Biomedical subjects

C W Leffler

Publications and source records attributed to C W Leffler.

At least 55 records · Page 3Linked to original sources

PubMed1997

Cerebral arteriolar dilation to hypoxia: role of prostanoids.

Experiments addressed the hypothesis that dilator prostanoids contribute to maintenance of low cerebral microvascular tone during hypoxia in the newborn. Anesthetized newborn pigs equipped with closed cranial windows were used to measure responses of pial arterioles (approximately 60 microns) to treatments. Hypoxia (Pao2 approximately equal to 25 mmHg) caused dilation of pial arterioles (approximately 50% increase in diameter). Hypoxia (5 min) caused an increase in cortical cerebrospinal fluid 6-ketoprostaglandin F1 alpha concentration from 907 +/- 171 (normoxia) to 1,408 +/- 213 pg/ml (hypoxia). Pretreatment with indomethacin (5 mg/kg) did not affect pial arteriolar dilation to hypoxia. Conversely, indomethacin treatment during hypoxia caused a rapid decrease in arteriolar diameter to nearly the normoxia diameter within 3 min, returning to the original hypoxia diameter by 10 min. Ibuprofen treatment (30 mg/kg) had no effect on pial arteriolar diameter during normoxia or hypoxia, and pretreatment did not alter dilation to hypoxia. However, pretreatment with ibuprofen abolished the constrictor effect of indomethacin given during hypoxia. These data suggest that the primary mechanism by which hypoxia produces cerebral vasodilation does not involve prostanoids, but prostanoids can contribute to cerebral vasodilation in response to hypoxia.

6-Ketoprostaglandin F1 alpha↗

PubMed1997

Mechanisms of hypoxia-induced cerebrovascular dilation in the newborn pig.

The hypothesis that endothelium-dependent components contribute to the cerebromicrovascular dilation to hypoxia in the newborn pig was addressed. Piglets anesthetized with ketamine-acepromazine and maintained on alpha-chloralose were equipped with closed cranial windows. Injury to the endothelium of pial arterioles was produced by light activation of fluorescein dye. Light/dye injury reduced the pial arteriolar dilation to hypoxia (5 min, arterial PO2 approximately 30 mmHg) from 57 +/- 9 to 19 +/- 5%. Light/dye injury abolished the pial arteriolar dilation to hypercapnia but did not affect dilation to sodium nitroprusside. The pial arteriolar dilation to hypoxia was not affected by tetrodotoxin, N(omega)-nitro-L-arginine, glibenclamide, iberiotoxin, charybdotoxin, tetraethylammonium, or 8-phenyltheophylline. Hypoxia caused increases in the cerebral cortical production of adenosine 3',5'-cyclic monophosphate and guanosine 3',5'-cyclic monophosphate. Cerebral vasodilation to hypoxia was inhibited by 5,8,11,14-eicosatetraynoic acid but was not greatly affected by cyclooxygenase or lipoxygenase inhibitors. In contrast, the cytochrome P-450 epoxygenase inhibitor miconazol decreased cerebral vasodilation to hypoxia from 45 +/- 5 to 17 +/- 4%. Therefore, the vascular endothelium appears to participate in cerebral microvascular dilation to hypoxia in newborn pigs. The mechanism may include cytochrome P-450 epoxygenase metabolites of arachidonic acid.

5,8,11,14-Eicosatetraynoic Acid↗

PubMed1997

Newborn piglet cerebral microvascular responses to epoxyeicosatrienoic acids.

The present study on the newborn pig cerebral microcirculation determined the vasoactive properties of epoxyeicosatrienoic acids (EETs) and the contributions of prostaglandin cyclooxygenase to these properties. Pial arterioles of anesthetized piglets were observed through closed cranial windows, EETs were applied topically, and artificial cerebrospinal fluid from beneath the cranial windows was collected for the determination of adenosine 3',5'-cyclic monophosphate and 6-ketoprostaglandin F1 alpha. EETs caused dilation of pial arterioles and increased adenosine 3',5'-cyclic monophosphate. 5,6-EET produced a dose-dependent dilation at 10(-8) M and above, whereas 10(-6) M was required for 8,9-EET, 11,12-EET, and 14,15-EET. Indomethacin abolished pial arteriolar dilation to the EETs. However, EETs did not increase cortical 6-ketoprostaglandin F1 alpha concentration. Treatment of indomethacin-treated piglets with iloprost (10(-12) M topically) restored dilation to 5,6-EET. Neither isoproterenol nor sodium nitroprusside allowed vasodilation to 5,6-EET in indomethacin-treated piglets. Therefore, in the newborn pig cerebral microvasculature. EETs are potent vasodilators and prostacyclin-receptor agonists are necessary to allow this dilation to occur.

