Oenothera biennis, commonly called evening primrose, is a member of evening primrose family (Onagraceae). It is found in fields, roadsides, prairies and waste places in the United States and south Canada (Gleason, Cronquist, 1963). O. biennis is a biennial with large yellow flowers. In its first year, it forms a rosette of basal leaves. A tall flowering stem is formed in the second year. Plants produce one or two new flowers every evening (Wit, 1967).
The plant has been used as an ornamental, food source, and medicinal herb. It was introduced into gardens in the eighteenth century as a fleshy root-vegetable (yellow lamb's lettuce) and as an ornamental. Since then, it has been used as a medicinal agent. The first year taproot is edible. It is cultivated for food in Germany where it is called German rampion (Elliott, 1976). O. biennis has attracted attention as a medicinal plant as the oil of the seed contains high concentrations of gamma-linolenic acid. As a result, O. biennis has demonstrated value in treating conditions like eczema, asthma, rheumatoid arthritis, breast problems and metabolic disorders (Caffey, 1993).
Due to its content of gamma-linolenic acid, Oenothera biennis has been shown to be effective in reducing blood lipid concentrations. Sugano, et al, (1986) found that male rats given high-cholesterol diet with O. biennis oil showed hypocholesterolemic effect. In a clinical trial O. biennis oil lowered low density lipoprotein in hypercholesterolemic patients (Ishikawa, et al, 1989). O. biennis oil brought favorable changes of HDL-cholesterol and platelet adhesiveness in insulin-dependent diabetes after two months (Uccella, et al, 1989). In an experiment with rats given a high cholesterol diet, linoleic acid and gamma-linolenic acid obtained from both wild plant and cultivated plant of O. biennis inhibited an increase of serum total cholesterol and very low density lipoprotein + intermediate density lipoprotein + low density lipoprotein (Fukushima, et al, 1997). An experiment performed using hyperlipemic diet supplemented with O. biennis oil showed increased antithrombotic capacity of the aortic endothelium and decreased vascular thrombogenesis (formation of blood clots inside blood vessels) caused by the hyperlipemic diet (Villalobos, et al, 1998). In another experiment when O. biennis oil was given to rats with hyperlipidemia due to high lipid diet, the ratio of high density lipoprotein cholesterol and total cholesterol and lecithin-cholesterol acyltransferase activity decreased (Guo, et al, 2001). Rats aged 24 weeks given diet containing O. biennis oil and 0.5% cholesterol for 15 weeks showed an inhibition of increase of serum total cholesterol and very low density lipoprotein + intermediate density lipoprotein + low density lipoprotein-cholesterol concentrations (Fukushima, et al, 2001).
Oenothera biennis oil is of value in treating skin conditions. When O. biennis oil was given orally to children with atopic eczema, the clinical condition improved dramatically in 4 weeks of therapy and this improvement was maintained during treatment of 20 weeks (Biagi, et al, 1988). Clinical study was performed assuming the fact that abnormalities in plasma composition of essential fatty acids may be associated with the etiology of pruritis in patients undergoing hemodialysis. The patients given Oenethora biennis oil showed a significant improvement in the skin sores and an increase of dihomo-gamma-Linolenic acid, a precursor of anti-inflammatory prostaglandin E1 (Yoshimoto-uruie, et al, 1999). In clinical trial, O. biennis oil as water-in-oil emulsion relieved symptoms in atopic dermatitis (Gehring, et al, 1999).
Gamma-linolenic acid improves functioning of immune system. Gamma-linolenic acid in the form of O. biennis oil affected rat serum cytokines decreasing interferon-gamma and monocyte chemotactic protein-1 (Dirks, et al, 1998). Diets containing gamma-linolenic acid in the form of O. biennis oil attenuated bleomycin-induced lung fibrosis in hamsters Ziboh, et al, 1997). When gamma-linolenic acid was given as O. biennis oil in diets to male Brown-Norway rats, total immunoglobulins IgG and IgE increased (Matsuo, et al, 1996).
Oenothera biennis oil proved useful in old age when delta-6-desaturation (delta-6-desaturate acts in the metabolism of linoleic and alpha-linolenic acid) activity decreases (Biagi, et al, 1991; Charnock, 2000). Experiments were performed to see the effect of O. biennis oil on antioxidant potential, given with hyperlipemic diet to New Zealand rabbits. It was observed that glutathione peroxidase activity reduced and the activities of glutathione reductase and transferase increased (De La Cruz, et al, 1999).
