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Biomedical subjects

N Ling

Publications and source records attributed to N Ling.

At least 397 records · Page 22Linked to original sources
PubMed1977

beta-Endorphin: endogenous opiate or neuroleptic?

The opiatelike neuropeptide beta-endorphin produces a spectrum of effects that contrasts with that induced by the neuroleptic haloperidol. Rats injected intraventricularly or directly into the periaqueductal gray with beta-endorphin (0.5 to 50 micrograms) exhibited rigid immobility accompanied by the loss of righting reflex; the period of rigidity was preceded or followed (depending upon dose) by a state of hyperactivity. In contrast, no dose of haloperidol tested (0.5 to 12 milligrams per kilogram) produced rigidity, loss of righting reflex, or behavioral excitation. Furthermore, whereas animals injected with haloperidol remained stationary on a vertical grid, rats injected with beta-endorphin typically slid off the grid. Moreover, combined beta-endorphin and haloperidol treatment produced flaccidity in most animals. These results do not support the contention that this opiatelike peptide may be a naturally occurring neuroleptic.

Animals↗
PubMed1977

beta-Endorphin and adrenocorticotropin are selected concomitantly by the pituitary gland.

The opiate-like peptide beta-endorphin and adrenocorticotropin are concomitantly secreted in increased amounts by the adenohypophysis in response to acute stress or long-term adrenalectomy as well as in vitro in response to purified corticotropin releasing factor and other secretagogues. Conversely, administration of the synthetic glucocorticoid dexamethasone inhibits the secretion of both adrenocorticotropin and beta-endorphin. Thus, both hormones possess common and identical regulatory mechanisms and there may be a functional role for circulating beta-endorphin.

Adrenocorticotropic Hormone↗
PubMed1977

Regional dissociation of beta-endorphin and enkephalin contents in rat brain and pituitary.

beta-Endorphin and enkephalin in extracts of whole brain, various brain regions, adenohypophysis, and combined pars intermedia and neurohypophysis of the rat were measured by radioimmunoassay. In brain extracts, the immunoreactive substances were further separated according to molecular size by gel filtration. beta-Endorphin was found in the diencephalon but not in the hippocampus, cerebral cortex, cerebellum, and striatum. Enkephalin was found predominantly in the striatum and diencephalon. Attention is called to possible artifactual interference by myelin basic protein in the immunoassays for beta-endorphin in some regions of the brain. In the pituitary, enkephalin was mainly restricted to the pars intermedia-neurohypophysis. Neither adrenalectomy nor hypophysectomy significantly altered levels of beta-endorphin in brain extracts. Adrenalectomy increased the levels of beta-endorphin in adenohypophysis and pars intermedia-neurohypophysis; after adrenalectomy, enkephalin was also increased in the adenohypophysis but less so in the pars intermedia-neurohypophysis. These results show that brain endorphin levels are independent of pituitary endorphin levels; they suggest that beta-endorphin-containing neurons and those containing enkephalin constitute two separate groups of brain cells.

Adrenalectomy↗
PubMed1977

Neuronal actions of endorphins and enkephalins among brain regions: a comparative microiontophoretic study.

The brain peptides alpha- and beta-endorphin, leucine- and methionine-enkephalin, as well as the opiate normorphine, have been evaluated by microiontophoresis for their effects on neuronal activity in several regions of the rat brain. In cerebral cortex, brainstem, caudate nucleus, and thalamus, most responsive cells were inhibited by the peptides and by normorphine, while in hippocampus all responsive cells were excited. Both inhibitory and excitatory responses were blocked by the narcotic antagonist naloxone. Occurrence of responsive cells encountered in a particular region was loosely correlated with density of stereospecific opiate binding sites as reported by others. These results are consistent with the hypothesis that the endorphins and enkephalins may represent a new class of central neurotransmitters; among other functions, these peptides may play a role in the regulation of behavior and the expression of psychopharmacological agents such as the opiate alkaloids.

Animals↗
PubMed1977

Common precursor to corticotropins and endorphins.

