 Pharmacodynamics
Marijuana is the term used to describe the leaves and flowering tops of
the Cannabis sativa plant. Like
other herbal medicines, the Cannabis plant plays host to a number of
chemicals. The plant houses approximately 460 known compounds.
Sixty of these are unique to the Cannabis plant and are called cannabinoids.
The primary psychoactive cannabinoid is
delta-9-tetrahydrocannabinol or THC.
Chemically the cannabinoids are classed as terpenoid
(terpene-like), these compounds occur as essential oils within many
plants and some are involved in vitamin, steroid and pigment formation. Because
of THC’s high lipid solubility, it was previously thought that THC affected
cells by interacting with the lipid components of the cell membrane.
However, studies in the late 1980’s discovered the
existence of endogenous cannabinoid receptors.
There are two known endogenous cannabinoid receptors creatively named CB1
and CB2. CB1 receptors are found
primarily but not exclusively in the brain.
They are most prevalent in
the hippocampus, cerebral cortex, basal ganglia, and cerebellum.
CB2 receptors are also found in the brain but more so expressed
by cells of the immune system, especially B cells.
The CB receptor is a G protein mediated receptor that affects primarily
calcium and potassium channel activation. Functional
changes are most notable in neuronal excitability and neurotransmitter release.
Initially, the receptors were considered orphaned receptors meaning that
there were no endogenous ligands. Subsequent
research turned up two endogenous cannabinoid ligands (anandamide and
2-arachidonylglycerol) that not only bind to the
receptors but also mimick many of the biological actions of plant derived
cannabinoids.
Pharmacokinetics
Marijuana is usually smoked but can be eaten or injected intravenously.
Peak plasma levels are reached ten minutes after smoking.
The psychoactive components are effective for two to three hours, however
THC has a long half-life due to its lipid soluble nature and redistribution
into fatty tissue. THC can be
detected in urine months after initial administration.
THC is metabolized through the cytochrome P450 system.
Approximately one third is eliminated renally and two thirds through
fecal excretion. |
