Search PubMed⌕ Search

Biomedical subjects

J S Chan

Publications and source records attributed to J S Chan.

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

Metabolic clearance rate and half-time disappearance rate of human N-terminal and adrenocorticotropin of pro-opiomelanocortin in the rat: a comparative study.

In metabolic clearance rate (MCR) and plasma half-time disappearance rate (t 1/2) of human N-terminal (1-76) and adrenocorticotropin(hACTH 1-39) of pro-opiomelanocortin were compared after intravenous bolus injection of both peptides simultaneously into rat. The level of immunoreactive (IR) hNT and IR-ACTH in plasma and urine samples were measured by specific and homologous radioimmunoassays (RIAs). The MCR and hNT and hACTH were 3.01 +/- 0.20 ml/min (M +/- S.D., N = 4) and 2.04 +/- 0.06 ml/min, respectively (p less than 0.05), The curve for the disappearance rate of IR-hNT was triphasic (rapid t 1/2 = 0.96 +/- 0.39 min, intermediate t 1/2 = 6.7 +/- 2.25 min, and slow t 1/2 = 74 +/- 15.8 min), while that of IR-ACTH was biphasic (rapid t 1/2 = 3.3 +/- 0.68 min, and slow t 1/2 = 41.5 +/- 3.03 min) as analyzed by the non-linear least-squares methods. Statistically significant difference (p less than 0.01) was found between IR-hNT and IR-hACTH in the rapid t 1/2 and in the slow t 1/2. Subsequent analysis of pooled plasma sample (30 min post-injection) by molecular sieve chromatography on Sephadex G-50 superfine column revealed that the majority of IR-hNT (90-95%) and IR-ACTH (60-70%) are co-chromatographed with [125I]iodo hNT and [125I]iodo ACTH respectively. Similarly, gel filtration of pooled urine sample (120 min post-injection) on Sephadex G-50 superfine revealed that 80-90% of IR-hNT and less than 50% of IR-ACTH co-eluted with [125I]iodo hNT and [125I]iodo ACTH, respectively. Smaller molecular forms of IR-hNT and IR-ACTH were definitely apparent in the urine sample. In conclusion, hNT has a larger MCR and a longer half-time disappearance rate (t 1/2) than IR-hACTH in rat plasma and it appears that hNT is more resistant to degradation by plasma and by kidney than hACTH.

Adrenocorticotropic Hormone↗
PubMed1983

Enzymatic maturation of pro-opiomelanocortin by anterior pituitary granules. Methodological approach leading to definite characterization of cleavage sites by means of high-performance liquid chromatography and microsequencing.

The coupling of high-performance liquid chromatography, gel-permeation, and reversed-phase chromatography with microsequencing proved to be advantageous for the unambiguous determination of specific sites in pro-opiomelanocortin, cleaved by secretory granule lysates of pig anterior pituitary. This system allows the unambiguous identification of a major chymotrypsin-like enzyme activity, optimal at pH 8.0, in the granule preparation, with a specificity directed towards some Phe decreases X and Tyr decreases X cleavage sites. The approach used emphasizes the necessity to use methodologies leading to the unambiguous determination of conversion activities.

Amino Acid Sequence↗
PubMed1983

Chronic ethanol treatment alters the biosynthesis of beta-endorphin by the rat neurointermediate lobe.

Tolerance to ethanol was induced in male Sprague-Dawley rats (225-250 g) by chronic feeding with a liquid diet containing 6.5% ethanol (v/v). Control rats were pair-fed with a liquid diet in which the ethanol was replaced by an equicaloric concentration of sucrose. Immediately following sacrifice of the animals the neurointermediate lobes (NIL) were removed and incubated with [3H]phenylalanine. The biosynthesized proopiomelanocortin (POMC), beta-lipotropin (beta-LPH), and beta-endorphin (beta-EP) were purified by immunoprecipitation with an antiserum to beta-EP and analyzed by sodium dodecyl sulfate polyacrylamide disc gel electrophoresis. Alcohol treatment for 3 days had no effect on the degree of incorporation of [3H]phenylalanine into POMC, beta-LPH, and beta-EP but treatment for either 15 or 21 days increased the incorporation of [3H]phenylalanine into all three peptides. Ethanol treatment also increased the beta-endorphinlike immunoreactivity (beta-EPLIR) found in the incubation medium, but no significant change was observed in the beta-EPLIR extracted from the NIL either immediately after sacrifice or after 3 h of incubation of the NIL. However, a significant decrease of beta-EPLIR was found in the anterior lobes of rats treated with ethanol for 21 days. Furthermore, the beta-EPLIR in the serum of alcohol-treated rats was significantly higher than in the serum of their corresponding controls. These results indicate an effect of ethanol on the endorphin system and are consistent with the suggestion that endorphins may be mediators of some of the ethanol effects.

Animals↗
PubMed1983

Human NH2 terminal of pro-opiomelanocortin as a potential marker for pulmonary carcinoma.

