PubMed Health⌕ Search

Biomedical subjects

V M Wiegant

Publications and source records attributed to V M Wiegant.

At least 127 records · Page 7Linked to original sources
PubMed1984

Isolation and characterization of alpha-endorphin and gamma-endorphin from single human pituitary glands.

alpha-Endorphin and gamma-endorphin, two closely related peptides of the pro-opiomelanocortin family with characteristic biological activities, were purified to homogeneity from single human pituitary glands and chemically identified. Isolation of the peptides was based on size fractionation by Sephadex G-75 chromatography followed by two HPLC steps using reverse-phase and paired-ion reverse-phase systems and was monitored by radioimmunoassay. During the isolation procedure alpha- and gamma-endorphin-sized material behaved chromatographically and immunologically indistinguishably from synthetic alpha- and gamma-endorphin. The amino acid composition and NH2-terminus of isolated peptides demonstrated their identity as authentic alpha-endorphin and gamma-endorphin. Acetylated forms were absent. In addition, evidence is provided that large forms with alpha- and gamma-endorphin immunoreactivity detected during gel filtration are human lipotropin-(1-74) and -(1-75), respectively. The data substantiate that alpha-endorphin and gamma-endorphin exist as endogenous peptides in the human pituitary gland.

Amino Acids↗
PubMed1984

ACTH and beta-endorphin secretion by three corticotrophic adenomas in culture. Effects of culture time, dexamethasone, vasopressin and synthetic corticotrophin releasing factor.

Dispersed corticotrophic cells of 3 patients with Nelson's syndrome were studied in tissue culture for up to 25 days. During this culture period a parallel decrease with time was seen in ACTH and beta-endorphin-like immunoreactivity ( LIR ) release. A concomitant decline was observed for intracellular hormones. The time course of hormone release showed a parallel secretion of ACTH and beta-endorphin- LIR up to 8 h. Both the release of ACTH and beta-endorphin LIR were stimulated by 0.1 microM lysine vasopressin (LVP) in all three adenoma cell cultures. Dexamethasone (0.1 and 1 microM) suppressed basal hormone secretion for 4 h. Synthetic ovine corticotrophin-releasing factor (CRF) at 10 and 100 nM stimulated the secretion of ACTH and beta-endorphin LIR maximally. This stimulation was higher than observed with maximal stimulative concentration of LVP (0.3 microM). The CRF-mediated hormone secretion was calcium-dependent. Dexamethasone (0.1 microM) blocked the stimulating effect of 10 nM CRF completely. Gel-filtration chromatography demonstrated the cells to secrete both beta-lipotrophin (beta-LPH) and beta-endorphin. The ratio of beta-LPH to beta-endorphin released remained constant upon stimulation by LVP and CRF. HPLC studies demonstrate the possibility that several beta-endorphin fragments, including alpha-endorphin and gamma-endorphin, were secreted by cells from a Nelson tumour. CRF caused a simultaneous parallel stimulation of the release of these peptides.

Adenoma↗
PubMed1984

The stimulatory effect of a non-opiate beta-endorphin fragment on arginine-vasopressin release in rats.

The effect of the non-opiate beta-endorphin (beta E) fragment 2-9 and related peptides on immunoreactive (IR) arginine8 -vasopressin (AVP) levels was studied in the rat eye plexus plasma. Additionally, the effect of beta E 2-9 on AVP release from pituitary neurointermediate lobes ( NILs ), in vitro was studied. IR AVP levels in the eye plexus plasma increased after subcutaneous (s.c.) injection of beta E 2-9. In female rats peak values were observed 2 min after the administration of beta E 2-9 (10 micrograms/rat). Male rats were 100 times more sensitive than female rats. A dose-response study revealed a U-shaped relationship for this effect of beta E 2-9 in animals of both sexes. From structure-activity studies it appeared that beta E 2-9 was the most effective fragment. Intracerebroventricular (i.c.v.) administration of beta E 2-9 did not affect the IR-AVP levels in eye plexus plasma. Moreover, AVP release from the rat NILs cells in vitro was stimulated by perfusion with beta E 2-9, indicating a direct effect of the peptide on the pituitary. Therefore we suggest that beta E 2-9 increases AVP release by a direct action on the posterior pituitary.