6-Ketoprostaglandin F1 alpha↗

PubMed1997

Role of lysophosphatidic acid in endothelin-1- and hematoma-induced alteration of cerebral microcirculation.

Cerebral hematoma increases cerebrospinal fluid (CSF) endothelin-1 (ET-1). Inhibitors of ET-1 synthesis prevent this increment and hematoma-induced modification of cerebral arteriolar reactivity. We hypothesized that intrathecal ET-1 injection could 1) modify pial arteriolar reactivity similarly to hematoma; 2) increase CSF lysophosphatidic acid (LPA), a potential contributor to altered cerebrovascular reactivity; and 3) reduce the level of adenosine 3',5'-cyclic monophosphate (cAMP) in the CSF. Either ET-1 (10(-7) M) or artificial CSF was injected over the left parietal cortex of newborn pigs. Four days later, cranial windows were implanted. CSF ET was increased from a basal level of 11 fmol/ml to 18 fmol/ml 4 days after ET-1 injection, whereas CSF cAMP was reduced from 2,700 to 950 fmol/ml. The mean diameter of pial arterioles was reduced 31%. In control animals, 10(-12) M ET caused dilation, and higher concentrations induced vasoconstriction. Four days after ET-1 injection topical ET-1 caused constriction instead of dilation at 10(-12) M, and constrictions at higher doses were enhanced. Norepinephrine-induced constrictions were potentiated in the ET-1-injected group. Dilations to cAMP-dependent (but not independent) vasodilators were attenuated after ET-1. The concentration of the vasoconstrictor lipid mediator LPA increased approximately fourfold. Thus intrathecal injection of ET-1 mimics hematoma-induced modification of cerebral vascular reactivity and increase in LPA production. The mechanism(s) of ET-1- and hematoma-induced modifications may involve LPA, which is known to contribute to the loss of dilator responses by inhibition of cAMP product on. The present study further suggests that ET-1 together with LPA could be causing changes in cerebrovascular reactivity following cerebral hemorrhage. ET-1 stimulates the release of LPA from brain parenchyma independent of serum so that LPA could serve as a secondary mediator.

Animals↗

PubMed1997

The effects of treatment with indomethacin on the cerebral vasculature of newborn piglets before and during hemorrhagic hypotension.

Substantial physiologic data point to a significant role for dilator prostanoids in the regulation of cerebral vascular tone in newborn pigs. This study begins to address the hypothesis that multiple dilator systems, including prostanoids, can provide for the initiation and maintenance of cerebral vasodilation in response to hypotension. Piglets were anesthetized, and cranial windows were implanted. Hypotension was achieved by hemorrhage to 50% of the control arterial pressure and maintained for 10 min. Each piglet served as its own control by the induction of hypotension and return to normotension before treatment. Pial arterioles dilated (38 +/- 5% increase in diameter) in response to hypotension. Pretreatment with indomethacin (5 mg/kg i.v.) at 20 min and immediately before hypotension did not block this response (28 +/- 7% and 23 +/- 9% increase in diameter, respectively). In contrast, when indomethacin was administered 10 min into the hypotensive period, the dilated arterioles (106 +/- 6 microns) constricted to the normotensive diameter (75 +/- 5 microns) and remained constricted for the duration of the observation. These findings suggest that compensatory mechanisms provide for cerebral vasodilation when prostanoid synthesis and prostacyclin receptors are blocked before hemorrhagic hypotension. However, removal of prostanoids after vasodilation is established in response to hypotension causes constriction without compensation from alternative mechanisms. Awareness of these findings may be important when considering giving indomethacin to sick preterm infants during periods of cardiac instability.

