Biomedical subjects

S Y Chai

Publications and source records attributed to S Y Chai.

At least 37 records · Page 2Linked to original sources

PubMed1998

Haemorphin peptides may be endogenous ligands for brain angiotensin AT4 receptors.

1. Angiotensin IV (AngIV), the (3-8) fragment of AngII, was previously believed to be an inactive metabolite. However, specific binding sites, termed AT4 receptors, have been identified in the brain and peripheral organs and the peptide has been reported to enhance memory recall in passive avoidance studies and to dilate pial and renal cortical vessels. 2. AT4 receptors are distinct from AngII AT1 and AT2 receptors with respect to function, ligand specificity and distribution. 3. In the brain, AT4 receptors are abundant in cerebral and cerebellar cortex, hippocampal formation and cholinergic systems, as well as sensory and motor systems. However, the peptide AngIV is low or undetectable in the central nervous system. This led us to search for an alternative peptide ligand of the AT4 receptor. 4. The decapeptide LVVYPWTQRF was isolated from cerebral cortex and binds with high affinity to brain AT4 receptors. This peptide sequence corresponds to an internal sequence of beta-globin and has previously been named LVV-haemorphin 7. 5. Haemorphin may represent a new class of endogenous neuropeptides, some of which interact potently with the brain AT4 receptor to elicit a range of actions.

Angiotensin II↗

PubMed1998

Characterization of binding sites for amylin, calcitonin, and CGRP in primate kidney.

Analysis of receptor distributions for 125I-labeled amylin, 125I-labeled calcitonin, and 125I-labeled calcitonin gene-related peptide (CGRP) in Macaca fascicularis kidney by in vitro autoradiography revealed distinct patterns of binding for each peptide. 125I-rat amylin bound primarily to the cortex, being associated with the distal tubule, including apparent binding to the juxtaglomerular apparatus. 125I-salmon calcitonin displayed high-density binding in the cortex with low-density binding to the medulla. Emulsion autoradiography indicated that binding was associated with both distal tubule and thick ascending limb of the loop of Henle. Intense binding was also found often over juxtaglomerular apparatus. 125I-rat CGRP-alpha exhibited low- to moderate-density binding to the inner medulla/papilla with high-density binding over small-, medium-, and large-caliber arteries. Weak binding to the glomerulus was also seen, but no binding was associated with cortical tubules. Competition binding studies, performed with each of the radioligands, revealed peptide specificity profiles for CGRP and calcitonin receptors that were similar to those described in rat. However, the monkey amylin receptors differed from those in rat, exhibiting relatively higher affinity for calcitonin peptides but reduced affinity for CGRP peptides. These studies suggest potential roles for amylin, calcitonin, and CGRP in primate renal function.

Amino Acid Sequence↗

PubMed1997

Perindopril chronically inhibits angiotensin-converting enzyme in both the endothelium and adventitia of the internal mammary artery in patients with ischemic heart disease.

BACKGROUND: ACE inhibitors are widely used in treating hypertension and heart failure, but the sites and mechanisms of ACE inhibition in human blood vessels are not understood. The present study was undertaken to assess the sites and extent of in vivo inhibition of ACE by long-term perindopril treatment in different layers of the internal mammary artery in patients with ischemic heart disease. METHODS AND RESULTS: Sixteen patients with ischemic heart disease were treated either with perindopril (4 mg/d PO) for up to 36 days before surgery (n = 9) or without the inhibitor as control subjects (n = 7). The segments of the internal mammary artery were collected for measurement of vascular free and total ACE by quantitative in vitro autoradiography with 125I-351A binding. The patients treated with perindopril had lower plasma ACE (P < .001) and plasma angiotensin (Ang) II-to-Ang I ratio (P < .05). In the internal mammary artery, free ACE was similarly inhibited by perindopril in the endothelium (P < .05) and adventitia (P < .05), and the free ACE-to-total ACE ratio, an index of ACE inhibition, was markedly decreased by perindopril in parallel in the endothelium (P < .001) and adventitia (P < .001). Moreover, plasma ACE correlated highly with vascular ACE in the endothelium (r = .85, P < .001) or adventitia (r = .78, P < .001), and mean arterial pressure correlated significantly with free ACE in the endothelium (r = .52, P < .05) or adventitia (r = .53, P < .05) and with the plasma Ang II-to-Ang I ratio (r = .53, P < .05). Light microscopic autoradiographs of 125I-351A binding revealed a marked inhibition of ACE by perindopril in both layers of the vascular wall. CONCLUSIONS: The present demonstrates that long-term administration of perindopril potently inhibits both endothelial and adventitial ACE to a comparable degree in the human internal mammary artery. These results indicate that perindopril effectively penetrates the vascular wall to inhibit ACE in the adventitia, thus providing evidence that perindopril may be beneficial in inhibiting both circulating Ang II and its local formation in the vascular wall.

