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B Trivedi

Publications and source records attributed to B Trivedi.

32 records · Page 2Linked to original sources
PubMed1988

Release of growth hormone binding protein from IM-9 lymphocytes by endopeptidase is dependent on sulfhydryl group inactivation.

The hydrophilic GH-binding protein of serum is a derivative of the GH receptor. Little is known how this GH binding protein is released from the receptor which is firmly anchored in the plasma membrane. The IM-9 lymphocytes provide a useful laboratory model for studying this process because they are richly endowed with GH receptors and, under special conditions, are able to shed these receptors during incubation. Incubation of IM-9 cells for 90 min at 30 C did not result in the appearance of significant [125I]hGH binding in conditioned medium as determined with an ultrogel AcA 44 minicolumn. When iodoacetamide, 20 mM, or N-ethylmaleimide, 5 mM, was added during incubation, the conditioned medium bound 20-35% of [125I]human(h)GH. p-Chloromercuriphenyl sulfonic acid was less effective in promoting shedding of GH-binding protein. In contrast, aprotinin, phenylmethylsulfonylfluoride (PMSF), bacitracin, leupeptin, pepstatin, phosphoramidon, or chloroquine did not promote release of GH binding protein and did not affect iodoacetamide-induced release. Release was not inhibited by the addition of serum lacking GH binding protein. GH binding protein release was markedly temperature sensitive and practically ceased at 4 C. GH binding protein incubated with [125I] hGH was cross-linked with disuccinimidyl suberate. After sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of dithiothreitol the complex migrated with an estimated molecular weight of 100,000 whereas [125I]hGH cross-linked to the membrane-bound GH receptor of the IM-9 cells migrated with an estimated molecular weight of 135,000. The smaller size of the binding protein is consistent with its derivation from the extracellular domain of the GH receptor. Because the release of this GH binding is greatly augmented by iodoacetamide and N-ethylmaleimide, two known sulfhydryl reactive reagents, we suggest that a free sulfhydryl group, either on the GH receptor or on a neighboring protein normally maintains the integrity of the receptor. The loss of this sulfhydryl group destabilizes the receptor and permits a membrane endopeptidase to release the GH binding protein. Cleavage is not dependent on lysosomal action and is not inhibited by protease inhibitors.

4-Chloromercuribenzenesulfonate↗
PubMed1987

Absence of serum growth hormone binding protein in patients with growth hormone receptor deficiency (Laron dwarfism).

It has recently been recognized that human serum contains a protein that specifically binds human growth hormone (hGH). This protein has the same restricted specificity for hGH as the membrane-bound GH receptor. To determine whether the GH-binding protein is a derivative of, or otherwise related to, the GH receptor, we have examined the serum of three patients with Laron-type dwarfism, a condition in which GH refractoriness has been attributed to a defect in the GH receptor. The binding of 125I-labeled hGH incubated with serum has been measured after gel filtration of the serum through an Ultrogel AcA 44 minicolumn. Nonspecific binding was determined when 125I-hGH was incubated with serum in the presence of an excess of GH. Results are expressed as percent of specifically bound 125I-hGH and as specific binding relative to that of a reference serum after correction is made for endogenous GH. The mean +/- SEM of specific binding of sera from eight normal adults (26-46 years of age) was 21.6 +/- 0.45%, and the relative specific binding was 101.1 +/- 8.6%. Sera from 11 normal children had lower specific binding of 12.5 +/- 1.95% and relative specific binding of 56.6 +/- 9.1%. Sera from three children with Laron-type dwarfism lacked any demonstrable GH binding, whereas sera from 10 other children with other types of nonpituitary short stature had normal relative specific binding. We suggest that the serum GH-binding protein is a soluble derivative of the GH receptor. Measurement of the serum GH-binding protein may permit recognition of other abnormalities of the GH receptor.

Adolescent↗
PubMed1987

The ontogeny of serum GH binding protein in man: a possible indicator of hepatic GH receptor development.

