9 -Tetrahydrocannabinol: a hypotensive effect in rats

A Systematic Review and Meta-Analysis of the In Vivo Haemodynamic Effects of Δ⁸-Tetrahydrocannabinol

∆⁹-Tetrahydrocannabinol (THC) has complex effects on the cardiovascular system. We aimed to systematically review studies of THC and haemodynamic alterations. PubMed, Medline, and EMBASE were searched for relevant studies. Changes in blood pressure (BP), heart rate (HR), and blood flow (BF) were analysed using the Cochrane Review Manager Software. Thirty-one studies met the eligibility criteria. Fourteen publications assessed BP (number, n = 541), 22 HR (n = 567), and 3 BF (n = 45). Acute THC dosing reduced BP and HR in anaesthetised animals (BP, mean difference (MD) −19.7 mmHg, p < 0.00001; HR, MD −53.49 bpm, p < 0.00001), conscious animals (BP, MD −12.3 mmHg, p = 0.0007; HR, MD −30.05 bpm, p < 0.00001), and animal models of stress or hypertension (BP, MD −61.37 mmHg, p = 0.03) and increased cerebral BF in murine stroke models (MD 32.35%, p < 0.00001). Chronic dosing increased BF in large arteries in anaesthetised animals (MD 21.95 mL/min, p = 0.05) and reduced BP in models of stress or hypertension (MD −22.09 mmHg, p < 0.00001). In humans, acute administration increased HR (MD 8.16 bpm, p < 0.00001). THC acts differently according to species and experimental conditions, causing bradycardia, hypotension and increased BF in animals; and causing increased HR in humans. Data is limited, and further studies assessing THC-induced haemodynamic changes in humans should be considered.

Cardiovascular effects of anandamide in anesthetized and conscious normotensive and hypertensive rats

We previously showed that in anesthetized rats anandamide elicits bradycardia and a triphasic blood pressure response: transient hypotension secondary to a vagally mediated bradycardia, followed by a brief pressor and prolonged depressor response, the latter two effects being similar to those of delta 9-tetrahydrocannabinol (THC). The prolonged depressor but not the pressor response was reduced after alpha-adrenergic receptor blockade or cervical spinal cord transection and was inhibited by the cannabinoid type 1 (CB1) receptor antagonist SR141716A, suggesting CB1 receptor-mediated sympathoinhibition as the underlying mechanism. Here we examined the relationship between sympathetic tone and the cardiovascular effects of anandamide by testing these effects in both conscious and anesthetized, normotensive and spontaneously hypertensive rats. In urethane-anesthetized normotensive rats, SR141716A inhibited the prolonged depressor and bradycardic effects of anandamide and THC with similar potency, whereas it did not affect the pressor response to either agent. Anadamide caused similar hypotension in spontaneously breathing and in paralyzed, mechanically ventilated rats, suggesting that the hypotension is not secondary to respiratory effects. In conscious normotensive rats, anandamide elicited transient vagal activation and a brief pressor response, but the prolonged hypotensive component was absent. SR141716A potentiated and prolonged the brief pressor response to anandamide, suggesting that the depressor response may have been masked by an increased pressor response. All three phases of the anadamide response were present in both anesthetized and conscious spontaneously hypertensive rats, and the hypotensive component, inhibited by SR141716A in both, was more prolonged in the absence (> 50 minutes) than the presence (10 to 15 minutes) of anesthesia. We conclude that anandamide causes a non-CB1 receptor-mediated pressor and a CB1 receptor-mediated prolonged depressor response. The depressor response can be elicited in both conscious and anesthetized animals, but its magnitude depends on preexisting sympathetic tone.

Cardiovascular effects of (-)-11-OH-delta 8-tetrahydrocannabinol-dimethylheptyl in rats

The effects of the stereochemically pure psychoactive cannabinoid (-)-11-OH-delta 8-tetrahydrocannabinol-dimethylheptyl (HU-210) on blood pressure (BP) and heart rate (HR) were determined in rats. In pentobarbital-anesthetized animals, the compound produced dose-related, long-lasting hypotension and bradycardia at doses between 10 and 1,000 micrograms/kg. BP began to decrease immediately after drug administration, and in no case was an initial pressor response observed. Previous vagotomy (VX) or pretreatment with 6-hydroxydopamine (6-OHDA) did not affect hypotension. Bradycardia was inhibited by VX, but only 60 min after administration of HU-210; it was enhanced by 6-OHDA. The cannabinoid blocked reflex bradycardia induced by phenylephrine (PE). HU-210 also decreased BP and HR in conscious rats. Hypotension lasted 2 h, whereas bradycardia was still present 8 h after drug administration. HU-210 thus shares with delta 9-tetrahydrocannabinol (THC) the ability to decrease BP and HR, but is 5-10 times more potent than the natural compound. Its lack of an initial pressor effect, such as that described for THC, could be related to its specificity for the type-1 cannabinoid (CB1) receptor. Hypotension and bradycardia after HU-210 administration are not due to sympathetic withdrawal. Enhanced parasympathetic tone is involved in bradycardia only at a late stage of the response.

