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Biomedical subjects

A Chaudhari

Publications and source records attributed to A Chaudhari.

At least 19 recordsLinked to original sources
PubMed1997

Recombinant human bone morphogenetic protein-2 stimulates differentiation in primary cultures of fetal rat calvarial osteoblasts.

Recombinant human bone morphogenetic protein (rhBMP-2) was examined for its in vitro effects on biochemical markers representing osteoblast phenotype. Primary cultures of fetal rat calvarial osteoblasts were used in this study. The results indicated that rhBMP-2 stimulated alkaline phosphatase activity, parathyroid hormone (PTH)-induced cyclic AMP production, and collagen biosynthesis in a dose-dependent manner in confluent cultures. The percent collagen synthesis also increased in a dose-dependent manner. Alkaline phosphatase activity was stimulated in a time-dependent manner by rhBMP-2 that reached its maximum 5 days after initiation. Cycloheximide (2 micrograms/ml) inhibited rhBMP-2-stimulated alkaline phosphatase indicating de novo protein synthesis of the enzyme. Transforming growth factor-beta 1 (TGF-beta 1)-induced inhibition of alkaline phosphatase activity observed in confluent primary cultures was completely abolished by rhBMP-2 at a concentration that was 43 times greater than the TGF-beta 1 concentration. Also, rhBMP-2 produced a small stimulation of alkaline phosphatase activity in cells grown in the absence of ascorbic acid; however, the effect was greatly enhanced in cells cultivated in the presence of ascorbic acid (50 micrograms/ml). In view of the potentiating effect of ascorbic acid on rhBMP-2-induced stimulation of alkaline phosphatase, we speculate that ascorbic acid could amplify the osteoinductive effects of rhBMP-2 and thereby augment the efficacy of the BMP when used as bone repair material in vivo. rhBMP-2 (4.3-86 ng/ml) did not exhibit mitogenic effects on cultured osteoblasts. These data suggest that rhBMP-2 has the ability to induce expression of various markers associated with the osteoblast phenotype in primary cultures of fetal rat calvarial osteoblasts. In addition, we speculate that TGF-beta 1 may play a regulatory role in BMP-induced bone formation and ascorbic acid may potentiate the effects of rhBMP-2 in vivo.

Alkaline Phosphatase↗
PubMed1995

Contribution of HEV and HCV in causing fulminant non-A, non-B hepatitis in western India.

During 1990, 38 patients with fulminant non-A, non-B hepatitis (NANB) died in Government Medical College Hospital, Aurangabad. Serum samples from these patients were tested for antibodies to hepatitis C virus (anti-HCV) and IgM antibodies to hepatitis E virus (IgM-anti-HEV). All samples were also subjected to polymerase chain reaction (PCR) for the detection of HBV DNA, HCV RNA and HEV RNA. None of the patients had circulating anti-HCV antibodies; three had HCV RNA. Based on anti-HEV-IgM positivity 14 patients (37%) could be diagnosed as suffering from hepatitis E. None was positive for HEV RNA. In the absence of serological markers, HBV DNA was present in three cases. None of the HBV DNA positive patients had anti-delta antibodies. Dual infections (HBV with HEV, and HBV with HCV) were seen in two cases. The aetiology of half of the NANB cases could not be assigned to the known hepatitis viruses using current techniques.

Adolescent↗
PubMed1994

Recombinant human bone morphogenetic protein-2 is superior to demineralized bone matrix in repairing craniotomy defects in rats.

The purpose of this study was to measure bone-regenerative effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) in rat calvarial critical-size defects (CSDs). CSDs (8 mm in diameter) were treated with either 1) 2.2 micrograms rhBMP-2 combined with insoluble collagenous bone matrix (ICBM), 2) 6.5 micrograms rhBMP-2 plus ICBM, 3) ICBM alone, or 4) demineralized bone matrix (DBM), for 7, 14, or 21 days. Multiple linear regression showed that rhBMP-2 had a significant time- and dose-dependent effect on bone regeneration (P < .05). After 7 days, new calcifying cartilage and remineralizing ICBM, with an occasional zone of new woven bone, was evident in defects treated with rhBMP-2/ICBM. By 14 days, both doses of rhBMP-2 reconstituted with ICBM had induced more bone formation than ICBM alone or DBM, and 6.5 micrograms was superior to 2.2 micrograms. There was no evidence of adverse cellular response. This study shows for the first time that rhBMP-2 could restore osseous form to a calvarial defect. In addition, osteoregeneration was accelerated by the higher dose of rhBMP-2.

