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Abstract: Pharmacologically active agents were employed to study the mechanisms that control the reduction in levels of acetyl-coA: arylamine N-acetyltransferase activity (NAT) (EC 2.3.1.5) in the rat pineal. Pretreatment of rats with phenoxybenzamine or phentolamine prevented the rapid light-mediated decrease in NAT activity, although pretreatment with yohimbine or atropine did not alter this effect of light. Administration of mecamylamine resulted in a rapid reduction in enzyme activity prior to light exposure. When clonidine was administered intraperitoneally to animals with elevated NAT levels, there was a rapid decrease in enzyme activity, mimicking the effects of light. However, intraperitoneal injections of norepinephrine, methoxamine and phenylephrine into similar groups of animals had no significant effect on enzyme acitivity. When clonidine and norepinephrine were administered intraventricularly, there was a rapid reduction in enzyme activity. On the other hand, intraventricular administration of phenylephrine did not result in reduced enzyme activity. Pretreatment of animals with phenoxybenzamine failed to block the reduction in NAT activity precipitated by low doses of clonidine. This clonidine-mediated reduction in enzyme activity was, however, blocked by yohimbine. When animals were simultaneously exposed to light and administered clonidine, the rapid reduction in NAT activity was affected only when animals were pretreated with both yohimbine and phenoxybenzamine. In contrast to the decrease in pineal NAT activity observed in in vivo preparations, incubation of pineals with clonidine in an organ culture system produced a moderate, but consistent, rise in enzyme activity. These results suggest that stimulation of a receptor with α-adrenergic characteristics mediates the reduction in NAT activity produced by light. Stimulation of yet a second adrenergic-like receptor appears to mediate a reduction in pineal NAT activity precipitated by clonidine. Our evidence suggests that one or both of these receptors are located within the central nervous system. 相似文献
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Human erythrocytes incubated without substrate in the presence of iodoacetate (0.2 mM), vanadate (0.5 mM) and ferricyanide (5 mM) form aqueous membrane leaks of equivalent radii of 0.5-0.8 nm leading to complete colloid-osmotic lysis within 180 min. All three components are indispensable for the effect. Inosine but not glucose markedly enhances the rate of hemolysis. These effects are due to oxidative damage, as indicated by concomitant destruction of polyunsaturated fatty acids and suppression of both effects by radical scavengers. Hemoglobin is not oxidized under these conditions. GSH and membrane SH levels remain almost normal, and no crosslinking or irreversible aggregation of membrane proteins is observed. In the absence of O2 no membrane damage can be observed. It is proposed that radical formation originates from reduction of O2 by NADPH, analogous to processes described in microsomal membranes. NADH seems not to be involved, since leak formation occurs in spite of the blockage of NADH formation by iodoacetate. Vanadate and ferricyanide are probably required to amplify the peroxidative reaction sufficiently to overcome the cellular antioxidative capacity. 相似文献
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OBJECTIVE--To see whether adults with high blood cholesterol concentrations (greater than 6.5 mmol/l) detected by case finding return to their doctor, receive appropriate advice, and report changes in their diet and whether adults found not to have high cholesterol concentrations on case finding are discouraged from changing their diet. DESIGN--Follow up study. SETTING--Seven general practices in the lower Hunter region of Australia. PARTICIPANTS--600 Men and women aged 25-65 who had their blood cholesterol concentrations measured three to four months earlier while attending their general practitioner. Analysis conducted on 552 (92%) who returned follow up postal questionnaires. MEASUREMENTS AND MAIN RESULTS--Of the 125 subjects found to have blood cholesterol concentrations greater than 6.5 mmol/l, 102 (82%) returned to their doctor and 83 of these recalled receiving dietary advice. 93 (75%) Subjects with high concentrations reported changing their diet compared with 72 (46%) subjects with concentrations of greater than 5.5-6.5 mmol/l and 44 (17%) subjects with lower concentrations. Overall 333 (61%) of all respondents who answered reported not changing their diet, the most common reason (nearly half the sample; n = 266) being that their cholesterol concentration was "all right." Adults without high cholesterol concentrations who returned to their doctor were also significantly more likely to recall their doctor saying that they did not need to lower their concentrations (less than or equal to 5.5 mmol/l = 61%; greater than 5.5-6.5 mmol/l = 12%; greater than 6.5 mmol/l = 5%) and significantly less likely to recall receiving dietary advice (less than or equal to 5.5 mmol/l = 13%; greater than 5.5-6.5 mmol/l = 60%; greater than 6.5 mmol/l = 82%). CONCLUSIONS--High risk strategies which require everyone to be tested for high cholesterol concentrations may interfere with population strategies designed to reduce everyone''s dietary intake of fat. 相似文献
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The velocities of single stranded DNA molecules in denaturing polyacrylamide gels during symmetric and asymmetric field inversion were measured at different pulse times and gel concentrations. Under the conditions chosen in our study, pulse times as short as a few milliseconds lead to a retardation of DNA molecules larger than 400 bases. We found that a field inversion with an electric field in the forward direction of about double the strength of that applied in the backward direction is a good compromise between the degree of retardation, the temperature control requirements and the run time of the gel. 相似文献
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Biochemical Plant Responses to Ozone : II. Induction of Stilbene Biosynthesis in Scots Pine (Pinus sylvestris L.) Seedlings 总被引:10,自引:3,他引:7
Formation of the stilbenes pinosylvin and pinosylvin 3-methyl ether, as well as the activity of the biosynthetic enzyme stilbene synthase (pinosylvin-forming), were induced several hundred- to thousandfold in primary needles of 6-week-old pine (Pinus sylvestris L.) seedlings upon exposure to a single pulse of ozone of at least 0.15 microliters per liter. The seedlings required 4 hours of exposure as a minimum for the induction of stilbene biosynthesis when exposed to 0.2 microliters per liter ozone. Both stilbene synthase activity and stilbene accumulation increased with the duration of ozone treatment. The activity of phenylalanine ammonia-lyase and the activity of chalcone synthase, a key enzyme of the flavonoid pathway that uses the same substrates as stilbene synthase, were also stimulated about twofold by ozone. Stilbene biosynthesis appears to represent the first example of a dose-dependent biochemical response to ozone in a conifer species and may serve as a useful biomarker to study stress impacts on pine trees. 相似文献