Effects of Δ9-tetrahydrocannabinol (THC) vapor inhalation in Sprague-Dawley and Wistar rats

A novel inhalation system based on e-cigarette technology has been recently shown to produce hypothermic and anti-nociceptive effects of {Delta}9-tetrahydrocannabinol (THC) in rats. Indirect comparison of some prior investigations suggested differential impact of inhaled THC between Wistar (WI) and Sprague-Dawley (SD) rats, thus this study was conducted to directly compare the strains. Groups (N=8 per strain) of age matched male SD and WI rats were prepared with radiotelemetry devices to measure temperature and then exposed to vapor from the propylene glycol (PG) vehicle or THC (25, 100, 200 mg/mL of PG) for 30 or 40 minutes. Additional studies evaluated plasma THC levels and anti-nociceptive effects after THC inhalation as well as the thermoregulatory effect of intraperitoneal injection of THC (5-30 mg/kg). Hypothermic effects of inhaled THC was more pronounced in SD rats however plasma levels of THC were identical across strains under either fixed inhalation conditions or injection of a mg/kg equivalent dose. Strain differences in hypothermia were even more pronounced after i.p. injection of THC with SD rats exhibiting dose-dependent temperature reduction after 5 or 10 mg/kg, i.p. and the WI rats only exhibiting significant hypothermia after 20 mg/kg, i.p. The anti-nociceptive effects of inhaled THC (100, 200 mg/mL) did not differ significantly across the strains. These studies confirm an insensitivity of WI rats, compared with SD rats, to the hypothermia induced by THC following inhalation conditions that produced identical plasma THC and anti-nociception. Thus strain differences were not due to differential THC delivery via vapor inhalation.