Rapid inhibitory effect of corticosterone on histamine release from rat peritoneal mast cells.

Glucocorticoids are steroids endowed with powerful anti-inflammatory properties, which are routinely believed to require several hours to take effect through modulation of gene expression. Our recent report has shown that glucocorticoids could inhibit allergic reaction within 10 minutes, which the classical genomic mechanism could not explain. Histamine is thought to be one of major mediators in the allergic reaction, and IgE-mediated histamine release from mast cells plays a pivotal role in allergic diseases. Here, we have determined a rapid effect of corticosterone on histamine release from rat peritoneal mast cells, using fluorometric assay. The results showed that corticosterone could inhibit antigen-induced histamine release from rat peritoneal cells within 15 minutes (p<0.05), which could be mimicked by membrane-impermeable BSA conjugated corticosterone (p<0.05). Neither glucocorticoid nuclear receptor antagonist nor protein synthesis inhibitor could block the rapid action (p<0.05). The study provided evidence that nongenomic mechanism might be involved in rapid effect of glucocorticoids on mast cells in allergic disease.     

Inhibitory effect of ouabain on epinephrine-induced stimulation of adrenal corticosterone secretion in rats.

Chronic administration of ouabain (3 mg/Kg body weight, subcutaneously, once daily for consecutive 15 days) definitely inhibited epinephrine-induced increase of adrenal corticosterone secretion. The inhibition rate increased along with frequency of ouabain administration. Increase in adrenal corticosterone synthesis and secretion by ACTH (20-50 mU/rat) administration was partially suppressed by pretreatment with chronic ouabain administration. A slight but significant increase of adrenal corticosterone secretion caused by epinephrine administration in hypophysectomized rats was also inhibited by pretreatment with ouabain administration. Chronic administration of neither phentolamine (1 mg/rat, intraperitoneally, once daily for consecutive 15 days) nor propranolol (3 mg/Kg body weight, subcutaneously, once daily for consecutive 15 days) caused significant changes in adrenal corticosterone secretion in response to ACTH as well as to epinephrine. Chronic administration of ouabain in rats causes not only elevated secretion of ACTH from anterior pituitary but also functional change in adrenals leading to suppression of corticosterone secretion in response to ACTH or epinephrine administration.     

Features of ginseng saponin-induced corticosterone secretion.

Ginseng saponin administered intraperitoneally to rats induced a significant rise in plasma corticosterone, while it tended to increase plasma glucose and to decrease plasma immunoreactive insulin. Oral or intraperitoneal administration of ginseng saponin increased plasma corticosterone in unanesthetized, pentobarbital-anesthetized or alloxan-diabetes rats. The histamine-induced rise in plasma corticosterone was suppressed by pretreatment with diphenhydramine, whereas the ginseng-induced rise was not. Ginseng saponin decreased rectal temperature while it increased plasma corticosterone. Ginseng-induced corticosterone secretion was superimposed on the basal levels of plasma corticosterone due to fasting and circadian rhythm. Thus ginseng saponin would be a kind of stressful agent and have different features associated with the stimulation of the pituitary-adrenocortical system from several other chemical agents.     

Direct effect of corticosterone upon insulin secretion studied by three different techniques.

The immediate effect of corticosterone upon insulin secretion rates estimated by three different techniques (perfusior of isolated rat pancreas and perifusion or incubation of isolated islets of Langerhans) was studied for one hour. Three corticosterone concentrations were used: 0.02, 0.2 or 20 mg/l. With 4.2 mmol/l glucose, corticosterone did not affect insulin secretion, whereas, with a stimulating glucose concentration (16.7 mmol/l), insulin secretion was inhibited by the three corticosterone concentrations tested during incubation experiments, and by only the two physiological ones (0.02 and 0.2 mg/l) during islets perifusion and pancreas perfusion experiments. Moreover the inhibitory effect appeared more rapid with perifused islets than perfused pancreas, where only the second insulin secretory phase was disturbed.     

