Synergistic effects of Bay K 8644 and bradykinin on norepinephrine release in the hypothalamus of spontaneously hypertensive rats

1. In the present study, we examined the effects of Bay K 8644, a dihydropyridine (DHP)-sensitive Ca2+ channel agonist, and bradykinin on norepinephrine release in the hypothalamus of spontaneously hypertensive rats (SHR). 2. In the preliminary studies using Sprague-Dawley rats, Bay K 8644 by itself had no significant effects on the stimulation-evoked [3H]-norepinephrine release from hypothalamic slices. Bradykinin increased the stimulation-evoked [3H]-norepinephrine release in a dose-related fashion. The facilitatory effects of bradykinin on norepinephrine release were potentiated by Bay K 8644. 3. In SHR, Bay K 8644 significantly increased the stimulation-evoked norepinephrine release from hypothalamic slices. However, exposure of slices to Bay K 8644 caused no significant effects on norepinephrine release in Wistar-Kyoto (WKY) rats. The effects of Bay K 8644 in combination with bradykinin on the stimulation-evoked norepinephrine release were also greater in SHR than in WKY rats. 4. These results demonstrate that Bay K 8644 significantly potentiated the facilitatory effects of bradykinin on norepinephrine release in rat hypothalamus. The finding indicates a possible interaction of bradykinin with DHP-sensitive Ca2+ channels in the central nervous system. Furthermore, the pronounced effects of Bay K 8644 and bradykinin in SHR suggest that bradykinin-related Ca2+ channels might have a role in the regulation of norepinephrine release in the hypothalamus of SHR.

[Assessment of right ventricular function by magnetic resonance imaging of old myocardial infarction]

The usefulness of magnetic resonance imaging (MRI) for estimating right ventricular function and the influence of left ventricular dysfunction on the performance of the right ventricle were assessed in 43 patients with chronic myocardial infarction (MI) and 14 control subjects (N) using electrocardiography-gated MRI and cardiac catheterization. Patients with MI were divided into three groups according to the location of the coronary lesions; 22 patients with left coronary artery lesion (LCA group), 13 with right coronary artery lesion (RCA group), and 8 with both left and right coronary artery lesions (L+R group). The right ventricular end-diastolic volume (RVEDV) and right ventricular ejection fraction (RVEF) were measured by Simpson's rule algorithm on transverse images of the right ventricle obtained at the end-systolic and end-diastolic phases. In 34 of the 43 patients, the same parameters of right ventricular function were calculated by the thermodilution method using a Swan-Ganz catheter with rapid response thermistor. Left ventricular ejection fraction (LVEF) and end-diastolic volume were determined from left ventriculography. The intraobserver reproducibility (11 cases, r = 0.97) and interobserver reproducibility (11 cases, r = 0.92) of RVEF measured by MRI were excellent. The RVEF and RVEDV determined from MRI were significantly correlated with those from the thermodilution method (RVEF: r = 0.56, RVEDV: r = 0.52). There was no difference in right ventricular end-diastolic volume index in any patient group. The RVEF was decreased in the L+R (41.0 +/- 4.5%, p < 0.01) and RCA (45.9 +/- 6.6%) groups, but there was no difference between the LCA (50.6 +/- 6.6%) and N (48.9 +/- 4.3%) groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of captopril on [3H]-norepinephrine release in rat central nervous system

1. The present study was performed to investigate the effects of captopril (an angiotensin converting enzyme inhibitor, ACE-I) on noradrenergic transmission in the rat central nervous system. 2. Slices of rat hypothalamus and medulla oblongata were prepared and prelabelled with [3H]-norepinephrine. Slices were continuously superfused with Krebs-Ringer solution, and electrical stimulation (1 Hz) was performed. 3. Captopril significantly inhibited the stimulation-evoked [3H]-norepinephrine release from rat hypothalamic slices in a dose-dependent manner (S2/S1 ratio: control 0.904 +/- 0.025, n = 6, captopril 1 x 10(-5) mol/L 0.617 +/- 0.043, n = 6, P < 0.05, captopril 5 x 10(-5) mol/L 0.547 +/- 0.037, n = 6, P < 0.05). However, the basal release of [3H]-norepinephrine was not affected by captopril. 4. Captopril also reduced the stimulation-evoked [3H]-norepinephrine release in the medulla oblongata (S2/S1 ratio: control 0.878 +/- 0.018, n = 6, captopril 3.3 x 10(-5) mol/L 0.624 +/- 0.046, n = 6, P < 0.05). 5. These results show that captopril might inhibit the stimulation-evoked norepinephrine release in rat hypothalamus and medulla oblongata. Although the precise mechanisms underlying the neurosuppressive effect of captopril are still uncertain, the finding suggests that the inhibition of noradrenergic transmission might be related to the central action of the ACE-I.

