Role of angiotensin converting enzyme in the vascular effects of an endopeptidase 24.15 inhibitor

1. We investigated the role of angiotensin converting enzyme (ACE) in the cardiovascular effects of N-[1-(R,S)-carboxy-3-phenylpropyl]-Ala-Ala-Tyr-p-aminobenzoate (cFP), a peptidase inhibitor selective for metalloendopeptidase (EP) E.C. 3.4.24.15. 2. In conscious rabbits, cFP (5 mg kg-1, i.v.) markedly slowed the degradation of [3H]-bradykinin, potentiated the depressor response to right atrial administration of bradykinin (10-1000 ng kg-1), and inhibited the pressor response to right atrial angiotensin I (10-100 ng kg-1). In each of these respects, the effects of cFP were indistinguishable from those of the ACE inhibitor, captopril (0.5 mg plus 10 mg kg-1h-1 i.v.). Furthermore, the effects of combined administration of cFP and captopril were indistinguishable from those of captopril alone. 3. In experimentally naive anaesthetized rats, cFP administration (9.3 mg kg-1, i.v.) was followed by a moderate but sustained fall in arterial pressure of 13 mmHg. However, in rats pretreated with bradykinin (50 micrograms kg-1) a more pronounced fall of 30 mmHg was observed. Captopril (5 mg kg-1) had similar hypotensive effects to those of cFP, and cFP had no effect when it was administered after captopril. 4. CFP displaced the binding of [125I]-351A (the p-hydroxybenzamidine derivative of lisinopril) from preparations of rat plasma ACE and solubilized lung membrane ACE (KD = 1.2 and 0.14 microM respectively), and inhibited rat plasma ACE activity (KI = 2.4 microM). Addition of phosphoramidon (10 microM), an inhibitor of a range of metalloendopeptidases, including neutral endopeptidase (E.C.3.4.24.11), markedly reduced the potency of cFP in these systems. 5. Taken together these findings suggest that the actions of cFP in vivo are attributable to inhibition of ACE rather than EP 24.15. Given that cFP is a poor inhibitor of ACE in the presence of phosphoramidon in vitro, it is likely that cFP is cleaved by a phosphoramidon-sensitive metallopeptidase in vivo to liberate N-[1-(R,S)-carboxy-3-phenylpropyl]-Ala-Ala, a potent ACE inhibitor.

Evidence for a two-step mechanism of gonadotropin-releasing hormone metabolism by prolyl endopeptidase and metalloendopeptidase EC 3.4.24.15 in ovine hypothalamic extracts

The metalloendopeptidase EC 3.4.24.15 is believed to degrade gonadotropin-releasing hormone (GnRH) (pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) by cleavage at the Tyr5-Gly6 bond. We compared the ability of crude and partially purified endopeptidase 24.15 from ovine hypothalamus with recombinant rat testicular endopeptidase 24.15 to degrade synthetic GnRH. Both soluble and membrane hypothalamic fractions degraded GnRH to GnRH1-5, with some production of GnRH1-9 and GnRH1-3. Generation of the smaller fragments was blocked by a specific endopeptidase 24.15 inhibitor (CFP-AAY-pAB), but production of GnRH1-9 was reciprocally enhanced, suggesting this peptide may be an intermediate generated by prolyl endopeptidase. Indeed, both bacitracin and Z-Pro-prolinal, inhibitors of this enzyme, markedly reduced GnRH degradation to any product. Degradation of synthetic GnRH1-9 was more rapid than that of GnRH and was inhibited by CFP-AAY-pAB but not bacitracin. Activity against either substrate was greater in the soluble fraction. Repeated washing of the membrane fraction followed by extraction with Triton X-114 suggested that both endopeptidase 24.15 and prolyl endopeptidase, although predominantly soluble, can be peripherally associated with membranes. When fractionated by hydrophobic interaction chromatography, soluble endopeptidase 24.15 degraded GnRH only in fractions that also exhibited prolyl endopeptidase activity. In contrast, maximal degradation of GnRH1-9 was observed in adjacent fractions, which also contained the highest levels of immunoreactive endopeptidase 24.15. The affinity of recombinant endopeptidase 24.15 for GnRH was low (Km = 1.35 mM), was improved 10-15-fold by removal of the COOH-terminal amide or glycinamide (Km = 90 and 119 microM, respectively), and could be inhibited by CFP-AAY-pAB but not bacitracin. Taken together, these results suggest that GnRH metabolism in the hypothalamus may occur via a two-step process involving first removal of Gly10-NH2 by prolyl endopeptidase, followed by cleavage by endopeptidase 24.15 at the Tyr5-Gly6 bond.