Levels of immunoreactive (IR) human NH2 terminal (HNT) of pro-opiomelanocortin were determined serially in 80 patients with various pulmonary carcinomas, 20 patients with various pulmonary diseases without proven carcinoma, and 32 normal control subjects. Sixty +/- 14% (S.E.) (95% confidence interval) of the patients with proven pulmonary carcinoma had elevated values of IR HNT in plasma (greater than 100 pg/ml); the highest frequency of elevated IR HNT was found in patients with small-cell carcinoma [74 +/- 14.5% (95% confidence interval)]. In eight patients with pulmonary tumor who underwent surgical thoracic exploration, the plasma level of IR HNT in the pulmonary vein was 50.6 +/- 21.4% (95% confidence interval; N = 8) higher than that in the pulmonary artery. The levels of IR HNT correlated well with those of plasma adrenocorticotropic hormone (IR ACTH) (r = 0.988; p less than 0.001); however, the level of IR HNT was 3- to 4-fold higher than that of IR ACTH. Gel permeation chromatography of plasma of patients with pulmonary carcinoma revealed a major peak of IR HNT coinciding with the elution volumes of authentic HNT (Mr 12,000) and a minor peak of IR HNT near the void volumes. These results suggest that HNT originating from pulmonary carcinoma is chemically and immunologically similar to that from human pituitary gland and that measurement of plasma IR HNT may indicate the state of secretion and/or metabolism of peptides related to the expression of the pro-opiomelanocortin gene in human pulmonary carcinoma. The HNT immunoassay is a simple procedure which, contrary to that of ACTH, does not require plasma extraction prior to the assay. This suggests the possibility that measurement of IR HNT alone and in conjunction with other biochemical markers could be a useful parameter for diagnosis and follow-up of patients with pulmonary carcinoma.

Adenocarcinoma↗
PubMed1982

Corticotropin releasing factor (CRF): effects on the release of pro-opiomelanocortin (POMC)-related peptides by human anterior pituitary cells in vitro.

The effect of synthetic ovine corticotropin-releasing factor (oCRF), alpha-melanotropin (alpha-MSH) and arginine-vasopressin (AVP) on the release of pro-opiomelanocortin (POMC)-related peptides (beta-endorphin, beta-lipotropin, adrenocorticotropin, and the 12K N-terminal) was studied in primary cultures of human anterior pituitary (HAP) cells. The peptides released into the medium were measured by specific radioimmunoassays. HAP cells responded to oCRF at concentrations as low as 10 ng/ml by significantly increasing peptide secretion (p less than 0.005). AVP was also effective, but, it is only 0.1% as potent as oCRF. alpha-MSH was ineffective even at a dose of 10 micrograms/ml. Immunoreactive (IR)-beta EP, IR-beta LPH, IR-ACTH, and IR-HNT were released in approximately equimolar ratios. Partial characterization of the peptides released by HAP cells with gel chromatography on Sephadex G-50 superfine revealed two peaks of IR-beta EP (as beta EP and beta-LPH), two peaks of IR-beta LPH (as beta-LPH and gamma-LPH), one peak of IR-ACTH, and two peaks of IR-HNT. In conclusion, oCRF is a potent secretagogue for the equimolar release of ACTH, HNT and related peptides in the human pituitary gland.

Adrenocorticotropic Hormone↗
PubMed1982

The cellular localization of chorionic somatomammotrophin in ovine chorion.

Sections of Days 12 to 55 sheep chorion, embedded at low temperature in glycol methacrylate, were exposed to rabbit anti-ovine chorionic somatomammotrophin (oCS) to ascertain the distribution of oCS. This hormone was first detectable on Day 14, when the cytoplasm of each chorionic cell displayed a low level of fluorescence surrounding droplets which were shown to be lipid containing. At this time, all chorionic cells were uninucleate. By Day 28, binucleate chorionic cells had appeared but showed no binding of the oCS antiserum which was confined to a significant proportion of the uninucleate chorionic cells surrounding lipid droplets, as at Day 14. The same pattern of hormone distribution, although with reduced fluorescence intensity, was observed on Day 55; fluorescence indicative of antibody binding was seen only in some of the uninucleate chorionic cells. Hence, oCS was detected in chorionic tissue before the differentiation of binucleate cells (Day 14) and, at all stages, it was confined to the cytoplasm of specific uninucleate chorionic cells in close association with lipid droplets.

Animals↗
PubMed1981

Detection from rat pituitary of beta-lipotropin and materials containing opiatelike activity by combined enzymatic radioreceptor assay.

Tonin, a proteolytic enzyme isolated from rat submaxillary gland, was allowed to react upon ovine beta-lipotropin (beta-LPH) at 37 degrees C at a variety of pH values and for different lengths of time. Opiatelike activity generated by the reaction was assessed using a radioreceptor assay for beta-endorphin with rat brain homogenate. [3H]naloxone, and beta-endorphin as receptors, tracer, and hormone standard, respectively. Cleavage of beta-LPH with tonin produced a 10-fold increase in opiatelike activity as compared with beta-LPH alone. Digestion of beta-LPH with other enzymes such as renin, cathepsin D, trypsin, and chymotrypsin produced much less opiatelike activity. beta-Endorphin and methionine-enkephalin were not cleaved by tonin. Using this new assay, we were able to detect beta-LPH and materials containing opiatelike activity from rat pituitary extracts after gel chromatography. It is more specific and more sensitive than trypsin digest.