DA1 receptor-mediated renin release from isolated rat glomeruli

The present study was performed in order to examine the effects of dopamine (DA) on renin release and to clarify which subtype of DA receptor, DA1 or DA2 contributes to renin release. Male Wistar rats aged seven weeks were used. Glomeruli were isolated by the modified Beierwaltes' sieving method and were transferred to a sealed chamber and superfused with Krebs-Ringer solution. In the first experiment, the changes in renin release induced by DA and the effects of a non-selective DA antagonist, haloperidol and a beta antagonist, propranolol on DA-induced renin release were examined. In the second experiment, the effect of a DA2 receptors antagonist, spiperone and of a DA1 receptor antagonist, SCH-23390 on renin release were investigated. Basal levels of renin release were 2.46 +/- 0.36 ng ATI/h/10(4) glomeruli (mean +/- SEM). DA caused a dose-dependent increase in renin release. The renin release induced by DA was inhibited by haloperidol but not by propranolol. The maximum level of renin release induced by 10(-5)M DA was 4.13 +/- 0.63 ng ATI/h/10(4) glomeruli. SCH-23390 at 10(-5)M caused significant suppression of DA-induced renin (p < 0.05). In contrast, 10(-5)M spiperone failed to suppress DA-induced renin release. These results suggest that DA induced renin release from isolated glomeruli through the DA1 receptors.

Role of protein kinase C in relationship between Ca2+ and contractile elements in rat alpha-toxin-permeabilized mesenteric artery

Phorbol ester, which activates protein kinase C (PKC), modulates vasoconstrictor-induced tension in vascular smooth muscle. Recently, Staphylococcal aureus alpha-toxin, which produces too small pores in the plasma membrane to allow passage of proteins, such as PKC, is used to investigate the signal transduction system in vascular smooth muscle cells. In order to elucidate the role of PKC on vascular smooth muscle contraction, we examined whether PKC activation influences the relationship between intracellular Ca2+ ([Ca2+]i) and tension in Wistar rat superior mesenteric artery (SMA) using vascular smooth muscle permeabilized with Staphylococcal alpha-toxin. [Ca2+]i was clamped at specified values (10(-8.5)-10(-4) mol/L) using EGTA-Ca2+ buffer. In alpha-toxin non-treated rings of SMA, isometric tension was evoked by 10 mmol/L caffeine and 10-30 mmol/L external potassium (high K+) in the absence or presence of phorbol 12, 13-dibutyrate (PDBu), a PKC activator, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), and staurosporine (PKC inhibitors). PDBu significantly augmented caffeine- and high K(+)-evoked contractions. H-7 and staurosporine significantly attenuated caffeine- and high K(+)-evoked contractions augmented by PDBu. Moreover, H-7 significantly suppressed high K(+)-induced contraction in the absence of PDBu. In alpha-toxin permeabilized artery, PDBu shifted the [Ca2+]i-force relationship curve to the left. These results suggest that PKC activates vascular smooth muscle contraction by increasing the sensitivity of the contractile apparatus to Ca2+.

