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Biomedical subjects

J B Field

Publications and source records attributed to J B Field.

At least 91 records · Page 5Linked to original sources
PubMed1983

The use of vitreous fluorophotometry to distinguish between diabetics with and without observable retinopathy: effect of vitreous abnormalities on the measurement.

Ten age-matched normals, diabetics with retinopathy, and diabetics without observable retinopathy were evaluated by vitreous fluorophotometry (VFL) using a 0.15 mm and a 0.45 fiberoptic probe in a photomultiplier system as well as a commercially available photodiode instrument to determine whether differences in intraocular sodium fluorescein levels could be detected among the three groups. Each subject was injected in the antecubital vein with 7 mg/kg of sodium fluorescein (25% solution) and measurements were taken 1 hr postinjection at 4.5 mm and 7.5 mm from the retina. The influence of choroidal fluorescein and ocular pigmentation are reduced at these locations. We found that a breakdown in the blood-ocular barrier may not be present early in the course of diabetes. Furthermore, no significant difference was found between normals and diabetics without retinopathy. Although the mean value for vitreous fluorescein was significantly higher in diabetics with retinopathy compared to normals, several of the diabetics with retinopathy had values in the normal range. These results differ from those previously reported in the literature. However, our studies took into consideration several factors not considered by other investigators, such as ocular pigmentation, choroidal fluorescence, slit width, and vitreous changes, that may have significant effects on the fluorophotometry values.

Adolescent↗
PubMed1982

Calmodulin-binding proteins of bovine thyroid plasma membranes.

Calmodulin binding proteins in bovine thyroid plasma membranes were investigated using the 125I-labeled calmodulin gel overlay technique. The purified thyroid plasma membranes contained two calmodulin binding proteins with molecular weights of approx. 220 000 and 150 000 respectively. The binding of 125I-labeled calmodulin to the calmodulin binding proteins was inhibited by excess unlabeled calmodulin, 100 microM trifluoperazine or 1 mM EGTA, indicating that the binding was calmodulin-specific and calcium-dependent. The calmodulin binding proteins appear to be components of the cytoskeleton since they remained in the pellet after treatment of the thyroid plasma membranes with 1% Triton X-100. Similar calmodulin binding proteins were present in rat liver plasma membranes, but not in human red blood cell plasma membranes. These two calmodulin binding proteins may interact with other components of the cytoskeleton and regulate endocytosis, exocytosis and hormone secretion in thyroid cells.

Animals↗
PubMed1982

Properties of enzyme activities involved in protein phosphorylation-dephosphorylation of thyroid plasma membranes.

Bovine thyroid tissue exhibited cAMP-dependent and Ca2+-dependent protein kinase activities as well as a basal (cAMP- and Ca2+-independent) one, and phosphoprotein phosphatase activity. Although the former two protein kinase activities were not clearly demonstrated using endogenous protein as substrate, they were clearly shown in soluble, particulate and plasma membrane fractions using exogenous histones as substrate. The highest specific activities were in the plasma membrane. The apparent Km values of cAMP and Ca2+ for the membrane-bound protein kinase were 5 . 10(-8) M and 8.3 . 10(-4) M in the presence of 1 Mm EGTA), respectively. The apparent Km values of Mg2+ were 7.10-4M (without (in the cAMP and Ca2+), 5 . 10(-4) M (with cAMP) and 1.3 . 10(-3) M (with Ca2+), and those of ATP were 3.5 . 10(-5)M (with or without cAMP) and 8.5 . 10(-5) M (with Ca2+). The Ca2+-dependent protein kinase could be dissociated from the membrane by EGTA-washing. The enzyme activity so released was further activated by added phospholipid (phosphatidylserine/1,3-diolein), but not by calmodulin. Phosphoprotein phosphatase activity was also clearly demonstrated in all of the fractions using 32P-labeled mixed histones as substrate. The activity was not modified by either cAMP or Ca2+, but was stimulated by a rather broad range (5-25 mM) of Mg2+ and Mn2+. NaCl and substrate concentrations also influenced the activity. Pyrophosphate, ATP, inorganic phosphate and NaF inhibited the activity in a dose-dependent manner. Trifluoperazine, chlorpromazine, dibucaine and Triton X-100 (above 0.05%, w/v) specifically inhibited the Ca2+-dependent protein kinase in plasma membranes. Repetitive phosphorylation of intrinsic and extrinsic proteins by the membrane-bound enzyme activities clearly showed an important co-ordination of them at the step of protein phosphorylation. These findings suggest that these enzyme activities in plasma membranes may contribute to regulation of thyroid function in response to external stimuli.

Animals↗
PubMed1982

Roles of GTP and GDP in the regulation of the thyroid adenylate cyclase system.

