Doxycycline treatment attenuates acute lung injury in mice infected with virulent influenza H3N2 virus: involvement of matrix metalloproteinases

Acute respiratory distress syndrome, a severe form of acute lung injury (ALI), is a major cause of death during influenza pneumonia. We have provided evidence for the involvement of recruited neutrophils, their toxic enzymes such as myeloperoxidase and matrix metalloproteinases (MMPs), and neutrophil extracellular traps in aggravating alveolar-capillary damage. In this study, we investigated the effects of doxycycline (DOX), an inhibitor of MMPs, on influenza-induced ALI. BALB/c mice were infected with a sublethal dose of mouse-adapted virulent influenza A/Aichi/2/68 (H3N2) virus, and administered daily with 20mg/kg or 60 mg/kg DOX orally. The effects of DOX on ALI were determined by measuring inflammation, capillary leakage, and MMP activities. Furthermore, levels of T1-α (a membrane protein of alveolar type I epithelium) and thrombomodulin (an endothelial protein) in the bronchoalveolar lavage fluid were evaluated by Western blot analysis. Our results demonstrate significantly decreased inflammation and protein leakage in the lungs after DOX treatment. Levels of MMP-2 and MMP-9 activity, T1-α and thrombomodulin were also diminished in the DOX-treated group. These findings were corroborated by histopathologic analyses, which demonstrated significant reduction in lung damage. Although DOX treatment reduced ALI, there were no effects on virus titers and body weights. Taken together, these results demonstrate that DOX may be useful in ameliorating ALI during influenza pneumonia. Further studies are warranted to determine whether DOX can be used in combination with anti-viral agents to alleviate severe influenza pneumonia.

Involvement of AT(1) angiotensin receptors in the vasomodulatory effect of des-aspartate-angiotensin I in the rat renal vasculature

Angiotensin II is known to act primarily on the angiotensin AT(1) receptors to mediate its physiological and pathological actions. Des-aspartate-angiotensin I (DAA-I) is a bioactive angiotensin peptide and have been shown to have contrasting vascular actions to angiotensin II. Previous work in this laboratory has demonstrated an overwhelming vasodepressor modulation on angiotensin II-induced vasoconstriction by DAA-I. The present study investigated the involvement of the AT(1) receptor in the actions of DAA-I on angiotensin II-induced vascular actions in the renal vasculature of normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR) and streptozotocin (STZ)-induced diabetic rats. The findings revealed that the angiotensin receptor in rat kidney homogenate was mainly of the AT(1) subtype. The AT(1) receptor density was significantly higher in the kidney of the SHR. The increase in AT(1) receptor density was also confirmed by RT-PCR and Western blot analysis. In contrast, AT(1) receptor density was significantly reduced in the kidney of the streptozotocin-induced diabetic rat. Perfusion with 10(-9)M DAA-I reduced the AT(1) receptor density in the kidneys of WKY and SHR rats suggesting that the previously observed vasodepressor modulation of the nonapeptide could be due to down-regulation or internalization of AT(1) receptors. RT-PCR and Western blot analysis showed no significant changes in the content of AT(1) receptor mRNA and protein. This supports the suggestion that DAA-I causes internalization of AT(1) receptors. In the streptozotocin-induced diabetic rat, no significant changes in renal AT(1) receptor density and expression were seen when its kidneys were similarly perfused with DAA-I.

Effect of des-aspartate-angiotensin I on the actions of angiotensin II in the isolated renal and mesenteric vasculature of hypertensive and STZ-induced diabetic rats

The present study investigated the action of des-aspartate-angiotensin I (DAA-I) on the pressor action of angiotensin II in the renal and mesenteric vasculature of WKY, SHR and streptozotocin (STZ)-induced diabetic rats. Angiotensin II-induced a dose-dependent pressor response in the renal vasculature. Compared to the WKY, the pressor response was enhanced in the SHR and reduced in the STZ-induced diabetic rat. DAA-I attenuated the angiotensin II pressor action in renal vasculature of WKY and SHR. The attenuation was observed for DAA-I concentration as low as 10(-18) M and was more prominent in SHR. However, the ability of DAA-I to reduce angiotensin II response was lost in the STZ-induced diabetic kidney. Instead, enhancement of angiotensin II pressor response was seen at the lower doses of the octapeptide. The effect of DAA-I was not inhibited by PD123319, an AT2 receptor antagonist, and indomethacin, a cyclo-oxygenase inhibitor in both WKY and SHR, indicating that its action was not mediated by angiotensin AT2 receptor and prostaglandins. The pressor responses to angiotensin II in mesenteric vascular bed were also dose-dependent but smaller in magnitude compared to the renal vasculature. The responses were significantly smaller in SHR but no significant difference was observed between STZ-induced diabetic and WKY rat. Similarly, PD123319 and indomethacin had no effect on the action of DAA-I. The findings reiterate a regulatory role for DAA-I in vascular bed of the kidney and mesentery. By being active at circulating level, DAA-I subserves a physiological role. This function appears to be present in animals with diseased state of hypertension and diabetes. It is likely that DAA-I functions are modified to accommodate the ongoing vascular remodeling.

Effects of des-aspartate-angiotensin I on the actions of angiotensin III in the renal and mesenteric vasculature of normo- and hypertensive rats

An earlier study showed that des-aspartate-angiotensin I (DAA-I) attenuated the pressor action of angiotensin III in aortic rings of the spontaneously hypertensive rat (SHR) but not the normotensive Wistar Kyoto (WKY) rat. The present study investigated similar properties of DAA-I in isolated perfused kidneys and mesenteric beds of WKY and SHR. In the renal vasculature, angiotensin III induced a dose-dependent pressor response, which was more marked in the SHR than WKY in terms of significant greater magnitude of response and lower threshold. DAA-I attenuated the pressor action of angiotensin III in both the WKY and SHR. The attenuation in SHR was much more marked, occurring at doses as low as 10(-15) M DAA-I, while effective attenuation was only seen with 10(-9) M in WKY. The effects of DAA-I was not inhibited by PD123319 and indomethacin, indicating that its action was not mediated by angiotensin AT2 receptors and prostaglandins. However, the direct pressor action of angiotensin III in the SHR but not the WKY was attenuated by indomethacin suggesting that this notable difference could be due to known decreased response of renal vasculature to vasodilator prostaglandins in the SHR. Pressor responses to angiotensin III in the mesenteric vascular bed was also dose dependent, but smaller in magnitude compared to the renal response. The responses in the SHR, though generally smaller, were not significantly different from those of the WKY. This trend is in line with the similar observations with angiotensin III and II by other investigators. In terms of the effect of DAA-I, indomethacin and PD123319 on angiotensin III action, similar patterns to those of the renal vasculature were observed. This reaffirms that in the perfused kidney and mesenteric bed, where the majority of the vessels are contractile, femtomolar concentrations of DAA-I attenuates the pressor action of angiotensin III. The attenuation is not indomethacin sensitive and does not involve the angiotensin AT2 receptor. The findings suggest that DAA-I possesses protective vascular actions and is involved in the pathophysiology of hypertension.

