Pancreatic acinar cell amylase gene expression: selective effects of adrenalectomy and corticosterone replacement

Determination of corticosterone in rat and mouse plasma by gas chromatography-selected ion monitoring mass spectrometry

A simple, highly sensitive and specific method based on gas-chromatography-selected ion monitoring (SIM) mass spectrometry has been developed for the quantitation of corticosterone in rat and mouse plasma. After extraction of the plasma with ethyl acetate, the residue was trimethy-silylated with pentafluorobenzyl hydroxylamine-trimethylsilyl (PFBO-TMS). Detection of the derivatives was accomplished by a quadruple mass spectrometer in the selected ion monitoring mode (m/z of 316, 648, 663 and 678). The detection limit of the assay was 0.1 pg on column. The results show that in the plasma of non-stressed animals, only minor amounts of corticosterone were found; whereas in the plasma of stressed animals, it was dramatically increased. The method developed here can be used to examine corticosterone levels as a marker of stress in rats and mice and may also be used for estimation of the effect of stress-release medications.

Quantitative analysis of human serum corticosterone by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry

An original method based upon high-performance liquid chromatography coupled to electrospray ionization mass spectrometry has been developed for corticosterone (B) quantification in human serum. After extraction by diethyl ether using triamcinolone (T) as an internal standard, solutes are separated on a C18 microbore column (250 X 1.0 mm, I.D.), using acetonitrile-water-formic acid (40:59.9:0.1, v/v/v) as the mobile phase (flow-rate 40 microl/min). Detection is performed on an API 1 single quadrupole mass spectrometer equipped with a ESI interface and operated in positive ionization mode. Corticosterone quantifications were realized by computing peak area ratios (B/T) of the serum extracts analyzed in SIM mode (m/z 347 and m/z 395 for B and T. respectively), and comparing them with the calibration curve (r=0.998).

The role of endogenous glucocorticoids in rat experimental models of acute pancreatitis

BACKGROUND & AIMS

Cytokines activate the hypothalamic-pituitary-adrenal axis and suppress inflammation by stimulating glucocorticoid secretion. The state of adrenocortical function during acute pancreatitis and its role in this disease were determined.

METHODS

Cerulein-induced pancreatitis or closed duodenal loop pancreatitis was produced in rats that had undergone adrenalectomy or sham adrenalectomy, and the serum corticosterone and interleukin 8 levels and the intensity of the pancreatitis were examined.

RESULTS

Serum corticosterone levels were significantly higher than basal levels in both models of experimental pancreatitis. In both models, adrenalectomy increased serum amylase and pancreatic edema and produced more severe inflammation. Adrenalectomy significantly increased mortality in animals with closed duodenal loop pancreatitis. Exogenous hydrocortisone administered to adrenalectomized animals suppressed the elevation of serum interleukin 8 levels and decreased both the severity of pancreatitis and mortality.

CONCLUSIONS

These results suggest that the adrenocortical function is stimulated during acute pancreatitis and that the secretion of endogenous glucocorticoids may play an important role in mitigating the progress of this disease, probably by inhibiting cytokine production.

Adrenocorticotropin secretagog release: stimulation by frustration and paradoxically by reward presentation

Colchicine blockade of axonal transport from the paraventricular nucleus to the median eminence was used to indirectly infer adrenocorticotropin (ACTH) secretagog release in response to a reward presentation and the psychological stressor of frustration. After training rats to drink at the same time of day for 30 min for 2-3 weeks, basal arginine vasopressin (AVP), but not corticotropin-releasing factor (CRF) or oxytocin (OT), concentrations were elevated. The frustration of presenting empty water bottles resulted in increased corticosterone concentrations. Concordantly, CRF, AVP, and OT contents in the median eminence decreased compared to controls. All three secretagogs are thus apparently involved in the corticosterone response to frustration. As expected, water presentation decreased both ACTH and corticosterone. Paradoxically, however, CRF, AVP, and OT contents also decreased compared to controls. The discrepancy of ACTH and corticosterone concentrations declining despite release of secretagogs cannot be explained by decreased adrenal or pituitary sensitivities since both exogenous ACTH and CRF elevated corticosterone and ACTH, respectively, in rewarded rats. Secretagog release, therefore, may not always be associated with stimulation of ACTH release.

