Common precursor to corticotropins and endorphins

beta-Endorphin is associated with overeating in genetically obese mice (ob/ob) and rats (fa/fa)

Small doses of the opiate antagonist naloxone selectively abolished overeating in genetically obese mice (ob/ob) and rats (fa/fa). Elevated concentrations of the naturally occurring opiate beta-endorphin were found in the pituitaries of both obese species and in the blood plasma of the obese rats. Brain levels of beta-endorphin and Leu-enkephalin were unchanged. These data suggest that excess pituitary beta-endorphin may play a role in the development of the overeating and obesity syndrome.

Construction of bacterial plasmids that contain the nucleotide sequence for bovine corticotropin-beta-lipotropin precursor

mRNA that encodes the common peptide precursor for the hormones corticotropin and beta-lipotropin was purified from the neurointermediate lobe of bovine pituitaries, and double-stranded cDNA species synthesized from this template were cloned in Escherichia coli X1776 by inserting them into the Pst I endonuclease cleavage site of the pBR322 plasmid using poly(dG)poly(dC) homopolymeric extensions. Certain of the cloned cDNA inserts contain nucleotides corresponding to the complete amino acid sequence of bovine corticotropin and a coding sequence that corresponds to at least the first portion of bovine beta-lipotropin. The nucleotide sequences coding for corticotropin and beta-lipotropin are separated on the cDNA by a 6-base-pair sequence encoding lysine and arginine, indicating that the carboxyl terminus of corticotropin is connected on the precursor peptide with the amino terminus of beta-lipotropin by these two amino acids. In addition, the cloned cDNA insert is characterized by an unusually high C+G nucleotide base content as well as by a number of DNA sequence duplications.

Presence of immunoreactive beta-endorphin in normal human plasma: a concomitant release of beta-endorphin with adrenocorticotropin after metyrapone administration

To elucidate whether or not beta-endorphin exists in plasma of normal subjects, plasma extracts obtained before and after metyrapone administration were subjected to gel exclusion chromatography, and fractions obtained were assayed by a sensitive radioimmunoassay for beta-endorphin. The basal plasma level of beta-endorphin was 5.8 +/- 1.1 pg/ml (mean +/- SE, n = 5), which rose significantly to the level of 48.9 +/- 3.8 pg/ml after a single oral dose (30 mg/kg of body wt) of metyrapone administration (P less than 0.001). Plasma ACTH levels also increased from the mean basal level of 73 +/- 4 pg/ml to 269 +/- 41 pg/ml after metyrapone administration. These results indicate that beta-endorphin, distinct from beta-lipotropin, exists in normal human plasma and that it is released from the pituitary concomitantly with ACTH.

Pituitary somatotrophs contain [Met]enkephalin-like immunoreactivity

Serial sections from epoxy resin-embedded rat anterior pituitaries were sequentially immunostained for endorphin, [Met]enkephalin, and growth hormone, respectively. We found that [Met]enkephalin immunoreactivity was confined to the growth hormone producing cells. Corticotropin/endorphin cells in the anterior pituitary from both normal and adrenalectomized rats did not contain any [Met]enkephalin immunoreactivity. When anterior pituitary cells were maintained in monolayer culture for 10 days, [Met]enkephalin immunoreactivity was still located in the growth hormone-producing cells although the staining was weaker than in the somatotrophs in pituitary tissue fixed immediately after death of the animals. This suggested that somatotrophs synthesize [Met]enkephalin. However, this cannot be proved conclusively until biosynthesis experiments have been performed. The following conclusions were drawn from these findings. (i) Anterior pituitary [Met]enkephalin is not an extraction artifact derived from beta-endorphin with which it shares the NH2-terminal pentapeptide sequence. (ii) In the anterior pituitary, beta-endorphin is not the precursor to [Met]enkephalin. [Met]Enkephalin in somatotrophs may be of brain origin and in the somatotrophs may be bound to intracellllar receptors as has been shown for luteotropin releasing hormone in gonadotropic cells.

