulin reduces glutamate concentration, making it uncertain whether its beneficial effect accrues from euglycemia. Glucagon decreases CNS glutamate, lessens neuronal cell injury, and improves neurological scores in mice after TBI. In vitro, glucagon limits NMDA-mediated excitotoxicity by increasing cAMP and protein kinase A (PKA). NMDA receptor activation couples cerebral blood flow (CBF) to metabolism. Dilation induced by NMDA is impaired after fluid percussion brain injury (FPI) due to upregulation of endogenous tPA, which further disturbs cerebral autoregulation during hypotension after fluid percussion injury (FPI). We hypothesized that glucagon prevents impaired NMDA receptor-mediated dilation after FPI by upregulating cAMP, which decreases release of tPA. NMDA-induced pial artery dilation (PAD) was reversed to vasoconstriction after FPI. Glucagon 30 min before or 30 min after FPI blocked NMDA-mediated vasoconstriction and restored the response to vasodilation. PAD during hypotension was blunted after FPI, but protected by glucagon. Glucagon prevented FPI-induced reductions in CSF cAMP, yielding a net increase in cAMP, and blocked FPI-induced elevation of CSF tPA. Co-administration of the PKA antagonist Rp 8Br cAMPs prevented glucagon-mediated preservation of NMDA-mediated dilation after FPI. The pKA agonist Sp 8Br cAMPs prevented impairment of NMDA-induced dilation. These data indicate that glucagon protects against impaired cerebrovasodilation by upregulating cAMP, which decreases release of tPA, suggesting that it may provide neuroprotection when given after TBI, or prior to certain neurosurgical or cardiac interventions in which the incidence of perioperative ischemia is high.

Topics: Analysis of Variance; Animals; Brain Injuries; Cerebral Cortex; Cerebrovascular Circulation; Cyclic GMP; Enzyme-Linked Immunosorbent Assay; Glucagon; Homeostasis; Hypotension; Neurons; Receptors, N-Methyl-D-Aspartate; Swine; Up-Regulation; Vasodilation

Atrial natriuretic peptide (ANP) plays an important role in the regulation of water and sodium in the body via cyclic GMP (cGMP) pathway. Although ANP has been shown to be protective in cerebral ischemia or intracerebral hemorrhage, its role in traumatic brain injury (TBI) has yet to be elucidated. We herein assessed ANP effects on brain water and sodium in TBI. Controlled cortical impact (3 mm depth, 6 m/sec) was used to induce an experimental cortical contusion in rats. Continuous administration of ANP 0.2 (n = 6) or 0.7 microg/kg/24 h (n = 6), cGMP analogue (8-Bromo-cGMP) 0.1 (n = 5) or 0.3 mg/kg/24 h (n = 5), or vehicle (n = 6) was begun 15 minutes after injury, using a mini-osmotic pump implanted into the peritoneal cavity. At 24 hours after injury, ANP significantly exacerbated brain edema in the injured hemisphere in a dose-dependent manner while it reduced brain sodium concentrations in both hemispheres. These ANP effects could be mimicked by a cGMP analogue. In the second series (n = 20), BBB integrity was assessed by evaluating the extravasation of Evans blue dye. ANP or cGMP analogue significantly worsened BBB disruption in the injured hemisphere at 24 hours after injury. These findings suggest that ANP administration exacerbates brain edema after the experimental cortical contusion in rats, possibly because of an increase in the BBB permeability via cGMP pathway, whereas it reduces brain sodium levels.

Topics: Animals; Atrial Natriuretic Factor; Blood-Brain Barrier; Body Weight; Brain Injuries; Coloring Agents; Cyclic GMP; Electrolytes; Evans Blue; Injections, Intraperitoneal; Male; Potassium; Rats; Rats, Sprague-Dawley; Sodium; Water; Water-Electrolyte Balance

