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Biomedical subjects

P C Chang

Publications and source records attributed to P C Chang.

At least 19 recordsLinked to original sources
PubMed1992

Extracellular autoprocessing of a metalloprotease from Streptomyces cacaoi.

We have previously demonstrated that the extracellular neutral metalloprotease (Npr) of Streptomyces cacaoi is synthesized as a 60-kDa preproenzyme (P60), then processed to the 35-kDa mature form (P35) (Chang, P. C., Kuo, T.-C., Tsugita, A., and Lee, Y.-H. W. (1990) Gene (Amst.) 88, 87-95). In this study, we investigated the active site and the mechanism involved in the maturation of the protease. Site-specific mutations at the putative zinc-binding ligands and active site of Npr at His202, Glu203, His206, and Glu240 led to complete abolishment of Npr activity and concomitant accumulation of a 57-kDa inactive protein (P57) which was secreted. Sequence analysis of the NH2 terminus indicated that P57 was derived from P60 after removal of the signal peptide and represented the proenzyme form of Npr (pro-Npr). Analysis of the zinc content of purified mutant P57 proteins revealed a dramatic loss of zinc atom as compared with the wild-type P35 protein. In vitro with the aid of exogenous active Npr, the mutant P57 protein could be converted to the mature inactive P35 with an identical NH2-terminal sequence and a molecular mass the same as that of the wild-type P35. From these studies, we conclude that these highly conserved residues (His202, Glu203, His206, and Glu240) are indispensable for zinc binding and protease activity, as well as processing of Npr. In addition, we have clearly demonstrated that maturation of Npr occurs extracellularly via an autocatalytic cleavage of the pro-Npr propeptide. This is the first report of such a maturation mechanism for an extracellular protease in streptomycetes which can serve as a model for further studies on the mechanism of secretion and processing of proteases from Gram-positive bacteria.

Amino Acid Sequence↗
PubMed1992

Changes in PETCO2 and pulmonary blood flow after bronchial occlusion in dogs.

The use of PETCO2 in detecting accidental bronchial intubation was investigated. The PETCO2 was measured in six mongrel dogs after occluding the left mainstem bronchus in three conditions; pentobarbital anaesthesia, 0.8% halothane insufflation together with pentobarbital anaesthesia, and simultaneous left pulmonary artery and bronchial airway occlusion with intravenous pentobarbital anaesthesia. An external flow probe measured left pulmonary artery blood flow. The PETCO2 decreased after bronchial occlusion during pentobarbital (35 +/- 3 vs 30 +/- 5 mmHg) and halothane-pentobarbital (30 +/- 6 vs 25 +/- 6 mmHg) conditions (P less than 0.05). However, within three minutes of bronchial occlusion, the values of PETCO2 had returned to their pre-occlusion values. After five minutes of bronchial occlusion pulmonary artery blood flow in the non-ventilated lung decreased (P less than 0.05) during pentobarbital (770 +/- 533 ml.min-1 vs 575 +/- 306 ml.min-1) and halothane-pentobarbital (495 +/- 127 ml.min-1 vs 387 +/- 178 ml.min-1) conditions. Simultaneous bronchial and pulmonary artery occlusion prevented any changes in PETCO2. It was concluded that accidental one-lung ventilation results in small and transient decreases in PETCO2. A redistribution of blood flow from the non-ventilated to ventilated lung occurs which restores PETCO2 to the original values observed with two-lung ventilation.

Airway Obstruction↗
PubMed1992

Effects of steady electric fields on human retinal pigment epithelial cell orientation and migration in culture.

Low-level, steady electric fields of 6-10 volts/cm stimulated directional orientation and translocation of cultured human retinal pigment epithelial cells. The orientative movements (galvanotropism) consisted of somatic elongation of the cells into spindle shapes, followed by pivotal alignment orthogonal to the field. The anodal edges of the cells underwent retraction of their plasmalemmal extensions, while the cathode edges and the longitudinal ends developed lamellipodia and ruffled membranes. These tropic movements were followed by a translocational movement (galvanotaxis) of the cells towards the cathode. Staining of these migrating cells for actin showed the accumulation of stress fibers at the leading (cathodal) edge, as well as at the longitudinal ends of the elongated somata. These results suggest that endogenous, biologically-generated electric fields (eg., injury currents) may play a role in the guidance and migration of retinal pigment epithelial cells after retinal injury.

Actins↗
PubMed1992

A case of recurrent adrenocortical carcinoma, with observations on long-term o,p'-DDD therapy and complications.