Secretion of melanophore-stimulating hormone (MSH) in long-term cultures of pituitary neurointermediate lobes

Neurointermediate lobes from pituitaries of the frog, Rana berlandieri forreri (Rana pipiens, sensu lato), were maintained in organ culture in media with and without serum for up to six months. The cultured tissues were examined periodically by light microscopy and transmission electron microscopy and by bioassay of the melanophore-stimulating hormone (MSH) secreted and present in the culture media. Light-microscopic observations revealed a high degree of preservation of the pars intermedia at four weeks with isolated areas of some glands maintaining histological integrity for the entire six months. Similarly, at the ultrastructural level the cells appeared morphologically intact and to be actively synthesizing and secreting hormone. Bioassays showed the glands to be continuously secreting MSH; however, larger yields of hormone were obtained in media lacking serum. No significant ultrastructural differences between cells grown in the presence or absence of serum were detected. The difference in concentration of MSH between the two groups therefore apparently results from enzymatic degradation of the hormone by the serum. Organ culture of the vertebrate neurointermediate lobe may provide a unique method for the production of large quantities of MSH and for the study of other melanotropic and opiate peptides as they may be synthesized and secreted by the pars intermedia.

Beta-lipotropin and endorphins: implications of current knowledge

Evidence that the endorphins, metabolites of the pituitary hormone beta-lipotropin, profoundly affect mood and behavior, are secreted with ACTH in response to stress, and may act as neurotransmitters in the GI tract, suggests that they play an important role in CNS homeostasis. The fact that these peptides are synthesized in the GI tract as well as the brain casts new light on CNS-endocrine-environmental interrelationships.

Immunologic localization of alpha- and beta-endorphins and beta-lipotropin in corticotropic cells of the normal and anencephalic fetal pituitaries

The use of antibodies to alpha-(17--39) ACTH, beta-LPH, and alpha- and beta-endorphins has enabled the detection of immunoreactive cells as early as the eight week of fetal life. Immunoreactive cells are located in the anterior and intermediate lobes of the pituitary gland in normal human fetuses. The same cells reacted with different antisera used in the present study. No immunoreactive cells were observed in the posterior lobe. The specificity of the immunocytological reaction has been controlled. In seven anencephalic fetuses, the presence of immunoreactive cells suggests that ACTH and beta-LPH can originate from a common precursor and are synthesized independent of the hypothalamus.

beta-Endorphin is not detectable in plasma from normal human subjects

beta-Endorphin is not detectable in plasma from normal human subjects when measured under baseline conditions or after the subjects have received vasopressin, an agent that elevates beta-lipotropin and adrenocorticotropic hormone (ACTH). Significant amounts of beta-endorphin are present in plasma of patients with endocrine disorders associated with increased ACTH and beta-lipotropin production. Highly purified, natural beta-lipotropin is not peripherally converted to beta-endorphin in vivo in normal subjects.

Coordinate control of corticotropin, beta-lipotropin, and beta-endorphin release in mouse pituitary cell cultures

Hypothalamic extract stimulates the release of corticotropin (ACTH) and endorphins 2.5- to 30-fold in mouse pituitary tumor cell cultures (AtT-20/D(16v) line) and primary cell cultures from mouse anterior pituitary. ACTH and endorphin activities were measured by radioimmunoassay and immunoprecipitation. Pretreatment of tumor cell cultures with 1 muM dexamethasone reduced the stimulatory effect of the extract on release of ACTH and endorphins. Pretreatment of primary cell cultures with 10(-6) M dexamethasone reduced the stimulatory effect of both vasopressin and the extract on the release of ACTH and endorphins. Release of ACTH and endorphin was coupled in both kinds of cultures in the basal, stimulated, and inhibited states. The molecular weight forms of ACTH and endorphin in tumor cell culture medium were analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Radioimmunoassay and immunoprecipitation show that the 13,000-dalton and 4500-dalton forms of ACTH were present in about equal amounts in medium from cultures incubated with or without hypothalamic extract for 15 min, 30 min, or 2 hr. Smaller amounts of the high molecular weight forms of ACTH (20,000- to 23,000-dalton and 31,000-dalton ACTH) were observed in the culture medium at these times. The predominant forms of endorphin released after 20 min or 3 hr of incubation had molecular weights of 31,000, 11,700 (beta-lipotropic hormone-size material) and 3500 (beta-endorphin-size material). No degradation of the forms of endorphin released into the culture medium was observed after incubating the culture medium for 1.5 hr in the absence of cells. The proportions of the different forms of endorphin and ACTH present in the culture medium resembles that seen in cell extracts.

