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Biomedical subjects

J R Gavin

Publications and source records attributed to J R Gavin.

At least 55 records · Page 3Linked to original sources
PubMed1985

Phorbol esters inhibit gluconeogenesis in canine renal proximal tubular segments.

Gluconeogenesis is a major metabolic function of the renal proximal tubular cell. To characterize the regulation of this process in proximal tubule, glucose production from gluconeogenic precursors was measured in proximal tubular segments prepared from dog kidney. Production of glucose was a linear function of time for up to 120 min of incubation at 37 degrees C under a variety of conditions. Lowering the pH of incubation media from 7.5 to 7.0 increased glucose synthesis. Production of glucose was inhibited by 3-mercaptopicolinate. Incubation of proximal tubular segments with insulin diminished synthesis of glucose. Incubation of segments with tumor-promoting phorbol esters, 12-O-tetradecanoylphorbol-13-acetate or phorbol 12,13-dibutyrate, resulted in decreased production of glucose. This effect was not observed following incubation with the inactive phorbol ester 4 alpha-phorbol. Changes in glucose synthesis could not be attributed to alterations in cell viability or in rates of glucose oxidation induced by experimental maneuvers. Our findings confirm the usefulness of proximal tubular segments for characterization of metabolic processes in this portion of the nephron. The experimental results are consistent with a role for protein kinase C in the control of gluconeogenesis in proximal tubule.

Adenosine Triphosphate↗
PubMed1985

Bone calcification and calcium homeostasis in rats with non-insulin-dependent diabetes induced by streptozocin.

The effect of mild, non-insulin-dependent diabetes (NIDDM) on bone calcification and calcium (Ca) homeostasis was studied in growing rats (males and females). The diabetic state was characterized by mild insulin deficiency, plasma levels being 73% of controls, and mild hyperglycemia, with nonfasting plasma glucose levels of 1.5 times normal. There was no difference in plasma levels of Ca, phosphate (Pi), magnesium (Mg), alkaline phosphatase, immunoreactive parathyroid hormone (iPTH), calcitonin, 25-(OH)vitamin D (25[OH]D), 1,25-dihydroxyvitamin D (1,25[OH]2D), and 24,25-dihydroxyvitamin D (24,25[OH]2D) between the NIDDM rats and their controls of either sex. Metabolic Ca and Pi balance studies revealed that the experimental animals of both sexes were in positive Ca and Pi balance similar to that of their controls. Histologic studies of the kidney and intestinal slices from the experimental group were normal. Ca and Pi bone content calculated per gram bone ash of the femur, mandible, and second and fourth caudal vertebrae, and the organic content in the bones of the NIDDM animals showed no difference from their controls. Femur bone density and tibial epiphyseal growth plate width and morphology were similar histologically in the experimental and control rats. No decreased osteoid content in the tibial bone was found in the diabetic rats compared with controls. Physiologic sex differences, consisting of lower plasma Pi, higher plasma calcitonin levels, increased ratio of femur dry bone weight to total body weight, and increased percentage of mineralized and total bone volume at the tibial metaphysis seen in female compared with male control rats were also seen in the diabetic animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Binding of insulin-like growth Factor ii and multiplication-stimulating activity-stimulated phosphorylation in basolateral membranes from dog kidney.

Biologic actions of insulin and insulin-like growth factors (IGFs) are thought to be initiated by binding of peptides to tissues, followed by phosphorylation of specific hormone receptors. Both insulin and IGF bind to renal membranes, suggesting functional roles for these peptides in kidney. The present studies further characterize the interaction of multiplication-stimulating activity (MSA)/IGF II with its renal receptor. Specific binding of 125I-IGF II was measured in basolateral membranes isolated from proximal tubular cells of dog kidney. Binding was half-maximal at 10(-9) M MSA and was not inhibited by human growth hormone, IGF I, insulin, or anti-insulin receptor antibodies. Concentration-dependent MSA-stimulated phosphorylation of a Mr 135,000 protein band was demonstrated in autoradiograms of sodium dodecyl sulfate-polyacrylamide gels from basolateral membrane suspensions. Insulin increased phosphorylation of this band only in the presence of MSA, while a Mr 92,000 band was consistently phosphorylated with insulin alone. The phosphorylated Mr 135,000 band which had been solubilized with detergent from basolateral membranes was immunoprecipitated using serum from a patient with anti-insulin receptor antibodies suggesting that the band is the alpha subunit of the insulin receptor. This was supported by the demonstration of covalent cross-linkage of 125I-insulin to the Mr 135,000 band. We conclude that receptor-mediated MSA-stimulated phosphorylation of isolated basolateral membranes may reflect a process by which biological actions of IGF II are mediated in vivo. Our data suggest that insulin and IGF II may interact by regulating protein phosphorylation.