This report describes a patient with a recurring, one stemline-aneuploid, adrenocortical carcinoma. The condition showed a number of unusual characteristics over a period of 22 yr. It changed from a biochemically functioning, low-grade malignant tumour into a non-functioning malignancy with pronounced mitotic activity, accompanied by an ovarian carcinosarcoma 1 yr before death. Quality of life was reasonable for many years despite chemotherapy, consisting of a total of almost 10 kg of o,p'-DDD administered over a period of 8 yr, and the subsequent side effects (e.g. low T4; increased bleeding time). A reduced mineralocorticoid activity, induced by o,p'-DDD, was reversed after discontinuation of o,p'-DDD treatment. During o,p'-DDD administration the substitution requirements for both hydrocortisone and fludrocortisone acetate increased, leading to periods of hypoadrenocorticism with prerenal uraemia.

Adrenal Gland Neoplasms↗
PubMed1991

Extracorporeal renal artery reconstruction for renovascular hypertension.

Extracorporeal reconstruction can be applied to the successful repair of stenoses in the distal renal artery and its hilar branches. This study evaluates the short- and long-term results of extracorporeal renal artery reconstruction in 65 patients, including 5 children, with renovascular hypertension who were treated from 1974 through 1989. The mean age of the patients was 37 years (range, 7 to 67 years). The cause of the stenoses was arteriosclerosis in 8 patients, fibrodysplasia in 54 patients, and miscellaneous in 3. Hypertension was severe before treatment with a mean blood pressure of 187/147 mm Hg that was reduced to a mean of 159/102 mm Hg after medical therapy. Ten patients had renal dysfunction. Results were evaluated both at short-term intervals (mean, 7.9 months; 64 patients) and long-term intervals (mean, 5.9 years; 60 patients), after surgery. Blood pressure responses were classified as beneficial (cured/improved) or failures. Anatomic results were evaluated by angiography in 98% of the patients at the short-term interval and in 77% of the patients at the long-term interval. Extracorporeal renal artery surgery was performed on 78 kidneys among 65 patients (unilateral, 45 patients; bilateral, 13 patients; unilateral extracorporeal and contralateral in situ, 7 patients). In most of the cases autologous arterial graft was used for reconstruction. Early in the series one patient died as a result of the operative procedure (1/65, 1.5%). A beneficial blood pressure response occurred in 53 patients (53/65; 82%) at the short-term interval and in 49 patients (49/61; 80%) at the long-term interval, with the average blood pressure at the short-term interval being 138/85 mm Hg and at the long-term interval being 139/85 mm Hg. Renal function improved in all patients with preoperative renal dysfunction. Graft stenosis or occlusion of the main renal artery was neither observed at the short-term interval nor at the long-term interval. However, residual stenoses were observed in 9 of the 163 reconstructed distal branches (5.5%). Extracorporeal renal artery reconstruction with autologous arterial grafts can be effectively applied to lesions of the distal main renal artery and its hilar branches with durable functional results.

Adolescent↗
PubMed1991

No effect of misoprostol on renal function of rheumatoid patients treated with diclofenac.

Non-steroidal anti-inflammatory drugs can reversibly decrease renal function in patients with rheumatoid arthritis (RA). To test whether orally administered prostaglandins could mitigate this decrease, we studied the effect of misoprostol in 24 RA patients during treatment with diclofenac in a randomized, placebo-controlled crossover trial. At baseline, 21 patients had a creatinine clearance below 80 ml/min/1.73 m2. The two treatment phases (with either misoprostol, 600 micrograms daily, or matching placebo tablets) were separated by a washout phase in which diclofenac (150 mg daily) was continued. After treatment with misoprostol/diclofenac the glomerular filtration rate was 72 +/- 5 ml/min (mean +/- standard error), and the effective renal plasma flow was 295 +/- 21 ml/min. After treatment with placebo/diclofenac, the corresponding values were 71 +/- 5 ml/min and 296 +/- 21 ml/min, respectively. We concluded that misoprostol has no effect on the renal function of RA patients treated with diclofenac.

Adult↗
PubMed1991

Positron emission imaging of cardiac sympathetic innervation and function using 18F-6-fluorodopamine: effects of chemical sympathectomy by 6-hydroxydopamine.