Aged↗

PubMed1997

Distribution of bradykinin B2 receptors in sheep brain and spinal cord visualized by in vitro autoradiography.

Bradykinin B2 receptors were localized in the sheep brain and spinal cord by quantitative in vitro autoradiography using a radiolabelled and specific bradykinin B2 receptor antagonist analogue, 3-4-hydroxyphenyl-propionyl-D-Arg0-[Hyp3,Thi5,D-Tic 7,Oic8]bradykinin, (HPP-HOE 140). This radioligand displays high affinity and specificity for bradykinin B2 receptors. The respective K(i) values of 0.32, 1.37 and 156 nM were obtained for bradykinin, HOE140 and D-Arg[Hyp3,D-Phe7,Leu8]bradykinin competing for radioligand binding to lamina II of sheep spinal cord sections. Using this radioligand, we have demonstrated the distribution of bradykinin B2 receptors in many brain regions which have not been previously reported. The highest density of bradykinin B2 receptors occur in the pleoglial periaqueductal gray, oculomotor and trochlear nuclei and the circumventricular organs. Moderate densities of receptors occur in the substantia nigra, particularly the reticular part, the posterior thalamic and subthalamic nuclei, zona incerta, the red and pontine nuclei, some of the pretectal nuclei and in discrete layers of the superior colliculus. In the hindbrain, moderate levels of bradykinin B2 receptor binding occur in the nucleus of the solitary tract, and in spinal trigeminal, inferior olivary, cuneate and vestibular nuclei. Laminae II, X and dorsal root ganglia display the most striking binding densities in the spinal cord, while the remainder of the dorsal and ventral horn display a low and diffuse density of binding. Bradykinin B2 receptors are extensively distributed throughout the sheep brain and spinal cord, not only to sensory areas but also to areas involved in motor activity.

Animals↗

PubMed1997

Upregulation of angiotensin II AT1 receptors in the mouse nucleus accumbens by chronic haloperidol treatment.

The distribution of angiotensin II AT1 and AT2 receptor subtypes were mapped in the mouse brain by in vitro autoradiography. Along with a differing distribution of AT1 and AT2 receptors in the hind brain compared to the rat, moderate densities of AT1 receptors were observed in dopamine-rich regions, namely the caudate putamen and nucleus accumbens, previously observed in the human, but not rat or rabbit. Considering our previous anatomical and functional studies demonstrating an interaction between brain angiotensin II and dopaminergic systems, the effect of chronic treatment with the dopamine antagonist, haloperidol, on AT1 and AT2 receptor levels was investigated in the mouse brain. Haloperidol treatment for 21 days resulted in an increase in angiotensin II AT1 receptor levels in the nucleus accumbens, accompanied by an increase in dopamine D2 receptors, but no change in dopamine D1 receptors. Striatal AT1 receptors did not alter with treatment, nor did AT1 or AT2 receptors in a number of brain regions not associated with dopaminergic systems, such as the median preoptic nucleus, paraventricular hypothalamic nucleus, and nucleus of the solitary tract. The present study suggests that brain angiotensin II-dopamine interactions extend beyond the known effects on the nigrostriatal dopaminergic system, to the mesocorticolimbic dopaminergic system.

Animals↗

PubMed1997

Angiotensin-converting enzyme modulates dopamine turnover in the striatum.

