Enhancement of antitumor activity of cisplatin on human gastric cancer cells in vitro and in vivo by buthionine sulfoximine

An attempt was made to evaluate the enhancement of the antitumor activity of cisplatin (DDP) by buthionine sulfoximine (BSO) in vitro and in vivo. In the in vitro study, pre-treatment with BSO (5, 10 and 25 mM) increased the antitumor activity of DDP against the gastric cancer cell lines MKN-28 and MKN-45, whereas BSO alone exhibited only slight antitumor activity (inhibition rate, 20-30%). In the in vivo study, the antitumor effects of DDP against human gastric cancer xenografts St-15 and SC-1-NU in BALB/c nu/nu mice were enhanced pretreatment with BSO, which was administered intraperitoneally at a dose of 500 mg/kg according to a schedule of qd x 3. BSO alone showed no antitumor effects against these tumors in nude mice. The side effects (assessed in terms of death rate and body weight loss) associated with the maximum tolerated dose of DDP (9 mg/kg) were not increased by BSO pretreatment. As BSO increased the antitumor activity of DDP without a corresponding increment of its toxicity, BSO appears to be a promising agent for further study.

Different chemo- and endocrino-sensitivity of MCF-7 cells with or without estradiol supplement in vitro

The sensitivity of MCF-7 cells to tamoxifen (TAM) and mitomycin C (MMC) was assessed in rapidly and slowly growing cells with or without estradiol supplementation, respectively. The growth of MCF-7 was inhibited by MMC in a concentration-dependent manner with or without estradiol (E2) supplementation. Preincubation with MMC suppressed subsequent E2 stimulated growth of MCF-7. TAM inhibited the growth of MCF-7 supplemented with E2 and preincubation with TAM prevented subsequent E2 stimulated growth of MCF-7. However, TAM did not inhibit the growth of MCF-7 cells in E2 free medium. These results suggested that MMC may be more effective than TAM on breast cancer cells in the dormant or slow-growth phase.

Thymidine phosphorylase activity associated with platelet-derived endothelial cell growth factor

Partial complementary DNA (cDNA) for thymidine phosphorylase (dThdPase) was cloned by means of a polymerase chain reaction. There was complete sequence identity between the amino acid sequence deduced from the nucleotide sequence of a clone (288 nucleotides) and the residues of platelet-derived endothelial cell growth factor (PD-ECGF). The amino acid sequence of all four peptide fragments from purified human dThdPase could be aligned with that of PD-ECGF. Our data indicate that residues 125-244 of PD-ECGF are identical to the sequence of human dThdPase. The molecular weights of human dThdPase and recombinant PD-ECGF (rPD-ECGF) that lacks 10 amino acids at the amino terminal were 55 and 52 kDa, respectively. Anti-PD-ECGF antibody recognized dThdPase, and anti-dThdPase antibody recognized rPD-ECGF. rPD-ECGF had dThdPase activity and its specific activity was similar to that of purified human dThdPase. dThdPase activity and molecules were detected in COS cells transfected with human PD-ECGF cDNA, but not in nontransfected cells. The sizes of PD-ECGF and dThdPase in the transfected COS cells were identical. These data suggest that human dThdPase is identical to PD-ECGF.

Modification of the adenosine 5'-triphosphate-sensitive K+ channel by trypsin in guinea-pig ventricular myocytes

1. The adenosine 5'-triphosphate (ATP)-sensitive K+ channel current was recorded in guinea-pig ventricular myocytes using the patch clamp technique with inside-out patch configuration. Modification of the channel activity by intracellular application of an endoprotease trypsin was studied, and was related to a possible model of regulation of this channel. 2. Maximal ATP-sensitive K+ channel activity was observed immediately upon formation of inside-out patches in the ATP-free internal solution, thereafter activity declined both spontaneously and gradually with time; a phenomenon known as rundown. When trypsin (1 mg/ml) was applied to the intracellular side of the membrane upon formation of inside-out patches, spontaneous run-down did not occur, and this trypsin action was irreversible. Neither trypsin (1 mg/ml) applied with trypsin inhibitor (0.25 mg/ml) nor heat-denatured trypsin (1 mg/ml) could mimic this effect. When trypsin was applied to the patches after run-down, channels were reactivated at approximately 13 min. 3. Treatment with trypsin did not affect unitary current amplitude, channel gating kinetics, or sensitivity to intracellular ATP. 4. Intracellularly applied Ca2+ induced run-down of channel activity in a dose-dependent manner. In membrane patches that were treated with trypsin (1 mg/ml) for 20 min, intracellularly applied Ca2+ up to 1 mM did not induce run-down of channel activity. 5. Intracellular application of an exopeptidase, carboxypeptidase A (1 mg/ml), but not Leu-aminopeptidase (0.5 mg/ml), prevented spontaneous or Ca(2+)-induced run-down of channel activity. 6. As postulated for several other channels, such as Na+ and Ca2+ channels, there may be a possible 'chemical gate' that is responsible for run-down of this channel activity. Application of trypsin might somehow modify this 'chemical gate', resulting in prevention of spontaneous or Ca(2+)-induced run-down. This target site for trypsin may be situated on the carboxy-terminus of the channel proteins, or of associated regulatory units. Because ATP sensitivity remained intact after trypsin treatment, the trypsin-selective site for channel inhibition is not related physically to the ATP binding site.