This study examined whether NMDA-stimulated cyclic GMP levels were altered at two different time points following lateral fluid percussion injury. At 60 min and 15 days postinjury, the left and right hippocampi were dissected and chopped into mini-prisms. Each hippocampus was divided into five equal parts and incubated with either the phosphodiesterase inhibitor IBMX (3-isobutyl-1-methylxanthine, 500 microM) alone, IBMX and N-methyl-D-aspartic acid (NMDA) OR IBMX, NMDA, and glycine (10 MM). Two concentrations of NMDA were used: 500 or 1,000 microM. Tissues were then assayed for levels of cyclic GMP. Results indicated that there were no changes in basal levels of cyclic GMP at either postinjury time point. At 60 min postinjury, there were no significant main effects for injury or drug concentration. There was a significant injury x side interaction effect with increased levels of NMDA-stimulated cyclic GMP in the hippocampus ipsilateral to the injury impact and decreased cyclic GMP levels in the contralateral hippocampus. There were no significant alterations in NMDA-stimulated cyclic GMP levels at 15 days postinjury. The data from this study indicated that NMDA-stimulated cyclic GMP accumulation is differentially altered in the hippocampus ipsilateral and contralateral to the site of the injury at 1 h after injury, but is normalized by 15 days postinjury. These findings implicate NMDA-mediated intracellular signaling processes in the acute excitotoxic response to injury.

Topics: Animals; Brain Injuries; Cognition Disorders; Cyclic GMP; Disease Models, Animal; Functional Laterality; Hippocampus; Male; N-Methylaspartate; Percussion; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Time Factors

We investigated the role of nitric oxide (NO) in the vascular response to high extraluminal K(+)-concentrations in the in vitro model of isolated rat middle cerebral arteries (MCA). Under control conditions, rat MCA dilated at 20, 30, 40 and 60 mM K(+). At 80 mM K(+), a slight vasoconstriction occurred. The unspecific NO synthase (NOS)-inhibitor L(omega)-nitro-L-arginine (L-NNA) increased the resting tone at 3 mM K(+) by 31+/-5% (P<0.01). While the vasodilatative effect of 20 mM K(+) was unaffected by L-NNA, NOS-inhibition resulted in vasoconstriction at > or = 40 mM K(+) (P<0.01). In presence of L-NNA, the basal vessel diameter was restored by either the NO-donor S-nitroso-N-acetylpenicillamine (SNAP) or the cell-permeable guanosine-3',5'-cyclic monophosphate (cGMP) analogue 8-Br-cGMP. Co-application of L-NNA with either SNAP or 8-Br-cGMP resulted in partial restitution of the vasodilatative effect of 40 mM K(+), respectively. In presence of the soluble guanylyl cyclase inhibitor 1 H-[l,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), the vascular response to 40 mM K(+) was abolished. Our findings together with findings from the literature indicate a modulator role of NO at K(+) > or = 40 mM K(+), involving a cGMP-dependent mechanism.

Topics: Animals; Brain Injuries; Cerebrovascular Circulation; Cyclic GMP; Enzyme Inhibitors; Extracellular Space; Male; Middle Cerebral Artery; Models, Biological; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Organ Culture Techniques; Oxadiazoles; Penicillamine; Potassium; Potassium Channels; Quinoxalines; Rats; Rats, Wistar; S-Nitroso-N-Acetylpenicillamine; Vasodilation

BACKGROUND AND PURPOSE--Endothelin-1, in concentrations similar to that present in cerebrospinal fluid after fluid percussion brain injury (FPI), increases superoxide anion (O2-) production. Endothelin-1 also contributes to altered cerebral hemodynamics after FPI through impairment of ATP-sensitive K+ (KATP) channel function through protein kinase C (PKC) activation. Generation of O2- additionally occurs after FPI. Nitric oxide and cGMP elicit pial artery dilation through KATP channel activation. The present study was designed to determine whether PKC activation generates O2-, which, in turn, could link such activation to impaired KATP channel function after FPI. METHODS--Injury of moderate severity (1.9 to 2.1 atm) was produced by the lateral FPI technique in anesthetized newborn pigs equipped with a closed cranial window. Superoxide dismutase-inhibitable nitroblue tetrazolium (NBT) reduction was determined as an index of O2- generation. RESULTS--Phorbol 12, 13-dibutyrate (10(-6) mol/L), a PKC activator, increased superoxide dismutase-inhibitable NBT reduction from 1+/-1 to 37+/-5 pmol/mm2. Staurosporine (10(-7) mol/L), a PKC antagonist, blocked the NBT reduction after phorbol 12,13-dibutyrate and blunted the NBT reduction observed after FPI (1+/-1 to 15+/-2 versus 1+/-1 to 5+/-1 pmol/mm2 after FPI in the absence versus presence of staurosporine). Exposure of the cerebral cortex to a xanthine oxidase O2--generating system increased NBT reduction in a manner similar to FPI and blunted pial artery dilation to the KATP channel agonists cromakalim and calcitonin gene-related peptide, the nitric oxide releasers sodium nitroprusside and S-nitroso-N-acetylpenicillamine, and the cGMP analogue 8-bromo-cGMP (10+/-1% and 21+/-1% versus 4+/-1% and 9+/-1% for 10(-8) and 10(-6) mol/L cromakalim before and after activated oxygen-generating system exposure). CONCLUSIONS--These data show that PKC activation increases O2- production and contributes to such production observed after FPI. These data also show that an activated system that generates an amount of O2- similar to that observed with FPI blunted pial artery dilation to KATP channel agonists and nitric oxide/cGMP. These data suggest, therefore, that O2- generation links PKC activation to impaired KATP channel function after FPI.

