The effect of cortisol on the secretion of ACTH by anterior pituitary cells of the horse in culture

1993 ◽  
Vol 137 (3) ◽  
pp. 403-412 ◽  
Author(s):  
M. J. Evans ◽  
N. E. Kitson ◽  
J. H. Livesey ◽  
R. A. Donald
Keyword(s):  
Anterior Pituitary ◽  
Inhibitory Effect ◽  
Peak Height ◽  
Percentage Change ◽  
Pituitary Cells ◽  
Acth Secretion ◽  
Maximum Percentage ◽  
Anterior Pituitary Cells ◽  
The Mean ◽  
Response Area

ABSTRACT Perifused equine anterior pituitary cells were used to investigate the effect of cortisol on the ACTH response to pulses of corticotrophin-releasing hormone (CRH; 0·01 nmol/l) and arginine vasopressin (AVP; 100 nmol/l), given for 5 min every 30 min for 690 min and ACTH measured in 5-min fractions. At the fourth pulse of secretagogue (0 min), a constant perifusion with cortisol began (0 nmol/l (control), 100, 200, 500, 5000 and 50 000 nmol/l) and continued until the ninth pulse (150 min). For each pulse of secretagogue, the amount of ACTH (pmol) secreted in response to each pulse (ACTH response area), the highest concentration of ACTH (μg/l) measured after each pulse (peak height) and the mean ACTH in the three prepulse fractions (ACTH baseline) were determined. Data from control columns in each experiment were fitted by least squares to an exponential function to produce a mean control value for each end-point; results in all columns were expressed as a percentage of the mean control values. The addition of cortisol had a highly significant negative effect on ACTH response area, peak height and baseline at all times from + 30 to + 240 min (columns given cortisol compared with the mean of control column values by t-test). Analysis of variance of the data showed that the higher the cortisol concentration, the quicker the ACTH response area (P = 0·0072) and peak height (P = 0·002) decreased to < 50% of mean control, and the greater the maximum percentage change (suppression) in ACTH response area (P <0·0001) and peak height (P <0·0001). The maximum percentage change (suppression) in base-line was independent of cortisol concentration. At + 30 min after the start of cortisol perifusion, the ACTH response area in CRH columns was significantly lower than in AVP columns (P = 0·0088), and remained lower 90 min after the end of perifusion (P = 0·0084) but the maximum percentage change (suppression) was not different between secretagogues. ACTH peak height was significantly (P < 0·0268) lower in CRH than in AVP columns (from + 30 min until 180 min after the end of cortisol perifusion) and the maximum percentage change (suppression) was also greater (P = 0·0011) in CRH columns. This study shows the effect of different concentrations of cortisol on CRH- and AVP-induced ACTH secretion by equine anterior pituitary cells, and the time-course for ACTH responses to be inhibited by, and recover from, cortisol perifusion. The highly significant inhibitory effect of cortisol on stimulated ACTH secretion was more apparent when CRH was the secretagogue than when AVP was the secretagogue. The significant inhibitory effect of cortisol on unstimulated baseline secretion of ACTH has not been described previously. These effects occur at physiological concentrations of secretagogues and cortisol. This suggests that, in vivo, circulating cortisol may have an important role in the control of ACTH secretion at pituitary level. Journal of Endocrinology (1993) 137, 403–412

scholarly journals Desensitization of the adrenocorticotrophin responses to arginine vasopressin and corticotrophin-releasing hormone in ovine anterior pituitary cells

2003 ◽  
Vol 178 (3) ◽  
pp. 491-501 ◽  
Author(s):  
A Hassan ◽  
S Chacko ◽  
D Mason
Keyword(s):  
Arginine Vasopressin ◽  
Anterior Pituitary ◽  
Prolonged Exposure ◽  
No Reduction ◽  
Pituitary Cells ◽  
Acth Secretion ◽  
Releasing Hormone ◽  
Anterior Pituitary Cells

