In vivo measurement by [3H]Tamsulosin of alpha1 adrenoceptors in rat tissues in relation to the pharmacokinetics

The present study was undertaken to simultaneously measure alpha1 adrenoceptors in rat tissues by [3H]tamsulosin in vivo. In vivo specific [3H]tamsulosin binding was observed in the prostate, vas deferens, aorta, submaxillary gland, spleen, heart, lung, and kidney after i.v. injection of the ligand but not in the cerebral cortex and liver. Specific [3H]tamsulosin binding in the kidney, lung, heart, and spleen was greatest at 3 min after i.v. injection and declined rapidly with the disappearance of [3H]tamsulosin from the plasma. On the other hand, [3H]tamsulosin binding in the prostate and aorta peaked at 10 to 60 min after i.v. injection, and a considerable level of specific binding in both tissues persisted up to 240 min. The most sustained binding of [3H]tamsulosin occurred in the submaxillary gland. In vivo specific [3H]tamsulosin binding in rat tissues was effectively inhibited by the coinjection of low doses of unlabeled tamsulosin, prazosin, and terazosin with the radioligand but not by relatively high doses of yohimbine and propranolol. Based on estimated ID50 values, in vivo inhibitory effect of tamsulosin compared with prazosin was 5 to 14 times greater in rat tissues except the spleen, which showed 1.6 times less potent than prazosin. From ratios of ID50 (spleen) to ID50 (submaxillary gland) or ID50 (prostate), tamsulosin was 9 and 19 times, respectively, greater than prazosin in selectivity of alpha1 adrenoceptors in the submaxillary gland and prostate versus the spleen, respectively, suggesting that tamsulosin binds to alpha1A subtype with higher affinity than alpha1B subtype in vivo. The present study suggests that [3H]tamsulosin is a useful radioligand for in vivo measurement of alpha1 adrenoceptors in rat tissues.

[Metabolism of 3,3',4,4',5-penta- and 2,2',3,3',4,4'-hexachlorobiphenyls in rats]

Following the i.p. administration of 3,3',4,4',5-pentachlorobiphenyl (CB126) and 2,2',3,3',4,4'-hexachlorobiphenyl (CB128) to rats, blood, liver, lung, kidney, adipose tissue and feces were analyzed for the metabolites. CB126 was biotransformed to three hydroxylated metabolites identified as 4-OH-3,3',4',5'-tetraCB, 4-OH-3,3',4',5,5'-pentaCB and 5-OH-3,3',4,4',5'-pentaCB at about 1:7:2 ratio, whereas to two methylthio metabolites as 5-MeS- and 6-MeS-3,3',4,4',5'-pentaCBs at 1:2 ratio. Among the metabolites, only 4-OH-3,3',4',5,5'-pentaCB was detected in all tissues and blood. The ratio of metabolite/unchanged CB126 was 1:1.3 in blood and 1:162 in liver, indicating the high blood affinity of this metabolite. Trace amounts of 5-methylsulfonyl-3,3',4,4',5'-pentaCB was also detected in the liver. CB128 was biotransformed to 5-OH-, 5-MeS- and 6-MeS-2,2',3,3',4,4' hexaCBs which were excreted to feces in about 5:5:1 ratio. No metabolites were detected in blood and any tissues except for liver where trace amounts of 5-hydroxylated metabolite was present, indicating the low tissue affinity of hydroxylated metabolites from CB128.

Comparative study on pharmacokinetics and in vivo alpha1-adrenoceptor binding of [3H]tamsulosin and [3H]prazosin in rats

The plasma concentration, total radioactivity and in vivo alpha1-adrenoceptor binding in rat tissues after intravenous (i.v.) injection of [3H]tamsulosin were measured and they were compared with those obtained after the injection of [3H]prazosin. The plasma concentration of [3H]tamsulosin was consistently higher than that of [3H]prazosin, with 1.4 times greater areas under the curve (AUC(0-infinity)) of plasma concentration. As there was a significantly lower value of apparent volume of central compartment (Vd(c)) and distribution volume at steady state (Vd(ss)) for [3H]tamsulosin than [3H]prazosin with little difference in elimination rate constant (beta), the higher concentration of [3H]tamsulosin in plasma might be associated mainly with the smaller volume of distribution. The ratio of total radioactivity in tissues to the plasma unbound concentration of [3H]tamsulosin after i.v. injection of the ligand was consistently lower than that of [3H]prazosin. These observations suggest that [3H]tamsulosin is distributed in rat tissues in a more limited manner than [3H]prazosin. A significantly lower level of in vivo specific binding of [3H]tamsulosin than [3H]prazosin was observed in the spleen, heart and liver. Further, the apparent dissociation constant (Kd) and maximal number of binding sites (Bmax) for in vivo specific [3H]tamsulosin binding were considerably lower than those for [3H]prazosin binding. Therefore, these findings suggest that [3H]tamsulosin labels preferentially a subpopulation of the alpha1-adrenoceptor sites in rat tissues labeled by [3H]prazosin. In conclusion, the present study has shown that there is a significant difference in the pharmacokinetics and in vivo alpha1-adrenoceptor binding characteristics between tamsulosin and prazosin.