[A resected case of sporadic myxoma of the right ventricle: the diagnosis was supported with DNA flow cytometry]

We report a rare case of a 16-year-old male who had myxoma originating from septal band of the right ventricle. His ECG anomaly was found incidentally upon a physical examination. Subsequently, echocardiography and angiocardiography demonstrated a tumor occupying the right ventricular outflow tract and protruding into the main pulmonary artery in systolic phase. He was operated upon using extracorporeal circulation. By right ventriculotomy the tumor was resected together with septal tissue 5 mm around the stalk, which branched into the myocardium. The defect was closed using mattress sutures with Dacron felt strips. We also analyzed the DNA content of the tumor. The DNA flow cytometry yielded a single cell population with diploid DNA content. This result showed that the tumor is sporadic form of cardiac myxoma. His postoperative course was uneventful. Thirty months after the surgery, patient has no sign of recurrence. The DNA flow cytometry is helpful for detecting clinical behavior of the cardiac myxoma, because microscopic examination can not readily distinguish sporadic myxoma from so-called complex myxoma.

Mutation of low affinity nerve growth factor receptor gene in spontaneously hypertensive and stroke-prone spontaneously hypertensive rats: one of the promising candidate genes for hypertension

There is evidence that abnormal formation of the sympathetic nervous system might be important for pathogenesis of hypertension. In the present study we analyzed nucleotide sequences of low affinity nerve growth factor receptor (LNGFR) genes in the spontaneously hypertensive rat and its stroke-prone substrain. There was a point mutation generating an amino acid substitution in signal peptide of these LNGFRs. This result suggested that the mutated LNGFR gene is one of the promising candidate genes for hypertension.

Deficient activity of stimulatory nucleotide-binding regulatory protein in lymphocytes from patients with essential hypertension

Lymphocytes are widely used as a model for the cardiovascular beta-adrenoceptor-adenylate cyclase system. We evaluated the role of this system in the pathogenesis of hypertension by studying lymphocytes obtained from patients with essential hypertension. Untreated hypertensive patients and normotensive control subjects were studied. The number and affinity of the beta-adrenoceptors were measured by a radioligand binding method with 125I-cyanopindolol. The responses of cyclic adenosine monophosphate (cAMP) to isoproterenol, cholera toxin, and forskolin were also determined. The concentration and affinity of beta-adrenoceptors did not differ significantly in the two groups, nor was a significant difference found in the basal level of cAMP. The effects of isoproterenol on the accumulation of cAMP were reduced in the lymphocytes from the hypertensive compared with the normotensive subjects. There was no significant difference in the effect of forskolin on cAMP accumulation in the two groups. These results indicate that the activity of the stimulatory nucleotide binding regulatory protein (Gs-protein) is reduced in lymphocytes from patients with essential hypertension. This defect of Gs-protein in the lymphocytes may represent a defect of Gs-protein in the cardiovascular system in such patients.

Glutamatergic regulation of [3H]-noradrenaline release in the medulla oblongata of normotensive and spontaneously hypertensive rats

OBJECTIVE

To assess in vitro the role of glutamate receptors in the regulation of noradrenaline release from the medulla oblongata of normotensive and hypertensive rats.

DESIGN AND METHODS

The effects of L-glutamate (an endogenous ligand for glutamate receptors), glycine (an allosteric agonist for the N-methyl-D-aspartate type of glutamate receptors) and MK-801 (an antagonist for N-methyl-D-aspartate receptors) on [3H]-noradrenaline release were examined in slices of rat medulla oblongata.

RESULTS

L-Glutamate elicited [3H]-noradrenaline release from slices of rat medulla oblongata in magnesium-free medium. Glycine also increased the release of noradrenaline. Moreover, the effect of L-glutamate on noradrenaline release was significantly potentiated by glycine. MK-801 inhibited the increase in noradrenaline release evoked by L-glutamate. In spontaneously hypertensive rats (SHR) the facilitatory effect of L-glutamate on noradrenaline release was significantly more pronounced than in Wistar-Kyoto (WKY) rats. Furthermore, glycine alone and in combination with L-glutamate increased the noradrenaline release to a greater extent in SHR than in WKY rats.

CONCLUSION

The present results show that the excitatory amino acids might increase noradrenaline release from rat medulla oblongata, which was partially dependent on the N-methyl-D-aspartate type of glutamate receptors. The greater effect of L-glutamate and glycine in SHR suggests that these amino acids might be involved in the regulation of noradrenaline release in the medulla oblongata of hypertension.

