Localization of multiple forms of ACTH- and beta-endorphin-related substances in the pituitary of the reptile, Anolis carolinensis

A Critical Review on the Pharmacodynamics and Pharmacokinetics of Non-steroidal Anti-inflammatory Drugs and Opioid Drugs Used in Reptiles

Non-steroidal anti-inflammatory drugs (NSAIDs) and opioids are analgesics used for moderate to severe pain in many animals, including reptiles. However, reptilian dosing regimens are often extrapolated from other animal species. This is not ideal as inter- and intra-species variability in physiology may result in varied drug disposition. Therefore, this critical review aims to collate data from pharmacological studies of selected NSAIDs and opioids performed in reptile and provide an analysis and discussion on the existing pharmacodynamic knowledge and pharmacokinetic data of NSAIDs and opioids use in reptiles. Additionally, key pharmacokinetic trends that may aid dosing of NSAIDs and opioids in reptiles will also be highlighted. Most of the existing reports of NSAID used in reptiles did not observe any adverse effects directly associated to the respective NSAID used, with meloxicam being the most well-studied. Despite the current absence of analgesic efficacy studies for NSAIDs in reptiles, most reports observed behavioural improvements in reptiles after NSAID treatment. Fentanyl and morphine were studied in the greatest number of reptile species with analgesic effects observed with the doses used, while adverse effects such as sedation were observed most with butorphanol use. While pharmacokinetic trends were drug- and species-specific, it was observed that clearance (CL) of drugs tended to be higher in squamates compared to chelonians. The half-life (t_1/2) of meloxicam also appeared to be longer when dosed orally compared to other routes of drug administration. This could have been due to absorption-rate limited disposition. Although current data provided beneficial information, there is an urgent need for future research on NSAID and opioid pharmacology to ensure the safe and effective use of opioids in reptiles.

Pain and Pain Management in Sea Turtle and Herpetological Medicine: State of the Art

Simple Summary

Rescue and rehabilitative medicine of sea turtles must deal with several circumstances that would be certainly considered painful in other species (trauma, situations that require surgery); thus, it would be natural to consider the use of analgesic drugs to manage the pain and avoid its deleterious systemic effects to guarantee a rapid recovery and release. However, in these animals (as well as in reptiles in general), many obstacles stand in the way of the application of safe and effective therapeutic protocols. It has been demonstrated that, anatomically and physiologically, turtles and reptiles in general must be considered able to experience pain in its definition of an “unpleasant sensory and emotional experience”. Unfortunately, specific studies concerning sea turtles and reptiles on pain assessment, safety, and clinical efficacy of analgesic drugs currently in use (mostly opioids and non-steroidal anti-inflammatory drugs—NSAIDs) are scarce and fragmentary and suffer from some basic gaps or methodological bias that prevent a correct interpretation of the results. At present, the general understanding of the physiology of reptiles’ pain and the possibility of its reasonable treatment is still in its infancy, considering the enormous amount of information still needed, and the use of analgesic drugs is still anecdotal or dangerously inferred from other species.

Abstract

In sea turtle rescue and rehabilitative medicine, many of the casualties suffer from occurrences that would be considered painful in other species; therefore, the use of analgesic drugs should be ethically mandatory to manage the pain and avoid its deleterious systemic effects to guarantee a rapid recovery and release. Nonetheless, pain assessment and management are particularly challenging in reptilians and chelonians. The available scientific literature demonstrates that, anatomically, biochemically, and physiologically, the central nervous system of reptiles and chelonians is to be considered functionally comparable to that of mammals albeit less sophisticated; therefore, reptiles can experience not only nociception but also “pain” in its definition of an unpleasant sensory and emotional experience. Hence, despite the necessity of appropriate pain management plans, the available literature on pain assessment and clinical efficacy of analgesic drugs currently in use (prevalently opioids and NSAIDs) is fragmented and suffers from some basic gaps or methodological bias that prevent a correct interpretation of the results. At present, the general understanding of the physiology of reptiles’ pain and the possibility of its reasonable treatment is still in its infancy, considering the enormous amount of information still needed, and the use of analgesic drugs is still anecdotal or dangerously inferred from other species.

