Search PubMed⌕ Search

Biomedical subjects

D K Agrawal

Publications and source records attributed to D K Agrawal.

At least 91 records · Page 5Linked to original sources
PubMed1989

Inhibitory effect of terfenadine on mediator release from human blood basophils and eosinophils.

The effect of terfenadine on histamine release from human basophils and LTC4 production and release from human eosinophils was evaluated. Eosinophils and basophils were obtained by discontinuous gradient centrifugation of the peripheral blood of atopic asthma patients who were off medication. Anti-IgE-induced histamine release from human basophils was significantly inhibited by terfenadine. Maximum inhibition was obtained at 1 x 10(-5) M terfenadine (percentage inhibition = 57.0 +/- 20.1; P less than 0.05). However, only the highest dose of terfenadine used in this study, i.e. 2 x 10(-5) M, significantly inhibited calcium ionophore (A23187)-induced histamine release from human basophils (percentage inhibition = 40.0 +/- 14.6; P less than 0.05), and LTC4 production from human eosinophils (percentage inhibition = 59.8 +/- 9.9; P less than 0.05. These findings demonstrate that terfenadine, in addition to its known antihistamine property, also has an inhibitory effect on chemical mediator release.

Adolescent↗
PubMed1989

Effect of platelet-activating factor inhalation on nonspecific bronchial reactivity in man.

Bronchial hyperactivity is a recognized hallmark of asthma, characterized by an exaggerated bronchial response to numerous mediators, including histamine. It is also well recognized that bronchial hyperresponsiveness is increased following allergen exposure, although no particular mediator has been shown to induce this response. The recent observation that PAF can induce increased nonspecific bronchial reactivity in normal subjects emphasizes its importance as an inflammatory mediator. In this report we sought to further elucidate the role of PAF in airway hyperreactivity by comparing the effect of PAF on methacholine-induced airway responsiveness in six non-asthmatic subjects. Nonspecific airway responsiveness was not significantly increased following PAF inhalation at 6 hours nor was it increased at 1, 2, 7, or 14 days. Further elucidation of the potential role of PAF in explaining changes in airway reactivity is necessary.

Adult↗
PubMed1988

Leukotriene C4 production from human eosinophils in vitro. Role of eosinophil chemotactic factors on eosinophil activation.

We studied the role of naturally occurring eosinophil chemotactic factors on leukotriene (LT)C4 production from highly purified (87.1 +/- 2.4%) normodense eosinophils. Platelet activating factor (PAF) directly induced LTC4 production from eosinophils in a dose (10(-9) to 10(-5) M) and a time-dependent manner. PAF (10(-5) M) induced 0.74 +/- 0.08 ng of LTC4 production/10(6) eosinophils. However, lyso-PAF, eosinophil chemotactic factor of anaphylaxis, and LTB4 failed to induce LTC4 production within the tested range. Furthermore, the pre-incubation of eosinophils with 5 micrograms/ml of cytochalasin B did not alter the chemotactic factor-induced LTC4 production. When eosinophils were stimulated by the submaximal concentration (1 microgram/ml) of calcium ionophore A23187, the pre-incubation of eosinophils with 10(-6) M or 10(-5) M of PAF, or 10(-5) M of eosinophil chemotactic factor of anaphylaxis significantly enhanced LTC4 production up to 163.9 +/- 17.5% (p less than 0.05), 279.2 +/- 32.9% (p less than 0.01) and 165.2 +/- 21.2% (p less than 0.05) of the control, respectively. However, the pre-incubation with lyso-PAF or LTB4 failed to enhance A23187-induced LTC4 production. The pre-incubation of eosinophils with phosphatidyl serine also failed to enhance A23187-induced LTC4 production. However, the direct stimulation of protein kinase C by PMA enhanced the submaximal concentration of A23187-induced LTC4 production from eosinophils up to 179.5 +/- 20.9% (p less than 0.05) of the control. Our findings indicate that PAF and ECF-A work not only as chemotactic factors but also induce a functionally active state of eosinophils probably through their post-receptor mechanisms, and contribute to the inflammatory processes.