Reduction of thyroid hormone levels by methylsulfonyl metabolites of tetra- and pentachlorinated biphenyls in male Sprague-Dawley rats

Male Sprague-Dawley rats received four consecutive intraperitoneal (i.p.) doses of five kinds of methylsulfonyl (MeSO2) metabolites of tetra- and pentachlorinated biphenyls (tetra- and pentaCBs) to determine their effects on thyroid hormone levels. The five MeSO2 metabolites, which were the major MeSO2-PCBs detected in human milk, liver and adipose tissue were 3-MeSO2-2,2',4',5-tetraCB (3-MeSO2-CB49),3-MeSO2-2,3',4',5-tetraCB (3-MeSO2-CB70), 3-MeSO2-2,2',3',4',5-pentaCB (3-MeSO2-CB87), 3-MeSO2-2,2',4',5,5'-pentaCB (3-MeSO2-CB101), and 4-MeSO2-2,2',4',5,5'-pentaCB (4-MeSO2-CB101). All five tested MeSO2 metabolites (20 mumol/kg once daily for 4 days) reduced serum total thyroxine levels 16-40% on days 2, 3, 4, and 7 (after the last dosage). The total triiodothyronine level was reduced 37% by treatment with 3-MeSO2-CB49 at day 7, but was increased 35% and 38% by 3-MeSO2-CB70 and 4-MeSO2-CB101 at days 3 and 4, respectively. The reductions in thyroid hormone levels led to an increase in thyroid stimulating hormone (TSH) levels by 3-MeSO2-CB49, 3-MeSO2-CB87 and 3-MeSO2-CB101. A 30% increase in thyroid weight was produced by 3-MeSO2-CB101 treatment. Thus, it is likely that all five tested MeSO2 metabolites could influence thyroid hormone metabolism. The results show that the tested 3- and 4-MeSO2 metabolites of tetra- and pentaCBs reduce thyroid hormone levels in rats, suggesting that the metabolites may act as endocrine-disrupters.

Brain proton magnetic resonance spectroscopy and brain atrophy in myotonic dystrophy

OBJECTIVES

To evaluate by magnetic resonance spectroscopy the age-related cerebral alterations present in myotonic dystrophy (MD) and to compare these results with those obtained by magnetic resonance imaging.

DESIGN

Twenty-one patients (aged 16-63 years) with MD were compared with 16 age-matched healthy control subjects.

RESULTS

In magnetic resonance spectroscopy, the mean (+/- SD) ratio of N-acetylaspartate to creatine and phosphocreatine in the patients with MD (1.09 +/- 0.32) was significantly lower than that in the control subjects (1.93 +/- 0.43) (P<.001). The mean ratio of N-acetylaspartate to choline-containing compounds in the patients with MD (1.70 +/- 0.44) was also significantly lower than that in the control subjects (2.75 +/- 0.53) (P<.001). These changes could be observed already in the younger patients. In magnetic resonance imaging, the mean brain area was significantly decreased and the mean ventricular space was significantly increased in patients with MD compared with the control subjects. Although we have confirmed brain atrophy in patients with MD in previous reports, a regression analysis indicated that the brain shrinks progressively with age in patients with this disorder and in control subjects, resulting in overlapping values for younger subjects.

CONCLUSION

Magnetic resonance spectroscopy indicates that the cerebral abnormalities in patients with MD may be present at an early stage, when the results of magnetic resonance imaging studies are still equivocal.

