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M K Raizada

Publications and source records attributed to M K Raizada.

At least 91 records · Page 5Linked to original sources
PubMed1993

Angiotensin II type 2 receptor expression in neuronal cultures from spontaneously hypertensive rat brain.

We have compared the levels of angiotensin II (AII) type 2 (AT2) receptors in neuronal cultures from 1-day-old Wistar Kyoto (WKY) and spontaneously hypertensive (SH) rat hypothalamus and brainstem. These studies were performed to determine if the increase in total AII receptors observed in SH neurons in previous studies includes the AT2 receptor subtype. Specific binding of the AT2 receptor selective ligand [125I]CGP42112 to WKY and SH rat neuronal cultures was time dependent and saturable in each case. Kd (approximately 0.35 nM) and Bmax (approximately 95 fmol/mg protein) values for [125I]CGP42112 specific binding did not significantly differ between WKY and SH rat cultures. In addition, AT2 receptor-mediated reductions in cellular cGMP exhibited no significant differences in WKY and SH rat neuronal cultures. We conclude that the greater levels of AII receptors found in SH rat hypothalamus/brainstem neuronal cultures, compared with WKY rat neurons from these areas, do not include the AT2 receptor subtype.

Angiotensin II↗
PubMed1993

The cellular and physiological actions of insulin in the central nervous system.

Insulin is a peptide hormone involved in the regulation of glucose homeostasis. Its synthesis and function in the peripheral tissues have been extensively studied and well understood. In contrast, demonstration of insulin in the brain has raised questions concerning its origin and physiological significance. In spite of extensive studies, the source of insulin present in the brain has not yet been conclusively identified. Evidence exists in support of both peripheral and central origins of this hormone in the brain. Recognized physiological effects of insulin in the central nervous system (CNS) include regulation of food intake, control of glucose uptake and trophic actions on neuronal and glial cells. These actions of insulin are mediated by insulin receptor resembling closely that in peripheral tissues and coupled with tyrosine kinase signal transduction pathway. In this review we will discuss theories concerning the origin of insulin in the CNS. In addition, we will present current information on both cellular and physiological effects of this hormone in the brain.

Animals↗
PubMed1993

Insulin stimulates phosphatidylinositol 3-kinase activity in rat neuronal primary cultures.

We investigated the effect of insulin on phosphatidylinositol (PtdIns) 3-kinase (PtdIns 3-kinase) activity in neuronal cultures to determine if this enzyme is involved with the neurotrophic actions of insulin. Insulin caused a concentration-dependent increase in PtdIns 3-kinase activity in anti-phosphotyrosine immunoprecipitates. The kinase activity was able to phosphorylate PtdIns, PtdIns 4-phosphate, and PtdIns 4,5-bisphosphate. In intact neurons, a 10-min 1 mM insulin treatment in the presence of [32P]orthophosphate increased the levels of both 3-[32P]PtdIns phosphate and 3,4-[32P]PtdIns bisphosphate by 55 and 193%, respectively. This increase was associated with an increase in neurite outgrowth mediated by insulin. Our results indicate that insulin treatment of neuronal cells in primary culture increases PtdIns 3-kinase activity and the formation of the unique D-3-phosphorylated phosphoinositides, suggesting that growth factor-mediated neuronal growth may include the formation of novel phosphoinositide 3-phosphate phospholipids.

Animals↗
PubMed1993

Angiotensin II type 1 receptor mRNA levels in the brains of normotensive and spontaneously hypertensive rats.

The type 1 angiotensin II (AII) receptor (AT1-R) has been implicated in the physiological actions mediated by AII in the brain. In view of the reported hyperactivity of the brain AII system in the spontaneously hypertensive rat (SHR), we compared the expression of AT1-R mRNAs in the brains of normotensive [Wistar Kyoto (WKY)] and SHR animals. Northern blot analysis showed about three- and approximately 20-fold increases in the levels of AT1-R mRNAs from the hypothalamus and brainstem areas, respectively, of the SHR compared with the WKY rat brain. This was attributable to greater levels of both AT1A- and AT1B-R mRNA subtypes in these areas from the SHR. These observations suggest that increased AII receptor levels in SHR brain may, in part, be a result of increased expression of the AT1-R gene.