The enkephalins. Peptides with morphine-like activity

Two penta-peptides with morphine-like properties have recently been found in the nervous system and gastrointestinal tract. These peptides known as enkephalins are unevenly distributed in the brain, the highest concentration being in the globus pallidus. The enkephalins are found to have analgesic properties and are also anti-tussive, anti-diarrheal and able to stimulate release of prolactin and growth hormone. Synthetic analogues of the enkephalins containing specific D-amino acid substitutions have been developed and show a wide spectrum of activities.

Biosynthesis of beta-endorphin from beta-lipotropin and a larger molecular weight precursor in rat pars intermedia

When isolated rat pars intermedia cells were incubated for 10 min with radioactive amino acids, one major labeled protein with a molecular weight of 30,000 +/- 1500 was extracted. This protein was shown to contain in its sequence the antigenic determinants for corticotropin and beta-melanotropin by immunoprecipitation. When the radioactivity incorporated into this large molecular weight protein during the first 10 min was chased by a further incubation in presence of an excess of unlabeled amino acid, the initial protein was degraded into several smaller peptides including beta-endorphin and beta-lipotropin. Another 18,000-dalton peptide was also observed and was tentatively identified as a large molecular form of corticotropin. From the kinetics of the maturation of the initial precursor, it is concluded that the initial cleavage of the 30,000-dalton peptide gives rise to beta-lipotropin and the 18,000-dalton form of corticotropin. beta-Lipotropin is subsequently cleaved to form beta-endorphin.

Appearance of beta-endorphin-like immunoreactivity in human ventricular cerebrospinal fluid upon analgesic electrical stimulation

beta-Endorphin-like immunoreactivity in human ventricular cerebrospinal fluid was measured with a specific radioimmunoassay. The subjects were undergoing a surgical procedure for relief of chronic intractable pain. This procedure involved the focal stimulation of a medial thalamic site adjacent to the wall of the third ventricle. Samples were collected before and during the analgesic stimulation. No beta-endorphin-like immunoreactivity could be detected prior to stimulation, suggesting that baseline levels are below 25 fmol/ml of cerebrospinal fluid. Electrical stimulation led to substantial increases (13- to 20-fold) in immunoreactive material in every subject. These results suggest that beta-endorphin-like material can be released into the ventricular system and may contribute to the pain blockade that results from periventricular stimulation.

Corticotropin, lipotropin, and beta-endorphin production by a human nonpituitary tumor in culture: evidence for a common precursor

A continuous line (DMS-79) of human pulmonary small cell carcinoma cells was shown to secrete immunoreactive adrenocorticotropin (ACTH), lipotropin, and beta-endorphin concomitantly into the culture medium. Gel filtration of the culture medium demonstrated at least five components: high molecular weight material(s) that had ACTH, lipotropin, and beta-endorphin immunoreactivities and materials similar to ACTH, beta-lipotropin, gamma-lipotropin, and beta-endorphin in their immunoreactivities and apparent molecular weights. The same components were observed when gel filtration was carried out in 6 M guanidine-HCl, and the high molecular weight material(s) appeared to consist of more than one component, with molecular weights in the range of 15,000-40,000. Immune affinity chromatography of the high molecular weight component(s) from gel filtration with a specific anti-(1-24)ACTH serum demonstrated that the ACTH, lipotropin, and beta-endorphin immunoreactivities were possessed by the same molecule(s), suggesting that ACTH, lipotropins, and beta-endorphin were derived from a common, high molecular weight precursor.

Isolation of the C-fragment and C'-fragment of lipotropin from pig pituitary and C-fragment from brain

Three novel peptides derived from lipotropin, the C-Fragment (residues 61-91), C'-Fragment (61-87) and N-Fragment (1-38), were isolated from pig pituitary, and the C-Fragment was shown to be present in brain. The experimental procedures developed for their isolation are described. The formation of each of the fragments involves enzymic cleavage of lipotropin at consecutive basic residues, with specificity identical with that involved in the activation of known prohormones. In brain assays C-Fragment exhibits a range of biological activities related to its ability to act as an inhibitory neurotransmitter.