Animals↗
PubMed1983

Naltrexone-sensitive behavioral actions of the ACTH 4-9 analog (Org 2766).

The effects of the ACTH 4-9 analog (Org 2766) and the COOH-terminal tripeptide of Org 2766 (Phe-D-Lys-Phe; PDLP) on retrieval of one-trial learning passive avoidance behavior were compared with those of beta-endorphin, [Met5]-enkephalin, [D-Ala2,Met5]-enkephalin, des-Tyr1-[Met5]-enkephalin and des-enkephalin-gamma-endorphin (DE gamma E). Amounts of intracerebroventricularly administered Org 2766, PDLP, [Met5]-enkephalin, [D-Ala2,Met5]-enkephalin and DE gamma E, which induced a comparable attenuation of passive avoidance behavior were determined. Pretreatment with the opiate antagonist naltrexone prevented the attenuating effect of these peptides on passive avoidance behavior except that of DE gamma E. The attenuating effect of Org 2766 and of [Met5]-enkephalin was reversed to facilitation of passive avoidance behavior in the presence of naltrexone. Subcutaneous treatment with Org 2766 and [D-Phe7]-ACTH 4-10 decreased electrical self-stimulation behavior elicited from the medial septal area. Naltrexone prevented the inhibitory effect of Org 2766 on this behavior, but not that of [D-Phe7]-ACTH 4-10. Although the attenuating effect of PDLP on passive avoidance behavior was not reduced by pretreatment with [Met5]-enkephalin- or beta-endorphin-antiserum, and PDLP induced neither analgesia nor excessive grooming, the data suggest that the inhibitory effect of Org 2766 and PDLP on passive avoidance behavior and electrical self-stimulation are mediated by endorphin systems in the brain.

Adrenocorticotropic Hormone↗
PubMed1983

Proteolytic conversion of angiotensins in rat brain tissue.

The proteolytic conversion of angiotensins in rab brain preparations was studied. Angiotensin I was converted into angiotensin II by enzymes which were associated with a synaptic membrane preparation, while angiotensin II was relatively resistant to proteolysis by these enzymes. Angiotensin II was rapidly metabolized at both pH 7.4 and pH 5.4 by enzymes in the soluble fraction of a synaptosomal preparation. One of the fragments formed at pH 7.4 was characterized as angiotensin III. At pH 5.4 only one fragment was generated which was characterized as angiotensin-(1-7)-heptapeptide. Enzymatically generated angiotensin II and III displayed pronounced biological activity in the brain, whereas angiotensin-(1-7)-heptapeptide was inactive. These data indicate a route for the generation, and the inactivation of biologically active angiotensins in the brain.

Angiotensin I↗
PubMed1983

Characterization of N alpha-acetyl-alpha-endorphin from rat neurointermediate lobe and its distribution in pituitary and brain.

N alpha-Acetyl-alpha-endorphin was characterized from rat neurointermediate lobe. The distribution of the acetylated and the non-acetylated form of alpha-endorphin in dissected areas of pituitary and brain appeared to be uneven. alpha-Endorphin appeared to be the main peptide in the anterior pituitary, whereas in the neurointermediate lobe N alpha-acetyl-alpha-endorphin accounted for most of the alpha-endorphin immunoreactivity. In the brain, the highest concentration of alpha-endorphin immunoreactivity was found in the hypothalamus. In hypothalamus and thalamus alpha-endorphin predominated, whereas in amygdala, hippocampus and septum N alpha-acetyl-alpha-endorphin represented most of the alpha-endorphin-immunoreactivity. In view of the non-opioid properties of acetylated endorphins, it is suggested that acetylation represents a mechanism allowing the organism to specifically select the non-opioid behavioral activities enclosed in the endorphin sequence.

Animals↗
PubMed1983

Binding of angiotensins to rat brain tissue: structure activity relationship.