Pharmacological characterization of linear analogues of vasopressin generated by the systematic substitution of positions 1 and 6 by L-amino acids

Eighteen linear analogues of [Arg8]vasopressin (AVP) were synthesized by systematically substituting the cysteine residues at positions 1 and 6 with a range of L-amino acids. Screening by competition ligand binding revealed that the combinations of amino acid residues tolerated at these positions was very restricted with respect to retention of vasopressin receptor (VPR) binding. Consequently, only three of the eighteen analogues investigated, [Pro1,Met6]AVP, [Gly1,Met6]AVP and [Phe1,Lys6]AVP, bound to the V1a receptor. Furthermore, these three peptides were all selective for the V1a receptor rather than the V1b, V2 and vasotocin receptors. In addition, although very homologous to the natural agonist, these analogues were in fact antagonists at V1a receptors. These data provide insights into the biophysical requirements at positions 1 and 6 of linear ligands for binding to V1a receptors and furthermore, supply clues to the nature of the receptor:ligand interaction.

Characterization of membrane-associated peptidase activities expressed by endothelial cells of the ovine median eminence

The capillary endothelial cells of the median eminence represent a potential site for the degradation/modification of both circulating and hypothalamic peptides passing through the hypophysial portal system toward the pituitary. This study examines endothelial cell peptidase expression in vitro by monitoring the metabolism of gonadotropin-releasing hormone (GnRH) by cultured endothelial cells from sheep median eminence. Cleavage of GnRH by median eminence endothelial cell membranes generated GnRH1-5 as the primary stable product, which was then degraded to GnRH1-3 and free amino acids. Degradation of GnRH was completely inhibited by TPCK, ZnCl2 and N-ethylmaleimide, and partially inhibited by EDTA and by a specific inhibitor of the metalloendopeptidase EC 3.4.24.15, CFP-AAY-pAB. Interestingly, an increase in GnRH1-9 production was seen with the latter inhibitors, suggesting a two-step mechanism of GnRH degradation involving a primary cleavage at the Pro9-Gly10-NH2 bond, inhibitable by TPCK, ZnCl2, and NEM, followed by cleavage by EC 3.4.24.15 to generate GnRH1-5. Phosphoramidon and angiotensin converting enzyme inhibitors (as well as other non-specific inhibitors) were without effect, indicating that endopeptidase EC 3.4.24.11 and angiotensin converting enzyme are not involved. Neither bovine aortic endothelial cell nor AtT-20 cell membranes exhibited this pattern of peptidase activity. Degradation of GnRH by intact median eminence endothelial cells in culture was also observed, suggesting an extracellular orientation for these enzymes; the potential role of such peptidases in the fine regulation of both pituitary function and local blood flow is currently under investigation.

The role of EC 3.4.24.15 in the post-secretory regulation of peptide signals

In the present studies, we characterized the degradation of gonadotropin-releasing hormone (GnRH) by tissues of the ovine hypothalamo-pituitary axis. Membrane and soluble fractions of the medial basal hypothalamus, the pre-optic area, the median eminence and the anterior pituitary demonstrated greater GnRH-degrading activity than either hypophysial-portal or jugular plasma. The primary stable product of the membrane fractions was GnRH1-3, while the major product of the soluble fractions was GnRH1-5, both fragments were generated by plasma. Of all tissue fractions, the highest specific activity was observed in the soluble median eminence. Partial purification and characterization of soluble hypothalamic peptidase activity suggested that GnRH degradation by this tissue occurs via a two-step mechanism involving both post-proline cleaving enzyme and the metalloendopeptidase 3.4.24.15.