Metabotropic glutamate receptor 2/3 in the hippocampus of patients with mesial temporal lobe epilepsy, and of rats and mice after pilocarpine-induced status epilepticus

A comparative study of the expression of metabotropic glutamate receptor 2/3 (mGluR2/3) was done in the hippocampus of rats and mice after pilocarpine-induced status epilepticus (APISE), and of patients with mesial temporal lobe epilepsy. At 1 day APISE, there was a marked increase in mGluR2/3 immunoreactivity in the stratum lacunosum moleculare (SLM) of CA1 area and in the middle one-third of the molecular layer (MM) of the dentate gyrus. Immuno-electron microscopic study showed degenerating mGluR2/3 positive axons in the SLM of CA1 area at 1 day APISE. From 7 days, mGluR2/3 immunopositive product decreased, and by 31 days APISE, it almost disappeared in two-thirds of the SLM near CA2. In the mouse model at 2 months APISE, mGluR2/3 immunopositive product in two-thirds of the SLM near the stratum radiatum disappeared, and so did in the whole SLM of CA1 area in patients with mesial temporal lobe epilepsy. Neuropharmacological study by intravenous injection of mGluR2/3 agonist 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate [(2R,4R)-APDC] at different doses at 1h during pilocarpine induced status epilepticus showed that (2R,4R)-APDC could not stop seizures and neuronal death in the hilus of the dentate gyrus. The present study, therefore, suggests that the reduction of mGluR2/3 immunopositive product in the SLM of CA1 is a consequence of neuronal loss in either the entorhinal cortex or CA1 area of the hippocampus, and at the dosage range from 12.5 to 600 mg/kg, (2R,4R)-APDC may not be effective in the prevention of seizures or neuronal death in the hilus of the dentate gyrus.

Effects of des-aspartate-angiotensin I on the expression of angiotensin AT1 and AT2 receptors in ventricles of hypertrophic rat hearts

The effects of des-aspartate-angiotensin I (DAA-I) on the expression of angiotensin AT1 and AT2 receptor in hearts of aortic coarcted rats were studied. The protocols used included competitive reverse transcription polymerase chain reaction (RT-PCR), Western blotting, and receptor-ligand binding assays. mRNA of the AT1 and AT2 receptors increased significantly after 4 days of aortic coarctation (7- and 4-folds of sham-operated, respectively). However, the protein of the AT1 receptor was not altered, and only increase in protein of the AT2 receptor was detected. There was an increase in [125I]Sar1-Ile8-angiotensin II binding sites in the ventricular membranes of hypertrophic hearts, which was attributed to an upregulation of the AT2 receptor. Treatment with i.p. DAA-I resulted in a significant reduction of cardiac hypertrophy, the maximum effect was achieved with a dose of 200 nmol/kg/day. The anti-cardiac hypertrophy effect appeared to be U-shape, and at a higher dose of 800 mol/kg/day, there was a loss of effect. DAA-I had no effect on the receptor protein in ventricles of hypertrophic hearts. However, DAA-I dose-dependently decreased the binding of [125I]Sar1-Ile8-angiotensin II to ventricular membranes. The decrease was due to a likely desensitization by internalization of the AT1 receptor, and this probably contributed to the loss of hypertrophic effects at 800 nmol/kg/day. Treatment of DAA-I also resulted in a remarkable increase in AT2 receptor mRNA (24-fold increase over the sham-operated), which was not coupled to translation. The present findings provide new information regarding the relationship between cardiac hypertrophy and the angiotensin receptors, and the anti-cardiac hypertrophic actions of DAA-I via the AT1 receptors.

Angiotensins in plasma of hypertensive rats and human

The plasma levels of des-aspartate-angiotensin I (DAA-I) in three models of hypertensive rats and hypertensive subjects were determined and compared with their normotensive controls. The rationale for the study was based on our earlier findings showing that DAA-I is a physiological angiotensin peptide that is involved in the pathophysiology of the cardiovascular system. The determination was carried out by the technique of capillary electrophoresis. Plasma level of angiotensin I, angiotensin II, and angiotensin III was also determined as a measurement of the status of the renin-angiotensin system in the different models of hypertension. DAA-I was found to be significantly lower in the spontaneously hypertensive rats (SHR) (46.6 +/- 2.5 pmol/l compared to 66.1 +/- 3.4 pmol/l for the normotensive control Wistar Kyoto rats), renal hypertensive rats (54.2 +/- 5.1 pmol/l compared to 72 +/- 2.5 pmol/l for the normotensive control Sprague-Dawley rats), and essential human hypertensive subjects (15.2 +/- 0.9 pmol/l compared to 19.5 +/- 2.5 pmol/l for the normotensive adult), whilst plasma concentration of angiotensin I and angiotensin II is reflective of the state of the renin-angiotensin system in the particular model of hypertension. When the SHR and human hypertensive subjects were treated with an angiotensin converting enzyme (ACE) inhibitor, the plasma level of DAA-I increased significantly. These findings suggest that the low plasma level of DAA-I could be a characteristic defect of the renin-angiotensin system in the two genetic models of hypertension (SHR and human essential hypertensive subjects). The increase of the nonapeptide following ACE inhibitor treatment could be an important hitherto unrecorded contributory factor to the effectiveness of ACE inhibitors in combating heart pathology.

Location of renin-angiotensin system components in the hypoglossal nucleus of the rat

The renin-angiotensin system (RAS) in the hypoglossal nuclei of the rat was studied by immunohistochemistry. Antibodies to angiotensin AT(1) receptor (AT1), angiotensinogen (ANG), renin (REN), angiotensin converting enzyme (ACE) and angiotensin II (AII) were used. All the components of the RAS with the exception of renin were detected. Light and electron microscopy revealed the following results: ANG was predominantly found in astrocytes, with small amounts in neuronal dendrites; ACE was found in the cytoplasm of neurons, dendrites and astrocyte processes; AT1 was found in the cytoplasm of neurons and dendrites, but not on the membrane; and AII was found mainly in astrocytes with some located in the dendrites and cytoplasm. Right hypoglossal nerve lesion caused an increase in expression of AT1 in neurons as early as 2 days post-lesion. An increase in expression of ANG in astrocytes was also seen, but at a much later time of 3 weeks post-lesion. For AII, staining occurred in both the neurons and astrocytes in the undamaged hypoglossal nucleus. Nerve lesion caused a disappearance of neuronal stains and an increase in astrocyte stains. There were no changes in ACE staining after nerve lesion. We speculate that ANG and AII are made within the astrocytes, whereas ACE could either be uptaken from blood or de novo synthesized. AT1 may potentially be internal soluble receptors. As to the function of AII in the hypoglossal nucleus, the data do not support AII as a neurotransmitter in the hypoglossal nucleus. It may function as a neuromodulator and also be involved in basic cellular activities, e.g. regulation of transcription factors.

Expression of metabotropic glutamate receptor 1alpha in the hippocampus of rat pilocarpine model of status epilepticus

The expression of metabotropic glutamate receptor 1alpha was studied in the rat hippocampus after pilocarpine-induced status epilepticus by Western blot and immunocytochemistry at both light and electron microscopic levels. At 1 day after pilocarpine-induced status epilepticus, there was marked decrease in metabotropic glutamate receptor 1alpha immunoreactivity at the border between stratum oriens and alveus in CA1 and CA3, and in the hilus of dentate gyrus. Between 3 and 31 days after pilocarpine-induced status epilepticus, metabotropic glutamate receptor 1alpha-immunoreactive dendrites and cell bodies in the border between stratum oriens and alveus gradually reappeared. Upregulation of metabotropic glutamate receptor 1alpha, however, was observed in the stratum oriens of CA1 at day 1, but returned to baseline by day 7. By electron microscopy, the metabotropic glutamate receptor 1alpha-immunoreactive product was demonstrated only in the post-synaptic elements in the border between the stratum oriens and alveus of CA1 and the hilus of the dentate gyrus in both control and experimental rats. At 1 day after pilocarpine-induced status epilepticus, metabotropic glutamate receptor 1alpha-immunoreactive degenerating neurons were identified in the border between stratum oriens and alveus of CA1 and the hilus of the dentate gyrus. At 7 and 31 days, many degenerating axons were also found. Present results suggest that excitoneurotoxicity mediated through post-synaptic metabotropic glutamate receptor 1alpha may be involved in degeneration and death of interneurons in the hilus of dentate gyrus, and the border between stratum oriens and alveus of CA1 in the early stage after pilocarpine-induced status epilepticus.