The binding of 3H-angiotensin II to a synaptosome-enriched fraction of the subcortical part of rat brain was studied. In this fraction specific high-affinity binding sites for angiotensin II were demonstrated. The binding sites were saturated at a ligand concentration of 2 X 10(-9) M. Scatchard analysis revealed a single class of binding sites with an apparent maximal binding capacity of 14 fmoles/mg of protein and an equilibrium dissociation constant, KD, of 0.9 X 10(-9) M. The specific binding at the KD concentration amounted to 59% of the total binding and was reversible. The association and dissociation rate constants (k1 and k-1) were 0.0212 nM-1 min-1 and 0.0196 min-1, respectively. Binding was dependent on both incubation time and tissue concentration in the incubation mixture. Angiotensins with biological activity in the brain, i.e., angiotensins I, II, III, and the fragments (3-8) and (4-8) competed with 3H-angiotensin II for the binding sites with IC50's of 9 X 10(-8) M, 2 X 10(-9) M, 4 X 10(-9) M, 4 X 10(-7) M and 4 X 10(-6), respectively. In the presence of 1 mM of the converting enzyme inhibitor SQ 14,225 the IC50 for angiotensin I was 2 X 10(-7) M. Competition by the biologically active fragment angiotensin (5-8) could not be demonstrated. The latter peptide, however, was highly metabolized during the incubation under the assay conditions used. The binding potency of the various angiotensins paralleled their dipsogenic and pressor potency. The present data indicate the possible physiological involvement of these binding sites as specific receptors in the actions of angiotensins in the brain.

Angiotensin II↗
PubMed1982

beta-Endorphin proteolysis by guinea-pig ileum myenteric plexus membranes: increased gamma-endorphin turnover after chronic exposure to morphine.

The influence of chronic morphine exposure in vitro on the biotransformation of beta-endorphin (beta E) was investigated using the myenteric plexus-longitudinal muscle of guinea-pig ileum. A membrane preparation was incubated with beta E and the degradation of beta E as well as the accumulation of several beta E fragments in the incubation medium were followed with time. The levels of peptides were determined by specific radioimmunoassays after separation by high-pressure liquid chromatography. It was found that exposure to morphine did not affect the disappearance of beta E, but altered the time course of accumulation of beta E fragments. In fact, the accumulation of gamma-endorphin, alpha-endorphin and des-tyrosine1-alpha-endorphin was enhanced, while that of des-tyrosine1-gamma-endorphin was not change. Additionally, the disappearance of gamma-endorphin appeared to be stimulated by morphine exposure. These data provide evidence that the fragmentation of beta E is changed by chronic morphine exposure in such a way that the turnover of gamma-endorphin is increased.

Animals↗
PubMed1982

Central effects of angiotensins on drinking and blood pressure: structure-activity relationships.

The dipsogenic and the pressor effect following intracerebroventricular injection of angiotensins and several C-terminal fragments were studied. Angiotensin I (ANG I), ANG II, ANG III and C-terminal hexa-, penta, tetra- and tripeptide stimulated water intake in water-replete rats and induced significant pressor responses. In both paradigms the most active peptides (in the pmol range) were ANG II, ANG I and ANG III, in that order. Shorter C-terminal peptides appeared to be active, but had to be injected in the nmol range. Latencies to the onset of drinking were less than 45 s for all peptides tested. The C-terminal dipeptide and other dipeptide fragments did not possess detectable dipsogenic activity. The dipsogenic effect of ANG I was inhibited by pretreatment of animals with the converting enzyme inhibitor SQ 14,225. Drinking induced by both ANG I and ANG (4-8) was antagonized by the ANG II-receptor blocking agent Sar1-Ala8-ANG II. It is concluded that conversion of ANG I into ANG II is a prerequisite for the expression of the observed biological activity in the brain. Short C-terminal fragments are capable of stimulating the ANG II receptors, but a peptide chain of 7 amino acids appears necessary for maximal agonistic activity.

Angiotensins↗
PubMed1982

Regional distribution of alpha- and gamma-type endorphins in rat brain.

The regional distribution of Met-enkephalin, beta-endorphin and alpha- and gamma-type endorphins in rat brain was investigated. To that end, brains were dissected into anatomically defined areas. Acetic acid tissue extracts were fractionated using an HPLC system suitable for separation of endorphins and peptide concentrations were subsequently measured by specific radioimmunoassay systems. The distribution of Met-enkephalin and beta-endorphin through the brain was fairly uneven and in accordance with results obtained by others. The peptides alpha-endorphin, gamma-endorphin, des-Tyr-alpha-endorphin (DT alpha E) and des-Tyr-gamma-endorphin (DT gamma E) were detectable in almost all brain areas. Their distribution, however, appeared to be uneven. Hypothalamus and septum showed the highest levels of alpha- and gamma-type endorphins. These regions also contained high amounts of beta-endorphin, underscoring a precursor function of this peptide in the formation of alpha- and gamma-type fragments. In general, levels of alpha-endorphin were higher than those of des-Try-alpha-endorphin, whereas the opposite was found for gamma- and des-Tyr-gamma-endorphin.

