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Biomedical subjects

C H Li

Publications and source records attributed to C H Li.

At least 289 records · Page 16Linked to original sources
PubMed1980

beta-Endorphin omission analogs: dissociation of immunoreactivity from other biological activities.

An analog of human beta-endorphine with omission of four residues at positions 11, 14, 20, and 22 has been synthesized. This analog and other synthetic analogs with deletion of a single amino acid at position 2, 5, 6, 10, 11, 12, 13, 15, or 22 have been assayed for analgesic potency, ileal opiate activity,opiate receptor-binding activity, andimmunoreactivity. Results show that deletion of a single amino acid of the beta-endorphin molecule outside of the enkephalin segment to give des-Gln11-, des-Thr12, des-Pro13-, des-Leu14-, des-Val15-, des-Asn20-, or des-Ile22-beta-endorphin markedly reduced or abolished the immunoreactivity yet gave substantial retention of opiate potencies. Deletion of a single amino acid of beta-endorphin within the enkephalin segment (des-Gly3- or des-Met5-beta-endorphin) did not markedly affect the immunoactivity; however, the opiate activities were abolished or markedly reduced. The data indicate a clear dissociation of immunoactivity from analgesic, ileal-opiate, and opiate receptor-binding activities.

Animals↗
PubMed1980

beta-Endorphin: stability, clearance behavior, and entry into the central nervous system after intravenous injection of the tritiated peptide in rats and rabbits.

Rabbits and rats were given intravenous injections of tritiated human beta-endorphin. The levels of beta-endorphin were followed by the decrease in radioactivity in the plasma of rats or rabbits and by the increase in radioactivity in the cerebrospinal fluid of the rabbit. The results were identical with the tritium label on either tyrosine-1 or -27. The plasma distribution times were 2 and 5 min in the rat and rabbit, respectively, with a later clearance time of approximately 1-8 hr. In the rat, approximately 50% of the radioactivity in the plasma was found to be intact human beta-endorphin 45 min after injection. Radioactivity appeared in the cerebrospinal fluid of the rabbit within 30 sec after injection and reached a plateau in approximately 60-90 min after injection. Approximately 75% of the radioactivity in the cerebrospinal fluid of the rabbit was intact human beta-endorphin. In the brain hemispheres of the rat and the rabbit, the only significant radiolabeled product was found to be radioactive tyrosine. Moreover, rat plasma levels of beta-endorphin decreased dramatically after hypophysectomy, which only slightly lowered the levels in the brain. It appears that beta-endorphin, upon entry into the plasma, is either not significantly taken up into the brain or is broken down with extreme rapidity upon entry into the brain, although it apparently does enter the cerebrospinal fluid.

Animals↗
PubMed1980

Peptide inhibitor of morphine- and beta-endorphin-induced analgesia.

The synthetic beta-endorphin analogs with the omission of the NH2-terminal [Met]enkephalin segment [beta-endorphin-(6-31) and beta-endorphin-(20-31)] are shown to inhibit morphine- or beta-endorphin-induced analgesia in mice by the tail-flick test, whereas the synthetic NH2-terminal pentadecapeptide beta-endorphin-(1-15) has no inhibitory activity. This study raises the possibility that endogenous inhibiting peptides exist in the brain which play a role in the regulation of endorphin actions.

Amino Acid Sequence↗
PubMed1980

Isolation and partial characterization of growth hormone from fin whale pituitary glands.

A highly purified somatotropin (growth hormone) has been isolated from fin whale (Balaenoptera physalus) pituitary glands in a yield of 1,014 mg/kg of wet weight tissue. The preparation was shown to be homogenous by isoelectric focusing on polyacrylamide with growth-promoting potency comparable to that of ovine growth hormone by the rat tibia test. The molecular weight was found to be 20,000 daltons by SDS gel electrophoresis and 40,000 daltons by exclusion chromatography on Sephadex G-100 at pH 8.2. The amino acid composition and alpha-helix content of fin whale somatotropin were similar to those of human, bovine, and ovine hormones. The circular dichroism in the side chain region, however, differed from those of the mammalian hormones. The NH2-terminal amino acid sequence was nearly identical with those of the bovine and ovine hormones as determined by the fluorescein isothiocyanate method.

Amino Acids↗
PubMed1980

Synthesis and analgesic activity of human beta-endorphin analogs substituted at positions 17, 18, or 19.