Adult↗
PubMed1988

Ketotifen prevents terbutaline-induced down-regulation of beta-adrenoceptors in guinea pig lung.

We examined the effect of ketotifen on the down-regulation of beta-adrenoceptors in guinea pig lung chronically treated with terbutaline. There was a significant decrease in the density of beta-adrenoceptors following chronic administration of terbutaline. Ketotifen prevented the decrease in beta-adrenoceptor density induced by terbutaline in a dose-dependent fashion; ketotifen alone, also increased the density of beta-adrenoceptors. However, neither ketotifen nor terbutaline significantly changed the KD values in either group. These findings suggest that ketotifen might be valuable when beta-agonists are administered for long term treatment in asthmatic patients.

Adrenergic beta-Agonists↗
PubMed1988

The development of a sensitive and specific radioreceptor assay for leukotriene B4.

To establish a simple and sensitive quantitation of leukotriene B4 (LTB4), we developed a radioreceptor assay (RRA) using a highly specific [3H]leukotriene B4[( 3H]LTB4) binding to a guinea pig spleen homogenate. The assay detected LTB4 levels as low as 0.12 pmol per tube. Fifty percent inhibition of bound [3H]LTB4 was obtained by 2.5 nM of unlabeled LTB4. [3H]LTB4 competition studies indicated that 20-hydroxy-LTB4 was 8 times, 6-trans-LTB4 was 640 times and 20-carboxy-LTB4 was 1000 times less effective than LTB4. The peptide leukotrienes C4, D4 and E4 showed no effect on [3H]LTB4 binding. Recovery rates averaged 97% after ethanol extraction and evaporation of known amounts of LTB4. The intra-assay coefficients of variation for three samples were 2.4%, 7.2% and 8.4%, respectively. This assay was validated by measuring LTB4 released from human granulocytes stimulated with calcium ionophore A23187. The LTB4 level was maximal at 10 min (156.8 +/- 36.2 pmol/3 x 10(6) cells) and decreased rapidly after 15 min. This radioreceptor assay for leukotriene B4 is highly sensitive and is comparable to the reported sensitivity by radioimmunoassay. The method is simpler and less expensive than other methods such as high pressure liquid chromatography and is suitable for routine measurement of leukotriene B4.

Animals↗
PubMed1987

Comparison of beta adrenoceptors in bovine airway epithelium and smooth muscle cells.

This study was undertaken to compare the characteristics of beta-adrenoceptors in bovine airway epithelium and smooth muscle cells. [3H]Dihydroalprenolol (DHA) was used as the radioligand. There was a significant difference in both the affinity and the density of the specific [3H]DHA binding in both the membranes. The maximum number of binding sites was about two fold higher and the affinity about six fold greater in the epithelial membranes as compared to those in the smooth muscle membranes. Because the integrity of airway epithelium is very important for pulmonary function and airway epithelium is very rich in beta-adrenoceptors, it is possible that the beneficial effects of beta-adrenoceptor agonists in asthma and other airway diseases could, at least in part, be due to their action on epithelium.

Animals↗
PubMed1987

Identification and characterization of leukotriene C4 and D4 receptors on a cultured smooth muscle cell line, BC3H-1.

We studied the characteristics of the leukotriene (LT) C4 and D4 receptors on a cultured smooth muscle cell line, BC3H-1. Specific [3H]LTC4 binding to the cell membrane was greater than 80% of total binding and saturable at a density of 3.96 +/- 0.39 pmol/mg protein, with an apparent dissociation constant (Kd) of 14.3 +/- 2.0 nM (n = 9). The association and dissociation of [3H]LTC4 binding were rapid and apparent equilibrium conditions were established within 5 min. Calculated Kd value of [3H]LTC4 binding from the kinetic analysis was 9.9 nM. From the competition analysis, calculated Ki value of unlabeled LTC4 to compete for the specific binding of [3H]LTC4 was 9.2 nM and was in good agreement with the Kd value obtained from the Scatchard plots or kinetic analysis. The rank order of potency of the unlabeled competitors for competing specific [3H]LTC4 binding was LTC4 much greater than LTD4 greater than LTE4 greater than FPL-55712. The maximum number of binding sites (Bmax) of [3H]LTD4 in the membrane of BC3H-1 cell line was about 11 times lower than that of the [3H]LTC4. The calculated values of Kd and Bmax of [3H]LTD4 binding were 9.3 +/- 0.8 nM and 0.37 +/- 0.04 pmol/mg protein, respectively (n = 3). The rank order of potency or the unlabeled competitors for competing specific [3H]LTD4 binding was LTD4 = LTE4 greater than FPL-55712 much greater than LTC4. These findings demonstrate that BC3H-1 cell line possess both LTC4 and LTD4 receptors with a predominance of LTC4 receptors. Thus BC3H-1 cell line is a good model to study the regulation of LTC4 and LTD4 receptors.

