Growth-dependent regulation of system A in SV40-transformed fetal rat hepatocytes

Acute hemodynamic effects of conivaptan, a dual V(1A) and V(2) vasopressin receptor antagonist, in patients with advanced heart failure

BACKGROUND

Arginine vasopressin may contribute to abnormalities in hemodynamics and fluid balance in heart failure through its actions on V(1A) (vascular and myocardial effects) and V(2) receptors (renal effects). Inhibiting the action of vasopressin may be beneficial in patients with heart failure.

METHODS AND RESULTS

A total of 142 patients with symptomatic heart failure (New York Heart Association class III and IV) were randomized to double-blind, short-term treatment with conivaptan, a dual V(1a)/V(2) vasopressin receptor antagonist, at a single intravenous dose (10, 20, or 40 mg) or placebo. Compared with placebo, conivaptan at 20 and 40 mg significantly reduced pulmonary capillary wedge pressure (-2.6+/-0.7, -5.4+/-0.7, and -4.6+/-0.7 mm Hg for placebo and 20 and 40 mg groups, respectively; P<0.05) and right atrial pressure (-2.0+/-0.4, -3.7+/-0.4, and -3.5+/-0.4 mm Hg for placebo and 20 and 40 mg groups, respectively; P<0.05) during the 3- to 6-hour interval after intravenous administration. Conivaptan significantly increased urine output in a dose-dependent manner (-11+/-17, 68+/-17, 152+/-19, and 176+/-18 mL/hour for placebo and 10, 20, and 40 mg groups, respectively; P<0.001) during the first 4 hours after the dose. Changes in cardiac index, systemic and pulmonary vascular resistance, blood pressure, and heart rate did not significantly differ from placebo.

CONCLUSIONS

In patients with advanced heart failure, vasopressin receptor antagonism with conivaptan resulted in favorable changes in hemodynamics and urine output without affecting blood pressure or heart rate. These data suggest that vasopressin is functionally significant in advanced heart failure and that further investigations are warranted to examine the effects of conivaptan on symptom relief and natural history in such patients.

Vasopressin and shock

Vasopressin (antidiuretic hormone) is emerging as a potentially major advance in the treatment of a variety of shock states. Increasing interest in the clinical use of vasopressin has resulted from the recognition of its importance in the endogenous response to shock and from advances in understanding of its mechanism of action. From animal models of shock, vasopressin has been shown to produce greater blood flow diversion from non-vital to vital organ beds (particularly the brain) than does adrenaline. Although vasopressin has similar direct actions to the catecholamines, it may uniquely also inhibit some of the pathologic vasodilator processes that occur in shock states. There is current interest in the use of vasopressin in the treatment of shock due to ventricular fibrillation, hypovolaemia, sepsis and cardiopulmonary bypass. This article reviews the physiology and pharmacology of vasopressin and all of the relevant animal and human clinical literature on its use in the treatment of shock following a MEDLINE (1966-2000) search.

Multiple adaptive mechanisms affect asparagine synthetase substrate availability in asparaginase-resistant MOLT-4 human leukaemia cells

Childhood acute lymphoblastic leukaemia is treated by combination chemotherapy with a number of drugs, almost always including the enzyme L-asparaginase (ASNase). Although the initial remission rate is quite high, relapse and associated drug resistance remain a problem. In vitro studies have demonstrated an adaptive increase in asparagine synthetase (AS) expression in ASNase-resistant cells, which is believed to permit ASNase-resistant human leukaemia cells to survive in vivo. The present results, obtained with ASNase-sensitive and -resistant human MOLT-4 leukaemia cell lines, illustrate that several other adaptive processes occur to provide sufficient amounts of the AS substrates, aspartate and glutamine, required to support this increased enzymic activity. In both cell populations, aspartate is derived almost exclusively from intracellular sources, whereas the necessary glutamine arises from both intracellular and extracellular sources. Transport of glutamine into ASNase-resistant cells is significantly enhanced compared with the parental cells, whereas amino acid efflux (e.g. asparagine) is reduced. Most of the adaptive change for the amino acid transporters, Systems A, ASC and L, is rapidly (12 h) reversed following ASNase removal. The enzymic activity of glutamine synthetase is also enhanced in ASNase-resistant cells by a post-transcriptional mechanism. The results demonstrate that there are several sites of metabolic adaptation in ASNase-treated leukaemia cells that serve to promote the replenishment of both glutamine and asparagine.

