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Plants with beneficial properties are known in traditional medicine. Nowadays, in spite of widespread availability of synthetic compounds, the search goes towards natural compounds to lower cost and few side effects. The increasing interest in preventive medicine encourages use of nutraceuticals, bioactive compounds of vegetable origin with important nutritional values. Among the medicinal plants, Opuntia ficus-indica (L.) Miller (Family Cactaceae, subfamily Opuntiodeae, Genus Opuntia, subgenus Platyopuntia, species Opuntia ficus-indica (L.) Miller) is widely known for its beneficial properties. The aim of the present review is to stress the major classes of Opuntia components and their medical interest through emphasis on some of their biological effects, particularly those having the most promising expected health benefits and therapeutic impacts on fish and mammals.

The protective effects of the juice of Opuntia ficus indica fruit (prickly pear) against carbon tetrachloride (CCl(4))-induced hepatotoxicity were examined in rats. The animals were treated orally with the juice (3 mL/rat) 2 h after administration of the hepatotoxic agent. Preventive effects were studied by giving the juice (3 mL/rat) for 9 consecutive days. On day 9 the rats received the hepatotoxic agent. Morphological and biochemical evaluations were carried out 24, 48 and 72 h after induction of the hepatic damage. Data show that O. ficus indica fruit juice administration exerts protective and curative effects against the CCl(4)-induced degenerative process in rat liver. Histology evaluation revealed a normal hepatic parenchyma at 48 h; the injury was fully restored after 72 h. Moreover, a significant reduction in CCl(4)-induced increase of GOT and GPT plasma levels is evident; these data are in agreement with the functional improvement of hepatocytes. O. ficus indica fruit juice contains many phenol compounds, ascorbic acid, betalains, betacyanins, and a flavonoid fraction, which consists mainly of rutin and isorhamnetin derivatives. Hepatoprotection may be related to the flavonoid fraction of the juice, but other compounds, such as vitamin C and betalains could, synergistically, counteract many degenerative processes by means of their antioxidant activity.

Nitric oxide (NO) is a gaseous neurotransmitter, which, in adult mammals, modulates the acute hypoxic ventilatory response; its role in the control of breathing in fish during development is unknown. We addressed the interactive effects of developmental age and NO in the control of piscine breathing by measuring the ventilatory response of zebrafish (Danio rerio) adults and larvae to NO donors and by inhibiting endogenous production of NO. In adults, sodium nitroprusside (SNP), a NO donor, inhibited ventilation; the extent of the ventilatory inhibition was related to the pre-existing ventilatory drive, with the greatest inhibition exhibited during exposure to hypoxia (P O2 =5.6 kPa). Inhibition of endogenous NO production using L-NAME suppressed the hypoventilatory response to hyperoxia, supporting an inhibitory role of NO in adult zebrafish. Neuroepithelial cells (NECs), the putative oxygen chemoreceptors of fish, contain neuronal nitric oxide synthase (nNOS). In zebrafish larvae at 4 days post-fertilization, SNP increased ventilation in a concentrationdependent manner. Inhibition of NOS activity with L-NAME or knockdown of nNOS inhibited the hypoxic (P O2 =3.5 kPa) ventilatory response. Immunohistochemistry revealed the presence of nNOS in the NECs of larvae. Taken together, these data suggest that NO plays an inhibitory role in the control of ventilation in adult zebrafish, but an excitatory role in larvae.