Expression of cyclooxygenase-2 in human hepatocellular carcinoma: relevance to tumor dedifferentiation

Cyclooxygenase (COX) is a key enzyme in the synthesis of prostanoids. Two isoforms of this enzyme have been identified: COX-1 and COX-2. Recent studies have suggested that COX-2, but not COX-1, may play a role in colorectal tumorigenesis. In the present study, we investigated the expression of COX-2 as well as COX-1 in human hepatocellular carcinoma (HCC) tissues using immunohistochemistry and immunoblotting. Forty-four surgically resected HCC tissues with adjacent nontumorous livers (NTs), involving 17 cases of chronic viral hepatitis and 27 cases of cirrhosis, and 7 surgically resected, histologically normal liver tissues were used. The well-differentiated HCC expressed COX-2 more frequently and strongly than less-differentiated HCC or hepatocytes of NTs. Less-differentiated HCCs expressed less COX-2 than hepatocytes of NTs, which showed scattered, strong COX-2 expression. Histologically normal liver was weakly positive for COX-2. The expression of COX-1 was weaker than that of COX-2 in hepatic neoplastic and non-neoplastic parenchymal cells. An enhanced expression of COX-1 was not observed in well-differentiated HCCs. Immunoblotting also confirmed up-regulation of COX-2, but not COX-1, in well-differentiated HCCs. The present study is the first to demonstrate a high expression of COX-2 in well-differentiated HCC and a low expression in advanced HCC, in contrast to its continuous expression during colorectal carcinogenesis. These findings suggested that COX-2 may play a role in the early stages of hepatocarcinogenesis, but not in the advanced stages, and may consequently be related to HCC dedifferentiation.

Ex vivo occupancy by tamsulosin of alpha1-adrenoceptors in rat tissues in relation to the plasma concentration

At 0.5-12 h after oral administration of tamsulosin (2.3 micromol/kg) in rats, there was a significant decrease in specific [3H]prazosin binding in the prostate as compared to the control value. The greater decrease occurred in the submaxillary gland. The effect of tamsulosin was mainly due to a marked reduction of [3H]prazosin binding sites (Bmax) rather than to an increase in the dissociation constant (Kd). In contrast, there was only a slight decrease or no change in the [3H]prazosin binding in the spleen, heart, and cerebral cortex of tamsulosin-administered rats at 0.5-12 h. Oral administration of terazosin (21.7 micromol/kg) significantly increased Kd values for [3H]prazosin binding with little effect on Bmax values in the rat prostate at 3 and 6 h. The greater increases in Kd values were observed in the submaxillary gland, spleen and heart at 0.5-12 h. Terazosin had a slight effect on Kd values for the cerebral cortical [3H]prazosin binding. Tamsulosin was absorbed rapidly after oral administration at a dose of 2.3 micromol/kg in rats, and at 6 h, plasma concentration decreased markedly to approximately one-twentieth of the 0.5 h peak level. alpha1-Adrenoceptor occupancy was estimated as a percentage of decrease in Bmax values for [3H]prazosin binding in tissues of tamsulosin-treated rats compared with control rats. The alpha1-adrenoceptor occupancy by tamsulosin in the prostate and submaxillary gland occurred rapidly in parallel with the rise in plasma concentration of tamsulosin, and lasted for over 12 h despite the marked decrease in plasma concentration. Consequently, it is suggested that tamsulosin produces more selective and sustained occupancy in vivo of alpha1-adrenoceptors in the submaxillary gland and prostate of rats than in other tissues.

Hydroxylation and methylthiolation of mono-ortho-substituted polychlorinated biphenyls in rats: identification of metabolites with tissue affinity

The metabolism of three mono-ortho-substituted congeners, 2,3,3',4, 4'-pentachlorobiphenyl (CB105), 2,3',4,4',5-pentachlorobiphenyl (CB118), and 2,3,3',4,4',5-hexachlorobiphenyl (CB156), was investigated with regard to the identification of hydroxy- and sulfur-containing metabolites and their tissue retention in rats. Hydroxylation proceeded primarily at the meta or para position either via an arene oxide, involving NIH shift and dechlorination, or by direct insertion of a hydroxyl group. CB105 was hydroxylated preferably in the 2,3,4-trichlorinated ring to yield 4-OH-2,3,3',4', 5-pentaCB, whereas CB118 was hydroxylated in the 2,4, 5-trichlorinated ring to yield the same hydroxy metabolite to a similar extent. The concentration of 4-OH-2,3,3',4',5-pentaCB in blood was >3 times higher than that in liver, lung, or kidney. The ratios of 4-OH-2,3,3',4',5-pentaCB to unchanged CB in blood were 11:1 for CB105 and 7:1 for CB118. The other two metabolites, 4'-OH-2, 3',4,5,5'-pentaCB from CB118 and 4'-OH-2,3,3',4,5,5'-hexaCB from CB156, also exhibited a high blood affinity. Another metabolism of mono-ortho-PCBs PCBs involved methylthiolation in the vicinal ortho and meta unsubstituted positions to give methylthio metabolites, which were detected as methylsulfonyl metabolites in liver and adipose tissue. The tissue retention of these metabolites might contribute to the toxic and biologic effects of mono-ortho-substituted PCBs.