Therapeutic and chemical developments of cholecystokinin receptor ligands

Cholecystokinin (CCK) is an important 'brain-gut' hormone located both in the gastrointestinal (GI) system and in the CNS. At least two different G-coupled high affinity receptors have been identified: the CCK-A and the CCK-B receptors. Although the complex biological role of CCK is, as yet, not fully understood, its connection with many different physiological processes both at the GI level and at the CNS level is now well established. There is much potential for therapeutic use of CCK receptor ligands, however, clear investigations have yet to be completed. Several chemical families have been investigated over the last 20 years to find potent, subtype selective and stable CCK receptor agonists and antagonists. The main goal was to discover new therapeutic drugs acting on GI and/or on CNS diseases and also, to obtain powerful pharmacological tools that could permit a better understanding of the biological role of CCK. Despite promising results from investigations into medicinal chemistry of CCK receptor ligands, the therapeutical applications of these ligands still remains to be defined. This article reviews the main biological role of CCK, the therapeutic potential of CCK-A and CCK-B receptor agonists and antagonists and the common compounds from the different families of ligands.

Identification and characterization of a new growth hormone-releasing peptide receptor in the heart

Hexarelin, a synthetic hexapeptide of the growth hormone-releasing peptide (GHRP) family with strong growth hormone (GH)-releasing activity, features protecting activity against postischemic ventricular dysfunction in hearts from GH-deficient and senescent rats. To document whether hexarelin action is mediated through specific cardiac receptors, perfusion of Langendorff rat hearts with hexarelin and binding studies were carried out. In the Langendorff rat heart system, hexarelin induced a dose-dependent increase in coronary perfusion pressure. Nifedipine, chelerythrine, and bisindolylmaleimide partially inhibited the vasoconstriction induced by hexarelin, suggesting that this effect was mediated at least in part by L-type Ca(2+) channels and protein kinase C. In contrast, diclofenac and 1-(7-carboxyheptyl)imidazole were without effect, suggesting that prostaglandins and thromboxanes were not involved in the coronary vasoconstriction induced by hexarelin. To characterize the hexarelin binding sites in the rat heart, [(125)I]Tyr-Bpa-Ala-hexarelin was used as photoactivatable radioligand in saturation and competitive binding studies. We specifically labeled a hexarelin receptor with an M(r) of 84 000 in rat cardiac membranes. Saturation binding curves revealed a single class of binding sites with a K(d) of 14.5 nmol/L and a density of 91 fmol/mg of protein. Competition binding studies gave an IC(50) of 2.9 micromol/L for hexarelin; MK-0677 and EP51389, both potent GH secretagogues, did not displace the binding of the photoactivatable derivative from rat cardiac membranes. Interestingly, both compounds were devoid of any vasoconstrictive activity. These results suggest the existence of a new class of hexarelin receptor in the heart, whose role in the regulation of the coronary vascular tone is yet to be determined.

