Cyclic Monophosphate Analogue Research Articles

SIN-1 reverses attenuation of hypercapnic cerebrovasodilation by nitric oxide synthase inhibitors.

We sought to determine whether the attenuation of the hypercapnic cerebrovasodilation associated with inhibition of nitric oxide synthase (NOS) can be reversed by exogenous NO. Rats were anesthetized (halothane) and ventilated. Neocortical cerebral blood flow (CBF) was monitored by a laser-Doppler probe. The NOS inhibitor N omega-nitro-L-arginine methyl ester (L-NAME; 40 mg/kg iv) reduced resting CBF [-36 +/- 5% (SE); P < 0.01, analysis of variance] and attenuated the increase in CBF elicited by hypercapnia (partial pressure of CO2 = 50-60 mmHg) by 66% (P < 0.01). L-NAME reduced forebrain NOS catalytic activity by 64 +/- 3% (n = 10; P < 0.001). After L-NAME, intracarotid infusion of the NO donor 3-morpholinosydnonimine (SIN-1; n = 6) increased resting CBF and reestablished the CBF increase elicited by hypercapnia (P > 0.05 from before L-NAME). Similarly, infusion of the guanosine 3',5'-cyclic monophosphate (cGMP) analogue 8-bromo-cGMP (n = 6) reversed the L-NAME-induced attenuation of the hypercapnic cerebrovasodilation. The NO-independent vasodilator papaverine (n = 6) increased resting CBF but did not reverse the attenuation of the CO2 response. SIN-1 did not affect the attenuation of the CO2 response induced by indomethacin (n = 6). The observation that NO donors reverse the L-NAME-induced attenuation of the CO2 response suggests that a basal level of NO is required for the vasodilation to occur. The findings are consistent with the hypothesis that NO is not the final mediator of smooth muscle relaxation in hypercapnia.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of C6 glioma cell steroidogenesis by adenosine 3',5'-cyclic monophosphate.

Incubation of C6 glioma cells in the presence of aminoglutethimide, an inhibitor of cholesterol metabolism, together with either adenosine 3',5'-cyclic monophosphate (cAMP) analogues or agents that increase cAMP synthesis, such as cholera toxin, forskolin, and isoproterenol, stimulated the rate of pregnenolone formation by their isolated mitochondria. This effect of cAMP was blocked by the antagonist (Rp)-cAMPS. The incorporation rate of mevalonolactone into pregnenolone was also increased by the stimulation of adenylyl cyclase activity in intact C6 cells. It is concluded that cAMP stimulates glial cell steroidogenesis by increasing the movement of the substrate, cholesterol, to the mitochondria, where it will be metabolized to pregnenolone by the side chain cleavage cytochrome P450 enzyme.

Control of intracellular calcium by membrane potential in human melanoma cells

The modulation of intracellular calcium ([Ca2+]i) by the membrane potential was investigated in human melanoma cells by combining the nystatin-perforated patch-clamp technique with Ca2+ measurements. Voltage steps to -100 mV induced a rise in [Ca2+]i and a creeping inward current. These effects were absent in Ca(2+)-free solution and could be blocked by Ni2+ or La3+. Voltage ramps revealed a close correlation between [Ca2+]i and voltage, with the strongest voltage dependence around the resting potential. Long-lasting tail currents, closely correlated with the rise in [Ca2+]i and a reversal potential close to the K+ equilibrium potential, occurred if the membrane potential was clamped back to 0 mV. They were absent if intracellular K+ was replaced by Cs+ and blocked by extracellular tetraethylammonium (5 mM), Ba2+ (1 mM), or a membrane-permeable adenosine 3',5'-cyclic monophosphate analogue. These observations are discussed in relation to cell proliferation. The enhanced expression of K+ channels during cell proliferation provides a positive-feedback mechanism resulting in long-term changes in [Ca2+]i required for the G1-S transition in the cell cycle.