Following repeated or prolonged exposure to either corticotrophin-releasing hormone (CRH) or arginine vasopressin (AVP), pituitary adrenocorticotrophin (ACTH) responsiveness is reduced. This study compared the characteristics of desensitization to CRH and AVP in perifused ovine anterior pituitary cells. Desensitization to AVP occurred at relatively low AVP concentrations and was both rapid and readily reversible. Treatment for 25 min with AVP at concentrations greater than 2 nM caused significant reductions in the response to a subsequent 5 min 100 nM AVP pulse (IC(50)=6.54 nM). Significant desensitization was observed following pretreatment with 5 nM AVP for as briefly as 5 min. Desensitization was greater following a 10 min pretreatment, but longer exposures caused no further increase. Resensitization was complete within 40 min following 15 min treatment with 10 nM AVP. Continuous perifusion with 0.01 nM CRH had no effect on AVP-induced desensitization. Treatment with 0.1 nM CRH for either 25 or 50 min caused no reduction in the response to a subsequent 5 min stimulation with 10 nM CRH. When the pretreatment concentration was increased to 1 nM significant desensitization was observed, with a greater reduction in response occurring after 50 min treatment. Recovery of responsiveness was progressive following 50 min treatment with 1 nM CRH and was complete after 100 min. Our data show that in the sheep AVP desensitization can occur at concentrations and durations of AVP exposure within the endogenous ranges. This suggests that desensitization may play a key role in regulating ACTH secretion in vivo. If, as has been suggested, CRH acts to set corticotroph gain while AVP is the main dynamic regulator, any change in responsiveness to CRH may significantly influence the overall control of ACTH secretion.

scholarly journals Mechanisms of desensitization of the adrenocorticotropin response to arginine vasopressin in ovine anterior pituitary cells

2005 ◽  
Vol 184 (1) ◽  
pp. 29-40 ◽  
Author(s):  
A Hassan ◽  
D Mason
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Protein Phosphatase ◽  
Anterior Pituitary ◽  
Receptor Internalization ◽  
Pituitary Cells ◽  
Acth Secretion ◽  
Kinase C ◽  
Anterior Pituitary Cells ◽  
Vasopressin Receptors

Arginine vasopressin (AVP) stimulates adrenocorticotropin (ACTH) secretion from corticotroph cells of the anterior pituitary via activation of the V1b vasopressin receptor, a member of the G protein-coupled receptor (GPCR) family. Recently, we have shown that treatment of ovine anterior pituitary cells with AVP for short periods results in reduced responsiveness to subsequent stimulation with AVP. The aim of this study was to investigate mechanisms involved in this desensitization process. Among the GPCR family, rapid desensitization is commonly mediated by receptor phosphorylation, with resensitization being mediated by internalization and subsequent dephosphorylation of the receptors by protein phosphatases. Since desensitization of V1a vasopressin receptors is mediated by protein kinase C-mediated receptor phosphorylation, we investigated the involvement of this enzyme in desensitization of the ACTH response to AVP. Treatment of perifused ovine anterior pituitary cells with the specific protein kinase C (PKC) activator 1,2-dioctanoyl-sn-glycerol (300 μM) did not induce any reduction in response to a subsequent 5-min stimulation with 100 nM AVP, despite potently stimulating ACTH secretion. Likewise, the results obtained using the PKC inhibitor Ro 31-8220 were not consistent with involvement of PKC in AVP desensitization: 2 μM Ro 31-8220 did not reduce the ability of a 10 nM AVP pretreatment to induce desensitization to a subsequent stimulation with 100 nM AVP. Pharmacologic blockade of receptor internalization by treatment with 0.25 mg/ml concanavalin A significantly impaired the ability of a 15-min pretreatment with 10 nM AVP to induce desensitization, rather than affecting resensitization. Treatment with 10 nM okadaic acid, an inhibitor of protein phosphatase 1 and 2A, had no effect on either resensitization or desensitization. In contrast, inhibition of protein phosphatase 2B (PP2B) with 1 μM FK506 decreased the rate of resensitization: complete recovery from desensitization took 40 min, whereas in controls recovery was complete 20 min after termination of the pretreatment. These results indicate that desensitization of the ACTH response to AVP is not mediated by PKC-catalyzed phosphorylation, suggesting subtype-specific differences in the regulation of V1a and V1b vasopressin receptors. The data demonstrate that desensitization was dependent, at least in part, upon receptor internalization and that resensitization was dependent upon PP2B-mediated receptor dephosphorylation.