Differential N-acetylation of alpha-MSH and beta-endorphin in the intermediate pituitary of the turtle, Pseudemys scripta

Steady-state analyses of the intermediate pituitary of the turtle, Pseudemys scripta, indicated that alpha-MSH-sized immunoreactive forms and beta-endorphin-sized immunoreactive forms are major end products of melanotropic cells. Three forms of alpha-MSH-related immunoreactivity were detected. The two major forms had the same reversed-phase HPLC properties as synthetic N,O-diacetyl-ACTH(1-13)-NH2 and N-acetyl-ACTH(1-13)-NH2. These forms accounted for 97% of the total alpha-MSH-related immunoreactivity detected. A minor peak of ACTH(1-13)-NH2 was also detected. Multiple forms of beta-endorphin-related immunoreactivity were detected, which varied in net positive charge (+1 to +5), apparent molecular weight (2.4 to 3.5 kDa), and degree of N-terminal acetylation. Although N-acetylated forms of beta-endorphin were detected in the turtle intermediate pituitary, the major forms of turtle beta-endorphin were nonacetylated. These features of the turtle intermediate pituitary POMC-specific N-acetylation mechanism are similar to, yet distinct from, the POMC N-acetylation mechanisms observed for mammals. These data suggest that POMC-specific N-acetylation mechanisms were present in reptiles prior to the divergence of the anapsid and synapsid lines.

Arginine vasotocin concentrations in the supraoptic nucleus of the lizard Anolis carolinensis are associated with reproductive state but not oviposition

Arginine vasotocin (AVT) is a neuropeptide involved in reproductive function in many nonmammalian vertebrates. We determined brain and plasma AVT concentrations during the estrous cycle and oviposition in the lizard Anolis carolinensis. There were no differences in AVT concentrations in the plasma or any brain region during the ovipositional sequence. However, we found that females with an egg in each oviduct and a large pre-ovulatory follicle (diameter > 4.5 mm) in one-ovary had significantly higher AVT concentrations in the supraoptic nucleus (SON) of the hypothalamus than did females with small pre-ovulatory follicles in both ovaries. In a second study, females with an egg in each oviduct and a large pre-ovulatory follicle had significantly greater AVT concentrations in the SON than females with only one oviductal egg and a large pre-ovulatory follicle or females with an egg in each oviduct and a small pre-ovulatory follicle in each ovary. Concentrations of AVT in other brain regions and in the plasma did not differ among these groups. Changes in steroid profiles during estrous and/or direct neural communication between the uterus, ovary, and brain may account for the changes in AVT concentrations seen in the supraoptic nucleus during the estrous cycle of Anolis carolinensis.

Distribution of mu, delta, and kappa opiate receptor types in the forebrain and midbrain of pigeons

Ligands that are highly specific for the mu, delta, and kappa opiate receptor binding sites in mammalian brains have been identified and used to map the distribution of these receptor types in the brains of various mammalian species. In the present study, the selectivity and binding characteristics in the pigeon brain of three such ligands were examined by in vitro receptor binding techniques and found to be similar to those reported in previous studies on mammalian species. These ligands were then used in conjunction with autoradiographic receptor binding techniques to study the distribution of mu, delta, and kappa opiate receptor binding sites in the forebrain and midbrain of pigeons. The autoradiographic results indicated that the three opiate receptor types showed similar but not identical distributions. For example, mu, delta, and kappa receptors were all abundant within several parts of the cortical-equivalent region of the telencephalon, particularly the hyperstriatum ventrale and the medial neostriatum. In contrast, in other parts of the cortical-equivalent region of the avian telencephalon, such as the dorsal archistriatum and caudal neostriatum, only kappa receptors appeared to be abundant. Within the basal ganglia, all three types of opiate receptors were abundant in the striatum and low in the pallidum. Within the diencephalon, kappa and delta binding was high in the dorsal and dorsomedial thalamic nuclei, but the levels of all three receptor types were generally low in the specific sensory relay nuclei of the thalamus. Kappa binding and delta binding were high, but mu was low in the hypothalamus. Within the midbrain, all three receptor types were abundant in both the superficial and deep tectal layers, in periventricular areas, and in the tegmental dopaminergic cell groups. In many cases, the distribution of opiate receptors in the pigeon forebrain generally showed considerable overlap with the distribution of opioid peptide-containing fiber systems (for example, in the striatal portion of the basal ganglia), but there were some clear examples of receptor-ligand mismatch. For example, although all three receptor types are very abundant in the hyperstriatum ventrale, opioid peptide-containing fibers are sparse in this region. Conversely, within the pallidal portion of the basal ganglia, opioid peptide-containing fibers are abundant, but the levels of opiate receptors appear to be considerably lower than would be expected. Thus, receptor-ligand mismatches are not restricted to the mammalian brain, since they are a prominent feature of the organization of the brain opiate systems in pigeons.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunological evidence for multiple forms of alpha-melanotropin (alpha-MSH) in the pars intermedia of the Australian lungfish, Neoceratodus forsteri

