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Biomedical subjects

J B Field

Publications and source records attributed to J B Field.

At least 109 records · Page 6Linked to original sources
PubMed1980

Effects of thyrotropin and cholera toxin on the thyroidal adenylate cyclase-adenosine 3',5'-monophosphate system.

The present experiments examined the relationship between cholera toxin and TSH stimulation of the adenylate cyclase system in bovine thyroid tissue. Preincubation of thyroid slices for 20 min at 4 C with a maximal concentration of cholera toxin (100 microgram/ml) did not impair the subsequent stimulation of cAMP by submaximal amounts of TSH (1 mU/ml) during a 5-min incubation at 37 C. Incubation of cholera toxin or TSH with mixed gangliosides, followed by the addition of thyroid slices resulted in inhibition of the cholera toxin but not the TSH stimulation of cAMP formation. Previous exposure of thyroid slices to TSH induced refractoriness to subsequent stimulation of cAMP formation by TSH, but the response to cholera toxin was unchanged. NAD is necessary for cholera toxin, but not TSH, stimulation of adenylate cyclase. In the absence of NAD, cholera toxin inhibited the effect of maximal concentrations of TSH and prostaglandin E1 on adenylate cyclase activity but had no effect on NaF stimulation. In the presence of NAD, the stimulation of adenylate cyclase activity of bovine thyroid plasma membranes by a maximal amount of TSH was not influeced by maximal amounts of cholera toxin. Cholera toxin had a biphasic action on the binding of [125I]iodo-TSH, with low concentrations enhancing and high concentrations inhibiting binding. TSH augmented the binding of [125I]iodo-cholera toxin over the range of 1-100 mU/tube. Cholera toxin at 10 microgram/ml maximally inhibited binding. In addition to the requirement for ribosylation of adenylate cyclase, the present results indicate that the mechanisms of action of TSH and cholera toxin on cAMP formation are different.

Adenylyl Cyclases↗
PubMed1980

Time-action characteristics of regular and NPH insulin in insulin-treated diabetics.

The time course of action of regular and NPH insulins injected sc was studied in 15 insulin-treated diabetics over a 24-h period during which they received a constant infusion of glucose. The blood glucose began to decline in 1.2 +/- 0.1 h (range, 0.5--2) and reached its nadir in 5.7 +/- 0.3 h (range, 4--8) after the sc injection of regular insulin. The peak effect of regular insulin usually persisted for several hours, and the total duration of action was 16.2 +/- 1.1 h (range, 9--24). Both the time of peak effect and the total duration of action were considerably prolonged compared to data provided in standard textbooks. Free insulin increased to a peak in 2.7 +/- 0.3 h (range, 1--4) after regular insulin injection and then returned to baseline by 8.8 +/- 0.96 h. Subcutaneous injection of NPH insulin decreased the blood glucose by 2.4 +/- 0.5 h (range, 1--7), with a maximal effect at 11.0 +/- 1.4 h (range, 5--19). The total duration of effect on blood glucose was 25.1 +/- 0.7 h (range, 20--29). These values are similar to those in standard textbooks. Although the total insulin levels increased after the injection of NPH insulin, there was very little if any elevation in free insulin. Recognition of the prolonged effect of regular insulin is important in establishing an insulin treatment regime for diabetic patients.

Adolescent↗
PubMed1980

Effect of endogenous TSH on the in vitro responsiveness and binding of TSH in rat thyroid tissue.

These studies examined the effect of deficient endogenous TSH (hypophysectomy) on in vitro TSH responsiveness and binding in rat thyroid tissue. The results showed that thyroid from hypophysectomized rats were hyper-responsive to stimulation of cyclic AMP by TSH while PGE1 stimulation of cyclic AMP was similar in hypophysectomized rats compared to controls. When iodide organification was measured, the TSH and dibutyryl cyclic AMP stimulation in hypophysectomized rats was equivalent to the response of control animals. Binding studies demonstrated there was an increased number of TSH receptors in the thyroid from hypophysectomized rats compared to the control group. The affinity constant was unchanged. The results demonstrate that endogenous TSH appears to inversely regulate the responsiveness and number of TSH receptors in thyroid tissue. The effect of an i.v. injection of TSH on the levels of cyclic AMP and binding characteristics of TSH was also examined. Although cyclic AMP levels were significantly increased after a 10 min in vitro incubation of the lobes from TSH-injected rats as an indication of persistently bound TSH, the number of TSH binding sites was the same in the saline the TSH-injected animals.

Animals↗
PubMed1979

Insulin release in response to calcium in the diagnosis of insulinoma.

A calcium infusion (4 mg Ca++/kg/hr) significantly increased plasma insulin levels and reduced blood glucose in 4 patients with insulin-secreting pancreatic islet cell tumors. These parameters were not altered by a similar infusion of calcium in normal volunteers, 2 patients with alimentary hypoglycemia, and 2 with functional hypoglycemia. No difference in response was observed between patients with benign and malignant beta-cell tumors. Infusion of diazoxide (600 mg) with calcium blocked the stimulation of the latter on insulin secretion. The results indicate the usefulness of calcium infusion in the diagnosis of insulin-secreting tumor.