Characterization of slow postsynaptic K + current of Aplysia LUQ neurons in culture

We have characterized the slow inhibitory synaptic connection between an left upper quadrant (LUQ) neuron and neuron L10, L12 or L13 in culture. A slow postsynaptic outward current in the LUQ neuron was elicited by repetitive firing of the co-cultured cholinergic neuron L10 as well as neuron L12 or L13 which were not cholinergic but FMRFamide synthesizing neurons. This outward current was due to an increase in K + conductance and was relatively insensitive to external application of tetraethylammonium and 4-aminopyridine. We also investigated the effects of injection of a guanosine 5′-triphosphate (GTP) analogue into the LUQ neuron and extracellular application of serotonin and an adenosine 3′,5′-cyclic monophosphate (cAMP) analogue on the current. In all the investigated properties, no significant difference was found among neuron L10, L12 and L13 as a presynaptic neuron. The slow postsynaptic current appeared to be virtually identical to the FMRFamide or acetylcholine (ACh)-induced K + current reported in vivo, which resembled the ‘S’ current in Aplysia sensory neurons. We performed experiments to see the effect of phenyltrimethylamminium, an ACh antagonist, on the postsynaptic, ACh-, and FMRFamide-induced currents, clearly indicating that the neurotransmitter used in the cultured synapses was not ACh.

Expression of CALLA/CD10 on human melanoma cells.

The reactivity spectrum of an anti-CALLA/CD10 monoclonal antibody for cutaneous melanoma was analysed by immunohistochemistry in a series of lesions of different Breslow thickness. Similar proportions of small primary tumours, advanced primary tumours and metastatic lesions were found to express CALLA/CD10 (31-47%). However the proportion of stained cells within a given lesion increased with tumour progression. Up to 23% of the advanced primary lesions (> 3.0 mm) showed 26-50% cells stained with the anti-CALLA/CD10 antibody and up to 14% of the metastatic lesions showed 76-100% stained cells. The expression of CALLA/CD10 was further analysed in 15 ocular melanoma lesions of different histiotype. All five spindle type lesions, three of six epitheloid and two of five mixed type lesions stained positively with the anti-CALLA/CD10 antibody. The percentage of stained cells within a given lesion varied from 30% to 100%. A total of 63% of the ocular melanomas and 38% of the cutaneous melanomas tested expressed CALLA/CD10. Experiments with cultured melanoma cell lines showed that the surface expression of CALLA/CD10 can be modulated in vitro by treatment with interleukin 2 (IL-2) and an adenosine 3',5'-cyclic monophosphate (analogue).

Vasopressin and protein kinase A activate G protein-sensitive epithelial Na+ channels

To determine the molecular steps involved in the vasopressin-induced renal Na+ reabsorption, the patch-clamp technique was utilized to study the role of this hormone in the regulation of apical Na+ channels in renal epithelial A6 cells. Addition of arginine vasopressin (AVP) induced and/or enhanced Na+ channel activity within 5 min of addition under cell-attached conditions. The AVP-induced channel activity was a reflection of both an increase in the average apparent channel number (0.2-1.7) and the percent open time (2-56%). Addition of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, the adenosine 3',5'-cyclic monophosphate (cAMP) analogues, 8-(4-chlorophenylthio)-cAMP and 8-bromo-cAMP, or forskolin elicited a comparable effect to that of AVP. The induced channels had similar properties to Na+ channels previously reported, including a channel conductance of 9 pS, Na(+)-to-K+ selectivity of 3-5:1, and high amiloride sensitivity. The cAMP-dependent protein kinase A (PKA) in the presence of ATP induced and/or enhanced Na+ channel activity in excised inside-out patches with a change in average apparent channel number and percent open probability similar to those observed with either AVP or cAMP analogues in intact cells. Addition of activated pertussis toxin (100 ng/ml) completely blocked the AVP- or PKA-induced Na+ channel activity in excised inside-out patches, whereas incubation of intact cells with the toxin completely prevented the effect of both activators. The data indicate that AVP mediates its effect through a cAMP-dependent pathway involving PKA activation whose target is the G protein pathway that regulates apical epithelial Na+ channel activity.

Exogenous cGMP prevents decrease in diuresis and natriuresis induced by inhibition of NO synthesis.