Animals↗
PubMed1993

Angiotensin II type 1 receptor-mediated stimulation of c-fos gene expression in astroglial cultures.

Angiotensin II (ANG II) stimulates plasminogen activator inhibitor 1 (PAI-1) gene expression in astroglial cells prepared from rat brains. In this study, we investigated whether c-fos gene expression may be involved in this cellular action of ANG II. Incubation of astroglial cultures with ANG II caused a time- and dose-dependent transient stimulation of the steady-state levels of c-fos mRNA, with a maximal stimulation of 50-fold observed with 100 nM ANG II within 30-45 min. This stimulation was completely abolished by the presence of the type 1 ANG II (AT1) receptor antagonist losartan but not by the type 2 ANG II receptor blocker PD-123177. Depolarization of brain cell cultures with 50 mM K+ also caused a 100-fold increase in c-fos mRNA levels, an effect partially blocked by losartan. These observations show that AT1 receptor activation stimulates expression of the c-fos gene, which may act as a third messenger in the regulation of cellular actions of ANG II, including PAI-1 gene expression in astroglial cells.

Angiotensin II↗
PubMed1993

Inhibition of central angiotensin responses by angiotensin type-1 receptor antibody.

Angiotensin type-1 receptor subtypes (AT1) are implicated in the physiological actions of angiotensin II in the brain. In the present study we used an AT1 receptor antibody and a polymerase chain reaction--synthesized AT1 receptor complementary DNA to show that the hypothalamus expresses significantly higher levels of AT1 receptor messenger RNA and protein compared with the brain stem. Intracerebroventricular injections of AT1-specific antibody blocks the dipsogenic and blood pressure responses induced by centrally injected angiotensin II. These results demonstrate the expression of AT1 receptor gene in the brain and that the AT1 receptor antibody is able to inhibit the physiological responses of angiotensin II mediated by the brain.

Angiotensin II↗
PubMed1993

Increased angiotensin II type-1 receptor gene expression in neuronal cultures from spontaneously hypertensive rats.

In this study we compared the expression of angiotensin II type 1 (AT1) receptor messenger RNA (mRNA) and AT1 receptors in neurons cultured from Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rat brains. Neuronal cultures from the hypothalamus and brain-stem of 1-day-old SH rats exhibited approximately 4-fold higher steady-state levels of AT1 receptor mRNA than the corresponding WKY cultures. This was attributable to greater levels of both AT1A and AT1B receptor mRNA subtypes in SH rat neuronal cultures compared with WKY rat neurons. SH rat neuronal cultures also exhibited increased numbers (approximately 2.3-fold) of binding sites for [3H]DuP753, an AT1 receptor selective ligand, and enhanced (approximately 3.4-fold) stimulation of inositol phospholipid hydrolysis by angiotensin II compared with WKY neurons. By contrast, cultured astroglia from SH and WKY rat brain exhibited no significant differences in either the levels of AT1 receptor mRNA or the specific binding of [3H]DuP753. These data suggest that in SH rat neurons, AT1 receptor transcription and translation is increased, compared with neurons from WKY rats.

Amino Acid Sequence↗
PubMed1992

Characterization of a polyclonal anti-peptide antibody to the angiotensin II type-1 (AT1) receptor.

A polyclonal antibody has been prepared against a synthetic peptide corresponding to amino acids 14-23 of the angiotensin II type-1 (AT1) receptor. The antibody is of high titer and mono-specific. Western blot analysis of membranes from rat liver, kidney, and adrenal gland showed that the antibody specifically recognizes a protein band of MW 70,000 whose amounts are highest in the liver, followed by kidney and adrenals. In addition, a relatively less prominent band of MW 95,000 was also detected. The relative distribution of this protein correlates well with the values obtained for [3H]-DuP753 binding and AT1 receptor mRNA.