Characterization of immunoreactive AVP in the ovine hypothalamo-pituitary axis

The aims of these studies were to determine the precise molecular nature of immunoreactive (IR-) vasopressin (AVP) in the ovine hypothalamo-pituitary axis and to examine a possible role for glucocorticoids in regulating both AVP processing and levels in this axis. The IR-AVP in extracts of paraventricular nucleus, median eminence, portal blood, and anterior and neurointermediate pituitary elutes as a single peak on two distinct HPLC solvent systems, suggesting that AVP is processed identically in these tissues. Identical profiles were also found in extracts from pituitaries and sheep subjected to chronic (10 days) glucocorticoid treatment, or hypothalamo-pituitary disconnection. The latter findings confirm that in sheep, like the rat, AVP is synthesized and processed in the anterior pituitary and is not sequestered from extrapituitary sources.

Monoclonal antibodies to arginine vasopressin receptor bind to liver, kidney and pituitary membranes

1. A vasopressin binding protein purified from rat liver membranes was used to immunize Balb/c mice and, subsequently, for the screening of hybrids raised in two different cell fusions. 2. Three hybrids were obtained which secreted monoclonal antibodies (MoAb) that bound to the purified solubilized receptor as detected by an enzyme-linked immunosorbent assay technique. All three MoAb immunoprecipitated the purified receptor. 3. In addition, the MoAb bound in a concentration-dependent manner to crude liver, kidney and anterior pituitary membranes, tissues known to contain arginine vasopressin (AVP) receptors but not to cardiac ventricle membranes which lack AVP receptors. 4. However, the binding of [125I]-[d(CH2)5,Sar7]AVP (a specific radiolabelled V1 antagonist) to the membrane-bound receptor was not inhibited by these antibodies. 5. These results suggest that MoAb recognize epitopes which are common to rat liver, kidney and anterior pituitary membranes but are not at the ligand binding site.

Identification and characterization of an amidating enzyme in ovine heart

1. Levels of peptidylglycine alpha-amidating mono-oxygenase (PAM) activity were examined in sheep and rat heart. This enzyme is responsible for alpha-amidation of a large number of peptide hormones, a modification essential for the bioactivity of these peptides. 2. PAM activity was measured in membrane and soluble fractions of atrial and ventricular homogenates by monitoring the amidation of iodinated synthetic substrate ([125I]-Ac-Tyr-Val-Gly). 3. PAM activity in both species resided almost exclusively in the atria rather than the ventricles, and similar levels of activity were found in left and right atria. Membrane-associated activity was 50-to 100-fold greater than soluble activity in the sheep, yet was only five- to 10-fold greater in the rat, indicating a larger proportion of soluble enzyme in the rat atrium. 4. Similar apparent Km values were found for atrial membrane-associated activity in both species (15.6 and 17.4 mumol/L for rat right and left atria, 16.7 and 15.6 mumol/L for sheep right and left atria); however, the maximum velocity (Vmax) levels were higher in the rat (40.5 and 43.9 pmol/micrograms per h vs 12.8 and 15.1 pmol/micrograms per h). 5. Because expression of many peptides and processing enzymes can be regulated by steroid hormones, the possible effects of chronic glucocorticoid administration (1 mg dexamethasone i.m. twice daily for 10 days) on PAM levels were tested in four sheep, with four sheep receiving saline only as controls. There was no discernible effect of dexamethasone on either the distribution or the kinetics of PAM activity in the sheep heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovine anterior pituitary proopiomelanocortin gene expression is not increased by ACTH secretagogues in vitro