The effect of pituitary-adrenal function in the modulation of pain sensitivity in the rat

1. The relationship between adrenalcortical hormones, adrenocorticotrophic hormone (ACTH), and pain sensitivity was investigated in the rat. Pain sensitivity was assessed by measuring paw-lick and jump latencies in response to being placed on a grid at 55 degrees C.2. Bilateral adrenalectomy increased the sensitivity to pain, but adrenal demedullation had no effect.3. Pain sensitivity was inversely related to the circadian changes in circulating corticosterone and was greater at 7 a.m. than at 7 p.m. However, the same variation in pain sensitivity existed if the adrenals were removed, suggesting that the increase in pain sensitivity after adrenalectomy was not related directly to the levels of corticosteriods.4. The time course of the increase in pain sensitivity after adrenalectomy paralleled that of the changes in circulating ACTH. Adrenalectomy markedly increased pain sensitivity at 9 and 18 days following surgery when circulating ACTH levels were markedly elevated and corticosterone was absent, but not at 3 days following adrenalectomy when ACTH levels were lower and corticosterone was absent.5. Hypophysectomy decreased the sensitivity to pain.6. The results indicate that ACTH can alter pain sensitivity and that the effect of corticosteroids on the sensitivity to pain is an indirect one by virtue of their negative feed-back action on the hypothalamic-pituitary system.

Opiate effects after adrenocorticotropin or beta-endorphin injection in the periaqueductal gray matter of rats

Injections of adrenocorticotropic hormone (ACTH) into the periaqueductal gray matter of drug-naive rats resulted in a dose-dependent opiate abstinence syndrome characterized by fearful hyperreactivity and explosive motor behavior. Injecting shorter chains of ACTH caused attenuated forms of this behavior. Injections of beta-endorphin at this same site caused opposite behavior: sedative, analgestic, and catatonic. If the effects of morphine are mediated by two classes of receptor) and the other which is not stereospecific and naloxone-insensitive--the endogtor)--and the other which is not stereospecific and naloxone-insensitive the endogenous ligand of the second receptor may be ACTH. The neuropeptides ACTH and endorphin may be part of an integrated neuromodulatory system, and the opiate abstinence syndrome may be the result of an altered interaction between the two receptor systems.

High molecular weight opioid-containing proteins in striatum

Striatal extracts of guinea pigs, rats, and cattle were found to contain two large proteins (greater than 40,000 and greater than 100,000 daltons) that on treatment with trypsin yield opioid peptides differing chromatographically from the opioid nonapeptide generated by trypsin digestion of endorphins, beta-lipotropin, or pro-opiocortin. Furthermore, the large opioid proteins found in the pituitary do not appear to be present in the striatum. These and other findings indicate that the striatal enkephalins are produced via a pathway from the one deduced from studies on the pituitary.

ACTH-like immunoreactivity in the gastrin cell. Independent changes in gastrin and ACTH-like immunoreactivity during ontogeny

Rat antral gastrin cells have been shown to contain ACTH-like immunoreactivity. Studies on the ontogeny of the antral gastrin cells reveal that these cells start to store gastrin before they contain detectable quantities of ACTH-like immunoreactivity. At no stage studied were duodenal gastrin cells found to contain ACTH-like peptides. The data indicate that the G cells synthetizes and/or releases the two hormonal peptides independently.

Effects of naloxone on schizophrenia: reduction in hallucinations in a subpopulation of subjects

Endogenous opiate-like peptides (endorphins) are putative neuroregulators located throughout the mammalian brainstem. There is some evidence for their role in pain, stress, and affect. We report that the opiate antagonist, naloxone, alters some schizophrenic symptoms. In a double-blind, cross-over study, naloxone produced decreases in auditory hallucinations in some schizophrenic patients. This finding supports the hypothesis that the endorphins may play a roll in modulating hallucinations in a highly selected subgroup of chronically hallucinating schizophrenic patients.

