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J R Gavin

Publications and source records attributed to J R Gavin.

At least 37 records · Page 2Linked to original sources
PubMed1988

Characterization of specific pancreatic polypeptide receptors on basolateral membranes of the canine small intestine.

We have identified specific binding sites for pancreatic polypeptide (PP) on the mucosal lining of canine small intestine. The present study was undertaken to further characterize these binding sites (receptors) on purified intestinal membranes and to establish their location on the brush border or basolateral surface of the intestinal enterocyte. Basolateral and brush border membranes were prepared by sorbitol density centrifugation. PP receptors were localized predominantly to the vascular surface, and thus binding of PP 125I-labeled on Tyr-27 to the basolateral preparation was used to evaluate receptor characteristics. Binding of PP was calcium, time, temperature, and pH dependent. Maximum specific binding of labeled PP occurred after an 8-hr incubation at 4 degrees C with 5 mM calcium at pH 6.8. Data analysis by Scatchard plot showed high- and low-affinity binding sites with relative affinities of 1.5 x 10(-9) M and 2.6 x 10(-8) M and with corresponding binding capacities of 0.23 pmol/mg and 0.84 pmol/mg of protein, respectively. This receptor was specific for PP since peptide YY and neuropeptide Y, peptides of the PP family, cross-reacted by less than 3%, as judged from comparisons of half-maximal displacement of label. Structurally dissimilar peptides, insulin and glucagon, did not compete for binding. Specific 125I-labeled PP binding was localized primarily to basolateral membranes (9.8 +/- 0.8%) with little binding by brush border membranes (0.8 +/- 0.2%). Thus, we have identified highly specific receptors for PP, located predominantly on the vascular surface of the small intestinal mucosa. These data suggest that the mucosal lining of the small intestine is a target tissue for PP and that PP participates in the hormonal regulation of fuel metabolism and substrate transport in the small intestinal mucosa.

Animals↗
PubMed1988

An assessment instrument to measure physicians' knowledge of diabetes management.

A 57-item multiple choice test to assess physicians' knowledge of current approaches to diabetes management was devised by a multidisciplinary team that developed the test's case studies and questions. This test was revised based on critiques by diabetologists and other specialists at the Washington University Medical Center and its Diabetes Research and Training Center. A pilot test of the instrument was conducted with 95 residents from five accredited residency training programs and 17 medical students, and the results demonstrated consistent gaps in the respondents' knowledge in several major categories of diabetes management. The test was validated by administering it to 20 endocrinologists with known diabetes expertise and 16 nonspecialist family practice and internal medicine physicians. Analysis of these results revealed significant differences in test performance between the nonspecialists and experts. This initial body of data was used to refine the instrument further to the 56-item test presently being administered nationwide by the diabetes center to groups of family practice and internal medicine physicians and to residents and medical students.

Diabetes Mellitus↗
PubMed1987

Spectrum of endocrine abnormalities associated with acanthosis nigricans.

Acanthosis nigricans is a marker for disorders of insulin action, endocrine abnormalities, and cancer of internal organs. To evaluate the clinical significance of this marker the systemic alterations and clinical features of 26 patients with acanthosis nigricans seen at two institutions were reviewed. Most subjects affected by acanthosis nigricans were female (20 patients), Caucasian (22 patients), in the third decade of life (13 patients), and overweight (24 patients greater than 120 percent ideal body weight). Gonadal disease, present in 17 patients, was expressed as polycystic ovary syndrome (11 cases), disorders of prolactin secretion (two cases, one with polycystic ovary syndrome), streak gonads (one case), and hypogonadism of the male (four cases). Thyroid disease and tinea versicolor were present in four patients each. Three patients were receiving insulin therapy for diabetes mellitus, and in two additional patients diabetes mellitus was detected during the diagnostic workup. All patients had elevated fasting insulin levels; most of them also had an exaggerated insulin response to a glucose load. Two of 18 patients tested had antibodies against the insulin receptor in the circulation. Skin biopsy of acanthosis nigricans lesions from all 26 patients showed a typical pattern of hyperkeratosis, acanthosis, and epidermal papillomatosis. Colloidal iron staining showed glycosaminoglycan infiltration of the papillary dermis (21 of 21 cases), consisting mainly of hyaluronic acid. It is concluded that: (1) hyperinsulinenemia and local dermal glycosaminoglycan deposition are regular features in acanthosis nigricans and (2) patients with acanthosis nigricans should be screened for diabetes mellitus, gonadal disease, and hypothyroidism.

