Opioid Peptide Content Research Articles

Enkephalin content in rat striatum during prolonged treatment with fluphenazine

Male Wistar rats were injected with fluphenazine /FLU/ i.p. in doses of 1 or 5 mg/kg for twelve months. Striatal met- and leu-enkephalin contents were determined after 1, 3, 6, 9 and 12 months of treatment, and one week after the drug withdrawal following a 12-month treatment, Enkephalin levels were significantly increased with slight fluctuations in some months and returned to normal one week after the last neuroleptic dose following a 12-month administration. Apomorphine, but not naloxone, prevented elevation of enkephalin levels after a one month FLU administration. Our findings confirm previous observations that prolonged disturbances in functions of the dopaminergic mechanism result in specific disturbances in the endogenous opioid peptide content, release and biosynthesis, and demonstrate that enkephalins are one of the factors with take part in the mechanism of neuroleptic action during a long-term treatment.

Influences of anti-inflammatory drugs on the opioid peptide content in the rat incisor pulp

Influences of anti-inflammatory drugs on the opioid peptide content in the rat incisor pulp

Effects of ascorbic acid, dexamethasone, and insulin on the catecholamine and opioid peptide stores of cultured adrenal medullary chromaffin cells

Bovine adrenal medullary chromaffin cells cultured in serum-free medium were examined for changes in their catecholamine and opioid peptide stores following exposure to dexamethasone, ascorbic acid, or insulin for 2 to 12 days. Dexamethasone failed to alter cellular catecholamine levels, measured by high performance liquid chromatography with electrochemical detection, or cellular opioid peptide content, measured by an enkephalin radioreceptor assay. Chromaffin cells cultured in medium supplemented with ascorbic acid retained high ascorbate contents for 2 to 3 days, despite the rapid loss of this vitamin from the culture medium (approximately 50% lost in 2 hr). The epinephrine and norepinephrine contents of chromaffin cell cultures supplemented with ascorbate for 7 days were increased approximately 10% compared to cultures without added ascorbic acid; ascorbate had no effect on chromaffin cell opioid peptide levels. Addition of insulin to chromaffin cell cultures produced a doubling of cellular protein and opioid peptide levels by 6 days and produced a concentration-dependent increase in the dopamine and norepinephrine contents of the cells with only a slight elevation in cell epinephrine. Chromaffin cells were also tested for the ability to resynthesize their catecholamine and opioid peptide stores following depletion as the result of secretion evoked by acetylcholine or nicotine. The cellular stores of norepinephrine and dopamine were resynthesized within 3 days following secretagogue-evoked depletion. Epinephrine stores were incompletely replenished with only 20% of the epinephrine lost via secretion recovered in 7 days. Opioid peptide levels were maximally recovered (50% of the amount secreted) within 1 day. Addition of ascorbic acid, dexamethasone, or insulin to the medium failed to enhance the recovery of catecholamine stores.

Opioid peptides, particularly dynorphin, after amygdaloid-kindled seizures.

The influence of amygdaloid kindling on brain and pituitary content of immunoreactive dynorphin (IR-DYN) and other opioid peptides was studied in rabbits. The kindling was very effective in increasing the hippocampal levels of IR-DYN, alpha-neoendorphin and Leu-enkephalin, but remained without any significant effect on the levels of IR-DYN and beta-endorphin in the majority of brain structures studied. The concentration of IR-DYN in the hippocampus remained at the control level throughout the development but was increased dramatically after completion of kindling. Biochemical alterations persisted for at least one month following the completion of kindling. The obtained results suggest that the hippocampal IR-DYN and related peptides may play some role in the maintenance of amygdaloid-kindled seizures.

The effect of gamma-hydroxybutyrate and anticonvulsants on opioid peptide content in the rat brain

Gamma-hydroxybutyrate administered in anaesthetic doses produced a profound increase in the levels of dynorphin A (DYN) in the hippocampus and pituitary. Simultaneously, a significant, short-lasting decrease in beta-endorphin (B-E) levels occurred in the brain and pituitary. Antiepileptic drugs strongly, though in various ways, influenced the brain DYN and B-E concentrations; though most of them caused a decrease in the hypothalamic opioid peptide content.

Proportional secretion of opioid peptides and catecholamines from adrenal chromaffin cells in culture

Bovine adrenal medullary chromaffin cells were used to study the relationship between opioid peptide and catecholamine secretion from the adrenal medulla. Stimulation of chromaffin cells by acetylcholine, nicotine, veratridine, barium, or Ionomycin produced secretion of opioid peptides and catecholamines which was proportional to the cellular content of these substances. Nicotine-evoked secretion of opioid peptides and catecholamines was dependent on extracellular calcium and was blocked by d-tubocurarine. Increased cellular content of opioid peptides and decreased catecholamine content induced by treatment of chromaffin cells with reserpine or tetrabenazine were reflected in the secretion of proportionally larger amounts of opioid peptides and smaller amounts of catecholamines when compared with secretion of these substances from untreated cells. Peptides of up to 25,000 daltons that express opiate activity only following digestion with enzymes, such s trypsin and carboxypeptidase B, also are secreted from chromaffin cells in the same proportion of their cellular content as are catecholamines and opioid peptides. Opioid peptides were secreted in proportion to total catecholamines but not in proportion to either epinephrine or norepinephrine alone, suggesting that the peptides are secreted from both epinephrine- and norepinephrine-containing cells in the cultures. The results are consistent with the co-storage of opioid peptides and opiate receptor-inactive peptides containing enkephalin sequences in chromaffin vesicles and with the all-or-none exocytotic secretion of chromaffin vesicles content in response to stimulation of the adrenal medulla.