Animals↗

PubMed1997

Protein kinase Cs and tyrosine kinases in permissive action of prostacyclin on cerebrovascular regulation in newborn pigs.

The involvement of protein kinase C (PKC) and protein tyrosine kinase (PTK) in hypercapnia-induced cerebral vasodilation in newborn pigs was investigated with closed cranial windows using the PKC stimulator phorbol 12-myristate 13-acetate (PMA), and the PTK inhibitors, genistein and herbimycin A. The influence of prostaglandin I2 was eliminated using the prostaglandin cyclooxygenase inhibitor, indomethacin. Changes in pial arteriolar diameters in response to hypercapnia [partial pressure of arterial CO2 approximately 9.3 kPa (70 torr)] were analyzed. Genistein (40 micrograms/mL), herbimycin A (10 microM), or PMA (1 microM) did not affect cerebral vasodilation to hypercapnia when applied topically. Indomethacin (5 mg/kg i.v.) treatment blocked the dilation to hypercapnia and attenuated hypercapnia-induced increase in cortical cAMP. Genistein and herbimycin A restored the response to hypercapnia to indomethacin-treated piglets. PMA also restored the pial arteriolar dilation and the cAMP response to hypercapnia to indomethacin-treated piglets. One-hour exposure to 10 microM PMA, to down-regulate PKC, blocked vasodilation to hypercapnia but did not inhibit vasodilation to sodium nitroprusside. After prolonged (2 h) topical exposure of indomethacin-treated piglets to 10 microM PMA, neither genistein nor iloprost could restore dilation to hypercapnia. These results indicate that PKC stimulation and/or PTK inhibition may permit hypercapnia-induced vasodilation. These data further suggest that PKC is downstream from PTK in the regulatory pathway. Because previous data showed prostaglandin I2 at subdilator concentrations can also return dilation to hypercapnia to piglets treated with indomethacin, prostaglandin I2 could provide its permissive input by activating PKC and/or inhibiting PTK.

Animals↗

PubMed1997

5-Hydroxytryptamine-induced vasoconstriction after cerebral hematoma in piglets.

Subarachnoid hematoma produces cerebral vasoconstriction that may lead to death or permanent disability. After hematoma, enhanced pial arteriolar responses to vasoconstrictor agents have been reported in newborn pigs. The present study was designed to address the hypothesis that 5-hydroxytryptamine (5-HT) constricts piglet pial arterioles, and hematoma augments this constriction. Piglets (1-3 d old) anesthetized with ketamine and acepromazine received either 3 mL of artificial cerebrospinal fluid (control) or autologous nonheparinized blood (hematoma) injected onto the cortical surface. Four days after injection, closed cranial windows were implanted over the injected area under alpha-chloralose anesthesia. Vascular reactivity to 5-HT was examined. In control piglets, topical application of 5-HT (10(-9), 10(-7), and 10(-5) M) induced very mild, dose-dependent constriction of pial arterioles (-6 +/- 1, -10 +/- 2, and -12 +/- 4%, respectively). These constrictions were substantially augmented in piglets with hematoma (-12 +/- 2, -19 +/- 1, and -30 +/- 2%, respectively). After topical application of 5-HT, cerebrospinal fluid samples were collected from under the window to determine the effects of 5-HT on the levels of 6-keto-prostaglandin F1 alpha and thromboxane B2. The baseline levels of 6-keto-prostaglandin F1 alpha and thromboxane B2 before 5-HT were 1791 +/- 387 and 434 +/- 74 pg/mL, respectively, in the control. 5-HT application had no significant effects on these prostanoid levels (levels at the highest concentration of 5-HT had a corresponding value of 1175 +/- 301 and 288 +/- 74 pg/mL for 6-keto-prostaglandin F1 alpha and thromboxane B2, respectively). However, indomethacin (5 mg/kg, i.v.) treatment of the control piglets potentiated the constriction in response to 5-HT (-11 +/- 1, -15 +/- 2, and -24 +/- 3%, respectively) sufficiently to produce constriction similar to that in the hematoma group. 5-HT has little effect on normal pial arterioles of newborn piglets but is a more potent cerebral vasoconstrictor in conjunction with cerebral hematoma.