The effect of chronic inhibition of the angiotensin-converting enzyme on dopamine content and release in the striatum was investigated using in vivo microdialysis in awake, freely moving rats. Rats were treated for 1 week with the angiotensin-converting enzyme inhibitor perindopril (1 mg/kg) via the drinking water, whereas the controls were given water alone. One week after perindopril treatment, striatal dopamine dialysate levels in the treated group were markedly elevated compared with control values: control, 233 +/- 43 pg/ml; perindopril, 635 +/- 53 pg/ml (p < 0.001). These results were confirmed by a complementary study in which dopamine content was measured in striatal extracts (3.5 +/- 0.4 micrograms of dopamine/g of tissue for controls compared with 9.2 +/- 2.4 micrograms of dopamine/g of tissue for the treated group; p < 0.05). In the rats that were dialyzed, angiotensin-converting enzyme levels in the striatum were decreased by 50% after perindopril treatment. Levels of dopamine D1 and D2 receptors and of preprotachykinin and tyrosine hydroxylase mRNAs were unchanged after angiotensin-converting enzyme inhibition. A small, but significant, increase was detected in striatal preproenkephalin mRNA levels in the angiotensin-converting enzyme inhibitor-treated group. These results indicate that peripherally administered angiotensin-converting enzyme inhibitors penetrate the blood-brain barrier when given chronically and modulate extracellular dopamine and striatal neuropeptide levels.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1997

The globin fragment LVV-hemorphin-7 is an endogenous ligand for the AT4 receptor in the brain.

Angiotensin IV (Val-Tyr-Ile-His-Pro-Phe) has been reported to interact with specific high-affinity receptors to increase memory retrieval, enhance dopamine-induced stereotypy behavior, and induce c-fos expression in several brain nuclei. We have isolated a decapeptide (Leu-Val-Val-Tyr-Pro-Trp-Thr-Gln-Arg-Phe) from sheep brain that binds with high affinity to the angiotensin IV receptor. The peptide was isolated using 125I-angiotensin IV binding to bovine adrenal membranes to assay receptor binding activity. This peptide is identical to the amino acid sequence 30-39 of sheep betaA- and betaB-globins and has previously been named LVV-hemorphin-7. Pharmacological studies demonstrated that LVV-hemorphin-7 and angiotensin IV were equipotent in competing for 125I-angiotensin IV binding to sheep cerebellar membranes and displayed full cross-displacement. Using in vitro receptor autoradiography, 125I-LVV-hemorphin-7 binding to sheep brain sections was identical to 125I-angiotensin IV binding in its pattern of distribution and binding specificity. This study reveals the presence of a globin fragment in the sheep brain that exhibits a high affinity for, and displays an identical receptor distribution with, the angiotensin IV receptor. This globin fragment, LVV-hemorphin-7, may therefore represent an endogenous ligand for the angiotensin IV receptor in the CNS.

Adrenal Glands↗

PubMed1996

Angiotensin IV inhibits neurite outgrowth in cultured embryonic chicken sympathetic neurones.

Angiotensin IV (Val-Tyr-Ile-His-Pro-Phe) is reported to enhance apomorphine induced stereotypy and to improve memory recall through actions on specific binding sites in the central nervous system. In the present study, 10 nM angiotensin IV or angiotensin II inhibited neurite outgrowth from cultured E11 chicken paravertebral sympathetic neurones by 25%. The effects of both peptides were inhibited by a 1 microM concentration of the angiotensin IV analogues. WSU 4042, Nle1-Y-I-amide or Nle1-AIV, but not by the avian angiotensin II antagonists, [Sar1,Ile8]Ang II or CGP 42112, suggesting that the inhibition of neurite outgrowth by both peptides is mediated by the angiotensin IV binding site. These results suggest that angiotensin IV may be involved in neurite modelling and may therefore have an important role in neuronal development.

Angiotensin II↗

PubMed1996

Characterization and localization of bradykinin B2 receptors in the guinea-pig using a radioiodinated HOE140 analogue.