Acanthosis Nigricans↗
PubMed1987

Mineral homeostasis in neonates of streptozotocin-induced noninsulin-dependent diabetic rats and in their mothers during pregnancy and lactation.

To assess the affect of mild diabetes on calcium metabolism in an animal model, we evaluated calcium homeostasis before pregnancy and during gestation and lactation in non-insulindependent (NIDD) diabetic rat mothers and their neonates (NeoDM). Plasma glucose, calcium (Ca), magnesium (Mg), phosphate (Pi), and immunoreactive parathyroid hormone (iPTH) were measured in the NIDD rats and controls before pregnancy, during the first, second, and third gestational week, and during lactation 12, 24, 48 and 72 h postpartum. The same measurements were performed on NeoDM and controls 12, 24, 48, and 72 h after birth. In the mothers, plasma calcitonin was assayed before pregnancy and at 72 h postpartum. Higher plasma glucose values before pregnancy (216 +/- 9 mg/dl vs 126 +/- 4) and during the second (105 +/- 5 vs 73 +/- 6) and third (114 +/- 8 vs 91 +/- 3) gestational week were observed in diabetic mothers when compared to controls. Glucose values decreased during the second and third gestational week in both groups compared to pregestational values. Plasma Ca, Mg, and Pi were similar in both groups during gestation and lactation except for the third gestational week when plasma Mg was lower in the diabetic mothers (P less than 0.05). Plasma iPTH rose to similar values in both groups during pregnancy. During lactation, plasma iPTH levels were higher and plasma calcitonin levels were lower compared to controls (P less than .05, P less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Characterization of serum growth hormone (GH) and insulin-like growth factor I in active acromegaly with minimal elevation of serum GH.

In most patients with acromegaly basal serum GH concentrations are elevated and remain above 5 micrograms/L after oral glucose administration. In some patients, however, serum insulin-like growth factor I (IGF-I) concentrations are elevated with only minimal elevations of serum GH. We studied the serum GH and IGF-I of two such patients to determine whether these peptide hormones are normal in this clinical situation. The serum GH of these patients was found to bind normally to receptors of the IM-9 lymphocyte. The elution pattern of IGF-I extracted from the patients' serum was similar to that of (Thr59) human IGF-I after passage through a Bio-Rad P-60 column in 0.5 M acetic acid. The IGF-I was further characterized by isoelectric focusing and C18 reverse phase high pressure liquid chromatography (HPLC). The isoelectric points of the IGF-I components were similar to those of IGF-I in normal serum. The IGF-I in one patient had two components by HPLC, while that of the other patient had only one major component. The IGF-I components isolated by HPLC were normally active in stimulating [3H] alpha-aminoisobutyric acid uptake by normal human fibroblasts. The elevated serum IGF-I concentrations of these two patients were GH dependent. Transsphenoidal adenomectomy in one patient resulted in a decline in serum IGF-I to a high normal concentration. Lowering the serum GH to subnormal concentrations by the administration of the somatostatin analog SMS 201-995 (Sandoz) restored normal IGF-I concentrations in the second patient. We conclude that the GH and IGF-I of these two patients cannot account for their apparent enhanced GH responsiveness.

Acromegaly↗
PubMed1987

Identification and characterization of insulin receptors in basolateral membranes of dog intestinal mucosa.