Recent reports have demonstrated that the secretion of ACTH from sheep anterior pituitary primary cultures is markedly stimulated by arginine vasopressin (AVP) but not by CRF, and that AVP-stimulated ACTH secretion is potentiated by CRF. It has also been reported that AVP increases total ACTH content (secreted plus intracellular ACTH), suggesting that AVP stimulates POMC biosynthesis in the ovine anterior pituitary. These observations differ from the rat, in which CRF is the most potent of the ACTH-releasing factors and the only ACTH secretagogue which stimulates POMC gene expression and biosynthesis. The second messenger pathways which mediate CRF- and AVP-stimulated ACTH release (protein kinase A and protein kinase C, respectively) are the same in sheep and rat corticotrophs. The present studies were undertaken to determine if ovine POMC gene expression, unlike the rat POMC gene, is stimulated by AVP via the protein kinase C pathway. A 295 base pair portion of the ovine POMC gene was isolated using polymerase chain reaction and sequenced. Ovine POMC messenger RNA (mRNA) levels were quantitated using this partial complementary DNA clone in a solution hybridization/nuclease protection assay with cytoplasmic RNA from sheep anterior pituitary primary cultures which had been treated with various combinations of ACTH secretagogues or with glucocorticoids for 18 h. Treatment with AVP, alone or with CRF, greatly increased total and secreted ACTH levels; however, the amount of POMC mRNA in these cells was not significantly increased. Treatments which stimulated secretion to a lesser extent and did not alter total ACTH levels (CRF alone, cAMP alone, or with phorbol ester) were associated with a decrease in POMC mRNA levels relative to untreated cells. Glucocorticoid treatment decreased both total ACTH and POMC mRNA levels. Taken together, the data demonstrate a lack of secretagogue-induced stimulation of POMC mRNA levels concomitant with increased total ACTH levels, an unexpected result given the close association between secretion of POMC-derived peptides and POMC gene expression in other mammalian corticotroph systems.

Distribution and characterization of peptidylglycine alpha-amidating monooxygenase activity in the ovine brain and hypothalamo-pituitary axis

The production of alpha-amidated peptide hormones from their glycine-extended precursors is catalyzed by the specific enzyme peptidylglycine alpha-amidating monooxygenase (PAM). In the present study, the distribution and subcellular localization of PAM activity in the sheep brain was examined and compared with known sites of amidated peptide synthesis and release. Of the brain regions assayed, the preoptic anterior and medial basal areas of the hypothalamus contained the greatest concentration of amidating activity. Lower concentrations (greater than 3-fold less) were found in the anterior and neurointermediate pituitary, median eminence, cerebral cortex, hippocampus, pons-medulla, and brainstem. Very low amounts of activity were present in the cerebellum and pineal gland. In most tissues tested, PAM activity was 40-75% higher in the membrane-associated fraction than in the soluble fraction. In the hypothalamus, affinity constants were identical for both membrane-associated and soluble fractions, and ranged from 12.3-13.3 microM. Maximal velocity was higher in the membrane fraction (4.7-4.8 pmol/microgram.h) than in the soluble fraction (2.6-2.9 pmol/microgram/h). Levels of amidating activity in hypophysial-portal and jugular plasma were similar and were 20- to 25-fold lower than in hypothalamic extracts. Insulin-induced hypoglycemia did not significantly alter PAM levels in portal or peripheral plasma, suggesting that amidating activity is not released during this stress. These results indicate that the hypothalamus is the richest source of amidating activity in the sheep brain, and suggest that amidation of neurohypophysial and hypothalamic releasing peptides may occur before axonal transport, given the much lower levels in median eminence, neurointermediate pituitary, and portal plasma.

The interaction of a Huntington disease factor with receptors for the neurotoxin kainic acid

A factor from mammalian and human brain, which inhibits the rate of migration of leukocytes obtained from sufferers from Huntington disease (Walls and Ruwoldt, 1984), inhibited the specific binding of the neurotoxin [3H]kainic acid to rat brain synaptic membranes. The factor was present in sucrose-particulate but not in soluble fractions from rat sub-cortical tissue, and was destroyed by tryptic digestion. Whereas an ammonium sulfate fraction of direct saline extracts of brain (Walls and Ruwoldt, 1984) gave poor chromatography on HPLC, prior separation of a sucrose-particulate fraction resulted in much improved chromatography. There was a good concordance between leukocyte migration inhibitory activity and [3H]kainic acid binding inhibitory activity. The factor may be an endogenous modulator of the kainic acid subset of receptors for the excitatory neurotransmitter glutamic acid.

Distribution, Isolation and Sequence Analysis of the C-Terminal Heptapeptide of Pro-Enkephalin A (YGGFMRF) from the Ovine Median Eminence

Abstract Using a polyclonal antiserum raised against the C-terminal heptapeptide of pro-enkephalin A, we have isolated the opioid heptapeptide Tyr-Gly-Gly-Phe-Met-Arg-Phe (MERF) from ovine median eminence and mapped its distribution in that structure. MERF-immunoreactivity was confined to the pars externa (neurosecretory zone) where it colocalized with corticotrophin-releasing factor in the majority of terminals. No larger, N-terminally extended forms of MERF were detected in median eminence extracts suggesting that pro-enkephalin is fully processed to its constituent enkephalin congeners, and that the bioactive products, including MERF, act at the level of the hypothalamus in regulating anterior pituitary function.