Animals↗
PubMed1984

Insulin stimulates Pi transport in brush border vesicles from proximal tubular segments.

Induction of hyperinsulinemia in dogs results in enhanced reabsorption of Pi from glomerular filtrate in the renal proximal tubule. To determine whether this may be a direct action of insulin mediated by altered transport characteristics of the proximal tubular brush border membrane, we measured Na+-dependent 32Pi transport in brush border membrane vesicles prepared from isolated proximal tubular segments originating from dog kidney that had been incubated with or without insulin. Specific high affinity binding sites for insulin were detected in proximal tubular segments. Increased initial rates (15 s) of Na+-dependent 32Pi transport were measured in brush border vesicles prepared from segments that had been incubated with insulin. This effect of insulin was concentration dependent over the range of 10(-10) to 10(-6) M insulin. These studies demonstrate the feasibility of using brush border vesicles prepared from proximal tubular segments to study solute transport. Our findings suggest that insulin-induced increased Pi reabsorption in the proximal tubule is mediated by a direct action of insulin on the proximal tubular cell, which results in increased Na+-Pi cotransport across the brush border membrane.

Adenosine Triphosphate↗
PubMed1984

Insulin-stimulated phosphorylation and insulin binding in canine renal basolateral membranes.

To characterize the interaction of insulin with the renal proximal tubular cell, we measured insulin-stimulated phosphorylation in basolateral membranes and brush border membranes isolated from canine renal cortex. Insulin stimulated the specific phosphorylation of a 92,000 Mr protein band demonstrable on autoradiograms of sodium dodecyl sulfate-polyacrylamide gels of basolateral membranes. Dephosphorylation of the 92,000 Mr band occurred over time. Insulin-stimulated phosphorylation was concentration dependent, being clearly detectable at 10(-9) M insulin and maximal at 10(-6) M. The phosphorylated 92,000 Mr protein band from detergent-solubilized basolateral membranes was immunoprecipitated using serum from a patient with anti-receptor antibodies. No insulin-stimulated phosphorylation was detected in brush border membranes. Binding of insulin to membranes was highly specific for native hormone and was severalfold greater in basolateral membranes than in brush border membranes. These observations are consistent with the asymmetrical distribution of insulin-stimulated protein kinase as well as specific insulin binding sites in the proximal tubular cell. The data suggest that insulin exerts physiological effects on the cell through binding to specific basolateral membrane receptors and phosphorylation of those receptors.

Animals↗
PubMed1984

Impaired insulin action in rats with non-insulin-dependent diabetes.

Studies were performed to test the hypothesis that impaired insulin action occurs as an acquired phenomenon in the streptozocin (STZ)-treated, non-insulin-dependent (NIDDM) diabetic rat model. A number of methods were used to evaluate impaired carbohydrate tolerance in these animals. Plasma glucose and insulin levels were measured at 6 and 14 wk of age, and insulin glucose tolerance tests were performed at 4 and 5 wk of age (before overt hyperglycemia ensues), and at 8 and 14 wk of age (after the animals manifest overt diabetes). The STZ-treated rats had higher plasma glucose levels than those of control animals (P less than 0.001) at 6 and 14 wk of age, while their plasma insulin values were decreased to levels 73% of the controls (1.7 ng/ml versus 2.3 ng/ml, P less than 0.04). Glucose disappearance rates after high (0.35 U/kg) and low (0.175 U/kg) insulin challenge were reduced in the experimental diabetic animals at all ages with both insulin doses. The data suggest that these animals have an early and progressive acquired impairment in insulin action, most compatible with a defect in cellular biologic response to insulin. The possibility that this abnormality is secondary to insulin deficiency is raised.