We previously demonstrated that the intravenous infusion of the specific inhibitor of nitric oxide (NO) synthesis, NG-nitro-L-arginine methyl ester (L-NAME), over a period of 60 min elevates mean arterial pressure (MAP) and reduces renal hemodynamics and excretory function. The objective of the present study was to determine the ability of a guanosine 3',5'-cyclic monophosphate (cGMP) analogue, 8-bromo-cGMP (8-BrcGMP), in preventing the increase in MAP and the reductions in renal plasma flow (RPF), glomerular filtration rate (GFR), urine flow (UV), and sodium excretion rate (UNaV) induced by intravenous infusion of L-NAME in rats. As expected, the infusion of L-NAME (50 micrograms.kg-1.min-1) increased (P < 0.05) MAP and reduced (P < 0.05) RPF, GFR, UV, and UNaV. The administration of 8-BrcGMP (100 micrograms.kg-1.min-1) and L-NAME resulted in no change in MAP, RPF, and GFR. However, decreased (P < 0.05) UV and UNaV were still observed. When 8-BrcGMP (200 micrograms.kg-1.min-1) and L-NAME were infused together, no significant changes in MAP or in renal function were observed. To prove the specificity of the 8-BrcGMP preventive effects, dibutyryl cAMP (200 micrograms.kg-1.min-1) and L-NAME (50 micrograms.kg-1.min-1) were infused together. Under these conditions, MAP, RPF, GFR, UV, and UNaV were modified in a manner similar to that observed during the infusion of L-NAME.(ABSTRACT TRUNCATED AT 250 WORDS)

Tyrosine kinase regulates epithelial sodium transport in A6 cells.

Insulin increases epithelial Na+ reabsorption, and many of its actions involve tyrosine kinase. We used tyrosine kinase inhibitors to examine the role of tyrosine kinase in the action of insulin. Pretreatment of Na+ transporting cells with tyrosine kinase inhibitors attenuates the subsequent action of insulin, suggesting that the action of insulin on epithelial Na+ transport involves tyrosine kinase activity. In addition to their effect on insulin-induced Na+ transport, the tyrosine kinase inhibitors also significantly reduce Na+ transport in Na(+)-transporting epithelial cells, suggesting that there is a significant tonic tyrosine kinase activity that modulates epithelial Na+ transport. Using patch-clamp methods, we found that one inhibitor, genistein, reduces the number of active Na+ channels in cell-attached patches without significantly affecting the open probability of any remaining channels. The effects of the tyrosine kinase inhibitors are not due to inhibition of protein kinase A (PKA), since H89, a PKA inhibitor, does not affect Na+ transport of control cells (as the tyrosine kinase inhibitors do), and the tyrosine kinase inhibitor, genistein or tyrphostin 23, does not alter the stimulation of ion transport by 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate, a membrane-permeable adenosine 3',5'-cyclic monophosphate analogue (as H89 does).

Beta-adrenergic inhibition of Na-K-Cl cotransport in lymphocytes.

Lymphocytes contain a homogeneous population of beta 2-adrenoceptors. However, their physiological role in the regulation of lymphocyte function, especially early in the activation/proliferation process, remains unclear. To study the role of beta-adrenergic activation on the regulation of membrane transport, we examined 86Rb uptake in the Jurkat human lymphoma cell line. 86Rb uptake was predominantly accounted for by bumetanide-sensitive uptake (74 +/- 2% total 86Rb uptake) and ouabain-sensitive uptake (20 +/- 2%). Bumetanide potently inhibited 86Rb uptake (50% inhibitory concentration = 210 +/- 40 nM), and bumetanide-sensitive uptake was dependent on extracellular sodium and chloride, consistent with uptake via Na-K-Cl cotransport. The beta-adrenergic agonist isoproterenol (10 microM) mediated a 50 +/- 11% reduction in bumetanide-sensitive uptake without a significant alteration in ouabain-sensitive uptake. The effect of isoproterenol was potent (50% effective concentration = 4.42 +/- 1.70 nM), stereoselective, and was inhibited by the beta-adrenergic antagonist nadolol. The effect of isoproterenol was mimicked by permeant adenosine 3',5'-cyclic monophosphate analogues but not by pindolol. These data indicate that beta-adrenoceptor activation decreases 86Rb uptake in lymphocytes via inhibition of Na-K-Cl cotransport. Modulation of this transporter could be one mechanism by which beta-adrenergic agonists regulate lymphocyte function.