Animals↗
PubMed1980

Chemical characterization of adrenocorticotropin and a novel peptide biosynthesized from a pituitary adenoma of a patient with Cushing's disease.

ACTH and another unidentified peptide have been biosynthesized in vitro and purified from a pituitary adenoma of a patient with Cushing's disease. The new peptide had an apparent molecular weightof 4000 daltons and was more acidic than ACTH as analyzed by sodium dodecyl sulfate/urea and acidic (pH 4.5) polyacrylamide gel electrophoreses, respectively. Sequence studies revealed the presence of [35S]methionine at position 3 of the new peptide. High performance liquid chromatographic analysis of [35S]methionine-labeled tryptic fragments of the peptide revealed that this peptide contained gamma MSH- (1-7) within its sequence. Our observations raise the possibility that this peptide contains at its N-terminus gamma MSH, a putative peptide proposed by Nakanishi et al.

Adenoma↗
PubMed1980

Concentrations of placental lactogen in chronically catheterized ewes and fetuses in late pregnancy.

The concentration of ovine placental lactogen (oPL) was measured by radioimmunoassay in plasma samples from chronically catheterized ewes and their fetuses from day 110 of gestation to term (about day 145). Concentrations of oPL in the plasma of the mother and fetus were raised after surgery, and remained raised for 3--5 days after the operation. Concentrations of oPL were greatest in the fetus at days 120--124 of gestation, and then declined until delivery. Mean concentrations of oPL in the fetus in late pregnancy for single, twin and triplet pregnancies were 101 +/- 6 (S.E.M.), 100 +/- 11 and 115 +/- 59 ng/ml respectively and were not significantly different. Mean concentrations of oPL in the mother in late pregnancy for single, twin and triplet pregnancies were 718 +/- 227, 1387 +/- 160 and 1510 +/- 459 ng/ml respectively; the difference between these means was significant (P less than 0.05). Peak concentrations were noted at days 130--139 of gestation after which concentrations fell and were significantly lower on the day of delivery (P less than 0.01). Concentration of oPL in the mother showed no circadian rhythm. The mean concentrations of oPL in maternal plasma during late pregnancy was significantly correlated to the combined fetal weight at birth (r = 0.624, P less than 0.01).

Animals↗
PubMed1978

Maternal and fetal concentrations of ovine placental lactogen measured by radioimmunoassay.

A specific and sensitive homologous RIA for ovine placental lactogen (oPL) has been developed. The assay is specific for oPL in that ovine pituitary PRL (oPRL), GH (oGH), and other pituitary hormones, as well as rat, caprine, bovine, monkey, and human PLs exhibit no cross-reaction in the assay. The lower limit of sensitivity of the assay is 1.0 ng/ml. In uterine vein samples oPL was measurable after day 40 of gestation and in peripheral sera after day 48 (3.5 +/- 1.9 ng/ml). Peripheral plasma oPL concentrations reached peak levels by day 131--141 (649 +/- 205--565 +/- 347 ng/ml), then began to decline approximately 5 days before parturition and disappeared rapidly after delivery. No significant circadian variation in serum oPL concentrations was found during a 4-day period of sampling from day 120--125 of gestation. Fetal serum oPL levels ranged from 24--150 ng/ml throughout pregnancy. oPL was measurable in fetal membranes as early as day 20--30 (0.21 +/- 0.06 microgram/g wet wt), whereas the concentration in maternal caruncles at this time was 0.1 +/- 0.06 microgram/g wet wt. In the placentomes, peak concentrations occurred around day 101--130. Peak concentrations of oPL in allantoic fluid were found between day 35--50, with detectable levels as early as day 18. In amniotic fluid, oPL was measurable between day 40--50. Concentrations of oPL in urine from the pregnant ewe never exceeded 5 ng/ml.

Allantois↗
PubMed1976

The purification and characterization of ovine placental lactogen.

Ovine placental lactogen (oPL), has been purified approximately 1,000-fold from sheep cotyledons using conventional protein purification procedures. Radioreceptor assays using rabbit liver particulate fractions for growth hormone (RRA-GH) and using rabbit mammary gland particulate fractions for prolactin (RRA-PRL) were employed to monitor the hormonal activities. The molecular weight of oPL is approximately 22,000 as determined by gel filtration on Sephadex G-100, and its isoelectric point as determined by isoelectric focusing is 8.8. In the two RRA's, the displacement curve of oPL is parallel to bovine growth hormone (bGH) and ovine prolactin (oPRL) standards and the ratio of GH-activity to PRL-activity of oPL is 1:2. In a body weight gain assay using hypophysectomized rats, oPL has a growth-promoting potency of 1.3 U/mg. In rabbit mammary explants, oPL stimulates casein synthesis. In a receptor assay for growth hormone using human liver, oPL and hGH are equipotent in competing for receptor sites, suggesting that oPL and hGH have common structural features that are lacking in other non-primate hormones.

Animals↗