Effects of guanine nucleotides on the adenylate cyclase activity of thyroid plasma membranes were investigated by monitoring metabolism of the radiolabeled nucleotides by thin-layer chromatography (TLC). When ATP was used as substrate with a nucleotide-regenerating system, TSH stimulated the adenylate cyclase activity in the absence of exogenous guanine nucleotide. Addition of GTP or GDP equally enhanced the TSH stimulation. Effects of GTP and GDP were indistinguishable in regard to their inhibitory effects on NaF-stimulated activities. The results from TLC suggested that GDP could be converted to GTP by a nucleotide-regenerating system. Even in the absence of a nucleotide-regeneration system, addition of GDP to the adenylate cyclase assay mixture resulted in the parallel decrease in ATP levels and formation of GTP indicating that thyroid plasma membrane preparations possessed a transphosphorylating activity. When an ATP analog, App[NH]p, was used as substrate without a nucleotide-regenerating system, no conversion of GDP to GTP was observed. Under such conditions, TSH did not stimulate the adenylate cyclase activity unless exogenous GTP or Gpp[NH]p was added. GDP no longer supported TSH stimulation and caused a slight decrease in the activity. GDP was less inhibitory than Gpp(NH)p to the NaF-stimulated adenylate cyclase activity. These results suggest: (1) TSH stimulation of thyroid adenylate cyclase is absolutely dependent on the regulatory nucleotides. (2) In contrast to GTP, GDP cannot support the coupling of the receptor-TSH complex to the catalytic component of adenylate cyclase. (3) The nucleotide regulatory site is more inhibitory to the stimulation of the enzyme by NaF when occupied by Gpp[NH]p than GDP.

Adenosine Triphosphate↗
PubMed1982

Ca2+-stimulated, Mg2+-dependent ATPase in bovine thyroid plasma membranes.

An isolated plasma membrane fraction from bovine thyroid glands contained a Ca2+-stimulated, Mg2+-dependent adenosine triphosphatase ((Ca2+ + Mg2+)-ATPase) activity which was purified in parallel to (Na+ + K+)-ATPase and adenylate cyclase. The (Ca2+ + Mg2+)-ATPase activity was maximally stimulated by approx. 200 microM added calcium in the presence of approx. 200 microM EGTA (69.7 +/- 5.2 nmol/mg protein per min). In EGTA-washed membranes, the enzyme was stimulated by calmodulin and inhibited by trifluoperazine.

Animals↗
PubMed1982

Actin in Triton-insoluble cytoskeleton of thyroid.

Treatment of bovine thyroid with the non-ionic detergent Triton X-100 extracts most of the cell protein and leaves insoluble residue. This Triton-insoluble cytoskeleton consists of five major polypeptides on sodium dodecyl sulfate polyacrylamide gels. One of these polypeptides is actin. Based on DNase inhibition assay, 30% of the total actin is associated with the cytoskeleton as the filamentous form. Thyroid actin from the cytoskeleton has been solubilized by dialysis against a low ionic strength buffer at pH 8.0 and purified to homogeneity by a polymerizing-depolymerizing cycle. The overall purification was about 144-fold with a yield of 10%. Bovine thyroid actin is very similar to actins from other tissues on the basis of: (1) comigration with rabbit skeletal muscle actin during gel electrophoresis in sodium dodecyl sulfate, (2) its amino acid composition, which includes about 1 mole of 3-methylhistidine per 42,000 g, (3) its ability to bind and inhibit pancreatic deoxyribonuclease I, and (4) its ability to form 7-8 nm microfilaments which is similar to that of skeletal filamentous actin. Thyroid actin contains beta- and gamma-isoactins, with isoelectric points more alkaline than the alpha-actin of rabbit skeletal muscle.

Actins↗
PubMed1982

Recovery from thyroid-stimulating hormone-induced refractoriness in thyroid slices: effect of removal of hormone and new protein synthesis.

An initial incubation of bovine thyroid slices with TSH causes decreased responsiveness to the subsequent addition of the hormone when the adenylate cyclase -cAMP system and other metabolic parameters are measured. After the initial incubation with TSH, refractoriness persists despite incubation of thyroid slices for 24 h in the absence of added TSH. Removal of persistently bound TSH by trypsin or antibody to TSH did not reverse the refractoriness during a subsequent 2 h incubation without added TSH. However, normal TSH responsivity was restored by the removal of TSH bound during the first incubation by the addition of either trypsin or antibody to TSH at the beginning of a 24-h second incubation. Restitution of TSH responsiveness after treatment with trypsin or antibody to TSH requires new protein synthesis. While TSH-induced refractoriness does not modify stimulation of cAMP by cholera toxin, its effect on glucose oxidation is significantly diminished. Menadiol stimulation of glucose oxidation is not inhibited in thyroid slices refractory to TSH. Thus, the effect of menadiol is subsequent to the block induced by TSH, whereas that of cholera toxin is proximal to it.