In vitro biosynthesis and chemical characterization of beta-lipotropin, gamma-lipotropin, and beta-endorphin in rat pars intermedia

Three 3-hr incubations of pars intermedia cells from 40 rat pituitaries with [35S]methionine, [3H]lysine, and [3H]leucine sufficed for the identification and chemical characterization of biosynthesized beta-lipotropin, gamma-lipotropin, and beta-endorphin. From the molecular weight, migration on polyacrylamide gels, and sequence Met5, Lys9, Leu14,17, rat beta-endorphin was shown to be identical to its sheep homologue and no trace of Leu5 beta-endorphin could be detected. Rat beta-lipotropin differs from that of sheep in its elution properties on CM-cellulose, and its sequence shows Leu2,10,14, Lys20. Rat gamma-lipotropin shows the same NH2-terminal sequence as beta-lipotropin and is again different from its sheep homologue. The identification of rat beta-lipotropin was confirmed by its selective cleavage into beta-endorphin after trypsin digestion of the citraconylated peptide, a property not observed with rat gamma-lipotropin.

Adrenocorticotropin in rat brain: immunocytochemical localization in cells and axons

By means of antiserum (purified by affinity chromatography) directed against adrenocorticotropin (ACTH) 11-24, cell bodies and beaded axons were visualized in rat brain. The ACTH-like immunoreactivity (ACTH-LI) was primarily located in the hypothalamus (cells and axons). Fibers were scattered throughout thalamus, amygdala, periaqueductal gray area, and reticular formation. There was no change in the distribution of ACTH-LI in rats that had been subjected to hypophysectomy. This distribution of ACTH-LI parallels that of beta-lipotropin and is altered by specific lesions in a similar fashion. The presence of ACTH-LI in cells and beaded axons in brain raises the possibility that it is a neuroregulator functioning as a neurotransmitter, neuromodulator, or neurohormone.

Isolation and thin-layer chromatographic identification of several peptides with NH2-terminal tryptophan and their histochemical demonstration in the ACTH cells of the rat hypophysis

Methods for the isolation and thin-layer chromatographic identification of amino-terminal tryptophyl-peptides presumably responsible for histochemical tryptophyl-peptide reactions in the ACTH cells of the rat hypophysis are described. In the hypophyseal extract several tryptophylpeptide bands--depending on the homogenization solution--were demonstrated on thin-layer chromatograms. Tryptophyl-peptides were demonstrated from their fluorescence induced 1) with glyoxylic acid (glyoxylic acid introduced into the homogenization solution), 2) by exposure of the chromatographic plates to combined formaldehyde and chloral vapour or 3) by exposure to combined formaldehyde and acetyl chloride vapour. A positive PAS reaction was demonstrated in some tryptophyl-peptide bands. Thus, some tryptophylpeptides seem to contribute to the observed PAS positivity of the ACTH cells.

Radioimmunoassay of beta-endorphin basal and stimulated levels in extracted rat plasma

A sensitive radioimmunoassay for beta-endorphin is described. Antibodies against human beta-endorphin which exhibit a high avidity for the C-terminal of the peptide were raised in rabbits following the injection of thyroglobulin-coupled human beta-endorphin (betah-E) as immunogen. Methionine-enkephalin, alpha-, gamma-endorphine, as well as ACTH peptides did not cause interference in the radioimmunoassay. beta-Lipotropin, however, showed a 50% cross-reactivity. The sensitivity of the assay is 25 pg/0.5 ml tube volume for beta-endorphin. beta-Endorphin was extracted with a high recovery from the rat plasma using silicic acid and beta-endorphin levels as low as 100 pg/ml could be measured. Basal levels of beta-endorphin-like immunoreactivity in plasma of rats were about 400 pg/ml. beta-Endorphin levels in adrenalectomized rats and in animals chronically treated with the cortisol synthesis blocker metyrapone were found to be markedly increased (about 7-fold). Exposure of the rats to electrically induced footshocks caused a similar increase of immunoreactive beta-endorphin in plasma. A significant increase was also seen after insulin injection.

beta-Lipotropin is the major opioid-like peptide of human pituitary and rat pars distalis: lack of significant beta-endorphin

beta-Lipotropin is the predominant opioid peptide of the human pituitary and rat pars distalis and is present in concentrations essentially equimolar with corticotropin. When freshly, obtained nonfrozen rat anterior pituitaries were homogenized with 0.2 M HCl, approximately 98% of the immunoreactivity detected utilizing an antiserum that crossreacts equally with beta-lipotropin and beta-endorphin coeluted with 125I-labeled human beta-lipotropin upon molecular sieve chromatography. The remainder of the activity eluted with synthetic human beta-endorphin. Similar results were obtained for human pituitary. HCl homogenization of thawed tissue or homogenization of fresh tissue with acetic acid yielded substantially greater concentrations of beta-endorphin and decreased concentrations of beta-lipotropin. In human subjects, acute anterior pituitary stimulation using either insulin-induced hypoglycemia or vasopressin administration was associated with increased plasma beta-lipotropin and corticotropin levels. At the time of peak concentrations, no significant levels of beta-endorphin were detectable. These data indicate the lack of significant amounts of beta-endorphin in human pituitary. Additionally, there appears to be no specific intrapituitary conversion of beta-lipotropin to beta-endorphin.