Animals↗

PubMed1997

Changes in cerebral cyclic nucleotides and cerebral blood flow during prolonged asphyxia and recovery in newborn pigs.

Cerebrovascular reactivity is preserved after acute severe asphyxia/reventilation in piglets. We hypothesize that prolonged, partial asphyxia with hypotension causes loss of cerebrovascular reactivity and altered cerebral hemodynamics during recovery. We investigated the changes in cerebrospinal fluid cAMP and cGMP, pial arteriolar diameters and flow, and cerebral blood flow during 1 h of asphyxia and 1 h of recovery. During asphyxia, blood pressure decreased from 10 +/- 0.7 to 4.7 +/- 0.3 kPa and increased during recovery to 6 +/- 0.7 kPa. cAMP increased 3-fold by 20 min of asphyxia, returning to baseline at 40 min of asphyxia. During recovery, cAMP increased 2-fold initially, followed by a decrease to 50% below baseline. cGMP increased after 20 min of asphyxia, with maximum levels observed at 40 min; reventilation resulted in a transient increase in cGMP. Pial arteriolar diameters increased at the onset of asphyxia, then decreased toward baseline; during recovery, a similar pattern occurred. Blood flow to the cerebrum (microspheres) decreased during asphyxia and remained very low during recovery. Pial arteriolar flow but not pial arteriolar diameters followed the changes in cortical cerebral blood flow (i.e. virtually no flow during recovery). During recovery, pial arteriolar reactivity to isoproterenol and histamine decreased significantly. We conclude that 60 min of asphyxic-hypotensive insult results in alterations of cerebral cAMP metabolism which may compromise cellular communications during recovery. Prolonged asphyxia induces "no-reflow" during recovery, even when partial pressures of arterial CO2 and O2 have returned to baseline values, and blood pressure is within the autoregulatory range.

Animals↗

PubMed1997

The effects of intraventricular/periventricular blood on cerebral 3',5'-cyclic adenosine monophosphate concentration and cerebrovascular reactivity in newborn pigs.

This study investigated the effects of intraventricular/periventricular blood on cerebral cAMP production and cortical cerebrovascular reactivity. Under halothane and N2O anesthesia, 3 mL of either autologous blood or artificial cerebrospinal fluid (CSF) were injected into the left caudate nucleus; volume was adequate to result in extrusion of fluid or blood into the lateral ventricles of 1-2-d-old piglets. Twenty-four hours later, a closed cranial window was implanted over the left parietal cortex. Pial arteriolar responses to vasodilator and vasoconstrictor stimuli were monitored. Before the application of vasoactive agents, cortical periarachioid CSF was collected for cAMP measurement. Pial arteriolar responses to topical application of endothelin-1 (10(-9) and 10(-8) M) and to leukotriene C4 (10(-10) and 10(-9) M) were similar between the two groups. However, pial arteriolar responses to topical application of cAMP-mediated vasodilators, prostaglandin E2 (10(-6) and 10(-5) M), and histamine (10(-6) and 10(-5) M), respectively, were markedly reduced in the blood group when compared with the artificial CSF (control) group. Mean CSF cAMP level in the blood group was significantly lower than the control group (199 +/- 31 versus 1092 +/- 238 fmol/mL, p = 0.0006). We conclude that in newborn pigs intraventricular/periventricular blood results in a marked reduction of CSF cAMP concentration and attenuation of the cerebrovascular responses to cAMP-mediated vasodilators on the cortical surface remote from the site of blood or hematoma.

Animals↗

PubMed1996

Role of endothelin-1 in cerebral hematoma-induced modification of cerebral vascular reactivity in piglets.

