Introduction: Diabetes mellitus (DM) is a chronic metabolic disorder associated with vascular complications, particularly cardiovascular disease. The use of natural compounds such as copaiba oil (Copaifera spp.) has gained attention due to its antioxidant and anti-inflammatory properties. This study aimed to evaluate the effects of copaiba essential oil (OEC) on the thoracic aorta of streptozotocin (STZ)-induced diabetic rats.

Methods: Forty male Wistar rats were randomly assigned to five groups: non-diabetic control (CT), non-diabetic + OEC 200 mg/kg (C200), diabetic control (DC), diabetic + OEC 100 mg/kg (D100), and diabetic + OEC 200 mg/kg (D200). Diabetes was induced using STZ (65 mg/kg, i.v.). OEC was administered orally for 20 days. Body weight, glycemia, heart weight, and thoracic aorta morphology were analyzed. Histological sections were stained and assessed for intima-media thickness and volume density (Vv%) of smooth muscle and collagen. ANOVA followed by Tukey’s test was used for statistical analysis (p<0.05).

Results: Diabetic groups showed significant weight loss and hyperglycemia compared to controls (p<0.0001). Treatment with OEC did not reverse these metabolic changes. No significant differences were found in intima-media thickness or Vv% of collagen and smooth muscle between diabetic groups. However, OEC-treated diabetic groups showed a non-significant trend toward preserved intima-media thickness.

Conclusions: OEC (100 and 200 mg/kg) did not significantly improve glycemic control or vascular morphology in diabetic rats within 20 days. Nevertheless, its safety in normoglycemic animals and possible protective trend on vascular structure support further long-term studies at higher doses.