The effect of partial noradrenergic denervation on corticosterone secretion in the rat

DSP₄ (N-(-2-chloroethyl)-N-ethyl-2-bromobenzylamine) treatment significantly decreased the noradrenaline content in the hippocampus, frontal cortex and hypothalamus of the rat brain. DSP₄ treatment did not affect plasma corticosterone levels. Clonidine, an ₂-adrenoceptor agonist, had no effect on corticosterone secretion in either DSP₄- or saline-treated rats. Isoproterenol, a -adrenoceptor agonist, significantly stimulated corticosterone secretion. This effect was inhibited by the prior administration of the -adrenoceptor antagonist propranalol. DSP₄ treatment did not alter the isoproterenol-induced stimulation of corticosterone secretion. The administration of a high dose of dexamethasone (100 g/kg, i.p.) significantly decreased the plasma corticosterone concentration of saline-treated controls, while an intermediate dose (25 g/kg, i.p.) did not suppress corticosterone release significantly. DSP₄-treatment did not influence dexamethasone-induced suppression of corticosterone secretion. These results show that significant decreases in noradrenaline content in the hippocampus, frontal cortex and hypothalamus appear to have no effect on the regulation of corticosterone secretion and that corticosterone secretion may be stimulated by catecholamines via -adrenoceptors.     

Characteristics of the inhibitory effect of alkalosis on insulin secretion

Glucose-induced insulin secretion by the perfused sodium pentobarbital-anesthetized-rat pancreases was studied under different extracellular pH ranging from 7.4 to 7.8. Under our experimental conditions the amount of insulin released was inversely correlated to the pH increase. Besides, metabolic (CO2H- excess) or gaseous (low pCO2) type of alkalosis, were equally effective inhibiting insulin secretion. During a 16.6 mM glucose stimulus, sequential modifications of extracellular pH (7.4-7.8-7.4) caused a dramatic decrease in insulin secretion during alkalosis and an enhancement of its release during the second 7.4 period. The installment and remotion of the inhibition followed almost immediately the changes in the pH of the perfusates. These findings indicate that extracellular diminution of H+ concentration produces a gradual and quickly reversible decrease upon glucose-induced insulin secretion. These characteristics suggest that the inhibitory effect may be mediated through changes in intracellular and/or transmembrane ion fluxes coupled to the variations in H+ concentration.     

Stress ulcer modulation by limbic system structures.

A number of studies suggest that the telencephalic limbic system modulates stress ulcer development. The amygdala is assumed to connect sensory experiences, including stressful stimuli, with the emotional reactions and gastrointestinal effects normally produce. The hippocampal formation (entorhinal cortex, dentate gyrus, hippocampus) is part of a gating system, modulating the organism's coping ability. Changes in transmission in this temporal brain region are linked to individual differences in stress ulcer severity. Interactions among "classical" transmitters and several neuropeptides mediate these differences.     

Analysis of the inhibitory effect of verapamil on adrenal medullary secretion

Verapamil blocked catecholamine (CA) secretion evoked by acetylcholine (ACh), Ba²⁺ or Ca²⁺ in isolated perfused bovine adrenals. This inhibitory effect was irreversible and not modified by increasing the Ca²⁺ concentration of the perfusion fluid. Tetracaine also inhibited CA secretion, although no additive effect was found when both verapamil and tetracaine were present simultaneously in the perfusion medium. It is concluded that verapamil and tetracaine inhibit CA secretion presumably at the same site, but verapamil effect cannot be reverted by excess of calcium ions.     

Effect of gamma-aminobutyric acid and muscimol on corticosterone secretion in rats.

The effect of gamma-aminobutyric acid-receptor agonists, GABA and muscimol on the pituitary-adrenocortical activity, measured indirectly through corticosterone secretion, and the receptors involved were investigated in conscious rats. GABA given ip induced a dual effect, in lower dose (10 mg/kg) it significantly decreased the resting serum corticosterone levels while in higher doses (100-500 mg/kg) it considerably raised that level. Muscimol (0.5 mg/kg ip) also increased the corticosterone concentration. Both GABA and muscimol given intracerebroventricularly (icv) induced a significant, dose-related increase in serum corticosterone levels. Bicuculline, a GABAA-receptor antagonist, totally abolished the corticosterone response to GABA but did not influence the response to muscimol. Pretreatment with atropine did not affect the corticosterone response to GABA but significantly diminished the response to muscimol. These results suggest that GABA moderately inhibits the pituitary-adrenal axis at the pituitary level but significantly stimulates it at the hypothalamic level. The stimulatory effect of GABA, but not muscimol, is mediated by hypothalamic GABAA-receptors, and in the effect of muscimol hypothalamic cholinergic, muscarinic receptors are involved to a significant extent.     

