Search PubMed⌕ Search

Biomedical subjects

C H Li

Publications and source records attributed to C H Li.

At least 181 records · Page 10Linked to original sources
PubMed1984

The response of plasma arginine vasopressin to 14 h water deprivation in the elderly.

The response of plasma arginine vasopressin (AVP) to 14 h water deprivation was investigated in 30 healthy elderly individuals ranging in age from 63 to 87 years, with a mean age of 76.5 years. The mean AVP concentrations, both at normal hydration and after the water deprivation test, were significantly lower than those in the young. Moreover, the post-test mean value of Uosm/Posm in the elderly increased up to 1.55 +/- 0.52, which is lower than that in the young in whom the value was greater than 2. These results suggest that the aged are prone to incomplete diabetes insipidus. This pathological state might predispose to electrolyte imbalance in the elderly.

Age Factors↗
PubMed1984

Two cases of hereditary diabetes insipidus, with an autopsy finding in one.

Two cases of hereditary diabetes insipidus (DI) are described, with an autopsy finding in one. The patients were brothers and 7 other relatives had symptoms of DI. The transmission of the disease in this family seemed to be an autosomal dominant trait with incomplete penetration. Both patients had the incomplete type of DI, which is diagnosed by the response of plasma AVP and the change in Uosm/Posm to 14 h water deprivation. The post-mortem examination in Case 1 showed that there was no atrophy of the supraoptic nucleus and paraventricular nucleus, but immunohistochemical studies revealed, that the paraventricular nucleus scarcely had any vasopressin positive cells in contrast to an autopsy control. This finding suggests that there may be a congenital defect in AVP synthesis in some cases of hereditary DI.

Adult↗
PubMed1984

Development and characterization of a homologous radioimmunoassay for equine prolactin.

A specific and sensitive homologous radioimmunoassay has been developed for equine prolactin, suitable for measuring prolactin concentrations in serum of horses. The sensitivity of the assay ranged from 0.4 to 0.6 ng/ml and the intra- and inter-assay coefficients of variation averaged 6.9 and 15.4%, respectively, for five doses of hormone. Cross-reactivity with other mammalian and nonmammalian prolactins and growth hormones was less than 20 and 0.3%, respectively. Cross-reactivity with equine growth hormone was less than 0.07%. Equine serum and pituitary extracts showed parallel dilution-response curves with equine prolactin. The percentage recovery of exogenous equine prolactin in serum was 89%. Preliminary analysis of several physiological samples (stallions, pregnant, and nonpregnant mares) yielded values from 0.6 to 12.0 ng/ml.

Animals↗
PubMed1984

Structural requirements and species specificity of the inhibition by beta-endorphin of heavy acetylcholinesterase from vertebrate skeletal muscle.

The molecular forms of acetylcholinesterase in extracts of gastrocnemius muscle from four vertebrate species and in electric eel (Electrophorus) electric organ were separated and identified by low-salt precipitation and velocity sedimentation. The activity of the heavy insoluble (A12) form of human muscle acetylcholinesterase was inhibited by synthetic human beta-endorphin (500 mM). The homologous form in rat muscle extracts was poorly inhibited by human beta-endorphin at the same concentration, but was more effectively inhibited by camel beta-endorphin. The activities of heavy forms of pseudocholinesterase, present in small amounts in both species, were not reduced by beta-endorphin. Selective inhibition of homologous heavy forms of acetylcholinesterase activity by camel and human beta-endorphin was also seen in skeletal muscle extracts from frog and pigeon, but with decreased effectiveness. No inhibition was detectable in the heavy acetylcholinesterase form from extracts of electric organ tissue of the electric eel. The inhibition of heavy acetylcholinesterase activity in human muscle by human beta-endorphin was dependent on the presence of its NH2-terminal pentapeptide sequence. Maximal inhibitory potency depended on the presence of the entire amino acid sequence, since potency was considerably reduced in synthetic peptide analogues lacking either middle or COOH-terminal segments of beta-endorphin. The relative potency of beta-endorphin from various species as inhibitors of rat heavy acetylcholinesterase activity was also investigated. beta-Endorphin sequences most closely resembling that of the rat peptide (camel, equine) were most potent, whereas those with sequence differences of more than one amino-acid were less potent (turkey, human) or had no inhibitory activity (ostrich). The selective inhibition of heavy acetylcholinesterase by beta-endorphin thus exhibits species specificity, even among mammals, in which homologues of this molecular form of the enzyme are otherwise indistinguishable.