Animals↗
PubMed1984

Elevated levels of plasma beta-endorphin and gamma 3-melanocyte stimulating hormone in the polycystic ovary syndrome.

The authors have suggested that dysfunction of a central structure (above the pituitary level) is the primary etiologic factor responsible for the production of the polycystic ovary syndrome. To investigate further the functional integrity of the hypothalamic pituitary axis, plasma levels of beta-endorphin, gamma 3-melanocyte stimulating hormone, and gamma 1-melanocyte stimulating hormone-like immunoreactivity were measured in six patients with polycystic ovary syndrome, and in ten women with normal ovarian function. The limit of sensitivity for the radioimmunoassays was 20 pg/mL. Plasma beta-endorphin was significantly higher in polycystic ovary syndrome than in control subjects: (mean +/- SE) 60 +/- 10 versus 30 +/- 4 pg/mL, respectively (P less than .05). gamma 3-Melanocyte stimulating hormone was detectable in four of six patients with polycystic ovary syndrome (mean for the whole group: 45 +/- 15 pg/mL); it was undetectable in all the control subjects. Control of plasma beta-endorphin and gamma 3-melanocyte stimulating hormone secretion in PCO was evaluated with metyrapone and dexamethasone. Overnight administration of metyrapone to polycystic ovary syndrome patients resulted in rises of beta-endorphin and gamma 3-melanocyte stimulating hormone. Dexamethasone suppressed only partially (to basal concentrations) beta-endorphin and gamma 3-melanocyte stimulating hormone levels. Plasma adrenocorticotropic hormone concentrations were within the normal range and displayed the expected changes in response to metyrapone and dexamethasone. The present report presents an additional central (hypothalamic-pituitary) abnormality in patients with the polycystic ovary syndrome.

Adrenocorticotropic Hormone↗
PubMed1983

Effects of exercise and lack of exercise on glucose tolerance and insulin sensitivity.

Physically trained individuals have a markedly blunted insulin response to a glucose load and yet have normal glucose tolerance. This phenomenon has generally been ascribed to long-term adaptations to training which correlate with maximal oxygen uptake (VO2max) and reduced adiposity. Our study was undertaken to test the hypothesis that residual effects of the last bouts of exercise play an important role in this phenomenon. Eight well-trained subjects stopped training for 10 days. There were no significant changes in VO2max (58.6 +/- 2.2 vs. 57.6 +/- 2.1 ml/kg), estimated percent body fat (12.5 +/- 0.7 vs. 12.5 +/- 0.8%), or body weight. The maximum rise in plasma insulin concentration in response to a 100-g oral glucose load was 100% higher after 10 days without exercise than when the subjects were exercising regularly. Despite the increased insulin levels, blood glucose concentrations were higher after 10 days without exercise. Insulin binding to monocytes also decreased with physical inactivity. One bout of exercise after 11 days without exercise returned insulin binding and the insulin and glucose responses to an oral 100-g glucose load almost to the initial "trained" value. These results support our hypothesis.

Adult↗
PubMed1983

Acanthosis nigricans in a patient with streak gonads.

Acanthosis nigricans (ACN) is associated with ovarian disorders or abnormalities of carbohydrate metabolism. We saw a 21-year-old woman who had primary amenorrhea and ACN. Results of endocrine studies showed anovulation and low serum estradiol levels with increased gonadotropin concentrations. Laparoscopic examination disclosed bilateral streak gonads; the ovaries were completely replaced by fibrous tissue. Cultures of peripheral lymphocytes, skin fibroblasts, and the right and left ovaries demonstrated normal female karyotype 46XX in all mitoses studied. An autoimmune disorder was excluded by the absence of antithyroid and antiadrenal antibodies. Specific antibodies against ovarian proteins were also absent. A glucose tolerance test demonstrated fasting hyperinsulinemia and exaggerated serum insulin response to the glucose load. The observations in this patient exclude a primary pathogenic role for the ovary in the production of ACN; they also lend further support to a connection between the cutaneous disorder and insulin resistance.