Distribution of fibres reacting with an alpha-endorphin antiserum in the neurohypophysis of Carassius auratus and Cyprinus carpio

A strong positive immunoreaction with an alpha-endorphin antiserum occurs in two distinct sites of the goldfish and carp neurohypophysis. Fluorescent nerve terminals are found in the laminar nerve processes located in the rostral pars distalis, but the immunocytological reaction is mainly localised on the nerve processes of the posterior neurohypophysis lying between the intermediate lobe cells. Almost all the digitations of the neurohypophysis are strongly fluorescent. The immunoreactive fibres probably originate from the hypothalamus, where perikarya displaying the same immunoreaction have been found in the pars lateralis of the nucleus lateralis tuberis and in some minor centres. The possibility that the immunoreactive substances revealed on the neurohypophyseal processes may originate in the intermediate lobe cells is also discussed. It has now to be established if this hypothalamo-hypophyseal system contains a substance with endorphic properties or only some immunologically related substance devoid of the corresponding physiological activities.

Behavioral neurochemistry: neuroregulators and behavioral states

There is compelling evidence that behavioral events after neurochemical function and that altered neurochemical function can change behavior. Such processes have been related both to neurotransmitters and to neuromodulators, together termed neuroregulators. Available research tools and theoretical constructs have begun to permit studies of certain types of behavior, primarily those related to emotional states and drives. This work is changing long-held concepts about severe mental disorders and the treatment of them.

Immunocytological detection and localization of a peptide reacting with an alpha-endorphin antiserum in the corticotropic and melanotropic cells of the trout pituitary (Salmo irideus Gibb)

In the pituitary of the trout, the corticotropic and melanotropic cells display a strong immunocytological reaction with alpha-endorphin antiserum. This reaction persists even when alpha-endorphin antisera treated with beta-1-24ACTH or alpha-MSH are used. In the absence of pharmacological tests on the endorphic potencies of the compounds involved in the immunoreaction, it is not yeat clear whether this reaction is due to the presence of an alpha-endorphin-like peptide or simply an immunologically related peptide without the properties of endorphin. However, the presence of such peptides in the fish pituitary is interesting from the comparative point of view.

Distribution of ACTH-like immunoreactivity in rat brain and gastrointestinal tract

Immunocytochemistry reveals ACTH-like immunoreactivity to reside not only in the pituitary but also in central nerves and in central nerves and in antral gastrin cells. In all probability, the central nerves store a peptide identical with or closely resembling true ACTH. Their pattern of distribution is, in some regions, similar to that of enkephalin-immunoreactive nerves. The antiserum demonstrating ACTH-like immunoreactivity in central nerves and in antral gastrin cells is directed towards the COOH-terminal part of the hormone. A peptide corresponding to this part, the corticotrophin-like intermediate peptide (CLIP) is manufactured by the pars intermedia of the pituitary. CLIP is devoid of adrenocortical activity, but has recently been shown to possess insulin-releasing activity. The occurrence of CLIP-like peptides in antral gastrin cells may indicate a role for such peptides in the gastrointestinal regulation of insulin release. The simultaneous occurrence of enkephalin-like and ACTH-like immunoreactivity in the antral gastrin cells is of particular interest since a large precursor molecule, containing both the enkephalin and the ACTH sequence has recently been identified.