"Facilitated" amino acid transport is upregulated in brain tumors

The goal of this study was to determine the magnitude of "facilitated" amino acid transport across tumor and brain capillaries and to evaluate whether amino acid transporter expression is "upregulated" in tumor vessels compared to capillaries in contralateral brain tissue. Aminocyclopentane carboxylic acid (ACPC), a non-metabolized [14C]-labeled amino acid, and a reference molecule for passive vascular permeability, [67Ga]-gallium-diethylenetriaminepentaacetic acid (Ga-DTPA), were used in these studies. Two experimental rat gliomas were studied (C6 and RG2). Brain tissue was rapidly processed for double label quantitative autoradiography 10 minutes after intravenous injection of ACPC and Ga-DTPA. Parametric images of blood-to-brain transport (K1ACPC and K1Ga-DTPA, microL/min/g) produced from the autoradiograms and the histology were obtained from the same tissue section. These three images were registered in an image array processor; regions of interest in tumor and contralateral brain were defined on morphologic criteria (histology) and were transferred to the autoradiographic images to obtain mean values. The facilitated component of ACPC transport (deltaK1ACPC) was calculated from the K1ACPC and K1Ga-DTPA data, and paired comparisons between tumor and contralateral brain were performed. ACPC flux, K1ACPC, across normal brain capillaries (22.6 +/- 8.1 microL/g/min) was >200-fold greater than that of Ga-DTPA (0.09 +/- 0.04 microL/g/min), and this difference was largely (approximately 90%) due to facilitated ACPC transport. Substantially higher K1ACPC values compared to corresponding K1DTPA values were also measured in C6 and RG2 gliomas. The deltaK1ACPC values for C6 glioma were more than twice that of contralateral brain cortex. K1ACPC and deltaK1ACPC values for RG2 gliomas was not significantly higher than that of contralateral cortex, although a approximately 2-fold difference in facilitated transport is obtained after normalization for differences in capillary surface area between RG2 tumors and contralateral cortex. K1ACPC, deltaK1ACPC, and K DTPA were directly related to tumor cell density, were higher in regions of "impending" necrosis, and the tumor/contralateral brain ACPC radio-activity ratios (0 to 10 minutes) were very similar to that obtained with 0 to 60 minutes experiments. These results indicate that facilitated transport of ACPC is upregulated across C6 and RG2 glioma capillaries, and that tumors can induce upregulation of amino acid transporter expression in their supporting vasculature. They also suggest that early imaging (e.g., 0 to 20 minutes) with radiolabeled amino acids in a clinical setting may be optimal for defining brain tumors.

Imaging experimental brain tumors with 1-aminocyclopentane carboxylic acid and alpha-aminoisobutyric acid: comparison to fluorodeoxyglucose and diethylenetriaminepentaacetic acid in morphologically defined tumor regions

The goal of this study was to evaluate the differences and define the advantages of imaging experimental brain tumors in rats with two nonmetabolized amino acids, 1-aminocyclopentane carboxylic (ACPC) acid and alpha-aminoisobutyric (AIB) acid compared with imaging with fluorodeoxyglucose (FDG) or the gallium-diethylenetriaminepentaacetic acid chelate (Ga-DTPA). 1-aminocyclopentane carboxylic acid, AIB, and FDG autoradiograms were obtained 60 minutes after intravenous injection to simulate positron emission tomography (PET) imaging, whereas the Ga-DTPA autoradiograms were obtained 5 or 10 minutes after injection to simulate gadolinium (Gd)-DTPA-enhanced magnetic resonance (MR) images. Three experimental tumors were studied (C6, RG2, and Walker 256) to provide a range of tumor types. Triple-label quantitative autoradiography was performed, and parametric images of the apparent distribution volume (Va, mL/g) for ACPC or AIB, relative glucose metabolism (R, micromol/100 g/min), vascular permeability to Ga-DTPA (K1, microL/min/g), and histology were obtained from the same tissue section. The four images were registered in an image array processor, and regions of interest in tumor and contralateral brain were defined on morphologic criteria (histology) and were transferred to the autoradiographic images. A comparative analysis of all measured values was performed. The location and morphologic characteristics of the tumor had an effect on the images and measurements of Va, R, and K1. Meningeal extensions of all three tumors consistently had the highest amino acid uptake (Va) and vascular permeability (K1) values, and subcortical portions of the tumors usually had the lowest values. Va and R (FDG) values generally were higher in tumor regions with high-cell density and lower in regions with low-cell density. Tumor areas identified as "impending" necrosis on morphologic criteria consistently had high R values, but little or no change in Va or K1. Tumor necrosis was seen consistently only in the larger Walker 256 tumors; low values of R and Va for AIB (less for ACPC) were measured in the necrotic-appearing regions, whereas K1 was not different from the mean tumor value. The highest correlations were observed between vascular permeability (K1 for Ga-DTPA) and Va for AIB in all three tumors; little or no correlation between vascular permeability and R was observed. The advantages of ACPC and AIB imaging were most convincingly demonstrated in C6 gliomas and in Walker 256 tumors. 1-aminocyclopentane was substantially better than FDG or Ga-DTPA for identifying tumor infiltration of adjacent brain tissue beyond the macroscopic border of the tumor; ACPC also may be useful for identifying low-grade tumors with an intact blood-brain barrier. Contrast-enhancing regions of the tumors were visualized more clearly with AIB than with FDG or Ga-DTPA; viable and necrotic-appearing tumor regions could be distinguished more readily with AIB than with FDG. [11C]-labeled ACPC and AIB are likely to have similar advantages for imaging human brain tumors with PET.