The expression of retinoic acid receptors in cultured human endometrial stromal cells and effects of retinoic acid

Patterns of expression of retinoic acid receptors (RAR) in cultures of human endometrial stromal cells are described. Transcripts for all three classes of RAR were expressed in these cells but RAR-beta was expressed at a low level by comparison with RAR-alpha and RAR-gamma. The abundance of RAR-beta transcripts was elevated by treating the cells with retinoic acid, but there was no effect on the level of expression of RAR-alpha and RAR-gamma. The induction of RAR-beta by retinoic acid was detectable within 4 h and at low concentrations of retinoic acid (10(-10) M). Adenosine 3':5'-cyclic monophosphate (cAMP) analogues and forskolin, an adenylate cyclase activator, had no effect on the retinoic acid-mediated induction of RAR-beta, contrary to recent observations on embryonal carcinoma cells. However, the phosphodiesterase inhibitor, 3-isobutyl-1-methyl-xanthine (IBMX), forskolin and 8-bromo-cAMP depressed basal levels of RAR-beta expression. These data suggest that endometrial stromal cells may be a target tissue of retinoic acid in vivo, and imply a role for retinoic acid in the cyclical differentiation of human endometrium.

Na-K-Cl cotransport in the shark rectal gland. II. Regulation in isolated tubules.

We examined the binding of [3H]benzmetanide, a potent inhibitor of Na-K-Cl cotransport, to secretory tubules isolated from dogfish shark rectal glands. Specific binding increased dramatically (from 3 to 40 pmol/mg protein) when the tubules were exposed to secretory stimuli [e.g., vasoactive intestinal peptide, adenosine, forskolin, and permeable adenosine 3',5'-cyclic monophosphate (cAMP) analogues]. Binding was also promoted by osmotically induced changes in cell volume; a 45% reduction in cell water content mimicked the effect of secretagogues on binding, whereas a 40% increase in cell water was only half as effective. Volume-responsive binding required extracellular sodium and chloride. The effect of cell shrinkage on binding was rapid and reversible (half-activation time = approximately 3 min, half-deactivation time = approximately 2 min). The binding sites evoked by secretagogues and by cell shrinkage had similar affinities for [3H]benzmetanide (Kd approximately 0.35 microM). Forskolin, a potent secretagogue, increased cell cAMP content 10-fold and respiration 7-fold, whereas hypertonicity affected neither parameter. The effects of cAMP-dependent stimuli and hypertonicity on binding were not additive. These results suggest the following. 1) Na-K-Cl cotransporters acquire the ability to bind [3H]benzmetanide with high affinity when activated. 2) Hormonal modulation of rectal gland secretion involves a coordinated regulation of basolateral Na-K-Cl cotransporters and apical Cl channels. 3) Separate signal transduction pathways, one sensitive to cAMP and another to cell volume, regulate the Na-K-Cl cotransporter.

Synergism between cAMP and ATP in signal transduction in cardiac myocytes.

ATP transiently increases the intracellular Ca2+ concentration in cardiac myocyte suspensions. Pretreatment with norepinephrine (NE) greatly potentiates the ATP response. We performed experiments on adult rat myocyte suspensions loaded with fura-2 to investigate the mechanism of NE potentiation. We found that forskolin (an activator of adenylate cyclase), 3-isobutyl-1-methylxanthine (an inhibitor of phosphodiesterase), and permeative adenosine 3',5'-cyclic monophosphate (cAMP) analogues potentiate the increase in cytosolic Ca2+ concentration induced by ATP. NE, forskolin, and 8-(4-chlorophenylthio)-cAMP all increase Vmax of the Ca2+ response curve of ATP. Measurement of cAMP by radioimmunoassay confirmed that the changes in the ATP response were accompanied by an increase in cAMP. These results suggest that the noradrenergic potentiation of the ATP-induced Ca2+ mobilization involves cAMP as a second messenger. Patch-clamp studies of isolated myocytes showed that neither NE nor forskolin alters the inward current elicited by ATP, but rather they increase the duration of secondary slow action potentials elicited by ATP. NE also increases the Ca2+ current through L-type Ca2+ channels in the myocytes. We conclude that NE potentiates the ATP-induced Ca2+ transient by increasing cAMP levels and that one of the early events is the increase of the inward Ca2+ current during the action potential.