Animals↗
PubMed1982

Subcellular localization in rat brain of angiotensin I-generating endopeptidase activity distinct from cathepsin D.

The generation of angiotensin I from the artificial renin substrate tetradecapeptide by proteolytic enzymes in rat brain tissue was studied. The involvement of endopeptidase activity in the enzymatical cleavage of the renin substrate was inferred from the simultaneous accumulation of both angiotensin I and the complementary tetrapeptide Leu-Val-Tyr-Ser on incubation of tetradecapeptide with rat brain tissue. This endopeptidase activity was active over a pH range of 3.5--7.5. In contrast, cathepsin D released angiotensin I from tetradecapeptide only at acidic pH. The angiotensin I accumulation on incubation of tetradecapeptide with brain endopeptidase activity was only partly inhibited in the presence of an excess of the carboxyl protease inhibitor N-acetyl pepstatin. Further, the brain endopeptidase activity displayed a subcellular localization different from that of acid protease activity. It is concluded that angiotensin I can be generated in the brain by soluble endopeptidases, which are distinct from cathepsin D.

Angiotensin I↗
PubMed1981

Angiotensin generation in the brain and drinking: indications for the involvement of endopeptidase activity distinct from cathepsin D.

The dipsogenic activity of two artificial renin substrates, tetradecapeptide and tridecapeptide, was studied. The dose-response curves obtained with these peptides, following intracerebroventricular administration, were similar to that of angiotensin I. The angiotensin II antagonist, Sar1, Ala8-angiotensin II, inhibited the dipsogenic effect of tetradecapeptide, indicating the conversion of the latter peptide into angiotensin II. The lower dipsogenic activity of tridecapeptide points to a conversion of this renin substrate into angiotensin III. Specific inhibition of tetradecapeptide induced drinking by the endopeptidase inhibitor N-acetyl-pepstatin suggests the involvement of an endopeptidase in the conversion of the renin substrates in the brain. Two endopeptidases present in the brain (cathepsin D and renin), were compared with respect to their capacity to generate angiotensin I from artificial renin substrate in vitro. Cathepsin D was active under only acidic pH conditions, whereas renin showed a wider pH range with maximal activity in the non-acidic region. Moreover, cathepsin D did not generate angiotensin I from natural, cerebrospinal fluid-angiotensinogen in vitro, and lacked dipsogenic activity following central administration. Small amounts of renin, however, were able to release angiotensin I from cerebrospinal fluid in vitro. In addition, this enzyme induced high dipsogenic activity upon intracerebroventricular injection. These results support the existence of a functionally active central renin-angiotensin system and provide an argument against the involvement of cathepsin D in the formation of angiotensin I in the brain.

Angiotensin I↗
PubMed1981

Interspecies comparison of brain ganglioside patterns studied by two-dimensional thin-layer chromatography.

Brain gangliosides from four vertebrate classes (fish, amphibia, aves, and mammalia) were studied by patterns generated with the use of two-dimensional thin-layer chromatography. In an effort to retain possible alkalilabile gangliosides, samples were not base-hydrolyzed. Resultant chromatograms revealed complex patterns of the major known gangliosides and a number of minor and trace molecular species previously unresolved. More than 30 resorcinol-positive components were detected in mammalian neural samples. Our data indicate both qualitative and quantitative differences in the chromatogram patterns between the vertebrate classes, but potentially greater qualitative similarity exists between the lower and higher classes than has previously been noted.

Animals↗
PubMed1980

Separation and quantification of angiotensins and some related peptides by high-performance liquid chromatography.

A high-performance chromatographic technique for the separation of angiotensins and some related peptides is described. Complete separation of angiotensin I, angiotensin II, tetradecapeptide and the tetrapeptide Leu-Val-Tyr-Ser is achieved in a single step, using reversed-phase high-performance liquid chromatography. The application of this technique for the detection of renin activity in crude biological samples, employing the artificial renin substrate tetradecapeptide, is demonstrated.

Angiotensin I↗