Neurons containing beta-endorphin in rat brain exist separately from those containing enkephalin: immunocytochemical studies

Well-characterized antisera to porcine beta-endorphin were used to localize immunoreactive sites in cryostat sections of formaldehyde-fixed rat brain by indirect immunohistochemistry. Specificity was established by absorption of immune sera with synthetic peptide fragments. Specific immunoreactivity was localized to neuronal perikarya in the basal tuberal hypothalamus, and to varicose nerve fibers which were distributed to midline nuclear areas throughout the diencephalon and anterior pons. These patterns of reactivity were unaffected by preabsorption of the immune sera with millimolar concentrations of Met5- or Leu5-enkephalin or alpha-endorphin. The beta-endorphin immunoreactive structures were morphologically separate from those cells and fibers reported to react with antisera to the enkephalins. One anti-beta-endorphin serum gave additional immunoreactivity with myelinated axons in limbic cortical zones; when absorbed with purified rat myelin basic protein, only the specific patterns of immunoreactivity remained. Thus, discrete beta-endorphin-containing neuronal circuits exist in rat brain and are anatomically distinguishable from enkephalin-containing nerve cell and fiber pathways.

Characterization of pro-opiocortin, a precursor to opioid peptides and corticotropin

The high molecular weight (approximately 30,000) precursor to opioid activity (pro-opiocortin) previously detected in extracts of rat pituitary was digested with trypsin and the resulting peptide mixture was resolved by high-performance reverse-phase chromatography. A peak of opioid activity was eluted at the position of the nonapeptide beta-LPH (61-69), which was also the same fragment obtained by trypsin digestion of betas-lipotropin or beta-endorphin. This identified the protein as a precursor to the endorphins and Met-enkephalin. No activity was detected in the position corresponding to the Leu5 analog of betas-LPH (61-69), thus ruling out the possibility of a beta-lipotropin-like precursor to Leu-enkephalin in pituitary extracts. Pro-opiocortin and beta-lipotropin are present in rat pituitary extracts in comparable amounts, approximately 10 pmol/mg of tissue.

Existence of a common precursor to ACTH and endorphin in the anterior and intermediate lobes of the rat pituitary

Extracts of rat anterior and intermediate-posterior pituitary were fractionated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and assayed for immunoactive ACTH and endorphin. In both lobes the major forms of immunoactive ACTH have apparent molecular weights of 31,000 (31K), 20--21K, 14K, and 4.5K, and the major forms of immunoactive endorphin have apparent molecular weights of 31K (coincident with the peak of immunoactive ACTH), 13K (a betaLPH-like peptide), and 3.5K (a beta-endorphin-like peptide). However, the quantitative distribution of immunoactivity among the various forms differs greatly between the lobes. Assays using an extreme COOH-terminal ACTH antiserum indicate that the 31K ACTH/endorphin molecule in rat anterior and intermediate pituitary is similar to the pro-ACTH/endorphin molecule from mouse pituitary tumor cells. A radioimmunoassay that is specific for the NH2-terminal non-ACTH, nonendorphin segment (referred to as 16K fragment) of the mouse pro-ACTH/endorphin molecule was used to assay extracts of rat pituitary. In addition to detecting material at 31K and 20--21K, the 16K fragment radioimmunoassay detects significant amounts of cross-reactive material with an apparent molecular weight of 16K in extracts of both lobes. This result also suggests that the structure and processing of the rat 31K ACTH/endorphin molecule is similar to that of mouse tumor cell pro-ACTH/endorphin. Cell suspensions were prepared from the anterior and intermediate lobes of the rat pituitary and maintained in culture for a 24-h period. The isolated cells from both lobes incorporate [3H] phenylalanine into immunoprecipitable ACTH- and endorphin-containing molecules. By sequential immunoprecipitation with ACTH and endorphin antisera, it is possible to demonstrate directly that a single molecule (31K ACTH/endorphin) has antigenic determinants for both ACTH and endorphin. Significant amounts of 31K ACTH/endorphin are released into the culture medium by isolated anterior lobe and intermediate lobe cells. The isolated intermediate lobe cells synthesize and secrete relatively large amounts of a beta-endorphin-like molecule; the isolated anterior lobe cells secrete significant amounts of both a betaLPH-like molecule and a beta-endorphin-like molecule. These same quantitative differences between anterior and intermediate lobe tissue were observed in immunoassays of extracts of the separated lobes and probably reflect differences in the processing of the common precursor. The isolated anterior lobe cells can be stimulated to release increased amounts of immunoprecipitable ACTH and endorphin by incubation with a cyclic AMP analog and a phosphodiesterase inhibitor.