Effects of L-arginine and N omega-nitro-L-arginine methyl ester on cardiac perfusion and function after 1-day cold preservation of isolated hearts

BACKGROUND

Coronary flow responses to endothelium-dependent (acetylcholine [ACh] or 5-hydroxytryptamine [5-HT]) and endothelium-independent (adenosine [ADE] or nitroprusside [NP]) vasodilators may be altered before and after 1-day hypothermia during the perfusion of arginine vasopressin (AVP), D-arginine (D-ARG), L-arginine (L-ARG), or nitro-L-arginine methyl ester (L-NAME).

METHODS AND RESULTS

Four groups of guinea pig hearts (37.5 degrees C [warm]) were perfused for 6 hours with AVP, L-ARG, L-NAME, or nothing (control). Five heart groups (cold) were perfused with AVP, D-ARG, L-ARG, L-NAME, or nothing (control), but after 2 hours they were perfused at low flow for 22 hours at 3.7 degrees C and again for 3 hours at 37.5 degrees C. ADE, butanedione monoxime, and NP were given for cardioprotection before, during, and after hypothermia. In warm groups, L-ARG did not alter basal flow or ADE, ACh, 5-HT, or NP responses, whereas L-NAME and AVP reduced basal flow and the ADE response, abolished ACh and 5-HT responses, and increased the NP response. In cold groups after hypothermia. L-ARG did not alter basal flow, but L-NAME, AVP, D-ARG, and control reduced flow. In the postcold L-ARG group, ACh increased peak flow, but NP did not increase flow in other cold groups. Effluent L-ARG and L-CIT in the cold control group fell from 64 +/- 9 and 9 +/- 1 micrograms/L at 1 hour to 36 +/- 5 and 5 +/- 1 micrograms/L at 25 hours, respectively. Left ventricular pressure and cardiac efficiency improved more in the postcold L-ARG group than in the postcold D-ARG, AVP, and L-NAME groups.

CONCLUSIONS

Endogenous effluent levels of L-ARG and L-CIT decrease after 24 hours in isolated hearts, whereas perfusion of L-ARG improves cardiac performance, basal coronary flow, and vasodilator responses. In contrast, L-NAME, L-ARG, and AVP limit flow and performance but maintain a partial vasodilatory response to NP. Sustained release of NO may account for improved performance after L-ARG after hypothermia.

Direct contractile effect of cholecystokinin octapeptide on caecal circular smooth muscle cells of guinea pig via both CCK-A and CCK-B/gastrin receptors

This study was designed to investigate the participation of cholecystokinin(CCK)-A and/or CCK-B/gastrin receptors in CCK-8-induced contraction of guinea pig caecal circular smooth muscle cells, using a novel selective CCK-A receptor antagonist, (S)-N-[1-(2-fluorophenyl)-3,4,6,7-tetrahydro-4-oxo-pyrrolo-[3,2,1-jk] [1,4]benzodiazepine-3-yl]-1H-indole-2-carboxamide (FK480), and a novel selective CCK-B/gastrin receptor antagonist, (R)-1-[2,3-dihydro-1-(2'-methylphenacyl)-2-oxo-5-phenyl-1H-1, 4-benzodiazepine-3-yl]-3-(3-methylphenyl)urea (YM022). Concentration-response curves for the contractile effect of CCK-8 alone and in the presence of 0.1nM FK480, 0.1 nM YM022, or a combination of 0.1 nM FK480 and 0.1 nM YM022 on isolated smooth muscle cells were determined. In addition, the inhibitory effects of various concentrations of FK480 or YM022 on 1 nM CCK-8-induced contraction were examined. At a concentration of 0.1 nM, both FK480 and YM022 shifted the concentration-response curve for CCK-8 to the right (about 100 times) with the same potency. In addition, a concentration-response curve for a combination of 0.1 nM FK480 and 0.1 nM YM022 was shifted to the right (about 100 times) of the curves for 0.1 nM FK480 alone or 0.1 nM YM022 alone. Both antagonists inhibited 1 nM CCK-8-induced contraction of caecal circular smooth muscle cells in a concentration-dependent manner, with the similar inhibitory potency. A significant inhibition was obtained at a concentration as low as 0.1 nM FK480 and 0.1 nM YM022. This study strongly suggested the presence of both CCK-A and CCK-B/gastrin receptors in caecal circular smooth muscle cells of guinea pig, and that the contractile effect of CCK-8 on these cells was mediated via both of these receptors.