[Simultaneous operation of gastrectomy, cholecystectomy and coronary artery bypass grafting using right gastroepiploic artery]

We present a case who received the simultaneous surgical corrections of unstable angina, acute gastric ulcer, and cholelithiasis. A 72-year-old man was admitted to our hospital due to unstable angina. An emergency coronary angiography was performed and we found severe 2 vessels disease (RCA ostium and proximal LAD lesions). After the admission, the angina was poorly controlled and the surgical treatment had been considered. The patient developed sudden hematemesis due to the uncontrolled bleeding from gastric ulcer. Then the emergency operation was performed. Partial gastrectomy with preservation of RGEA and cholecystectomy were done followed by CABG to RCA with RGEA and to LAD with autologous saphenous vein. The postoperative course was uneventful and the patient is in good condition to date.

The modulation by L-leucovorin of 5-fluorouracil antitumor activity on human colon carcinoma cells in vitro and in vivo

We investigated the modulating effect of L-leucovorin (LV) on the antitumor effect of 5-fluorouracil (5-FU) against human colon carcinoma cells (C-1) in vitro and human colon carcinoma xenografts (Co-4) in nude mice. The modulating effect of LV on 5-FU reached an optimal concentration of 40-80 micrograms/ml in vitro which was detected by a colorimetric MTT assay. An optimal dose of 200 mg/kg was also observed in the nude mouse system. The modulating effect of LV increased according to the increment of thymidylate synthetase inhibition in vivo. Since the pharmacokinetic pattern of LV in the nude mice administered LV at 200 mg/kg was similar to that in patients treated with LV at a dose of 100 mg/m2, this clinical method of administration was thought to be adequate for modulating the antitumor activity of 5-FU against clinical colon carcinomas.

[Common acute lymphoblastic leukemia showing hypo-gamma-globulinemia and cerebral infarction due to cerebral artery obstruction]

A patient who developed hypo-gamma-globulinemia and cerebral infarction during the treatment for acute lymphoblastic leukemia (ALL) is reported. In this patient fever and rash during radio-therapy for central nervous system (CNS) prophylaxis and nausea and vomiting were observed during maintenance therapy. On the laboratory findings high level of the protein level in the cerebrospinal fluid and the eosinophil count of the peripheral blood were found in every examination. We attempted to isolate various viruses in consideration of the possibility of infection, but no virus could be detected. The effects of methotrexate (MTX) and l-asparaginase were also suspected. Since nausea and vomiting disappeared after discontinuation of MTX administration, the drug may had some effect, and the possibility of cerebral damage by MTX can not be excluded. Complication of irradiation are reported to occur often more than 10 years after the treatment, but this patient had the onset only 2 years after the treatment. Therefore, irradiation was unlikely to be responsible for the symptoms. The relation between the hypo-gamma-globulinemia and cerebral infarction was also unknown.

[Therapeutic efficacy of cefodizime in combination with aminoglycosides against systemic infections caused by Pseudomonas aeruginosa in immunocompromised tumour bearing mice]

In vivo synergistic effects of cefodizime (CDZM) were investigated in combination with aminoglycosides (AGs), sisomicin (SISO) or dibekacin (DKB) against Pseudomonas aeruginosa in immunocompromised tumour bearing mice. Fractional effective dose (FED) indices showed that either synergistic or additive effects were observed between CDZM and AGs. The synergistic intraperitoneal bactericidal effect of CDZM in combination with SISO or DKB was also observed in immunocompromised tumour bearing mice. The post antibiotic effect (PAE) of AGs was prolonged by the addition of CDZM. Moreover, the strong synergistic bactericidal effects of CDZM and AGs against P. aeruginosa were observed in the presence of immunocompromised tumour bearing murine polymorphonuclear leukocytes (PMN). These results suggest that the strong therapeutic efficacy of CDZM in combination with AGs was caused by synergistic bactericidal effect of CDZM and AGs in the presence of PMN.