Regulation of ACTH secretory pathways in cultured pituitary cells

1991 ◽  
Vol 261 (5) ◽  
pp. C793-C798 ◽  
Author(s):  
J. Schwartz ◽  
S. Gibson ◽  
A. White
Keyword(s):  
Anterior Pituitary ◽  
Adrenocorticotropic Hormone ◽  
Corticotropin Releasing Factor ◽  
Pituitary Cells ◽  
Receptor Complex ◽  
Response Mechanism ◽  
Acth Secretion ◽  
Secretory Pathways ◽  
Anterior Pituitary Cells ◽  
Acth Release

Although chloroquine, an agent that disrupts regulated protein secretion, has previously been shown to decrease the adrenocorticotropic hormone (ACTH) secretory response to adenosine 3',5'-cyclic monophosphate or corticotropin-releasing factor (CRF) in AtT-20 and rat anterior pituitary cells, respectively, it has no effect on the response to vasopressin. The present study extended experiments with chloroquine to cultured sheep anterior pituitary cells, which have a greater maximum response to vasopressin. Chloroquine (200 microM) had no effect on basal ACTH secretion or on stimulation by vasopressin. In contrast to the rat, the net response to CRF was tripled by chloroquine in ovine cells. The effect of chloroquine on the response to CRF was more effective by coexposure of cells to CRF and chloroquine than by pretreatment with chloroquine. Monensin or vinblastine did not increase the ACTH response to CRF. The results indicate ACTH release in response to vasopressin is chloroquine insensitive in this way, can be dissociated from the mechanism that responds to CRF, and would be consistent with the CRF response mechanism involving pathways that can alter the secretory pool of ACTH. When chloroquine acts to increase the response to CRF, it is likely not to act by stabilizing the CRF-receptor complex.

Blockage of K+ channels reverses the inhibitory action of atriopeptin on secretagogue-stimulated ACTH release by perifused isolated rat anterior pituitary cells

1990 ◽  
Vol 126 (2) ◽  
pp. 183-191 ◽  
Author(s):  
F. A. Antoni ◽  
G. Dayanithi
Keyword(s):  
Anterior Pituitary ◽  
Inhibitory Action ◽  
Calcium Ionophore ◽  
Delayed Rectifier ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Acth Secretion ◽  
Anterior Pituitary Cells ◽  
Isolated Rat ◽  
Acth Release

ABSTRACT The aim of the present study was to investigate how atriopeptin inhibits secretagogue-stimulated ACTH secretion in vitro. Perifused isolated rat anterior pituitary cells were used throughout; the ACTH content of the perifusate was measured by radioimmunoassy. In the presence of a constant (0·05 nmol/l) concentration of 41-residue corticotrophin-releasing factor (CRF), arginine vasopressin (AVP; 0·05–50 nmol/l) stimulated ACTH secretion in a concentration-dependent manner, the combination of 0·05 nmol CRF/l and 0·5 nmol AVP/l (CRF/AVP) stimulated ACTH release to six- to eightfold above baseline. The effect of CRF/AVP was not modified by tetrodotoxin, but was abolished by CoCl2 and reduced to about 70% of the control stimulus by nifedipine. Application of 103–126 residue atriopeptin for 10 min before and 2·5 min during the CRF/AVP stimulus strongly suppressed the evoked release of ACTH, the maximal inhibition was 75–90% at 10 nmol atriopeptin/l. The calcium ionophore ionomycin (200 nmol/l) reversed the effect of atriopeptin while it had no secretagogue activity of its own, and did not enhance the response to CRF/AVP. A variety of blockers of K+ channels, 4-amino pyridine, tetraethylammonium, apamine, quinine, but not tolbutamide, effectively antagonized the inhibitory action of atriopeptin (10 nmol/l). None of these drugs altered ACTH release evoked by CRF/AVP. In concentration–response experiments, the half effective concentration of 4-aminopyridine and tetraethyl-ammonium were around 1 mmol/l and 10 nmol/l for apamine. Finally, tetraethylammonium and apamine also antagonized the inhibition of CRF/AVP-evoked ACTH release by 8-Br-cGMP. These data suggest that (1) at least two types of K+ channels, a delayed rectifier and the apamine-sensitive Ca2+-activated channel, are functionally important in pituitary corticotroph cells; (2) atriopeptin inhibits CRF/AVP-stimulated ACTH secretion by hyperpolarizing the plasma membrane and thus reducing the uptake of Ca2+ into the cells; (3) cGMP is the intracellular mediator of the action of atriopeptin on corticotroph cells. Journal of Endocrinology (1990) 126, 183–191