Duration of anti-cholecystokinin (CCK) action on the rat exocrine pancreas of new CCK receptor antagonist FK480 administered orally

We assessed the duration of the anti-cholecystokinin (CCK) action of FK480, a new non-peptide CCK-A receptor antagonist developed in Japan, in an in vivo study in rats, comparing it with CR 1505. Pancreatic exocrine secretion stimulated by intravenous infusion of CCK-8 (0.06 microgram/kg per h) was measured at intervals of 0-24 h after the oral administration of FK480 (1.5 mg/kg) and CR 1505 (30 mg/kg). FK480 significantly inhibited both CCK-stimulated pancreatic juice volume flow and amylase output 0, 4, 8, and 12 h after oral administration, whereas the inhibitory effect of CR 1505 had completely disappeared by 8 h after oral administration. It was concluded that orally administered FK480 has a prolonged anti-CCK action.

Arginine vasopressin-induced potentiation of unitary L-type Ca2+ channel current in guinea pig ventricular myocytes

The effects of arginine vasopressin (AVP) on L-type Ca2+ channels were studied by recording single-channel activity from cell-attached patches on isolated guinea pig ventricular myocytes, with 100 mmol/L Ba2+ used as the charge carrier. Bath application of AVP (100 nmol/L) reversibly increased channel open probability by a factor of 2.92 +/- 1.43 (n = 15) because of the increased number of channel openings and increased open times. AVP did not change the amplitudes of single-channel currents (1.17 +/- 0.10 pA in the control condition and 1.12 +/- 0.11 pA after AVP, at +20 mV; n = 6). In our experimental conditions, in which myocytes were bathed in Ca(2+)-free high-potassium solutions, AVP-induced potentiation was observed without changes in [Ca2+]i measured by fura 2 fluorescence signals (estimated [Ca2+]i, approximately 80 nmol/L). The AVP-induced increase in channel open probability was abolished by OPC-21268 (8 mumol/L), a specific blocker of V1 receptor, but not by a V2 blocker, OPC-31260 (5 mumol/L). AVP-induced potentiation was also suppressed by a broad-spectrum protein kinase inhibitor, H7 (100 mumol/L, bath application), but not by H89 (1 mumol/L), a blocker with high specificity to protein kinase A. AVP application after the treatment by phorbol ester (phorbol 12-myristate 13-acetate, 100 nmol/L for 1 hour) failed to potentiate the channel activity. These results raised the possibility that protein kinase C might be involved during signal transduction. Our results provide direct evidence that AVP potentiates cardiac L-type Ca2+ currents via V1 receptor stimulation.

Regulatory and molecular aspects of mammalian amino acid transport

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Characterization of a new diphenylpyrazolidinone cholecystokinin antagonist in vitro isolated rat pancreatic acini

The effects of a newly developed diphenylpyrazolidinone cholecystokinin (CCK) antagonist LY219,057 were examined in the isolated rat pancreatic acini and compared with those of devazepide (previously designated L364,718 or MK-329). LY219,057 caused a concentration-dependent inhibition of 100 pM CCK octapeptide (CCK-8)-stimulated amylase release, with a half-maximal inhibition (ID50) at 287.5 +/- 28.4 nM and was 200 times less potent than devazepide (ID50 = 1.4 +/- 0.2 nM). The antagonism was competitive in nature because LY219,057 caused a parallel rightward shift of the dose-response curve for CCK-8-stimulated amylase secretion without altering the maximal increase. LY219,057 significantly inhibited amylase release in response to CCK-8 and cerulein but had no effect on amylase release stimulated by other receptor secretagogs or agent bypassing receptors. LY219,057, whether added at the beginning or 20 min after the CCK-8 stimulation, inhibited amylase release. This compound caused a residual inhibition of the action of CCK-8. Acini preincubated with 1.0 microM LY219,057 for 30 min at 37 degrees C were threefold less sensitive to CCK-8 than the acini preincubated without LY219,057. These results indicate that LY219,057 acts as a potent, competitive, and specific CCK receptor antagonist of the action of CCK on the exocrine pancreas.

