Nigella sativa L., commonly known as black seed, belongs to the botanical family Ranunculaceae. It has being used in countries bordering the Mediterranean Sea, Pakistan, India and Iran, as a natural remedy for over 2000 years . Black seed components display a remarkable array of biochemical, immunological and pharmacological actions, including bronchodilatory , anti-inflammatory , antibacterial , hypoglycaemic  and immunopotentiating effects .
N. sativa extract has been shown to possess immunopotentiating, anti-oxidant, anti-tumoral, and anti-diabetic properties. The oil of N. sativa exhibits analgesic and anti-inflammatory effects in rats. Most of these properties have been attributed mainly to the quinone constituents of N. sativa, of which thymoquinone is the main active ingredient of the volatile oil isolated from the black seeds. Thymoquinone has been shown to possess strong antioxidant properties and to suppress the expression of inducible NO synthase in rat macrophages .
Many studies have also examined the anti-diabetic effect of N. sativa in diabetic animal models. Aside from the effect of its crude aqueous extract to restore glucose homeostasis. N. sativa petroleum ether extract significantly lowered fasting plasma levels of insulin and triglycerides and normalized HDL-cholesterol. In this latter study by Le and collaborators, N. sativa was also shown to enhance liver cell insulin sensitivity [1, 3, 7].
β cell defect and insulin resistance are essential features of non-insulin-dependent diabetes mellitus (NIDDM) and both features are the focus of intensive investigations. In this context, plants are source of many biochemical substances that present interesting therapeutic properties. Some plants with anti-diabetic properties have been in use in many Middle Eastern countries as a natural remedy for diabetes in traditional medicine; N. sativa is one of these plants. It has a great potential in the treatment of diabetic animals because of its combined hypoglycemic [2, 4, 7].
In earlier experiments we have shown that streptozotocin, given at 45 days post-infection (dpi) affected the morphology of the reproductive organs of male and female worms and lowered the number of viable eggs in the intestine and the amount of eggs in the feces. However, the morphological changes were caused directly by the drug [5–7].
STZ, an antibiotic produced by Streptomyces achromogenes, is the most commonly used agent in experimental diabetes. The mechanism by which STZ destroys β-cells of the pancreas and induces hyperglycemia is still unclear. Many actions have been attributed to STZ that are similar to those that have been described for the diabetogenic action of alloxan, including damage to pancreatic β-cell membranes and depletion of intracellular nicotinamide adenine dinucleotide (NAD) in islet cells. In addition, STZ has been shown to induce DNA strand breaks and methylation in pancreatic islet cells [8, 9]. Its diabetogenic action has been ascribed to an increase in the intracellular methylation reaction, DNA strand breaks, and the production of nitric oxide (NO) and free radicals.NO is involved in pancreatic destruction, where the interaction between NO and ROS modulates oxidative damage. STZ can be used to induce different types of diabetes. For example, to produce experimental models of Type 1 diabetes, mice are treated with high doses of STZ, which depletesb -cells [8, 10, 11].
It is known that people suffering from diabetes mellitus are related to higher incidence of bacterial and fungal infections. Diabetes Mellitus is a chronic disease which affects the metabolism of proteins, carbohydrates and lipids. The major characteristic is hyperglycaemia as a consequence of abnormal secretion of insulin in the pancreas (type I) or inefficient action of insulin in the target tissues (type II) . Type 2 diabetes is sharply increasing globally, including in many parts of the developing world, in major part as a consequence of the worldwide “epidemic” of obesity. For centuries, prior to and after the discovery of insulin, medicinal plants have been used to normalize glycemia in diabetic patients. This disorder promotes adverse effects in all organic systems. Diabetes exerts a negative action on the neuroendocrine axis and those effects can enhance the action of diabetes on other organs that are dependent on the axis .
Diabetics and experimental animal models of diabetes exhibit high oxidative stress due to persistent and chronic hyperglycemia, which may deplete the activity of the anti-oxidative defense system and promote the generation of free radicals . Streptozotocin (STZ) is frequently used to induce diabetes in experimental animals through its toxic effects on pancreatic β -cell  and as a potential inducer of oxidative stress. It has been reported that diabetes induced by STZ is the best characterized system of xenobiotic-induced diabetes and the commonly used model for the screening of anti-hyperglycemic activities .
The present study was designed to investigate the mechanism(s) of the hypoglycaemic effect of N. sativa hydroalcholic extract, especially with respect to hepatic gluconeogenesis, and to investigate its possible streptozotocin effects in diabetic rats.