In vitro effect of Dilazep on the release and metabolism of arachidonic acid (AA) in human platelets was studied. Dilazep reduced in dose-dependent manner platelet aggregation and thromboxane B₂ (TXB₂) formation when stimulated by adenosine diphosphate, collagen and epinephrine. Dilazep decreased thrombin-induced release of [¹⁴C]arachidonic acid ([¹⁴C]AA) from platelets prelabeled with [¹⁴C]AA. The conversion of [¹⁴C]AA to cyclooxygenase metabolites was reduced by the addition of Dilazep, while that to 12-lipoxygenase metabolite was rather increased. Adenosine 3', 5'-cyclic monophosphate and guanosine 3', 5'-cyclic monophosphate levels in washed human platelets were not affected by the addition of Dilazep. These results suggest that the decreased TXB₂ formation by Dilazep may be ascribed to the impairment of AA release from plateler membrane phospholipids and the reduced conversion of released AA to TXA₂.

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The two spectrally distinguishable bound forms of 2-(4'-hydroxyphenylazo) benzoic acid (HABA) on bovine serum albumin (BSA), i.e, the azo and hydrazone forms, were suggested to form ion pairs with basic amino acid residues in our previous study. Arginine (Arg), lysine (Lys), tyrosine (Tyr) and tryptophan (Trp) were modified to estimate the amino acid residues participating in the formation of an ion pair with HABA. Decrease of the binding of only hydrazone form was observed following mocification of Arg residues. The modification of Lys, Tyr and Trp residues caused no decrease in binding to either form. However, the induced circular dichroism (CD) spectra of HABA bound to N- and Oacetylated BSA were reversed at 360 and 440 nm, respectively. But two bands of these spectra were capable of taking on the same shape of the spectra of native BSA only by Odeacetylation. The induced CD spectra of bound HABA by Trp modified BSA changed as if the bound amounts of the azo form were increased. The binding sites of the azo form may possibly be situated in the vicinity of Trp 212 on the tertiary structure.

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The initial rate of uptake of bromosulfophthalein (BSP) by isolated rat hepatocytes analyzed as a function of the unbound concentration of BSP was greater in the presence of albumin than in its absence, though the presence of albumin in the medium apparently decreased the uptake of BSP by hepatocytes analyzed as a function of the total concentration of BSP. This suggests that the uptake of BSP by isolated rat hepatocytes in the presence of albumin is not only dependent on the unbound concentration of BSP, but also is driven by the bound fraction of BSP.

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The mechanisms of renal damage produced by sulfanilamide and phenacetin were studied. N-Hydroxyphenacetin, 4-hydroxylaminobenzenesulfonamide (4-HABSA) and p-aminophenol were established to be nephrotoxic metabolites. As well as N-hydroxylase activity of sulfanilamide, that of phenacetin in kidney microsomes of rats was increased about 4 times by pretreatment with 3, 4, 5, 3', 4'-pentachlorobiphenyl (PenCB) which is a potent inducer of cytochrome P-448. Parallel to this enzyme induction, pretreatment with PenCB enhanced the nephrotoxicity of phenacetin and sulfanilamide in rats. On the other hand, the formation of p-aminophenol from phenacetin was also confirmed in rat kidney in vitro. These results suggested that 4-HABSA, N-hydroxyphenacetin and p-aminophenol formed in kidney play an important role in the renal damage produced by sulfanilamide and phenacetin.

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Toxicity of local anaesthetics on chick myogenic cells (mononucleated myoblasts and multinucleated myotubes) in culture was examined. Following treatment with the drugs, myogenic cells showed some morphological changes and finally detached from the culture dishes. In most cases, the toxic effect was estimated by the amount of cells detached quantitatively. The indices used to show the amount of cells were the deoxyribonucleic acid (DNA) and creatine kinase activity content of mono- and multinucleated cells remaining on the dishes, respectively. Dibucaine was more toxic than bupivacaine, mepivacaine, tetracaine and procaine, and was examined in detail. The toxicity was dependent on its concentration, pH and temperature of the reaction medium in both mono- and multinucleated cells, and paralleled the concentration of uncharged form of the drug, suggesting that this form in external medium was actually toxic.