Topics: Adenosine Triphosphate; Animals; Animals, Newborn; Arterioles; Brain; Brain Chemistry; Brain Injuries; Calcitonin Gene-Related Peptide; Carrier Proteins; Cerebral Arteries; Cromakalim; Cyclic GMP; Enzyme Activation; Female; Male; Membrane Proteins; Nitroprusside; Oxygen; Pia Mater; Potassium Channels; Protein Kinase C; Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; Superoxides; Swine; Vasodilation; Vasodilator Agents; Vesicular Transport Proteins; Xanthine Oxidase

Previous studies observed that endothelin-1 (ET-1) contributed to ATP-sensitive K+ (K(ATP)) channel impairment 1 h following fluid percussion brain injury (FPI) in the newborn pig. The present study was designed to determine the effect of FPI on K(ATP) channel activity as a function of time in newborn (1-5 days old) and juvenile (3-4 weeks old) pigs equipped with a closed cranial window. FPI of moderate severity (1.9-2.1 atm) was produced by using a pendulum to strike a piston on a saline-filled cylinder that was fluid coupled to the brain via a hollow screw inserted through the cranium. Cromakalim, a K(ATP) agonist, produced dilation that was blunted for at least 72 h post FPI, but dilator responsiveness was restored within 168 h post FPI in the newborn pig (15+/-1% and 27+/-2% vs. 5+/-1% and 11+/-1% vs. 13+/-1% and 26+/-2% for responses to 10(-8), 10(-6) M cromakalim before, and 72 and 168 h after FPI). Similar inhibited responses were observed for calcitonin gene-related peptide, 8-Bromo cGMP, and the nitric oxide (NO) releasers SNP and SNAP. In contrast, cromakalim-induced dilation was blunted for at least 4 h, but dilator responsiveness was restored within 8 h post FPI in the juvenile pig (15+/-1% and 27+/-1% vs. 9+/-1% and 15+/-2% vs. 18+/-1% and 28+/-1% for 10(-8), 10(-6) M cromakalim before, and 4 and 8 h post FPI). Similar inhibition of dilations of other agonists also occurred in the juvenile. CSF ET-1 increased to a greater level and remained elevated for a longer period of time in the newborn compared to the juvenile pig. BQ123, an ET-1 antagonist, pretreatment partially restored decremented agonist induced dilation following FPI in the newborn and juvenile pig (5+/-1% and 11+/-1% vs. 11+/-1% and 21+/-1% for responses to 10(-8), 10(-6) M cromakalim 72 h post FPI in the newborn in the absence and presence of BQ123). These data indicate that K(ATP) channel function is impaired to a greater extent and for a longer time period in the newborn versus the juvenile pig. These data also show that ET-1 contributes to such impaired vascular responsiveness to a greater extent in the newborn versus the juvenile pig. These data furthermore suggest that the newborn is more sensitive to traumatic vascular injury than the juvenile.

Topics: Aging; Animals; Animals, Newborn; Arterioles; Brain; Brain Injuries; Calcitonin Gene-Related Peptide; Cerebrovascular Circulation; Cromakalim; Cyclic GMP; Endothelin Receptor Antagonists; Endothelin-1; Female; Male; Nitric Oxide Donors; Penicillamine; Peptides, Cyclic; Pia Mater; Potassium Channels; S-Nitroso-N-Acetylpenicillamine; Swine; Vasodilation