Adenoma, Islet Cell↗
PubMed1979

Purification and characterization of a troponin C-like phosphodiesterase activator from bovine thyroid.

A troponin C-like phosphodiesterase activator from bovine thyroid has been purified to homogeneity. The overall purification was about 9,800-fold with a yield of 8%. Bovine thyroid activator protein is identical in biologic properties to that isolated from bovine brain. They have the same specific activity regarding stimulation of bovine brain cyclic nucleotide phosphodiesterase. Both proteins form a Ca2+-dependent complex with heart muscle troponin I which is stable in 6M urea-polyacrylamide gel and which is similar, but not identical, to the troponin C-troponin I complex. The physiochemical properties of bovine thyroid activator protein are identical with those of bovine brain and other phosphodiesterase activator proteins and are similar to heart muscle and skeletal muscle troponin C as follows: (A) they bind 3-4 exchangeable calcium ions/mol with dissociation constants between 10(-5) and 10(-6) M, (B) they are highly acidic with a high content of aspartic and glutamic acids and isoelectric points of approximately 4.1, (C) these proteins have an unusual ultraviolet absorption spectrum with six discrete maxima between 250 and 284 nm which are characteristic of phenylalanine and tyrosine, and (D) these proteins have a low content of cysteine, histidine, tyrosine and proline. The tryptic peptide maps of bovine thyroid and brain activator protein are very similar. However, despite a very similar amino acid composition, the peptide map of bovine heart muscle troponin C is significantly different from that of the other two proteins. The molecular weight of thyroid and brain activator protein is 16,500, while that of heart troponin C is 18,500. Thyroid and brain activator protein, as well as heart troponin C, appear to undergo significant Ca2+-dependent conformational changes, as measured by the difference in the circular dichroism spectrum and electrophoretic mobility observed in the presence and absence of calcium ion.

Amino Acids↗
PubMed1979

In vitro and in vivo refractoriness to thyrotropin stimulation of iodine organification and thyroid hormone secretion.

Earlier studies indicated that initial exposure of thyroid slices to thyrotropin diminished responsiveness of the adenylate cyclase-cyclic AMP system, glucose oxidation, and (32)P(i) incorporation into phospholipids upon readdition of the hormone. The present studies demonstrate that slices from dog, beef, and human thyroid glands initially incubated with thyrotropin (TSH) were less responsive to subsequent addition of the hormone when organification of iodide was examined. Increasing the amount of TSH did not overcome the refractoriness induced by the initial exposure to the hormone. Furthermore, the stimulatory effects of dibutyryl cyclic AMP and prostagladin E(1) were abolished in slices previously incubated with TSH. Development of such refractoriness did not depend upon new protein synthesis and was not abolished by 1 mM prophylthiouracil in the first incubation. Addition of 0.1 muM thyroxine or triiodothyronine or 1.5 muM iodide during all three incubations did not modify the response to TSH, added for the first time in the third incubation. However, 1 mM iodide in the buffer during all three incubations inhibited the response to TSH during the third incubation. During the refractory period, effects of TSH on colloid droplet formation were also diminished. The in vivo effect of TSH on serum l- triiodothyronine in rats was significantly reduced when the rats had been injected with TSH 8 h earlier. These studies demonstrate that TSH-induced refractoriness also includes effects on organification of iodine and secretion of thyroid hormone. The results cannot be adequately explained by unresponsiveness of adenylate cyclase because effects of dibutyryl cyclic AMP and prostagladin E(1) were also inhibited by prior exposure to TSH.

Animals↗
PubMed1979

Effects of diamide on basal and thyrotropin-stimulated thyroid metabolism.

The effect of diamide on basal and TSH-stimulated thyroid metabolism was studied using bovine and dog thyroid slices. Diamide (10 mM) inhibited basal and TSH-stimulated net cAMP production, basal and cAMP-stimulated protein kinase activity, and stimulation by TSH of colloid droplet formation and organification of iodide and abolished basal and TSH-stimulated uptake of 32P into phospholipids. In thyroid slices incubated with 0.1 mM diamide, none of these activities, whether basal or TSH-stimulated, was affected. However, 0.1 mM diamide increased the net basal production of cAMP and potentiated the effect of TSH on this process. These results demonstrate that the previously reported inhibition of protein kinase by 2-20 mM diamide is not specific and that this compound cannot be used to determine which of the metabolic effects of TSH are dependent upon cAMP activation of protein kinase. While 0.1 mM diamide increased cAMP in thyroid slices, it did not reproduce any of the other effects of TSH.

Animals↗
PubMed1978

Hepatic insulin and glucagon extraction after their augmented secretion in dogs.