Endothelin-1 (ET-1) has been implicated in hematoma-induced cerebral vasoconstriction and modification of cerebral microvascular reactivity, particularly attenuation of vasodilation to cAMP-dependent dilators and enhanced vasoconstriction to ET-1. We examined effects of the ET-1 antagonist, BQ-123, on hematoma-induced modification of pial arteriolar responses to ET-1 and iloprost, a cAMP-dependent dilator, in vivo, plus the effects of such treatment on the cortical CSF cAMP. Closed cranial windows were implanted in alpha-chloralose anesthetized piglets 4 days following cortical subarachnoid injection of: (1) artificial cerebrospinal fluid (aCSF); (2) autologous blood; (3) BQ-123 alone; or (4) BQ-123 in combination with blood. ET-1 in CSF was significantly elevated from 3 in control to 45 fmol/ml 6 h following hematoma, dropping to 24 fmol/ml at 24 h but remaining above control 4 days later (14 fmol/ml). The mean diameters of pial arterioles were reduced 30% 4 days following blood injection. This reduction was prevented by pretreatment with BQ-123. In the control piglets, pial arterioles dose-dependently dilated to topical application of iloprost with increases in diameter of 10%, 16% and 21% at 10(-12) M, 10(-10) M and 10(-8) M, respectively. Iloprost-induced dilation was attenuated by hematoma to 4%, 9% and 14% at 10(-12) M, 10(-10) M and 10(-8) M, respectively. Treating piglets with BQ-123 along with hematoma on day 1 prevented the hematoma-induced attenuation of pial arteriolar dilation to iloprost on day 4 (14%, 21% and 29% at 10(-12) M, 10(-10) M and 10(-8) M, respectively). Conversely, dilation to sodium nitroprusside (SNP) was not different among the groups. Topical ET-1 dilated pial arterioles at 10(-12) M and produced dose-dependent constriction at higher doses in the control piglets. The dilation at 10(-12) M ET-1 was reversed to constriction 4 days following hematoma and constrictions to higher doses were enhanced. BQ-123 treatment along with hematoma prevented both the loss of low dose dilation and the enhanced vasoconstriction to ET-1. Treatment with BQ-123 alone on day 1 did not affect the dilation to iloprost or constriction to ET-1, 4 days later. The cortical CSF level of cAMP was significantly reduced from 1637 fmol/ml in controls to 294 fmol/ml in piglets with hematoma. Treatment with BQ-123 along with hematoma blocked the reduction in cAMP (3369 fmol/ml). Initial elevation of ET-1 and the subsequent activation of ETA, receptor may play an important role in hematoma-induced alterations of cerebral vascular reactivity and prolonged cerebral vasoconstriction that occur 4 days later. Thus, cerebral hematoma appears to attenuate iloprost-induced dilation and reduce basal cAMP level 4 days following hematoma via release that involves ET-1 of substance(s) on day 1 of hematoma. This substance(s) may act by inhibiting adenylyl cyclase. These results suggest that ET-1 plays an important role in the blood-induced prolonged cerebral vasoconstriction and altered vasoreactivity that follows cerebral hemorrhage via stimulation of ETA receptor.

Animals↗

PubMed1996

Prostaglandin production after experimental discectomy.

STUDY DESIGN: This study ascertained the effects of discectomy on prostaglandin synthesis. OBJECTIVES: The purpose of these novel experiments was to measure the levels of two prostaglandins in lumbar epidural fluid obtained from an area subjected to discectomy. For comparison, lumbar epidural fluid from a site not disturbed by discectomy and fluid from a subcutaneous site were analyzed for the prostaglandins. SUMMARY OF BACKGROUND DATA: Previous studies have shown that nuclear material obtained from degenerative discs manifests an extraordinarily high level of phospholipase A2 activity. Others have hypothesized that the known inflammatory effects of phospholipase A2 are due to the release of arachidonic acid, which is converted to various eicosanoids, including several algesic prostaglandins (PGI2 and PGE2). No previous study has continuously measured prostaglandin levels in epidural fluid or assessed the effect of discectomy on prostaglandin production. METHODS: An ultrafiltrate of lumbar epidural fluid of dogs was obtained from indwelling catheters located adjacent to spinal areas that were and were not subjected to discectomy as well as from subcutaneous tissue. The fluid was collected daily for 14 days and analyzed for PGE2 and 6-keto PGF1(alpha) (the stable metabolite of PGI2) by radioimmunoassay. RESULTS: The concentration of 6-keto PGF1(alpha) and PGE2 in fluid collected during the first 24 hours was significantly higher in the area of discectomy than in the epidural region that was not subjected to discectomy and significantly higher than in fluid obtained from the subcutaneous site. The high level of these prostaglandins at the discectomy site fell rapidly, so that by the end of 48 hours the differences in values between spinal fluid from the discectomy and nondiscectomy regions were not statistically significant. The concentration of the prostaglandins in epidural fluid decreased with time and became minimal within the second week. CONCLUSION: The removal of normal discs is accompanied for 24 hours by a marked rise in the synthesis of two prostaglandins known to produce pain. Because the concentration of prostaglandins in epidural fluid decreased rapidly thereafter, the initial surge obtained appears to be associated more with chemical factors such as phospholipase A2 than with wound healing.

