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Biomedical subjects

C H Li

Publications and source records attributed to C H Li.

At least 307 records · Page 17Linked to original sources
PubMed1980

beta-Endorphin: radioreceptor binding assay. Relative potency of synthetic analogs with various chain lengths.

An assay system is described to measure the specific binding of beta-endorphin to opiate sites (receptors) in rat brain membrane preparations using the tritiated hormone as the primary ligand. By this assay procedure, the radioreceptor activity of beta-endorphin and synthetic analogs with various chain lengths has been determined. The results suggest that both NH2- and COOH-terminal sequences of the molecule are involved in the interaction of beta-endorphin with opiate receptors.

Animals↗
PubMed1979

Studies on prolactin. Selective reduction of the disulfide bonds of the ovine hormone.

Methods for selective reduction of the disulfide bonds in ovine prolactin are reported. Cleavage of all three disulfide bonds abolishes biological activity and denatures the hormone. Reduction-carbamidomethylation of one or two of the disulfide bridges does not diminish the biological activities in the pigeon crop-sac and mouse mammary gland bioassays. When compared to the native hormone, monomers of these two partially reduced-carbamidomethylated derivatives also show only modest changes in properties measured by exclusion chromatography, circular dichroism, and immunological cross-reactivities. However, cleavage of cystine-4--11 and cystine-191--199, followed by carbamidomethylation, destroys the biological activity of this derivative in a teleost fish bioassay (Gillichthys urinary bladder). In contrast, reduction of cystine-4--11 actually increased the teleost potency of this derivative compared to the intact hormone. Since teleost prolactin appears to lack a homologue to the cystine-4--11 disulfide bond in the amino-terminal loop of the ovine hormone, selective reduction of this bond in ovine prolactin may produce a derivative whose properties more closely resemble the fish hormone.

Amino Acid Sequence↗
PubMed1979

Effect of beta-endorphin on calcium uptake in the brain.

The uptake of 45Ca2+ by nerve-ending fractions from brains of mice was inhibited in vitro by 10(-9)M concentrations of beta-endorphin and in mice injected intraventricularly with 7 picomoles of beta-endorphin. That the effect was a specific opiate agonist response of beta-endorphin was demonstrated by use of the opiate antagonist, naloxone, which reversed the action. A role for beta-endorphin in the regulation of calcium flux and neurotransmitter release should be considered.

Animals↗
PubMed1979

Behavioral activities of opioid peptides and morphine sulfate in golden hamsters and rats.

The behavioral effects of beta-endorphin, [D-Ala2, D-Leu5]-enkephalin and morphine were investigated in golden hamsters and in rats. In golden hamsters, beta-endorphin and [D-Ala2, D-Leu5]-enkephalin induced loss of righting reflex, whereas morphine caused no such effect. Both opiate peptides and morphine caused the inhibition of tail-flick response and catalepsy in rats. beta-Endorphin was the most potent, followed by [D-Ala2, D-Leu5]-enkephalin and then by morphine. The catalepsy induced in rats by [D-Ala2, D-Leu5]-enkephalin was different from that of beta-endorphin and morphine in that it produced catalepsy without muscular rigidity. beta-Endorphin and [D-Ala2, D-Leu5]-enkephalin caused hypothermia in golden hamsters; morphine was less active in altering the body temperature. beta-Endorphin caused hypothermia at high doses and hyperthermia at low doses in rats. These heterogenous behavioral responses indicate that multiple types of receptors mediate the effects of opiates in the central nervous system.

Animals↗
PubMed1979

Human EEG response to beta-endorphin.

Beta-endorphin, morphine, and saline were given intravenously to a single schizophrenic subject on separate occasions in a double-blind design. EEG spectral analyses performed on data collected before and after drug injection demonstrated that beta-endorphin and morphine produced similar increases in alpha power within 5 to 15 minutes after injection. This effect could be distinguished from two placebo (saline) injections. These data suggest that intravenous beta-endorphin can produce changes in the central nervous system in humans.

Adult↗
PubMed1979

beta-Endorphin: analgesic and hormonal effects in humans.

