Biomedical subjects

L S Jacobs

Publications and source records attributed to L S Jacobs.

At least 19 recordsLinked to original sources

PubMed1993

Sphingolipids as mediators of effects of platelet-derived growth factor in vascular smooth muscle cells.

The role of sphingolipids in mediating the action of platelet-derived growth factor (PDGF) has been investigated in the vascular smooth muscle-derived A7r5 cell line. L-Cycloserine (2 mM), an inhibitor of sphingolipid synthesis, caused time-dependent inhibition of [3H]serine incorporation into [3H]sphingomyelin in A7r5 cells. PDGF-AB (10 ng/ml), PDGF-BB (10 ng/ml), or sphingosine (10 microM) independently stimulated [3H]thymidine incorporation into DNA in A7r5 cells. L-Cycloserine (2 mM) inhibited stimulation of DNA synthesis by both PDGF-AB and PDGF-BB. L-Cycloserine (2 mM, 16 h) did not affect the ability of PDGF or sphingosine to increase intracellular free calcium ([Ca2+]i) in A7r5 cells loaded with the fluorescent indicator fura 2. Measurement of adenine nucleotide levels in A7r5 cell extracts by reverse-phase high-performance liquid chromatography indicated that treatment with L-cycloserine did not adversely affect cellular metabolism. To determine directly whether PDGF activates sphingolipid metabolism, A7r5 cells were labeled with [3H]serine for 48 h and then treated with PDGF-AB (10 ng/ml) for 1 h. Sphingolipids were separated by thin-layer chromatography and quantified by liquid scintillation counting. PDGF-AB stimulated an increase in [3H]sphingosine from 25.5 +/- 3.0 to 37.5 +/- 4.1 counts.min-1 (cpm).micrograms protein-1 and a concomitant decrease in [3H]ceramide from 24.3 +/- 3.2 to 18.5 +/- 2.9 cpm/micrograms protein. These data suggest that the PDGF-stimulated increase in [Ca2+]i is not sufficient for induction of DNA synthesis and that mitogenic effects of PDGF in vascular smooth muscle cells are mediated by sphingolipid metabolism.

Adenine Nucleotides↗

PubMed1991

Lymphocytic hypophysitis with involvement of the cavernous sinus and hypothalamus.

Two cases of lymphocytic hypophysitis are reported, in which hypothalamic involvement causing diabetes insipidus was a prominent clinical feature. In one case, a man had clinical and radiological evidence of the involvement of the cavernous sinus. This represents the second reported case of a man with lymphocytic hypophysitis. A transsphenoidal biopsy established the diagnosis in both cases. Neither the involvement of the cavernous sinus nor permanent diabetes insipidus has been reported previously. A review of the literature is provided.

Adult↗

PubMed1991

Regulation of phospholipase D and primary granule secretion by P2-purinergic- and chemotactic peptide-receptor agonists is induced during granulocytic differentiation of HL-60 cells.

We have compared the abilities of extracellular ATP (acting via P2-purinergic receptors) and formylated peptides (FMLP) to stimulate both phospholipase D (PLD)-based signal transduction and primary granule (azurophilic) secretion in HL-60 cells induced to differentiate along the granulocytic pathway. In undifferentiated HL-60 cells, neither ATP nor FMLP elicited significant PLD activation or increased secretion despite the previously documented ability of ATP to stimulate large increases in polyphosphoinositide hydrolysis and Ca2+ mobilization. Conversely, within 1 d after induction of granulocytic differentiation by dibutyryl cAMP, both ATP and FMLP induced large increases in azurophilic secretion and corresponding increases in PLD activity. ATP-activated PLD activity was near-maximal within 1 d after dibutyryl cAMP treatment, while the FMLP-induced activity increased continuously over 4 d, with a maximal level twice that stimulated by ATP. Additional experiments characterized the activation of PLD by receptor-independent pathways at different stages of differentiation; these included studies of phorbol ester action in intact cells and GTP gamma S action in electropermeabilized cells. An apparent role for guanine nucleotide-binding regulatory proteins in PLD regulation was also indicated by the significant reduction in FMLP- and ATP-stimulated PLD activity observed in cells pretreated with pertussis toxin. At all stages of differentiation, there was good correlation between the relative efficacies of ATP versus FMLP in stimulating both secretion and PLD activity. These data indicate: (a) that the receptor-regulated phospholipase D signaling pathway is induced during differentiation of myeloid progenitor cells; and (b) that differential activation of this signaling system by various Ca(2+)-mobilizing receptor agonists may underlie the differential regulation of secretion and other phagocyte functions by such agents.

