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Biomedical subjects

J W Hamilton

Publications and source records attributed to J W Hamilton.

At least 109 records · Page 6Linked to original sources
PubMed1986

Characteristics of bovine parathyroid cell organoids in culture.

Adult bovine parathyroid glands were enzymatically dispersed and groups of 2 to 5 million cells were reassociated into multicellular aggregates (organoids) by rotation in roller tubes in serum-free medium. Fifty to seventy percent of the seeded cells were incorporated into each organoid at 3 d of culture, and in a typical experiment where DNA content was assayed before and after culture 49 +/- 3% of the original seeded DNA was present after 19 d of culture. No significant differences in DNA content were observed between experimental groups at any time of culture. The morphology of the cells in organoids was similar to that of cells in fresh tissue as determined by light and electron microscopy. The organoids secreted intact parathyroid hormone (PTH) and COOH-terminal hormone fragments which were similar to those released from monolayer cell cultures. Organoids maintained the ability to modulate PTH secretion in response to extracellular calcium for over 2 wk in culture. Each organoid was cultured separately and secreted PTH such that the mean standard deviation of secretion within groups on a per organoid basis was 16.3% of the mean. Using a perifusion system to study acute regulation over a 2-wk period of culture, PTH secretion was suppressed 58 +/- 4% by 2.5 mM compared to that at 0.25 mM calcium. To examine PTH secretion over a range of calcium concentrations, the perifusion system was used to apply 4-h linear gradients of decreasing calcium to fresh tissue slices and to organoids. The results indicated that the calcium (ionized) concentration at 50% secretory suppression (set-point) were 1.30 +/- 0.11 and 1.20 +/- 0.9 mM for the organoids and slices, respectively. Acute secretory control by calcium decreased after 14 d and was not detectable at 22 d of culture. The results demonstrated that the organoids maintained their differentiated function and tissuelike morphology for extended periods in vitro and therefore represent a suitable model system for studies on the long-term modulation of PTH secretion by vitamin D metabolites, ions, and other agents.

Animals↗
PubMed1986

Structural characterization of adrenal chromogranin A and parathyroid secretory protein-I as homologs.

We have isolated and purified adrenal chromogranin A (Ch A) for the purpose of making structural comparisons to parathyroid secretory protein-I (SP-I), because our earlier data indicated these two molecules may be the same protein. An improved purification step, using high-performance liquid chromatography (HPLC), has enabled us to demonstrate that both SP-I and Ch A consists of two species, one of approximately 72,000 Da and one of approximately 66,000 Da. The amino acid composition is the same for all four species. The difference in molecular mass is assumed to be due to carbohydrate content. Cyanogen bromide digestion of each of the four samples, followed by HPLC separation of the generated peptides, resulted in a chromatographic profile that was the same for each digest. Amino acid analysis of the eight peptide fragments obtained from each digest indicates that both species of Ch A and both species of SP-I yielded the same peptide mixtures following this cleavage reaction. One large (approximately 50,000 Da) CNBr peptide was obtained and seven smaller ones, one of which contains cysteine. The large fragment behaved similarly to the intact molecule in a radioimmunoassay. HPLC separation of tryptic digests of Ch A (72,000 Da) and SP-I (72,000 Da) also resulted in elution profiles that were very similar to each other. Amino acid analysis revealed 23 peptides common to each digest. Ch A contained four peptides ranging in size from 4 to 30 residues that were not observed in the SP-I digest. SP-I contained two peptides, each with about 30 residues, that were not found in the Ch A digest. Nothing unusual was noted in any of the uncommon peptides. Thus, both a chemical and an enzymatic digestion of these molecules followed by analysis of the peptides generated, indicates that SP-I and Ch A are nearly identical homologs.

Adrenal Glands↗
PubMed1986

Carnitine transport in human intestinal biopsy specimens. Demonstration of an active transport system.