Different signal transduction by epidermal growth factor may be responsible for the difference in modulation of amino acid transport between fetal and adult hepatocytes

[1-14C]-2-aminoisobutyric acid (AIB) uptake and signal transduction pattern after epidermal growth factor (EGF) stimulation were examined in freshly isolated hepatocytes from 20-day-old fetuses and 3-month-old rats. EGF induced a transient increase of AIB transport after 10 min only in adult animals; the observed unresponsiveness of fetal liver is not dependent on a lack of EGF receptors which are present though to a lesser extent on the plasma membrane in this period. As far as the production of the second messengers, inositol trisphosphate (IP3) and calcium, is concerned, substantial differences were found: EGF increased IP3 production in adult hepatocytes, whereas it had no effect in fetal ones. Moreover, the addition of EGF induced a calcium transient in hepatocytes from adult animals, while there was no increase in fetal cells. The lack of EGF effect on amino acid transport in fetal cells could be due to its inability to produce both IP3 and calcium transients, suggesting that this transduction pathway is not activated during fetal life.

Amino acid uptake regulation by cell growth in cultured hepatocytes isolated from fetal and adult rats

Amino acid uptake mediated by system A was studied in cultured fetal and adult hepatocytes, subjected to growth stimulation by EGF and insulin, or to growth inhibition by high cell density. The mitogenic stimulation induced a strong transport increase only in fetal cells, while the cell density-dependent growth inhibition, probably mediated by molecules present on adult hepatocyte membranes, provoked the decrease of amino acid uptake only in the adult cells. The results indicate that the different modulation of amino acid transport by cell growth is dependent on the age and the differentiation stage of hepatocytes.

Inhibitory effects of the cholecystokinin antagonist loxiglumide on pancreatic exocrine secretion and pancreatic growth in conscious rats

The effects of cholecystokinin (CCK) receptor antagonist Loxiglumide (CR 1505) on pancreatic exocrine secretion and growth stimulated by chronic bile-pancreatic juice diversion to the ileum were studied in conscious rats. Pancreatic secretion was measured each day at 0900 h for 7 d. Pancreatic flow and protein output were significantly increased 24 h after bile-pancreatic juice diversion. Protein output increased each successive day, reaching maximal values of 3.6-fold above basal by the 6th and 7th d of chronic bile-pancreatic juice diversion. Fluid output reached maximal values of approx. 3.5-fold above basal by the 3rd d of chronic bile-pancreatic juice diversion. Plasma CCK increased threefold above basal levels after 24 h of bile-pancreatic juice diversion and remained three- to fourfold above basal. Intragastric bolus infusion of CR 1505 (50 mg/kg) on the 7th d of chronic bile-pancreatic juice diversion inhibited pancreatic protein and fluid secretion by 80 and 75%, respectively, 60 min after administration and by 52 and 71%, respectively, 5 h later. Pancreatic wet wt after 7 d of chronic bile-pancreatic juice diversion was significantly increased by 56%, and this was completely suppressed by 50 mg/kg of CR 1505 given intragastrically every 12 h. These rests indicate that the rat with chronic bile-pancreatic juice diversion is a useful model to examine both potency and duration of the action of CCK receptor antagonists and show that CR 1505 inhibits pancreatic exocrine secretion and growth induced by endogenous CCK.

Changes in alanine transport in plasma membrane vesicles from rat liver during the early stages of diethylnitrosamine-induced hepatocarcinogenesis

The transport of L-alanine, a natural substrate of system A, across liver plasma membrane vesicle preparations was modified during the early stages of rat DENA hepatocarcinogenesis. Kinetic studies indicated an increase of the Vmax, with normal Km values, at 30 h in rats undergoing a partial hepatectomy. Normal Vmax and drastically reduced Km values were present using membrane preparations from liver tissue showing enzyme-altered hyperplastic foci and/or preneoplastic nodules. The results suggest that alanine transport is differently affected by initiating and promoting stimuli during rat DENA hepatocarcinogenesis. The changes of the Vmax could be related to the promoting effect of partial hepatectomy on cell proliferation whereas the changes of the affinity constant (Km) could be the result of intrinsic modifications of the transporter in initiated cells.