Acetylcholinesterase↗
PubMed1984

Human beta-endorphin. Synthesis and biological activity of analogs with modifications in residue positions 3, 4 or 5.

Three analogs of human beta-endorphin (beta h-EP) have been synthesized by the solid-phase method: [Phe2, Gly4]-beta h-EP(I), [Tyr5]-beta h-EP (II), and [Trp5[-beta h-ET (III). Analogs I and II are related to the highly potent hybrid analog [dermorphin1-7]-beta c-EP (beta c-EP). Radio-receptor-binding and analgesic assays gave relative potencies as follows, respectively: beta h-FP, 100, 100; I, 51, 43; II, 64, 30; III, 15, 4. The high potency of [dermorphin 1-7]-beta c-EP is not due to any one of the following structural elements: D-Ala2, Phe3-Gly4, Tyr5, and Pro6. Increasing hydrophobicity in position 5 (Met in beta-EP) leads to decreasing biological activity.

Amino Acid Sequence↗
PubMed1984

Human beta-endorphin. Synthesis and biological activity of analogs with modification in residue positions 8, 27, and 9 or 11.

Three analogs of human beta-endorphin (beta h-ER) were synthesized by the solid-phase method: [Gln8,Trp27]-beta h-EP (I), [Gln8,Arg9,Trp27]-beta h-EP (II), and [Gln9,Arg11,Trp27]-beta h-EP (III). Radioreceptor binding assay with use of tritiated beta h-EP as primary ligand gave relative potencies as follows: beta h-EP, 100;I, 778;II, 467;III, 449. Relative potencies in an analgesic assay were: beta h-EP, 100;I, 114;II, 165;III, 83. The 8-11 segment of beta h-EP can tolerate a net increase in charge of +2 without diminishing analgesic potency. The substitution of Glu8 may be one of the more dependable means of designing beta-endorphin antagonists.

Amino Acid Sequence↗
PubMed1984

Beta-endorphin. Binding activity of synthetic analogs with various chain lengths in neuroblastoma x glioma NG108-15 cell membranes.

Inhibition of binding of beta h-endorphin or Leu-enkephalin by beta h-endorphin analogs of various chain lengths in memmbrane preparations of the neuroblastoma x glioma NG108-15 cells has been investigated. The removal of even a single residue from the C-terminus results in the inability of the resulting peptide to completely displace beta h-endorphin. In addition, the proportion of nondisplaceable binding increases with decreasing chain length.

Animals↗
PubMed1983

Peptide E: opiate receptor binding profile in the rat brain membrane assay. Comparison with beta-endorphin.

Beta-endorphin (beta-EP) and peptide E were compared in respect to their binding potency in the rat brain membrane by radioreceptor binding assay using tritiated human beta-EP, [D-Ala2,D-Leu5]-enkephalin (DADLE), dihydromorphine (DHM) and ethylketocyclazocine (EKC) as primary ligands. When the potency of beta h-EP was chosen to be 100%, peptide E was equipotent with beta-EP in displacing DHM (95%) and EKC (103%) less potent for competing with beta h-EP (60%) and least active (7%) for displacing DADLE. It may be concluded that peptide E binds preferentially with the opiate mu and kappa receptors in the rat brain membrane.

Animals↗
PubMed1983

Evidence for tertiary structure in aqueous solutions of human beta-endorphin as shown by difference absorption spectroscopy.

The presence of a distinct tertiary structure in aqueous solutions of human beta-endorphin has been demonstrated by difference absorption spectroscopy of thermolysin digests of the hormone and synthetic analogues. The results demonstrate that the alpha-amino group of Tyr1, Lys28, and some residue(s) between Thr6 and Ser10 are involved in forming and stabilizing the folded form of the molecule. Although a peptide corresponding to the first nine residues of human beta-endorphin shows definite evidence of tertiary structure, the pentapeptide methionine-enkephalin does not.

Amino Acid Sequence↗
PubMed1983

beta-endorphin: characteristics of binding sites in the rabbit cerebellar and brain membranes.