Little is known about hormonal regulation of substrate transport and metabolism in the mucosal lining of the small intestine. Because insulin regulates these functions in other tissues by binding to its receptor, we have investigated the presence of insulin receptors in canine small intestinal mucosa with basolateral membranes (BLM) and brush border membranes (BBM) prepared by sorbitol density centrifugation. A14-[125I]iodoinsulin was used to study binding and structural characteristics of specific insulin receptors in BLM. Analysis of receptors in BLM identified binding sites with high affinity (Kd 88 pM) and low capacity (0.4 pmol/mg protein) as well as with low affinity (Kd 36 nM) and high capacity (4.7 pmol/mg protein). Binding was time, temperature, and pH dependent, and 125I-labeled insulin dissociation was enhanced in the presence of unlabeled insulin. Cross-reactivity of these receptors to proinsulin, IGF-II, and IGF-I was 4, 1.8, and less than 1%, respectively. Covalent cross-linking of labeled insulin to BLM insulin receptors with disuccinimidyl suberate revealed a single 135,000-Mr band that was completely inhibited by unlabeled insulin. There was a 16-fold greater specific binding of insulin to BLM (39.0 +/- 2.4%) than to BBM (2.5 +/- 0.6%). These results demonstrate the presence of a highly specific receptor for insulin on the vascular, but not the luminal, surface of the small intestinal mucosa in dogs, and suggest that insulin may play an important role in the regulation of gastrointestinal physiology.

Animals↗
PubMed1986

Multiplication-stimulating activity-induced alkalinization of canine renal proximal tubular cells.

The actions of a variety of polypeptide growth factors on isolated cells are thought to be initiated by stimulation of Na+-H+ exchange across the plasma membranes of the cells resulting in intracellular alkalinization. To determine whether insulin-like growth factors (IGFs) exert actions through such a mechanism, we incubated suspensions of canine renal proximal tubular segments with insulin or IGF I or with multiplication-stimulating activity (MSA)/IGF II. Changes in intracellular pH were detected by measurements of the distribution of [14C]5,5-dimethoxazolidine-2,4-dione. Incubation of segments with 10(-9) M MSA under conditions such that extracellular [Na+] greater than intracellular [Na+] effected intracellular alkalinization detectable within 1-2 min. Alkalinization was not observed under conditions where this gradient was not present. Alkalinization was not prevented by inclusion of 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid or 1 mM ouabain in incubations, but was inhibited by amiloride. Incubation of proximal tubular segments with as little as 10(-11) M MSA effected intracellular alkalinization. Incubation with as much as 10(-6) M insulin or IGF I did not. Our findings are consistent with an action of MSA/IGF II to stimulate Na+-H+ exchange across the plasma membrane of the renal proximal tubular cell. It is possible that the stimulation represents a mechanism by which actions of IGF II are initiated in growth factor-sensitive cells.

Animals↗
PubMed1986

(Na+ +K+)-ATPase activity in kidney basolateral membranes of non insulin dependent diabetic rats.

Insulin resistant, Type II diabetes mellitus (NIDD) in a rat animal model results in profound changes in basal and insulin-stimulated membrane (Ca2+ +Mg2+)-ATPase activity in kidney basolateral membrane (BLM) preparations. We find that NIDD in these animals does not result in similar changes in membrane (Na+ +K+)-ATPase activity. Basal enzyme activity was the same in diabetic and control animals. Insulin treatment of diabetic animals in vivo resulted in hyperinsulinemia and increased BLM (Na+ +K+)-ATPase, while food restriction for 18 hr resulted in lowered enzyme activity. There was no direct effect of insulin on (Na+ +K+)-ATPase activity in isolated membranes from any of the animal groups. Thus, physiologic perturbations which alter insulin sensitivity and glucose homeostasis are accompanied by altered levels of (Na+ +K+)-ATPase activity. Lower levels of this membrane enzyme activity appear to be associated with optimal insulin action.

Animals↗
PubMed1986

Plasma calcium and phosphate levels in an adult noninsulin-dependent diabetic population.