Hypotheses concerning the pathophysiology of hypertension, cardiac failure and other cardiovascular disorders have imputed abnormal cardiac sympathoneural activity. Here we describe a technique to examine cardiac sympathetic innervation and function using positron emission tomographic (PET) scanning after systemic intravenous injection of 18F-6-fluorodopamine, and the effects of chemical sympathectomy by the neurotoxin, 6-hydroxydopamine (6-OHDA). Uptake of 18F-6-fluorodopamine by the heart of anesthetized dogs resulted in striking delineation of the left ventricular myocardium. Myocardial radioactivity declined bi-exponentially, with a half-life of approximately 2 h during the longer phase. In 6-OHDA-treated animals, the ventricular myocardium was barely distinguishable from the chamber; myocardial radioactivity declined rapidly and was virtually absent within 30 min after injection of 18F-6-fluorodopamine. The rates of decline in myocardial radioactivity in dogs treated with 6-OHDA were similar to those in dogs treated with reserpine, but the mechanisms of sympatholysis by these drugs were distinguished by arterial plasma levels of 6-fluorodihydroxyphenylacetic acid (6-FDOPAC). Plasma 6-FDOPAC levels were diminished in 6-OHDA-treated dogs and elevated in reserpinized dogs. The results confirm that, after injection of 18F-6-fluorodopamine, cardiac sympathetic nerve endings are radiolabeled, allowing visualization of sites of sympathetic innervation. Combined assessments of PET time-activity curves and plasma levels of metabolites of 18F-6-fluorodopamine constitute a new, potentially clinically applicable means by which to examine cardiac sympathetic function.

Animals↗
PubMed1991

Effects of 5-hydroxytryptamine on capillary and arteriovenous anastomotic blood flow in the human hand and forearm and in the pig hind leg.

The effects of intraarterially infused serotonin (5-HT) on capillary and arteriovenous anastomotic (AVA) blood flow were investigated in the hand and forearm of 19 healthy volunteers, and in the hind leg of six anesthetized pigs using radioactive microspheres with a diameter of 15 microns. The 5-HT2-receptor antagonist ketan-serin was used in an attempt to identify the receptors involved. None of the drugs in the doses used induced systemic hemodynamic effects. Low doses of 5-HT significantly increased forearm blood flow with a maximum response at the dose of 1 ng/kg/min (68 +/- 14%, p less than 0.05), whereas only at the highest dose of 80 ng/kg/min was a net decrease in forearm blood flow measured (-28 +/- 6%, p less than 0.05). Conversely, finger blood flow was not influenced by the lower doses of 5-HT, whereas a major reduction was observed at the highest dose (-90 +/- 3%). Ketanserin increased both total forearm blood flow and AVA blood flow. The drug blunted the constrictor response to 5-HT in the forearm but only slightly attenuated this response in the finger. The percentage AVA blood flow in the human hand and forearm was not influenced by an infusion of 5-HT at 80 ng/kg/min alone. However, after pretreatment with ketanserin, which itself increased the AVA component, this dose of 5-HT significantly reduced AVA flow. In the pig, total femoral blood flow was not influenced by 5-HT, but AVA blood flow was significantly reduced and capillary skin blood flow increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Tracer norepinephrine kinetics: dependence on regional blood flow and the site of infusion.

The rate of appearance of the sympathetic neurotransmitter norepinephrine (NE) in the regional venous drainage (NE spillover) can be estimated based on intravenous or intra-arterial infusions of [3H]NE. The present study examined whether forearm NE spillover (FASO) in humans depends on forearm blood flow (FBF) and on the site of infusion of the tracer. Healthy volunteers underwent infusions of [3H]NE and [3H]isoproterenol (Iso) administered intravenously (n = 21), intra-arterially (n = 32), or by both routes in the same experimental session (n = 7). FBF was manipulated by intra-arterial infusions of the vasodilator sodium nitroprusside (n = 7) or the vasoconstrictor methoxamine (n = 7). Forearm extraction percents of [3H]NE exceeded those of [3H]Iso in all subjects undergoing intravenous infusions (54 vs. 46%, P less than 0.001), whereas extraction percents of [3H]Iso exceeded those of [3H]NE when the tracers were infused intra-arterially. Regardless of the infusion site, FASO was positively correlated with FBF (r = 0.44, P less than 0.005). Nitroprusside increased FBF and FASO, and methoxamine decreased FBF and FASO. When the tracers were added to whole blood, 89% of [3H]NE and 83% of [3H]Iso remained in plasma after 1 min; although no further loss of [3H]NE occurred over time, only 60% of the added [3H]Iso remained in plasma by 20 min. The results indicate that regional NE spillover is flow dependent, complicating inferences about regional sympathoneural activity. Intra-arterial infusion of [3H]NE results in higher estimates of regional NE spillover than does intravenous infusion of the tracer.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Does regional norepinephrine spillover represent local sympathetic activity?