Acanthosis Nigricans↗
PubMed1983

Glycosaminoglycan deposition in the acanthosis nigricans lesions of the polycystic ovary syndrome.

Skin biopsy specimens of acanthosis nigricans (AN) lesions were obtained from seven women with the polycystic ovary (PCO) syndrome and insulin resistance (IR). All the patients had normal thyroid function test results and fasting hyperinsulinemia with an exaggerated insulin response to oral glucose. Acanthosis nigricans lesions exhibited prominent deposits of glycosaminoglycan (GAG) consisting mostly of hyaluronic acid in the papillary dermis. Normal amounts of GAGs were found in control biopsy specimens obtained from areas of the skin not involved by AN and from skin of the nape of the neck or axillae in three normal women. These studies demonstrate that GAG deposition is a regular component of AN skin in patients with PCO and IR. The cause of these infiltrates remains to be determined.

Acanthosis Nigricans↗
PubMed1983

Therapeutic benefits of exercise training for hemodialysis patients.

Twenty-five hemodialysis patients were randomized into comparable exercising (E, N = 14) and sedentary control (N = 11) groups. After baseline testing, training was 3 to 5 times weekly for a mean of 12 +/- 4 (SD) months. Maximal aerobic capacity increased 21% (P less than 0.01), and the durations for the graded exercise stress test improved 19% (P less than 0.01) in E, but did not change in controls (8 +/- 4 months). Declining blood pressures in 8 hypertensive E led to reductions in antihypertensive medications; no changes occurred in 9 hypertensive controls. Exercise lowered plasma total triglyceride levels 33% (280 +/- 258 to 175 +/- 95 mg/dl; P less than 0.01), but no change occurred in total and low-density lipoprotein cholesterol concentrations. High-density lipoprotein cholesterol levels rose 16% in E (31 +/- 9 to 36 +/- 12 mg/dl; P less than 0.02), but did not change in controls. An increase in the affinity of insulin for receptors on mononuclear cells was associated with a 20% decrease in fasting plasma insulin levels (24 +/- 7 to 19 +/- 2 microU/ml, N = 8; P less than 0.05) and a 42% improvement in glucose disappearance rates (1.9 +/- 1.0 to 2.6 +/- 1.2% per min, N = 6) in E. There were no changes in the body weights or diets of the patients. A 27% increase in red blood cell mass (P less than 0.02) with no change in plasma volume resulted in a 27% increase in hematocrit (24 +/- 3% to 31 +/- 5%, P less than 0.01) and a 20% increase in hemoglobin (8 +/- 1 to 10 +/- 2 g/dl; P less than 0.01) in E.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1982

Inducible expression of insulin receptors on T lymphocyte clones.

This study demonstrates that the insulin receptors are expressed on the surface of some T cell clones after specific antigenic stimulation. The insulin receptors on these lymphocytes are physicochemically similar to insulin receptors present on cells which express the receptors constitutively (adipocytes, hepatocytes, etc.). The kinetics of expression of insulin receptors on cloned, noncytotoxic T cells after specific antigenic stimulation closely parallels that of [3H]thymidine incorporation in such cultures.

Animals↗
PubMed1982

Growth hormone--dependent growth failure.