Animals↗
PubMed1991

Characterization and physiologic regulation of atrial natriuretic factor receptors in rabbit preglomerular renal microvessels.

There has been no direct demonstration of the presence of guanylate cyclase-linked atrial natriuretic factor receptors in renal preglomerular microvasculature. Using [125I]ANF, we have demonstrated the presence of high affinity (Kd = 80 pM) and low affinity (Kd = 7.2 nM) ANF receptors in membranes derived from rabbit renal preglomerular microvessels (afferent arterioles and interlobular arteries). These microvessels also exhibited the presence of particulate bound ANF-sensitive guanylate cyclase. The density of the high affinity ANF receptor in desoxycorticosterone-treated rabbits on a high-salt diet (31 +/- 3 fmol/mg protein) was nearly half of that seen in rabbits on a normal diet (53 +/- 4 fmol/mg protein; p less than 0.01, n = 4). Data from this study demonstrated the presence of renal preglomerular ANF receptors and suggested that these receptors (perhaps in addition to glomerular ANF receptors) may participate in the regulation of extracellular volume.

Animals↗
PubMed1990

Biochemical evidence for PGI2 and PGE2 receptors in the rabbit renal preglomerular microvasculature.

It has been proposed that a portion of the biologic actions of vasodilator prostaglandins occurs via an interaction with specific adenylate cyclase-linked receptors. This hypothesis was explored further in the renal microvasculature by examining the effects of PGI2, PGE1, and PGE2 on rabbit preglomerular microvascular adenylate cyclase. A membrane preparation derived from freshly isolated rabbit renal preglomerular microvessels was used in these studies. NaF, forskolin, or 5'-guanylyl imidodiphosphate were found to be effective in increasing adenylate cyclase activity in the absence of exogenous guanosine-5'-triphosphate. A dose-dependent stimulation of adenylate cyclase was also observed with guanosine-5'-triphosphate. PGE1, PGE2, and PGI2 produced a dose-dependent stimulation of adenylate cyclase activity only in the presence of guanosine-5'-triphosphate suggesting that this nucleotide is essential for prostaglandin-induced stimulation of the enzyme. PGI2 exhibited a time-dependent increase in adenylate cyclase activity and this increased activity reached a plateau at 20-25 min. When PGE1 and PGE2 were added together, no additive effect on adenylate cyclase stimulation was noted whereas PGI2 and PGE2 when added together produced an additive stimulatory effect. When viewed together, these data suggest the presence of separate PGI2 and PGE adenylate cyclase-linked receptors in rabbit renal preglomerular microvessels. These findings also suggest that in the renal microvasculature, cyclic AMP may be a second messenger mediating the vasodilatory effects of both PGI2 and PGE2.

Adenylyl Cyclases↗
PubMed1990

Cyclic AMP does not inhibit A23187-induced prostaglandin biosynthesis in cultured rabbit renal microvascular endothelial cells.

We have previously shown that cultured rabbit renal preglomerular microvascular endothelial cells have the ability to synthesize a number of common prostaglandins. In the present study we have examined whether endogenous cyclic AMP is involved in the regulation of PGI2 and PGE2 biosynthesis in these cultured cells. Isoproterenol and forskolin produced an increase in cyclic AMP accumulation in these cells but had no effect on PGI2 or PGE2 biosynthesis either in the presence or absence of A23187. Similar results were noted in the presence of 3-isobutyl-1-methylxanthine, a cyclic AMP-phosphodiesterase inhibitor. These studies suggested that endogenous cyclic AMP does not regulate the biosynthesis of PGI2 or PGE2 in cultured renal preglomerular microvascular endothelial cells either under basal or A23187-stimulated condition. They further suggested that the effect of 3-isobutyl-1-methylxanthine on prostaglandin biosynthesis in these cultured cells was not secondary to its effects on phosphodiesterase.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Prostanoid biosynthesis in cultured rabbit renal microvascular smooth muscle cells. Effect of arachidonic acid, calcium, and A23187.

It is known that prostanoids are local regulators of vascular tone. Since Ca2+ is known to stimulate prostanoid biosynthesis, we examined this interaction in cultured smooth muscle cells derived from rabbit renal preglomerular microvessels by methods developed in this laboratory. These cells produced prostaglandin (PG)I2, PGE2, PGF2 alpha, and thromboxane A2 under in vitro conditions and biosynthesis was augmented in response to arachidonic acid, A23187, and Ca2+, and diminished in the presence of either mepacrine, aspirin, indomethacin, or meclofenamate. These data indicated that smooth muscle cells cultured in this laboratory were metabolically active and the data suggested that the effect of Ca2+ may be modulated by vasodilator prostanoids produced by the smooth muscle cells. These data failed to explain the greater ratio of the production of PGI2:PGE2 observed in freshly isolated rabbit renal preglomerular microvessels when compared with that seen in cultured endothelial cells derived from the same tissue which was previously reported by this laboratory.