Corticotropin-like peptides in central nerves and in endocrine cells of gut and pancreas

Extrapituitary corticotropin-like peptides have been found in central nerves and in gastrointestinal and pancreatic endocrine cells. Previous biological and immunological data strongly indicate that the immunoreactivity present in the central nerves represents corticotropin (A.C.T.H.) or a closely related peptide. In some areas of the brain, the distribution of A.C.T.H. nerves parallels that of nerves containing the endogenous opioid ligand, enkephalin. Since A.C.T.H. fragments bind to the opioid receptor the two neuronal peptides may interact. The antiserum used demonstrates the COOH-terminus of the A.C.T.H. molecule, which is devoid of adrenocortical stimulatory activity. A COOH-terminal A.C.T.H.-peptide, corticotropin-like intermediate peptide (C.L.I.P.), originally isolated from the pars intermedia, has been shown to stimulate release of pancreatic insulin. The presence of C.L.I.P.-like molecules in gut and pancreatic endocrine cells may indicate that C.L.I.P.'s insulin-releasing activity is physiologically important. Further, the occurrence of A.C.T.H.-related molecules in such cells may account for the ectopic A.C.T.H. syndrome associated with some tumours of gut and pancreas.

Characterization of a common precursor to corticotropin and beta-lipotropin: identification of beta-lipotropin peptides and their arrangement relative to corticotropin in the precursor synthesized in a cell-free system

Radioactive proteins synthesized in an mRNA-dependent reticulocyte cell-free system under the direction of mRNA from AtT-20/D-16v mouse cells were isolated by specific immunoprecipitation using antiserum to either alpha(1-24) corticotropin or beta-endorphin [beta(61-91) lipotropin]. Each immunoprecipitate was fractionated by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and shown to contain only one labeled protein with an apparent molecular weight of 28,500. Tryptic peptide analysis of the Mr 28,500 corticotropin and beta-lipotropin molecules isolated from the gels demonstrated that the two proteins had the same lysine, methionine, and tryptophan peptides. Four tryptic peptides from the cell-free product exhibited the same electrophoretic and chromatographic mobilities as marker tryptic peptides from bovine beta-melanotropin and porcine beta-endorphin. The identification of these peptides was confirmed by amino acid composition studies with a variety of labeled amino acids. The beta-lipotropin tryptic peptides were also shown to be located carboxy terminal to the corticotropin tryptic peptides.

Effects of peptides of pituitary origin on the formation of C21 steroid by fetal calf adrenal cells in culture

Corticotrophic activity of opiate-like peptides was assessed by their ability to stimulate the formation of C21 steroids from [3H] progesterone by three-day old cultures of fetal calf adrenal cells. ACTH1-39, ACTHα1-24 and a purified preparation of pituitary ovine β-endorphin caused a marked increase in 17α and 21-hydroxylation while a preparation of pure synthetic porcine β-endorphin gave a minimal stimulation. The activity of the purified ovine β-endorphin preparation could not be accounted for by contamination by ACTH or by a synergistic action between the two peptides. The novel pituitary factor described here may be due to a contaminant of the β-endorphin peak which is different from ACTH1-39.

Characterization of a common precursor to corticotropin and beta-lipotropin: cell-free synthesis of the precursor and identification of corticotropin peptides in the molecule

mRNA was isolated from cultures of AtT-20/D-16v tumor cells and translated in a mRNA-dependent reticulocyte cell-free system. The corticotropin (ACTH) product was purified by a double-antibody immunoprecipitation procedure using antisera specific for the alpha(1-24) sequence of ACTH. The product is shown by sodium dodecyl sulfate/gel electrophoresis and gel filtration on guanidine-HCl columns to be homogeneous with an apparent molecular weight (Mr) of 28,500. A product with the same molecular weight is synthesized when membrane-bound polysomes from D-16v cells are allowed to complete their nascent chains in a reticulocyte cell-free system. Mr 31,000 ACTH isolated from tumor cells has been separated into three proteins of different apparent Mr:29,000, 32,000, and 34,000. The cell-free product contains the same lysine-, methionine-, and phenylalanine-labeled tryptic peptides as the Mr 29,000 ACTH synthesized in the tumor cells. Tryptic peptide analysis also reveals the presence of the alpha(1-39) sequence in the Mr 28,500 cell-free product and suggests that there is only one copy of this sequence in the Mr 28,500 molecule.

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.