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Biomedical subjects

H L Chang

Publications and source records attributed to H L Chang.

At least 55 records · Page 3Linked to original sources
PubMed1987

Potent vasopressin antagonists modified at the carboxy-terminal tripeptide tail.

In a continuing effort to design more potent renal vasopressin (V2 receptor) antagonists, we have focused our attention on the carboxy-terminal tripeptide tail (Pro-Arg-Gly-NH2), a fragment common to both agonists and antagonists. Vasopressin antagonist analogues having a dibasic dipeptide tail, e.g., Arg-Arg-NH2 or Arg-Lys-NH2, attached directly to the cyclic hexapeptide ring are potent V2-receptor antagonists. Similar modification of a representative agonist drastically reduces its potency. We report the synthesis and pharmacological properties of a series of potent V2-receptor antagonists 3-9 where a combination of D or L dibasic dipeptide has been utilized to replace the common tripeptide fragment. Our results suggest a difference in the way agonists and antagonists bind to vasopressin receptor and further support the difference in the structure-activity relationships of agonists and antagonists. These results provide potentially useful insights for the design of novel V2-receptor antagonists.

Animals↗
PubMed1986

Potent vasopressin antagonists lacking the proline residue at position 7.

As part of a program to design potent antidiuretic vasopressin antagonists and to define the minimum effective pharmacophore requirements for vasopressin (VP) antagonist activity, we studied the importance of the C-terminal tripeptide of a previously reported peptide antagonist of arginine-vasopressin (AVP,1). The proline residue at position 7 in AVP is proposed to impart a conformational constraint to the peptide backbone that is essential for V2-receptor agonist activity. Since the structure-activity relationships for VP agonists and antagonists are different, we investigated the effect of proline on antagonist activity, by synthesizing analogue 3 lacking this residue. This analogue was found to retain a high degree of antidiuretic antagonist activity. Since deletion of the Gly residue at position 9 of the antagonist did not adversely affect VP antagonist potency, several vasopressin antagonist analogues (4-7 and 9) that lacked both the Pro and Gly residues were also studied. These, too, were found to block vasopressin V2-receptor activity. Our results indicate that neither the proline nor glycine residues are essential for antagonism of the V2 receptor.

Animals↗
PubMed1983

Changes of the Met-enkephalin-like peptide content induced by noxious stimuli in the rat incisor pulp.

It was examined what mechanism involved in an increase of met-enkephalin (met-EK)-like peptide content in the pulp induced by noxious stimuli. The increased content of the peptides by cavity formation as noxious stimulation was not influenced by cycloheximide, but attenuated by FOY-305 [N,N-dimethyl carbamoyl-methyl 4-(4-guanidinobenzoyloxy) phenyl acetate methanesulfonate], a trypsin-like enzyme inhibitor, and enhanced by captopril, and attenuated by infusion of saline in the pulp cavity. From these results, it was suggested that noxious stimuli on the pulp led to activation of trypsin-like enzymes followed by an increased content of met-EK-like peptides, and thereafter, the peptides, such as met-EK, might be degraded by angiotensin converting enzyme (ACE). Furthermore, an immunohistochemical study demonstrated that met-EK-like immunoreactivity (met-EK-IR) of cells in the rat incisor pulp was clearly increased following tryptic digestion of the pulp section, supporting a suggestion mentioned above.

Animals↗
PubMed1983

A possible relationship between processing from precursor proteins to opioid peptides and noxious stimulation in the rat incisor pulp.

The content of met-enkephalin (met-EK)-like peptides in a crude extract from intact pulp of the rat markedly increased with tryptic digestion but not with carboxypeptidase B(CPase B) digestion, while the content of leu-enkephalin (leu-EK)-like peptides more markedly with CPase B- than with tryptic digestion. On the other hand, results by High Performance Liquid Chromatography (HPLC) showed that the contents of both met-EK-Arg-Phe and leu-EK in cavity formed pulp increased 6 times as much as those contents in intact pulp, while the met-EK content in cavity formed pulp increased 2 times as much as that in intact pulp. Furthermore, results by gel filtration of crude extract from intact pulp showed that one peak of met-EK-like immunoreactivity (met-EK-IR) appeared at position of approximately 30,000 of molecular weight and a broad peak of leu-EK-IR appeared at position of approximately 60,000 of molecular weight following tryptic digestion. From these results, it was suggested that noxious stimuli might cause activation of trypsin-like enzymes followed by processing from one precursor protein to met-EK-like peptides as well as from another to leu-EK-like peptides in the rat incisor pulps.

Animals↗
PubMed1983

Rapid high pressure liquid chromatographic determination of aflatoxin M1 in milk and nonfat dry milk.

A modification of the current revised AOAC method, 26.A10-26.A15, is described for the rapid analysis of aflatoxin M1 in milk and nonfat dry milk. The method incorporates chloroform extraction and eliminates the need for column chromatography by using liquid-liquid partition for sample extract cleanup. Quantitation is carried out by using fluorescence detection combined with high pressure liquid chromatography (HPLC) of aflatoxin M1 which has been converted to aflatoxin M2a with trifluoroacetic acid. The method has a detection limit of 0.014 micrograms/L (2 X signal/noise) for whole milk. For 6 samples of naturally contaminated nonfat dry and freeze-dried milk, the modified method gave an average result of 0.698 micrograms/L; the AOAC method gave an average result of 0.386 micrograms/L.

Aflatoxin M1↗
PubMed1982

Comparison of rapid high pressure liquid chromatographic and CB methods for determination of aflatoxins in corn and peanuts.

A method is described for the rapid determination of aflatoxins in corn and peanut samples by high pressure liquid chromatography. The method was compared with the current CB method (AOAC 26.026). For 7 samples of corn and 14 samples of peanut meal and peanut butter, the correlation between methods is 0.991, and no significant difference exist between methods, using the Student's t-test at 15.7% alpha-risk.

Aflatoxins↗
PubMed1979

Distribution of the multiple molecular forms of glucose-6-phosphate dehydrogenase in different physiological states.

The distribution of the multiple molecular forms of rat liver and mammary gland glucose-6-phosphate dehydrogenase was determined by electrophoresis on 5% polyacrylamide gels. In both of these organs, changes in the distribution of enzyme activity among the several forms was slight even when approximately 20- to 40-fold changes in enzyme specific activity were achieved by fasting-refeeding experiments (for liver) or during pregnancy and lactation (for mammary gland). It was concluded that the induction of glucose-6-phosphate dehydrogenase in these two organs occurs without any major redistribution among the multiple molecular forms of this enzyme.

Animals↗