Animals↗
PubMed1987

Effect of platelet-activating factor on beta-adrenoceptors in human lung.

We examined the effect of platelet-activating factor (PAF) on beta-adrenoceptors in the membranes of human lung and the functional responses to methacholine, histamine and isoproterenol in human lung parenchyma and tracheal strips. Preincubation of the human lung slices with 0.1 microM PAF decreased the density of beta-adrenoceptors without a change in the affinity. In the functional studies, a subthreshold dose of PAF (0.1 microM) significantly reduced the potency of isoproterenol to reverse methacholine or histamine-induced contraction. BN 52021, a PAF antagonist, protected against these PAF-induced changes. These findings suggest that PAF-induced down-regulation of beta-adrenoceptors could be a mechanism of the non-specific airway hyperreactivity in asthma.

Cell Membrane↗
PubMed1987

Effects of platelet activating factor on the chemotaxis of normodense eosinophils from normal subjects.

Highly purified eosinophils were obtained from normal subjects, and their chemotactic responses to platelet activating factor (PAF) were evaluated. PAF induced both eosinophil chemotactic and chemokinetic responses, and was 100 fold more potent eosinophil chemotactic factor as compared to eosinophil chemotactic factor of anaphylaxis. On the other hand, leukotriene B4 did not show any eosinophil chemotactic activity. A selective PAF antagonist, BN52021, inhibited eosinophil chemotaxis in a dose dependent manner. Preincubation of eosinophils with PAF induced the deactivation of eosinophils for further chemotactic responses to PAF. These findings suggest that PAF is a potent chemotactic factor for normal eosinophils.

Adult↗
PubMed1987

A simple and sensitive radioreceptor assay for leukotrienes.

A simple and sensitive radioreceptor assay (RRA) for leukotrienes (LTs) was developed using a highly specific [3H]leukotriene D4 (LTD4) binding to guinea pig lung membrane homogenates. The assay can detect down to 0.15 pmol of LTD4. The values for fifty percent inhibition of bound [3H]LTD4 was 1.5 nM for LTD4, 45 nM for LTC4 and 24 nM for LTE4. LTB4 at 3.0 X 10(-5)M had no effect on [3H]LTD4 binding. The RRA for LTs in the absence of serine-borate complex was bi-specific for both LTC4 and LTD4. However, in the presence of 20 mM serine-borate this method was highly specific for LTD4. Recovery rate averaged 87.2% after ethanol extraction and evaporation of known amounts of LTD4. When the radioreceptor assay and radioimmunoassay data for leukotriene levels in the samples were compared to each other, an excellent correlation was observed with a correlation coefficient 'r' of 0.992. The assay was also validated by quantitation of Lts released from human granulocytes stimulated with calcium ionophore, A23187. The method is simpler, less expensive, and more specific for LTD4 than the other methods such as high pressure liquid chromatography and radioimmunoassay and is suitable for routine measurement of either LTD4 specifically or LTC4 plus LTD4 simultaneously in one cell system.

Animals↗
PubMed1987

A specific radioreceptor assay for leukotriene C4 and the measurement of calcium ionophore-induced leukotriene C4 production from human leukocytes.