Reduction of thyroid hormone levels by methylsulfonyl metabolites of polychlorinated biphenyl congeners in rats

Male Sprague-Dawley rats received four consecutive intraperitoneal doses of four kinds of methylsulfonyl (MeSO2) metabolites of polychlorinated biphenyl (PCB) congeners: 3-MeSO2-2,2',3',4',5,6-hexachlorobiphenyl (3-MeSO2-CB132); 3-MeSO2-2,2',3',4', 5,5'-hexachlorobiphenyl (3-MeSO2-CB141); 3-MeSO2-2,2',4',5,5',6-hexachlorobiphenyl (3-MeSO2-CB149) and 4-MeSO2-2,2',4',5,5',6-hexachlorobiphenyl (4-MeSO2-CB149). The congeners were major MeSO2-PCBs determined in human milk, liver and adipose tissue, and the aim was to determine their effect on thyroid hormone levels. All four tested MeSO2 metabolites (20 micromol/kg once daily for 4 days) reduced serum total thyroxine levels by 22-44% at a much lower dose than phenobarbital (PB; 431 micromol/kg once daily for 4 days) on days 2, 3, 4 and 7 after the final doses. Total triiodothyronine levels were reduced 37% by treatment with 4-MeSO2-CB149 at day 7. A 30% increase in thyroid weight was produced by 3-MeSO2-CB141 treatment. Total cytochrome P450 content was increased by 3-MeSO2-CB132, 3-MeSO2-CB141 and 3-MeSO2-CB149, but not by 4-MeSO2-CB149. Thus, it is likely that the 3-MeSO2-hexachlorobiphenyls and 4-MeSO2-CB149 could influence the thyroid hormone metabolism by different mechanism(s). The results show that tested 3- and 4-MeSO2 metabolites of PCB congeners reduce thyroid hormone levels much more than PB in rats. Our finding suggests that the metabolites may act as endocrine-disrupters.

Embryogenesis-promoting factors in rat serum

Regarding whole rat embryo cultures in vitro, rat serum as a culture medium is known to support the normal growth of rat embryos in the organogenesis phase. The purpose of the present study was to isolate the embryogenesis-promoting factors from rat serum as a first step in the development of a defined serum-free medium for a whole embryo culture system. Pooled rat serum after heat inactivation was fractionated into three major peaks (frA, containing a region of void volume, frB, and frC) by gel filtration. The 9.5-day rat embryos that were cultivated for 48 hr in essential salt medium containing frB (with a molecular size range of 100-500 kDa) revealed normal growth. Three proteins (27 kDa, 76 kDa, and 190 kDa) that had the embryogenesis-promoting effects were isolated from 3-hr delayed centrifuged rat serum by the ion exchange chromatography. The 76-kDa protein was found to be rat transferrin by immunoblotting. The 27-kDa protein was identified as apo-AI (the major apoprotein of high-density lipoprotein) by immunoblotting. High-density lipoprotein obtained from pooled rat serum by a NaBr density gradient ultracentrifugation was found to have a positive effect on embryogenesis. The 10-kDa protein was also identified as alpha 1-inhibitor 3 by immunoblotting. In addition, the embryogenesis-promoting effect of the fraction containing 27-kDa and 190-kDa proteins declined within a short period of storage at -20 degrees C. This decrease was countered by supplementing its fraction (D-2) with albumin isolated from rat serum. These results in the present study suggest that transferrin, high-density lipoprotein, and alpha 1-inhibitor 3 in rat serum may be embryogenesis-promoting factors, and that albumin appeared to play a role in the embryogenesis of rat embryos in whole embryo cultures.

Receptor occupancy in myocardium, adrenal cortex, and brain by TH-142177, a novel AT1 receptor antagonist in rats, in relation to its plasma concentration and hypotensive effect

PURPOSE

To study the relationship between angiotensin II (AII) receptor occupancy ex vivo in tissues plasma concentration and hypotensive effect of a novel AII receptor antagonist, TH-142177 and losartan in rats.

METHODS

At 2, 8 and 24 hr after oral administration of TH-142177 and losartan in rats, AII receptors in myocardium, adrenal cortex and cerebral cortex were determined by radioligand binding assay using [125I]Sar1,Ile8-AII. Plasma concentrations of both drugs and metabolite in rats were also measured using validated HPLC assays. Further, systolic blood pressure (SBP) in conscious renal hypertensive rats treated orally with TH-142177 and losartan were measured by using a tail cuff plethysmographic method.