Adenylyl Cyclases↗
PubMed1982

Three types of desensitization of metabolic responses to thyrotropin in thyroid tissue: a review.

The evidence is reviewed that a desensitization to thyrotropin is of three distinct types. Type 1 is proximal to the production of cyclic AMP and is manifested by a fall of cyclic AMP concentration in the thyroid tissue despite the continued presence of TSH or phosphodiesterase inhibitors in the medium. Type 2 is distal to this event and involves the metabolic effects of TSH mediated by cyclic AMP such as colloid droplet formation, iodide organification and, in dog thyroid, glucose oxidation. All these effects may be due to a reduced amount of cyclic AMP which is not capable of stimulation the protein kinase. They may be prevented by a pre-exposure to similar concentrations of TSH and cannot be overcome by other stimulators acting through the same adenylate cyclase-cyclic AMP pathway. Type 3 involves the processes not regulated by cyclic AMP. Thus, a desensitization of thyroid tissue by pre-exposure to TSH results in a reduced response of phospholipid turnover, a process not mediated by cyclic AMP, either to homologous (TSH) or heterologous (acetylcholine) stimulation.

Acetylcholine↗
PubMed1982

Polycythemia rubra vera and artifactual hypoglycemia.

A patient with polycythemia rubra vera had had a leukocyte count between 55,000 and 86,000/cu mm and had had serum glucose levels as low as 8 mg/dL. Despite these low serum glucose values, the patient was asymptomatic, and a more careful investigation disclosed that the hypoglycemia was artifactual. This phenomenon, reported in other leukemic states, to our knowledge, has not been previously described in patients with polycythemia rubra vera. Our case broadens the spectrum of the causes of artifactual low serum glucose concentration due to excessive glucose consumption by the WBCs. This phenomenon is related to extreme leukocytosis, regardless of the underlying disease. Unnecessary workup for hypoglycemia can be avoided if its artifactual nature is suspected in any patient with a reported low serum glucose level and high WBC count.

Aged↗
PubMed1981

Effects of interferon on the cAMP-adenylate cyclase system of human, mouse, and bovine thyroid tissue.

This report studied the action of interferon on the thyroidal adenylate cyclase-cAMP system. It was found that human interferon did not increase cAMP levels in human or bovine thyroid slices during a 60-min incubation. Mouse interferon also had no effect on cAMP levels in mouse thyroidal lobes over the 60-min incubation, nor did it increase adenylate cyclase activity in mouse homogenates.

Adenylyl Cyclases↗
PubMed1981

The effect of tolbutamide and hepatic extraction of insulin and glucagon and hepatic glucose output in anesthetized dogs.

The effects of tolbutamide and insulin infusion on hepatic extraction of insulin and glucagon and on hepatic glucose output were compared in anesthetized dogs. The basal hepatic extraction of insulin was not significantly different in the two experiments (62 +/- 7% vs. 49 +/- 8%). The fraction of insulin extracted by the liver was not changed by either tolbutamide or insulin administration. In contrast, hepatic extraction of glucagon significantly increased from a basal value of 12 +/- 8% to 41 +/- 12% 30 min after tolbutamide, coincident with hypoglycemia and increased secretion of glucagon. The percent hepatic extraction of glucagon did not change during insulin infusion despite similar hypoglycemia and an even greater increase in the amount of glucagon reaching the liver. Tolbutamide and insulin produced a transient fall in hepatic glucose output which was associated with a significant increase in the insulin to glucagon molar ratio of the portal vein. Despite the persistence of hypoglycemia, hepatic glucose production returned to control values, and the portal venous insulin to glucagon molar ratio returned toward normal. Thus, the initial hypoglycemia after tolbutamide and insulin treatment reflects decreased hepatic glucose production, while the later effects represent increased peripheral glucose utilization. Hepatic glucose output correlated better with the portal venous insulin to glucagon molar ratio than the ratio of the hormones removed by the liver. These findings indicate that insulin and glucagon extraction by the liver are quite different and are independently regulated. Tolbutamide directly increases the fraction of glucagon removed by the liver. Because of changes in hepatic extraction after tolbutamide, increased pancreatic secretion of glucagon might not be reflected in its peripheral concentration.

Animals↗
PubMed1981

Hepatic extraction of plasma immunoreactive glucagon components. Predilection for 3500-dalton glucagon metabolism by the liver.