Previous studies have observed that ATP- and calcium-sensitive K+ (KATP and Kca) channel function is impaired after fluid percussion brain injury (FPI). The present study was designed to characterize the effect of FPI on prostaglandin (PG)E2 and 12 pial artery dilation and the role of activation of these K+ channels in that dilation in newborn pigs equipped with a closed cranial window. FPI of moderate severity (1.9-2.1 atm) was produced by using a pendulum to strike a piston on a saline-filled cylinder that was fluid coupled to the brain via a hollow screw inserted through the cranium. PGE2 vasodilation was blunted by FPI (9+/-1%, 13+/-1%, and 19+/-1% vs. 2+/-1%, 5+/-1%, and 9+/-1%, for 1, 10, and 100 ng/ml PGE2 before and after FPI, respectively). PGE2 dilation was associated with increased CSF cGMP and cAMP concentration and such changes in cyclic nucleotides were blunted by FPI (448+/-10 and 793+/-38 vs. 316+/-11 and 403+/-27 fmol/ml for control and PGE2 induced change in cGMP before and after FPI, respectively). PGI2-induced dilation and associated changes in CSF cyclic nucleotide concentration were similarly blunted by FPI. PGE2 dilation was attenuated by either glibenclamide or iberiotoxin, KATP and K,ca channel antagonists, and coadministration of both K+ channel antagonists further decremented the dilator response (9+/-1%, 14+/-1%, and 21+/-1%; vs. 4+/-1%, 7+/-1%, and 12+/-1%; vs. 2+/-1%, 4+/-1%, and 7+/-1%, for 1, 10, and 100 ng/ml PGE2 during control, after glibenclamide, and after combined glibenclamide and iberiotoxin, respectively). Glibenclamide and iberiotoxin had similar effects on PGI2 dilation. These data show that prostaglandin dilation is attenuated after FPI. These data also show that prostaglandin dilation is dependent on activation of both KATP and Kca channels. Further, these data suggest that attenuated prostaglandin dilation following FPI results from diminished prostaglandin-associated elevation in cyclic nucleotide concentration and impaired KATP and Kca channel function.

Topics: Animals; Animals, Newborn; Arterioles; Blood Gas Analysis; Brain Chemistry; Brain Injuries; Calcium Channels; Cerebral Arteries; Cerebrovascular Circulation; Cyclic AMP; Cyclic GMP; Dinoprostone; Epoprostenol; Female; Glyburide; Hypoglycemic Agents; Male; Peptides; Pia Mater; Potassium Channels; Swine; Vasodilation

Traumatic injury is the leading cause of death for infants and children, and mortality is increased with head injury. Previous studies have shown that pial arteries constricted and that responses to several nitric oxide (NO)-dependent dilator stimuli were blunted after fluid percussion injury (FPI) in newborn pigs. Membrane potential of vascular muscle is a major determinant of vascular tone, and activity of K+ channels is a major regulator of membrane potential. Recent data show that the NO releasers sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) and 8-bromo-cGMP elicit dilation via ATP-sensitive K+ channel (KATP) activation. The present study was designed to investigate the effect of FPI on KATP channel function.. Chloralose-anesthetized newborn pigs equipped with a closed cranial window were connected to a percussion device that consisted of a saline-filled cylindrical reservoir and a metal pendulum. Brain injury of moderate severity (1.9 to 2.1 atm) was produced by allowing the pendulum to strike a piston on the cylinder. Pial artery diameter was measured with a video microscaler. Data were analyzed by repeated measures ANOVA. An alpha level of P < .05 was considered significant.. FPI blunted dilation to cromakalim (10(-8), 10(-6) mol/L), a KATP agonist (10 +/- 1% and 27 +/- 2% versus 3 +/- 1% and 7 +/- 2% before and after FPI, respectively, n = 8). Similarly, FPI blunted dilation to calcitonin gene-related peptide, an endogenous KATP activator. FPI also blunted dilator responses to SNP, S-nitroso-N-acetylpenicillamine, and 8-bromo-cGMP (10(-6) to 10(-8) mol/L) (10 +/- 1% and 20 +/- 1% versus 2 +/- 1% and 8 +/- 2% for SNP before and after FPI; 9 +/- 1% and 16 +/- 1% versus 2 +/- 1% and 4 +/- 1% for 8-bromo-cGMP before and after FPI, respectively, n = 8). In contrast, responses to papaverine and brain natriuretic peptide were unchanged after FPI.. These data show that KATP channel function is impaired after FPI. Furthermore, these data suggest that impaired function of mechanisms distal to NO synthase contribute to altered cerebral hemodynamics after FPI.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Triphosphate; Animals; Animals, Newborn; Blood; Brain Injuries; Cerebral Arteries; Cyclic AMP; Cyclic GMP; Female; Male; Nitric Oxide; Pia Mater; Potassium Channels; Swine; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents; Wounds, Nonpenetrating