Acid extracts of individual pars intermedia from the Australian lungfish, Neoceratodus forsteri, were fractionated by gel filtration chromatography and analyzed for alpha-melanotropin (alpha-MSH) immunoreactivity. In these studies a C-terminal-specific alpha-MSH radioimmunoassay (RIA) was used. Following gel filtration chromatography on a Sephadex G-75 column, a major peak of immunoreactive alpha-MSH-sized material was detected. On the average there was 338 +/- 72 pmol (SD) of immunoreactive alpha-MSH per lungfish pars intermedia (n = 3). Following gel filtration the immunoreactive alpha-MSH was further analyzed by reverse-phase high-performance liquid chromatography (HPLC). Three peaks of immunoreactivity were detected. These peaks were designated Peaks 1, 2, and 3. The retention times of these peaks corresponded to, respectively, mammalian ACTH(1-13)amide, N-acetyl-ACTH(1-13)-amide, and N,O-diacetyl-ACTH(1-13)amide. Peaks 2 and 3 represented approximately 95% of the immunoreactive alpha-MSH recovered. Analysis of immunoreactive Peaks 2 and 3 by cation-ion-exchange indicated that both peaks had a net charge of +3 at pH 2.5. Since O-acetyl groups are sensitive to high pH, Peak 3 was incubated for 1 hr at 37 degrees in 0.01 N NaOH, pH 12. Under these conditions, Peak 3 eluted with the same retention time as untreated Peak 2. Collectively, these results indicate that Peaks 2 and 3 correspond to mono- and diacetylated lungfish alpha-MSH, respectively.

The isolation of multiple forms of beta-endorphin from the intermediate pituitary of the Australian lungfish, Neoceratodus forsteri

The pituitary of the Australian lungfish, Neoceratodus forsteri, was screened immunohistochemically with heterologous antisera specific for either the C-terminal of mammalian beta-endorphin or the acetylated N-terminal of beta-endorphin. Immunopositive cells were only detected with the N-terminal specific antiserum; these cells were restricted to the intermediate pituitary. Acid extracts of the intermediate pituitary were fractionated by Sephadex gel filtration chromatography, CM cation exchange chromatography and reverse phase HPLC. Fractions were analyzed by radioimmunoassay (RIA) with a N-acetyl specific beta-endorphin RIA and by radioreceptor assay for the presence of opiate active forms of beta-endorphin. Both immunoreactive and opiate active forms of beta-endorphin were detected. Of the total beta-endorphin-related material isolated from the intermediate pituitary, approximately 97% was detected with the N-terminal specific RIA and approximately 3% was detected by the radioreceptor assay. The N-acetylated immunoreactive beta-endorphin could be separated into two forms. The major form had an apparent molecular weight of 3.2 Kda. This material had a net charge at pH 2.5 of +5. The minor form of immunoreactive beta-endorphin had an apparent molecular weight of 1.4 Kda and a net charge at pH 2.5 of +1. Neither immunoreactive form exhibited receptor binding activity in the radioreceptor assay. A single peak of opiate active beta-endorphin was detected. This material had an apparent molecular weight of 3.5 Kda and a net charge at pH 2.5 of +7.

Isolation of alpha-melanotropin from the pars intermedia of the larval amphibian, Ambystoma tigrinum

The effect of background adaptation on the steady-state levels of alpha-melanotropin in the pars intermedia of the larval amphibian. Ambystoma tigrinum, was investigated. Acid extracts of pars intermedia obtained from light-adapted and dark-adapted animals were analyzed by radioimmunoassay following Sephadex gel filtration chromatography, reverse-phase HPLC, and Sulfopropyl Sephadex cation-ion-exchange chromatography. For both background adaptation conditions similar results were obtained. The major form of alpha-melanotropin present in the pars intermedia has the following properties: (1) an apparent molecular mass of 1.5 kDa; (2) a net charge at pH 3.5 of +4; and (3) a retention time following reverse-phase HPLC similar to that of synthetic ACTH(1-13)amide. In dark-adapted animals a minor form of alpha-melanotropin which has a net charge of +3 at pH 3.5 was also detected. The latter form represented approximately 10% of the total alpha-melanotropin immunoreactivity in the pars intermedia of dark-adapted animals. These results strongly suggest that the predominant form of alpha-melanotropin in the pars intermedia of larval A. tigrinum is a nonacetylated ACTH(1-13)amide-like polypeptide.