Duplicate or triplicate measurements of fasting plasma glucose, calcium (Ca), phosphate (Pi), and glycosylated hemoglobins were performed on a group of non-insulin dependent diabetic patients and controls at 3-6 month intervals. In the diabetic group (48 males and 44 females), 18 were on diet only, 21 on diet and oral hypoglycemic treatment, and 51 on diet and insulin. These were a total of 217 measurements for each parameter. Results were compared to 416 measurements obtained from sex and age-matched controls. Plasma Ca levels were higher in the diabetic group (2.48 +/- 0.004 vs 2.38 +/- 0.006 mmol/liter) P less than 0.001; plasma Pi levels were similar to those of controls. The difference in plasma Ca was not influenced by age, sex, or mode of treatment. No correlation was found in the three treatment groups between plasma Ca and duration of diabetes nor with patients' weights. The results are consistent with the view that an alteration in calcium homeostasis accompanies the diabetic state.

Adult↗
PubMed1986

Acanthosis nigricans, hypothyroidism, and insulin resistance.

Acanthosis nigricans has been associated with multiple endocrinopathies. The common denominator appears to be insulin resistance. Three patients are described (one woman and two men) who presented with hypothyroidism and acanthosis nigricans. All the patients had elevated insulin levels in the fasting state and in response to an oral glucose load. The mechanism for the resistance to insulin was a post-receptor binding defect or a structural abnormality in circulating insulin, since glucose tolerance and plasma cortisol, somatomedin, growth hormone, and insulin receptor concentrations in peripheral monocytes were all normal. Antibodies to insulin or the insulin receptor were absent. Neither insulin resistance nor acanthosis nigricans diminished following correction of the hypothyroidism. It is concluded that hypothyroidism may be associated with acanthosis nigricans, that hyperinsulinemia is a regular correlate of the skin disorder, and that treatment of the hypothyroidism does not resolve the hyperinsulinemia or the acanthosis nigricans.

Acanthosis Nigricans↗
PubMed1986

Binding of IGF I and IGF I-stimulated phosphorylation in canine renal basolateral membranes.

To characterize the interaction of the renal proximal tubular cell with insulin like growth factor I (IGF I), we measured binding of 125I-IGF I to proximal tubular basolateral membranes from dog kidney and induced IGF I-stimulated phosphorylation of basolateral membranes. Specific binding of 125I-IGF I to basolateral membranes was observed that was half-maximal at between 10(-9) and 10(-8) M IGF I. 125I-IGF I was affinity cross-linked to a 135,000 Mr protein in basolateral membranes that was distinct from the alpha-subunit of the insulin receptor and from the IGF II receptor. IGF I-stimulated phosphorylation of a 92,000 Mr protein was effected in detergent-solubilized membranes incubated with 100 microM [gamma-32P]ATP. The 32P-labeled protein was distinct from the beta-subunit of the insulin receptor, the 32P phosphorylation of which was stimulated by insulin. We conclude that specific receptors for IGF I are present in the basolateral membrane of the renal proximal tubular cell. Physiological actions of IGF I at this nephron site may occur through the binding of this peptide circulating in plasma, to specific basolateral membrane receptors, followed by IGF I stimulated phosphorylation.

Animals↗
PubMed1986

Phorbol ester-stimulated phosphorylation of basolateral membranes from canine kidney.