Three peptide analogs of beta-endorphin which are substituted in positions 17, 18 or 19 have been synthesized and their analgesic potencies have been measured by the tail-flick method in mice. The results showed that the replacement of Phe-18 or Lys-19 by alanine reduced the potency to 15% whereas the replacement of Leu-17 by alanine reduced the analgesic potency to 68%.

Amino Acid Sequence↗
PubMed1980

Human beta-endorphin: synthesis and characterization of analogs iodinated and tritiated at tyrosine residues 1 and 27.

Three tritiated analogs of human beta-endorphin have been prepared from their corresponding iodinated analogs. The iodinated analogs (diiodotyrosine at positions 1, 27 or 1 and 27) were synthesized by the solid-phase method and were found to have biological and physical properties which were altered when compared with the native molecule. Catalytic exchange of these iodinated analogs in the presence of tritium yielded tritiated human beta-endorphins having full biological activity and specific activity of 50-100 Ci/mmol. Both the iodinated and tritiated beta-endorphin analogs were shown to be homogeneous by chromatography on carboxymethylcellulose, partition chromatography, paper chromatography, amino acid analysis, electrophoresis, high performance liquid chromatography, and isoelectric focusing on polyacrylamide.

Amino Acid Sequence↗
PubMed1980

Synthesis of human beta-endorphin in solution using benzyl-type side chain protective groups.

A solution synthesis of human beta-endorphin (beta-EP) was carried out by condensation of protected peptide segments bearing N alpha-tert.-butyloxycarbonyl groups and benzyl-derived groups for the protection of functionalities in amino acid side chains. Five intermediate segments were assembled in a stepwise manner starting at the carboxyl terminus. Thus, the segment of sequence region (27-31) was coupled to segment (22-26) by the azide method. Segment (19-21) was incorporated into the growing chain by azide coupling, and segment (10-18) by dicyclohexylcarbodiimide coupling in the presence of 1-hydroxybenzotriazole (DDC-HOBt). Solubility problems in condensing the ensuing 22-peptide with segment (1-9) by DDC-HOBt were overcome by using a dimethylformamidephenol mixture as a solvent. Protecting group cleavage by Na in liquid NH3 was much superior to liquid HF which gave rise to many decomposition products. Homogeneous betah-EP indistinguishable from authentic material in physiochemical and biological properties, was obtained in a single preparative reversed phase liquid chromatographic step after protecting group cleavage.

Amino Acid Sequence↗
PubMed1980

beta-Endorphin: hyperthermia in mice by intravenous injection.

Effects of intravenous beta-endorphin on body temperature and body weight loss were studied in naive and morphine-dependent mice. beta-Endorphin at doses 2.6-25.5 mg/kg injected intravenously caused hyperthermia in naive mice as well as in morphine-dependent mice. In addition, beta-endorphin and morphine reduced body-weight loss during the morphine withdrawal.

Animals↗
PubMed1980

beta-endorphin: synthesis of analogs with extension at the carboxyl terminus with high radioreceptor binding activity.

Four analogs of human beta-endorphin (beta h-EP) have been synthesized: [Gly31]-Beta h-EP-Gly-NH2, [CH3(CH2)4NH231]-beta h-EP, [Gly31]-beta h-EP-Gly-Gly-NH2, and [Gln8, Gly31]-betah-EP-Gly-Gly-NH2. All are more active than beta h-EP in an opiate receptor binding assay. Stepwise extension at the COOH-terminus shows a progressive increase in binding activity. The last analog, which combines extension at the COOH-terminus with elimination of the remaining anionic charge in beta h-EP, is nine times more active than the parent molecule.

Amino Acid Sequence↗
PubMed1980

Isolation and properties of a tryptophan-containing peptide from bovine and turkey brains.

A tryptophan-containing peptide has been isolated from bovine cerebral hemispheres. A similar peptide has also been isolated from the turkey brain. Isoelectric focusing on polyacrylamide gels shows the peptides to be essentially homogeneous. Both peptides consist of 67 amino acids with isoleucine at the COOH-terminus. The NH2-terminal residues cannot be detected by end-group analysis. Both peptides exhibit 45--50% alpha-helix as revealed by circular dichroism spectra.

Amino Acids↗
PubMed1980

Hormone ontogeny in the ovine fetus. X. The effects of beta-endorphin and naloxone on circulating growth hormone, prolactin, and chorionic somatomammotropin.