RESULTS

Oral administration of TH-142177 (1.8 and 5.5 micromol/kg) and losartan (6.5 and 21.7 micromol/kg) in rats brought about dose-dependent decreases in [125I]Sar1,Ile8-AII binding sites (Bmax) in myocardium and adrenal cortex. The extent of receptor occupancy by both drugs in adrenal cortex was maximal at 2 hr later but that in myocardium at 8 hr later. Further, the receptor occupancy was more sustained in myocardium than adrenal cortex. The ex vivo binding affinity of TH-142177 for AII receptors in these tissues was roughly three times higher than that of losartan. Also, cerebral cortical [125I]Sar1,Ile8-AII binding was significantly reduced by oral administration of losartan but not by TH-142177. The time course of AII receptor occupancy by both drugs in adrenal cortex appeared to be in parallel with that of their plasma concentrations, while the time course in myocardium correlated with that of their hypotensive effects rather than plasma concentrations.

CONCLUSIONS

TH-142177 produced a relatively selective and sustained occupancy ex vivo of AII receptors in myocardium and adrenal cortex of rats with approximately three times greater potency than losartan. Its time course of myocardial receptor occupancy was in parallel with that of hypotensive effect rather than plasma concentration.

In vivo receptor binding of novel alpha1-adrenoceptor antagonists for treatment of benign prostatic hyperplasia

New types of alpha1-adrenoceptor antagonists (tamsulosin, KMD-3213 and JTH-601) are currently receiving a great deal of attention, especially in terms of developing effective therapeutic agents to treat bladder outlet obstruction with less side effects, such as postural hypotension, in patients with benign prostatic hyperplasia (BPH). In vivo alpha1-adrenoceptor binding properties of these antagonists in prostate and other tissues of rats were examined. Intravenous injections of tamsulosin, KMD-3213 and JTH-601 inhibited dose-dependently in vivo specific [3H]tamsulosin binding in various tissues. Ratios of ID50(aorta) to ID50(prostate) of KMD-3213 and JTH-601 were greater than those of tamsulosin and prazosin. Further, the ratios of ID50(spleen) to ID50(submaxillary gland) of these drugs were greater than that of prazosin. Following intravenous injections of [3H]KMD-3213 in rats, the amount of specific binding in prostate was significantly greater than that of [3H]prazosin, but that in aorta or spleen was much smaller. Interestingly, [3H]JTH-601 showed little in vivo specific binding in aorta. These data suggest that KMD-3213 and JTH-601 exhibit higher affinity to alpha1-adrenoceptors in prostate and submaxillary gland than in vascular tissues in vivo.

[Metastasis of small cell lung cancer to the parotid gland as the initial clinical manifestation, followed by metastases to the pituitary gland and lumber spinal cord]

The patient was a 48-year-old woman. In January 1995, she noted swelling in the left parotid gland, and saw an otorhinolaryngologist. Needle biopsy showed small cell carcinoma, and she was subsequently admitted to our hospital. Chest radiography revealed a tumor shadow in the hilus of the right lung. Bronchial biopsy revealed small cell carcinoma of the lung (T 4 N 3 M 1, stage IV). Chemotherapy, with a CDDP-VP-16 regimen, achieved no response. She later developed bitemporal hemianopsia and abducens nerve palsy. Brain MRI revealed metastasis in the pituitary gland. Chemotherapy and radiotherapy were efficacious for only a few months. She also developed pain and numbness in the left leg, attributable to intramedullary metastasis (L 1/2, L 4/5) shown on MRI. It is extremely rare for a metastasis to the parotid gland to be the initial clinical manifestation of a small cell lung cancer which later develops widespread metastases to the pituitary gland and lumbar spinal cord.

Inhibition of cell-cell communication by methylsulfonyl metabolites of polychlorinated biphenyl congeners in rat liver epithelial IAR 20 cells

The effects of three polychlorinated biphenyl (PCB) congeners and their six methylsulfonyl (MeSO2)-metabolites on cell communication have been investigated in the scrape-loading/dye-transfer assay in IAR 20 rat liver epithelial cells. The results demonstrated that at non-cytotoxic concentrations 2,2',4',5-tetrachlorobiphenyl, 2,2',4',5,5'-pentachlorobiphenyl (2,2',4',5,5'-pentaCB), 2,2',4',5,5',6-hexachlorobiphenyl (2,2',4',5,5', 6-hexaCB), and their 3- and 4-MeSO2 derivatives completely inhibited the cell communication within 1 h. 4-MeSO2-2,2',4',5,5'-pentaCB and 4-MeSO2-2,2',4',5, 5',6-hexaCB appeared to inhibit the cell communication at slightly lower concentration than their parental PCB congeners and 3-MeSO2 derivatives. The results show that 3- and 4-MeSO2 derivatives of the PCB congeners tested inhibit gap junction intercellular communication at about the same potency as their parental compounds. Since inhibition of cell communication is often observed after treatment with many tumor promoters, our findings suggest that the metabolites may also act as tumor promoters.