Cardiovascular actions of chicken-meat extract in normo- and hypertensive rats

The cardiovascular actions of a commercial chicken-meat extract known as Brand's Essence of Chicken (Cerebos Pacific Ltd, Singapore; BEC) were investigated in normo- and hypertensive rats. The spontaneously-hypertensive rat (SHR), Wistar Kyoto rat (WKY) and Sprague Dawley rat (SD) were used. The effect of oral feeding of BEC on hypertension, cardiac hypertrophy and arteriosclerosis in these animals was studied. The data showed the following effects of oral feeding of BEC: (1) feeding for 30 d did not affect the blood pressure and heart rate (determined telemetrically) of adult SHR and WKY; (2) feeding for 90 d did not affect the development of hypertension in 1-month-old prehypertensive SHR; (3) feeding for 4 d dose-dependently (0.2--3.2 ml/kg per d) attenuated cardiac hypertrophy in experimentally-induced (coarctation of the abdominal aorta) cardiac hypertrophic SD; (4) feeding to 1-month-old prehypertensive SHR for 11 months did not affect the age-related development of hypertension in this animal; (5) there was significant attenuation of the age-related development of hypertension (determined by tail-cuff plethysmography) in the WKY (P = 0.011) when the animals drank an average of 7.5 ml BEC/kg body weight per d, measured during the last 2 months of the 11-month treatment period; (6) there was chronic, as in the previous treatment, attenuation of the age-related development of cardiac hypertrophy and arteriosclerosis (quantified morphometrically) in the SHR when the animals drank an average of 2.4 ml BEC/kg per d, measured during the last 2 months of the 11-month treatment period. A parallel study using laboratory-prepared chicken-meat and pork extracts showed that the former, but not the latter, attenuated cardiac hypertrophy in experimentally-induced cardiac hypertrophic SD. These findings, showing that chicken-meat extract (both BEC and laboratory prepared) could have anti-cardiac hypertrophic, anti-hypertensive and anti-arteriosclerotic actions, were unexpected and provoking, and would challenge nutritional scientists with an interest in meat consumption and cardiovascular diseases.

Metabotropic glutamate receptor 8 in the rat hippocampus after pilocarpine induced status epilepticus

The expression of metabotropic glutamate receptor 8 (mGluR8) was studied in the rat hippocampus after pilocarpine-induced status epilepticus (APISE) by light immunohistochemistry and immunoelectron microscopy. At 1 day APISE, mGluR8 immunoreactivity was up-regulated in the entire molecular layer of the dentate gyrus. At 7 days APISE, mGluR8 immunoreactive cells began to appear in the stratum lacunosum moleculare of CA1, and by day 31, they were seen in all layers of CA1. By electron microscopy and double labelling study, the mGluR8 immunoreactive cells were identified as astrocytes. The present novel finding of induced expression of mGluR8 in astrocytes APISE suggests that it may be linked to gliosis.

Effects of des-aspartate-angiotensin I on angiotensin II-induced incorporation of phenylalanine and thymidine in cultured rat cardiomyocytes and aortic smooth muscle cells

Des-aspartate-angiotensin I, a pharmacologically active nine-amino acid angiotensin peptide, and losartan, an AT(1) angiotensin receptor antagonist, but not angiotensin-(1-7), another active angiotensin peptide, completely attenuated the angiotensin II-induced incorporation of [3H]phenylalanine in cultured rat cardiomyocytes. The attenuation by des-aspartate-angiotensin I but not that of losartan was inhibited by indomethacin. The data support an earlier suggestion that the nonapeptide attenuates cardiac hypertrophy in rats via an indomethacin-sensitive angiotensin AT(1) receptor subtype. In rat aortic smooth muscle cells, both des-aspartate-angiotensin I and angiotensin-(1-7) had no effect on the angiotensin II-induced [3H]phenylalanine incorporation. However, the two peptides significantly attenuated the angiotensin II-induced [3H]thymidine incorporation in the smooth muscle cells. The attenuation by angiotensin-(1-7) but not by des-aspartate-angiotensin I was inhibited by (D-Ala(7))-angiotensin-(1-7), a specific angiotensin-(1-7) antagonist. Des-aspartate-angiotensin I also attenuated FCS-stimulated [3H]thymidine incorporation. This attenuation was inhibited by the peptide angiotensin receptor antagonist, (Sar(1), Ile(8))-angiotensin II, but not by losartan. These data indicate that des-aspartate-angiotensin I and angiotensin-(1-7) do not participate in the process of protein synthesis in vascular smooth muscle cells and that the nonapeptide and heptapeptide act on different non-AT(1) receptors to mediate their anti-hyperplasic action. Although the exact mechanisms of action remain to be elucidated, the findings indicate that des-aspartate-angiotensin I acts as an agonist on angiotensin AT(1) and non-AT(1) receptor subtypes and induces responses that oppose the actions of angiotensin II.

Acetylcholinesterase-independent action of diisopropyl-flurophosphate in the rat aorta

Recent studies have shown that many organophosphates can bind competitively and noncompetitively to membrane muscarinic receptors. The present study investigated the responses of the rat aortic rings to diisopropyl-flurophosphate (DFP), an organophsophorus cholinesterase inhibitor, and the possible involvement of muscarinic receptors. DFP caused a concentration-dependent contraction when added cumulatively from 10(-8) to 10(-4) M. This contraction was inhibited in a noncompetitive manner by high concentrations of atropine (1.5 x 10(-6) and 1.8 x 10(-6) M) but was unaffected by similar concentrations of selective muscarinic receptor subtype antagonists, pirenzepine, 11-2[2-[(diethylamino)methyl]-1-piperidinyl]acetyl-5, 11-dihydro-6H-rido[2,3-b][1,4]benzodiazepin-6-one (AF-DX116) and 4-Diphenylacetoxy-N-methyl piperidine methiodide (4-DAMP). Phentolamine, an alpha-adrenoceptor antagonist, was able to inhibit the DFP-induced contraction in a noncompetitive manner at a concentration of 10(-7) M. These findings suggested that the DFP-induced contraction in the rat aortic rings was mediated by norepinephrine that was released from sympathetic nerve terminals present in the aortic rings.

Actions of angiotensin peptides on the rabbit pulmonary artery

The presence of the angiotensin AT1A-like receptor subtype in the pulmonary artery and AT1B-like receptor subtype in the pulmonary trunk of the rabbit has been reported in two earlier studies. The present study further investigated these receptor subtypes using five other angiotensins (namely angiotensin II, angiotensin III, angiotensin IV, angiotensin-(1-7) and angiotensin-(4-8)). The direct action of the angiotensins on the rabbit pulmonary arterial and trunk sections and the ability of each angiotensin to further contract or relax preconstricted sections of the pulmonary artery and trunk were studied using the organ bath set-up. The effects of angiotensin III on the 3H overflow from re-uptaken [3H]noradrenaline in the electrically-contracted rabbit pulmonary arterial and trunk sections were also studied. The contractile response of the arterial and trunk section had the following rank order potency: angiotensin II > angiotensin III > angiotensin IV. The contractile response to these angiotensins was greatly reduced or absent in the pulmonary trunk. Angiotensin II further contracted the preconstricted arterial and trunk sections. In contrast, angiotensin III further contracted the preconstricted arterial section but relaxed the preconstricted trunk section. Angiotensin IV similarly relaxed the preconstricted trunk section but had minimum effect on the preconstricted arterial section. Angiotensin-(1-7) and angiotensin-(4-8) had no effect on both sections. The actions of the three angiotensins were inhibited by losartan, an AT1-selective antagonist. Indomethacin, a cyclo-oxygenase inhibitor, inhibited the relaxation caused by angiotensin III and angiotensin IV in the trunk section. The effects of angiotensin III on the electrically preconstricted sections of the pulmonary trunk and artery were not accompanied by any significant changes in 3H overflow. The differential responses produced by angiotensin II and its immediate metabolites via two positionally located and functionally opposing receptor subtypes suggest that the pulmonary trunk and artery is not a passive conduit but an important regulator of blood flow from the heart to the lung.

