The effects of δ 9-tetrahydrocannabinol on serum thyrotropin levels in the rat

Abstract

The effects of acute treatment with δ 9-tetrahydrocannabinol (δ 9-THC) on serum levels of thyrotropin (TSH) and the thyroid hormones triiodothyronine (T 3) and thyroxine (T 4) were determined in the rat. Intraperitoneal doses of δ 9-THC greater than 3 mg/kg reduced serum TSH levels to less than 10% of control. The ED50 for δ 9-THC was approximately 0.3 mg/kg. After a 10 mg/kg dose of δ 9-THC, the maximum decrease in serum TSH occurred at one hour. Both serum T 3 and serum T 4 levels were decreased by a single 10 mg/kg δ 9-THC injection with maximal decreases at 6 hr post-injection. The effects of δ 9-THC on the ability of thyrotropin releasing hormone (TRH) to increase serum TSH and T 3 were determined. TRH produced a 10-fold increase in serum TSH levels and this increase was unaffected by δ 9-THC pretreatment. Serum T 3 levels were slightly increased by TRH and this increase was also unaffected by δ 9-THC. These findings indicate that acute treatment with δ 9-THC results in a decrease in circulating TSH, T 3 and T 4 levels but has no effect on the pituitary or thyroid response to exogenous TRH.