Involvement of cyclic guanosine monophosphosphate (cGMP) and cytosolic guanylate cyclase in the regulation of synaptic ribbon numbers in rat pineal gland

In the rat pineal gland N-acetyltransferase (NAT) activity and synaptic ribbon (SR) numbers display a circadian rhythm. It is well-known that NAT activity is regulated by adrenergic mechanisms involving cyclic adenosine monophosphate (cAMP) as a second messenger. However, the mechanism involved in the regulation of SR numbers has not been established so far. In the present in vitro study, we have investigated the effects of 8-bromo-cyclic guanosine monophosphate (8-bromo-cGMP), a cyclic guanosine monophosphate (cGMP) analog, and stimulation of guanylate cyclase on SR numbers. Incubation with 8-bromo-cGMP increased SR numbers in a dose- and time-dependent manner. Further, stimulation of the cytosolic guanylate cyclase also resulted in increased SR numbers. Adrenergic agonists stimulated cGMP but did not alter SR numbers. These findings suggest that cGMP is involved as a second messenger in the regulation of SR numbers. Since the adrenergically stimulated increase in cGMP did not influence SR numbers, a non-adrenergic cGMP metabolic pathway seems to be involved in the regulation of SR numbers in the rat pineal gland.

Cyclic guanosine monophosphate analogs do not reverse bacterial toxin modulation of lactogen-stimulated NB2 cell mitogenesis.

Pertussis toxin (PT) and cholera toxin (CT) have been shown to modulate lactogenic hormone-stimulated Nb2 cell mitogenesis, a lactogen-dependent cell line. As both toxins have been shown to alter guanylate cyclase activity in other cell systems, cyclic guanosine monophosphate (cGMP) analogs, 8-bromo or dibutyryl cGMP, were added to determine if they could reverse the toxin-mediated effects. In the absence of bacterial toxins, both cGMP analogs enhanced lactogen-stimulated Nb2 cell mitogenesis in a multiphasic pattern. At maximal enhancement, the effect was statistically significant but not marked (113 +/- 5%; p less than 0.01). Neither cGMP analog increased lactogenic binding site number or affinity so cGMP must affect lactogen action following receptor binding. Neither analog could stimulation Nb2 cell mitogenesis in the absence of lactogens so cGMP is not a second messenger for lactogens in this cell system. Finally, neither cGMP analog reversed the inhibitory effects of either bacterial toxin on lactogen-stimulated Nb2 cell proliferation. In summary, although bacterial toxins may be capable of altering guanylate cyclase activity, as addition of cGMP analogs do not reverse toxin-mediated effects on lactogen-stimulated mitogenesis, these toxins' actions must be mediated predominantly through other mechanisms that may have significant importance to lactogen signal transduction.

Interaction of nitric oxide and cGMP with signal transduction in activated platelets.

Although nitric oxide (NO), one of the endothelium-derived relaxing factors, prevents formation of platelet aggregates, the mechanism by which this occurs is not fully understood. Accordingly, the effect of NO on signal transduction of gel-filtered human platelets was measured and compared with that of a cell-permeant guanosine 3',5'-cyclic monophosphate (cGMP) analogue, 8-bromo-cGMP (8-BrcGMP). NO inhibited the rise in intracellular Ca2+ concentration ([Ca2+]i), phosphorylation of the 47-kDa substrate (p47) of protein kinase C (PKC), serotonin secretion, and phosphatidic acid production induced by thrombin or the endoperoxide analogue U-46619. Similar effects were seen with 8-BrcGMP, and NO induced a concentration-related rise in cGMP. Neither NO nor 8-BrcGMP inhibited platelet aggregation, [Ca2+]i mobilization, or serotonin secretion induced by the Ca2+ ionophores A23187 or ionomycin or directly activated PKC purified from platelets. However, both NO and 8-BrcGMP enhanced p47 phosphorylation induced by the Ca2+ ionophores without augmenting phosphatidic acid production. Thus, if [Ca2+]i is elevated, a rise in cGMP enhances PKC activation. Both NO and 8-BrcGMP, however, prevent Ca2+ mobilization and platelet aggregation induced by receptor-mediated agonists by interfering with signal transduction at a point proximal to phospholipase C activation.