Brain pharmacokinetics and in vivo receptor binding of 1,4-dihydropyridine calcium channel antagonists

Brain pharmacokinetics of 1,4-dihydropyridine (DHP) calcium channel antagonists and their in vivo receptor binding in mice were characterized. The area under the concentration vs time curve (AUCbrain) for [3H]nifedipine, [3H]nimodipine and [3H]PN 200-110 in mouse brain after intravenous injection was higher than that for [3H]amlodipine. Brain/plasma concentration ratios (AUCbrain/AUCplasm) for [3H]nimodipine and [3H]PN 200-110 were 3 to 5 times higher than those for [ H]nifedipine and [3H]amlodipine. Further, brain/heart concentration ratios (AUCbrain/AUCheart) for [3H]nifedipine, [3H]nimodipine and [3H]PN 200-110 were about 20 times higher than the ratio for [3H]amlodipine. A significant amount of specific binding in particulate fractions of mouse brain was detected in vivo by intravenous injection of [3H]nifedipine, [3H]nimodipine and [3H]PN 200-110 but not [3H]amlodipine. These data suggest that [3H]nifedipine, [3H]nimodipine and [3H]PN 200-110 are more extensively taken up into brain from plasma than [3H]amlodipine and bind to the receptor sites in brain parenchymal cells in a significant amount in vivo. In conclusion, the present simultaneous measurement of pharmacokinetics and in vivo receptor binding in mouse brain suggests an usefulness of calcium channel antagonists such as nimodipine in the pharmacotherapy of brain diseases.

Abnormality in plasma catecholamines and myocardial adrenoceptors in cardiomyopathic BIO 53.58 Syrian hamsters and improvement by metoprolol treatment

The catecholaminergic neuronal activity and the densities of alpha-1 and beta adrenoceptors and angiotensin II receptors were simultaneously determined in BIO 53.58, a model of idiopathic dilated cardiomyopathy, and F1B control hamsters. Further, we examined the effect of repeated p.o. administration of metoprolol on these biochemical parameters. Compared with F1B control hamsters, there was a significant decrease in Bmax of specific binding of both (-)-[125I]iodocyanopindolol and [3H]prazosin with a marked elevation of plasma catecholamine (mainly norepinephrine and epinephrine) concentrations, in BIO 53.58 hamsters at 11 and 18 weeks of age (severe cardiomyopathic stage), but not at 5 weeks of age. On the other hand, the Bmax value of myocardial [125I]angiotensin II binding in BIO 53.58 hamsters was almost identical to that in F1B hamsters. These results suggest a development of down-regulation of myocardial beta and alpha-1 adrenoceptors because of an increased catecholaminergic neuronal activity with aging in BIO 53.58 hamsters. Repeated p.o. administration of a relatively low dose (1 mg/kg/day) of metoprolol for 7 weeks in 11-week-old BIO 53.58 hamsters caused a significant increase of myocardial (-)-[125I]iodocyanopindolol binding sites with a marked reduction in plasma catecholamine levels; this indicated a significant recovery to the F1B levels. The improvement of these biochemical parameters by metoprolol treatment was also accompanied by a significant decrease in the fibrosis in the heart in BIO 53.58 hamsters. These data suggest that catecholaminergic neurons and adrenoceptors play a part in the development of heart failure in idiopathic dilated cardiomyopathy. Consequently, the present study may provide a further pharmacological basis for the use of beta-1 adrenoceptor antagonists in patients with idiopathic dilated cardiomyopathy.