Adenosine Triphosphate↗

PubMed1990

Calcium release from pituitary secretory granules: modulation by thiols, disulfides, and dihydropyridine calcium channel blockers.

The distribution of calcium in isolated bovine pituitary secretory granules was studied by atomic absorption. The total granule calcium (in 26 preparations) averaged 14.5 nmol/mg protein, or 21.2 +/- 1.6% of the total pituitary homogenate calcium. Incubation of granules with KCl resulted in calcium release (78% at 15 mM and 100% at 50 mM, for example). Calcium release was also pH dependent, with greater release at acidic pH values; it was not influenced by either 500 microM strontium or 500 microM lanthanum. Release was augmented by reduced glutathione (GSH), with significant release observable at thiol levels as low as 10 microM. In addition to GSH, cysteine also stimulated release; mercaptoethanol and dithiothreitol were less potent. Interestingly, the disulfides cystine and oxidized glutathione also stimulated calcium release. Since the latter compounds are known to inhibit hormone release from granules, calcium and protein release appear to be regulated independently. A number of dihydropyridines were tested as potential blockers of calcium release from granules. Nimodipine inhibited basal calcium release at high concentrations and potently inhibited GSH-stimulated calcium release, with an apparent Ki in the 10-20 nM range; it also inhibited K(+)-stimulated release but to a lesser extent. Nimodipine, however, did not significantly influence protein or hormone release. GSH-stimulated calcium release was also inhibited by nifedipine, and this inhibition was qualitatively and quantitatively similar to that by nimodipine. Nisoldipine and nitrendipine, however, displayed no significant inhibition. In summary, it appears that the release of secretory granule calcium in vitro is independent of protein release. Thiols and some disulfides stimulate calcium release, and its inhibition by dihydropyridines suggests that granule membranes may contain specific ion channels. The role of granule calcium in the cell remains to be defined.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1990

Dihydropyridine actions on calcium currents of frog sympathetic neurons.

Dihydropyridines (DHPs) generally have little effect on whole-cell calcium currents of neurons, even at concentrations far higher than those effective on muscle. Either neuronal calcium currents are much less sensitive to DHPs, or only a small proportion of the current is DHP-sensitive. We find that DHP agonists and antagonists act at low concentration on calcium currents in frog sympathetic neurons but that the effects are small even at optimal concentrations. The half-maximal dose (EC50) of the agonist Bay K 8644 is approximately 50 nM, and the effect of Bay K 8644 is blocked by 50% at approximately 300 nM nifedipine, from a holding potential of -80 mV. Nifedipine is more effective from a holding potential of -50 mV. These results suggest the presence of an L-type calcium current, with DHP sensitivity similar to L-currents in cardiac muscle. The predominant (greater than 90%) calcium current in frog sympathetic neurons is a DHP-resistant N-type current. However, high concentrations of DHPs (10 microM) partially block N-type calcium current, as well as voltage-dependent sodium and potassium currents.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1989

Crisis screening and diversion services.

In Hawaii, crisis intervention services have become an increasingly pressing concern of the mental health and substance abuse systems. Since 1983, the Crisis Response System Project (CRSP) provided mobile crisis intervention services 24 hours a day, seven days a week. This paper describes the community's utilization of CRSP services, with special emphasis on the seriously disabled mentally ill (SDMI).

Adolescent↗

PubMed1988

Preferential interaction of [35S]cysteamine with pituitary secretory granule storage forms of prolactin.

Cysteamine (CySH) inhibits the immunodetectability and bioactivity of prolactin (PRL), and we have proposed that it may act by impeding the conversion from secretory granule hormone storage forms to releasable and assayable hormone. This process appears to be dependent upon thiol:disulfide interchange reactions, which can be inhibited by the aminothiol. The present studies utilized [35S]CySH to determine whether preferential interactions could be demonstrated between CySH and bovine pituitary storage hormone forms as opposed to monomeric PRL. [35S]CySH was incubated with purified intact secretory granules, with granule 'core' preparations enriched in oligomeric forms by prior hypotonic exposure, with chromatographically isolated oligomers, and with monomeric PRL. Binding to granules was saturable and pH-dependent with greatest binding observed at pH 7.5-8.0. Binding to monomer was much less than binding to all other fractions, being 20% or less than that to any other form. HPLC studies of granules treated with [35S]CySH indicated that exposure to CySH was associated with a predominance of very high molecular weight oligomers. These forms were entrapped on the gel permeation columns, resulting in decreased protein and PRL recovery; as little as 6.6% of the PRL was eluted after 60 min of CySH exposure. CySH not only bound to storage forms of PRL but also to secretory granule membranes; whether the bioeffect is mediated through membrane modifications is unknown. Despite its relative ineffectiveness at altering growth hormone immunoactivity or secretion, CySH nonetheless also bound to growth hormone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Distribution of calmodulin and calmodulin-binding proteins in bovine pituitary: association of myosin light chain kinase with pituitary secretory granule membranes.