A case of orthostatic and postexertional hypotension with ischemic electrocardiographic changes

A case of orthostatic and postexertional hypotension with ischemic electrocardiographic changes is reported. The etiology was considered to be the partial dysfunction of efferent sympathetic nerve endings. Peripheral adrenergic receptors (alpha and beta) were up-regulated, which might have caused pseudoischemic electrocardiographic changes and abnormal vasodilation after exercise.

Effect of temocapril on haemodynamic and humoral responses to exercise in patients with mild essential hypertension

1. This study was carried out to evaluate the effect of temocapril on haemodynamic and humoral responses to exercise in nine patients with mild essential hypertension (WHO stages I and II). 2. After a 4-week placebo period, temocapril was administered at a dose of 1.0 mg once daily for 2-4 weeks. Graded submaximal bicycle ergometer exercise was performed before and after temocapril treatment, and the changes in arterial blood pressure, heart rate, cardiac output (CO), and systemic vascular resistance (SVR) were evaluated. In addition, the plasma norepinephrine (NE) level was determined both at rest and peak exercise before and after temocapril treatment. 3. Both the systolic and diastolic blood pressure were reduced at rest and during exercise by temocapril treatment. No significant change in the resting heart rate and CO was observed, and the exercise-induced increase of these parameters was also not affected by temocapril. In contrast, the resting SVR was significantly decreased by temocapril, although the exercise SVR was similar during both temocapril and placebo treatment. 4. Although there was no significant change in the plasma NE level with temocapril treatment, the exercise-induced increase of plasma NE was significantly suppressed by temocapril. 5. These results indicate that temocapril reduces the blood pressure without causing any significant changes in the heart rate and CO at rest, and that it does not produce any changes in the haemodynamic response to exercise.

Efficacy of inhaled nitric oxide in a porcine model of adult respiratory distress syndrome

OBJECTIVE

To assess the efficacy of inhaled nitric oxide (NO) in reducing pulmonary hypertension in a porcine model of adult respiratory distress syndrome.

DESIGN

Nonrandomized, controlled experiment without blinding.

SETTING

Surgical research laboratory.

PARTICIPANTS

Twelve pigs, matched equally for body weight.

INTERVENTION

Acute lung injury was induced by intravenous injection of oleic acid. Animals were then divided into either a control group, for monitoring without any further intervention, or a NO-treatment group, in which NO was administered at concentrations of 10 to 80 ppm, with each step separated by a NO-free interval to assess duration of effect.

MAIN OUTCOME MEASURES

Pulmonary artery pressure, systemic blood pressure, PaO2, intrapulmonary shunt fraction, and extravascular lung water. Nitrosylated hemoglobin, arterial methemoglobin, and plasma nitrite and nitrate concentrations.

RESULTS

All animals responded to oleic acid injection with rapid development of pulmonary hypertension and deterioration of PaO2 and intrapulmonary shunt fraction. Inhaled NO reversed these changes in a concentration-dependent manner. Cessation of NO administration led to a prompt return of pulmonary hypertension. A small but significant drop in systemic blood pressure was observed only at the highest concentration of NO administered (80 ppm). Extravascular lung water almost doubled following oleic acid injury. This increase was sustained in all animals for the remainder of the experiment. Significant increases in circulating methemoglobin and plasma nitrite and nitrate concentrations were measured during NO inhalation.

CONCLUSION

Inhaled NO appears to be a selective pulmonary vasodilator and may prove to be useful in improving gas exchange in adult respiratory distress syndrome.

Effects of bradykinin on [3H]-norepinephrine release in rat hypothalamus

1. We examined the regulatory actions of bradykinin on norepinephrine release in the hypothalamus of rats. 2. Bradykinin increased the stimulation-evoked [3H]-norepinephrine release from hypothalamic slices of Sprague-Dawley rats in a dose-dependent manner (1 Hz: S2/S1 ratio, mean +/- s.e.m., control 0.868 +/- 0.016, n = 6; bradykinin 1 x 10(-6) mol/L 1.039 +/- 0.018, n = 6, P < 0.05; bradykinin 3.3 x 10(-6) mol/L 1.130 +/- 0.064, n = 6, P < 0.05). The basal release of [3H]-norepinephrine was not affected by the peptide. 3. Bay K 8644, a dihydropyridine-sensitive calcium channel agonist, significantly potentiated the facilitatory effect of bradykinin on norepinephrine release, although Bay K 8644 by itself had no significant effect. By contrast, nicardipine, a dihydropyridine-sensitive calcium channel blocker, reversed the increase in norepinephrine release induced by bradykinin and Bay K 8644. 4. These results indicate that bradykinin may increase norepinephrine release in rat hypothalamus, partially mediated by interactions with dihydropyridine-sensitive calcium channels.