This study examines quantitatively the extraction of plasma immunoreactive glucagon (IRG) components by the liver. It was shown that the liver has a predilection for removal of the 3500-dalton biologically active IRG component with virtually no extraction of the other IRG fractions. Hepatic extraction of whole plasma IRG was 25.2 +/- 2.5%. Analysis of the hepatic extraction of the four plasma immunoreactive components, separated by gel filtration, revealed variable but quantitatively insignificant extraction of all components other than the 3500-dalton fraction, which was 33.4 +/- 3.2% (P less than 0.001). Hepatic extraction of whole plasma IRG was significantly less than that of the 3500-dalton component during periods of basal glucagon secretion when IRG fractions other than the 3500-dalton fraction contribute substantially to the whole plasma IRG level. However, during periods of stimulation of glucagon secretion by arginine or arginine plus cholecystokinin-pancreozymin, when the 3500-dalton component accounts for virtually all of the whole plasma IRG level, hepatic extraction of whole plasma IRG was similar to that of the 3500-dalton fraction.

Animals↗
PubMed1980

The effect of somatostatin on the hepatic extraction of insulin and glucagon in the anesthetized dog.

Effects of somatostatin (250 ng/kg . min) or saline infusion on hepatic extraction of endogenous and exogenous insulin and glucagon were investigated in anesthetized dogs. After a 20-min control period, somatostatin or saline was infused into the superior mesenteric vein for 100 min. During the final 50 min of the somatostatin or saline infusion, insulin (1.7 mU/kg . min) and glucagon (20 ng/kg . min) were also infused. These infusions were then replaced with a saline infusion for an additional 30 min. Somatostatin rapidly and significantly decreased portal vein insulin and glucagon concentrations. Hepatic extraction of endogenous insulin decreased from the control value of 61 +/- 5% to 29 +/- 10% during the final 20 min of somatostatin infusion before exogenous insulin and glucagon were added to the infusion. The decrease in hepatic extraction of endogenous insulin is based on the mean of the individual values of the eight dogs in the group and may be spurious because of the very low concentrations of insulin which were being measured and the fact that at such low concentrations, some dogs appeared to have negative hepatic extraction of inulin. Glucagon extraction was unchanged (9 +/- 6% compared to 7 +/- 12%) during the first 50 min of infusion of somatostatin. Column chromatography demonstrated that the 3500 mol wt fraction of glucagon comprised 75 +/- 4% of the total glucagon immunoreactivity in the portal vein during the control period and 67 +/- 13% during the infusion of somatostatin. During the final 20 min of somatostatin infusion before the addition of insulin and glucagon, the blood glucose significantly decreased and hepatic glucose output fell from 2.4 +/- 0.4 to 1.4 +/- 0.3 mg/kg . min. However, the insulin to glucagon (3500 mol wt fraction) molar ratio did not change significantly (4.2 +/- 1.1 to 2.6 +/- 0.5). During the final 20 min of the combined infusion of somatostatin, insulin, and glucagon, hepatic extraction of insulin returned to control values and glucagon extraction rose from 7 +/- 12% to 35 +/- 11%. Hepatic glucose output increased without any significant change in the portal vein insulin to glucagon molar ratio. After the termination of the combined infusion, hepatic extraction of insulin was unchanged, but glucagon removal returned to control values. At this time, the portal vein insulin to glucagon ratio rose, and hepatic production of glucose fell below control values. These results demonstrate that somatostatin may influence peripheral insulin and glucagon values by modifying their hepatic extraction and inhibiting their pancreatic secretion. Hepatic glucose output did not always reflect the portal vein insulin to glucagon molar ratio.

Anesthesia↗
PubMed1980

Effect of increased circulating thyroid-stimulating hormone on in vitro thyroid-stimulating hormone stimulation of thyroid and adipose tissues.

Hormones have been shown to regulate the number and/or binding properties of their own receptors. The present studies examined the effect of chronic increased endogenous TSH levels, induced by tapazole or thyroidectomy, on in vitro TSH responsiveness and binding in thyroid and adipose tissues. The results showed that TSH and prostaglandin E1 significantly increased cAMP levels in the thyroids of weight- and age-matched controls, whereas thyroids from tapazole-treated rats responded only to prostaglandin E1. Iodide organification was also measured, and the thyroids from tapazole-treated rats showed a significantly reduced effect of TSH compared to weight- and age-matched controls, although stimulation by dibutyryl cAMP was equivalent in all three groups. TSH or epinephrine stimulation of cAMP and glucose oxidation was equivalent in adipose tissue from control and hypothyroid rats. There was a significant 50% reduction in the number TSH-binding sites in thyroids from tapazole-treated rats: the affinity remained unchanged. [125I]TSH binding to adipose tissue plasma membranes was similar in control and hypothyroid groups. These studies demonstrate that elevated levels of TSH appear to regulate the number of TSH receptors in thyroid, but not adipose, tissue.

Adipose Tissue↗