Isolation of immunoreactive beta-endorphin-related and Met-enkephalin-related peptides from the posterior pituitary of the amphibian, Xenopus laevis

Acid extracts of the posterior pituitary of the amphibian, Xenopus laevis, were analyzed with two heterologous region specific beta-endorphin RIAs. Following gel filtration chromatography and cation exchange chromatography four peaks of immunoreactivity were detected. All four peaks were detected with a N-acetyl specific beta-endorphin RIA. Peak I represented 92% of the total immunoreactivity isolated following cation exchange chromatography. This peak had a net positive charge at pH 2.5 of +1 and an apparent molecular weight of 1.4 Kd. Following reverse phase HPLC, Peak I fractionated into two peaks: Peak Ia and Peak Ib. Both peaks were detected with the N-acetyl specific beta-endorphin RIA and a Met-enkephalin RIA, however, neither peak co-migrated with either Met-enkephalin or N-acetyl-beta-endorphin(1-16). At present it is not clear whether Peak I is derived from pro-opiomelanocortin or one of the other opioid polyproteins. Peaks II, III, and IV represented 8% of the total immunoreactivity recovered following cation exchange chromatography. These peaks had net positive charges of +3, +4, and +5, respectively, and apparent molecular weights of 2.8, 3.2, and 3.5 Kd, respectively. These apparently N-acetylated beta-endorphin-sized forms are minor end products of the pro-opiomelanocortin biosynthetic pathway.

Steady-state analysis of alpha-melanotropin in the pars intermedia of Anolis carolinensis: effect of background adaptation

The steady-state levels of alpha-melanotropin-stimulating hormone (alpha-MSH)-related peptides were examined in the pars intermedia of the reptile Anolis carolinensis as a function of background adaptation. After a 7-day period, the content of immunoreactive alpha-MSH-related material in the pars intermedia of light-adapted animals was approximately fourfold higher than that of animals maintained on a dark background for the same period. The immunoreactive alpha-MSH-related material present in the pars intermedia of light-adapted and dark-adapted animals was separately analyzed by gel filtration chromatography, reverse-phase HPLC, and cation-exchange chromatography. For light-adapted animals the major form of alpha-MSH had an apparent molecular weight of 1.5 kDa and a net charge of +4 at pH 3.5. Following reverse-phase HPLC this material eluted as a single peak of immunoreactivity with a retention time distinct from that of both mammalian ACTH(1-13)amide and N-acetyl-ACTH(1-13)amide. For dark-adapted animals a peak of alpha-MSH-sized material with an apparent molecular weight of 1.5 kDa was also detected. Following reverse-phase HPLC analysis this material eluted as an apparent single peak of immunoreactivity with a retention time distinct from that of the mammalian standards. Subsequent analysis of this major HPLC peak by cation-exchange chromatography revealed the presence of at least two forms of immunoreactive alpha-MSH. These forms differed in relative proportions. The major peak of immunoreactivity had a net charge of +4, whereas the minor peak had a net charge of +3. The +3 immunoreactive form was not detected to any appreciable degree in light-adapted animals.

The distribution of proenkephalin-derived peptides in the central nervous system of turtles