The potential role of beta-endorphin (beta-EP) as a stimulus to fetal GH, PRL, and chorionic somatomammotropin secretion was investigated in the chronically catheterized ovine fetus. beta-EP (500 microgram/kg, iv) was administered to six fetuses between 84-100 days gestation and to four fetuses between 112-131 days gestation (term, 147 days). The peak incremental GH response of 104.4 +/- 21.1 ng/ml in the younger fetuses was greater (P less than 0.01) than that of the older fetuses (38.0 +/- 11.9 ng/ml). Pretreatment of the fetus with naloxone (100-500 microgram/kg, iv) 5 min before beta-EP reduced (P less than 0.02) the GH response to beta-EP, which suggests that the GH stimulating action of beta-EP was mediated via opiate receptors. Naloxone alone (400 microgram/kg, iv bolus, followed by 400 microgram/kg over 1 h of infusion) had no significant effect on fetal plasma GH. There was no significant change in plasma PRL after beta-EP; however, fetal PRL rose in the three oldest fetuses studied (122, 126, and 131 days). Fetal ovine chorionic somatomammotropin was not altered by either beta-EP or naloxone. The fetal hypothalamic pituitary unit can respond by mid-gestation to exogenous beta-EP with increasing GH secretion. However, in late gestation, the GH responsiveness to beta-EP decreases significantly. It is postulated that this decreased responsiveness is a consequence of the maturation of hypothalamic inhibitory mechanisms regulating GH secretion. The effects of beta-EP on GH and PRL secretion are dissociated in the ovine fetus.

Animals↗
PubMed1980

Intravenous infusion of beta-endorphin increases serum prolactin, but not growth hormone or cortisol, in depressed subjects and withdrawing methadone addicts.

In a randomized, double blind, cross-over study, human beta-endorphin or saline was infused iv over 30 min into six depressed psychiatric patients and four methadone addicts. All depressed subjects showed prompt, 2- to 4-fold increases in serum PRL levels, which lasted at least 2 h. The addicts, who were undergoing acute methadone withdrawal, showed similar PRL increases, which were dose dependent. beta-Endorphin did not increase serum levels of cortisol or GH in either group of subjects. These results suggest that iv beta-endorphin has potent but selective neuroendocrine effects in depressed patients and subjects withdrawing from methadone.

Adult↗
PubMed1980

Growth hormone polypeptides stimulate proliferation of K562 human erythroleukemia cells.

The growth-promoting effect of growth hormones and related polypeptides was examined in vitro with a clonogenic assay using human erythroleukemic cells (K562). The erythroleukemia cells were grown in a serum-substituted methylcellulose culture system and colonies counted after 4 days' incubation. Human growth hormone (hGH) was a potent stimulant for K562 cell growth (60% augmentation). The cys(Cam)53-hGH(1-134) fragment of hGH and human chorionic somatomammotropin had less than half the activity of the intact hGH molecule. Bovine growth hormone was inactive in enhancing K562 colony formation. K562 cell proliferation was stimulated by hGH at concentrations as low as 0.1 ng/ml. Insulin stimulated K562 cell proliferation most effectively at a concentration of 1 ng/ml. The K562 culture system may conveniently be employed for determining the in vitro bioactivity of hGH.

Cell Division↗
PubMed1980

beta-Endorphin: central sites of analgesia, catalepsy and body temperature changes in rats.

beta-Endorphin was microinjected into rat brain in order to localize central sites associated with some of its pharmacologic effects: namely, analgesia (inhibition of the tail-flick response), catalepsy and changes in body temperature. Microinjections (1 microliter) were made bilaterally under halothane anesthesia and the effects of beta-endorphin were repeatedly assessed at 15- or 30-min intervals for 2 hr. beta-Endorphin produced analgesia and catalepsy when it was injected at low doses (ED50, 1.3 to 2.7 micrograms) into the medial preoptic area, nucleus accumbens, anterior hypothalamus and the periaqueductal gray-4th ventricular spaces. Brain areas of intermediate sensitivities (ED50, 3.7 to 16 micrograms) were the medial thalamus, posterior hypothalamus and areas around the fasciculus retroflexus. The frontal cortex, striatum and lateral areas of the brain were relatively insensitive (ED50 greater than 17 micrograms) to the effects of beta-endorphin on analgesia and catalepsy. beta-Endorphin had complex effects on body temperature. For example, when beta-endorphin was injected into the nucleus accumbens or preoptic area, low doses (1.1--2.1 micrograms) produced hyperthermia; higher doses (8.5 micrograms) produced hypothermia. The brain regions in which low doses of beta-endorphin elicit pharmacologic effects correspond to the anatomic areas in which the endogenous beta-endorphin system is distributed. Similar correspondence to the endogenous enkephalin system was not obtained.

Analgesics↗