Pre- and/or post-synaptic localisation of metabotropic glutamate receptor 1alpha (mGluR1alpha) and 2/3 (mGluR2/3) in the rat spinal cord

Using immunocytochemical techniques (light and electron microscopy), weakly stained metabotropic glutamate receptor (mGluR) 1alpha immunoreactivity was detected in lamina I of the rat spinal cord. Immunoreactivity for mGluR2/3 was almost undetectable in this lamina and outer lamina II. In lamina II, there was mGluR1alpha immunoreactivity. Strongly stained mGluR2/3 was seen in the inner layer of lamina II and the dorsal part of lamina III. In laminae III X, weakly to moderately stained mGluR1alpha immunoreactive product was demonstrated. Similar staining for mGluR2/3 was also seen in lamina III-VI and in lamina X, but mGluR2/3 immunoreactivities were few in lamina VII-IX. With electron microscopy, mGluR1alpha immunoreactivity was seen in neuronal cell body and dendrites in lamina II of the dorsal horn. In the lateral and ventral horns, only dendrites of neurons were mGluR1alpha immunopositive. Some mGluR2/3 immunopositive dendrites were demonstrated in lamina II of the dorsal horn, lateral and ventral horns. In the ventral horn, mGluR2/3 immunopositive axon and axon terminals were demonstrated. Some mGluR2/3 immunopositive astrocytes were also demonstrated in the three areas and their strongly stained processes wrapped around neuronal cell bodies and synapses.

M3/M1-Selective antimuscarinic tropinyl and piperidinyl esters

The binding affinities of some tropinyl and piperidinyl esters for the submandibulary glands (M3/M1) and heart ventricle (M2) were determined from displacement experiments using 3H-labelled N-methylscopolamine as radioligand. The antimuscarinic activities of these esters were also evaluated on guinea pig bronchi. The esters inhibited the M3-mediated carbachol-induced contraction of the bronchial smooth muscle and a reasonable correlation was obtained between the binding affinities of the esters for the submandibulary glands (pKM3,M1) and their inhibitory activities (pIC50) on guinea pig bronchi. A promising compound, N-methylpiperidinyl cyclohexylphenylpropionate (NCPP) which combined good antimuscarinic activity (pA2=9.34) with a 20-fold selectivity at the M3/M1 receptors, was identified. Quantitative structure-activity relationships (QSAR) showed that the size of the ester was the main structural feature determining both binding affinity for the M3/M1 receptors and inhibitory activity on guinea pig bronchi. Esters with substituted acyl side chains (fewer hyperconjugable H atoms at the alpha-carbon) are generally associated with better activity and affinity.

Eurycoma longifolia increases sexual motivation in sexually naive male rats

The aim of this study is to provide evidence on the aphrodisiac property of Eurycoma longifolia Jack. An electric grid was used as an obstruction in the electrical copulation cage in order to determine how much an aversive stimulus the sexually naive male rat for both the treated with E. longifolia Jack and control groups were willing to overcome to reach the estrous receptive female in the goal cage. The intensity of the grid current was maintained at 0.12 mA and this was the intensity in which the male rats in the control group failed to crossover to reach the goal cage. Results showed that E. longifolia Jack continued to enhance and also maintain a high level of both the total number of successful crossovers, mountings, intromissions and ejaculations during the 9-12th week observation period. In conclusion, these results further enhanced and strengthened the aphrodisiac property of E. longifolia Jack.

Angiotensin AT1 receptor subtypes in the rabbit pulmonary artery. A ligand binding study

The present ligand binding study showed that the rabbit pulmonary artery contained two subtypes of losartan-sensitive angiotensin receptor. The two receptor subtypes are differentially distributed. The high affinity receptor subtype is located predominantly in the cardia end of the artery while the low affinity receptor subtype is found mainly in the pulmonary portion of the artery. The Kd for the high and low affinity receptors for sar1, Ile8-angiotensin II was found to be 0.25 +/- 0.005 and 0.88 +/- 0.02 nM, respectively; and for angiotensin II to be 0.43 +/- 0.001 and 0.96 +/- 0.02 nM, respectively. In the presence of 1 mM GppNHp, the high affinity receptor subtype was converted to the low affinity subtype, indicating that it is G-protein coupled. 1 mM GppNHp had no effect on the low affinity receptor subtype. The present data support the findings of an earlier functional study which also showed the existence and similar differential distribution of two losartan-sensitive angiotensin receptors in the rabbit pulmonary artery. However, the significance of these findings in regard to the regulation of pulmonary circulation in normal and pathological conditions remains to be investigated.

Synthesis and pharmacological characterization of O-alkynyloximes of tropinone and N-methylpiperidinone as muscarinic agonists

A number of O-alkynyloximes of tropinone and N-methyl-4-piperidinone have been synthesized and evaluated for muscarinic activity. The affinities of these oximes were tested in homogenates of cerebral cortex, heart, and submandibulary glands from rats using [3H]pirenzepine and [3H]-N-methylscopolamine as radioligands. The oximes bind to the cortical muscarinic receptors with pKi values varying from 3 to 7. Higher binding affinities were observed for the O-alkynyl tropinone oximes than the corresponding piperidinone analogues. Binding to the muscarinic sites in the heart and submandibulary glands was also observed but with lower affinities. Good M1 subtype selectivity (10-fold or greater) was observed with some oximes (26a, 28a, 32a) at the cortical sites. These oximes also attenuated scopolamine-induced impairment of the water mask task in mice. Functional assays for M3 activity on the rat aorta showed that all oximes possessed M3 agonist action but M2 agonist activity was not observed at the endothelium-denuded rabbit aorta. Analysis of the quantitative structure-activity relationship (QSAR) indicated that the Connolly surface area is an important determinant of activity, accounting for 70% of the variation in cortical binding affinity among the oximes.

Hypothalamic angiotensin receptor subtypes in normotensive and hypertensive rats

The binding of 125I-labeled [Sar1,Ile8]angiotensin II to the hypothalamic membranes of the normotensive Wistar-Kyoto rat (WKY) and the spontaneously hypertensive rat (SHR) was studied. Displacement experiments with four centrally active angiotensins, losartan, and PD-123319 confirm the known existence of angiotensin AT1 and AT2 receptors in the rat hypothalamus. The values of the inhibitory constants for angiotensin II and PD-123319 in the SHR were significantly lower than the corresponding values in the WKY, indicating the possible existence of high-affinity hypothalamic AT1 and AT2 receptors for the two ligands in the SHR. The angiotensin AT1 receptor was further separated into a 5'-guanylyl imidodiphosphate-sensitive and -nonsensitive subtype, indicating that one of the subtypes is G protein coupled. The SHR has significantly higher numbers of measurable AT1-receptor subtypes as well as AT2 receptor subtypes. The former data support the findings of other investigators showing that the hypothalamus of the SHR expressed more AT1A and AT1B mRNAs than that of the normotensive rat. Des-Asp1-angiotensin I, which is known to attenuate the central pressor action of angiotensin II and angiotensin III, acts on both the AT1 and AT2 receptors, although it has a higher affinity for the AT1 receptors. The overall increase in the number of AT1 and AT2 receptors in the SHR is in line with the contention that the brain of the hypertensive rat, compared with that of the WKY, has a hyperactive renin-angiotensin system.