Calcium is necessary for secretion of pituitary hormones. Many of the biological effects of Ca2+ are mediated by the Ca2+-binding protein calmodulin (CaM), which interacts specifically with proteins regulated by the Ca2+-CaM complex. One of these proteins is myosin light chain kinase (MLCK), a Ca2+-calmodulin dependent enzyme that phosphorylates the regulatory light chains of myosin, and has been implicated in motile processes in both muscle and non-muscle tissues. We determined the content and distribution of CaM and CaM-binding proteins in bovine pituitary homogenates, and subcellular fractions including secretory granules and secretory granule membranes. CaM measured by radioimmunoassay was found in each fraction; although approximately one-half was in the cytosolic fraction, CaM was also associated with the plasma membrane and secretory granule fractions. CaM-binding proteins were identified by an 125I-CaM gel overlay technique and quantitated by densitometric analysis of the autoradiograms. Pituitary homogenates contained nine major CaM-binding proteins of 146, 131, 90, 64, 58, 56, 52, 31 and 22 kilodaltons (kDa). Binding to all the bands was specific, Ca2+-sensitive, and displaceable with excess unlabeled CaM. Severe heat treatment (100 degrees C, 15 min), which results in a 75% reduction in phosphodiesterase activation by CaM, markedly decreased 125I-CaM binding to all protein bands. Secretory granule membranes showed enhancement for CaM-binding proteins with molecular weights of 184, 146, 131, 90, and 52,000. A specific, affinity purified antibody to chicken gizzard MLCK bound to the 146 kDa band in homogenates, centrifugal subcellular fractions, and secretory granule membrane. No such binding was associated with the granule contents. The enrichment of MLCK and other CaM-binding proteins in pituitary secretory granule membranes suggest a possible role for CaM and/or CaM-binding proteins in granule membrane function and possibly exocytosis.

Animals↗

PubMed1987

Oral hyperalimentation and the prevention of severe weight loss in burned patients.

It is well known that the marked hypermetabolic response of the human body to thermal injury requires aggressive nutritional support. In order to minimize catabolic conditions resulting in severe weight loss, an oral hyperalimentation regimen has been successfully implemented in the burns unit of Tygerberg Hospital, Cape Town. Ninety-eight patients with deep burns, varying from 20 per cent to more than 60 per cent of body surface area, were included in this study. The results indicated a general increase in the percentage of patients who gained weight from week to week after week 2 post-burn in all burns categories. An exception was the 60 per cent and more burns category in which an increasing number of patients lost weight until week 4 post-burn. The results of this study and the apparent discrepancy in the above 60 per cent category are presented.

Adult↗

PubMed1987

Osmotic pressure regulation of prolactin and growth hormone release from bovine secretory granules.

PRL and GH are stored in bovine pituitary secretory granules in part as intermolecular disulfide-linked multimers (as many as 50 monomers/oligomer). In vitro incubation of granules with reduced glutathione (GSH) results in the production of monomeric hormones and increased hormone release. We tested the hypothesis that increases in intragranular osmolality due to conversion of oligomers to lower mol wt forms are key to granule rupture. Hormone release was measured after granule incubations in medium made hyperosmotic by the addition of raffinose or sucrose. PRL release at pH 7.8 with 0.7 M raffinose was reduced to 43.5% of the control value, whereas GH release ranged from 70-100% of the control value. Augmented release stimulated by 2 mM GSH was also diminished by raffinose, to 17.9% (PRL) and 75.6% (GH) of control values. The IC50 for raffinose inhibition of PRL release was 0.62 M; this shifted to 0.38 M in the presence of 2 mM GSH. Raffinose also blunted the granule response to GSH at all other GSH concentrations tested and decreased stimulated release at pH 9 as well as at 7.8. Interference with the ability to maintain an osmotic gradient, a maneuver accomplished by partial disruption of granule membranes with 0.5% deoxycholate treatment, reduced or abolished the raffinose inhibition. Molecular sizing of granule fractions on Superose-6 (Pharmacia) indicated that PRL monomers remaining in the pelletable granule fraction increased with raffinose about 2-fold under both basal and GSH-stimulated conditions. These data support the concept that thiol:disulfide equilibria may be important in PRL and GH storage and secretion by their influence on intragranular osmolality. In exocytosis in vivo, osmotically mediated granule rupture may be triggered by thiols during granule:plasma membrane fusion.