Although carnitine is present in a variety of foods, the mechanism of its absorption has not been previously studied in humans. We investigated the absorption of carnitine by studying uptake into human intestinal mucosal biopsy specimens. We found evidence of active transport in the duodenum and ileum, but not in the colon. We demonstrated that intracellular concentrations exceeded concentrations in the incubation media at steady states and that uptake against a concentration gradient was abolished by anoxia and by replacement of sodium ion with potassium. Studies of initial rate of uptake over a range of concentrations revealed a curve consistent with a two-component system: a saturable system with a KT of 558 microM and a linear component probably representing passive diffusion. Addition of D-carnitine and L-acetylcarnitine resulted in diminished uptake of L-carnitine, suggesting that these substrates utilize the same transport mechanism. These studies demonstrate the presence of an active intestinal transport system for L-carnitine in human intestinal mucosa.

Adult↗
PubMed1986

Characterization of coho salmon (Oncorhynchus kisutch) islet somatostatins.

Three different somatostatins have been isolated from the pancreatic islet tissue of the coho salmon (Oncorhynchus kisutch) by gel filtration and HPLC. Two of these peptides contain 14 amino acids and the larger third peptide consists of 25 amino acids. The sequence of the salmon SST-25 is Ser-Val-Asp-Asn-Leu-Pro-Pro-Arg-Glu-Arg-Lys-Ala-Gly -Cys-Lys-Asn-Phe-Tyr-Trp-Lys-Gly-Phe-Thr-Ser-Cys. The sequence of the salmon SST-14-I is Ala-Gly-Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys. The other small somatostatin (SST-14-II) which was not sequenced has an amino acid composition identical to the C-terminal 14 amino acids of the SST-25 and it is probably derived from this larger form. Evidence for low levels of a somatostatin containing 28 amino acids is also presented. This SST-28 appears to be an N-terminal extended precursor of SST-25 or a peptide derived via alternative processing of a common preprosomatostatin. Injected into juvenile salmon, SST-25 caused a decline in circulating levels of plasma insulin, depletion of liver glycogen, and activation of lipolytic pathways. Juvenile salmon treated with anti-SST-25 serum revealed elevated levels of plasma insulin as well as an increase of the glycogen content of the liver.

Amino Acid Sequence↗
PubMed1986

Isolation and structures of coho salmon (Oncorhynchus kisutch) glucagon and glucagon-like peptide.

Glucagon and glucagon-like peptide (GLP) containing 31 amino acids have been isolated from the principal islet of coho salmon (Oncorhynchus kisutch) by gel filtration of acid alcohol extracts followed by HPLC, and the complete amino acid sequence of both peptides has been determined. Salmon glucagon is a simple 29 residue peptide differing at 3 positions when compared to catfish glucagon and at 8 positions when compared to porcine glucagon. Salmon GLP differs at 6 positions when compared with the N-terminal 31 amino acids of the 34 amino acid catfish GLP. Both coho salmon glucagon and GLP cross-react weakly in our mammalian glucagon radioimmunoassay and therefore this technique could not be used to determine tissue content. Glucagon and GLP isolated amounted to 156 micrograms/g and 350 micrograms/g wet tissue, respectively.

Amino Acid Sequence↗
PubMed1986

Formation of parathormone 8-34 by cathepsin-D digestion of parathormone and its efficacy as a hormone antagonist.

It previously has been shown that digestion of bovine parathormone (bPTH) with cathepsin-D results in rapid cleavage of the hormone between Phe34 and Val35 yielding PTH(1-34) and PTH(35-84). Since bPTH also contains a Phe at residue 7 we have conducted additional studies to determine whether cleavage at this position could occur. We have found that following longer incubation periods of hormone and enzyme, 2 additional peptides are generated; PTH(8-34) and PTH(1-7). Time course studies demonstrated that these 2 fragments are formed from the (1-34) peptide generated through the initial cleavage at Phe34-Val35 of PTH. The identification of the bPTH(8-34) was accomplished through amino acid analysis and N-terminal sequencing. bPTH(8-34) behaved as a PTH antagonist in an in vitro mouse calvarial bone resorption assay. Although bPTH(8-34) did not affect the PTH-stimulated cAMP response when added simultaneously with PTH, preincubation of bone cells with this peptide caused desensitization of the PTH-stimulated cAMP response.

