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

The effects of acute treatment with delta 9-tetrahydrocannabinol (delta 9-THC) on serum levels of thyrotropin (TSH) and the thyroid hormones triiodothyronine (T3) and thyroxine (T4) were determined in the rat. Intraperitoneal doses of delta 9-THC greater than 3 mg/kg reduced serum TSH levels to less than 10% of control. The ED50 for delta 9-THC was approximately 0.3 mg/kg. After a 10 mg/kg dose of delta 9-THC, the maximum decrease in serum TSH occurred at one hour. Both serum T3 and serum T4 levels were decreased by a single 10 mg/kg delta 9-THC injection with maximal decreases at 6 hr post-injection. The effects of delta 9-THC on the ability of thyrotropin releasing hormone (TRH) to increase serum TSH and T3 were determined. TRH produced a 10-fold increase in serum TSH levels and this increase was unaffected by delta 9-THC pretreatment. Serum T3 levels were slightly increased by TRH and this increase was also unaffected by delta 9-THC. These findings indicate that acute treatment with delta 9-THC results in a decrease in circulating TSH, T3 and T4 levels but has no effect on the pituitary or thyroid response to exogenous TRH.