Systemic endotoxin induces Fos-like immunoreactivity in rat spinal sympathetic regions

Immunocytochemical detection of Fos protein was used to evaluate the activation of neurons in sympathetic preganglionic regions of rat spinal cord after systemic treatment with endotoxin. Administration of relatively low doses of bacterial lipopolysaccharide (LPS) to conscious rats caused transient hypotension and stress hormone elevation. Three hours after LPS injection, Fos protein was detected in large numbers of neurons throughout the thoracic spinal cord. Fos-immunoreactive neurons were found in spinal cord segments T3-T13 in the four sympathetic preganglionic nuclei: the intermediolateral cell column (77.7%), the intercalated nucleus (10.6%), the central autonomic nucleus (10.1%) and the lateral funiculus (1.5%). These regions in control animals showed no Fos staining. We conclude that sublethal endotoxemia is a potent stimulus causing Fos expression in sympathetic preganglionic regions.

Patterns of adrenocorticotropin secretagog release in response to social interactions and various degrees of novelty

Colchicine blockade of axonal transport from the paraventricular nucleus to the median eminence was used to indirectly infer ACTH secretagog release in response to the psychological stressors of social interactions and various degrees of novelty. Placing a rat in a new cage with either the smell or presence of a novel conspecific decreased arginine vasopressin and oxytocin (OT) contents, but not corticotropin-releasing factor content. Secretagog contents were unchanged in rats in their home cages faced with a novel conspecific. Secretagog release during social stress is thus primarily a function of being in a novel setting. For different degrees of novelty, rats were placed in either a novel cage, a novel bucket, or a novel bucket smelling of another rat. Whereas secretagog contents were unchanged with a novel cage, OT content alone decreased in response to both the bucket and the unclean bucket. Despite a graded corticosterone response, there was no distinction in the OT response, suggesting that the colchicine technique cannot accurately reflect gradations of stressors.

Analysis of corticosterone in rat plasma by high-performance liquid chromatography

A sensitive and specific high-performance liquid chromatographic assay for the determination of corticosterone in rat plasma using dexamethasone as the internal standard is reported. Rat plasma (0.5 ml) is extracted with methylene chloride, washed with 0.1 M sodium hydroxide and then with water. The extract is analyzed by HPLC on a C18 column with ultraviolet absorbance detection at 254 nm. Pooled rat plasma was treated with activated decolorizing carbon to remove endogenous corticosterone, and was then used to prepare standards for the assay. Using 0.5 ml plasma for extraction, the detection limit of the assay is 10 ng/ml. The standard curve is linear over the concentration range 10-500 ng/ml. The recovery of corticosterone after extraction was independent of concentration and ranged from 87 to 95%. The coefficient of variation for intra-day and inter-day precision ranged from 2.4 to 7.4% and 2.1 to 8.7%, respectively. In addition, for concentrations ranging from 10 to 500 ng/ml the accuracy is within 5% of the spiked standards. The assay was utilized to examine the circadian rhythm of plasma corticosterone, and to examine the effect of immobilization stress on corticosterone levels in rats.

Caerulein and gastrin(2-17 ds) regulate differently synthesis of secretory enzymes, mRNA levels and cell proliferation in pancreatic acinar cells (AR4-2J)