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We examined the intestinal absorption of ursodeoxycholic acid (UDC), glycoursodeoxycholic acid (GUDC) and tauroursodeoxycholic acid (TUDC) using an everted gut sac technique. UDC was absorbed throughout rat small intestine almost to the same extent. Absorption of both GUDC and TUDC, however, varied between jejunum and ileum. Absorption of these conjugated bile acids in the jejunal segments was less than that of UDC. While, absorption of GUDC and TUDC in the terminal ileum was more efficient than UDC. Although 2, 4-dinitrophenol had no effect on the jejunal uptake, ileal uptake of these three bile acids was inhibited by 2, 4-dinitrophenol.

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The responses of Purkinje cell dendrites to iontophoretically applied L-glutamate, L-aspartate, kainate and quisqualate were intradendritically recorded in the in vitro slice preparation of guinea pig cerebellum. Kainate and quisqualate were found to be very potent excitants, while N-methyl-DL-aspartic acid (NMDLA) caused little or no effect on Purkinje cell dendrites. Thus, kainate and quisqualate receptors were certainly present, while there appeared to be no NMDA-preferring receptor in Purkinje cell dendrites in the guinea pig cerebellum. The effects of several antagonists such as 2-amino-5-phosphonovaleric acid (APV), γ-D-glutamylglycine (γ-DGG), NMLA and glutamic acid diethylester (GDEE) etc. on responses to L-glutamate and L-aspartate were compared in order to search for potent and selective antagonists capable of differentiating the response to L-glutamate from that to L-aspartate. Among these compounds tested, APV andγ-DGG were found to be potent and selective antagonists to the L-aspartate-induced depolarization without affecting responses to L-glutamate. These two agents may be useful, at least in the in vitro study, to the identification of the excitatory amino acid which function as a neurotransmitter at the synapses formed by the climbing fiber or parallel fiber with Purkinje cell dendrites.

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Hypotensive activities of 11 synthetic derivatives of platelet activating factor (PAF) were examined and compared with their activities to produce endothelium-related relaxation of isolated rat thoracic aorta. The derivatives showed variety of hypotensive activities ; some of the derivatives were more potent than natural PAF and some were virtually inactive compared to PAF. However, all of the compounds tested exhibited exactly the same activities to produce endothelium-related vasodilation. These results confirmed our previous view that the PAF-induced hypotension is not solely due to the endothelium-related vascular relaxation observed in vitro.

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4-[3-(tert-Butylamino)-2-hydroxypropoxy]-N-methylisocarbostyril hydrochloride (N-696) is new β-adrenoceptor blocking drug with direct vasodilatory activity, and may be classified into the fourth generation. Antihypertensive effects of N-696 were studied for 12-weeks in spontaneously (SHR), two kidney, one clip (CLIP), and deoxycorticosterone-salt (DOC) hypertensive rats. Propranolol (PPL) was used as the reference drug. In indirect blood pressure (BP) determination at the tail, milder prewarming condition was employed to observe antihypertensive effects clearly. Rats were prewarmed in rat holders on a hot plate for 30-60 min. Surface temperature of the hot plate was 35-45°C. N-696 (20 mg/kg per day p.o.) and PPL (100 mg/kg per day, p.o.) treatments significantly decreased heart rate (HR) and maximum BP determined indirectly in SHR rats, even at the early stage of the experiments. These antihypertensive effects were shown also by mean BP determined directly at the 12th week. N-696 and PPL treatments showed no significant antihypertensive effects in CLIP rats, and slight antihypertensive effects in DOC rats. N-696 treatments showed a tendensy to decrease plasma renin concentration (PRC) in SHR and DOC rats, whereas PPL treatments significantly decreased PRC in these hypertensive rats. N-696 and PPL treatments prevented nephrosclerosis and vascular lesions in SHR and DOC rats only slightly.

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The mechanism of the intestinal transport of sulfonamides and the effect of chlorpromazine (CPZ) on it were studied using rat everted intestine in vitro. Sulfamethoxazole (SMZ) was accumulated in the serosal solution in the everted sac obeying the pH partition theory, while sulfisoxazole (SIX) was not accumulated despite the presence of the pH difference between the serosal and mucosal solutions. The reason was suggested that the microclimate pH on the mucosal surface of the intestine so decreased the amount of the unionized molecules of SIX that the transport rate of SIX was decreased to show no accumulation in the serosal solution within the sampling period. CPZ as well as metabolic inhibitors blocked the SMZ accumulation by inhibiting the growth of the pH difference. This effect was caused by the inhibition of the serosal alkalinization.

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