Effects of des-Asp-angiotensin I on experimentally-induced cardiac hypertrophy in rats

We studied the effects of des-Asp-angiotensin I, a nine amino acid peptide, on cardiac hypertrophy caused by coarctation of the abdominal aorta in Sprague-Dawley rats. The nonapeptide was effective when given either intravenously or orally. Maximum attenuation was observed with an i.v. dose of 153 pmol/day for 4 days, and an oral dose of 250 nmol/day for 4 days. Three mg p.o. losartan, an angiotensin AT1 receptor antagonist, produced comparable attenuation. However, the attenuation produced by des-Asp-angiotensin I but not by losartan was blunted by 30.4 micromol of indomethacin. The oral efficacy of the nonapeptide was partly due to its low effective i.v. doses which were in the nM range. This range is below the Km of most enzymes including those of the intestinal peptidases (the Km of most enzymes is in the microM range). However, the mechanism of absorption of the peptide from the GIT into the systemic circulation remains to be investigated. The findings demonstrate for the first time, the anti-cardiac hypertrophic action of an angiotensin peptide. Unlike the ACE inhibitors and angiotensin receptor antagonists, the nonapeptide acts as an agonist on an indomethacin-sensitive angiotensin receptor to exert its action.

Synthesis, antimuscarinic activity and quantitative structure-activity relationship (QSAR) of tropinyl and piperidinyl esters

A series of tropinyl and piperidinyl esters was synthesized and evaluated for inhibitory activities on the endothelial muscarinic receptors of rat (M3) and rabbit (M2) aorta. Some of the esters (cyclohexylphenylglycolates and cyclohexylphenylpropionates) were found to be better antimuscarinic compounds than standard M2 and M3 inhibitors such as AFDX116 and 4-diphenylacetoxy-N-methylpiperidine (DAMP), with pKEC50 values in the range of 8-9. A few esters were found to be more selective M3 than M2 inhibitors, but these tended to have low activities. The hydrophobic, electronic and steric characteristics of these esters were correlated with antimuscarinic activity by using appropriate parameters representing hydrophobicity (HPLC capacity factor, log kw), size (molecular volume) and electronic character (Taft's polar substituent constant sigma * and 13C chemical shift difference delta delta). Finally, 92% of the M2-inhibitory activities of the esters could be accounted for by the size and electronic character sigma * of the side chain. In contrast, the M3-inhibitory activities of these esters were mainly attributed to the electronic nature (sigma *, delta delta) of the side chain, with good activity being associated with electron-withdrawing groups. Visualization of the comparative molecular field analysis (CoMFA) steric and electrostatic fields provided further confirmation of the structure-activity relationship (SAR) derived from traditional quantitative structure activity relationship (QSAR) approaches.

Eurycoma longifolia JACK and orientation activities in sexually experienced male rats

The effects of Eurycoma longifolia JACK were studied on the orientation activities of sexually experienced male rats towards receptive females (mounting, licking, anogenital sniffing), environment (exploration, raring, climbing), themselves (genital grooming, non-genital grooming) and mobility (unrestricted, restricted) after dosing them with 200, 400 and 800 mg/kg body weight twice daily for 10 d prior to the test. The results showed that E. longifolia JACK modified the orientation activities of the treated male rats in that they significantly displayed more frequent and vigorous mounting, licking and anogenital sniffing towards the receptive females, and it further intensified self orientation as indicated by the increased grooming of the genitals compared to the controls (p<0.05). In addition, rats treated with 800 mg/kg of methanol, water and butanol extracts of E. longifolia JACK continued to show confinement to a particular area of the cage (around the female), thus showing restriction in movement as compared to the controls (p<0.05). However, the treated males possessed a lack of interest in the external environment as indicated by a reduction in exploration, raring and climbing on the cage wall. Hence, the present study further supports the folk use of E. longifolia JACK as an aphrodisiac.

Actions of des-Asp angiotensin I on the aortic rings of the normo- and hypertensive rats

The actions of des-Asp angiotensin I, a nine aminoacid peptide, on the contractility of the aortic rings of the normotensive Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were studied. In the presence of captopril which prevented its degradation to angiotensin III by angiotensin converting enzyme, des-Asp-angiotensin I exerted direct concentration-dependent contractile action on the aortic rings. The contractile action was concentration-dependently attenuated by the AT1 receptor antagonist, losartan, but was not affected by the AT2 receptor antagonist, PD123319; indicating that angiotensin AT1 receptors mediate the direct contractile action. The response to des-Asp-angiotensin I was qualitatively different from that to angiotensin III i.e. lower potency and a likely higher efficacy suggesting that the two angiotensins act on different subtypes of angiotensin receptor. The response of the aortic rings to angiotensin III and des-Asp-angiotensin I in the SHR was significantly lower than the corresponding responses in WKY. Des-Asp-angiotensin I attenuated in a concentration-dependent and U-shape manner the response of the aortic ring to angiotensin III in the SHR but not in the WKY. Significant attenuation occurred in the pico to nano molar range of des-Asp-angiotensin I which is within the physiological concentration of the nonapeptide. Although these findings are the first demonstration of a direct and modulatory action of des-Asp-angiotensin I on the blood vessels of the SHR and raise the possibility of its involvement in blood pressure control, its exact role remains to be further studied.

Expression of glutamate receptor subunits 2/3 and 4 in the hypoglossal nucleus of the rat after neurectomy

The immunoreactivity of glutamate receptor subunits 2/3 (GluR2/3) and 4 (GluR4) was studied following neurectomy of the hypoglossal nucleus (NH). After a short period of survival (at 1, 2, and 7 days postoperation, dpo), GluR2/3 immunoreactivity was barely dectectable in the operated side of HN. During these periods, GluR4 immunoreactivity was present, but was greatly reduced when compared with the GluR4 immunoreactivity in the unoperated side. The data suggest that of the 4 subunits of the AMPA receptor, GluR2/3 is the most susceptible receptor to the early stage of hypoglossal neurectomy, and GluR4 tolerated the lesion more than the others. It is also suggested that both GluR2/3 and 4 may play a very important neuroprotective role in the early stage of neuronal degeneration after axotomy, especially the former. Following a midterm survival period (14, 21, and 35 dpo), GluR2/3 immunoreactivity gradually reappeared in some neurons on the operated side of HN, which may indicate functional recovery. However, the number of GluR4-immunopositive neurons on the operated side of HN was greatly reduced. The reason for such a reduction is not known, but, from the speculative point of view, it is possible that the disappearance of GluR4-positive neurons may be related to their excitotoxic property, especially at 35 dpo, when neuronal cell death had already occurred. Following a long-term period of survival (i.e., 56, 90, and 120 dpo), the numbers of surviving neurons remained fairly constant, suggesting the possible cessation of neuronal death.

Eurycoma longifolia Jack enhances libido in sexually experienced male rats

The effects of Eurycoma longifolia Jack were studied on the libido of sexually experienced male rats after dosing them with 200, 400 and 800 mg/kg body weight twice daily of different fractions of E. longifolia Jack for 10 days. Results showed that E. longifolia Jack produced a dose-dependent increase in mounting frequency of the treated animals with 400 mg/kg of chloroform, methanol, water and butanol fractions resulting in mounting frequencies of 5.3 +/- 1.2, 4.9 +/- 0.7, 4.8 +/- 0.7 and 5.2 +/- 0.1, and 800 mg/kg further increased them to 5.4 +/- 0.8, 5.4 +/- 0.8, 5.2 +/- 0.6 and 5.3 +/- 0.2 respectively but there were no erections, intromissions, ejaculations or seminal emissions during the 20-min observation period which allowed for the measurement of sexual arousal reflected by mounting frequency uninfluenced by other behavioural components. This study provides evidence that E. longifolia Jack is a potent stimulator of sexual arousal in sexually vigorous male rats in the absence of feedback from genital sensation.