In order to characterize the biological functions coupled to cholecystokinin (CCK) A and B receptors, the effects of gastrin(2-17 ds) and caerulein were compared. An isolated cell model, the pancreatic acinar cell line AR4-2J, was used and the experiments were carried out in serum-free media. Caerulein was found to evoke no mitogenic effects either alone or in the presence of the CCK antagonists L364,718 and CR1409. Gastrin(2-17 ds) increased cell proliferation by 2-fold with an IC50 of 150 pM, corresponding to the occupancy of the CCK B receptors. CR1409, at concentrations that fully occupied CCK B receptors, inhibited the gastrin(2-17 ds) effects. Caerulein enhanced chymotrypsinogen biosynthesis by 100% and the corresponding mRNA level by 75%; amylase biosynthesis and mRNA level were enhanced by 40% only. Half-maximal increases in chymotrypsin activity and mRNA level were recorded in response to caerulein at concentrations of 100 pM and 50 pM respectively. Gastrin(2-17 ds) at 100 nM enhanced chymotrypsinogen biosynthesis by 26% and its mRNA level by 35%; these responses were lower than those evoked by 0.1 nM caerulein. Furthermore, CR1409 completely inhibited caerulein- and gastrin(2-17 ds)-stimulated chymotrypsinogen synthesis, with similar IC50 (4 microM). These results suggest that both peptides induced the synthesis of the secretory enzyme after occupancy of CCK A receptors.

Regulation of amylase and chymotrypsinogen expression by dexamethasone and caerulein in serum-free-cultured pancreatic acinar AR4-2J cells. Influence of glucose

The direct effects of dexamethasone and caerulein on two pancreatic enzymes, amylase and chymotrypsin, were determined in AR4-2J cells cultured under serum-free conditions at two glucose concentrations (1.0 and 4.5 g/l). In the absence of any hormone, the higher glucose concentration resulted in a 1.6-1.8-fold increase in the basal levels of amylase and chymotrypsinogen. Dexamethasone (50 nM) increased the biosynthesis and mRNA levels of both enzymes at both glucose concentrations. However, dexamethasone had a more pronounced effect on amylase biosynthesis (5-fold induction) than on chymotrypsinogen biosynthesis (1.8-fold induction). The parallel increases in mRNA and protein indicated the existence of pre-translational regulation. This is in contrast with what was observed in serum-containing media, where a translational regulation of amylase biosynthesis took place, probably under the control of both glucose and some serum factors. By contrast, caerulein (10 nM) exerted a more specific action on chymotrypsinogen. The increases in chymotrypsinogen mRNA were 2.2- and 2.1-fold, and increases in chymotrypsin activity were 1.6- and 2.9-fold at 1.0 and 4.5 g of glucose/litre respectively. Thus the regulation by caerulein occurred mainly through the enhancement of chymotrypsinogen transcription and/or mRNA stabilization.

Up regulation of calbindin-D28K mRNA in the rat hippocampus following focal stimulation of the perforant path

Calbindin-D28K is a constitutive Ca2(+)-binding protein expressed in hippocampal neurons that are resistant to various forms of excitotoxic injury. However, the local factors controlling calbindin-D28K expression within the central nervous system are unknown. We report that neuronal excitation via the perforant path leads to an increased expression of calbindin-D28K mRNA within dentate granule cells. This response is related specifically to stimulation that induces prolonged periods of bursting afterdischarges and precedes cellular injury. The up regulation of calbindin-D28K mRNA occurs during the type of neuronal activation associated with elevated cytosolic Ca2+ and suggests that the maintenance of Ca2+ homeostasis includes a system of feedback control at the level of gene expression.

Expression of the amylase gene in the rat exocrine pancreas during postnatal development: effect of dexamethasone

Pancreatic amylase enzyme activity starts to increase rapidly around weaning (17-21 days) and reaches the adult level during postnatal development in the rat. To see whether the maturation of amylase involves changes in amylase gene expression, total pancreatic RNA was prepared from rats of various ages (term-fetus, 5, 10, 15, 20, 28 days and adult). Northern blots of these RNAs were probed with amylase cDNA. Levels of amylase mRNA peaked around 10 days i.e., about 1 week prior to peak amylase enzyme activity. The role of glucocorticoid in pancreatic amylase development was studied by giving rat pups at ages 5, 10 and 30 days a single injection (i.p.) of dexamethasone (DX). They and their littermates (controls) were killed 24 and 48 h after the injection. Increases in amylase mRNA levels were seen in the DX treated 5- and 10-day-old groups with corresponding increases in amylase enzyme activities. A slight decrease in amylase mRNA level was, however, observed in the DX treated 30-day-old pups which also had a slight decrease in amylase enzyme activity suggesting an age dependent differential responsiveness to DX. A time sequence study with 10-day-old pups killed after a single injection of DX at 6, 12, 24 and 48 h showed a rapid increase in mRNA levels which peaked around 12 h. Amylase enzyme activity, however, did not peak until 24 h after DX injection. These results suggest that pancreatic amylase is regulated at the level of gene expression in both normal- and DX-induced maturation. Regulation appears to occur at the transcription level as both increases to amylase activity and mRNA were blocked by actinomycin D.