Experiments in rabbits suggest that a serum GH binding protein (GH-BP) probably is derived largely from hepatic membrane bound GH receptors. Human serum contains a specific GH binding protein which can be easily measured by incubation with [125I] hGH and separation of [125I] hGH-BP complexes from free [125I] hGH by gel filtration through an Ultrogel AcA 44 minicolumn. In each assay GH-BP activity of a reference (normal young adult) serum is similarly run and the results are expressed as a percentage of the activity of the unknown serum divided by the GH-BP activity of the reference serum after correction for the expected inhibition of GH binding resulting from the GH content of the unknown serum. The mean relative specific GH binding protein (RSGH-BP) of cord serum from 11 premature infants was only 3.2 +/- 1.4% (SE) and of cord serum from 17 full term infants was 14.9 +/- 2.5%. During the first two decades of life there was a progressive rise of RSGH-BP with considerable individual variation. The mean serum RSGH-BP of 13 such subjects was 54.5 +/- 6.2%. More uniform RSGH-BP results were obtained in serum from 15 young adults, 91.7 +/- 7.4%. Lower RSGH-BP 77.2 +/- 5.4% was found in serum from 12 healthy older adults (age 60 to 70 years). The low levels of RSGH-BP in fetal serum are consistent with the reported low concentrations of GH receptors in sheep and rat fetal liver membranes. We suggest the measurement of GH-BP activity provides a simple, noninvasive measure of the ontogeny of GH receptors of human beings.

Adolescent↗
PubMed1986

Effect of respiratory acidosis on intracellular pH of the proximal tubule.

In contrast to chronic metabolic acidosis, chronic respiratory acidosis does not result in an adaptation in either renal ammonia or glucose production. To examine the possibility that this might be explained by a difference in proximal tubule intracellular pH, the response of two pH-sensitive metabolites, citrate and alpha-ketoglutarate, were assessed. Metabolic acidosis of 3 days duration, induced by drinking 1.5% NH4Cl, significantly reduced urinary citrate excretion (172 to 15 mumol/day) and renal cortical citrate (1.33 to 0.88 mumol/g) and alpha-ketoglutarate (0.90 to 0.46 mumol/g) concentrations in comparison with normal rats. Chronic respiratory acidosis, produced by 3 days in a 10% CO2 environment, lowered systemic pH similar to metabolic acidosis but had no effect on either urinary citrate excretion or renal cortical citrate and alpha-ketoglutarate concentrations. By contrast, acute respiratory acidosis (3, 6, or 24 h duration) reduced urinary citrate excretion and renal cortical citrate and alpha-ketoglutarate concentrations in a fashion similar to acute metabolic acidosis. These data suggest that acute acidosis of either respiratory or metabolic origin lowers the intracellular pH of the proximal tubule. However, when the acid-base abnormality enters the chronic phase, proximal tubular intracellular pH remains low with metabolic acidosis but returns to normal values with respiratory acidosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis, Respiratory↗
PubMed1982

Measurement of somatomedin-related peptides in fetal, neonatal, and maternal rat serum by insulin-like growth factor (IGF) I radioimmunoassay, IGF-II radioreceptor assay (RRA), and multiplication-stimulating activity RRA after acid-ethanol extraction.

Previous measurements of somatomedins (Sms) and insulin-like growth factors (IGFs) in maternal and fetal serum have yielded contradictory results. We have, therefore, measured maternal, fetal, and neonatal rat serum with two highly specific assays: 1) IGF-I/Sm-C RiA and 2) a highly specific IGF-II/rat placental membrane radioreceptor assay (RRA). In addition, we have made measurements with a less specific multiplication-stimulating activity (MSA)-rat placental membrane RRA. To avoid possible serious artifacts created by Sm-binding proteins, preliminary acid-ethanol extraction of serum was performed. Results are expressed in terms of a reference human serum with an assigned potency of 1 U/ml. Maternal RIA IGF-I fluctuated between 1.1-1.4 U/ml from the 17th day of pregnancy to the 25th day after delivery (nonpregnant rat serum pool, 1.25 +/- 0.22 U/ml). On day 21 of gestation, fetal serum radioimmunoassayable IGF-I was 1.03 +/- 0.03 U/ml. After birth, radioimmunoassayable IGF-I fell and reached .19 +/- 0.03 U/ml at 18 days of age, but rose to 0.71 +/- 0.04 U/ml at 25 days of age. At term, maternal radioreceptor assayable IGF-II was 2.18 +/- 0.27 U/ml (nonpregnant female pool, 1.4 +/- 0.12). By the 25th postpartum day, radioreceptor assayable IGF-II was 1.39 +/- 0.12 U/ml. Radioreceptor assayable IGF-II in fetal serum on day 19 was 3.26 +/- 0.48 U/ml and rose to 5.37 +/- 0.66 U/ml on the day of delivery. A further rise to 8.92 +/- 1.03 occurred on day 5. A subsequent fall to 2.41 +/- 0.05 U/ml was observed on day 25. The patterns of results of the MSA RRA in fetal and neonatal rat serum were similar to that obtained with the IGF-II RRA. We now conclude that radioimmunoassayable IGF-I is present in higher concentrations than previously reported in term fetal rat serum and that radioreceptor assayable IGF-II is selectively elevated in rat fetal and neonatal life and may have unique metabolic and growth-promoting significance.U