Animals↗

PubMed1996

Tumor necrosis factor-alpha induces pial arteriolar dilation in newborn pigs.

The present study in piglets was designed to examine cerebrovascular effects of tumor necrosis factor-alpha (TNF alpha) and potential mechanisms involved. Anesthetized new-born pigs with closed cranial windows implanted were used. Effects of nitric oxide synthase (NOS) inhibitors, NG-nitro-L-arginine (L-NNA) and aminoguanidine, and a prostaglandin H synthase inhibitor, indomethacin, on pial arteriolar responses to TNF alpha were determined. In addition, cortical cerebrospinal fluid (CSF) prostanoids (PGE2 and 6-keto-PGF1 alpha) and cyclic nucleotides (cAMP and cGMP) were examined as indices of local cerebral production. Diameters of pial arterioles were recorded every 5 min for 30 min following topical infusion of TNF alpha under the window. CSF was sampled at the end of the 30-min recordings. TNF alpha (10(-8) and 10(-7) M) caused dilation of pial arterioles and increased CSF prostanoids and cyclic nucleotides. Indo-methacin blocked TNF alpha-induced vasodilation and the increase of prostanoids and cAMP, but not of cGMP. L-NNA and amino-guanidine blocked TNF alpha-induced vasodilation. Both inhibitors attenuated TNF alpha-induced prostanoid increase. Aminoguanidine blocked TNF alpha-induced increased cGMP and attenuated the increase in cAMP. These results are consistent with the hypothesis that TNF alpha increases cAMP via prostanoid synthesis. They also suggest that TNF alpha increases cGMP through nitric oxide synthesis, which, in addition, may promote production of prostanoids and, thus, cAMP.

Animals↗

PubMed1996

Effects of hypercapnia on prostanoid and cAMP production by cerebral microvascular cell cultures.

In the newborn pig cerebral circulation, arteriolar dilation in response to hypercapnia requires the presence of intact endothelium and is accompanied by an indomethacin-sensitive increase in cortical adenosine 3',5'-cyclic monophosphate (cAMP). The effects of short-term hypercapnia on production of dilator prostanoids and cAMP were investigated using newborn pig cerebral microvascular smooth muscle cells and endothelial cells cultured both separately and in noncontact coculture. Microvascular smooth muscle cells respond to hypercapnia (pH 7.00 +/- 0.05 PCO2 75 +/- 3 mmHg) by a 1.3- to 1.7-fold increase in basal cAMP production that is not affected by indomethacin, whereas hypercapnia and 80 mM sodium propionate do not affect iloprost-stimulated cAMP production. Microvascular endothelial cells cultured on Millicel inserts respond to hypercapnia by a two- to fourfold increase in prostacyclin (as 6-keto-prostaglandin F1 alpha) and prostaglandin E2 production in both luminal and abluminal compartments. For noncontact coculture, Millicel inserts with endothelial cells (as hypercapnia-sensitive producers of prostanoids) were installed into cell culture dishes with aspirin-pretreated smooth muscle cells (as targets for endothelium-derived dilator prostanoids). Exposure of noncontact microvascular cell cocultures to hypercapnia results in a three- to fourfold stimulation of prostanoid and cAMP production. Therefore, short-term hypercapnia increases cAMP production by microvascular smooth muscle cells via 1) a direct (prostanoid independent) mechanism and 2) an endothelial-dependent pathway that involves prostanoids. Endothelium-produced prostanoid signals are necessary for a full increase in cAMP production by cerebral microvascular smooth muscle cells in response to hypercapnia.