Animals↗
PubMed1989

Decreased atrial natriuretic factor receptors and impaired cGMP generation in glomeruli from the cardiomyopathic hamster.

To determine a possible basis for the decreased action of atrial natriuretic factors (ANF) in congestive heart failure, we compared the cardiomyopathic hamster (CMH) in frank congestive failure, and the age-matched, normal, F1B strain of Golden Syrian Hamsters. Scatchard analysis of competitive binding studies revealed two classes of glomerular receptors. The CMH exhibited decreased binding overall and a markedly decreased number of high affinity receptors but comparable receptor affinity compared to the F1B. In contrast, the low affinity receptor population in the CMH had a much greater affinity compared to the F1B while receptor number was similar. Plasma ANF levels were substantially elevated in the CMH compared to the F1B and in-vitro generation of cGMP was significantly lower in the CMH. Such abnormalities could contribute to the resistance to ANF in this disease.

Animals↗
PubMed1989

Decreased renal preglomerular microvascular PGI2 and PGE2 biosynthesis in cholesterol-fed rabbits.

Although atherosclerosis is a common disease afflicting the kidney, few studies have examined the biochemical disturbances associated with this process directly in the renal microvasculature. Using a technique developed in this laboratory to isolate renal preglomerular microvessels, we have examined whether these vascular segments have a reduced capacity to synthesize vasodilator prostanoids (i.e., PGI2 and PGE2), an observation which has been made in atherosclerotic blood vessels from other vascular beds. The synthesis of these two prostanoids was assessed by radioimmunoassay in a group of white New Zealand rabbits fed a 2% cholesterol diet for 30 days and the results compared to that obtained in a similar group of rabbits fed a normal diet. The results of these studies showed the development of hypercholesterolemia in the cholesterol-fed rabbits which was associated with a 35% decrease in the biosynthesis of PGI2 and a 51% decrease in PGE2 in freshly isolated renal preglomerular microvessels. These findings are similar to those observed in non-renal major blood vessels and suggest that common biochemical mechanisms may operate in the development of atherosclerosis in many organ systems.

Animals↗
PubMed1989

PGI2 is not a major prostanoid produced by cultured rabbit renal microvascular endothelial cells.

The microvasculature is known to be a source of a number of vasoregulatory prostanoids. In the kidney, these prostanoids have been proposed to influence vascular, tubular, and glomerular function. A rapid method for isolation of large numbers of preglomerular renal microvessels (interlobular arteries and afferent arterioles) from the rabbit kidney has recently been developed in this laboratory. In the current report, we describe methods to culture endothelial cells derived from these isolated renal microvessels. Endothelial cells in primary and continuous cultures were grown in monolayers on culture dishes and plates. These cells demonstrated morphology consistent with that described for other endothelial cells in culture including the presence of Weibel-Palade bodies as seen by electron microscopy. The presence of factor VIII immunofluorescence and angiotensin converting-enzyme activity was also observed. The cultured endothelial cells synthesized a number of common prostanoids under in vitro conditions and the hierarchy of biosynthesis was PGE2 greater than PGF2 alpha greater than PGI2 greater than TxA2. The ratio of the in vitro biosynthesis of PGI2:PGE2 was approximately 1:5, as compared with a 3-5:1 ratio seen in freshly isolated intact microvessels. Prostanoid biosynthesis increased in the cultured endothelial cells in the presence of arachidonic acid (1 and 10 microM), A23187 (10 microM), thrombin (5 U/ml), or bradykinin (1 microM) and decreased with mepacrine (10 microM)-or indomethacin (100 microM), suggesting that these cells were metabolically responsive to a variety of prostanoid stimulators and inhibitors. In summary, endothelial cells can be cultured from freshly isolated preglomerular renal microvessels and have the ability to produce a number of vasoregulatory prostanoids under in vitro conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Lack of effect of captopril on preglomerular renal microvascular prostanoid biosynthesis.