A highly specific radioreceptor assay (RRA) for leukotriene (LT) C4 using BC3H-1 cell membrane as a source of LTC4 receptors was developed and demonstrated its use in the measurement of calcium ionophore A23187-induced LTC4 production from purified eosinophils, neutrophils, and mononuclear cells. Unlabeled LTC4 competed for the specific [3H]LTC4 binding to the BC3H-1 cell membranes in a dose-dependent manner. Under the experimental conditions used in this study, the calculated IC50 value of unlabeled LTC4 was 27.2 +/- 1.2 nM (n = 5). The sensitivity of the method for LTC4 was 0.6 pmol. The cross-reactivities of LTD4, LTE4, and FPL 55712 were negligible. The recovery of the exogenously added LTC4 with eosinophils was greater than 90% in both the presence and the absence of calcium ionophore A23187. Calcium ionophore induced 73.0 +/- 17.0 ng of LTC4 production/10(6) eosinophils (n = 8), and this was about 20-40 times more than those from neutrophils and from mononuclear cells.

Calcium↗
PubMed1987

Effect of chronic experimental diabetes on vascular smooth muscle function in rabbit carotid artery.

To understand the effects of diabetes on vascular smooth muscle function and the underlying mechanism(s) involved, we examined the responses to alpha-adrenoceptor agents, serotonin (5-HT), K+, and prostaglandins in the carotid artery of male New Zealand white rabbits with chronic diabetes (16 weeks) induced chemically by alloxan (100 mg/kg, intravenously) treatment. Isolated ring segments of diabetic rabbit carotid artery exhibited an increased (20-60%) maximal response to norepinephrine (NE), methoxamine, phenylephrine, and K+ as compared with controls. Responses to 5-HT were not significantly increased. Nevertheless, there were no significant differences in ED50 values of the agonists in either of the groups. Putatively selective alpha 2-adrenoceptor agonists (clonidine and guanabenz), prostaglandin E1 (PGE1) and prostaglandin I2 (PGI2) did not elicit any response in control vessels. In the diabetic state, however, these drugs contracted the artery in a dose-dependent fashion. Isoproterenol (0.1-10 microM) relaxed arterial rings previously contracted with all the agonists except PGE1 and PGI2, which were potentiated by isoproterenol. Contractions to PGE1 or PGI2 alone or in the presence of isoproterenol were reduced or abolished by 10(-5) M phentolamine. Under these conditions, isoproterenol exhibited its typical relaxatory action. Nifedipine was more potent in inhibiting the K+ response in diabetic carotid artery than in the controls. These results suggest an increased reactivity of diabetic rabbit carotid artery to alpha 2-adrenoceptor agonists, K+, PGE1, and PGI2 which may, at least in part, be due to an increased sensitivity of calcium channels in diabetic vessels. Contractile responses to PGE1 and PGI2 could be attributed to their action on adrenergic neurotransmission, thereby facilitating the release of NE from presynaptic nerve terminals. Furthermore, isoproterenol at a high dose (1 microM or more) may directly stimulate alpha-adrenoceptors. Whether or not this effect of isoproterenol is only prostaglandin-dependent is not clear.

Alloxan↗
PubMed1987

Vascular responses to agonists in rat mesenteric artery from diabetic rats.

The effect of diabetes on vascular smooth muscle function was investigated in the muscular arteries from spontaneously and chemically induced diabetic rats. Isolated ring segments of superior mesenteric arteries from BB diabetic and streptozotocin (STZ)-diabetic rats (12 weeks after onset of diabetes) were used for isometric tension studies. Contractile responses to alpha-adrenoceptor agonists (norepinephrine, methoxamine, phenylephrine, B-HT 920, guanabenz, SKF 89748-A), serotonin, and K+ were significantly higher in STZ-diabetic rat arteries as compared with the controls. In spontaneously diabetic rat arteries only the contractile responses to the putatively selective alpha 2-adrenoceptor agonists, K+ and prostaglandin E1, were significantly increased. pD2 values of the agonists in both groups of diabetic arteries were not significantly different from the respective controls. Nifedipine inhibited all contractile responses in a dose-dependent fashion. The responses to K+ and alpha 2-adrenoceptor agonists were attenuated to a greater extent by nifedipine in both groups of diabetic blood vessels. The calcium channel activator, BAY K 8644, produced a twofold increase in force of contraction in streptozotocin-diabetic and spontaneously diabetic rat arteries as compared with the responses in their respective controls. These results suggest caution in extrapolating all the findings from the streptozocin-induced diabetic model to the spontaneously diabetic model. However, increased activity of calcium channels in vascular muscle cells in both groups of diabetics may be responsible, at least in part, for the increased vascular contractility in diabetes mellitus.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1987

Effect of diabetes on vascular smooth muscle function in normotensive and spontaneously hypertensive rat mesenteric artery.