Amino acid uptake in plasma membrane vesicles isolated from proliferating tumor cells and tissues

The transport of L-alanine, a natural substrate of system A, across plasma membrane vesicle preparations has been studied in the early stages of rat DENA-PH hepato-carcinogenesis and in a very undifferentiated rat ascites hepatoma cell line (Yoshida AH-130) in the exponential and stationary phase of growth.Kinetic analyses indicated an increase of the Vmax value in DENA-PH-treated rats 30 h after partial hepatectomy as well as in exponential growing Yoshida ascites cells. In DENA-PH-treated rats the Km value was drastically reduced 7 and 60 days after surgery, when enzyme-altered hyperplastic and preneoplastic lesions were present in rat liver. Drastically reduced Km values were also found in Yoshida ascites cells.The results suggest that an altered alanine transporter might take place in liver plasma membranes from carcinogen-treated rats. This appears to occur also in an established tumor cell line, grown in vivo.

Perspectives of CCK antagonists in pancreatic research. Part II. Experimental studies

In this article, the effects of different classes of cholecystokinin (CCK) receptor antagonists in CCK-related physiological processes of the pancreas have been discussed. Both glutaramic acid derivatives and natural (benzodiazepine) analogs are potent, competitive antagonists of peripheral CCK receptors. These compounds thus provide a powerful tool for investigating the physiological and pharmacological actions of CCK in the gastrointestinal system, and have already clarified the role of CCK in pancreatic secretion and trophism or growth.

Activation of the simian virus 40 (SV40) genome abrogates sensitivity to AVP in a rabbit collecting tubule cell line by repressing membrane expression of AVP receptors

To analyze the role of SV40 genome in the phenotypic alterations previously observed in SV40-transformed cell lines, we infected rabbit renal cortical cells with a temperature-sensitive SV40 mutant strain (tsA58) and compared the cell phenotypes at temperatures permissive (33 degrees C) and restrictive (39.5 degrees C) for SV40 genome expression. At both temperatures, the resulting cell line (RC.SVtsA58) expresses cytokeratin and uvomorulin, but epithelial differentiation is more elaborate at 39.5 degrees C as shown by the formation of a well-organized cuboidal monolayer with numerous tight junctions and desmosomes. Functional characteristics are also markedly influenced by the culture temperature: cells grown at 33 degrees C respond only to isoproterenol (ISO, 10(-6) M) by a sevenfold increase in cAMP cell content above basal values; in contrast, when transferred to 39.5 degrees C, they exhibit increased sensitivity to ISO (ISO/basal: 19.1) and a dramatic response to 10(-7) M dDarginine vasopressin (dDAVP/basal: 18.2, apparent Ka: 5 X 10(-9) M) which peaks 48 h after the temperature shift. The latter is associated with membrane expression of V2-type AVP receptors (approximately 50 fmol/10(6) cells) which are undetectable when SV40 genome is activated (33 degrees C). Clonal analysis, additivity studies, and desensitization experiments argue for the presence of a single cell type responsive to both AVP and ISO. The characteristics of the RC. SVtsA58 cell line at 39.5 degrees C (effector-stimulated cAMP profile, lack of expression of brush-border hydrolases and Tamm-Horsfall protein) suggest that it originates from the cortical collecting tubule, and probably from principal cells.