The potent bradykinin B2 receptor antagonist analogue, [125I]HPP-HOE140, ([125I]-3-4-hydroxyphenyl-propionyl-D-Arg0-[Hyp3, Thi5,D-Tic7, Oic8]bradykinin), was used to localize and characterize guinea-pig tissue bradykinin B2 receptors. Analysis of competition for the radioligand binding, using membrane preparations of lung, ileum and uterus, revealed the presence of a high- and low-affinity binding site: at the high-affinity site, the apparent Ki for the various bradykinin B2 receptor ligands ranged from 0.26 to 2.13 nM for HPP-HOE140, from 0.25 to 1.45 nM for HOE140, from 129 to 625 nM for D-Arg0[pHyp3,Phe7]bradykinin and from 0.05 to 1.11 nM for bradykinin. At the low-affinity site, the apparent Ki values ranged from 4.90 to 10.5 nM, from 1.23 to 1.90 nM, 4760 nM and from 2.01 to 62.1 nM, respectively. By contrast, the bradykinin Bi receptor antagonist, des-Arg9[Leu8]bradykinin did not compete for [125I]HPP-HOE140 binding from membrane preparations at concentrations up to 1 microM. Using in vitro autoradiography on tissue sections, intense binding was observed in the lamina propria of the villi of ileum and the arteriolar smooth muscle cells in lung. In the uterus, dense binding was found in the inner third of the myometrium and over epithelial cells of the glandular endometrium, while diffuse binding was observed throughout the endometrial stroma. In the brain, intense binding was observed in the nucleus of the solitary tract, spinal trigeminal tract and area postrema of the hindbrain, the middle cerebral arteries, and the choroid plexus of the third and lateral ventricles. Moderate binding was observed in the CA3 region of the hippocampus and posterior and ventroposterior thalamic nuclei. In the spinal cord, high-density binding occurred in the laminae I and II of the dorsal horn. Unlike previous autoradiographic localization studies of the bradykinin B2 receptor using radiolabeled bradykinin, the radiolabeled antagonist HPP-HOE140 did not bind to bradykinin-degrading peptidases, such as angiotensin-converting enzyme, and displayed subtype specificity. Therefore, binding studies with [125I]HPP-HOE140 offers high sensitivity and specificity for characterization, quantitation and localization of subtypes of bradykinin B2 receptors in tissues, and offers new information on uterine and brain bradykinin B2 receptors.

Animals↗

PubMed1996

Localization and quantitation of angiotensin AT1 and AT2 receptors in the pregnant and non-pregnant sheep uterus.

The two angiotensin II receptor subtypes, AT1 and AT2, have been reported to be differentially expressed in the myometrial membrane preparations of nulliparous and pregnant sheep, however, their distribution in the sheep reproductive tract has not been reported. The aim of this study is to map the distribution of AT1 and AT2 receptors in the anoestrus reproductive tract of the sheep by quantitative in vitro autoradiography and to investigate if the density and distribution of the receptors change during pregnancy. The AT2 receptor is abundant in a discrete layer in the myometrium of the anoestrus sheep uterus, whilst the AT1 receptor is expressed at lower levels, predominantly in the endometrium. Near-term pregnant uteri, show a marked change in the expression of angiotensin II receptors: the myometrium no longer expresses detectable AT2 receptors but rather, expresses low levels of AT1 receptors. Angiotensin converting enzyme is found in high concentrations in the blood vessels of the pregnant and non-pregnant sheep reproductive system and on the epithelial cells of the fallopian tubes of the non-pregnant sheep. These studies reveal marked reciprocal changes of angiotensin II receptors, with myometrial AT1 receptors increasing during pregnancy, whilst AT2 receptors fall markedly. These changes suggest that angiotensin II may be involved in regulating changes of uterine structure and function during pregnancy by interaction with multiple receptor subtypes.

1-Sarcosine-8-Isoleucine Angiotensin II↗

PubMed1996

Distribution of AT4 receptors in the Macaca fascicularis brain.