The present study was carried out to examine if peptides similar to the various opioid peptide products of mammalian proenkephalin are present in the turtle central nervous system and to determine their distribution. Antisera against several enkephalin peptides were used: leucine-enkephalin (LENK), methionine-enkephalin (MENK), methionine-enkephalin-arg6-phe7 (MERF), methionine-enkephalin-arg6-gly7-leu8 (MERGL), Peptide E (PEPE), and BAM22P. Their specificity and cross-reactivity were carefully examined. The results indicated that LENK, MENK, and MERF (or highly similar peptides) are present in the turtle central nervous system, and that a peptide showing immunological similarity to BAM22P and PEPE also appeared to be present. In contrast, MERGL did not appear to be present. The distributions of the immunoreactive labeling for LENK, MENK, MERF, BAM22P, and PEPE were indistinguishable, and double-label studies showed that LENK, MERF, and BAM22P were colocalized within individual neurons and fibers. Although all of the above substances were observed in the same cell groups, there was some regional variation, in terms of which enkephalin peptide appeared to be most abundant. The distributions of these enkephalin peptides were very similar to those previously described in mammals and birds. Enkephalin was more abundant in the basal ganglia than in overlying telencephalic regions. Within the basal ganglia, enkephalin was present in striatal neurons and fibers and in pallidal fibers, thereby suggesting the existence of an enkephalinergic striatopallidal projection. Sensory relay nuclei of the thalamus were generally poor in enkephalinergic fibers, whereas the hypothalamus was rich in enkephalinergic neurons and fibers. Enkephalinergic neurons and fibers were present in the midbrain central gray. As is true of neurons of the nucleus spiriformis lateralis of the avian pretectum, the neurons of the homologous cell group in turtles, the dorsal nucleus of the posterior commissure of the pretectum, were found to contain enkephalin and have an enkephalinergic projection to the deep layers of the ipsilateral tectum. Enkephalinergic neurons and fibers were also abundant in the entry zones of the trigeminal nerve and dorsal root fibers of the spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for the presence of adrenocorticotropic and opiate-like hormones in the brains of two sea snakes, Hydrophis cyanocinctus and Lapemis hardwickii

The brain acetone powders of the sea snakes Hydrophis cyanocinctus and Lapemis hardwickii were extracted with a mixture of acetone:water:hydrochloric acid (40:21:1 by volume) and the extracts were then added to a copious volume of acetone, in accordance with the method of C. H. Li (1952, J. Amer. Chem. Soc., 74, 2134) for preparing adrenocorticotropin and beta-endorphin from mammalian pituitaries. The resultant precipitate, designated acid acetone powder, possessed adrenocorticotropic activity as evidenced in its ability to stimulate corticosterone production in isolated rat adrenal decapsular cells and lipolysis in isolated hamster adipocytes, and in its cross-reactivity in an ACTH radioimmunoassay. The presence of opioid molecules was indicated by activity in opiate radioreceptor assay using either 3H-D-Ala2-D-Leu5 enkephalin or [3H]naloxone as ligand and rat brain membranes. The brain acetone powders possessed neither "lactogenic" nor "somatogenic" activity as evidenced by their inability to displace the primary ligand in the rat hepatic prolactin receptor- and growth hormone receptor-binding assays, respectively.

Characterization of endorphins from the pituitary of the spiny dogfish Squalus acanthias

Opioid-like immunoreactive material was extracted from the pituitary and brain of the Spiny Dogfish Shark Squalus acanthias. The immunoreactive material in the pituitary extracts was purified to apparent homogeneity by reverse phase high performance liquid chromatography and subsequently characterized by amino acid analysis, Edman degradation and fast atom bombardment mass spectrometry. The largest opioid-like peptide isolated contained 30 amino acids and showed 80 percent homology with salmon endorphin-II but less than 50 percent homology with human beta-endorphin. Three structural variants of this molecule were also characterized. These variants were shown to be shorter N-terminal fragments, two of which corresponded to cleavage products at the single basic residues arginine and lysine. Cleavage at a single lysine residue has not been reported for posttranslational processing of beta-endorphin in mammals and could represent a modification seen only in lower vertebrates. The remaining fragment corresponded to a loss of 3 residues from the C-terminus of the parent molecule. No alpha-N-acetylated peptides were detected. These results provide the first unequivocal confirmation of beta-endorphin in an elasmobranch and provide evidence of novel N-terminal variants of beta-endorphin.

Stress-induced elevation of plasma alpha-MSH and endorphin in brown trout, Salmo trutta L

Handling and confinement caused a pronounced elevation in the plasma cortisol levels of brown trout. This response was more rapid, and the elevation greater, at 13.4 than at 5 degrees although basal cortisol levels were also higher at the warmer water temperature. The large increase in plasma cortisol caused by handling and confinement was not accompanied by any changes in the plasma levels of either alpha-MSH or endorphin. However, when handling and confinement was combined with a thermal shock, not only was there a rapid and pronounced elevation in plasma cortisol, but there were also concomitant and sustained rises in the plasma levels of both alpha-MSH and endorphin. The levels of a alpha-MSH and endorphin induced by the thermal shock were considerably higher than those recorded in long-term, black-adapted brown trout, the only other circumstance in fish known to cause an elevation of the plasma levels of these two peptides. These results indicate that handling and confinement only activated the corticotrophs of the pars distalis, not the melanotrophs of the neurointermediate lobe, whereas when combined with a thermal shock, both cell types were activated.