Animals↗

PubMed1996

Age dependence of cerebrovascular response mechanisms in domestic pigs.

Hypercapnia-induced cerebral vasodilation in the newborn pig is a prostanoid-associated response. In some adult models, hypercapnic cerebral vasodilation is associated with the generation of nitric oxide (NO). Acetylcholine (ACh) produces a NO-dependent cerebral vasodilation in many adult models, but topical ACh is a prostanoid-associated cerebral vasoconstrictor in the newborn pig. We hypothesized that mediators influencing cerebral response can be age dependent. Juvenile domestic pigs were compared with newborn pigs, and pial arteriolar diameters were measured by use of a closed cranial window during hypercapnia and topical ACh (10(-5) M). Four different conditions were explored: control, topical N omega-nitro-L-arginine (L-NNA, 10(-3) M), indomethacin (5 mg/kg i.v.), and both L-NNA and indomethacin. All animals were anesthetized with alpha-chloralose. As opposed to the complete block in the newborn, indomethacin only partially attenuated the hypercapnic cerebral vasodilation in the juvenile pig.L-NNA, which had no effect on the response of the newborn, produced a partial attenuation of the hypercapnic response of the juvenile. The combination of indomethacin and L-NNA blocked the response in both age groups. Topical ACh in both age groups initially produced cerebral vasoconstriction, but, in the juvenile, this was followed by a sustained cerebral vasodilation. Indomethacin blocked the early vasoconstriction in both age groups. L-NNA, which had no effect in the response of the newborn to ACh, blocked the vasodilation seen in the juvenile. The combination of both inhibitors blocked all response to ACh in the juvenile. These data indicate that although the cerebral vascular responses to ACh and hypercapnia are prostanoid associated and NO independent in the newborn pig, NO assumes an increasing role in dilatory responses with development.

Acetylcholine↗

PubMed1996

Interleukin-1 beta peptides induce cerebral pial arteriolar dilation in anesthetized newborn pigs.

Inflammatory cytokines may affect cerebral circulation under pathological conditions. Responses of cerebral pial arterioles to one such cytokine, interleukin (IL)-1 beta and its inhibitor [soluble IL-1 receptor (sIL-1R)] were examined in anesthetized newborn pigs using closed cranial windows. Levels of prostanoids and cyclic nucleotides in periarachnoid cerebral spinal fluid (CSF) were measured. To examine the structure-activity relationship of the parent IL-1 beta molecule, two IL-1 beta fragments with amino acid sequences of 187-204 [IL-1 beta-(187-204)] and 208-240 [IL-1 beta-(208-240)] were tested for their effects on pial arterioles. Diameter changes of pial arterioles were sequentially recorded every 5 min for 30 min after topical application of IL-1 peptides. CSF was sampled at the end of the 30 min. IL-1 beta dose dependently induced arteriolar dilation and increased prostaglandin E2 (PGE2), 6-keto-PGF1 alpha adenosine 3',5'-cyclic monophosphate (cAMP), and guanosine 3',5'-cyclic monophosphate (cGMP). Intravenous indomethacin blocked the IL-1 beta-induced vasodilation, the increased prostanoids, and the increased cAMP, but not the increased cGMP. Neither heat-inactivated IL-1 beta nor IL-1 beta vehicle affected arteriolar diameter or CSF levels of prostanoids. The sIL-1R blocked the IL-1 beta-induced vasodilation and the increased CSF prostanoids. IL-1 beta-(208-240) also induced pial arteriolar dilation; however, its vasodilatory potency was 1,000 times less than that of the whole IL-1 beta molecule. IL-1 beta-(187-204) did not induce pial arteriolar dilation even when its dose was increased to the level of IL-1 beta-(208-240). These results suggest that IL-1 beta, through the activation of membrane-bound IL-1 beta receptors, induces pial arteriolar dilation via mechanisms that involve prostanoids and cyclic nucleotides. The results also indicate that the 208-240 amino acid sequence of IL-1 beta has a sequence-specific physiological function.

