Reintoxication: the release of fat-stored delta(9)-tetrahydrocannabinol (THC) into blood is enhanced by food deprivation or ACTH exposure

Abstract

Background and purpose: Delta(9)-tetrahydrocannabinol (THC), the main psychoactive constituent of cannabis, accumulates in adipose tissue where it is stored for long periods of time. Here we investigated whether conditions that promote lipolysis can liberate THC from adipocytes to yield increased blood levels of THC.

Experimental approach: In vitro studies involved freshly isolated rat adipocytes that were incubated with THC before exposure to the lipolytic agent adrenocorticotrophic hormone (ACTH). A complementary in vivo approach examined the effects of both food deprivation and ACTH on blood levels of THC in rats that had been repeatedly injected with THC (10 mg.kg(-1)) for 10 consecutive days. Lipolysis promoted by ACTH or food deprivation was indexed by measurement of glycerol levels.

Key results: ACTH increased THC levels in the medium of THC-pretreated adipocytes in vitro. ACTH also enhanced THC release from adipocytes in vitro when taken from rats repeatedly pretreated with THC in vivo. Finally, in vivo ACTH exposure and 24 h food deprivation both enhanced the levels of THC and its metabolite, (-)-11-nor-9-carboxy-Delta(9)-tetrahydrocannabinol (THC-COOH) in the blood of rats that had been pre-exposed to repeated THC injections.

Conclusions and implications: The present study shows that lipolysis enhances the release of THC from fat stores back into blood. This suggests the likelihood of 'reintoxication' whereby food deprivation or stress may raise blood THC levels in animals chronically exposed to the drug. Further research will need to confirm whether this can lead to functional effects, such as impaired cognitive function or 'flashbacks'.

Figure 1

The effect of ACTH (2 nM) on the release of (A) THC and (B) glycerol from adipocytes (10⁵ cells per sample) that were pretreated with either 1 or 10 µM THC (n= 5 per group). **P < 0.01 and ***P < 0.001, significant difference between ACTH and VEH. Adipocytes were isolated from rats weighing between 250 and 300 g. ACTH, adrenocorticotrophic hormone; THC, Δ⁹-tetrahydrocannabinol; VEH, vehicle.

Figure 2

The effect of ACTH (2 nM) on the release of (A) THC and (B) glycerol from adipocytes (10⁵ cells per sample) that were dissected from rats repeatedly pretreated with THC (10 mg·kg⁻¹·day⁻¹) for 10 days before a 2 day washout period (n= 5 per group). **P < 0.01 and ***P < 0.001, significant difference between ACTH and VEH. Adipocytes were isolated from rats weighing between 300 and 350 g. ACTH, adrenocorticotrophic hormone; THC, Δ⁹-tetrahydrocannabinol; VEH, vehicle.

Figure 3

The effect of ACTH (0.2 mg·kg⁻¹) on blood THC and THC-COOH concentrations in rats (200–250 g) that were repeatedly pretreated with THC (10 mg·kg⁻¹·day⁻¹) for 10 days before a 2 day washout period (n= 8 per group). *P < 0.05 and ***P < 0.001, significant difference between ACTH and VEH. ACTH, adrenocorticotrophic hormone; THC, Δ⁹-tetrahydrocannabinol; THC-COOH, (-)-11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol; VEH, vehicle.

Figure 4

The effect of 24 h FD on (A) blood THC and THC-COOH concentrations and (B) plasma glycerol in rats (300–400 g) that were repeatedly pretreated with THC (10 mg·kg⁻¹·day⁻¹) for 10 days before a 2 day washout period (n= 10 per group). The effect of 24 h FD on (C) blood THC and THC-COOH concentrations and (D) plasma glycerol in rats that were repeatedly pretreated with THC (10 mg·kg⁻¹·day⁻¹) for 10 days and given a 7 day washout period (n= 7–8 per group). *P < 0.05, **P < 0.01 and ***P < 0.001, significant difference between FD and NFD group. FD, food deprivation; NFD, non-food deprived; THC, Δ⁹-tetrahydrocannabinol; THC-COOH, (-)-11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol.

Figure 5

ACTH-induced THC release from adipocytes (10⁴ cells per sample) of FD or NFD rats (300–400 g) repeatedly pretreated with THC (10 mg·kg⁻¹·day⁻¹) for 10 days after a 2 (n= 8 per group) or 7 day (n= 6 per group) washout period. ***P < 0.001, significant difference between FD and NFD group. ACTH, adrenocorticotrophic hormone; FD, food deprivation; NFD, non-food deprived; THC, Δ⁹-tetrahydrocannabinol.