Expression of the multidrug transporter, P-glycoprotein, in renal and transitional cell carcinomas

BACKGROUND

Renal cell carcinomas (RCC) respond poorly to anthracyclines, Vinca alkaloids, and other agents. P-glycoprotein is overproduced in multidrug-resistant cells and thought to function as an energy-dependent drug efflux pump. The authors thus examined the expression level of P-glycoprotein in RCC and transitional cell carcinomas (TCC).

METHODS

P-glycoprotein was detected using immunoblotting with a monoclonal antibody against it, C219.

RESULTS

Thirty-three of 38 patients with RCC and 3 of 17 patients with TCC had P-glycoprotein positive tumors. The expression level of P-glycoprotein in most of RCC was lower than that in the normal kidney tissues and that of P-glycoprotein in the TCC was very low. The size of P-glycoprotein in 14 RCC and 3 TCC was 5-10 kilodaltons smaller than in the normal renal tissues. The variation of P-glycoprotein size in the RCC was attributed to differential N-linked glycosylation. P-glycoprotein in a RCC was photolabeled by tritiated azidopine, and the labeling was inhibited by some organic agents. P-glycoprotein distributed on the apical or marginal cell surface of the RCC.

CONCLUSIONS

These data show that P-glycoprotein was expressed in many RCC, and its expression level, glycosylation, and distribution were altered. These data also suggest that the P-glycoprotein in RCC had similar drug binding site(s) to that in multidrug-resistant cells.

Differential chemosensitivity of local and metastatic human gastric cancer after orthotopic transplantation of histologically intact tumor tissue in nude mice

We have established a metastatic model of human gastric cancer using orthotopic transplantation of histologically intact tissue in nude mice, and have used this model to evaluate the effects of immunochemotherapy using OK-432, 5-fluorouracil (5-FU) and mitomycin C (MMC) against SC-I-NU, a human stomach cancer line. One-quarter or one-half maximum tolerated doses (MTDs) of 5-FU or MMC resulted in a significant reduction of stomach tumor growth, while liver metastases were not reduced, possibly due to suppression of natural killer (NK)-cell activity by both drugs. On the other hand, when combined with OK-432, half MTDs of 5-FU and MMC significantly reduced liver metastases, with synergistic reduction of stomach tumor growth, possibly reflecting a rescue of NK-cell activity by treatment with OK-432. This metastatic model of human stomach cancer shows that locally growing and metastatic tumors may have different chemosensitivities, and provides the opportunity to test both with various treatment regimens.

A metastatic model of human colon cancer constructed using cecal implantation of cancer tissue in nude mice

COL-2-JCK, a human colon cancer xenograft line able to be transplanted into nude mice, was implanted in the subserosal layer of the cecum, either as cancer tissue or as a single cell suspension. When cancer tissue was used for the cecal implantation, 100% extensive local tumor growth and a high incidence of metastases to the regional lymph nodes, peritoneum, liver, and lung was observed. In contrast, when the cell suspension of this line was injected into the cecal wall, no metastases were observed, with significantly reduced local tumor growth. The use of cancer tissue maintaining the original cancer tissue structure is therefore considered imperative for allowing full expression of the biological characteristics of cancer cells. This nude mouse model using the cecal implantation of cancer tissue should thus prompt further study on the biology of human colon cancer.