Elevation of met 5-enkephalin and β-endorphin hypothalamic content in rats receiving anorectic drugs: Differences between d-fenfluramine and d-amphetamine

D-Fenfluramine, an anorectic that releases serotonin (5-HT), repeatedly injected in rats (15 mg/kg per day) enhanced the met 5-enkephalin and β-endorphin content of the hypothalamus. The onset of this effect was slow, reaching a peak at 5 days; the increase in β-endorphin gradually declined toward control level while the drug was still being administered although that of met-enkephalin persisted for 15 days. The elevation of the opioid peptide content of the hypothalamus was temporally associated with a slowing in the rate of body weight increase. A transient, small, increase in striatal met-enkephalin content was also induced by repeated D-fenfluramine injections: however the metenkephalin content of frontal cortex, hippocampus and brainstem was not affected. A modification of the β-endorphin content of hypothalamus was not seen after acute injection of D-fenfluramine or D-amphetamine but an increase was observed during repeated treatment with D-fenfluramine. Repeated injections of D-amphetamine for 5 days (4.5 mg/kg per day) failed to increase either the met-enkephalin or the β-endophin content of the hypothalamus. These data suggest that the anorexia elicited by repeated injections of D-fenfluramine but not that elicited by D-amphetamine, includes a participation by hypothalamic and β-endosphin stores.

Opioid peptide synthesis in bovine and human adrenal chromaffin cells

Addition of inhibitors of chromaffin vesicle catecholamine uptake, reserpine or tetrabenazine, to cultures of bovine adrenal chromaffin cells led to a depletion of cellular catecholamine stores and to an increased opioid peptide content. Addition of monoamine oxidase inhibitors, catecholamines or catecholamine receptor agonists to the cultures produced similar increases in the opioid peptide content without altering catecholamine stores, suggesting that an extravesicular catecholamine pool influences chromaffin cell opioid peptide content. This elevated peptide content resulted from increased synthesis by the cells and led to enhanced stimulus-evoked secretion of opioid peptides. Dissociated cells obtained from a human pheochromocytoma tumor also increased their opioid peptide content following treatment with reserpine or a secretagogue. The results obtained with cultured chromaffin and pheochromocytoma cells suggest that a mechanism for replenishing and increasing adrenal medullary opioid peptide stores and secretory capacity may function in vivo. The observed regulation of opioid peptide stores may also be important in the clinical pathology of opioid peptide containing tumors.

Synthesis of enkephalins by adrenal medullary chromaffin cells: reserpine increases incorporation of radiolabeled amino acids.

Adrenal medullary chromaffin cells maintained in a chemically defined, serum-free medium retain high levels of both catecholamines and opiate-like peptides. At least 25% of the opioid activity as measured by radioreceptor assay is present as [Met]- and [Leu]enkephalin. Incubation of chromaffin cells with [3H]tyrosine and [35S]methionine for 3 days results in incorporation of 3H and 35S into [Met]enkephalin and 3H incorporation into [Leu]enkephalin, demonstrating de novo enkephalin synthesis. Addition of 100 nM reserpine to the culture medium causes an 80% depletion of catecholamines and a 100% increase in opioid peptide content 3-4 days later. [Met]Enkephalin content is preferentially induced (290% above control) compared with [Leu]enkephalin (70%) Reserpine increases the fractional radiolabeling of [Met]- and [Leu]enkephalin in excess of control cultures, suggesting that the increase in opiate-like peptides results from an increased rate of synthesis rather than decreased degradation, decreased secretion, or increased processing of preformed precursor(s).

Radioimmunoassay of brain peptides: Evaluation of a methodology for the assay of β-endorphin and enkephalin

The brain levels of β-endorphin, α-endorphin and enkephalin were measured by radioimmunoassay after different methods of sacrifice. Microwave irradiation proved not to be better than decapitation followed by boiling of the intact tissue, the latter procedure giving values of β-endorphin 10 fold higher than decapitation alone. Concurrently when decapitation was followed by boiling, α-endorphin was no longer detected. Evaluation in brain tissue of several extraction media--phosphate buffered saline, 5% TCA, HCl methanol, and 1N HOAc--showed the last to be the most satisfactory for both β-endorphin and enkephalin. Since β-endorphin was found to be readily hydrolized by brain homogenates with consequent appearance of α-endorphin, these results indicate that disruption of tissue modifies the content of opioid peptides in brain.