Angiotensin IV (Val Tyr Ile His Pro Phe), administered centrally, increases memory retrieval and induces c-fos expression in the hippocampus and piriform cortex. Angiotensin IV binds to a high affinity site that is quite distinct in pharmacology and distribution from the angiotensin II AT1 and AT2 receptors and is known as the AT4 receptor. These observations suggest that the AT4 receptor may have multiple central effects. The present study uses in vitro receptor autoradiography, and employs [125I]angiotensin IV to map AT4 receptors in the macaca fascicularis brain. The distribution of the AT4 receptor is remarkable in that its distribution extends throughout several neural systems. Most striking is its localization in motor nuclei and motor associated regions. These include the ventral horn spinal motor neurons, all cranial motor nuclei including the oculomotor, abducens, facial and hypoglossal nuclei, and the dorsal motor nucleus of the vagus. Receptors are also present in the vestibular, reticular and inferior olivary nuclei, the granular layer of the cerebellum, and the Betz cells of the motor cortex. Moderate AT4 receptor density is seen in all cerebellar nuclei, ventral thalamic nuclei and the substantia nigra pars compacta, with lower receptor density observed in the caudate nucleus and putamen. Abundant AT4 receptors are also found in areas associated with cholinergic nuclei and their projections, including the nucleus basalis of Meynert, ventral limb of the diagonal band and the hippocampus, somatic motor nuclei and autonomic preganglionic motor nuclei. AT4 receptors are also observed in sensory regions, with moderate levels in spinal trigeminal, gracile, cuneate and thalamic ventral posterior nuclei, and the somatosensory cortex. The abundance of the AT4 receptor in motor and cholinergic neurons, and to a lesser extent, in sensory neurons, suggests multiple roles for the AT4 receptor in the primate brain.

Acetylcholinesterase↗

PubMed1996

Interactions of angiotensin II with central dopamine.

There is a large body of evidence to support the concept of a relationship between brain Ang II and catecholamine systems. This interaction may participate in some central actions of Ang II such as cardiovascular control, dipsogenesis, and complex behaviours. It also extends to the nigrostriatal dopaminergic system which bear AT1 receptors, both on their cell bodies in the substantia nigra presynaptically, and on their terminals in the striatum, where Ang II can markedly potentiate DA release. This observation suggests that drugs which modulate central Ang II may be useful in regulating central dopaminergic activity.

Angiotensin II↗

PubMed1996

Localization of bradykinin B2 receptors in sheep uterus.

The localization and characterization of bradykinin B2 receptors in sheep uterus was carried out using a radiolabelled B2 receptor ligand, 3,4-hydroxyphenypropionyl-D-Arg0-[Hyp3,Thi5,D-++ +Tic7,D-Oic8] bradykinin (HPP-HOE140). Competition of the radioligand, [125I]HPP-HOE140, from membrane preparations of anoestrus sheep uterus by bradykinin agonists and antagonists revealed the presence of high- and low-affinity binding sites with ligand specificity typical of the bradykinin B2 receptor. Using in vitro autoradiography on tissue sections, intense binding was visible over the superficial epithelial layer of the endometrium and inner third of the myometrium of anoestrus sheep uterus. Bradykinin B2 receptors in the myometrium were down regulated in pregnant sheep uterus. We demonstrate that binding studies using [125I]HPP-HOE140 offer high sensitivity and specificity for characterization, quantitation and localization of the bradykinin B2 receptors in tissues and offers new information on uterine bradykinin B2 receptors.

Anestrus↗

PubMed1995

Localization of angiotensin IV binding sites to motor and sensory neurons in the sheep spinal cord and hindbrain.

In the sheep spinal cord, a high density of [125I]angiotensin IV binding sites was localized to the perikaryon and processes of all somatic motor neurons, the autonomic motor neurons in the lateral horns of thoracic and lumbar segments and all dorsal root ganglia, but was low in lamina II of all dorsal horns. At supraspinal levels, [125I]angiotensin IV binding was abundant in numerous motor associated regions, with weaker binding observed in the sensory regions. This wide distribution pattern suggests an important role for the binding site in the central nervous system.

Angiotensin II↗

PubMed1995

Intrastriatal angiotensin II induces turning behaviour in 6-hydroxydopamine lesioned rats.

In rats with unilateral 6-hydroxydopamine lesions in the nigrostriatal pathway, injection of angiotensin II (2 nmol) into the unlesioned striatum elicited dose-related tight rotations ipsilateral to the lesion. This rotation was suppressed by coadministration of the angiotensin AT1 receptor antagonist, losartan (2 nmol), which had no significant effect when injected alone. Preadministration of the dopamine antagonist, haloperidol (2 mg/kg i.p.) completely blocked angiotensin II-induced turning at doses of 0.3-3 nmol, and partially at 10 nmol. These results further confirm the hypothesis that Ang II is intrinsically involved in modulating dopamine release in the striatum, an effect which is mediated predominantly by AT1 receptors.