Adrenal Glands↗
PubMed1992

Insulin-like growth factor I receptor binding in brains of Alzheimer's and alcoholic patients.

Patients with chronic alcoholism and/or Alzheimer's disease show degenerative changes in the cerebral cortex and hippocampus. To investigate possible changes in insulin-like growth factor I receptor binding sites in brain tissue of patients with these pathological conditions, the number of 125I-insulin-like growth factor I binding sites was determined in tissues obtained from control patients and those with Alzheimer's and/or with a history of alcoholism. The four experimental groups examined consisted of patients from similar age groups. Postmortem histology and a clinical history were used for the diagnosis of Alzheimer's disease and alcoholism, respectively. Careful clinical records were kept concerning other variables such as immediate cause of death and medications administered before death. Specific binding of 125I-insulin-like growth factor I to homogenates prepared from cerebral cortex of Alzheimer's, alcoholic, alcoholic Alzheimer's, and age-matched control patients was similar, although Alzheimer's patients tended to have slightly higher binding values. No significant differences in insulin-like growth factor I binding in cerebral cortex were found with regard to age of patients, the interval between death and autopsy, and CNS-active medications. No statistical differences in 125I-insulin-like growth factor I binding were noted in hippocampal tissue from the four patient groups. Thus, human insulin-like growth factor I binding sites in cerebral cortex and hippocampus appear unaffected by several variables.

Alcoholism↗
PubMed1992

Angiotensin II stimulation of plasminogen activator inhibitor-1 gene expression in astroglial cells from the brain.

In this study, we investigated the mechanism of angiotensin II (Ang II) induced secretion of plasminogen activator inhibitor-1 (PAI-1) from astroglial cells prepared from 21-day-old rat brain. Competition-inhibition experiments with the use of selective antagonists for Ang II receptor subtypes indicated that astroglial cells contain chiefly Ang II type 1 (AT1) receptors. The interaction of Ang II with AT1 receptors resulted in a time- and concentration-dependent stimulation of PAI-1 gene expression. A maximal, 20-fold induction of PAI-1 messenger RNA (mRNA) steady-state levels was observed with 10 nM Ang II. This effect of Ang II was blocked by DuP753, an AT1 receptor antagonist, but not by PD123177, an AT2 receptor antagonist. Raise in PAI-1 mRNA levels was followed by an elevation in PAI-1 concentration in culture media reaching its maximum after 24 h. Interaction of Ang II with AT1 receptors also resulted in a time- and concentration-dependent stimulation of inositol phospholipid (IP) hydrolysis. A maximal, 3- to 5-fold stimulation of IP hydrolysis was observed with 10 nM Ang II. The time course experiments indicated that Ang II-induced stimulation of IP hydrolysis precedes the stimulation of PAI-1 mRNA. This suggested that activation of phospholipase C, IP hydrolysis system and possibly protein kinase C (PKC) may mediate Ang II's effect on PAI-1 mRNA. Direct stimulation of PKC by phorbol ester, phorbol 12,13-dibutyrate (PDB), resulted in a time- and concentration-dependent elevation of PAI-1 mRNA levels, similar to that caused by Ang II (maximal stimulation of 20-fold with 100 nM PDB for 4 h). This effect was totally blocked by the protein kinase C inhibitor, H7. In addition, Ang II stimulation of PAI-1 mRNA was also blocked by H7. In contrast, Ang II did not elevate PAI-1 mRNA levels in astroglial cultures from neonatal rat brains. However, treatment of neonatal cultures with PDB increased levels of this mRNA species. These observations indicate that the coupling of AT1 receptors with IP hydrolysis and PKC activation may be important for Ang II stimulation of PAI-1 gene expression. The lack of Ang II's effect on PAI-1 mRNA in neonatal astroglia may be explained either by a low coupling efficiency between AT1 receptors and the second messenger system, or by a low AT1 to AT2 receptor level ratio.

Angiotensin II↗
PubMed1992

Angiotensin-II induction of plasminogen activator inhibitor-1 gene expression in astroglial cells of normotensive and spontaneously hypertensive rat brain.