We have examined the functional responses to alpha-adrenoceptor agonists (alpha 1-selective: methoxamine and phenylephrine; alpha 2-selective: clonidine and B-HT 920; non-selective: norepinephrine, serotonin and K+ in ring segments of mesenteric artery of control and streptozotocin-induced diabetic spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Systolic blood pressure and contractile responses were examined after 12 weeks of diabetes. There was no significant change in the diabetic WKY rats as compared with the control WKY rats. However, diabetic SHR had significantly less hypertension than control SHR. Responses to serotonin and alpha 2-adrenoceptor agonists were augmented significantly in arteries from control SHR animals as compared with vessels from WKY animals. There was no significant difference in the force of contraction generated by other agonists in both nondiabetic groups. Responses to all agonists in WKY diabetic and to methoxamine and K+ in SHR diabetic arteries were increased as compared with their respective controls. ED50 values for each agonist were similar in all groups. Indomethacin (5 microM) shifted the dose-response curve to norepinephrine to the right in arteries from all groups of animals. However, in the diabetic SHR and WKY, there was a significant reduction in norepinephrine maximum response. Nifedipine was more potent in inhibiting the contraction to K+ and serotonin in WKY diabetic arteries as compared with WKY controls. However, nifedipine inhibited the responses to all agonists with equal potency in the control and diabetic SHR vessels. These results suggest the involvement of alpha 2-adrenoceptors and serotonin receptors in the development and (or) the maintenance of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Determination of molecular size of alpha-1 and alpha-2 adrenoceptors in rat mesenteric artery by radiation inactivation.

Radiation inactivation of alpha-1 and alpha-2 adrenoceptors in the purified plasma membranes of rat mesenteric artery has been performed with high energy electrons at -45 to -55 degrees C. Alpha-1 and alpha-2 adrenoceptor inactivation was monitored with [3H] prazosin and [3H]yohimbine binding, respectively. Internal endogenous and external standards of known molecular weight were used in these studies to determine the molecular size. The average value of D37 for the [3H]prazosin binding site was 6.75 +/- 0.62 Mrad (n = 4) with an estimated molecular size of 122,921 +/- 11,329 Daltons. However, the average value of D37 for the [3H] yohimbine binding site was higher (D37 = 10.05 +/- 0.91 Mrad) and accordingly the molecular size of this binding site was less than the [3H]prazosin binding sites (molecular weight = 82,540 +/- 7478 Daltons; n = 4). Irradiation did not change the dissociation constant of either radioligand, suggesting that the loss of the radioligand binding sites after radiation is due to receptor protein inactivation. These results confirm our earlier finding that [3H]prazosin and [3H]yohimbine bind to two distinct sites in the plasma membranes of rat mesenteric artery. Whether both of these sites are the subunits of a common macromolecule of alpha adrenoceptor on vascular smooth muscle in rat mesenteric artery cannot be concluded from these results. This report is the first one in the literature on the molecular size of alpha-1 and alpha-2 binding sites in vascular smooth muscle.

Animals↗
PubMed1986

Influence of polyethylene glycol 6000 and mannitol on the in-vitro dissolution properties of nitrofurantoin by the dispersion technique.

Employing the dispersion technique the influence of mannitol and polyethylene glycol (PEG) 6000 on the in-vitro dissolution of nitrofurantoin was investigated. Dispersions of the drug with PEG 6000 showed faster dissolution rates when compared with dispersions of the drug in mannitol. Tablet formulation of the drug--PEG 6000 dispersion exhibited better drug releasing properties as compared to tablets prepared from the drug's PEG 6000 physical mixture, or the drug's formulation with Avicel PH 101.

Chromatography, Thin Layer↗