Determination of aminopeptidase X activity in tissues of normo- and hypertensive rats by capillary electrophoresis

Aminopeptidase X, an enzyme that degrades angiotensin I to des-asp-angiotensin I, was determined in the lung, liver, kidney, plasma, endothelium and aortic smooth muscle of the spontaneously hypertensive rat (SHR) and its normotensive control, the Wistar Kyoto rat (WKY). The enzyme activity in the lung, kidney, plasma and endothelium of the SHR was elevated and this supports an earlier suggestion that in certain critical tissues of the SHR, the degradation of angiotensin I is shunted in favour of the des-asp-angiotensin I pathway. In these tissues, the formation of pressor angiotensin II would be curtailed and that of des-asp-angiotensin I enhanced. As des-asp-angiotensin I lacks direct vasopressor action, its preferential formation over that of angiotensin II could be a physiological response to the prevailing hypertension in the SHR.

Metabotropic glutamate receptor subtype-1 alpha (mGluR1 alpha) immunoreactivity in ependymal cells of the rat caudal medulla oblongata and spinal cord

Immunohistochemical study of the distribution of glutamate receptor subunits 1-4 (GluR1-4), NMDA receptor subunit 1 and metabotropic glutamate receptor subtypes 1-3 (mGluR1-3) in the ependymal cells of the caudal medulla oblongata and upper thoracic spinal cord was carried out. The results showed that ependymal cells and tanycytes expressed only the metabotropic receptor subtype, mGluR1 alpha. Some of the mGluR1 alpha-positive long basal processes of the tanycytes reached the pia mater; some made contact with capillaries. It was suggested that the activity of the these mGluR 1 a-positive tanycytes may be regulated by the CSF and blood. The presence of many mGluR1 alpha positive fibres in the area postrema suggests that mGluR1 alpha subtype in this region may be involved in cardiovascular regulation.

Effect of oral feeding of essence of chicken on the level of 5-hydroxyindole acetic acid in the cerebrospinal fluid of the rat

The effect of oral feeding of a commercial preparation of essence of chicken (Brand's Essence of Chicken, BEC) on the level of 5-hydroxyindole acetic acid (5-HIAA) in the cerebrospinal fluid (CSF) of the rat was investigated. BEC, when fed to the rat for a period of 3 days, significantly increased the CSF level of 5-HIAA in seven out of 12 animals studied. As the level of CSF 5-HIAA is taken as an indication of 5-hydroxytryptamine (5-HT) activity in the brain, it is possible that BEC increased brain 5-HT activity. This increase was not due to the ingestion of tryptophan, the primary precursor of 5-HT, because BEC contains undetectable level of tryptophan. The data indicate that by causing an increase in brain 5-HT activity, consumption of BEC may lead to the activation of 5-HT-dependent physiological process like sleep improvement, mood elevation, analgesia, facilitation of motor output and regulation of circadian rhythm. However, such a possibility remains to be further investigated.

Subtypes of losartan-sensitive angiotensin receptor in the rabbit pulmonary artery

1. The short rabbit pulmonary artery was denuded of endothelium and divided into three sections, the cardiac end (cardiac), middle and pulmonary end (pulmonary) sections, respectively. Des-Asp-angiotensin I attenuated the contractions of the cardiac and middle sections to transmural nerve stimulation but potentiated the contractions in the pulmonary section. 2. The actions of the nonapeptide were inhibited completely by 10(-6) M losartan; however, a similar concentration of PD123319 had no effect. Indomethacin (10(-6) M) also inhibited completely the attenuation in the cardiac and middle sections but had no effect on the potentiation seen in the pulmonary section. 3. The data suggest that the two differential responses of the pulmonary artery to des-Asp-angiotensin I are mediated by two separate subtypes of the losartan-sensitive angiotensin AT1 receptor.

Actions of D-amino acid-substituted analogues of des-Asp-angiotensin I on the central pressor action of angiotensin III

The ability of intracerebroventricularly (i.c.v.) administered D-amino acid-substituted analogues of des-Asp-angiotensin I to attenuate the central pressor action of angiotensin III in the rat was investigated. Of the 9 D-amino acid-substituted analogues, only D-tyrosine-des-Asp-angiotensin I was active. I.c.v. D-tyrosine-angiotensin I but not i.c.v. D-isoleucine-angiotensin I (when prevented from degradation by angiotensin converting enzyme with captopril) also attenuated the central pressor action of angiotensin III. In vitro incubation of angiotensin I, D-tyrosine-angiotensin I and D-isoleucine-angiotensin I with brain homogenate resulted in the formation of des-Asp-angiotensin I, D-tyrosine-des-Asp-angiotensin I and D-isoleucine-des-Asp-angiotensin I, respectively. This shows that i.c.v. angiotensin I and D-tyrosine-angiotensin I were converted by brain aminopeptidase to des-Asp-angiotensin I and D-tyrosine-des-Asp-angiotensin I, respectively, which then attenuated the pressor action of angiotensin III. When compared to the findings of similar D-substitution studies carried out with angiotensin II and [Sar1,Ile8]angiotensin II by other investigators, des-Asp-angiotensin I has a stringent structural-activity relationship. These findings suggest that, at the physiological level, des-Asp-angiotensin I is formed from angiotensin I and that the nonapeptide probably acts on a distinct subtype of angiotensin receptors.

Reduction of dihydroxyphenylacetic acid by a novel enzyme in the rat brain

A novel enzyme that converts dihydroxyphenylacetic acid (DOPAC) to dihydroxyphenylethanol (DOPET) was found to be present in the microdialysate of the rat brain. The enzyme, named DOPAC reductase, was inhibited by EDTA and stimulated by divalent cations like Zn2+, Mn2+, Co2+ and Cu2+. Its Km, pH optimum and temperature optimum were found to be 32 +/- 2 microM, 7.5 and 40 degrees, respectively. The equivalent acid metabolite of noradrenaline, 3,4-dihydroxymandelic acid, and the methoxylated acids of both noradrenaline and dopamine, 3-methoxy-4-hydroxymandelic acid and 3-methoxy-4-hydroxyphenylacetic acid, were found not to be substrates of DOPAC reductase. Thus, DOPAC reductase may be an enzyme that is specifically involved in the one-step conversion of DOPAC to DOPET in the central metabolism of dopamine.

Effects of des-Asp-angiotensin I on the electrically stimulated contraction of the rabbit pulmonary artery

In the presence of 3 x 10(-6) M captopril, 5 x 10(-7) M des-Asp-Angiotensin I was found to inhibit the electrically (1 and 2 Hz) induced contraction of the rabbit pulmonary artery but had no significant effect on the noradrenaline-stimulated contraction. 2.8 x 10(-6) M indomethacin and 10(-6) M losartan but not 10(-6) M (S) 1-([4-(dimethylamino)-3-methylphenyl]methyl)-5-(diphenylacetyl)-4, 5,6,7- tetrahydro-1H-imidazo(4,5-c]pyridine-6-carboxylic acid, ditrifluoroacetate, dihydrate (PD123319) attenuated the inhibition. The inhibition of the electrically stimulated contraction by 5 x 10(-7) M des-Asp-angiotensin I coincided with a significant drop in the accompanying evoked 3H overflow from re-uptaken [3H]noradrenaline. The results indicate that des-Asp-angiotensin I acts presynaptically on a subtype of angiotensin receptor that involves the release of prostaglandin(s). In addition, this receptor subtype is susceptible to blockade by angiotensin AT1- but not AT2-specific receptor antagonists. It was suggested that this receptor subtype is identifiable with the recently described angiotensin AT1B receptor subtype found in the brain, pituitary and adrenal glomerulosa. These findings demonstrated a direct action of sub-micromolar concentrations of des-Asp-angiotensin I on a blood vessel and indicate that the nonapeptide is an active angiotensin per se.