Angiotensin-II (AII) stimulates plasminogen activator inhibitor-1 (PAI-1) gene transcription, translation, and protein secretion from astroglial cells derived from normotensive [Wistar-Kyoto (WKY)] rat brain, an effect mediated by AII type 1 (AT1) receptors. Since abnormal expression of the brain AII system has been demonstrated in spontaneously hypertensive (SH) rats, we investigated the regulation of PAI-1 gene expression by AII in astroglial cells from the brains of these animals. AII caused an increase in PAI-1 gene expression in SH rat astroglia in a manner similar to that observed in WKY-derived cultures. However, both the basal and AII-stimulated levels of PAI-1 mRNA in SH rat astroglia were only 20% of those observed in WKY rat astroglial cultures. Consequently, there was a significant reduction in the de novo synthesis and secretion of PAI-1 from astroglia of SH rat brain. The reduced synthesis and secretion of PAI-1 from SH rat brain astroglia was associated with lower numbers of AT1 receptors in these cells. However, the steady state levels of AT1 receptor mRNA were comparable in both WKY and SH rat astroglia. This reduction in AII-modulated PAI-1 levels in SH rat astroglia is consistent with a proposed role of these interactions in the development of hypertension in these animals.

Angiotensin II↗
PubMed1991

Angiotensin II receptor subtypes are coupled with distinct signal-transduction mechanisms in neurons and astrocytes from rat brain.

Both neurons and astrocytes contain specific receptors for angiotensin II (AII). We used selective ligands for the AT1 and AT2 types of AII receptors to investigate the expression of functional receptor subtypes in astrocyte cultures and neuron cultures from 1-day-old (neonatal) rat brain. In astrocyte cultures, competition of 125I-labeled AII (125I-AII) specific binding with AT1 (DuP753) or AT2 (PD123177, CGP42112A, [Phe(p-NH2)6]AII) selective receptor ligands revealed a potency series of AII greater than DuP753 much greater than CGP42112A greater than [Phe(p-NH2)6]AII greater than PD123177. These results suggest a predominance of the AT1 receptor subtype in neonatal astrocytes. Also, in astrocyte cultures, AII stimulated increases in inositolphospholipid hydrolysis that were significantly reduced by the AT1 receptor antagonist DuP753 but not altered by the AT2 receptor antagonist PD123177. In neonatal neuron cultures, competition of 125I-AII specific binding with the above ligands revealed a potency series of CGP42112A = AII greater than [Phe(p- NH2)6]AII greater than PD123177 much greater than DuP753. 125I-AII specific binding to neonate neuronal cultures was reduced 73-84% by 1 microM PD123177, and the residual 125I-AII specific binding was eliminated by DuP753. Also, in neuron cultures, AII induced decreases in basal cGMP that were completely blocked by PD123177 or CGP42112A but not by DuP753. Our results suggest that astrocyte cultures from neonatal rat brains contain predominantly AT1 receptors that are coupled to a stimulation of inositophospholipid hydrolysis. In contrast, neuron cultures from neonatal rat brain contain mostly AT2 receptors that are coupled to a reduction in basal cGMP levels, but a smaller population of AT1 receptors is also present in these neurons.

Angiotensin II↗
PubMed1991

Insulin-like growth factor I (IGF-I) receptors and IGF-I action in oligodendrocytes from rat brains.