Usefulness of fecal alpha-1-antitrypsin for detection of gastrointestinal bleeding in patients with gastric cancer

Hemoglobin (Hb), albumin (Alb), immunoglobulin G (IgG) and alpha-1-antitrypsin (AAT) were measured in 87 fecal samples from 29 normal volunteers and 68 fecal samples from 33 patients with gastric cancer before surgery to evaluate the usefulness of fecal AAT as an indicator of gastrointestinal bleeding in patients with gastric cancer. Mean values and standard deviation of fecal Hb, Alb, IgG and AAT in normal volunteers were 0.13 +/- 1.19 micrograms/g, 6.96 +/- 20.48 micrograms/g, 17.52 +/- 10.16 micrograms/g, and 0.483 +/- 0.315 mg/g, respectively. These parameters in the patients with gastric cancer were significantly higher than those in the normal volunteers. No statistically significant correlations were observed between these fecal parameters, except between fecal Alb and IgG. Data obtained from peripheral blood also showed no significant correlation with these fecal parameters. When the cut-off levels of fecal Hb, Alb, IgG and AAT were set at M + 2SD of the values obtained from the normal volunteers, sensitivity, specificity and accuracy were 80.0%, 86.2% and 84.1% for fecal AAT, and 66.7%, 96.6% and 86.4% for fecal Hb in the patients with advanced gastric cancer in a cohort consisting of patients with advanced gastric carcinoma and normal volunteers. Since fecal AAT showed higher sensitivity in patients with advanced gastric cancer with a low number of false negative cases, we concluded that measurement of fecal AAT could be a promising method for assessment of gastrointestinal bleeding in patients with advanced gastric carcinoma instead of immunological detection of fecal Hb.

Magnetic resonance images of hematospermia

Seminal vesicles and their adjacent structures were studied using magnetic resonance imaging (MRI) in 7 normal volunteers and 15 patients with hematospermia. Normal seminal vesicles are depicted on T2-weighted images either as a mixture of high- and low-signal granules or as a convolution of tubules with a diameter of less than 0.5 cm. Fourteen of the 15 patients with hematospermia exhibited abnormalities on MRI. Dilatation or cyst formation in the seminal vesicle was observed in 13 patients, and a dilatation of the midline structure was seen in 3 patients. Abnormal signal intensity of the seminal vesicles was seen in 11 patients and was thought to be due to subacute hemorrhage.

A newly developed hexamethylmelamine derivative, SAE9 with both antitumor and aromatase-inhibitory activity

Hexamethylmelamine (HMM) has previously been shown to be active against ovarian, breast and small cell lung cancer. However HMM dose not have aromatase-inhibitory activity. A newly developed HMM derivative, 2-N,N-dimethylamino-4, 6-bis (1-H-imidazol-1-yl)-1,3,5-triazine (SAE9), was found to have direct antitumor activity as well as aromatase-inhibitory activity. The direct antitumor activity on breast carcinoma cell lines (MCF-7, R-27 and MDA-MB-231) was assessed using the 3-(4,5-dimethylthiazol-2yl)-2, 5-diphenyl tetrazolium bromide (MTT) on cells growing in monolayer culture. The 50% inhibitory concentrations (IC50) of SAE9 were found to be approximately 10(-4) M for each cell line, roughly equivalent to those of HMM. When the aromatase-inhibitory effect was assessed using a human placental aromatase-inhibitory assay, the IC50 of SAE9 was 5.5 x 10(-7) M, which was superior to that of aminoglutethimide (AG) (3.8 x 10(-5) M). In a rat uterine growth model treated with androstenedione as the in vivo aromatase inhibition assay, SAE9 had an effect equivalent to that of AG. Since SAE9 has both antitumor and aromatase-inhibitory activity on breast carcinoma cell lines with estrogen dependency, this and similar non-steroidal aromatase inhibitors are thought to be promising for further study.

Site-specific chemosensitivity of human small-cell lung carcinoma growing orthotopically compared to subcutaneously in SCID mice: the importance of orthotopic models to obtain relevant drug evaluation data

We have developed a novel in vivo model of human small-cell lung carcinoma (SCLC) using orthotopic reconstitution by injecting human SCLC in the tail vein of severe combined immunodeficient (SCID) mice whereby the SCLC grows in the lung and other organs. Cisplatin (DDP) had significant antitumor effects on the SCLC growing orthotopically in the lung whereas mitomycin C (MMC) did not, thereby reflecting the clinical situation. However, the opposite effects were found when the SCLC was growing subcutaneously, where the tumors responded to MMC and not to DDP. This suggests that the tumors growing orthotopically reflect the clinical effects of drugs on human SCLC more closely than the tumors growing subcutaneously. Therefore, this orthotopic reconstitution model of human SCLC in SCID mice is thought to be useful for studies on the treatment of human SCLC and emphasizes the need for orthotopic models for relevant cancer drug evaluation.