Effects of des-Asp-angiotensin I on the contractile action of angiotensin II and angiotensin III

Nanomolar concentrations of des-Asp-angiotensin I potentiated the contractile action of angiotensin II on the rabbit aortic ring but attenuated the contractile action of angiotensin III in the same tissue. Indomethacin had no effect on the potentiation of angiotensin II but inhibited the attenuation of angiotensin III. The action of angiotensin II, angiotensin III and des-Asp-angiotensin I was not inhibited by (S)-1-}[4-(dimethylamino)-3-methylphenyl]methyl}-5-(diphenylacetyl )-4,5,6, 7-tetrahydro-1H-imidazo-[4,5-c]pyridine-6-carboxylic acid, ditrifluoroacetate, dihydrate (PD123319), an angiotensin AT2 receptor antagonist. The data show that angiotensin II and angiotensin III act on different subclasses of angiotensin receptors and that their actions are differentially modulated by des-Asp-angiotensin I. The data also indicate the possibility that des-Asp-angiotensin I is a functional peptide that modulates the contractile action of the two angiotensins at sub-nanomolar concentrations.

Degradation of angiotensin I to [des-Asp1]angiotensin I by a novel aminopeptidase in the rat hypothalamus

The particulate enzyme that degrades angiotensin I (ANG I) to [des-aspartate1]angiotensin I ([des-Asp1]ANG I) in the hypothalamic homogenate of the rat has been established as a specific aminopeptidase. The major characteristics is its resistance to inhibition by 10(-4) M amastatin, bestatin and EDTA. Among the four amino acyl-beta-naphthylamides (aspartyl, glutamyl-, arginyl- and leucyl-beta-naphthylamide), aspartyl-beta-naphthylamide is the most susceptible substrate of the enzyme; being degraded at twice the rate of arginyl-, and leucyl-beta-naphthylamide, and six times that of glutamyl-beta-naphthylamide. Although the precise role of this aminopeptidase has yet to be determined, its presence establishes the existence of a specific pathway for the degradation of ANG I that bypasses the formation of ANG II. The relationship between degradation and hypertension is shown by our recent findings that the formation of [des-Asp1]ANG I form ANG I in the hypothalamic homogenate of the spontaneously hypertensive rat (SHR) is significantly enhanced, and the findings of other investigators that the production of ANG II by neuronal cultures of the SHR is significantly decreased.

Formation of des-Asp-angiotensin I in the hypothalamic extract of normo- and hypertensive rats

Exogenous angiotensin I (ANG I) was degraded to mainly des-Asp-ANG I instead of ANG II in the hypothalamic homogenate of the Sprague Dawley (SD), Wistar Kyoto (WKY), left renal artery stenosed hypertensive SD (LRAS), deoxycorticosterone acetate/salt-induced hypertensive SD (DOCA-salt) and spontaneously hypertensive rats (SHR). In the same homogenate, ANG II was degraded to ANG III and ANG III remained unchanged during the first 10 min of incubation. However, all the homogenates were able to catalyse hippuryl-L-histidyl-L-leucine to hippuric acid and the catalysis was completely inhibited by 3 microM captorpil. The data show that the angiotensin converting enzyme present in the hypothalamus when extracted by the normal laboratory procedures is not able to hydrolyse ANG I to ANG II. In addition, the aminopeptidase that degraded ANG I to des-Asp-ANG I was not inhibited by amastatin, bestatin and EDTA, indicating that it is not aminopeptidase A or B. The formation of hippuric acid was significantly higher in the homogenate of the LRAS whilst the SHR and DOCA-salt showed significant higher rate of des-Asp-ANG I formation than in the normotensive control rats.

Enhanced pressor response to angiotensin III in spontaneously hypertensive rats: effects of losartan

The conscious spontaneously hypertensive rat (SHR), compared to its normotensive control Wistar Kyoto rat (WKY), exhibited a significantly greater pressor response to i.v. angiotensin II and angiotensin III. Losartan (10 mg/kg i.v.) lowered the basal blood pressure of the SHR but had no significant effect on that of the WKY. However, it attenuated the pressor response to both angiotensins in the SHR and WKY, the degree of attenuation being significantly greater with angiotensin III. In addition, the pressor responses induced by both angiotensin II and angiotensin III in the WKY, compared to those of the SHR, were more markedly inhibited by losartan. The results indicate a possible over-expression of angiotensin AT1 receptors in the SHR, and that both angiotensin II and angiotensin III contribute to the hypertension by acting on these receptors.

Novel central action of des-Asp-angiotensin I

Intracerebroventricularly administered des-Asp-angiotensin I, when prevented from degradation by prior administration of captopril, attenuated dose-dependently the central pressor actions of angiotensin II and angiotensin III in the spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats. This finding is the first demonstration of an intrinsic action of des-Asp-angiotensin I and, together with earlier finding of its increased production in the hypothalamus of the spontaneously hypertensive rat, may support the suggestion that the nonapeptide is a functional angiotensin that regulates the pressor action of angiotensin II and angiotensin III in the brain.

Determination of angiotensins by capillary electrophoresis

A protocol to separate ten peptides of the angiotensin family by capillary electrophoresis was described. The experiment was carried out using the Waters Quanta 4000 Electrophoresis system and the steps taken to determine the optimum electrophoretic conditions include (i) the use of different electrolytes, (ii) variation of ionic composition and pH of the electrolytes, (iii) variation of applied voltage and the wavelength of ultraviolet detection. Successful separation of the ten angiotensin peptides was obtained using a voltage of 10 kV, 0.1 M phosphoric acid (pH 1.95) as electrolyte and ultraviolet detection at 185 nm. The protocol was then used to follow the metabolism of exogenous angiotensin I (ANG I) in rat lung homogenate and the separation and identification of an angiotensin peptide in human plasma. In addition to these two applications, the protocol can be used to separate and identify angiotensins and other peptides for which specific antibodies have yet to be developed.

In vivo study of angiotensin II tachyphylaxis in freely moving normo- and hypertensive rats

In vivo tachyphylaxis to the angiotensin II-induced increase in mean arterial blood pressure was studied in conscious freely moving rats by telemetry blood pressure monitoring. The animals studied were the normotensive Sprague Dawley rats (SD), the spontaneously hypertensive rats (SHR), and two models of experimentally-induced hypertensive rats, namely, the left renal artery stenosed SD hypertensive rat (LRAS) and the deoxycorticosterone acetate/salt SD hypertensive rat (DOCA). Two consecutive dose-response curves to angiotensin II in each rat were obtained. The increase in mean arterial pressure (MAP) at each bolus dose of the first dose-response curve was found not to be significantly different from the corresponding value of the second dose-response curve in the four models of rat studied (i.e. no significant difference in the intra-rat response to AII). In addition, the slope of the dose-response curve is similar for each model of rat indicating that there was no inter-model variation to the response of AII. The results show that the response to AII in the SD and the three models of hypertensive rats was remarkably similar and that they did not develop tachyphylaxis to the pressor response of AII at concentrations ranging from circulating level of 0.0005 nmoles/kg (10(-11) M) to 10 nmoles/kg (2 x 10(-7) M). This was despite the fact that the SD had normal blood pressure and the genesis of hypertension in each model of the hypertensive rats was different.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of pentobarbital and chlordiazepoxide on the central pressor action of angiotensins in normo- and hypertensive rats

Pentobarbital and chlordiazepoxide administered intracerebroventricularly (i.c.v.) attenuated dose dependently the pressor action of i.c.v. angiotensin II and angiotensin III in the conscious spontaneously hypertensive rat (SHR) and the normotensive control Wistar Kyoto rat (WKY). Attenuation of the pressor action by the two drugs was more marked in the WKY than in the SHR. Based on the fact that both drugs act via the gamma-aminobutyric acid (GABA) receptors, the data support the suggestions (i) that a central GABAergic system regulates blood pressure, (ii) that there is probable dysfunction of the GABA receptors in SHR.