Localization of neurons containing pro-opiomelanocortin-related peptides in the hypothalamus and midbrain of the lizard, Anolis carolinensis: evidence for region-specific processing of beta-endorphin

Immunohistochemical analyses of the lizard-brain, following colchicine pretreatment, revealed two populations of POMC-producing cell bodies located in medial-basal hypothalamus and the mesencephalic tegmentum. Analyses of extracts of lizard brain regions by radioimmunoassay and gel filtration chromatography indicate that beta-endorphin-sized and alpha-MSH-sized peptides are the major POMC-related end products. Evidence is presented for region-specific processing of beta-endorphin in the lizard brain.

Beta-endorphin/ACTH immunocytochemistry in the CNS of the lizard Anolis carolinensis: evidence for a major mesencephalic cell group

The immunocytochemical distribution of beta-endorphin and other proopiomelanocortin (POMC) peptides in the central nervous system of the lizard Anolis carolinensis was determined. Colchicine pretreatment was used to enhance perikaryal immunoreactivity. A major finding of this study is the localization of a previously undetected mesencephalic cell group which exhibits immunoreactivity to beta-endorphin, ACTH, and alpha-MSH. The perikarya of these neurons are large, bipolar, and situated in the mesencephalic tegmental area. They appear to project to the mesencephalic central gray and other brainstem structures. In contrast, the immunoreactive parvicellular perikarya of the medial-basal hypothalamus, corresponding to the POMC perikarya of the rodent arcuate nucleus, exhibit major rostral projections to various telencephalic and diencephalic structures. The exact extent of fiber projections and innervation patterns arising from either of these two groups is not clear at this time and will require further analyses. Scattered fiber immunoreactivity was also seen in the medial cerebral cortex and the striatal complex, regions which apparently are not innervated by beta-endorphin fibers in the rodent brain. Also, no immunoreactivity was seen to an antiserum to the 16K peptide of POMC. Other similarities and differences in the brain distribution of POMC in reptiles and mammals are discussed.

In vitro synthesis of ACTH- and beta-endorphin-related substances in the pars distalis of Anolis carolinensis

In order to investigate the biosynthesis of ACTH- and beta-endorphin-related substances in the pars distalis of Anolis carolinensis, explants of pars distali were incubated for 24 hr in a complete medium which contained [3H]tyrosine. Acid extracts of the incubates were immunoprecipitated with either an affinity-purified ACTH antiserum or an affinity-purified beta-endorphin antiserum and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Three distinct peaks of ACTH-related material were detected. The major peak comigrated with human ACTH(1-39), while two minor peaks corresponded in apparent molecular weight to ACTH biosynthetic intermediate and precursor-sized material. Three peaks of beta-endorphin-related material were also detected. The major peak comigrated with beta-endorphin(1-31), while two minor peaks corresponded to beta-lipotropin (LPH) and precursor-sized material. Sequential immunoprecipitation experiments indicated that the precursor-sized material had antigenic determinants for both ACTH and beta-endorphin. In addition this peak was identical in apparent molecular weight to the common precursor for alpha-melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin in the pars intermedia of A. carolinensis (R.M. Dores, Peptides 3, 925-935). Analysis of extracts of reptile pars distalis by gel-filtration chromatography revealed a single peak of naloxone-reversible opiate bioactivity which coeluted with the peak of beta-endorphin-sized immunoreactivity. On a molar basis there is tenfold more opiate bioactivity in the reptile pars distalis than in the reptile pars intermedia.

Strategies for studying opioid peptide regulation at the gene, message and protein levels

Three opioid peptide precursors have been isolated and characterized in endocrine and nervous tissue: pro-opiomelanocortin, pro-enkephalin, and pro-dynorphin. Since each of those opioid peptide systems have been extensively characterized both biochemically and anatomically, this review will focus on strategies for studying the regulation of these systems at the levels of gene transcription, message translation, post-translational processing, secretion, and target cell receptor interaction.