Oligodendrocyte progenitor cells were prepared by mechanical dissociation of 1-day-old rat brain cultures. These cells undergo proliferation and differentiation into oligodendrocytes as demonstrated by the expression of proliferation and differentiation-related specific antigens. We have used this unique culture system to characterize insulin-like growth factor I (IGF-I) receptors and their action in the central nervous system (CNS). 125I-IGF-I specifically binds to these cultures with high affinity. Competition-inhibition data suggest that IGF-I is most potent in competing for 125I-IGF-I binding, followed by IGF-II and insulin. Scatchard analyses of the binding data indicate a curvilinear plot with a Kd for high affinity of 0.2 nM, and a Bmax of 247 fmol/mg, and a Kd for low affinity of 3.2 nM and Bmax of 1213 fmol/mg protein. Covalent cross-linking followed by SDS-PAGE analysis demonstrated a radioactive band of Mr 135,000 which corresponds to the alpha subunit of the IGF-I receptor. Solution hybridization/RNase protection assay produced a single protected band corresponding to IGF-I receptor messenger RNA, further confirming the presence of these receptors. Incubation of progenitor cells with IGF-I resulted in a time- and concentration-dependent increase in [3H]thymidine incorporation and cell numbers. This effect appears to be mediated by IGF-I receptors since IGF-II and insulin were proportionately less potent. In addition to its effect on proliferation, IGF-I also increased the number of 4E7- and GC-antigen positive cells. These observations indicate that oligodendrocytes in primary culture express specific IGF-I receptors and that the interaction of IGF-I with these receptors results in the proliferation as well as differentiation of oligodendrocytes.

Animals↗
PubMed1991

Angiotensin II induces secretion of plasminogen activator inhibitor 1 and a tissue metalloprotease inhibitor-related protein from rat brain astrocytes.

The present study investigates angiotensin (Ang) II effects on secretory protein synthesis in brain astrocytes cultured from neonatal and 21-day-old rats. Ang II-induced changes in the de novo synthesis of [35S]methionine-labeled secretory proteins were visualized using two-dimensional NaDodSO4/PAGE. Astrocytes from 21-day-old rat brain possess specific high-affinity receptors for Ang II. These cells express two Ang II-induced secretory proteins with Mr 55,000 (AISP-55K) and Mr 30,000 (AISP-30K), which were time- and dose-dependent (EC50, 1 nM). [Sar1, Ile8]Ang II (where Sar is sarcosine) inhibited Ang II-induced secretion of AISP-55K but not AISP-30K. N-terminal amino acid sequencing indicates that AISP-55K is identical to rat plasminogen activator inhibitor 1, whereas AISP-30K exhibits 72-81% identity to three closely related proteins: human tissue inhibitor of metalloproteases, a rat phorbol ester-induced protein, and the murine growth-responsive protein 16C8. Immunofluorescent staining with rat plasminogen activator inhibitor 1 antibody was induced in the majority of cells in culture after Ang II treatment of astrocytes from 21-day-old rat brains. Absence of this response to Ang II in astrocytes from neonatal rat brain provides evidence that this action of Ang II on astrocytes is developmentally regulated.

Aging↗
PubMed1991

Binding of [125I]-insulin-like growth factor-1 (IGF-1) in brains of Alzheimer's and alcoholic patients.

Patients with chronic alcoholism and/or Alzheimer's disease suffer from degenerative changes in the cerebral cortex and hippocampus. To investigate possible changes in IGF-1 receptor binding sites in brain tissue of patients with these pathological conditions, the binding of [125I]-IGF-1 was determined in tissues obtained from control, Alzheimer's and/or patients with a history of alcoholism. The four experimental groups examined consisted of patients from similar age groups. Specific binding of [125I]-IGF-1 to cerebral cortical membranes from Alzheimer's patients had significantly more binding sites than age-matched controls, alcoholic patients and alcoholic patients with Alzheimer's disease. Regression analyses indicated that there were no significant differences in [125I]-IGF-1 binding in cerebral cortex with regard to age of patients (1.1% of total variance with a range of 52 to 92 years). Likewise, the time interval between death and autopsy contributed only 1.4% to the total variance in IGF-1 binding. No statistical differences in [125I]-IGF-1 binding were noted in hippocampal tissue from the various patient groups. Thus, human IGF-1 binding sites in cerebral cortex and hippocampus appear to be relatively stable for a number of variables. The increase in cerebral cortical [125I]-IGF-1 binding sites could be due to upregulation of IGF-1 receptors resulting from a decrease in IGF-1 levels in Alzheimer's patients.

Alcoholism↗