Regional spillover of norepinephrine (NE), based on isotope dilution and single-compartment steady-state kinetics, is considered one of the best parameters for estimating organ sympathetic activity. However, the effects of local changes in clearance of NE on the spillover have not yet been investigated. We studied local NE kinetics and clearance in the forearm of 10 healthy subjects using intra-arterial infusions of NE, tritiated NE, the neuronal uptake inhibitor desipramine, and tyramine, which competes with NE for the neuronal uptake carrier. Before and during complete blockade of neuronal uptake by desipramine the venous concentration-time curves for tritiated NE and for NE released by tyramine were biexponential, consistent with the presence of (at least) two compartments for circulating tritiated NE and for locally released NE. The time constants for tyramine-induced release of NE and, in the same subjects during desipramine infusion, for tritiated NE were almost equal at the same level of forearm blood flow. This argues against possible diffusion or transport differences for NE to and from the circulation and the synapse. The regional intrinsic clearance capacity (a measure of the maximal ability of an organ to irreversibly remove drug by all pathways in the absence of any flow limitations) for NE decreased in the forearm by 65% (p less than 0.01) during neuronal uptake blockade by desipramine; the forearm clearance decreased by 59% (p less than 0.001), whereas the spillover rate of NE increased from 33 +/- 5 to 63 +/- 11 pmol.min-1 (p less than 0.05). Nitroprusside-induced increments in blood flow increased the spillover of NE from 18 +/- 4 to 35 +/- 6 pmol.min-1 (p less than 0.01); the clearance of circulating NE also increased (by 58%, p less than 0.05), and the intrinsic clearance capacity remained unchanged. This demonstrates that regional spillover of NE is markedly influenced by local changes in clearance and flow. The new parameter plasma appearance rate of NE is proposed. Although also derived from isotope dilution, this parameter may better approximate the regional entry of NE into the blood pool than spillover. This is corroborated by the nonsignificant changes of plasma appearance rate of NE during our desipramine and nitroprusside infusions.

Adult↗
PubMed1991

Evidence for functional alpha 2-adrenoceptors on vascular sympathetic nerve endings in the human forearm.

The role of alpha 2-adrenoceptors on vascular sympathetic nerve endings in modulating release of the sympathetic neurotransmitter norepinephrine (NE) in humans was examined by measuring the regional rate of appearance of NE in forearm venous plasma (forearm NE spillover [FSO]) in 32 healthy volunteers during intra-arterial infusion of drugs acting at adrenoceptors or directly on vascular smooth muscle. Simultaneous intra-arterial infusions of tracer amounts of [3H]NE were used to calculate the extraction rate of NE in the forearm. Methoxamine or propranolol with epinephrine (PRO + EPI) was used to stimulate alpha-adrenoceptors, yohimbine was used to inhibit alpha-adrenoceptors, and sodium nitroprusside (NIP) was used to produce increases in forearm blood flow directly. Sympathetic efferent activity was manipulated by systemic intravenous infusions of NIP or trimethaphan. Yohimbine and NIP increased and PRO + EPI and methoxamine decreased NE FSO, without effects on systemic blood pressure, heart rate, or arterial levels of catechols. Changes in FSO were flow dependent; therefore, the slope of the relation between the changes in FSO and forearm blood flow was used to evaluate the effects of each drug on regional sympathoneural activity. During administration of yohimbine, the mean slope of the relation between the change in estimated FSO and the change in forearm blood flow was about four times that of the mean slope during administration of NIP (F = 6.35, p less than 0.05). The slopes of the relations between changes in FSO and forearm blood flow were unaffected by systemic trimethaphan or NIP infusion, indicating that the activity of alpha 2-adrenoceptors was not altered during inhibition or reflexive stimulation of sympathetic outflow. The results suggest that alpha 2-adrenoceptors modulate release of NE from vascular sympathetic nerve endings in humans and that the function of these receptors is unchanged during acute changes in junctional NE concentrations.

Adult↗
PubMed1991

Dosimetric estimates for clinical positron emission tomographic scanning after injection of [18F]-6-fluorodopamine.