Amino Acid Sequence↗
PubMed1986

Chromium (VI)-induced DNA damage in chick embryo liver and blood cells in vivo.

Uptake of chromium (VI) and subsequent induction of DNA damage was examined in liver and blood cells of 14-day chick embryos after injection of sodium dichromate onto the inner shell membrane. Maximal loss of chromium from the inner shell membrane and distribution of chromium in liver, lung and blood was observed 2 h after injection. DNA strand breaks, interstrand cross-links and DNA--protein cross-links were measured using the alkaline elution technique. In chick embryo liver, chromium (VI) induced DNA cross-links in the absence of strand breaks. Maximal DNA cross-linking was detected in the liver 8 h after injection. Little or no DNA damage remained in the liver 10-24 h after injection. In contrast, chromium (VI) induced DNA strand breaks in the absence of cross-links in chick embryo blood cells. Maximal DNA strand breakage was observed in blood cells 8 h after injection. High levels of DNA strand breaks were present in blood cells even 24 h after treatment. These intra-embryonic tissue differences in chromium (VI)-induced DNA damage may be a result of the differences in glutathione, cytochrome P-450, other pathways of chromium (VI) metabolism or chromatin organization which exist in liver and blood cells.

Animals↗
PubMed1986

Correlation between induction of xenobiotic metabolism and DNA damage from chemical carcinogens in the chick embryo in vivo.

Chick embryo liver and lung have high levels of basal mixed-function oxidase (MFO) enzyme activities during embryonic development. These activities are differentially inducible by 3,4,3',4'-tetrachlorobiphenyl (TCB) and phenobarbital (PB) in liver but are not inducible in lung. Nucleated chick embryo erythrocytes have no detectable basal or inducible MFO activities. Following induction by TCB or PB, embryos were exposed to the direct-acting carcinogen methyl methane-sulfonate (MMS) or the indirect-acting carcinogens aflatoxin B1 (AFB1) or 7,12-dimethylbenz[a]anthracene (DMBA). DNA damage was measured in liver, lung and blood by the DNA alkaline elution technique. Maximum DNA damage by MMS in liver, lung and blood and by AFB1 and DMBA in liver and lung occurred approximately 3 h after exposure. DNA damage was rapidly repaired in liver and lung, but was not repaired in blood. AFB1 and DMBA caused no detectable DNA damage in blood, even following PB or TCB induction. MMS-induced DNA damage was unaffected by induction in all groups with the exception that PB decreased DNA damage in liver at the low dose of MMS. AFB1- and DMBA-induced DNA damage was increased in liver and decreased in lung following induction by PB and TCB in 14-day embryos. In contrast, AFB1-induced DNA damage was increased by PB and decreased by TCB in 7-day embryonic liver. These results suggest that MFO induction can increase or decrease DNA damage in vivo, but that the direction and magnitude of change in DNA damage can vary depending on the inducer, carcinogen, tissue and the developmental age being investigated.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1986

Structural analysis of parathormone fragments elaborated by cells cultured from a hyperplastic human parathyroid gland.

Parathyroid cells were obtained by collagenase digestion of 2 g of human parathyroid tissue obtained at surgery from a patient with end stage renal failure and hypercalcemia. Cells were placed into monolayer culture in supplemented Waymouth's MB752/1. Secretion of parathyroid hormone (PTH) from monolayer cultures was inhibited for 3 weeks by 2.5 mM compared to 0.5 mM calcium. The inhibition was 50% on day 3 of culture, and decreased to 19% by day 21. When cultures were incubated with [3H]leucine, radioactive PTH and COOH-terminal PTH fragments were secreted. Sequence analyses were performed on material in radioactive and immunoreactive peaks following gel filtration and high performance liquid chromatography of media. The results indicated that cleavage of PTH or fragments thereof occurred at the 23-24, 27-28, and 33-34 peptide bonds. NH2-terminal fragments of PTH were not detected in media.

Cells, Cultured↗
PubMed1985

Evidence for two pathways for stimulation of collagenolysis in bone.