Identification of a non-covalent oxytocin/neurophysin-I complex in the bovine ovary

Acid extracts of bovine preovulatory granulosa cells and corpora lutea (CL) were subjected to high-performance liquid chromatography (HPLC) and found to contain two peaks of immunoreactive (ir) oxytocin (OT), one corresponding to authentic OT and the second eluting 8 min later. The second peak was more abundant than authentic irOT in preovulatory follicles and in the early CL, but became less abundant as the CL matured (mid luteal) and was close to the limit of detection in the late CL. This peak could be detected only by an OT antiserum which recognized both the biologically active form of OT, as well as the post-translational processing intermediate Gly10-extended oxytocin. A second more specific OT antiserum (OT-933) did not recognize the second peak as strongly. Further analysis of the second peak revealed a complex of OT bound to its neurophysin (NP-I) which could be dissociated under denaturing conditions. Furthermore, we were able to create this complex in vitro by combining the two materials together under acid conditions, similar to the pH predicted in secretory granules, but not under neutral conditions. Measuring irNP-I by radioimmunoassay showed a single peak with a similar retention time to the OT/NP-I complex, confirming the identity of the unknown peak. Incubation of CL slices in culture showed a time-related release of both OT and NP-I, with OT having a greater rate of release in the mid luteal CL. These data suggest the presence of an OT/NP-I complex in the bovine preovulatory granulosa cells and CL, as well as the unbound peptide presumably within the secretory granules. The ratio of OT/NP-I complex and free peptide changes with ageing of the the CL, perhaps indicating regulated differences in the post-translational processing of the prohormone.

Morphine decreases LH secretion in ovariectomized ewes only after steroid priming and not by direct pituitary action

To determine whether opiates directly modulate pituitary LH secretion in vivo, morphine was administered to hypothalamo-pituitary-disconnected (HPD) ewes which were receiving exogenous pulses of GnRH. To define the steroidal background which is permissive to a morphine-induced decrease in LH secretion, ovariectomized (OVX) ewes were treated as follows in groups of four: group 1, no implant; group 2, small 17 beta-estradiol (E2) (1 cm long x 0.33 diameter) and progesterone (P) implants; group 3, medium E2 (1 cm long x 0.46 diameter) and P implants, and group 4, medium E2 implants. Jugular blood samples were taken at 10-min intervals for 9 h, during which there was a 3-hour pretreatment period, a 3-hour treatment period when the sheep were given six intravenous injections of 10 mg morphine every 30 min, and a 3-hour run-off period. Morphine inhibited the mean plasma concentrations of LH and LH pulse frequency in group 3 only, and in 2/4 ewes in this group LH secretion was abolished and did not return to a pulsatile mode during the 3-hour run-off sampling period. In a second experiment designed to test the pituitary action of morphine, OVX-HPD ewes were primed with medium E2 and P implants and were given hourly pulses of 250 ng GnRH intravenously. Jugular blood samples were taken around each GnRH pulse over an 8-hour period. The first three pulses served as a control sampling period, after which the sheep were treated with morphine (six intravenous injections of 10 mg morphine every 30 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Arginine vasopressin and corticotropin releasing factor: binding to ovine anterior pituitary membranes

In the sheep, in contrast to the rat, arginine vasopressin (AVP) is a more potent stimulus to ACTH secretion from the anterior pituitary (AP) than CRF. To further explore this difference, we have compared [3H]AVP and [125I]-[Nle21 Tyr32]ovine CRF binding in membranes prepared from rat and sheep AP. Between species, no difference in affinity of binding was found for either ligand. In contrast, the concentration of AVP receptors in sheep AP was twice that in rat, whereas that of CRF receptors was only one tenth. AVP receptor concentration in sheep AP was not altered by chronic (10 day) dexamethasone administration, but fell to 60% of control after chronic (60 day) hypothalamo-pituitary-disconnection. The increased level of AVP receptors and the much lower level of CRF receptors in sheep compared with rat may thus provide an explanation for our previous findings of increased sensitivity to AVP and a very poor response to CRF in stimulating ACTH release from the sheep AP. In addition the finding that AVP receptor numbers are reduced in the hypothalamo-pituitary-disconnected sheep suggests that hypothalamic factors may play a role in regulating AVP receptor concentration in the ovine AP gland.