Angiotensin II↗

PubMed1995

In vitro autoradiographic localization of the calcitonin receptor isoforms, C1a and C1b, in rat brain.

In this study the distribution of the calcitonin receptor isoforms, C1a and C1b, were mapped in rat brain using in vitro autoradiography and manipulation of their different pharmacological specificities. While salmon calcitonin binds to both receptors with high affinity, only the C1a receptor interacts with human calcitonin. Thus, the distribution of C1a specific binding sites was mapped using [125I]human calcitonin. The C1b receptors were mapped using [125I]salmon calcitonin in the presence of unlabelled human calcitonin and rat amylin, displacing binding of [125I]salmon calcitonin to C1a and C3 (amylin) sites, respectively. The distribution of C1a and C1b receptors was found to predominantly overlap. Brain regions displaying C1a, but little or no C1b, binding sites included the nucleus of the solitary tract, area postrema and the intermediate lobe of the pituitary. Although there were no nuclei expressing exclusively C1b receptors, parts of the mesencephalic and pontine reticular formation, and the thalamic paraventricular nucleus were enriched in C1b receptors relative to the density of C1a receptors in other brain regions. These data indicate that the relative expression of the two receptor isoforms, although predominately parallel, is not uniform in the rat brain.

Animals↗

PubMed1995

Localization of angiotensin converting enzyme by in vitro autoradiography in the rabbit brain.

The distribution of angiotensin converting enzyme was examined in the rabbit brain by in vitro autoradiography with the specific radiolabelled inhibitor 125I-351A. In the rabbit, the highest concentrations of radioligand binding were found in the choroid plexus, blood vessels, subfornical organ, vascular organ of the lamina terminalis, area postrema and inferior olive. High levels of binding were found throughout the basal ganglia, consistent with the results in all other species studied. In the midbrain the central gray and the superior colliculus displayed high levels of binding. In the medulla oblongata high levels of binding were associated with the nucleus of the solitary tract and dorsal motor nucleus of vagus, consistent with the pattern in other species. There was moderate labelling throughout both the cerebral and cerebellar cortices, which contrasts to the rat but is consistent with the situation in primates. Angiotensin converting enzyme (ACE) is more widely distributed in rabbit brain that in rat, human and Macaca fascicularis, and the results suggest ACE has a very general role in the metabolism of neuropeptides. Inhibitors of converting enzyme are very widely used in the treatment of hypertension and heart disease, and the rabbit should provide a useful model for examining the effects of these drugs in the brain.

Animals↗

PubMed1993

Distribution of angiotensin II receptor subtypes in the rabbit brain.

We have determined the distribution of angiotensin II receptor subtypes in rabbit brain using in vitro autoradiography. AT1 receptors were found in very high concentrations in the forebrain circumventricular organs--the subfornical organ, organum vasculosum of the lamina terminalis, and the median eminence as observed in other mammals. However, there was very little labeling in the area postrema. In the paraventricular nucleus, median preoptic nucleus, supraoptic nucleus there were high levels of predominantly AT1 receptors. High densities of AT1 receptors were also found in the nucleus of the solitary tract and the rostral and caudal ventrolateral medulla. All of these regions have putative roles in the regulation of blood pressure and fluid and electrolyte balance. In the rabbit brain there is less AT2 receptor binding than the rat, with most AT2 binding found in the molecular layer of the cerebellum and in the septohypothalamic nucleus. In the subthalamic nucleus, the mediodorsal and ventroposterior nuclei of the thalamus, locus coeruleus and inferior olivary nuclei, areas containing mostly AT2 receptors in the rat, no binding was detected in the rabbit except in the locus coeruleus which contains moderate levels of AT1 receptors. Taken in conjunction with our previous results in the rat and human brains, these results reveal that AT1 receptors predominate in rostral forebrain, hypothalamus and autonomic control centers of the medulla oblongata in all three species. However, the distribution and density of AT2 bearing sites in regions such as the septum, thalamus subthalamic nuclei, locus coeruleus, cerebellum and inferior olivary nuclei show marked species differences.

Amygdala↗