Secretion of adrenocorticotrophin (ACTH) and ACTH precursors in ovine anterior pituitary cells: actions of corticotrophin-releasing hormone, arginine vasopressin and glucocorticoids

1994 ◽  
Vol 140 (2) ◽  
pp. 189-195 ◽  
Author(s):  
J Schwartz ◽  
P Ash ◽  
V Ford ◽  
H Raff ◽  
S Crosby ◽  
...  
Keyword(s):  
Arginine Vasopressin ◽  
Anterior Pituitary ◽  
Secretory Response ◽  
Target Cells ◽  
Pituitary Cells ◽  
Basal Secretion ◽  
Acth Secretion ◽  
Releasing Hormone ◽  
Anterior Pituitary Cells ◽  
Synthetic Glucocorticoid

Abstract Although corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) have been extensively characterized as stimulators, and glucocorticoids as inhibitors of ACTH secretion, far less is known about the control of the secretion of ACTH precursors from the anterior pituitary or about the types of corticotrophs involved. The present study was designed to systematically evaluate the actions of stimulatory and inhibitory factors on the secretion of ACTH and ACTH precursors (pro-opiomelanocortin, Mr 31 000; pro-ACTH, Mr 22 000) from dissociated ovine anterior pituitary cells. The cells were stimulated for 3 h with CRH (10 nmol/l) and AVP (100 nmol/l), alone or in combination with the synthetic glucocorticoid dexamethasone. In designated wells, cells were treated with dexamethasone, (100 nmol/l), beginning 16–18 h before and continuing through the 3-h secretion experiments in the presence of CRH and AVP. Secretion of ACTH-like peptides from intact cultures was compared with that from cultures which had been pretreated with a cytotoxic CRH conjugate (cytotoxin) to eliminate CRH-target cells specifically. Immunoreactive (ir)-ACTH was measured by radioimmunoassay (RIA); ACTH(1–39) and ACTH precursors were specifically measured by two-site immunoradiometric assays that discriminate between the two. In intact populations of cells, dexamethasone had no effect on basal ACTH(1–39) secretion, but decreased the secretion of ACTH(1–39) in response to CRH or AVP. Pretreatment of cells in the same experiments with cytotoxin (for 18 h, beginning 3·5 days before secretion studies) also had no significant effect on basal ACTH(1–39) secretion, but eliminated the response to CRH and decreased the response to AVP. In contrast to the situation in intact populations, dexamethasone had no effect on the residual secretion of ACTH(1–39) in response to AVP. These results mirrored those for secretion of ir-ACTH, measured by RIA. Secretion of ACTH precursors followed a different pattern from that for ir-ACTH and ACTH(1–39). In intact populations, dexamethasone decreased the secretion of ACTH precursors in response to CRH, but had no effect on basal secretion or the precursor response to AVP. Elimination of CRH-target cells also had no effect on basal precursor secretion and eliminated the secretion of precursors in response to CRH. Loss of CRH-target cells was accompanied by a smaller decrease in the secretion of ACTH precursors than ir-ACTH and ACTH(1–39) in response to AVP. Interestingly, dexamethasone significantly increased the secretion of ACTH precursors in response to AVP after cytotoxin. These results suggest either that the inhibition by glucocorticoids of the ACTH(1–39) secretory response to AVP is confined to those AVP-responsive cells that are sensitive to the CRH-target-specific cytotoxin, or that glucocorticoid-induced inhibition of the response to AVP depends on the functional presence of CRH-responsive cells. The results further suggest that the secretion of ACTH precursors in response to AVP is resistant to inhibition by glucocorticoids, regardless of the presence of CRH-target cells and is, generally, much less influenced by, or dependent upon, CRH-target cells. Taken together, the data suggest that those corticotrophs which are resistant to cytotoxin are the source of ACTH precursors secreted in response to AVP, and resist inhibition by glucocorticoids. Journal of Endocrinology (1994) 140, 189–195