In clinical trial on rheumatoid arthritis with gamma-linolenic acid in the form of O. biennis oil, it was seen that the patients were improved with no adverse reaction (Leventhal, et al, 1993; Belch & Hill, 2001). Cytokines help form free radicals responsible for development and maintenance of rheumatoid arthritis. Some prostaglandins suppress cytokine formation. So O. biennis oil, which suppliesgamma-linolenic acid, precursor of prostaglandin E1, ameliorates arthritic symptoms (Darlington & Stone, 2001).
Platelet aggregation was diminished when O. biennis oil was given with atherogenic diets to New Zealand rabbits (De La Cruz, et al,1997).
Gamma-linolenic acid given as Oenothera biennis oil corrected sciatic motor nerve conduction velocity that is the speed of impulse along the nerve increases and sciatic blood flow in streptozotocin-diabetic rats (Dines, et al, 1995). The study on the interval between oral intake of O. biennis oil and its effect in peripheral nerves of streptozotocin diabetes rats suggested that the neuroactivity of O. biennis is due to its metabolic products synthesized in the body (Julo, 1996). O. biennis oil corrects deficient nitric oxide production responsible for development of neural ischaemia in experimental diabetic rats (Omawari, et al, 1996). Gamma-linolenic acid given as O. biennis oil improves vasodilator eicosanoid synthesis correcting nerve blood flow and increase nerve conduction velocity, thereby curing / or preventing diabetic neuropathy (Cameron, Cotter, 1997). Experiments were performed to see how gamma-linolenic acid, contained in O. biennis oil, prevents sciatic nerve conduction deficit in diabetic rats. The result showed that this effect was not due to nerve phospholipid fatty acid profile, sugar and polyol content, Na+-K+-exchange ATPase activity and ouabain binding; but possibly by its role as a precursor of vasodilatory prostaglandins (Head, et al, 2000).
Linoleic acid and gamma-linolenic acid when increased in diet in the form of Oenothera biennis oil showed diminished vascular reactivity to the vasopressor stimuli of renin and angiotensin II. This is due to endogenous biosynthesis of prostaglandins in vessel wall and kidney as linoleic acid and gamma-linolenic acid act as biosynthetic precursors of prostaglandins (Scholkens, et al, 1982). O. biennis oil, when introduced via an intragastric catheter significantly lowered systolic and diastolic blood pressure in pregnant animals (Zielinski, et al, 1994).
The onset and complications of diabetes such as neuropathy, atherosclerosis, and retinopathy were prevented in rats fed on O. biennis after streptozotocin injection (Fang, et al, 1997; Garland, et al, 1997). Streptozotocin selectively destroys beta-islet cells of the pancreas and causes diabetes in animals (Melmon, et al, 1992).
Oenothera biennis oil decreases urinary calcium excretion in normal and streptozotocin-diabetic rat suggesting that diet supplemented by gamma-linolenic acid may be used for treatment of idiopathic hypercalciuric urolithiasis (Tulloch, et al, 1994).
Experiments performed by administering Oenothera biennis oil showed that it produced a significant inhibition of gastric mucosal damage induced by pylorus ligation, non-steroidal anti-inflammatory drugs, hypothermic restraint stress and necrotizing agents (al-Shabanah, 1997).
O. biennis oil was recommended as a first line specific treatment for Oriental women with disturbing cyclical mastalgia that is mastalgia developing during periods (Cheung, 1999).
A study performed on mice showed that Oenothera biennis oil inhibited the formation of papilloma to a significant degree only during the promotion stage (Ramesh & Das, 1998). Feeding of O. biennis oil slowed down most of the mammary gland adenocarcinoma in mice suggesting that the oil may be of value in nutritional approaches to overcome mammary gland tumors (Munoz, et al., 1999).
Gamma-lenolenic acid as O. biennis oil was used for therapy of bronchial asthma and was found that it can replace bronchodilative beta2 agonist when given with steroid hormones (Hassig, et al., 2000).
Oenothera biennis oil was used to differentiate between schizophrenia and temporal lobe epilepsy, in those schizophrenic cases which were refractory to conventional drugs. This was due to the presence of gamma-linolenic acid and linoleic acid in the diet (Vaddadi, 1981).
Thus, extracts of Oenothera biennis have been shown to be beneficial in treating a wide variety of conditions, particularly hyperlipemia, eczema, rheumatoid arthritis, complications of diabetes, cyclical mastalgia and idiopathic hypercalciuric urolithiasis.
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