To determine whether protein kinase C is present in the basolateral membrane of the renal proximal tubular cell, we performed experiments to ascertain whether specific binding of [3H]phorbol 12,13-dibutyrate could be demonstrated in basolateral membranes isolated from canine kidney. Specific binding was demonstrable that was half maximal at between 10(-7) and 10(-8) M phorbol 12,13-dibutyrate. Binding was inhibited by 12-O-tetradecanoylphorbol-13-acetate (TPA) and other tumor-promoting phorbol esters, but not by inactive phorbol esters, including 4 alpha-phorbol. Incubation of basolateral membranes with TPA and phorbol 12,13-dibutyrate, but not with 4 alpha-phorbol, in the presence of submicromolar concentrations of free calcium, enhanced phosphorylation of several proteins demonstrable in autoradiograms of sodium dodecyl sulfate-polyacrylamide gels originating from membranes subsequently exposed to [gamma-32P]ATP for 30 s. Dephosphorylation of [32P]phosphoproteins was observed in gels from membranes incubated with [gamma-32P]ATP over time. TPA-stimulated phosphorylation of one protein band with Mr 135,000 was quantitated and was found to increase as a function of [TPA]. Half-maximal TPA-stimulated phosphorylation of this protein band occurred at slightly less than 10(-9) M TPA. Our findings are consistent with a role for protein kinase C-effected phosphorylation of basolateral membrane proteins in the mediation or modulation of hormonal actions in the proximal tubular cell.

Adenosine Triphosphate↗
PubMed1986

Exercise training reduces coronary risk and effectively rehabilitates hemodialysis patients.

This study examines the effects of 12 months of endurance exercise training (cycling, walking and jogging) on lipid profiles, glucose metabolism, blood pressure, anemia and psychological function in 14 hemodialysis patients. Maximal aerobic capacity (VO2max) increased 18% in the exercisers (p less than 0.01), but did not change in 11 controls. This was associated with a reduction in depression, a decrease in dosages of antihypertensive medications, a significant increase in hematocrit and hemoglobin levels (red cell mass rose, plasma volume did not change), a decrease in plasma triglyceride by 23% (p less than 0.05) and an increase in high-density lipoprotein cholesterol (HDL-C) levels by 21% (p less than 0.01) (both HDL-C and triglyceride levels worsened in the sedentary controls), and an 18% increase in glucose disappearance rates (p less than 0.05) in spite of a 52% decrease in fasting insulin levels (p less than 0.01), suggesting that insulin sensitivity improved. These results demonstrate that some of the complications present in hemodialysis patients may be caused by their sedentary life-style, rather than endstage renal disease itself. This suggests that rehabilitation through exercise is possible for these patients. By reducing coronary risk factors in hemodialysis patients, exercise training may also decrease their heightened morbidity and mortality from atherosclerotic complications. These possibilities need to be examined in a longitudinal study.

Adult↗
PubMed1986

Hormonal regulation of (Ca2+ + Mg2+)ATPase activity in canine renal basolateral membrane.

High affinity (Ca2+ + Mg2+)ATPase activity was demonstrated in proximal tubule basolateral membranes (BLM) obtained from canine kidney. The Km of the enzyme for free Ca2+ was 0.12 +/- 0.02 microM, and at 3 microM free Ca2+, the enzyme reached its maximal velocity. To evaluate hormonal regulation of this enzyme, we studied the in vitro effects of several polypeptide hormones on enzyme activity. We measured the effects of insulin and human (h) PTH-(1-34) and their inactive analogs desoctapeptide insulin, bovine (b) PTH-(3-34), and oxidized hPTH-(1-34); insulin-like growth factors (IGFs) I and II; calcitonin; and the common cellular mediator for PTH and calcitonin, cAMP. At 0.1 microM free Ca2+, insulin (25-100 microU/ml) increased (Ca2+ + Mg2+)ATPase activity in a dose-dependent manner by 35-52% (P less than 0.01) and by 8-13% (P less than 0.05 to P less than 0.01) at a 3-microM free Ca2+ concentration; hPTH-(1-34) PTH (10(-9)-10(-7) M) increased the enzyme activity at a free Ca2+ concentration of 0.1 microM by 13-25% (P less than 0.05 to P less than 0.01). IGF-I increased (Ca2+ + Mg2+)ATPase activity by 40% (P less than 0.05) at 0.1 microM free Ca2+ at high peptide concentrations (10 ng/ml). No effect was obtained at 2 ng/ml IGF-I. cAMP (10(-7)-10(-4) M) stimulated enzyme activity by 18-27% (P less than 0.05 to P less than 0.02) at 0.1 microM Ca2+ and by 8-12% (P less than 0.05 to P less than 0.01) at 3 microM Ca2+. The effects of insulin and cAMP on (Ca2+ + Mg2+)ATPase activity were additive. No effect on the enzyme activity was obtained by the inactive analogs desoctapeptide insulin, bPTH-(3-34), and oxidized hPTH-(1-34), or by calcitonin or IGF-II. The data suggest that insulin and PTH have a specific stimulatory effect on (Ca2+ + Mg2+)ATPase activity in canine kidney proximal tubular BLM. While the insulin action is independent of cAMP, a role of cAMP in the regulatory effect of PTH on this enzyme cannot be ruled out. The direct stimulatory effect of insulin and PTH on (Ca2+ + Mg2+)ATPase in canine kidney proximal tubular BLM suggests that these hormones mediate their cellular effects in part by changes in cellular calcium homeostasis.