Mechanisms by which endothelin 1 induces pulmonary vasoconstriction in the rabbit.

To investigate the mechanisms by which endothelin 1 (ET-1) causes pulmonary vasoconstriction, we studied the effect of synthetic ET-1 on pulmonary vascular tone in the buffer-perfused isolated rabbit lung. In nanomolar concentrations (1.2-8 nM), ET-1 causes a dose-dependent increase in pulmonary arterial pressure that persists for greater than or equal to 1 h (increase in pressure 19 +/- 2 mmHg with ET-1 vs. 2 +/- 1 with vehicle, P less than 0.0001). Reduction of calcium availability with verapamil, cadmium, or a calcium-free buffer significantly blunts the increase in pressure caused by ET-1. Pretreatment with a calcium-free buffer plus the chelator ethylene glycol-bis(beta-aminoethyl ether)-N,N,N', N'-tetraacetic acid (EGTA) completely eliminates the vasoconstriction. Three different inhibitors of protein kinase C, phloretin, staurosporine, and dihydrosphingosine, significantly diminish the response to ET-1. Indomethacin and a thromboxane synthase inhibitor partially decrease the response to the highest concentration of ET-1. Isoproterenol and dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP) are significantly more effective in preventing the vasoconstriction caused by ET-1 than are nitroprusside and guanosine 5'-cyclic monophosphate (cGMP) analogues. ET-1 in doses of 1.2-8 nM is a potent pulmonary vasoconstrictor in the isolated rabbit lung. ET-1 appears to cause pulmonary vasoconstriction by increasing calcium entry and by activating protein kinase C. Vasodilators that increase cAMP are substantially more effective in preventing the increase in pressure than are drugs that increase cGMP.

Effect of exogenous cAMP and aminophylline on alveolar and lung liquid clearance in anesthetized sheep.

A substantial body of evidence indicates that active transport of ions is important in modulating the resolution process of pulmonary edema. The biochemical regulation of this ion transport mechanism is still under investigation. In this study we evaluated the effect of an adenosine 3',5'-cyclic monophosphate (cAMP) analogue [dibutyryl cAMP (DBcAMP)] and a phosphodiesterase inhibitor (aminophylline) given alone or together on lung liquid and protein clearance. To study lung liquid and protein clearance, we measured the removal of 100 ml of autologous serum from the air spaces of anesthetized and ventilated adult sheep. Either serum alone or serum mixed with 10(-3) M DBcAMP, 10(-3) M or 10(-5) M aminophylline, or 10(-3) M aminophylline plus 10(-3) M DBcAMP was instilled. After 4 h, the residual lung water was 73.5 +/- 8.7 ml when serum alone was instilled and 56.8 +/- 13.6 ml when aminophylline and DBcAMP were given together. Neither aminophylline nor DBcAMP alone increased lung liquid clearance. However, the increase in clearance cannot be explained by an increase in protein clearance or changes in the pulmonary hemodynamics. These data suggest that the cAMP second messenger system can stimulate lung liquid clearance in vivo.