Effects of CCK-receptor antagonists on CCK-stimulated pepsinogen secretion and calcium increase in isolated guinea pig gastric chief cells

The effects of CCK-receptor antagonists such as dibutyryl cyclic GMP (dbcGMP), L-364,718, and CR1409 on COOH-terminal octapeptide of CCK (CCK-8)-stimulated chief cell responses were examined using isolated guinea pig gastric chief cells. L-364,718 and CR1409 inhibited CCK-8-stimulated pepsinogen secretion over the same concentration range as they inhibited CCK-8-stimulated increases in intracellular Ca2+ concentration ([Ca2+]i), respectively. Schild analysis of the CCK dose-response curve indicates that L-364,718 and CR1409 exert their inhibitory effects on CCK-8-stimulated chief cell responses in a competitive manner. By contrast, dbcGMP inhibited not only CCK-8- but also carbachol-stimulated pepsinogen secretion. Furthermore, dbcGMP inhibited CCK-8-stimulated pepsinogen secretion more potently than the increases in [Ca2+]i. These results suggest that L-364,718 and CR1409 act as CCK-receptor antagonists, but dbcGMP has another inhibitory effect on pepsinogen secretion in addition to the effect as a CCK-receptor antagonist in guinea pig gastric chief cells.

Effects of a high-fat diet and L364,718 on growth of human pancreas cancer

The effects of a high-fat diet and the CCK-receptor antagonist, L364,718, were examined on growth of human pancreas cell line SW-1990 xenografted to nude mice. Sixty animals were fed either low-fat (4.3%) or high-fat (20.25%) diet. Fifteen mice in each diet group were treated with L364,718 (2 mg/kg) subcutaneously twice daily for 23 days. On day 24 the animals were sacrificed. Tumor and animal pancreases were dissected and evaluated for weight, protein, and DNA content. When comparing within each diet group, L364,718 significantly decreased tumor volume, weight, protein, and DNA content compared to untreated mice (P less than 0.005). Tumor volume and protein content were significantly larger in untreated animals on the high-fat diet (P less than 0.05) compared to the low-fat diet. Mouse pancreatic weight, protein, and DNA content per kilogram of animal weight were all significantly lower (P less than 0.005) in mice on the low-fat diet treated with L364,718. Pancreatic DNA content was also decreased in both groups of animals on the high-fat diet compared to untreated mice on the low-fat diet. These findings suggest that diets high in unsaturated fat promote the growth of human pancreatic cancer. Since both tumor and pancreas growth are inhibited by the specific CCK-antagonist, L364,718, it is possible that endogenous CCK promotes the growth.

Epinephrine regulation of amino acid transport in rat hepatocytes isolated during development

The effect of epinephrine on the amino acid transport mediated by system A was investigated by determining the uptake of 2-amino [1-14C]isobutyric acid (AIB) in rat hepatocytes, freshly isolated at different stages of pre- and postnatal development. The data obtained show that the hormone increased AIB uptake, enhancing the Vmax, while Km was unchanged. This effect was evident in cells from adult, 18- to 20-day-old fetus, and neonate rat. Actinomycin D or cycloheximide abolished the hormone dependent increase. Experiments carried out with alpha- and beta-antagonists showed that the effect of epinephrine was beta-mediated in fetal life and alpha-mediated in adult life. Membrane binding experiments showed a higher value for epinephrine and beta-agonist dihydroalprenolol in the fetus versus the adult. The calcium depletion obtained after cell incubation with EGTA or calcium ionophore A23187 reduced the hormonal stimulation in the adult, and was ineffective in the prenatal period. An involvement of cAMP was present in the epinephrine modulation of AIB transport, both in adult and in fetal life.

Role of cholecystokinin in the regulation of pancreatic enzyme secretion in the rat

Whereas pancreatic exocrine secretion in the rat varies considerably depending on the condition under which a study is performed, it is of great importance to study pancreatic pathophysiology in vivo, while the rat is conscious. In recent years several studies were performed in the conscious rat with a cannulated pancreatic duct, and much progress was made in delineating the role of cholecystokinin (CCK) in the regulation of pancreatic enzyme secretion in more detail. This progress was mainly due to the development of specific and sensitive radioimmunoassays for CCK and the availability of specific CCK-receptor antagonists. In the rat it was shown that a negative feedback regulation mechanism of pancreatic enzyme and CCK secretion exists in which intraluminal trypsin and, to a lesser extent, bile acids and plasma CCK, plasma secretin, and the cholinergic system play important roles. Probably by interference with this feedback mechanism in the rat, casein is a stronger stimulant of plasma CCK release and pancreatic exocrine secretion than fat. Finally, CCK does not play an important role in bombesin-stimulated pancreatic enzyme secretion in the rat.