Animals↗
PubMed1986

Ca2+-Mg2+-ATPase activity in kidney basolateral membrane in non-insulin-dependent diabetic rats. Effect of insulin.

The direct effect of insulin on the high-affinity Ca2+-Mg2+-ATPase was studied in kidney proximal tubular basolateral membranes (BLM) obtained from control and streptozocin-induced non-insulin-dependent diabetes mellitus (NIDDM) rats. Plasma glucose of the diabetic animals was only mildly elevated (217 +/- 9 vs. 138 +/- 3 mg/dl). Both high- and low-affinity calcium-dependent Ca2+-Mg2+-ATPase activities were identified in the BLM. Enzyme activity in BLM from diabetic rats was higher at all Ca2+ concentrations tested due to a higher maximum velocity of the enzyme from NIDDM rats. The high-affinity Ca2+-Mg2+-ATPase activity was inhibited by trifluoroperazine (TFP) in both membranes. No difference in calmodulin content was found in the membranes from the diabetic and control rats. Insulin (16-200 microU/ml) significantly increased the high-affinity Ca2+-Mg2+-ATPase activity (17-40%) in membranes from control animals but had no effect on the enzyme activity in the membranes from the NIDDM rats. The basal activity of the enzyme at 0.1 microM free Ca2+ was higher in the BLM from the NIDDM animals compared to controls (17.8 +/- 0.5 vs. 14.7 +/- 0.8 nM Pi X mg-1 X min-1; P less than .02). There was no effect of insulin on the Ca2+-independent ATPase activity of BLM preparations. These findings demonstrate a defect in the ability of insulin to regulate the high-affinity Ca2+-Mg2+-ATPase activity in BLM from diabetic rats. Such a defect in enzyme activity may play a role in the mechanism of impaired insulin action observed in these NIDDM rats.

Animals↗
PubMed1985

Dual actions of sulfonylureas and glyburide. Receptor and post-receptor effects.

Glyburide and other sulfonylureas consistently enhance receptor binding in cells from patients with non-insulin-dependent diabetes mellitus, whereas no effects and mixed effects have been demonstrated in cells from patients with insulin-dependent diabetes mellitus and in normal cells, respectively. These findings indicate that the experimental model may be critical in demonstrating sulfonylurea effects on receptor binding. Postbinding function studies have shown a definite enhancement of peripheral glucose metabolism by sulfonylurea drugs; such post-receptor changes have not clearly correlated with receptor binding alterations. Studies using mouse-cultured myocytes indicate that both glyburide and tolazamide have stimulatory effects on glucose uptake, whereas only glyburide caused an increase in receptor binding. The data suggest a major and widespread post-receptor function for the sulfonylurea drugs, particularly glyburide, possibly mediated through pathways similar but not identical to insulin pathways. The direct receptor effects, in contrast, are possibly more tissue-specific and/or disease-dependent. In non-insulin-dependent diabetes mellitus, these drugs exert clinical efficacy by acting through both mechanisms.

Adipose Tissue↗