The pharmacokinetics and the hormonal, analgesic, and behavioral effects of several doses of human beta-endorphin were evaluated after intravenous administration to three patients and intracerebroventricular administration to one patient with pain caused by cancer. These effects were compared to the hormonal effects of intravenously administered morphine sulfate in two patients and an enkephalin analog in two baboons. The mean terminal half-life after intravenous administration of 5 or 10 mg of human beta-endorphin to three patients was 37 min; the mean volume of distribution was 178 ml/kg, and the metabolic clearance rate was 3.2 (ml/min)/kg. The half-life of beta-endorphin in cerebrospinal fluid after intracerebroventricular administration was 93 min, and the volume of distribution was 0.74 ml/kg. A rapid rise in plasma prolactin followed both intravenous and intracerebroventricular beta-endorphin. Intravenous administration did not affect plasma growth hormone, but intracerebroventricular administration suppressed plasma growth hormone. No significant change in plasma growth hormone was noted after intravenous administration of morphine to humans, but plasma growth hormone decreased in one baboon after administration of the enkephalin analog. beta-Endorphin-stimulated release of prolactin occurred at doses lower than those required to produce analgesic and other behavioral effects. When both hormonal and analgesic effects were observed (after 7.5 mg were given intracerebroventricularly), the onset of the hormonal response slightly preceded the analgesic and behavioral responses. These studies suggest that the hormonal effects of beta-endorphin are species dependent and are similar to those of morphine. Hormonal and analgesic effects of beta-endorphin appear to result from the activation of opiate receptors that differ in their locations and characteristics.

Adult↗
PubMed1979

Properties and localization of beta-endorphin receptor in rat brain.

Stereospecific high-affinity binding sites for beta h-[3H]endorphin could be demonstrated in the P2 pellet of rat brain homogenate. Scatchard analysis of the binding data revealed binding sites with Kd values of 0.81 and 6.8 nM and density of 120 and 240 fmol/mg of protein. Distribution of beta h-[3H]endorphin binding in various brain regions parallels that of opiate receptor:striatum greater than thalamus greater than amygdala greater than hypothalamus, septum greater than cortex greater than midbrain, brainstem. Similar to their effect on 3H-labeled agonist binding, Na+ and other monovalent cations, GTP, trypsin, chymotrypsin, phospholipase A2, and N-ethylmaleimide all inhibited the specific binding of beta h-[3H]endorphin. In contrast to their action on alkaloid and enkephalin binding, Ca2+, Mg2+, and Mn2+ also inhibited beta h-[3H]endorphin binding. These data suggest a difference between beta h-endorphin and alkaloid/enkephalin binding sites.

Animals↗
PubMed1979

Semisynthesis of human somatotropin analogs.

Complementation of the natural NH2-terminal 134-amino acid fragment of the reduced, carbamoylmethylated human somatotropin with synthetic analogs of COOH-terminal fragments of 57, 42, or 38 amino acids of reduced, carbamoyl-methylated human somatotropin has been investigated. It was found that synthetic fragments of 57 and 42 amino acids gave recombinants with full growth-promoting activity, whereas attempts to obtain a recombinant with the synthetic 38-amino acid fragment were unsuccessful. The synthesis of two analogs of the COOH-terminal fragment of human somatotropin, human [N]e170, Ala165,182,189] somatotropin-(150-191) and human [Nle170, Ala165,182,189] somatotropin-(154-191), is herein described.

Amino Acid Sequence↗
PubMed1979

beta-Endorphin: synthesis of analogs modified at the carboxyl terminus with increased activites.

Three analogs of human beta-endorphin (beta h-EP) have been synthesized: [Gly31]beta h-EP, [Gly31]beta h-endorphinamide, and [Gly31]beta h-endorphinylglycine. All are more active than beta h-EP in both the guinea pig ileum bioassay and the opiate receptor binding assay. The last two analogs are about twice as active as beta h-EP in an assay for analgesia. Modification at position 31 and extension at the COOH terminus may afford a route toward analogs with even greater biological activity.

Analgesics↗
PubMed1979

beta-Endorphin: formation of alpha-helix in lipid solutions.

Human beta-endorphin adopts a partial helical conformation in aqueous solutions of cerebroside sulfate, ganglioside GM1, phosphatidylserine, and phosphatidic acid, but not of cerebroside and phosphatidylcholine, as evidenced by circular dichroic spectra. Addition of Ca2+ to the peptide in cerebroside sulfate solution can break up the helix; at 10 mM Ca2+ the peptide (12 microM) essentially exists in an unordered form. For comparison, sheep beta-lipotropin in acidic cerebroside sulfate solution (pH less than 4) also has a partial helical conformation of the complex between human beta-endorphin and lipids may be related to the opiatelike function of this peptide hormone.

Adrenocorticotropic Hormone↗