Pharmacological profile of TH-142177, a novel orally active AT1-receptor antagonist

The pharmacological properties of TH-142177 (N-n-butyl-N-[2'-(1-H-tetrazole-5-yl) biphenyl-4-yl]-methyl-(N-carboxymethyl-benzylamino)-acetamide), a novel antagonist of the angiotensin II (AII) AT1 receptor, were studied in vitro and in vivo, and compared to those of losartan. In the rat isolated aorta, TH-142177 produced parallel shifts to the right of the concentration-response curves for AII-induced contractions without affecting the maximal response (pA2 = 9.07). The inhibitory potency of TH-142177 in the aorta was about three times greater than that of losartan. TH-142177 completely inhibited the specific binding of [125I]AII to AT1 receptor in rat aortic membranes (Ki = 1.6 x 10(-8) M), whereas specific [125I]AII binding to AT2 receptor in bovine cerebellum and human myocardium was not affected by concentrations of TH-142177 up to 10(-5) M. Losartan also inhibited the [125I]AII binding to rat aortic membranes (Ki = 2.2 x 10(-8) M). Following the intravenous administration to anesthetized normotensive rats, TH-142177 dose-dependently inhibited the increase in systolic blood pressure induced by an intravenous bolus injection of AII that was 1.5 times less potent than losartan. Furthermore, the oral administration of TH-142177 to conscious renal hypertensive rats exerted a dose-dependent reduction of systolic blood pressure without significantly effecting the heart rate. TH-142177 was at least three times more potent than losartan. These results demonstrate that TH-142177 is a potent and selective antagonist of AT1 receptors and by oral administration has a long-lasting antihypertensive activity.

End of life decisions in amyotrophic lateral sclerosis: a cross-cultural perspective

In an era where life-sustaining technology offers physicians unprecedented powers to prolong survival in terminal illness, the question of how end of life decisions are made has become a major subject of study and debate. Amyotrophic lateral sclerosis (ALS) is a disease in which physical ability declines while mental capacity most often remains intact. Since most patients with ALS die of respiratory failure, a distinguishing feature of this disease is whether a patient is offered and accepts a chance to go on long-term mechanical ventilation. This unusual feature makes ALS a compelling model for studying end of life decisions in different countries. This paper reviews the literature and presents preliminary data on how end of life decisions in ALS are made in the US, Great Britain, and Japan. We address this issue by examining how cultural differences in truth-telling and informed consent, societal differences in attitudes toward the use of artificial life support, and legal differences in the role and status of advance directives in each country influenced decisions in the following three groups of patients: (1) the mentally competent; (2) mentally incompetent patients who previously completed advance directives when competent; and (3) mentally incompetent patients who have not provided advance guidance about their wishes.

Metabolism of 3,3',4,4'-tetrachlorobiphenyl via sulphur-containing pathway in rat: liver-specific retention of methylsulphonyl metabolite

1. Single doses of 3,3',4,4'-tetrachlorobiphenyl (TCB) were administered intraperitoneally to the male Wistar rat for metabolism studies. 2. Seven sulphur-containing metabolites of TCB were isolated from faeces, in addition to previously reported 4-hydroxy-3,3',4',5-tetrachlorobiphenyl and 5-hydroxy-TCB. Major sulphur-containing metabolites were 5- and 6-methylthio-TCBs, and 6-methylsulphonyl-3-methylthio-3',4,4'-trichlorobiphenyl. 3. The faecal excretions of hydroxy metabolites, methylthio metabolites and unchanged TCB accounted for 7.1, 0.5 and 0.3% of the dose respectively within 4 days after administration. 4. 5-Methylsulphonyl-TCB was detected and selectively retained in liver. The concentration ratio of 5-methylsulphonyl-TCB and unchanged TCB in liver was 1:4. 5. Following administration of 5- and 6-methylsulphonyl-TCBs to rat, 5-methylsulphonyl-TCB was localized in liver, whereas 6-methylsulphonyl-TCB was rapidly biotransformed to 6-methylsulphonyl-3-methylthio-3',4,4'-trichlorobiphenyl and excreted in the faeces.

Role of 3,4-dichlorophenyl methyl sulfone, a metabolite of o-dichlorobenzene, in the changes in hepatic microsomal drug-metabolizing enzymes caused by o-dichlorobenzene administration in rats