Growth failure may be associated with low serum somatomedin concentrations despite normal to increased concentrations of serum growth hormone. We have recognized five patients who responded to GH administration with an increase in serum Sm and an acceleration in skeletal growth, and have characterized the circulating GH in an homologous human GH radioreceptor assay employing the IM-9 lymphocyte as a source of human GH receptor. These five prepubertal children, who had a mean height 7.8 SD below the mean for age, had a mean RIA-GH of 34.2 +/- 3.5 ng/ml in response to stimulation, a basal Sm activity by hypophysectomized rat cartilage bioassay of less than 0.3 IU/ml, and a mean peak Sm of 0.9 +/- 0.1 IU/ml in response to 48 hours of GH therapy. During a one-year trial of GH therapy, four of these children significantly increased their growth velocity as compared to their growth rate before GH therapy. These children had a mean RIA-GH/RRA-GH ratio of 2.f. The fifth patient had a low RIA-GH/RRA-GH ratio and had no increase in growth rate. These studies suggest that growth in certain growth retarded children may be dependent on exogenous GH, even though they are not GH deficient by standard criteria.

Body Height↗
PubMed1982

Growth hormone receptors in isolated rat adipocytes.

Specific GH binding sites in isolated rat adipocytes have been partially characterized. Binding of [125I]iodohuman(h)GH was rapid, reversible, and was time and temperature dependent. Maximum specific binding occurred at 37 C in approximately 40 min at pH 7.4. Bound labeled hGH was rapidly dissociable, with the addition of excess unlabeled hormone. Specific binding is inhibited by as little as 1.0-1.5 ng/ml hGH, and 50% inhibition was obtained with 15-20 ng/ml. No inhibition was observed with insulin, glucagon, hPRL, or hTSH at concentrations up to 1 micrograms/ml. This receptor does not discriminate between monkey GH, rat GH, bovine GH, and porcine GH. Specific binding varied linearly with cell concentration. Scatchard analysis revealed linear plots with a Ka of approximately 10(9) M-1 and 15,000 sites per cell. There was less than 15% degradation of [125I]iodo-hGH over 90 min at 37 C. There was a striking increase in [125I]iodo-hGH binding to adipocytes at pH 4.85. Scatchard analysis of binding at pH 4.85 revealed a curvilinear plot with an apparent increase of sites per cell from 15,000 to 60,000, and a modest increase in the apparent affinity constant of the high affinity, low capacity sites using the two-compartment model for curvilinear plots. The GH receptors in rat fat cells displayed no ability to bind labeled hPRL or human placental lactogen, consistent with minimal recognition of lactogenic peptides by these receptors. Thus, the rat adipocyte contains specific binding sites for GH that fulfill the major criteria for receptor binding. The presence of such receptors in these cells may facilitate the study of GH receptors in relation to the biological effects of the hormone on adipose tissue in various metabolic settings.

Adipose Tissue↗
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↗
PubMed1976

Water-soluble specific growth hormone binding sites from cultured human lymphocytes: preparation and partial characterization.

Cultured human lymphocytes (IM-9 cell line) have specific binding sites or receptors for human growth hormone (hGH). Under appropriate conditions, this specific binding material is spontaneously released into the incubation medium and is solubilized without the use of detergents. This water-soluble preparation binds [125I]iodo-hGH with the same specifictiy as receptors on the intact cell. Unlabeled hGH, but not porcine growth hormone or insulin, competes with labeled hGH for binding to the soluble preparation. Growth hormone preparations of varying purity compete for binding to the soluble binding preparation in the same rank order as they compete for binding to the intact IM-9 lymphocyte. [125I]iodo-hGH incubated with, but not bound to, the soluble preparation is partially degraded, while the [125I]iodo-hGH that is bound to the soluble preparation is protected from degradation, and its ability to rebind to fresh cells is enhanced. The [125I]iodo-hGH-soluble binding preparation complex can be dissociated by the addition of large quantities of unlabeled hGH or by lowering the pH, and [125I]iodo-hGH in both instances remains intact and undegraded. The soluble binding preparation did not sediment when centrifuged at 200,000 X g for 4 hours and was not retained on 0.20 micron Millipore filters. The soluble binding preparation was not retarded on Sephadex G-200. Binding activity was abolished by tryptic digestion. These studies demonstrate that hGH-binding sites, like previously reported insulin binding sites, can be spontaneously solubilized from cultured human lymphocytes, without the use of detergents; these soluble binding preparations are of high molecular weight and are, at least in part, protein in nature.

Animals↗