The effect of parathormone (PTH), lipopolysaccharide (LPS), or interleukin-1 (IL-1) on calcium release and collagen degradation in bone was examined in vitro using labeled neonatal calvaria of normal mice and also of osteopetrotic microphthalmic (mi/mi) mice that have defective osteoclasts. All three agents stimulated calcium release from normal bone but not from mi/mi bone. PTH stimulated the degradation of both noncalcified and calcified collagen in normal bone as well as the degradation of noncalcified collagen in mi/mi bone. However, LPS and IL-1 only stimulated the degradation of calcified collagen in normal bone. One-half maximal stimulation of noncalcified collagen degradation in normal or mi/mi bone was achieved by about 3 nM PTH compared with about 1 nM PTH for that of calcium release from normal bone. While calcitonin (CT) and leupeptin inhibited calcium release and thereby the degradation of calcified collagen, neither agent inhibited PTH-stimulated noncalcified collagen degradation in normal or mi/mi bone. The data indicate the existence of two pathways that lead to collagen degradation in bone. One is intimately connected with the resorptive process stimulated by a variety of agents, and is probably mediated by osteoclasts. A second mechanism is sensitive only to PTH and appears to be associated with nonosteoclastic cells since it can operate under conditions in which osteoclasts are thought to be inactive or are inhibited.

Acetazolamide↗
PubMed1985

Characterization of coho salmon (Oncorhynchus kisutch) insulin.

Insulin has been isolated from islet tissue of coho salmon (Oncorhynchus kisutch) by gel filtration and HPLC and the complete amino acid sequence has been determined. The sequence differs from bovine insulin at 14 sites but all interchanges are conservative from the viewpoint of preservation of conformation. A comparison of insulin sequences from other fish is presented. Salmon insulin cross-reacts very weakly with antiserum to bovine insulin and vice versa. A completely homologous radioimmunoassay has been developed and used to estimate the insulin in salmon islet tissue and in plasma. The hypoglycemic effect of salmon insulin in salmon was more pronounced and persisted longer than that caused by identical doses of bovine insulin.

Amino Acid Sequence↗
PubMed1985

Comparative studies of aryl hydrocarbon hydroxylase and the Ah receptor in nonmammalian species.

In vivo treatment of chicks, quail and rats with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or 3-methylcholanthrene (MC) caused a dose-dependent increase in hepatic microsomal aryl hydrocarbon hydroxylase activity. A much lower level of AHH induction was observed following similar treatment of trout with high concentrations of TCDD or MC. No induction was apparent in midgut tissues from southern armyworm larvae exposed to the same inducers. A low level of receptor exhibiting specific binding of [3H]TCDD was demonstrated in chick hepatic cytosol, but no evidence of receptor was obtained with the other species. Although the specific binding of the receptor in chick cytosol was only 6-8 fmoles TCDD bound/mg protein compared to 135 fmoles/mg in rat hepatic cytosol, the chick receptor exhibited properties similar to those of Ah receptors in mammals.

Animals↗
PubMed1984

Inhibition of parathormone-stimulated bone resorption by type I interferon.

The effect of Type I interferon on bone resorption was studied by measuring its effect on parathormone-stimulated calcium release from neonatal murine calvaria in vitro. A pure human recombinant leukocyte interferon hybrid of the A and D subtypes was used, which has high antiviral activity on mouse cells. Calcium release was inhibited in a dose dependent fashion with 50% inhibition at about 10(-10) M or 600 U/ml, and the inhibition was reversible. The presence of interferon was required before or during the activation phase of the resorptive response, when the formation of osteoclasts from precursor cells would occur. When added to actively resorbing bone it had no effect. The data suggest that Type I interferon can inhibit the parathormone-regulated development of active osteoclasts, possibly by inhibiting osteoclast precursor differentiation.

Animals↗
PubMed1984

The structure of a naturally occurring 10K polypeptide derived from the amino terminus of bovine thyroglobulin.