Effects of nicardipine on the release of acetylcholine in the rat central nervous system

Recent studies have indicated that specific dihydropyridine-sensitive Ca2+ channel binding sites are present in the brain, and that they play a crucial role in synaptic function. The present study was performed to determine the effects of nicardipine, a dihydropyridine-sensitive Ca2+ channel blocker, on the release of acetylcholine in the rat central nervous system. Striatal slices of rats which had been prelabelled with [3H]acetylcholine were superfused with Krebs-Ringer solution. The slices were stimulated with either electrical pulses (1 Hz) or an excitatory amino acid, L-glutamate, and the effects of nicardipine on the release of acetylcholine were examined. Electrical stimulation produced an increase in [3H]acetylcholine release from the striatal slices. Exposure of the slices to nicardipine significantly inhibited the stimulation-evoked [3H] acetylcholine release. An endogenous excitatory amino acid, L-glutamate, also elicited release of [3H]acetylcholine. Nicardipine significantly reduced the L-glutamate-induced release of [3H]acetylcholine, and the effect was pronounced in the presence of Mg2+. These results demonstrate that nicardipine inhibits both electrically and chemically stimulated [3H]acetylcholine release from rat striatum. The ability of nicardipine to inhibit cholinergic transmission may be related to the central effect of this Ca2+ channel blocker.

Membrane fluidity of erythrocytes and its modulation by ouabain in essential hypertension--an electron paramagnetic resonance study

The purpose of the present study was to examine alterations in membrane fluidity of erythrocytes in essential hypertension by means of an electron paramagnetic resonance (EPR) and a spin labeling method. In addition, we investigated the effects of ouabain on the fluidity of erythrocytes, and elucidated a possible role of Na+, K(+)-ATPase in the regulation of membrane fluidity in hypertension. Erythrocytes obtained from patients with essential hypertension were examined compared with those from age-matched normotensive subjects. The EPR spectra for 5-nitroxide stearate incorporated into erythrocyte membranes were studied. The values of the outer hyperfine splitting and order parameter (S) of the EPR spectra were significantly higher in patients with essential hypertension than in normotensive subjects. This finding shows that the membrane fluidity of erythrocytes might be lower in essential hypertension. Ouabain-loading of erythrocytes decreased the membrane fluidity (S value was increased). The ouabain-induced changes were significantly greater in essential hypertension than in normotensive subjects. These results demonstrate that the membrane fluidity of erythrocytes might be lower in essential hypertension than in normotensive subjects. Furthermore, the membrane fluidity might be highly dependent on the Na+, K(+)-ATPase activity in essential hypertension, which would suggest an abnormality in Na(+)-related cellular functions in hypertension.

Production of nerve growth factor by cultured vascular smooth muscle cells from spontaneously hypertensive and Wistar-Kyoto rats

OBJECTIVE

Nerve growth factor (NGF) is a neurotrophic protein which acts on peripheral sympathetic nerves. Elevated NGF in vascular tissues of young spontaneously hypertensive rats (SHR) has been reported. The aim of the present study was to compare the amount of NGF secreted from cultured vascular smooth muscle cells (VSMC) and mesenteric artery and thoracic aorta segments from SHR and Wistar-Kyoto (WKY) rats.

METHODS

VSMC prepared by the enzyme digestion method from the thoracic aortic media of 14-week-old SHR and age-matched WKY rats were subcultured in Dulbecco's modified Eagle's medium containing 10% fetal calf serum. Segments of mesenteric artery and thoracic aorta from 4-week-old SHR and age-matched WKY rats were similarly cultured. The NGF content in conditioned medium was measured using an enzyme immunoassay. The protein content of VSMC was measured by the Lowry method.