The present study was designed to investigate the effect of fluid percussion brain injury (FPI) on vasopressin-induced pial artery vasodilation and the role of superoxide anion generation in those observed effects. In the piglet, it was observed previously the FPI produces pial artery constriction associated with free radical generation. Anesthetized piglets equipped with a closed cranial window were connected to a percussion device consisting of a saline-filled cylindrical reservoir with a metal pendulum. FPI of moderate severity (1.9-2.3 atm) was produced by allowing the pendulum to strike a piston on the cylinder. Vasopressin in physiological and pharmacological concentrations (10 and 1,000 microU/ml) produced vasodilation that was reversed to constriction after FPI (15 +/- 1 vs. -8 +/- 1 and 25 +/- 1 vs. 13 +/- 1% for 10 and 1,000 microU/ml before and after injury, respectively). Vasopressin-induced dilation was associated with increased cerebrospinal fluid guanosine 3', 5'-cyclic monophosphate, and these biochemical changes were blunted by FPI (407 +/- 12 and 720 +/- 28 vs. 4 and 272 +/- 5 fmol/ml for control and 10 microU/ml before and after injury, respectively). In contrast, polyethylene glycol superoxide dismutase (PEG-SOD) and catalase pretreatment 30 min before FPI partially restored vasopressin-induced pial artery dilation (14 +/- 1 vs. 3 +/- 1 and 22 +/- 1 vs. 2 +/- 4% for 10 and 1,000 microU/ml before and after FPI, respectively). Similarly, biochemical changes associated with vasopressin dilation were also partially restored by PEG-SOD and catalase after FPI. These data show that vasopressin is reversed from a dilator to a vasoconstrictor after FPI and suggests the superoxide anion generation contributes to the alteration of vasopressin cerebrovascular effects after injury and that such altered vasopressin cerebrovascular effects contribute to pial vasoconstriction after FPI.

Topics: Animals; Blood Pressure; Brain Injuries; Catalase; Cerebral Arteries; Cyclic GMP; Female; Male; Nitric Oxide Synthase; Nitroarginine; Pia Mater; Polyethylene Glycols; Superoxide Dismutase; Swine; Vasodilation; Vasopressins

This study was designed to investigate the effect of fluid percussion brain injury on opioid-induced pial artery vasodilation in the newborn pig. Previous observations have shown that brain injury produces pial artery vasoconstriction associated with elevated cerebral spinal fluid (CSF) opioid levels in the piglet. Additionally, opioids produce pial vasodilation that is attenuated by the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA). Anesthetized newborn pigs equipped with a closed cranial window were connected to a percussion device consisting of a saline-filled cylindrical reservoir with a metal pendulum. Brain injury of moderate severity (1.9-2.3 atm) was produced by allowing the pendulum to strike a piston on the cylinder. Methionine enkephalin (Met), an endogenous mu-opioid agonist in physiological and pharmacological concentrations (10(-10), 10(-8), 10(-6) M), produced vasodilation that was attenuated following brain injury (7 +/- 1 vs. 3 +/- 1%, 11 +/- 1 vs. 5 +/- 1% and 16 +/- 1 vs. 8 +/- 1% for 10(-10), 10(-8), 10(-6) M Met before and after injury, respectively, n = 5). Met-induced dilation was associated with increased cortical periarachnoid CSF guanosine 3',5'-cyclic monophosphate (cGMP), and these biochemical changes were blunted by brain injury (342 +/- 12 and 640 +/- 13 fmol/ml vs. 267 +/- 6 and 321 +/- 17 fmol/ml for control and Met 10(-6) M before and after injury, respectively, n = 5). Leucine enkephalin, an endogenous delta-agonist, induced pial dilation and associated changes in CSF cGMP, which were similarly altered by brain injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood Pressure; Brain Injuries; Cerebral Arteries; Cyclic GMP; Endorphins; Female; Male; Narcotics; Pia Mater; Receptors, Opioid; Swine; Vasodilation; Wounds, Nonpenetrating