Biosynthesis of multiple forms of beta-endorphin in the reptile intermediate pituitary

Fractionation of the beta-endorphin-sized material from freshly dissected reptile intermediate pituitaries by ion exchange chromatography on sulfopropyl Sephadex (SP) revealed at least three distinct forms of immunoreactive beta-endorphin. These forms eluted at 0.25 M NaCl, 0.28 M NaCl, and 0.32 M NaCl and represent respectively, 6%, 65% and 29% of the total immunoreactivity. Only the 0.28 M NaCl peak and the 0.32 M NaCl peak exhibited naloxone reversible opiate bioactivity when tested in the isolated guinea pig ileum bioassay system; taking into account the molar amount of immunoreactive peptides the 0.32 M NaCl peak was 6 fold more potent than the 0.28 M NaCl peak. Intermediate pituitaries in culture were incubated with either [3H]tyrosine, [3H]arginine, or [35S]methionine for periods up to 24 hours and beta-endorphin-sized peptides were prepared by immunoprecipitation and gel filtration. Fractionation of the labeled beta-endorphin-sized peptides by ion exchange chromatography yielded profiles nearly identical to the immunoassay analyses of freshly dissected tissue. Further analysis of the major labeled forms of reptile beta-endorphin by chromatography on Sephadex G-50 equilibrated in 6 M guanidine HCl indicated that the 0.32 M NaCl peak had an apparent molecular weight of 3500 +/- 100 and the 0.28 M NaCl peak had an apparent molecular weight of 3200 +/- 100. Furthermore, pulse/chase experiments showed that the 0.32 M NaCl peak was the precursor for the 0.28 M NaCl peak. These results coupled with the relative opiate bioactivities of the major argue that the principal post-translational modification of reptile beta-endorphin is COOH-terminal proteolytic cleavage.

Evidence for a common precursor for alpha MSH and beta-endorphin in the intermediate lobe of the pituitary of the reptile Anolis carolinensis

In order to investigate the biosynthesis of alpha MSH and beta-endorphin in a non-mammalian vertebrate, individual lizard intermediate pituitaries were incubated in complete medium containing a radioactive amino acid, using either a steady label or a pulse/chase protocol. Following incubation, acid extracts of the tissue were immunoprecipitated with either an NH2-terminal ACTH antiserum or a beta-endorphin antiserum and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. After a 24 hr steady label in medium containing [3H]tyrosine, multiple molecular weight forms of beta-endorphin-related and NH2-terminal ACTH-related radioactivity were detected. The major peak of beta-endorphin-related radioactivity co-migrated with synthetic beta-endorphin(1-31); minor peaks of beta LPH-sized material and precursor-sized material were also detected. The major peak of NH2-terminal ACTH-related material co-migrated with synthetic alpha MSH; in addition, smaller amounts of material designated ACTH biosynthetic intermediate 1, ACTH biosynthetic intermediate 2, and precursor-sized material were detected. Sequential immunoprecipitation experiments revealed that the precursor-sized material had antigenic determinants for both alpha MSH and beta-endorphin. Pulse/chase experiments established that this material is the common precursor for alpha MSH and beta-endorphin. Based on gel filtration chromatography in 6 M guanidine HCl, the molecular weights of these various peptides are: common precursor, 23,300 daltons; ACTH biosynthetic intermediate 1, 12,200 daltons; ACTH biosynthetic intermediate 2, 4,200 daltons; alpha MSH, 1,500 daltons; beta LPH, 8000 daltons; beta-endorphin, 3,400 daltons. None of the peptides precipitated with either antiserum incorporated [3H]glucosamine; thus glycosylation does not appear to be involved in this biosynthetic pathway in the lizard. The results of the kinetic experiments and molecular weight determinations indicate that the major biosynthetic pathway involves the following events: common precursor is first cleaved to yield ACTH biosynthetic intermediate 1 plus beta LPH; subsequently, beta LPH is cleaved to produce beta-endorphin; ACTH biosynthetic intermediate 1 is cleaved to produce ACTH biosynthetic intermediate 2 which is subsequently cleaved to produce alpha MSH. The pulse/chase experiments indicate minor pathways exist for cleaving beta-endorphin directly from the common precursor or via a high molecular weight form intermediate in size between the common precursor and beta LPH.