Specific binding of human beta-endorphin to rabbit cerebellar and brain membranes was measured using [3H2-Tyr27]-beta h-endorphin as the primary ligand. In both tissues binding was time dependent and saturable, with apparent equilibrium dissociation constants of 0.275 nM and 0.449 nM in the cerebellum and brain, respectively. The binding capacity of cerebellum is greater than that of brain. Kinetic studies showed that the association rate constants were 2.7 X 10(7) M-1min-1 for cerebellum and 2.4 X 10(7) M-1min-1 for brain. Dissociation of tritiated beta h-endorphin from both cerebellum and brain is not consistent with a first order decay from a single site. In the cerebellum there is a time-dependent increase in slowly dissociating complex. The potency of several opioid peptides and opiates to inhibit the binding of tritiated beta h-endorphin was determined. Ligands with preference for mu, delta, and kappa opiate receptor (morphine, Metenkephalin and ethylketocyclazocine) all have similar affinities toward beta h-endorphin sites in both brain and cerebellar membranes.

Animals↗
PubMed1983

beta-Endorphin: characteristics of binding sites in the mouse brain.

Binding of human beta-endorphin to mouse brain membrane preparations has been characterized using the tritiated hormone as primary ligand. The binding was shown to be time and temperature dependent. The dissociation constant of the saturable binding was determined to be 0.5 nM. Both [Met5]enkephalin and naloxone were found to compete with tritiated beta-endorphin for the binding with a potency of 6.3 and 6.5% of the unlabeled hormone, respectively. Phospholipase A2 isolated from Formosan cobra venom was shown to be a potent inhibitor of the binding with a 50% inhibition concentration of 26 nM. Although Na+, K+, Ca2+, Mg2+ were found individually to exert a profound inhibition on the binding, the combined salt solution (Tyrode) did not abolish the specific binding of tritiated beta-endorphin to the mouse brain membrane preparations.

Animals↗
PubMed1983

Beta-endorphin and the endocrine pancreas. Studies in healthy and diabetic human beings.

Beta-endorphin is present in the endocrine pancreas, suggesting that endorphins may have a role in islet-cell function. To evaluate this possibility, we infused synthetic human beta-endorphin intravenously in healthy volunteers and in insulin-dependent diabetic patients. In both groups, beta-endorphin increased plasma glucagon concentrations, and this rise was accompanied by a significant increase in plasma glucose concentrations. In nondiabetic subjects, beta-endorphin also increased plasma insulin concentrations. The threshold dose of beta-endorphin for producing increased plasma concentrations of glucose and glucagon was 0.005 mg--a dose that acutely increased plasma concentrations of beta-endorphin by approximately 40-fold. Glucose, glucagon, and insulin responses to beta-endorphin could not be blocked by intravenous naloxone. These studies suggest that endorphins may be involved in gluco-regulation, that their hyperglycemic action is mediated at least in part by glucagon, and that the effect of beta-endorphin on islet-cell function is relatively resistant to naloxone.

Adult↗
PubMed1983

Synthesis of adrenal peptide E and some of its biological activities.

A synthesis of peptide E, a highly potent, 25-amino acid adrenal opioid peptide containing both a [Met]enkephalin at the NH2-terminus and [Leu]enkephalin sequence at the COOH-terminus, originally isolated from bovine adrenal medulla [D. L. Kilpatrick, T. Taniguchi, B. N. Jones, A. S. Stern, J. E. Shively, J. Hullihan, S. Kimura, S. Stein, and S. Udenfriend (1981) Proc. Natl. Acad. Sci. USA 78, 3265-3268], is reported. The synthesis was accomplished by the solid-phase method employing the 4-(aminoacyloxymethyl)phenylacetamidomethyl(Pam)-copoly(styrene-1% divinylbenzene) resin. Two synthetic strategies (N-indole formyl protected vs unprotected tryptophan) were followed and results compared and evaluated. It was determined that peptide E prepared with protection of tryptophan (residues 13 and 14) was preferred and gave final product that was readily purified by HPLC. The biological activity of the synthetic material was found to be equivalent to the reported activity of the natural compound.

Amino Acid Sequence↗
PubMed1983

Studies on prolactin 48: isolation and properties of the hormone from horse pituitary glands.

Isolation of prolactin from equine pituitary glands has been described. It has a potency of 42 IU/mg in the pigeon crop-sac test and consists of 199 amino acids. The hormone has only four half-cystine residues in contrast to other mammalian prolactins which have six residues. From NH2-terminal sequence analysis and amino acid composition of cyanogen bromide fragments, the NH2-terminal disulfide loop is missing in the equine prolactin molecule. Circular dichroism spectra indicate that the alpha-helical content of equine prolactin appears to be lower (50%) than that found in the ovine hormone (65%).

Amino Acids↗