Animals↗
PubMed1982

Homologous IM-9 lymphocyte radioreceptor and receptor modulation assays for human serum growth hormone.

Radioreceptor assays for human GH (hGH) have been developed using the IM-9 cultured human lymphoid cell receptor. Varying degrees of nonspecific interference with [125I] hGH binding to these cells occurs in the presence of serum. We have modified the traditional IM-9 competitive binding assay for hGH and abolished the nonspecific serum effects. The modified competitive assay is sensitive to as little as 2 ng/ml hGH, and it has been validated by the quantitative recovery of purified pituitary hGH in hypopituitary serum. Sera from stimulated normals, acromegalics, and patients with severe growth retardation were assayed. The RIA to radioreceptor assay ratios for these groups were 0.98 +/- 0.10, 0.97 +/- 0.18, and 2.43 +/- 0.54, respectively. The assay has potential usefulness in screening and predicting growth-retarded patients most likely to respond to exogenous hGH therapy. In addition, a sensitivity receptor modulation assay, which uses the ability of hGH to regulate its homologous IM-9 receptors, is described. This is 8- to 10-fold more sensitive than the nonregulatory assays and has been applied to the measurement of hGH in sera from unstimulated normals and acromegalics. The ratios of RIA to receptor modulation assay for the two groups were 1.17 +/-0.68 ad 1.07 +/- 0.26, respectively. These sensitive receptor assays offer a powerful technique for the measurement of biologically active and inactive GH peptide in serum, and may be particularly useful in the evaluation of statural growth disorders.

Acromegaly↗
PubMed1982

Characterization of somatomedin binding in human serum by ultracentrifugation and gel filtration.

It is known that the somatomedins exist in human serum complexed to specific binding proteins. The existence of unbound somatomedins in serum has never unequivocally been demonstrated. We have characterized the distribution of insulin-like growth factor (IGF) I in different fractions after gel filtration of serum through Sephadex G-200 in neutral buffer. IGF-I was measured by RIA after acid extraction. Seventy-two percent of serum IGF-I was associated with large complexes with an estimated size of about 150,000 daltons and 25% was associated with smaller complexes of about 50,000 daltons. No unbound IGF-I was detected. Ultracentrifugation of 10 ml fresh serum was carried out at 106,000 X g for 17 h, after which the tube was aspirated in 1-ml fractions beginning at the top. IGF-I by RIA in fractions 2 and 3 sedimented with albumin; in fractions 4 to 7, the sedimentation pattern approached that of immunoglobulin G. This shift is consistent with the size distribution of IGF-I complexes demonstrated by gel filtration. The failure to find any significant increase in the concentration of IGF-I relative to albumin in the top 30% of the tube (fractions 1-3) after centrifugation argues against the presence of measurable free IGF-I in these fractions. The ability of upper fractions to bind added [125I]IGF-II proved to closely approximate the binding of the initial serum, indicating little sedimentation of the accessible binding protein. The relative binding of [125I]IGF-II by serum aliquots proved to be markedly concentration dependent. At concentrations above 5% serum, the incremental increase of binding as a function of serum concentration was much reduced. We interpret this to indicate that with dilution there is a dissociation of complexes and an increase in accessible binding sites. This phenomenon may modify tissue delivery of somatomedins in interstitial fluid. The data suggest that in undiluted serum there is no significant concentration of free somatomedins but at the dilution of serum that exists in the interstitial fluid, dissociation of bound somatomedins may be facilitated.