6-Ketoprostaglandin F1 alpha↗

PubMed1996

pHi in piglet cerebral microvascular endothelial cells: recovery from an acid load.

Cerebral microvascular endothelial cells form a barrier between the blood and brain, which is critical for normal neuronal functions. These endothelial cells can be challenged by metabolic and respiratory acidosis, especially in newborn babies. We investigated mechanism(s) by which cerebral endothelial cells recover intracellular pH (pHi) when challenged with an intracellular acid load. pHi in piglet cerebral microvascular endothelial cells in primary culture was monitored using the pH-sensitive fluorescent dye BCECF (2',7'-bis-2-carboxyethyl-5(6)-carboxy-fluorescein acetoxymethyl ester), with dual wavelength fluorescence spectroscopy. Endothelial cells attached to coverslips and continuously superfused with HCO3-/CO2 containing medium (25 mM HCO3-, 5% CO2; pH 7.40) have a steady state of pHi of 7.18 +/- 0.02. Under basal conditions, amiloride (100 microMol) and H2DIDS (0.5 mM) decreased pHi 0.12 +/- 0.01 and 0.05 +/- 0.01 pH units, respectively. Removal of external Na+ lowered pHi 0.18 +/- 0.02pH units, while Cl- free medium decreased pHi 0.16 +/- 0.03pH units. These data suggest the presence of an amiloride-sensitive Na+-H+ exchanger and a Na+-dependent HCO3- -Cl- anion exchanger in endothelial cells. Propionate and high PCO2 cause rapid intracellular acidification at constant pH. The cells recover to control pHi over 10 min. Recovery from propionate was largely inhibited by amiloride, slightly inhibited by H2DIDS, and completely prevented by the combination. pHi recovery during elevated PCO2 was blocked by amiloride, H2DIDS, or Na+-free media. These results indicate that recovery from intracellular acidosis can involve amiloride-sensitive Na+-H+ exchange and a Na+-dependent HCO3-/Cl- anion exchange. Relative contributions of pumps and their independence appears to depend on the nature of the acid load.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1995

Functional study on vasodilator effects of prostaglandin E2 in the newborn pig cerebral circulation.

Cerebral vascular reactivity to prostaglandin E2 was investigated in newborn pigs using closed cranial windows. Exogenous prostaglandin E2 is a dilator of pial arterioles that elevates cyclic AMP in cortical cerebrospinal fluid. Pial arterioles are less sensitive to prostaglandin E2 than to the prostacyclin receptor agonist iloprost, but their maximal responses to the dilator prostanoids are similar. The cerebrovascular effects of prostaglandin E2 and iloprost are not additive. Pretreatment with either iloprost or prostaglandin E2 decreases pial arteriolar responsiveness to iloprost without affecting responses to isoproterenol. The homologous desensitization of pial arterioles suggests that auto- and cross-tachyphylaxis in vascular effects of iloprost and prostaglandin E2 occur at the receptor level. Indomethacin, which selectively inhibits prostacyclin receptor-mediated responses in cerebral vascular smooth muscle, greatly reduces the vascular responses to prostaglandin E2. These results suggest that vasodilator effects of prostaglandin E2 in the newborn cerebral circulation are mediated via prostacyclin receptors coupled to adenylyl cyclase.

Animals↗

PubMed1995

Detection of loss of cerebral vascular tone by correlation of arterial and intracranial pressure signals.

With the use of a laboratory model, arterial and intracranial pressure signals were obtained under conditions of intact regulation of cerebral blood flow and massive dilation. During elevated intracranial pressure and intact regulation, positive pressure inhalation appears to briefly occlude venous flow into the cranial sinuses during inspiration. As a result, the intracranial pressure and arterial pressure signals are not similar. In contrast, when maximal dilation causes failure of regulation of cerebral blood flow, the intracranial pressure signal is approximately proportional to the arterial pressure signal. Comparison of the cross-correlation function derived from the intracranial and arterial pressure signals to the autocorrelation function of the arterial signal reveals that the two correlation functions are: 1) different during intact regulation and 2) nearly identical during dilation induced failure of regulation of cerebral blood flow.

Animals↗