Background: Holothuria scabra is the potential source of terpene with high antioxidant capacity and one of the most valuable species in the trade. Results: The results indicated that antioxidant activity of crude methanol extracts and three pure compounds, Friedelin, 3-Hydroxybenzaldehyde and 4-Hydroxybenzaldehyde, from sea cucumber was determined using DPPH, Folin-Cioccalteau reagent. The results indicated the total phenolic contents at 30.52.28 ± 0.21 GAE/g dry weight equivalent and the effective concentration (EC 50) value were found to be 33.77 ± 0.24, 14.63 ± 0.01, 14.62 ± 0.01 and 14.78 ± 0.11 mg/ml whole body of Holothuria scabra, Friedelin, 3-Hydroxybenzaldehyde and 4-Hydroxybenzaldehyde, respectively. Conclusion: In conclusion, the methanol extract and pure compounds of whole body parts of sea cucumber showed the highest antioxidant activity with EC 50 value of 33.77 ± 0.24, 14.63 ± 0.01, 14.62 ± 0.01 and 14.68 ± 0.11 mg/ml. It also showed the highest total phenolic content at 30.52 ± 0.21 GAE/g dry weight.

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In the present study, the distribution and dynamic expression of serotonin and dopamine in the nervous system and ovary of the sea cucumber, Holothuria scabra, during different ovarian stages were investigated. We found that serotonin-immunoreactivity was more intense in the neurons and neuropils of the outer ectoneural part, the inner hyponeural part, and the wall of hyponeural canal of radial nerve cord during the mature stages of ovarian cycle, whereas dopamine-immunoreactivity was detected at a higher intensity in these tissues during the early stages. Both neurotransmitters were detected in the ectoneural part of the nerve ring. In the ovary, serotonin intensity was more intense in the cytoplasm of late oocytes, while dopamine-immunoreactivity was more intense in the early stages. The changes in the levels serotonin in the radial nerve cord and oocytes are incremental towards the late stages of ovarian maturation. In contrast, dopamine levels in the nervous tissues and oocytes were more intense in early stages and became decremental towards the late stages. These findings suggest that serotonin and dopamine may have opposing effects on ovarian development in this sea cucumber species.