Extensive research has focused on the mechanisms by which converting enzyme inhibitors, such as captopril, lower the systemic blood pressure. In addition to inhibiting the conversion of angiotensin I to angiotensin II, these agents have been proposed to influence other systems which might affect vascular resistance including the kinins and the prostanoids. This study was designed to evaluate whether captopril has any direct effect to increase the synthesis of endogenous vasodilator prostanoids in either freshly isolated rabbit renal preglomerular microvessels or in endothelial cells derived from them. The results indicate that captopril, in a variety of doses, had no effect on the synthesis of either prostacyclin or PGE2 by renal preglomerular microvessels. Bradykinin, on the other hand, increased prostanoid production significantly in the same tissue preparations. Finally, captopril had no effect in altering bradykinin-induced increases in renovascular prostanoid biosynthesis. Thus, captopril appears to have no ability to enhance the production of vasodilator prostanoids in rabbit renal preglomerular resistance vessels. These data question the role of prostanoid-related mechanisms in the non-renin-related antihypertensive actions of captopril.

6-Ketoprostaglandin F1 alpha↗
PubMed1988

A rapid method for isolating rabbit renal microvessels.

A technique has been described to isolate rabbit renal preglomerular microvessels using an infusion of a magnetized iron oxide suspension into the renal artery. An initial separation of the vascular tissue was performed with a magnet and a final separation was performed using a nylon sieve allowing nonvascular, tubular, and glomerular contaminants to be filtered free from the microvessels. Light and electron microscopy showed morphology consistent with interlobular arteries and afferent arterioles. The purity of the preparation was greater than 95%. In the absence of exogenous arachidonic acid, the microvessels were able to synthesize prostacyclin (7.5 +/- 1.2 ng.mg protein-1.min-1) in excess of prostaglandin E2 (2.2 +/- 0.7 ng.mg protein-1.min-1). The tissue exhibited a time-dependent increase in prostanoid biosynthesis up to 60 min and responded to stimulators (e.g., melittin and arachidonic acid) and inhibitors (e.g., meclofenamate and indomethacin) of prostanoid biosynthesis. These studies indicate that a high-yielding and versatile preparation of renal preglomerular microvessels can be rapidly obtained. The microvessels are viable and may represent an excellent model for studying a variety of biochemical interactions under in vitro conditions.

Animals↗
PubMed1988

Alterations in rabbit renal microvascular prostanoid synthesis in acute renal failure.

Vasodepressor prostanoids have been suggested to regulate renal hemodynamics after nephrotoxic injury and thus protect the kidney against the effects of prolonged ischemia. This study assessed whether changes in two microvascular vasodilator prostanoids would correlate with changes seen in renal hemodynamics in rabbits with nephrotoxic renal injury produced by either uranyl nitrate or mercuric chloride. Rabbits were killed at 3, 24, and 72 h after the nephrotoxin injections and 6-ketoprostaglandin (PG) F1 alpha and PGE2 synthesis was measured in vitro in isolated renal microvessels. At the end of 24 h, synthesis of both prostanoids was significantly increased in all nephrotoxin-treated animals, an observation not noted at the end of 3 h. At 72 h, 6-keto-PGF1 alpha production remained elevated. Pretreatment with mepacrine blocked the increased prostanoid production seen in uranyl nitrate-treated animals. Thus, renal microvascular vasodilator prostanoid biosynthesis is increased 24-72 h after nephrotoxin administration. These data suggest that the biosynthesis of prostacyclin and PGE2 may contribute to the maintenance of renal blood flow in the first few days after acute renal injury and further suggest that a mechanism for this increase may be stimulation of phospholipase A2.

6-Ketoprostaglandin F1 alpha↗
PubMed1987

Effects of a low-fat, low-cholesterol diet on serum lipids, platelet aggregation and thromboxane formation.

The purpose of this study was to test the effects of a low-fat, low-cholesterol diet on serum lipids, platelet aggregation, thromboxane formation and blood pressure. Fifteen hyperlipidemic males with normal blood pressure were treated for 2 weeks. Resting supine blood pressure, total serum cholesterol, HDL-cholesterol, the ratio of total cholesterol/HDL-cholesterol and triglycerides all were significantly reduced. The maximum aggregation and velocity of aggregation for isolated platelets stimulated with either ADP or collagen was significantly reduced. Thromboxane formation during 5 min of platelet aggregation with collagen or ADP was also significantly reduced. These results have important implications for hypertension and atherosclerotic cardiovascular disease.

Blood Pressure↗
PubMed1987

EGF-induced mitogenesis in proximal tubular cells: potentiation by angiotensin II.