Animals↗

PubMed1986

Cysteamine, zinc, and thiols modify detectability of rat pituitary prolactin: a comparison with effects on bovine prolactin suggests differences in hormone storage.

Little is known about the structure of prolactin (PRL) within secretory granules. Evidence from our previous studies in bovine tissue preparations suggests that control of secretion may reside, in part, in the conversion of storage hormone to releasable PRL. The conversion can be monitored by measuring changes in immunodetectability since the oligomeric, storage form is poorly recognized by antisera raised against monomeric PRL. Since many investigators use rats to study the secretory process and changes in detectability of rat pituitary PRL occur during lactation ("depletion-transformation"), we undertook the present immunodetectability studies to gain insight into the storage structure of rat (r) PRL. Cysteamine and zinc inhibited tissue PRL immunoassayability in male rat pituitary homogenates and also in partially purified secretory granules as they had inhibited bovine (b) PRL; however, zinc inhibited the rodent hormone less potently than the bovine. In vitro incubation of rat tissue samples without additions resulted in increases in rPRL detectability of up to 84% after 180 minutes; such incubation of bovine samples had no significant effect. A striking additional difference between the species was that exposure to reduced glutathione (GSH), cysteine, homocysteine, mercaptoethanol, and dithiothreitol inhibited rPRL by up to 44%. This compared to thiol stimulation of bPRL by as much as 450%. The inhibitory GSH effect on rPRL was abolished when 0.5% sodium dodecyl sulfate (SDS) was included; in contrast, the stimulatory GSH effect on bPRL did not change with added SDS. SDS alone had no effect on rat homogenate PRL, and only increased rat granule rPRL by 23% compared to its ability to increase bPRL assayability by 44%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Cholinergic but not serotonergic mediation of exercise-induced growth hormone secretion.

In order to clarify the roles of cholinergic and serotonergic neurotransmission in the mediation of exercise-induced growth hormone (GH) release, normal young volunteers of both sexes were studied. Exercise was for 20 minutes at 800 kpm for the men and 500 kpm for the women. Pretreatment with 0.4 mg atropine 1 hour prior to exercise, or with methysergide 2 mg po q 6 h for 48 hours prior to exercise, were used to evaluate the influence of cholinergic and serotonergic blockade, respectively. Five of the ten men studied failed to raise GH values with exercise, perhaps because the exercise was not vigorous enough for their high degree of fitness. Of three non-responders restudied, at the same workload, one responded on the second occasion. The mean peak GH with exercise 13.4 +/- 3.27 ng/ml, was reduced to 2.4 +/- 1.28 ng/ml (p less than 0.01) after atropine, but was unaffected by methysergide (15.2 +/- 6.58 ng/ml, p greater than 0.5). Prolactin did not rise with exercise, and was not affected by atropine, but lowered by methysergide as expected. Cholinergic neurotransmission therefore represents a key link in exercise-induced GH secretion, but serotonergic influences are probably not involved.

Acetylcholine↗

PubMed1985

Pharmacological evidence for opioid and adrenergic mechanisms controlling growth hormone, prolactin, pancreatic polypeptide, and catecholamine levels in humans.

A group of 14 healthy subjects received 50 mg/kg body weight of 2 deoxy-D-glucose (2DG) IV in a 20-minute infusion to induce glucoprivation and stimulate the release of growth hormone (GH), prolactin (PRL), pancreatic polypeptide (hPP), and catecholamines. Six subjects having spontaneously high GH baseline levels (greater than 8 ng/mL) failed to mount a GH response to 2DG-induced glucoprivation while eight subjects having low GH baseline levels (less than 8 ng/mL) all had increases (greater than 10 ng/mL) of GH levels after 2DG (P less than 0.05). Baseline level of GH was a reliable predictor of subsequent GH response to 2DG. Administration of the alpha 2-adrenoreceptor agonist clonidine (0.5 mg po) reliably increased GH levels (P less than 0.05). Elevated GH levels following clonidine administration abolished GH responses to subsequently infused 2DG (P less than 0.05). While these data do not exclude the possibility of a short loop feedback control of GH secretion, they strongly suggest that the direction of the GH response to a provocative stimulus is determined by the antecedent GH level and that an alpha-adrenoreceptor mechanism is involved in such a biphasic modulation of GH levels. Clonidine administration significantly reduced total catecholamine, pancreatic polypeptide, and prolactin response to 2DG while opiate receptor blockade with naloxone (10 mg IV bolus followed by 2 mg/hr) did not affect catecholamine and pancreatic polypeptide response but did slightly attenuate the GH and PRL response to glucoprivation. We conclude that alpha adrenoreceptor mechanisms are of major importance while opiate receptor mechanisms are of relatively minor importance in modulating the effects of glucoprivation on sympathetic outflow and hPP, GH, and PRL levels.