Effects of vasopressin and elimination of corticotropin-releasing hormone-target cells on pro-opiomelanocortin mRNA levels and adrenocorticotropin secretion in ovine anterior pituitary cells

1997 ◽  
Vol 154 (1) ◽  
pp. 139-147 ◽  
Author(s):  
S A van de Pavert ◽  
I J Clarke ◽  
A Rao ◽  
K E Vrana ◽  
J Schwartz
Keyword(s):  
Protein Kinase C ◽  
Steady State ◽  
Anterior Pituitary ◽  
Target Cells ◽  
Pituitary Cells ◽  
Mrna Levels ◽  
Acth Secretion ◽  
Kinase C ◽  
Pomc Mrna ◽  
Anterior Pituitary Cells

Abstract Although arginine-vasopressin (AVP) is reported to produce greater ACTH biosynthetic and secretory responses than does corticotropin-releasing hormone (CRH) in sheep anterior pituitary cells, neither factor appears to increase pro-opiomelanocortin (POMC) mRNA levels, as does CRH in the cells of some other species. Since only a fraction of cells that express POMC mRNA may be able to respond to AVP, the aim of this study was to further delineate the regulation of POMC mRNA in ovine anterior pituitary corticotrophs, as a whole and in functional subpopulations of corticotrophs. We measured the effects of AVP, CRH or activation of protein kinase C by phorbol myristate acetate (PMA) in cultured cells. We compared responses in intact populations with those of cultures from which CRH-target cells were pharmacologically eliminated. Dissociated adult ovine anterior pituitary cells were cultured overnight, treated with either vehicle (intact) or a CRH-toxin conjugate that specifically eliminates CRH-target cells (CRH-target-depleted), washed, returned to culture and subsequently challenged with vehicle, AVP (100 nm), CRH (10 nm) or PMA (1 μm) for 5 h. The media were assayed for ACTH by RIA and the cells for POMC mRNA by Northern blot analysis. In intact populations, AVP and CRH increased ACTH secretion from 6·5 ±1·2 to 216 ±22 and 81 ± 14 ng/well respectively, but only AVP caused an increase in steady-state POMC mRNA levels (+48 ± 10%). Direct activation of protein kinase C with PMA mimicked the effect of AVP on ACTH secretion (318 ± 16 ng/well), but did not alter POMC mRNA levels. In CRH-target-depleted populations, control ACTH secretion (11 ± 3 ng/well) and POMC mRNA (+69 ±7%) were elevated, compared with intact populations. AVP (55 ± 8 ng/well) and PMA (120 ± 17 ng/well), but not CRH, increased ACTH secretion; POMC mRNA was not significantly elevated by any of the treatments. Taken together, these data provide further support for the notion of dissociation between secretion of ACTH and expression of POMC mRNA, and demonstrate that AVP increases steady-state POMC mRNA levels in ovine anterior pituitary cells. The data are also consistent with the concept that complex interactions, possibly including those between cells, influence ACTH secretion and steady-state POMC mRNA levels. Journal of Endocrinology (1997) 154, 139–147

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