Positron emission tomographic (PET) scanning after systemic i.v. injection of fluorine-18-6-fluorodopamine ([18F]-6F-DA) is a method for visualizing and measuring regional sympathetic nervous system innervation and function. Based on results of preclinical studies of rats and dogs and on previous literature about the fate of injected tracer-labeled catecholamines, dosimetric estimates for clinical studies are presented here. After injection of 1 mCi of [18F]-F-DA, the radiation dose would be highest to the wall of the urinary bladder (1.40 rem/mCi), due to accumulation of radioactive metabolites of [18F]-F-DA in urine. Radioactivity also would accumulate in bile. Organs receiving the next highest dose would be the kidneys (0.9 rem/mCi) and small intestine (0.2 rem/mCi). The parenchymal radiation dose would be lowest in the brain, since there is an effective blood-brain barrier for circulating catecholamines. Radiation doses to all organs after administration of 1 mCi of [18F]-F-DA to humans would be less than 3 rem and, therefore, within current FDA guidelines.

Animals↗
PubMed1990

Extracellular metalloprotease gene of Streptomyces cacaoi: structure, nucleotide sequence and characterization of the cloned gene product.

The gene (npr) encoding an extracellular neutral metalloprotease (Npr) from Streptomyces cacaoi YM15 was cloned in Streptomyces lividans using pIJ702 as a vector. The nucleotide (nt) sequence of npr was determined. The deduced open reading frame encoded 550 amino acids (aa) (60 kDa) with a putative signal sequence of 34 aa at the N terminus. High-resolution S1 mapping identified the transcriptional start point at about 132-134 nt upstream from the start codon. The nt sequences at both -10 and -35 regions resemble the consensus sequence of typical Escherichia coli promoters and a fragment containing the promoter was functional in an E. coli promoter probe plasmid. In vitro transcription and translation of the cloned npr sequence revealed a 60-kDa protein product, correlated with the sequence data but not with the size (35 kDa) of the extracellular Npr. The N-terminal aa sequence in conjunction with the aa composition analyses on the purified mature Npr led to the conclusion that it was processed from the 60-kDa pre-proenzyme form encoded by npr. The Npr protease contained putative zinc ligand-binding regions and two repeated motifs, Asp-Ser-Gly, similar to the active site residues of the aspartic acid and retroviral proteases.

Amino Acid Sequence↗
PubMed1990

Subclinical renal dysfunction in rheumatoid arthritis.

We studied renal function in 35 patients with chronic, seropositive rheumatoid arthritis (RA), of whom 7 had vasculitis, 10 had hypergammaglobulinemia, and 18 had neither of these 2 conditions. Findings included a decreased glomerular filtration rate in 8 patients, (micro)proteinuria in 11, a defective urine concentration in 10, and increased urinary tubular enzyme levels in 15. These results indicate that subclinical renal dysfunction is common in patients with chronic, seropositive RA. In addition, vasculitis and hypergammaglobulinemia were not identified as risk factors for renal dysfunction in the RA patients studied.

Arthritis, Rheumatoid↗
PubMed1990

Metabolic fate of injected radiolabelled dopamine and 2-fluorodopamine in rats.

In evaluating positron-emitting analogs of dopamine (DA) as possible imaging agents for visualizing tissue sympathetic innervation and function, the metabolic fate of systemically injected [3H]-DA or [14C]-DA was compared with that of [3H]-2-fluoroDA in plasma and in sympathetically innervated tissues (left ventricle, spleen and salivary glands) of rats. By 60 min after the injection of [3H]-DA or [3H]-2-fluoroDA, concentrations of [3H]-DA. [3H]-2-fluoroDA, [3H]-norepinephrine ([3H]-NE) and [3H]-2-fluoroNE in tissue exceeded concentrations in plasma by up to several thousand-fold. Whereas most of the radioactivity in tissue was in catechols, radioactivity in plasma was due to O-methylated metabolites of DA, including homovanillic acid (HVA) and of NE, including normetanephrine (NMN) and methoxyhydroxphenylglycol (MHPG). Estimated ratios of tissue: blood radioactivity at 60 min after injection of [3H]-2-fluoroDA were 4.10 for the heart, 1.91 for the spleen and 2.10 for the salivary glands. The patterns of levels of catechol metabolites and analogs of HVA in plasma and effects of blockade of neuronal uptake with desipramine suggested that [3H]-2-fluoroDA was not as efficiently removed by neuronal uptake and not as efficiently beta-hydroxylated as the non-fluorinated compound. Concurrent administration of [3H]-DA and large amounts of non-radioactive 2-fluoroDA did not substantially alter the pattern of metabolites of [3H]-DA in plasma. After injection of [18F]-fluoroDA, visualization of sympathetic innervation of tissue should be feasible by position emission tomography.

Animals↗