Fasting and exercise increase plasma cannabinoid levels in THC pre-treated rats: an examination of behavioural consequences.
BACKGROUND
Δ(9)-Tetrahydrocannabinol (THC), the main psychoactive constituent of cannabis, accumulates in fat tissue where it can remain for prolonged periods. Under conditions of increased fat utilisation, blood cannabinoid concentrations can increase. However, it is unclear whether this has behavioural consequences.


OBJECTIVE
Here, we examined whether rats pre-treated with multiple or single doses of THC followed by a washout would show elevated plasma cannabinoids and altered behaviour following fasting or exercise manipulations designed to increase fat utilisation.


METHODS
Behavioural impairment was measured as an inhibition of spontaneous locomotor activity or a failure to successfully complete a treadmill exercise session. Fat utilisation was indexed by plasma free fatty acid (FFA) levels with plasma concentrations of THC and its terminal metabolite (-)-11-nor-9-carboxy-∆(9)-tetrahydrocannabinol (THC-COOH) also measured.


RESULTS
Rats given daily THC (10 mg/kg) for 5 days followed by a 4-day washout showed elevated plasma THC-COOH when fasted for 24 h relative to non-fasted controls. Fasted rats showed lower locomotor activity than controls suggesting a behavioural effect of fat-released THC. However, rats fasted for 20 h after a single 5-mg/kg THC injection did not show locomotor suppression, despite modestly elevated plasma THC-COOH. Rats pre-treated with THC (5 mg/kg) and exercised 20 h later also showed elevated plasma THC-COOH but did not differ from controls in their likelihood of completing 30 min of treadmill exercise.


CONCLUSIONS
These results confirm that fasting and exercise can increase plasma cannabinoid levels. Behavioural consequences are more clearly observed with pre-treatment regimes involving repeated rather than single THC dosing.
The Discipline of Pharmacology, The University of Sydney, Darlington, NSW, 2006, Australia.
Alexander
A
Wong
Kirily
K
Keats
Kieron
K
Rooney
Callum
C
Hicks
David J
DJ
Allsop
Jonathon C
JC
Arnold
Iain S
IS
McGregor
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D002186:Cannabinoids / Q000008:administration & dosage* / Q000097:blood; D013759:Dronabinol / Q000008:administration & dosage* / Q000097:blood; D005215:Fasting / Q000097:blood*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D010805:Physical Conditioning, Animal / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar
D002186:Cannabinoids; D005230:Fatty Acids, Nonesterified; D013759:Dronabinol