The triple effect induced by delta 9-tetrahydrocannabinol on the rat blood pressure

The intravenous injection of delta 9-tetrahydrocannabinol (2-10 mg/kg) produced dose-related changes in the rat blood pressure. Three effects were detected: (1) an immediate and short-lasting hypotension related to bradycardia, blocked after atropine, vagotomy hexamethonium and pithing; (2) A rise in blood pressure 30 seconds after injection, insensitive to yohimbine, hexamethonium, pithing and reserpine treatment; (3) a slow and persistent hypotension, 5 min later, insensitive to atropine and vagotomy but inhibited by hexamethonium, pithing and reserpine treatment. It was concluded that intravenous injection of THC in rats may induce vagal stimulation and hypotension. This effect was reversed and followed by hypertension due to direct vasoconstriction not dependent on sympathetic activity. After this action a central decrease in sympathetic tonus led to a persistent hypotension an effect which is commonly reported for mammals.

BRL 13776: a novel antihypertensive agent with interesting monoamine depleting properties

1. Oral doses of 10-100 mg/kg of BRL 13776 lowered the blood pressure of both deoxycorticosterone acetate (DOCA)/NaCl-treated hypertensive rats and untreated normotensive rats. 2. BRL 13776 (100 mg/kg, orally) also reduced the blood pressure of renal hypertensive cats (cellophane perinephritis model). 3. No tolerance developed to the blood-pressure lowering action of BRL 13776 when an oral daily dose of 100 mg/kg was administered repeatedly for up to 15 days to hypertensive rats and cats. 4. The fall in blood pressure to BRL 13776 in rats was associated with a reduction of tissue catecholamines. 5. The catecholamine depletion occurred in all the peripheral tissues examined but in the brain was restricted to certain regions, these being the hind-brain on single dosing and the hind-brain, hypothalamus and mid-brain on repeated dosing. Catecholamine levels in the cerebral hemispheres were not affected by either single or repeated doses of BRL 13776. 6. BRL 13776 caused some reduction of the 5-hydroxytryptamine content of the heart but not of whole brain or any brain region. 7. Neither single doses (up to 900 mg/kg orally) nor repeated doses (100-300 mg/kg orally) of BRL 13776 produced any significant behavioural effects in animals. 8. BRL 13776 is a new type of agent to display both antihypertensive and monoamine-depleting properties. The reduction of noradrenaline in certain brain regions may be a cause of the antihypertensive response but depletion in the periphery could contribute in a major or minor way. The differential action on noradrenaline in the brain together with the lack of effect on 5-hydroxytryptamine might also explain the apparent absence of behavioural effects.

Tolerance to the cardiovascular effects of delta9-tetrahydrocannabinol in the rat

1. Daily intraperitoneal injections of delta9-tetrahydrocannabinol (delta9-THC, 10 mg/kg) resulted in tolerance to the effects of the cannabinoid on body weight and body temperature within 1-2 weeks of treatment. 2. Tolerance failed to develop to the suppression of spontaneous motor activity produced by delta9-THC during 28 days of treatment with the cannabinoid (10 mg/kg, i.p. per day). 3. Following treatment with vehicle for 28 days, intravenous administration of delta9-THC in anaesthetized rats produced a transient pressor response followed by a sustained hypotension and bradycardia. 4. Tolerance to the hypotensive and negative chronotropic responses to intravenous delta9-THC was readily apparent in animals which had received daily intraperitoneal injections of delta9-THC (10 mg/kg) for 28 days. 5. Tolerance failed to develop to the pressor actions of intravenous delta9-THC after 28 days of preptreatment. 6. There was no difference in the pressor response to intravenous noradrenaline in vehicle-treated animals (1.0 ml/kg, i.p., per day for 28 days) and delta9-THC-treated animals (10 mg/kg, i.p., per day for 28 days).