RESULTS

Total NGF content in the cell culture medium was increased during an exponential growth phase and then gradually decreased during a quiescent phase in both rat strains. There were no significant differences in the levels of NGF secreted from mesenteric artery and thoracic aorta segments between the SHR and WKY rats. The differences in cellular protein content between SHR and WKY rats were very small.

CONCLUSIONS

In contrast to the reports of increased NGF in SHR tissues, our data demonstrate that NGF secretion was lower in VSMC from SHR, and was equivalent in mesenteric artery and thoracic aorta segments from SHR and WKY rats. We have no clear explanation for these observations, but the present results indicate that upregulation of NGF in SHR tissues is not responsible for a simple enhancement of NGF synthesis in VSMC, and suggest a breakdown of the regulatory mechanism or mechanisms of NGF gene expression in SHR tissues.

[The effects of anesthetic techniques and insufflating gases on ventilation during laparoscopy]

The present study was performed to clarify the influences of anesthetic methods and insufflating gases on arterial blood gas and ventilation during laparoscopy. Forty five women undergoing laparoscopy for gynecological procedure were studied after dividing into four groups; general anesthesia with control ventilation or epidural anesthesia with spontaneous breathing, plus insufflation with carbon dioxide (CO2) or nitrous oxide (N2O). After CO2 insufflation, PaCO2 increased significantly in the patients who were mechanically ventilated, but not in the patients breathing spontaneously. After N2O insufflation, the decrease in tidal volume (VT) and the increase in VD/VT were significant, but minute ventilation was well maintained by the compensatory increase in respiratory frequency during spontaneous breathing. On the other hand, after CO2 insufflation VE and VD/VT increased significantly without any change in VT. PaO2 decreased significantly after both insufflation and Trendelenburg tilt in all groups, probably secondary to the decrease in functional residual capacity. These findings suggest that during laparoscopy, ventilation could be well maintained by spontaneous breathing, although the increase in VD/VT and costal breathing indicate the increase in respiratory work load. We recommend that ventilation and oxygenation should be closely monitored during laparoscopy to avoid hypercapnia and hypoxia.

[Effect of succinylcholine on serum potassium concentration in children with chronic renal failure]

Serum potassium (K+) levels were measured after intravenous injection of succinylcholine (SCh) in 10 children with chronic renal failure, 10 normal children aged 1 to 10 years and 10 children with chronic renal failure after pretreatment with pancuronium prior to SCh. Arterial blood gas was maintained within normal ranges. The serum K+ level increased significantly during 10 minutes after SCh in normal children. There was no significant difference between serum K+ levels in normal children and those in children with chronic renal failure. Administration of pancuronium in small doses (20 micrograms.kg-1) prior to SCh (1 mg.kg-1) was not effective to prevent serum K+ elevation completely. Our results indicate that the administration of SCh in children with chronic renal failure might be possible without increasing serum potassium level.

[Mitral valve replacement with concomitant coronary bypass for the papillary muscle rupture after acute myocardial infarction in situs inversus]

A 53-year-old man, who was known to have situs inversus totalis all of his life, had acute myocardial infarction complicated by partial rupture of the posterior papillary muscle causing mitral regurgitation and pulmonary edema. The patient underwent mitral valve replacement (Omnicarbon 27 mm) with concomitant aortocoronary saphenous vein bypass, and he is now doing well 9 months following the operation. To our knowledge, this is the first case of the successful mitral valve replacement and concomitant aortocoronary saphenous vein bypass on a patient with situs inversus totalis (mirror-image dextrocardia) in Japan.