Central dopaminergic neurons in tilapia: effects of gonadectomy and hypothalamic lesion

The effects of gonadectomy, testosterone and estrogen on the dopamine (DA) neurons were examined by measuring the concentrations of DA and 3,4-dihydroxyphenylacetic acid (DOPAC) in the brain and pituitary of male tilapia. The tuberal area and the pituitary had significantly high levels of DA and low levels of DOPAC, indicating the existence of a rich dopaminergic innervation in these areas. Gonadectomy and sex steroid replacement had no effect on DA and DOPAC levels. Preoptic lesions (14 days survival period) significantly increased DA levels of the pituitary, indicating a possible existence of a preoptico-hypophysial neural system that inhibits pituitary DA synthesis in tilapia. The lack of effect by preoptic (4 days survival period) and posterior hypothalamic lesions on the DA content of the pituitary indicates the absence of dopaminergic innervation of the pituitary by the preoptic and the posterior hypothalamus. Instead, the overall results do suggest the anterior periventricular area as a possible source of pituitary dopaminergic innervation.

Degradation of angiotensin I in the endothelium and smooth muscle of the rat aorta

In homogenates of the endothelium and smooth muscle cum adventitia of the rat aorta, exogenous angiotensin (ANG) I was found to be degraded to des-aspartate-ANG I (des-Asp-ANG I) instead of ANG II. ANG II and ANG III were not detectable in either of the homogenates after 5, 10 and 30 min of incubation with the decapeptide. However, both the homogenates were able to catalyse hippuryl-L-histidyl-L-leucine (HHL) to hippuric acid and the catalysis was completely inhibited by 3 microM captopril. The data show that the angiotensin converting enzyme (ACE) present in the homogenates of rat aorta, prepared by normal laboratory procedures, is not able to hydrolyse ANG I to ANG II. This finding has important consequences in the study of vascular ACE as the assay of the enzyme is often carried out using crude homogenate and HHL or other artificial substrates. In addition, the aminopeptidase that degraded ANG I to des-Asp-ANG I was not inhibited by either amastatin or bestatin, indicating that it was not aminopeptidase A or B. Together with the recent findings of other investigators which show that the de novo production of ANG II in vascular tissues is stimulated and inhibited by beta- and alpha-agonists, respectively, our present data may suggest that production of vascular ANG II occurs only in intact tissues and is probably under adrenergic regulation.

Angiotensin II-induced tachyphylaxis in aortas of normo- and hypertensive rats: changes in receptor affinity

Angiotensin II-induced tachyphylaxis was found to be associated with changes in agonist affinity (Ka) and EC50 values, as assessed by using Furchgott's equation derived for the determination of full agonist affinity. The diminished affinity during tachyphylaxis was observed in aorta ring preparations from both Wistar-Kyoto and spontaneously hypertensive rats. Noradrenaline (10(-9) M) reduced the increase in the Ka value during tachyphylaxis in both strains. The results suggest that tachyphylaxis occurs at the level of the receptor, resulting in changes in the affinity of the ligand for the receptor and in the coupling efficiency of the receptor system. The results also support the probable role of modulators acting on allosteric receptor sites.

Muscarinic receptors in the aortae of normo- and hypertensive rats: a binding study

The muscarinic receptors in the aorta of the normo- and hypertensive rats were characterised with tritiated acetylcholine (3H-ACh) and various muscarinic receptor antagonists. The binding of 3H-ACh to the endothelial membranes of the normotensive Wistar Kyoto rats (WKY) and the spontaneously hypertensive rats (SHR) was displaceable by nanomolar range of scopolamine but only by micromolar range of atropine and homatropine. The reverse was observed with the muscle binding sites, i.e. the 3H-ACh was displaceable by nanomolar range of atropine and homatropine but only by micromolar range of scopolamine. Pirenzepine and 4-diphenyl-acetoxy-N-methyl-piperidine metobromide (4-DAMP) displaced the binding of 3H-ACh from both tissues in the nano to micromolar range, with the displacement from the endothelial binding sites occurring at lower concentration range of the ligands. The apparent IC50 values of both compounds for the smooth muscle were 9 and 16 times greater than those for the endothelial binding sites respectively. When saturated with guanylyl-imididiphosphate (GppNHp), conversion of high to low-affinity binding site occurred in both tissues of the WKY but only in the smooth muscle of the SHR. GppNHp had no apparent effect on the binding of 3H-ACh to the endothelial binding sites confirming that the high-affinity site for 3H-ACh was missing in the endothelium of the SHR.

Actions of norepinephrine and angiotensin II on aortic rings of adult and aged normotensive and hypertensive rats

Development of desensitization to physiologic concentration of norepinephrine (NE 10(-9) M) and its effects on angiotensin II (AII) tachyphylaxis in the aortic rings of adult and aged normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were investigated. Aortic rings of all animals developed desensitization to 10(-9) M NE and tachyphylaxis to AII (10(-9)-10(-6) M). In normotensive WKY, the response to NE and AII was not affected by age, whereas in SHR desensitization to NE and tachyphylaxis to AII were significantly more marked in aged animals. The desensitization to 10(-9) M NE appeared to be homologous because this physiologic concentration of NA significantly attenuated tachyphylaxis to AII (for concentrations of 10(-8)-10(-6) M) in the aortic rings of both adult and aged WKY. Tachyphylaxis to AII was not affected by 10(-9) M NE in either adult or aged SHR, however. These data support our previous finding of similar attenuation of AII tachyphylaxis by NE in aortic rings of normotensive Sprague-Dawley rats, and indicate that absence of such attenuation in SHR; the latter finding could reflect a probable lesion in the interactive pathways of these two vasoconstrictors in hypertensive rats.

The effects of centrally acting drugs on the EEG correlates of meditation

The present study investigated the effects of three centrally acting drugs on the significant increase in the intermediate alpha frequency of the electroencephalogram (EEG) that accompanied meditation in a male volunteer. When compared to the EEG recorded before each of the three drugs was administered, naloxone tended to enhance the increase in the power of the intermediate alpha EEG (9.4-10.4 Hz), while diazepam tended to spread the increase to the slow (7.4-9.4 Hz) alpha EEG, and flumazenil was without much effect on the overall EEG pattern. However, these EEG changes when compared to similar changes obtained with saline administration were not significantly different from the latter. Thus, it is unlikely that the EEG correlates of meditation are causally related to the rise or fall of endogenous opioid peptides or benzodiazepinelike substances in the brain.

Effects of noradrenaline and prostaglandin F2 alpha on angiotensin-induced contraction and tachyphylaxis in rat aortic rings

The aim of this study was to examine the effects of noradrenaline (NA) and prostaglandin F2 alpha (PGF2 alpha) on angiotensin II (AII)-induced contraction and tachyphylaxis in aortic rings of the rat. Neither NA (10(-9) M) nor PGF2 alpha (10(-7) M) had significant effect on the response of the rings to the spasmogenic concentrations (10(-10) to 10(-7) M) of AII, but lowered significantly the threshold response of the aortic rings to AII (from 10(-9) to 10(-12) M). In rings that were tachyphylatic to AII, both NA and PGF2 alpha attenuated significantly the tachyphylaxis of the rings to AII at the concentrations of 10(-10) and 10(-7) of the octapeptide; and also lowered the threshold of the tachyphylatic rings to AII (from 10(-9) to 10(-11) M for NA, and from 10(-9) to 10(-10) M for PGF2 alpha). The specific properties of noradrenaline and PGF2 alpha were not shared by the non-specific potassium chloride. Because the lowering of threshold and attenuation of tachyphylaxis occurred at the physiological levels of AII and NA, it is possible that the in vivo actions of AII are under constant modulation by circulating and localised (higher than circulating) levels (e.g. of PGF2 alpha) of spasmogens. The results also call into question the physiological significance of angiotensin tachyphylaxis and may suggest that it is only an in vitro phenomenon occurring in the absence of endogeneous spasmogens.