Significance of in vitro attachment of human colon cancers to extracellular matrix proteins in experimental and clinical liver metastases

The attachment of 7 human colon cancer lines transplantable into nude mice, and primary tumors and liver metastases from 30 patients with colon cancer to 4 extracellular matrix proteins (EMPs)--Matrigel, laminin, fibronectin, and type IV collagen--was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H (MTT) assay. Cancer cells from the 4 established tumor lines which produced experimental liver metastases in vivo showed significantly greater attachment to each EMP than those from the other 3 tumor lines which did not. Although there were no significant differences between attachment to EMPs of cancer cells from 15 clinical primary tumors with liver metastases and those without, attachment to each EMP of cells derived from liver metastases was significantly greater than that of the cells from the corresponding primary tumors in 8 cases for which liver metastases and primary tumors were examined simultaneously. Attachment to EMPs, which could be determined simply and rapidly using the MTT assay, is thus considered a significant factor in experimental and clinical liver metastases of human colon cancers.

The ionic mechanism of reperfusion-induced early afterdepolarizations in feline left ventricular hypertrophy

Left ventricular hypertrophy (LVH) potentiates reperfusion-associated ventricular fibrillation. To study the mechanism responsible, patch-clamp techniques were used to evaluate transmembrane ionic currents during "reperfusion" after a CN(-)-induced metabolic surrogate for ischemia in isolated myocytes from a feline model of experimental LVH. Reperfusion caused the generation of early afterdepolarizations (EADs) from an average take-off potential of -33 mV in LVH cells but not in cells from normal hearts. 10 min after initiating reperfusion of normal cells, action potential duration (APD) at 50% repolarization (APD50) lengthened from 198 +/- 41 to 233 +/- 57 ms whereas in LVH cells APD50 lengthened from 262 +/- 84 to 349 +/- 131 ms (P < 0.05). Among the LVH cells, APD50 lengthening was significantly greater in the cells that had developed EADs. During reperfusion, steady state outward current in the voltage range of the action potential plateau (between -20 and +20 mV) was reduced from the control values in LVH cells but not in normal cells. Reperfusion-related reduction of steady state outward current in LVH cells was abolished under experimental conditions in which L-type Ca2+ current was isolated from other classes of currents whereas it was still observed under the condition in which pure K+ currents could be recorded. Thus, reduction of steady state outward current due to the reduction of outward K+ current over the action potential plateau voltage range appears to be responsible for an excessive prolongation of APD, leading to the development of EADs.

Antitumor activities of ellagitannins against sarcoma-180 in mice

Forty-five ellagitannins and related compounds were intraperitoneally injected into mice once, 4 d before intraperitoneal inoculation of S-180 cells, and their antitumor activities were evaluated. When an antitumor-active tannin was defined as one producing a 70% increase or more in the mean life span of mice or one regressor out of six mice, twenty-one ellagitannins were active. Among monomeric ellagitannins, tellimagrandin II was most active. Most of the oligomeric ellagitannins, consisting of tellimagrandins I and II as the monomer unit, had a significant antitumor activity. Macrocyclic ellagitannins were all active. Oenothein B, among them, had the most potent antitumor activity. In contrast, ellagitannins containing a casuarictin or potentillin moiety in their molecules, except for extensively oligomerized ones, showed very low or negligible activity. These results suggest that tannins need the ellagitannin monomer units, having galloyl groups at the O-2 and O-3 positions on the glucose core(s), such as tellimagrandins, in order to exhibit a strong antitumor activity.

[Therapeutic efficacy of cefodizime in combination with minocycline against systemic infection caused by methicillin-resistant Staphylococcus aureus in immunocompromised tumour bearing mice]

The in vivo synergistic effect of cefodizime (CDZM) in combination with minocycline (MINO) against methicillin-resistant Staphylococcus aureus (MRSA) was investigated. A study of fractional effective dose (FED) index showed that either synergistic or additive effect was observed between CDZM and MINO. The postantibiotic effect (PAE) of MINO was not altered by the addition of CDZM. However, a strong synergistic bactericidal effect of CDZM and MINO against MRSA CT-18 was observed for more than 14 hours in the presence of immunocompromised tumour bearing murine polymorphonuclear leukocytes (PMN). These results suggest that the strong therapeutic efficacy of CDZM in combination with MINO was caused by synergistic bactericidal effect of the 2 drugs in the presence of PMN.