Adolescent↗

PubMed1984

Inhibitor studies with adenohypophyseal granule membrane ATPase. Evidence for a membrane environment which modulates sensitivity to inhibitors.

The limiting membranes of pituitary growth hormone and prolactin secretory granules contain a Mg2+-ATPase sensitive to anions. This enzyme is in many ways similar to mitochondrial ATPase. The enzyme was potently inhibited by oligomycin (Ki 6.5 X 10(-9) M), and was much more sensitive to the inhibitor than pituitary mitochondrial ATPase (Ki 2.7 X 10(-7) M). In contrast, the enzyme activity of intact secretory granules was only sparingly inhibited by oligomycin (maximal inhibition close to 30% at 5 X 10(-4) M). However, oligomycin (5 microM) did diminish to basal levels the enhanced granule ATPase activity observed in the presence of a stimulatory anion (25 mM sodium sulfite). Other compounds known to inhibit the proton translocating mitochondrial ATPase were also tested for their ability to inhibit the secretory granule ATPase. A similar pattern of limited inhibition in granules and greater sensitivity in isolated membranes was seen with the inhibitors N,N-dicyclohexylcarbodiimide and efrapeptin. In contrast, tri-n-butyltin chloride was a potent inhibitor of the ATPase of intact granules, and the susceptibility of the enzyme to inhibition by this compound was less after isolation of membranes. These observations suggest that pituitary secretory granule membrane ATPase may have a proton pumping function similar to that of the mitochondrial enzyme. In addition, the data imply that the inhibitor binding site(s) may be masked, inaccessible, or ineffective in intact granules, but exposed (or activated) in isolated membranes. The greater sensitivity of granule ATPase to tri-n-butyltin chloride, in contrast to the greater sensitivity of membrane ATPase to the other inhibitors, indicates that the tin compound may be effective at a membrane site(s) distinct from the others, or that the mechanism of inhibition is different.

Adenosine Triphosphatases↗

PubMed1984

Secretory granule growth hormone and prolactin release: independence from granule membrane ATPase.

To assess the role in hormone release of the recently characterized anion-sensitive Mg+2-ATPase of pituitary secretory granules, three types of evidence were accumulated. First, granule suspensions were incubated with varying quantities of MgCl2 and ATP, and the effects on ATPase activity and release were measured. The main stimulatory influence on ATPase activity was the concentration of the complex between Mg+2 and ATP (MgATP), although very high concentrations of complex inhibited. In contrast, release of hormone was nearly totally independent of MgATP. Rather, release was primarily controlled by free Mg+2, which inhibited release at concentrations as low as 0.1 mM and reduced basal release by approximately 65-75% at concentrations approximating 2.0 mM or higher. Free ATP had small consistent inhibitory effects on ATPase activity, but stimulated protein release. Second, granules were incubated with other nucleotides and related compounds. Incubation with GTP, ITP, CTP, TTP, and UTP resulted in augmentation of hormone release duplicating that seen with ATP. Some increase was also seen with the nonhydrolyzable ATP derivative 5'-adenylylimido-diphosphate, whereas adenosine was inhibitory. Since the catalytic activity of the granule ATPase demonstrates purine nucleotide substrate specificity, these results provide additional evidence for the dissociation of ATPase activity from hormone release. Third, granules were incubated with several ATPase inhibitors. Though all inhibited ATPase activity to a comparable extent, only tri-n-butyltin inhibited hormone release; oligomycin, efrapeptin, and other tin compounds were inactive. Taken together, these data indicate that the conditions that influence ATPase differ strikingly from those affecting hormone release. Whatever the role of the anion-sensitive granule membrane ATPase, we suggest that it is not involved in the process of hormone release from isolated granules.