Adult↗
PubMed1981

Measurement of insulin-like growth factor II by a specific radioreceptor assay in serum of normal individuals, patients with abnormal growth hormone secretion, and patients with tumor-associated hypoglycemia.

A radioreceptor assay for insulin-like growth factor II (IGF-II) is described in which [125I]IGF-II is bound by rat placental membranes. IGF-I and other insulin-related peptides have less than 1% of the potency of IGF-II in displacing [125I]-IGF-II. IGF-II is extracted from its serum binding protein with a simple acid-ethanol step. After neutralization with Tris base, the extract is introduced directly into the radioreceptor assay. Results are expressed in terms of a reference serum with an assigned potency of 1 U/ml. By this method, serum from normal adults, 20-69 yr of age, had a mean (+/-SE)IGF-II activity of 0.73 +/- 0.03; higher concentrations were noted in adults more than 70 years of age (1.05 +/- 0.05), in cord serum (1.55 +/- 0.24), and in short children with normal GH secretion (0.88 +/- 0.42). In hypopituitary dwarfism, serum IGF-II activity was reduced (0.50 +/- 0.05), but in acromegaly, it was not increased (0.77 +/- 0.06). In 10 of 14 serum samples from patients with tumor-related hypoglycemia, the IGF-II exceeded the normal 95.5% confidence limits. In 8 of these sera, IGF-I by RIA was low, and in 5, it was essentially unmeasurable. These results with a new radioreceptor assay for IGF-II provide additional evidence that the regulation of this serum peptide differs from that of IGF-I.

Acromegaly↗
PubMed1979

The effect of hypophysectomy on rat chorionic somatomammotropin as measured by prolactin and growth hormone radioreceptor assays: possible significance in maintenance of somatomedin generation.

We have previously reported that serum somatomedin concentrations are maintained in pregnant rats after hypophysectomy. Because rat chorionic somatomammotropin (rCS) might replace pituitary GH during pregnancy, the concentration of rCS was measured at intervals after hypophysectomy on day of pregnancy. By day 16 of pregnancy, the serum rCS of hypophysectomized (hypox) rats was actually higher than that of normal pregnant rats when measured by a lactogenic radioreceptor assay. Increased levels of lactogenic radioreceptor activity (L-RRA) were maintained in the serum of hypox rats throughout the remainder of pregnancy. The GH radioreceptor activity (GH-RRA) of serum of hypox pregnant rats was also greater than that of normal rats during the last days of pregnancy, but the activity was only about 1/20th that of the L-RRA with the assays employed. There was no significant difference between placental L-RRA and GH-RRA of normal and hypox pregnant rats. The difference in concentration could not be attributed to differences in the number of fetuses. We conclude that the high levels of rCS were sufficient to maintain serum somatomedin concentration in hypox pregnant rats. This effect of rCS could have been due to binding by GH or PRL receptors of the maternal liver.

Animals↗
PubMed1975

Suppression of sleep-related prolactin secretion and enhancement of sleep-related growth hormone secretion.

Methysergide, a clinically-used blocker of serotonin receptors, was administered to 10 normal young men at a dose of 2 mg every 6 h for 48 h. After drug treatment, serum levels of growth hormone during sleep were 41.9% higher than placebo values (less than 0.001). In contrast, drug treatment was associated with a 36.4% decrease in stimulated growth hormone secretion during insulin tolerance testing (P less than 0.01). These opposite effects of methysergide suggest that different mechanisms are responsible for sleep-related and insulin-induced growth hormone secretion. Accordingly, data obtained with pharmacologic stimuli may lead to erroneous inferences regarding physiologic growth hormone control mechanisms. Administration of methysergide profoundly suppressed sleep-related prolactin secretion; overall nocturnal mean prolactin fell by 70.3% from 4.30+/-0.19 to 1.28+/-0.06 ng/ml (P less than 0.0001). It appears that serotonin may be significant modulating neurotransmitter for the control of growth hormone secretion, limiting sleep-related release, and enhancing insulin-induced release. It seems likely from these data that the role of serotonin in the control of prolactin secretion is relatively more important, since serotonin receptor blockade dramatically reduced sleep-related prolactin secretion.

Adult↗