The anticoordinate changes of pancreatic lipase and colipase activity to amylase activity induced by adrenalectomy in normal and diabetic rats

The effect of adrenalectomy (Adx) on pancreatic lipase and colipase activities in normal, streptozotocin-induced diabetic, and obese Zucker rats was studied. It was found that Adx induced a rapid decrease in amylase activity, a rapid increase in lipase activity, and a slow increase in colipase activity in normal rats. Twenty days after Adx, the levels of amylase activity were 70% lower than control, whereas the activities of lipase and colipase were 55 and 25% higher than control, respectively. The replacement of hydrocortisone normalized the changes in the three enzyme activities. Injection of insulin partially corrected the amylase activity, but had no significant effect on the activities of lipase and colipase. In streptozotocin-induced diabetic rats and obese Zucker rats, amylase activity was decreased, and lipase and colipase activities increased, compared to normal rats. These changes of enzyme activity were further enhanced by Adx. It is concluded that Adx results in an anticoordinate change in pancreatic lipase, colipase, and amylase activities, suggesting that glucocorticoid also influences the synthesis of the pancreatic lipolytic enzymes.

Response of exocrine pancreas to corticosterone and aldosterone after adrenalectomy

The long-term effect of adrenalectomy (Adx) on the exocrine pancreas was examined in female adult rats. Pancreatic amylase concentration decrease to 50% of the control level starting 10 days after Adx, whereas the levels of trypsinogen and lipase remained unchanged. Replacement studies beginning 24 h after surgery with corticosterone (B, 1 mg/100 g body wt) or aldosterone (ALDO, 8 micrograms/100 g body wt) alone did not prevent the decline in amylase after Adx. However, when both hormones were administered together, pancreatic amylase concentration was maintained at a level similar to that of the control group. Serum corticosterone levels in the rats receiving B alone or B + ALDO were not different, and were comparable to levels found in normal rats. Both ALDO and B, given for 5 days starting 10 days after Adx, were required to restore amylase concentrations toward control values. When spironolactone (SPIRO, 3 mg/100 g body wt), a specific mineralocorticoid receptor blocker was administered bid together with ALDO + B, it blocked the increase in pancreatic amylase seen in ALDO + B treated rats but did not affect the serum corticosterone levels. These results suggest that mineralocorticoids are also involved in modulating the level of amylase in the rat exocrine pancreas.

Pancreatic kallikrein gene expression: effects of glucocorticoids in vivo and in vitro

We examined the role of glucocorticoids in the regulation of pancreatic glandular kallikrein gene expression in vivo and in vitro. Adult male rats were adrenalectomized (Adx). Corticosterone pellets were administered to maintain either physiologic (Adx 1+) or high physiologic (Adx 3+) plasma corticosterone levels. Pancreatic kallikrein mRNA levels were examined by Northern hybridization and quantitated by slot-blot hybridization. Adrenalectomy resulted in a 75% +/- 14% (n = 4) increase in kallikrein mRNA as compared with sham-operated controls. This increase was completely reversed by exogenous corticosterone replacement to normal physiologic concentrations. Replacement with high corticosterone levels (Adx 3+) resulted in a decrease of kallikrein mRNA levels to 53% +/- 4% (n = 4) of controls. A significant negative correlation was observed between individual kallikrein mRNA levels and plasma corticosterone (r = -0.81, n = 12). In vitro, using the rat pancreatic acinar cell line AR42J, dexamethasone decreased kallikrein mRNA steady-state levels in a time- and dose-dependent manner. These data, therefore, indicate that physiologic concentrations of plasma corticosterone decrease pancreatic kallikrein mRNA levels in vivo, and that this is a direct effect on pancreatic acinar cells.