2,3- and 3,4-Dichlorophenyl methyl sulfoxides and 2,3- and 3,4-dichlorophenyl methyl sulfones (2,3- and 3,4-DCPSO2Mes) were detected in the urine of rats administered o-dichlorobenzene (o-DCB). After administration of o-DCB to rats, swift decreases were observed in the concentrations of o-DCB in blood, liver, and kidneys, whereas 3,4-DCPSO2Me appeared in blood, liver, kidneys, and adipose tissue. The concentrations of 3,4-DCPSO2Me in the blood and three tissues reached maxima at 24 hr. Both aminopyrine N-demethylase and aniline hydroxylase activities and cytochrome P450 content of hepatic microsomes decreased 24 hr after administration of o-DCB. In contrast, 3,4-DCPSO2Me increased the activities of these enzymes and cytochrome P450 and b5 contents in rat liver microsomes. In both antibiotic-pretreated and bile duct-cannulated rats dosed with o-DCB, the concentrations of 2,3- and 3,4-DCPSO2Mes in blood, liver, kidneys, and adipose tissue were dramatically reduced. These findings suggest that the process of formation of methylsulfonyl metabolites of o-DCB involves biliary secretion of DCPSO2Mes and/or their precursors which will be subjected to metabolism by intestinal microflora. In antibiotic-pretreated rats, the inhibitory effects of o-DCB administration on the activities of aminopyrine- and aniline-metabolizing enzymes and the contents of cytochromes P450 and b5 in hepatic microsomes were greater than those observed in the intact rats. In bile duct-cannulated rats, the decrease in aminopyrine N-demethylase activity after administration of o-DCB was greater than that observed in the intact rats. These findings suggest that the apparent inhibition of drug-metabolizing enzymes by o-DCB is the result of simultaneous contrary effects, namely, the inductive effect of 3,4-DCPSO2Me and the stronger inhibitory effect of an unknown factor(s) on drug-metabolizing enzymes.

Metabolism of the intravenously administered recombinant human basic fibroblast growth factor, trafermin, in liver and kidney: degradation implicated in its selective localization to the fenestrated type microvasculatures

The fate of trafermin (recombinant human basic fibroblast growth factor) was examined after intravenous administration of its iodinated form to rats. Autoradiography at 5 and 30 min after the injection showed that 125I-trafermin is localized specifically in the fenestrated endothelium through binding to heparan sulfate proteoglycans (HSPG) in liver, kidney, adrenal, spleen, hypophysis and bone marrow. Metabolites in the organs were examined at 5 min and 24 h after the injection. More than 73% of radioactivity in liver and kidney was extractable at either time point, and a large majority of the extracted radioactivity was heparin-binding. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) revealed that the substantial radioactivity recovered from liver and kidney can commonly be attributed to a peptide with the same molecular weight as the intact trafermin (B-1, 17.7 kDa) and only three truncated metabolites (B-2, 15.0 kDa; B-3, 7.2 kDa; B-4, 4.2 kDa). Because no truncated metabolites were found in serum, these metabolites seem to be produced inherently in liver and kidney. Although they all retained heparin-binding capacity, only B-1 and B-2 exhibited a stimulatory effect on proliferation of endothelial cells, and these bioactive peptides disappeared completely from liver within a day, indicating a rapid inactivation process in the organs. Taken together with the morphological evidence on autoradiography, it seems most likely that the injected trafermin could be inactivated in sinusoidal endothelial cells, probably through a well-known internalization mechanism of the basic fibroblast growth factor-HSPG complex.

Comparative study on formation of hydroxy and sulfur-containing metabolites from different chlorinated biphenyls with 2,5-substitution in rats

2,4',5-Trichlorobiphenyl (TriCB), 2,3',4',5-tetrachlorobiphenyl (TetraCB), 2,2',4',5,5'-pentachlorobiphenyl (PentaCB), and 2,2',3',4',5,5'-hexachlorobiphenyl (HexaCB) were studied with regard to the fecal excretion and tissue distribution of their metabolites after intraperitoneal injection to rats. Major fecal metabolites were 3- and 4-hydroxy and 3- and 4-methylthio derivatives, the substitution ratios depending largely on the degree of chlorination. As the degree of chlorination increased, hydroxy products were more efficiently excreted, whereas the formation of methylthio metabolites greatly decreased. As a result, the excretion ratios of methylthio and hydroxy products varied with 2.8 for TriCB, 1.3 for TetraCB, 0.04 for PentaCB, and 0.02 for HexaCB. The 3-/4-hydroxy substitution ratios were 0.6 for TriCB, 1.4 for TetraCB, 21 for PentaCB, and 35 for HexaCB, whereas the 3-/4-methythio substitution ratios were 1.2 for TriCB, 0.8 for TetraCB, 0.18 for PentaCB, and 0.12 for HexaCB. The formation rate of 3- and 4-methylthio metabolites from each congener was correlated to the accumulation and distribution of 3- and 4-methylsulfonyl derivatives in tissues. The tissue/blood concentration ratios of methylsulfonyl metabolites showed that the 3-methylsulfonyl derivatives from higher chlorinated biphenyls had a relatively high affinity for liver and adipose tissue, whereas the 4-methylsulfonyl derivatives were selectively retained in the lung in all cases.