A combination of data derived from peptide sequencing and nucleic acid sequencing of cloned cDNA fragments has been used to define the complete amino acid sequence of a 10,000 M.W., thyroxine containing polypeptide derived from bovine thyroglobulin. This fragment, TG-F, which was obtained following reduction and alkylation, has been placed at the amino terminus of the parent protein with hormone located at residue 5 in the primary sequence of the thyroglobulin molecule. The carboxyl terminal sequence of this fragment -Cys-Gln-Leu-Gln is found on the N-terminal side of a lys residue, suggesting that the peptide bond cleavage which occurs to produce this 80 residue fragment from the parent (330K) thyroglobulin chain is a gln-lys. In addition, the amino acid sequence of this 10K fragment contains: No sequence which would be a substrate for glycosylation and no carbohydrate. Several repeated homologous amino acid sequences. A striking number of beta-bends predicted from Chou-Fasman analyses, particularly near its carboxyl terminus.

Amino Acid Sequence↗
PubMed1984

The isolation of identical thyroxine containing amino acid sequences from bovine, ovine and porcine thyroglobulins.

Identical, thyroxine containing tryptic peptides have been isolated from digests of bovine, ovine and procine thyroglobulins. This 19 residue hormone containing sequence, NH2-Asn-Ile-Phe-Glu-T4-Gln-Val-Asp-Ala-Gln-Pro-Leu-Arg-Pro-Cys-Glu-Leu-G in-Arg- COOH, is completely conserved across these three species, and it represents a principal site of thyroxine synthesis. HPLC maps of tryptic digests of the thyroglobulins have been monitored at several wavelengths and suggest that, in each case, only a small number of tryptic peptides are iodinated in vivo and that an even smaller number of tryptic peptides contain thyroid hormone. These data are consistent with a high degree of selectivity in iodination of tyrosines within thyroglobulin and the subsequent coupling of these selected tyrosines to form thyroid hormone.

Amino Acid Sequence↗
PubMed1984

Correlation between mixed-function oxidase enzyme induction and aflatoxin B1-induced unscheduled DNA synthesis in the chick embryo, in vivo.

The unscheduled DNA synthesis (UDS) technique has been adapted for use in the chick embryo, in vivo, to determine the relationship between induction of the mixed-function oxidase (MFO) enzyme system and genetic damage from an indirect-acting mutagen-carcinogen. Embryos were injected at 6 days of incubation (DI) with either phenobarbital (PB), a specific inducer of P-450-associated enzyme activities, or 3,4,3',4'-tetrachlorobiphenyl (TCB), a specific inducer of P1-450-associated enzyme activities. Aflatoxin B1 (AFB1) was injected 24 hr later (7 DI), followed by a 5-hr continuous 3H-thymidine exposure. The livers were removed, prepared for autoradiography, and hepatocytes were scored for an increase in grains/nucleus, indicative of UDS. Aflatoxin B1 caused a dose-related increase in UDS in all control and induction groups. Phenobarbital-induced embryos had an increased UDS response while TCB-induced embryos had a decreased UDS response, relative to noninduced embryos, for each dosage of AFB1. This suggests that the genotoxicity of an indirect-acting mutagen-carcinogen can be either increased or decreased, in vivo, depending on the inducer used. The chick embryo provides an excellent system for studying the effect of MFO induction on the genotoxicity of promutagen-carcinogens in a developing system.

Aflatoxin B1↗
PubMed1984

Isolation and characterization of reptilian insulin, glucagon, and pancreatic polypeptide: complete amino acid sequence of alligator (Alligator mississippiensis) insulin and pancreatic polypeptide.

The insulin, glucagon, pancreatic polypeptide, and somatostatin contents of acid-alcohol extracts of alligator pancreas have been estimated by heterologous radioimmunoassay, and the insulin, glucagon, and pancreatic polypeptide have been isolated. The amino acid sequences of the insulin and pancreatic polypeptide were determined. The sequence of the insulin A chain is identical to that of chicken insulin A chain, while the B chain exhibits three conservative substitutions when compared to that of the chicken. Pancreatic polypeptide from the alligator is similar in sequence to that of chicken PP, but contains seven substitutions, most of which are conservative and preserve characteristics essential for conformation. The amino acid composition of alligator glucagon is identical to that of duck glucagon.

Alligators and Crocodiles↗