Early Post-Treatment with Pentoxifylline or Dibutyryl cAMP AttenuatesEscherichia coli-induced Acute Lung Injury in Guinea Pigs

We examined effects of early post-treatment with the methylxanthine pentoxifylline (PTXF), or the cell-permeable adenosine 3', 5'-cyclic monophosphate (cAMP) analog dibutyryl cAMP (db-cAMP) on Escherichia-coli-induced acute lung injury in guinea pigs. Acute lung injury was assessed by measurements of lung water (lung wet/dry weight ratio; W/D ratio), the concentration ratio of 125I-albumin in bronchoalveolar lavage (BAL) fluid and lung tissue compared with plasma (albumin index; BAL-AI or tissue-AI), and total differential leukocyte count in BAL fluid. Mean arterial pressure (Pa) and peripheral WBC counts were monitored continuously over the 8-h experiment. Septicemia was induced by a bolus injection of 2 x 10(9)/kg live E. coli. Thirty minutes later the animals received a bolus injection followed by continuous infusion of PTXF (20 mg/kg + 20 mg/kg/h; n = 8) or db-cAMP (2 mg/kg + 2 mg/kg/h; n = 8) or saline (septic control; n = 8). Nonseptic control groups were also studied. The lung W/D ratio, BAL-AI, lung tissue-AI, and BAL leukocyte count increased significantly in the septic control group. The PTXF-septic and db-cAMP-septic groups showed no significant increase in lung W/D ratio, BAL-AI, and lung tissue-AI. However, there was no difference in BAL total and differential leukocyte count as compared with the septic control group. PTXF and db-cAMP had no effect on E. coli-induced changes in peripheral WBC count and Pa. Comparison in vitro experiments demonstrated that PTXF and db-cAMP inhibited the endotoxin-induced (E. coli) chemiluminescent response of isolated guinea-pig polymorphonuclear leukocytes (PMN).(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrocortisone treatment increases the sensitivity and responsiveness to cholecystokinin in rat pancreas

The effects of hydrocortisone treatment on the secretory abilities of pancreatic acini to various secretagogues were studied. Rats were given subcutaneous injections of hydrocortisone at doses of 1.25, 2.5, or 5.0 mg/kg body wt once daily for 7 days. Hydrocortisone led to a small dose-dependent increase in pancreatic wet weight per 100 g body wt, which was associated with an increase in both total protein and DNA contents. In acini prepared from hydrocortisone-treated rats, both the responsiveness and the sensitivity to cholecystokinin octapeptide (CCK-8) was increased. The concentration dependence of cellular Ca2+ mobilization in response to CCK-8 was also shifted to lower concentrations in acini from hydrocortisone-treated rats compared with control rat acini. In vivo administration of hydrocortisone caused a significant increase in the affinity of 125I-CCK-8 binding to high-affinity receptors. The secretory responsiveness to carbamylcholine and bombesin, but not to secretin, was also increased but without any change in the sensitivity. Moreover, the hydrocortisone treatment increased the secretory responsiveness of acini to the Ca2+ ionophore A23187 and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate but did not to an adenosine 3',5'-cyclic monophosphate analogue, 8-bromoadenosine 3',5'-cyclic monophosphate. The present observations suggest that in vivo glucocorticoid administration affects both the CCK receptors and a postreceptor loci.

Evidence for regulation of sodium transport from airspace to vascular space by cAMP

Evidence has been accumulating that regulation of the rate of solute and fluid removal from the alveolar spaces may play an important role in the prevention and/or resolution of alveolar pulmonary edema. In this study, the isolated perfused rat lung was used to investigate the effects of an adenosine 3',5'-cyclic monophosphate (cAMP) analogue or a phosphodiesterase inhibitor on active sodium transport from airspace to vascular space. Three tracers were instilled into the airways of isolated Krebs-Ringer bicarbonate solution (KRB)-perfused rat lungs. The appearance of tracers in the single-pass perfusate was measured, and the apparent permeability-surface area products (PS) were calculated for each tracer at each sample time based on Fick's first law of diffusion. After steady-state PS values had been reached, a cAMP analogue or phosphodiesterase inhibitor was added to the perfusate. Both agents caused significant increases in the PS for 22Na. In another group of experiments, a cAMP analogue was added to the perfusate, followed by the subsequent addition of a sodium transport inhibitor and the resultant large decrease in the PS for 22Na. These data are consistent with the regulation of active sodium transport across the intact mammalian alveolar epithelium by a cAMP-mediated process leading to removal of sodium from the alveolar spaces, with anions and water following passively.