Facilitatory effects of diltiazem on dopamine release in the central nervous system. Focus on interactions with D2 autoreceptors and guanosine triphosphate binding proteins

The purpose of the present study was to investigate the effects of a Ca antagonist (diltiazem) on dopamine release in the central nervous system. Rat striatal slices prelabeled with [3H]dopamine (DA) and superfused with Krebs-Ringer solution were stimulated electrically at a frequency of 1 Hz. Exposure to diltiazem (3.3 x 10(-7) to 1 x 10(-5) mol/L) significantly increased both the basal and stimulation-evoked [3H]DA release in a dose-dependent manner. Exogenously applied unlabeled DA inhibited the stimulation-evoked [3H]DA release. Diltiazem significantly antagonized the capacity of the unlabeled DA to inhibit stimulation-evoked [3H]DA release. The blockade of D2 receptors by a preferential D2 antagonist, sulpiride, reduced the facilitatory effect of diltiazem on stimulation-evoked [3H]DA release. Pretreatment with pertussis toxin, which interferes with the coupling of the inhibitory guanosine triphosphate-binding proteins to adenylate cyclase, significantly diminished the effects of diltiazem on stimulation-evoked [3H]DA release. These results show that diltiazem increased DA release in rat striatum, at least partially by interactions with the D2 autoreceptors and pertussis toxin-sensitive guanosine triphosphate-binding proteins.

Modulation of norepinephrine release by galanin in rat medulla oblongata

Galanin, a 29-amino acid peptide, is widely distributed in both the central and peripheral nervous systems and is colocalized with catecholamines, although its physiological significance remains to be elucidated. In the present study we investigated the regulatory mechanisms of galanin on norepinephrine release in rat medulla oblongata. In slices of medulla oblongata of Sprague-Dawley rats, galanin inhibited the stimulation-evoked [3H]norepinephrine release in a concentration-dependent manner (fractional release ratio during electrical stimulation: control 0.937 +/- 0.043, mean +/- SEM, n = 6; galanin 1 x 10(-7) M 0.501 +/- 0.037, n = 6, p less than 0.05; and galanin 1 x 10(-6) M 0.299 +/- 0.018 n = 6, p less than 0.05). Galanin potentiated inhibition of [3H]norepinephrine release by the alpha 2-agonists (UK 14,304 and clonidine). The blockade of alpha 2-adrenergic receptors by RX 781094 diminished the inhibition of norepinephrine release by galanin. Pretreatment of pertussis toxin, which interferes with the coupling of inhibitory guanosine triphosphate-binding proteins to adenylate cyclase, significantly attenuated the suppressive effects of galanin on norepinephrine release. In slices of medulla oblongata obtained from spontaneously hypertensive rats (SHR), the inhibitory effect of galanin on norepinephrine release was significantly less than in those from age-matched Wistar-Kyoto rats. These results show that galanin might inhibit the stimulation-evoked norepinephrine release in rat medulla oblongata, at least partially mediated by alpha 2-adrenergic receptors and the pertussis toxin-sensitive guanosine triphosphate-binding proteins. Moreover, less suppression of norepinephrine release by galanin in SHR suggests that galanin might be involved in the regulation of central sympathetic nervous activity in hypertension.

The role of endogenous Na+, K(+)-adenosine triphosphatase inhibitory factor in the regulation of membrane fluidity of erythrocytes in essential hypertension

OBJECTIVE

To investigate the regulatory mechanisms of membrane functions in hypertension, we examined the relationship between endogenous Na+, K(+)-adenosine triphosphatase (ATPase) inhibitor (digitalis-like factor; DLF) and erythrocyte membrane fluidity in essential hypertension by means of an electron spin resonance (ESR) and spin labelling methods.

DESIGN AND METHODS

Erythrocytes were obtained from patients with essential hypertension and normotensive subjects, and the ESR spectra for a fatty acid spin label agent (5-nitroxide stearate) incorporated into the erythrocyte membranes were studied. The DLF content in plasma was expressed as the inhibitory potency of dog kidney Na+, K(+)-ATPase activity in vitro.

RESULTS

The values of outer hyperfine splitting and of order parameter in ESR spectra were significantly higher in hypertensive patients than in normotensive subjects. This finding shows that the erythrocyte membrane fluidity may be decreased in essential hypertension. The level of plasma DLF content was greater in hypertensive patients than in normotensive subjects and was significantly correlated with the decrease in erythrocyte membrane fluidity.

CONCLUSIONS

These results suggest that the decrease in erythrocyte membrane fluidity may be partially dependent upon the increased plasma DLF content.