Guanosine nucleotides modulate the inhibitory effect of brefeldin A on protein secretion

Brefeldin A (BFA) causes rapid redistribution of Golgi proteins into the endoplasmic reticulum (ER), leaving no definable Golgi-apparatus, and blocks transport of proteins from the ER to distal secretory compartments of the cell. Using pulse-chase experiments the present study shows that BFA (1 microgram/ml) inhibits basal and CCK-stimulated protein secretion in isolated pancreatic acinar cells by 65 +/- 6% and 84 +/- 5%, respectively. In isolated permeabilized cells higher concentrations of BFA (30 micrograms/ml) were necessary to obtain inhibition of protein secretion. In parallel experiments protein secretion was stimulated by GTP (1 mM). BFA had no inhibitory effect on protein secretion in the presence of GTP, indicating that BFA might act on a GTP-binding protein. Investigating the effect of BFA on small molecular weight GTP-binding proteins we observed that [alpha-32P]GTP binding to a 21 kDa protein in a subcellular fraction enriched in ER was increased in the presence of BFA. We conclude that this 21 kDa and possibly also other GTP-binding proteins may be the molecular target of Brefeldin A in pancreatic acinar cells.     

The inhibitory effect of strophanthidin on secretion by the isolated gastric mucosa

The unidirectional fluxes of Na⁺ and Cl^- were measured across the isolated gastric mucosa of the bullfrog (R. catesbiana). The addition of strophanthidin, a cardiac aglycone, resulted in marked reductions of the spontaneous potential and short-circuit current. Associated with these changes, the isolated gastric mucosa ceased secreting chloride and hydrogen ion. Although the active component of chloride transfer was inhibited, the exchange diffusion component seemed to increase. No significant changes in membrane conductance or sodium flux were noted. Possible mechanisms of strophanthidin inhibition were discussed in view of its effect on chloride transport across the gastric mucosa and on sodium and potassium transfer in other tissues. It was concluded that the cardiac glycosides may not be specific inhibitors of sodium and potassium transport. This non-specific inhibition suggests that active chloride transport is affected by strophanthidin directly and/or anion secretion is dependent upon normal functioning of cation transport systems in the tissue.     

Flanking host sequences can exert an inhibitory effect on the cleavage step of the in vitro mu DNA strand transfer reaction.

The effect of flanking host sequences on the cleavage step of the in vitro Mu DNA strand transfer reaction was investigated. Insertion of a mini-Mu molecule into certain sites in pUC19 results in insertions that demonstrate a decreased ability to form Type 1 complexes in subsequent rounds of transposition. Similarly, changes in the flanking host sequences directly adjacent to the Mu ends by in vitro mutagenesis can also result in Type 1-deficient mini-Mu molecules. Further examination of the inhibition revealed that Type 1 deficient mini-Mu molecules are capable of forming uncut synaptic complexes at normal levels but are compromised in their ability to serve as substrates for phosphodiester bond hydrolysis at the Mu ends. This cleavage defect can be overcome by addition of the Mu B protein and ATP to the reaction. Our data suggest that one of the roles of the B protein may be to provide a mechanism whereby Mu prophages with inhibitory flanking sequences can overcome this obstacle and avoid being trapped at unproductive locations.     

Effects of estradiol on corticosterone secretion in ovariectomized rats

The effects of estradiol benzoate (EB) on steroidogenesis in rat zona fasciculata-reticularis (ZFR) cells were studied. Female rats were ovariectomized (Ovx) for 2 weeks and then injected subcutaneously with oil or EB for 3 days before decapitation. ZFR cells were isolated and incubated with adrenocorticotropin (ACTH) or prolactin (PRL) for 1 h. Corticosterone concentrations in plasma and cell media, and adenosine 3',5'-cyclic monophosphate (cAMP) production in ZFR cells were determined by radioimmunoassay. The effects of EB replacement in vivo on the activities of steroidogenic enzymes in ZFR cells were measured by the amounts of intermediate steroidal products separated by thin-layer chromatography. Replacement of EB in vivo resulted in a dose-dependent increase of plasma PRL and corticosterone in Ovx rats. The basal, ACTH-, and PRL-stimulated release of corticosterone by ZFR cells was greater in EB- than in oil-treated animals. Forskolin-induced production of cAMP was greater in the EB-replaced rats than in oil-treated animals, which correlated with the increase of corticosterone production. The 3-isobutyl-l-methylxanthine (IBMX) plus ACTH-, IBMX plus PRL-, and forskolin plus PRL-stimulated productions of cAMP were higher in EB- than in oil-treated rats. The enzyme activities of postpregnenolone were not affected by EB replacement in Ovx rats. These results suggest that the EB-related increase of corticosterone production in Ovx rats is associated with an increase of cAMP generation and the stimulatory effect of PRL on ZFR cells.