The mitogenic effect of epidermal growth factor (EGF) and the characteristics of EGF binding were studied on primary cultures of rabbit proximal tubular cells. EGF was found to be a potent mitogen and stimulated DNA synthesis 18-fold above the level observed in quiescent cells. Using 125I-EGF as a ligand, two classes of specific EGF receptors were identified on the proximal tubular cell in culture, i.e., a high-affinity receptor with a dissociation constant (Kd) of 0.3 nM and maximal binding (Bmax) of 1.7 X 10(4) receptors/cell and a low-affinity receptor with a Kd of 1.9 nM and Bmax of 5.3 X 10(4) receptors/cell. Because angiotensin II (ANG II) appeared to possess many properties common to growth factors, we also examined the interaction of ANG II and EGF on these cells. ANG II was not mitogenic, but it potentiated the mitogenic effect of EGF with a maximal effect at 10(-9) M. The dose-response curve of EGF-induced mitogenesis was shifted to the left in the presence of 10(-9) M ANG II, decreasing the approximate half-maximal stimulatory concentration from 3 X 10(-8) to 5 X 10(-9) M. ANG II also stimulated prostaglandin E2 (PGE2) release, but inhibition of basal and ANG II-stimulated PGE2 synthesis had no effect on mitogenesis. ANG II had no effect on the binding of EGF to the high-affinity receptor from 1 to 20 h and did not alter receptor downregulation. ANG II (10(-9) M) had no effect on cell protein content, RNA and protein synthesis, Na+-H+ antiport, and intracellular free Ca2+ concentration. Higher concentrations of ANG II (5 X 10(-8) to 5 X 10(-6) M) led to a rapid and transient dose-dependent rise in cytosolic free Ca2+ concentration. These studies demonstrate that ANG II potentiates EGF-induced mitogenesis at one or more postreceptor steps that may include small changes in cytosolic Ca2+ concentration.

Angiotensin II↗
PubMed1986

Effect of protein on glomerular filtration rate and prostanoid synthesis in normal and uremic rats.

Normal and uremic conscious rats that had been maintained on a low-protein diet were given oral protein or carbohydrate loads, and clearance studies were performed. Both the normal and uremic animals demonstrated a approximately 30% increase in glomerular filtration rate (GFR) in response to the protein bolus, but no significant increase in GFR was seen following the carbohydrate bolus. Similar studies were performed in uremic rats on a standard protein diet. The changes in GFR that were seen after an albumin bolus were similar but not as pronounced as those noted in the animals on the low-protein diet. Pretreatment with either aspirin or meclofenamate, cyclooxygenase inhibitors, completely blocked the protein-induced rise in GFR. The rats of glomerular production of prostaglandin (PG) E2 and 6-keto-PGF1 alpha (a stable metabolite of prostacyclin, PGI2) were determined by radioimmunoassay in a similar group of normal rats. The synthetic rates of PGE2 and 6-keto-PGF1 alpha following the protein bolus were 40 and 52% greater, respectively, than those observed following the carbohydrate load (P less than 0.005). Aspirin decreased glomerular prostanoid production in protein-treated animals by greater than 60%. Thus it appears that in the setting of protein restriction, the percent increase in GFR following a protein load is similar in both the normal and uremic rats, the increase in GFR in uremic rats is attenuated when animals were allowed to ingest a normal protein diet prior to study, and the increase in GFR seen in response to a protein load may be related to an increase in the synthesis of one or more vasodilatory glomerular prostanoids.

Animals↗
PubMed1986

Effect of experimental diabetes on glomerular filtration rate and glomerular prostanoid production in the rat.

Glomerular hyperfiltration is an early functional renal lesion seen both in experimental and human diabetes mellitus. This increase in the glomerular filtration rate has been thought to be mediated, in part, by changes in vasoregulatory hormones such as the prostanoids. The present study was designed to measure glomerular prostanoid production in rats with experimental diabetes to determine whether the biochemical changes in prostanoid production could be consistent with the hemodynamic alterations noted. Sprague-Dawley rats were studied either 7 or 28 days after intravenous streptozotocin administration (60 mg/kg). Measurements of the glomerular filtration rate were performed in two groups of diabetic animals 28 days after streptozotocin administration: one group with intact prostanoid production, the other having received a cyclooxygenase inhibitor for the 4-week period. Similar studies were performed in nondiabetic control rats. Measurements of glomerular prostanoid production were performed in control and diabetic animals 7 days after streptozotocin administration. The results of these studies indicate that experimental diabetes mellitus is associated with an increase in the glomerular filtration rate and that this increase can be blocked by the administration of a cyclooxygenase inhibitor. In addition, the determination of levels of various glomerular prostanoids indicated an increased production of prostacyclin and a decreased production of thromboxane during this period of hyperfiltration. Thus, these data support the premise that altered prostanoid biosynthesis may be one of the biochemical mediators of the hyperfiltration seen in early experimental diabetes mellitus.

Animals↗