Double-antibody immunoprecipitation procedures with antisera to endorphins and to corticotropin (ACTH) were used to study the biosynthesis of these peptides in a mouse pituitary tumor cell line. Cultures were incubated with a (3)H-labeled amino acid, and aliquots of culture medium were immunoprecipitated. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis of [(3)H]phenylalanine-labeled immunoprecipitates prepared with endorphin antisera resolved three forms of endorphin with apparent molecular weights of 31,000, 11,700, and 3500; immunoprecipitates prepared with the ACTH antiserum contained four forms of ACTH with apparent molecular weights of 31,000, 23,000, 13,000 and <4500. Sequential immunoprecipitation of culture medium with the ACTH antiserum and then with the endorphin antiserum (or the reverse order) indicated that both antisera precipitated the same 31,000 dalton molecule. Purified pools of the different forms of ACTH and endorphin were prepared by immunoprecipitation and gel filtration. The tryptic peptides found in [(3)H]phenylalanine- or [(3)H]tryptophan-labeled 31,000 dalton ACTH were identical to the tryptic peptides found in digests of 31,000 dalton endorphin labeled with the same amino acid. A tryptic peptide similar to the lipotropin tryptic peptide [betaLPH(61-69)] that contains the opiate-active methionine-enkephalin sequence could be identified in 31,000 dalton ACTH and in all the different forms of endorphin. Most of the peptide cleaved from 31,000 dalton ACTH when it is converted to 23,000 dalton ACTH could be precipitated by endorphin antisera; this 11,700 dalton endorphin molecule is similar to the pituitary hormone betaLPH in size and structure. The 3500 dalton endorphin is similar to beta-endorphin in size and structure. The culture medium from the AtT-20 mouse pituitary tumor cells contained approximately equimolar amounts of ACTH-related peptides and endorphin-related peptides.

Adrenocorticotropic Hormone↗
PubMed1977

Stimulation in vivo of the secretion of prolactin and growth hormone by beta-endorphin.

Morphine sulfate (MS) and the opioid peptide beta-endorphin beta-LPH-(61-91) stimulate prolactin and growth hormone release in steroid-primed and non-treated male rats when injected intravenously or intracisternally. On a molar basis beta-endorphin is at least 20 times more potent than MS, whereas Met5-enkephalin (beta-LPH-(61-65)) and alpha-endorphin (beta-LPH-(61-76)) are devoid of activity at the dose injected (300 mug). The in vivo stimulatory effects of beta-endorphin on prolactin secretion are reversed by the opiate antagonist naloxone. The absence of in vitro effect of MS and beta-endorphin on prolactin and growth hormone secretion by cultured rat pituitary cells suggest that they have a central nervous system site of action.

Animals↗
PubMed1977

beta-Endorphin secretion of arginine vasopressin in vivo.

The effect of beta-endorphin upon plasma arg8-vasopressin release was studied in vivo in rabbits and in vitro in rat neural lobes. Following intravenous administration of 200 mug/kg synthetic beta-endorphin plasma AVP rose significantly by five minutes after injection and remained elevated for twenty-five minutes compared to controls. In contrast beta-endorphin had no significant effect on AVP release from isolated rat neural lobes in vitro. beta-Endorphin stimulates AVP secretion in vivo, but this is not due to a direct action upon the neural lobe.

Animals↗
PubMed1976

Endorphins: profound behavioral effects in rats suggest new etiological factors in mental illness.

The endogenous morphinomimetic brain peptides Met5-enkephalin and alpha-, beta-, and gamma-endorphins have been evaluated in rats after intracerebrospinal fluid injection. beta-Endorphin produces marked, prolonged muscular rigidity and immobility similar to a catatonic state, counteracted by the opiate antagonist naloxone; this effect occurs at molar doses 1/100 to 1/400 that at which the other peptides or morphine block the response to painful stimuli. All peptides evoked dose-related, naloxone-reversible, wet-dog shakes in rats that had not been exposed to drugs. beta-Endorphin produced hypothermia, whereas gamma-endorphin produced hyperthermia. Such potent and divergent responses to naturally occurring subtances suggest that alterations in their homeostatic regulation could have etiological significance in mental illness.

Animals↗
PubMed1976

[Endorphins, hypothalamic and neurohypophysial peptides with morphinomimetic activity: isolation and molecular structure of alpha-endorphin].

From a crude extract of Porcine neurohypophysis-hypothalamus we have isolated several peptides called endorphins which mimic opiated in a classical bioassay for morphine. Similarly they bind to the stereospecific synaptosomal opiates receptors of Rat brain in competition to 3 H-etorphine. The primary structure of alpha-endorphin is H-Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-OH. Met-enkephalin is the N-terminal pentapeptide of alpha-endorphin. Alpha-endorphin has the same sequence as that of the fragment TYR 61 to Thr 76 of the beta-lipotropins.

Amino Acid Sequence↗