Abstract
Background:
Polycystic ovarian syndrome (PCOS) is characterized by hyperandrogenism, anovulation, and abnormal polycystic ovarian morphology.

Aim:
This study aimed to investigate the effect of Nigella sativa oil extract (NSOE) on ovarian histopathology, reproductive hormone irregularities, and body weight changes in letrozole-induced PCOS in rats.

Methods:
Thirty female albino rats were divided equally into 5 experimental groups; as negative control (NC), positive control (PC), and three different NSOE treatment groups. Letrozole (LTZ) was used to induce PCOS in all groups, except NC. Once PCOS was confirmed after 21 days, the rats were then received distilled water (NC and PC), or treated with either 30, 60, and 90 mg/kg of NSOE, respectively. On day 52, blood was collected, serum was obtained and sent for hormonal analysis to measure serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (TS), and estradiol (EST). Whereas ovaries were excised for histopathological assessments. Body weights were also recorded on days 0, 21, and 52.

Results:
LTZ causes an increase in LH and TS levels with multiple cystic, high follicular atrophy, and high stromal depletion in ovaries, together with an increase in body weight, confirming successful PCOS induction. While, treatment with NSOE decreased TS and LH levels, increased FSH and EST, and improved ovarian histopathology by reduced cyst formation and decreased number of follicular atrophy and stromal depletion. Also, body weight decreased in a dose dependent manner.

Conclusion:
NSOE treatments markedly improved the hormonal imbalance produced by LTZ, as well as decreased ovarian cyst, restored folliculogenesis, improved stromal thickness, and reduced body weight gain, especially at the HD.

Key words: Extracted oil; Histopathological study; Hormonal assay; PCOS; Plant metabolite.