Extracts of plants from the Malaysian rainforest and other fragile habitats are being researched intensively for identification of beneficial biological actions, with assessment of antioxidant behavior being a common component of such assessments. A number of tests for antioxidant behavior are used, with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reduction activity potential (FRAP) assays often being used in parallel, and also with measurement of total phenolics content (TPC) as a surrogate marker for antioxidant capacity. The present study investigated the possible redundancy in using all three assays to determine antioxidant capacity in 92 extracts obtained from 27 plants from the Malaysian rainforest. The results demonstrated that the assays displayed a high (R ≥ 0.82) and significant (P < 0.0001) correlation with one another, indicating a high level of redundancy if all three assays are used in parallel. This appears to be a waste of potentially valuable plant extracts. Because of problems with the FRAP assay relating to color interference and variable rates of reaction point, the DPPH assay is the preferred assay in preliminary screening of extracts of plants from the Malaysian rainforest.

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1 In this study we compared the vasoconstrictor activity of melatonin in rat isolated tail artery using two dierent recording systems, the Halpern pressure myograph and the Halpern-Mulvany wire myograph, with the view to determining a reliable method for obtaining pharmacological data on vascular melatonin receptors. In addition, we characterized the melatonin receptor in this preparation, using analogues of melatonin, and examined the activity of various naphthalenic derivatives with biological activity in non-vascular models of melatonin receptors. 2 Using the Halpern pressure myograph, cumulative addition of melatonin (0.1 nM to 1 mM) produced direct vasoconstriction (19.3+6.4% reduction in lumen diameter, n=5) in ®ve of 11 pressurized segments, with pEC 50 of 9.14+0.17. Similarly, non-cumulative application of melatonin caused vasoconstriction (19.7+4.6% reduction in lumen diameter, n=7) in seven of 20 preparations examined with pEC 50 of 8.74+0.26. The selective alpha 2 -adrenoceptor agonist, UK-14304 (5-bromo-6-[2-imidazolin-2-ylamino]-quinoxaline bitartrate), produced vasoconstriction in all`melatonin-insensitive' preparations.3 Melatonin (0.1 nM to 1 mM) failed to elicit isometric contractions of tail artery segments in the Halpern wire myograph, but produced concentration-dependent potentiation of electrically-evoked, isometric contractions (maximum eect of 150 ± 200% enhancement) when applied either noncumulatively (seven of seven preparations) or cumulatively (four of seven preparations). The pEC 50 value of melatonin (non-cumulative) was 8.50+0.10 (n=7) which was not dierent from that obtained in the pressure myograph. All further experiments were conducted using a non-cumulative protocol against electrically-evoked, isometric contractions. 4 Based on the pEC 50 values for the melatonin analogues examined, the pharmacological pro®le for the enhancement of electrically-evoked contractions was 2-iodomelatonin46-chloromelatonin5(7)-AMMTC 5 S216345melatonin5S200984S202425S2030446-hydroxymelatonin4S209324 (+) -AM-MTC4N-acetyl-5-HT. Our data suggests the vascular receptor belongs to the MEL 1 -like subtype. All the indole-based analogues of melatonin, 2-iodomelatonin, (7)-AMMTC, (+)-AMMTC, S20932, 6-chloromelatonin, 6-hydroxymelatonin and N-acetyl-5-HT, behaved as full agonists. All the naphthalenic derivatives examined, S21634, S20098, S20242 and S20304 behaved as partial agonists relative to melatonin. 5 The naphthalenic-based antagonists, S20928 and S20929, did not modify electrically-evoked, isometric contractions of the tail artery, but produced a parallel, rightward displacement of the melatonin concentration-response curve. Based upon the eect of 1 mM S20928 and S20929, the estimated pK B values for these antagonists were 7.18+0.25 (n=4) and 7.17+0.25 (n=5), respectively. 6 We demonstrated that enhancement of electrically-evoked, isometric contractions of the rat isolated tail artery (using the Halpern-Mulvany wire myograph) is a simple and reproducible model for assessing the activity of putative a...

1 In this study reverse transcriptase-polymerase chain reaction (RT ± PCR) has been used to identify mt 1 and MT 2 receptor mRNA expression in the rat tail artery. The contributions of both receptors to the functional response to melatonin were examined with the putative selective MT 2 receptor antagonists, 4-phenyl-2-propionamidotetraline (4-P-PDOT) and 2-benzyl-N-pentanoyltryptamine. In addition, the action of melatonin on the second messenger cyclic AMP was investigated. 2 Using RT ± PCR, mt 1 receptor mRNA was detected in the tail artery from seven rats. In contrast MT 2 receptor mRNA was not detected even after nested PCR. 3 At low concentrations of the MT 2 selective ligands, neither 10 nM 4-P-PDOT (pEC 50 =8.70+0.31 (control) vs 8.73+0.16, n=6) nor 60 nM 2-benzyl-N-pentanoyltryptamine (pEC 50 =8.53+0.20 (control) vs 8.83+0.38, n=6) signi®cantly altered the potency of melatonin in the rat tail artery. 4 At concentrations non-selective for mt 1 and MT 2 receptors, 4-P-PDOT (3 mM) and 2-benzyl-Npentanoyltryptamine (5 mM) caused a signi®cant rightward displacement of the vasoconstrictor e ect of melatonin. In the case of 4-P-PDOT, the estimated pK B (6.17+0.16, n=8) is similar to the binding a nity for mt 1 receptor. 5 Pre-incubation with 1 mM melatonin did not a ect the conversion of 6 Based on the above ®ndings, we conclude that melatonin receptor on the tail artery belongs to the MT 1 receptor subtype, and that this receptor is probably independent of the adenylyl cyclase pathway.