The methyltrienolone binding protein of human placenta requires nicotinamide adenine dinucleotide cofactor(s) for steroid binding

The methyltrienolone binding protein (MTBP) found in human placental cytosol was found to require a low molecular weight modulator for steroid binding activity. Purification and characterization of the modulating activity showed that NAD+ is the endogenous substance responsible for activating MTBP to a form capable of steroid binding. The hierarchy of potency of exogenously added nucleotides is NADH greater than NAD+ = NADPH = NADP+. An investigation of the tissue distribution of human MTBP demonstrated that MTBP binding activity was present in placenta and chorion but absent from amnion and umbilical cord. Preliminary studies showed that rat, mouse, and rabbit placenta do not contain MTBP and suggest that MTBP may be a species-specific protein.

Immunocytochemical demonstration of mineralocorticoid receptors in rat and human kidney

Using a polyclonal antiserum against the hinge region of the recently cloned human mineralocorticoid receptor (MR) and indirect peroxidase immunohistochemistry, we have shown MR-like immunoreactivity (LI) in superficial nephron segments, including distal convoluted tubule, connecting piece and initial cortical collecting duct. The absence of staining in cells tentatively identified as intercalated cells on light microscopy was confirmed by pre-embedding electron microscopy. Though the intracellular distribution of immunostaining varied with the fixative used, the cellular distribution of MR-LI is in good general agreement with earlier micropuncture and autoradiographic studies.

Stress-Related Changes in beta-Endorphin Processing: The Limitations of Slaughterhouse Material

Abstract In the sheep, unlike many other species, a significant proportion (>25%) of immunoreactive beta-endorphin in the anterior pituitary is post-translationally modified to opioid-inactive, alpha-N-acetylated forms. In a study to determine the precise molecular nature of alpha-N-acetylated beta-endorphin immunoreactivity, we noted a striking difference in high-performance liquid chromatography profiles of anterior pituitary extracts between sheep killed on the farm, and age-, sex- and strain-matched slaughterhouse animals. These altered patterns of a-N-acetylated beta-endorphin processing were reproduced in farm animals by chronic (</= 4 days) treatment with the synthetic glucocorticoid dexamethasone; in contrast dexamethasone had no effect on a-N-acetylated beta-endorphin processing in hypothalamo-pituitary disconnected sheep. These data suggest that (1) the change in processing is a stress response, mediated by prolonged glucocorticoid exposure, (2) this effect is central, rather than a direct effect on the pituitary, and (3) the relative abundance of various peptide sequences in slaughterhouse-derived material may not reflect their abundance under more physiological conditions.

Arginine vasopressin is a much more potent stimulus to ACTH release from ovine anterior pituitary cells than ovine corticotropin-releasing factor. 1. In vitro studies

Cultured rat and ovine anterior pituitary cells were treated with a range of doses (0.01-1,000 nM) of arginine vasopressin (AVP) and ovine corticotropin-releasing factor (CRF), alone or in combination, and medium and cell content of immunoreactive (ir-)ACTH determined. In rat cells, a dose-response curve to CRF was obtained, with a threshold dose of 0.1 nM; AVP was much less effective alone, but augmented CRF responses when administered with CRF. In ovine pituitary cells AVP markedly stimulated ACTH release in a dose-dependent fashion, and with a threshold of 0.1 nM; in contrast, CRF increased ACTH release over basal only at doses greater than 100 nM. In combination, subthreshold doses of AVP potentiated rat pituitary cell responses to CRF; addition of 1 nM of AVP to varying doses of CRF was more effective in terms of ACTH release than addition of 1 nM of CRF to increasing doses of AVP. In contrast, in ovine cells the addition of 1 nM CRF to increasing doses of AVP elicited a larger ACTH response than the addition of 1 nM AVP to increasing doses of CRF. Dexamethasone pretreatment (5 nM) for 48 h significantly decreased CRF potentiation of AVP-stimulated ACTH release in ovine cells. These studies confirm that CRF is a more potent stimulus of ACTH release than AVP in the rat, and establish that in contrast AVP is a much more potent stimulus of ACTH secretion than CRF in isolated ovine pituitary cells.