Effects of intravenous arginine and cholecystokinin-pancreozymin (CCK-PZ) infusion on hepatic extraction of insulin (EI) and glucagon (EGG) and also on hepatic glucose output (HGO) were studied in anesthetized dogs. Because insulin and glucagon exert antagonistic effects on HGO, insulin:glucagon (I/GG) molar ratios were determined in the portal vein and also in peripheral vessels. During the arginine-CCK-PZ infusion the amount of insulin and glucagon coming to the liver increased 12- and 15-fold, respectively. In contrast EI decreased significantly from a control value of 62 +/- 6% to a nadir of 22 +/- 13%. EGG (control value 19 +/- 9%), however, was unaffected by arginine-CCK-PZ. The absence of any alteration in EGG cannot be attributed to the molecular heterogeneity of the immunoreactive glucagon. HGO increased fourfold in response to the pancreatic stimulation, whereas portal I/GG decreased significantly from 8.2 +/- 0.9 to 5.0 +/- 0.7. The concurrent femoral arterial I/GG (control 3.7 +/- 1.0) and mesenteric venous I/GG (control 2.1 +/- 0.5) increased significantly. These observations indicate that portal, but not peripheral, I/GG measurements reflect hepatic events in anesthetized dogs, probably because of the different extraction patterns for insulin and glucagon.

Animals↗
PubMed1978

Thyroid plasma membrane-associated protein kinases: properties and substrates of solubilized and insoluble enzymes.

The protein kinase activities of thyroid plasma membranes were characterized after treatment by the nonionic detergent, Triton X-100. With endogenous substrate the protein kinase activity of intact plasma membranes appeared to be cAMP independent, whereas the solubilized plasma membranes contained a cAMP-dependent protein kinase. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of intact plasma membranes demonstrated approximately 30 protein bands, of which several were substrates for endogenous protein kinase, cAMP had a slight, but reproducible, stimulatory effect on some of these. In solubilized plasma membranes cAMP significantly augmented phosphorylation of at least seven of these proteins. Solubilized plasma membranes bound significantly more cAMP per mg protein than intact plasma membranes. The inability to unequivocally detect cAMP-dependent protein kinase in intact membranes using endogenous substrate probably reflects the much greater activity of the cAMP-independent enzyme activity. The protein kinase activity of intact plasma membranes which was stimulated by cAMP when histone was the substrate was primarily recovered in the solubilized plasma membranes. Most of the protein kinase activity of the intact plasma membranes was insoluble and was not augmented by cAMP. The solubilized protein kinase demonstrated the same Km values for ATP, cAMP, and MgCl2 as did the cytosolic protein kinase of the thyroid. Cytosolic and solubilized protein kinase activities were more sensitive to cAMP and cGMP stimulation when histone and protamine were used as substrates. Both enzyme activities were depressed by protein kinase modulator when histone, but not protamine and casein, were used as substrates. The protein kinase activity of insoluble plasma membranes was not inhibited by the protein kinase modulator.

Adenosine Triphosphate↗
PubMed1978

Normal iodide efflux from nonfunctioning nodules of human thyroid glands.

The kinetics of iodide efflux were studied in four benign thyroid nodules and one carcinoma by observing the fractional rate of radioiodide release from slices prelabeled in vitro. The thyroid:medium ratio for iodide (T:M) of the benign nodular tissue was 1.9 +/- 0.3 (mean +/- SE) with a value of 9.1 +/- 3.3 obtained from adjacent normal tissue. Despite the reduction in iodide concentrating activity, the rate constant for iodide efflux (ko) from the nonfunctioning, benign thyroid nodular tissue (0.112 +/- 0.044 min-1) was not significantly different as compared to normal tissue (0.102 +/- 0.033 min-1). In a papillary carcinoma, the efflux of radioactive iodide appeared markedly enhanced. These studies indicate that in non-functioning, benign thyroid adenomas, the reduction in iodide concentrating activity is not the consequence of an increased iodide efflux.

Adenoma↗
PubMed1978

Effects of thyroid-stimulating hormone on human thyroid carcinoma and adjacent normal tissue.

Effects of TSH on the adenylate cyclase-cAMP system and some parameters of intermediary metabolism were investigated in human thyroid carcinoma and adjacent normal thyroid tissue. Basal adenylate cyclase activity and cAMP concentrations were significantly higher in carcinomatous tissue. Basal [1-14C]glucose oxidation, 32Pi incorporation into phospholipids, and organification of iodide were similar in both tissues. Stimulation of cAMP by TSH was significantly greater in normal compared to carcinomatous tissue. In neither tissue was there a good correlation between TSH stimulation of adenylate cyclase activity and cAMP concentrations. The TSH stimulation of 32Pi incorporation into phospholipids by TSH was significantly greater in normal tissue. The mean effect of TSH on iodide organification and glucose oxidation was similar in normal and carcinomatous tissue. Although specific binding of TSH was demonstrated in both normal and carcinomatous tissue, it did not correlate very well with stimulation of adenylate cyclase activity. Hormones other than TSH also augmented adenylate cyclase activity in two of the carcinomas. In individual patients, the relative responsivity of carcinomatous tissue compared to normal was not always consistent when all of the metabolic parameters were considered.

Adenylyl Cyclases↗