External pH regulates the slowly activating potassium current IsK expressed in Xenopus oocytes

A slowly activating, delayed rectifier potassium current, IsK, was expressed in Xenopus laevis oocytes by injection of cRNA transcribed from a rat kidney cDNA clone. External acidification reversibly decreased the current amplitude. The effects were concentration dependent on protons with Kd at pH approximately 5.5 and a Hill coefficient of 1.0. External acidification reduced the maximal conductance (Gmax) without affecting the activation kinetics; this effect was not dependent on membrane voltages. These data suggest that H+ ions bind to the channel with a one-to-one stoichiometry, and this binding site may be located outside of the membrane electric field.

[High clinical predictability of histoculture drug response assay (HDRA) for drug-sensitivity of cancer of the digestive organs]

Fresh surgical specimens from 250 patients with cancer were used for the histoculture drug response assay (HDRA) with MTT method. Scissor cut small pieces of the specimens were placed onto collagen-gel-matrix which was incubated in 24 well-plate dishes filled with medium containing mitomycin C (MMC), adriamycin (ADM), 5-fluorouracil (5-FU) or cisplatin (CDDP). The cutoff concentrations of the drugs used are 7.5 micrograms/ml for MMC, 15 micrograms/ml for ADM, 300 micrograms/ml for 5-FU and 20 micrograms/ml for CDDP. After 7 days incubation, the specimens were assessed the inability to reduce MTT. A 50% or greater inhibition of MTT reduction at the cutoff concentrations indicated in vitro sensitivity. The clinical effect of the drugs was evaluated according to the criteria of the Japanese Society for Cancer Therapy. Two hundred thirty two (93%) cases were evaluable, and in vitro and in vivo correlation was compared in 42 cases. Of the 33 patients whose tumors showed drug resistance in HDRA, 33 failed treatment with one or more of these agents. Of the nine patients whose tumors showed drug sensitivity in HDRA, six had chemo-responses (2 CRs and 4 PRs) for a total accuracy of 93% (34/42). The advantages of HDRA include, three-dimensional tumor cell growth in in vitro culture with cell to cell contact and maintenance of tissue architecture, 7 days to assess the effect of antitumor agents, ability to evaluate both growing and resting tumor cells, small amounts of specimen required for assay, and high evaluable and predictable rates for clinical use in designing optimal chemotherapy regimens for cancer patients.

Immunochemotherapy prevents human colon cancer metastasis after orthotopic onplantation of histologically-intact tumor tissue in nude mice

A metastatic model of human colon cancer has been previously established using orthotopic onplantation of histologically intact in tissue nude mice. In this study, effects of immunochemotherapy using OK-432, 5-fluorouracil (5-FU) and mitomycin C (MMC) on Col-2-JCK, a human colon cancer xenograft, were evaluated using this model. When 5-FU and MMC were administered without OK-432, liver metastases were not reduced even at maximum tolerated doses of both drugs, although cecal tumor growth was significantly reduced. On the other hand, when combined with OK-432, both 5-FU and MMC reduced liver metastases with synergistic reduction of cecal tumor growth, demonstrating the potential of combining immunotherapy with chemotherapy against metastases.

Potentiation of the antidipsogenic action of alpha-human atrial natriuretic polypeptide at the preoptic area in spontaneously hypertensive rats

The effect of alpha-human atrial natriuretic polypeptides on fluid intake following administration of angiotensin II and 48 hr water deprivation was assessed at the preoptic area in spontaneously hypertensive and normotensive Wistar-Kyoto rats. Angiotensin II (100 ng), injected into the preoptic area, and water deprivation increased the intake of water and of a 2.7% NaCl solution in spontaneously hypertensive as well as in Wistar-Kyoto rats. These intakes were potentiated in the spontaneously hypertensive rats. The fluid intakes evoked by angiotensin II were dose-dependently antagonized by alpha-human atrial natriuretic polypeptide and angiotensin II, administered into the preoptic area, in spontaneously hypertensive but not in Wistar-Kyoto rats. In 48 hr water-deprived rats, alpha-human atrial natriuretic polypeptide also inhibited the fluid intake in spontaneously hypertensive but not in Wistar-Kyoto rats. The results suggest that atrial natriuretic polypeptide and angiotensin II may play an important role in controlling fluid intake at the preoptic area level and that these peptides might be involved in the pathogenesis of spontaneously hypertensive rats.