Immunolocalization of renal mineralocorticoid receptors with an antiserum against a peptide deduced from the complementary deoxyribonucleic acid sequence

We have synthesized three peptides corresponding to putative antigenic regions in the immunogenic domain, hinge region, and carboxy-terminus of the protein. A rabbit immunized with a peptide derived from the hinge region of the receptor produced an antiserum which showed 50% displacement with 20 pg peptide at a final serum dilution of 1:35,000. When the antiserum was immunopurified and applied to sections of intact rat and human kidney it stained cells lining segments corresponding to distal tubule, connecting piece, and initial cortical collecting duct, consistent with the known sites of mineralocorticoid action. In both human (formaldehyde-fixed) and rat (Bouin's solution) there was ample evidence for both nuclear and cytoplasmic staining. The thymus, in which previously we have found [3H]aldosterone binding to be below detection limits, showed little or no staining. Western blot analyses demonstrated that the polyclonal antibody recognized an epitope of the expected molecular size. The availability of antibodies to the mineralocorticoid receptor should, thus, facilitate investigation of the steroid specificity-conferring mechanism which allows mineralocorticoids, but not glucocorticoids, access to the nonselective receptor in the kidney.

Dopaminergic agents differentially regulate both processing and content of alpha-N-acetylated endorphin and alpha-MSH in the ovine pituitary intermediate lobe

Hypothalamo-pituitary disconnection (HPD) in the sheep results in a two-fold increase in pituitary intermediate lobe (IL) immunoreactive (ir)-alpha-N-acetylated endorphin (NacEP) and ir-alpha-melanocyte-stimulating hormone (alpha MSH) content. The rise in IL NacEP content is accompanied by a markedly altered pattern of processing, in that NacEP1-27 becomes the dominant molecular species with a complementary fall in Nac alpha-EP and Nac gamma-EP. To determine if these effects reflect the loss of descending dopaminergic neuronal input to the IL, we have chronically treated two groups (n = 4 per group) of normal sheep with the dopamine antagonist haloperidol or the dopamine agonist bromocriptine; a group of HPD sheep were also treated with bromocriptine. Acid extracts of IL were diluted and ir-alpha-MSH and ir-NacEP content determined by radioimmunoassay; aliquots were submitted to reversed-phase HPLC and collected fractions similarly assayed. Bromocriptine lowered ir-NacEP and ir-alpha-MSH by about 30%; on HPLC the ir-NacEP profiles, and perhaps to a lesser extent those for ir-alpha-MSH were qualitatively similar to untreated controls. In contrast, haloperidol increased by about 45% both ir-NacEP and ir-alpha-MSH levels and produced a marked change in the ir-NacEP molecular profile, with NacEP1-27 becoming the predominant molecular form and other species representing only minor components in the chromatogram. In the treated HPD group, bromocriptine partially restored the processing profiles previously observed in HPD animals to those found in untreated intact animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Generation of Met-enkephalin Arg6Phe7 immunoreactivity by proteolytic cleavage of mammalian plasma precursors by pepsin

A region-specific antiserum raised against the C-terminal heptapeptide of proenkephalin A (Met-enk Arg6Phe7) was used in RIA studies to show that rat, human, and ovine plasma contain substrates (mol wt, 68K) that yield nanomolar amounts of Met-enk Arg6Phe7 (ME-RF) after treatment with pepsin under acid conditions. This ovine plasma-derived immunoreactivity diluted in parallel to the ME-RF standard in RIA and chromatographed as two low mol wt species (approximately 1K) which were less hydrophobic than the standard on size exclusion and reverse phase chromatography. The pepsin-generated material displaced [3H]naloxone from rat brain binding sites; its potency was about 1000-fold that of ME-RF, assuming near 100% cross-reactivity with the antiserum. Taken together these observations suggest that the pepsin-generated material is of similar mol wt and amino acid sequence to ME-RF, but differs with respect to opiate-binding efficacy, and that the plasma precursor is distinct from proenkephalin in both size and processing sites.