Adenosine Triphosphatases↗

PubMed1984

Cysteamine inhibition of prolactin immunoassayability and secretion: studies with aminothiophenols and other analogs.

Analogs of the aminothiol cysteamine (CySH) have been studied to clarify the structural features required for exertion of inhibitory effects on PRL. The inhibited functions examined were the detectability of PRL by RIA and the release of PRL from suspensions of isolated secretory granules. The influence on GH assayability and release was also tested. The aromatic compounds 2-aminothiophenol, 3-aminothiophenol, and 4-aminothiophenol shared with CySH the ability to inhibit PRL assayability and release, but were all more potent. Derivatization of the thiol, as in 4-aminothioanisole, was associated with a substantial loss of inhibitory potency, whereas derivatization of the primary amine, as in N-dimethylaminoethanethiol, had no influence. Thiols such as mercaptoethanol, cysteine, glutathione, and others without nearby amino groups were stimulators of PRL assayability and release. The inhibitory effects of the aminothiols were highly pH dependent, being marked at pH 5.5, 6.5, and 7.5, but modest or marginal at 8.5. After CySH exposure, inhibition was reversible in part by extraction of samples with reduced glutathione or at pH 10.5. Though CySH and 4-aminothiophenol induced changes in the electrophoretic migration of granule PRL, similar changes occurred in the migration of standard purified hormone despite the known absence of immunochemical effects. There was close quantitative correlation between the potency of a compound to inhibit PRL assayability and its potency to inhibit PRL release. We conclude that the inhibitory aminothiol action on PRL requires the thiol rather than the sulfide form and involves a reversible interaction which diminishes the immunochemical recognition of granule PRL. This change also results in diminished secretion.

Aniline Compounds↗

PubMed1984

Depletion of bovine pituitary prolactin by cysteamine involves a thiol:disulfide mechanism.

Cysteamine [2-aminoethanethiol (CySH)] reduces measurable PRL concentrations in vivo and in vitro. Since secretion is also inhibited, CySH may block conversion from a poorly assayable hormone storage form(s) to readily assayable, releasable PRL. This would represent a previously unrecognized mechanism for secretory regulation. We undertook the present study to identify the sites involved in the loss of measurable PRL (depletion) induced by cysteamine. The disulfide cystamine was ineffective on secretory granules unless combined with reduced glutathione, indicating the generation of the active CySH-thiol form. Pretreatment of granules with thiol-blocking agents resulted in dose-dependent enhancement of CySH inhibition, achieving nearly complete inhibition with 5 mM iodoacetamide. In contrast, pretreatment with reduced glutathione or dithiothreitol, respectively, impaired or abolished the CySH effect. Similar results were obtained when tissues were exposed to thiols and/or alkaline conditions after CySH treatment; for example, exposure to 50 mM glutathione reduced the lowering of measured pituitary homogenate PRL from 76% to 37%. These data suggest that the mechanism by which CySH causes PRL depletion is mediated by granule disulfides and the -SH of CySH. The regulation of thiol:disulfide equilibria appears to be an important determinant of the detectability of PRL storage forms and of their secretion.

Animals↗

PubMed1983

Divalent cation inhibition of hormone release from isolated adenohypophysial secretory granules.

Divalent cations inhibited in vitro release of growth hormone (GH) and prolactin (PRL) from bovine adenohypophysial secretory granules. Zinc, nickel, and cadmium were most potent, exerting 50% inhibition of protein release near 0.1 mM; relative potency was Ni2+ greater than or equal to Zn2+ greater than Cd2+ much greater than Mn2+ greater than Co2+ greater than Cu2+ much greater than Mg2+ greater than Ca2+. The pH optimum for inhibition, 8.0, was lower than that for stimulation of release by thiols. EDTA augmented release and reversed metal inhibition. Both immunoassay and polyacrylamide gel electrophoresis results indicated that metals inhibited both PRL and GH release in a dose-related fashion, and that PRL was more sensitive to all cations tested. With zinc present, known stimulators of release (reduced glutathione, ATP, and bicarbonate) restored GH release, but only ATP restored PRL release. Bicarbonate potently stimulated GH release, but only affected PRL when Mg2+ and ATP were present. We suggest that divalent cations influence GH and PRL release in a reversible fashion and at multiple sites. Some loci may be common to both lactotrope and somatotrope granules; however, the different sensitivities to metals and differential reversal by stimulators of release indicate that metal-protein interactions may also be specific for either granule, or for the hormones themselves.

Adenosine Triphosphate↗