Pulmonary actions of anandamide, an endogenous cannabinoid receptor agonist, in guinea pigs
Introduction
Anandamide (arachidonylethanolamide), 5,8,11,14-eicosatetraenamide (N-2-hydroxyethyl), has been isolated from porcine brain and subsequently identified as an endogenous ligand of the cannabinoid receptor (Devane et al., 1992). Although anandamide does not share much structural similarities with the classical cannabinoid agonist Δ9-tetrahydrocannabinol, recent investigations have demonstrated that anandamide interacts competitively at the cannabinoid receptor (Devane et al., 1992; Felder et al., 1993; Vogel et al., 1993; Childers et al., 1994). In addition, anandamide possesses similar in vitro pharmacological actions such as inhibition of forskolin-stimulated cyclic AMP production (Felder et al., 1993; Vogel et al., 1993) and N-type calcium channel currents (Mackie et al., 1993). Much of the work to date with anandamide has been limited to studying its in vivo pharmacological actions in the central nervous system (Fride and Mechoulam, 1993; Crawley et al., 1993; Smith et al., 1994; Wiley et al., 1995). From these studies, it has been suggested that anandamide possesses similar behavioral and physiological responses associated with psychotropic cannabinoids.
Although much is known about the psychoactive effects of Δ9-tetrahydrocannabinol, it appears to have other pharmacological properties such as bronchodilator and anti-inflammatory activities (Dewey, 1986; Hollister, 1986). Specific airway conductance of healthy and asthmatic subjects has been shown to increase significantly after either oral or aerosol administration of marijuana or its active ingredient Δ9-tetrahydrocannabinol (Tashkin et al., 1973, Tashkin et al., 1977; Vachon et al., 1973). In addition, inhaled marijuana (Δ9-tetrahydrocannabinol) has been found to reverse methacholine- and exercise-induced bronchospasm in asthmatics as rapidly as the β-agonist isoproterenol (Tashkin et al., 1975). The anti-inflammatory effects of Δ9-tetrahydrocannabinol appear to be more controversial. In one study, Δ9-tetrahydrocannabinol at the oral dose of 10.0 mg/kg was found to be equally effective as hydrocortisone, but 20 times more potent than aspirin, in inhibiting carrageenan-induced edema in rats (Sofia et al., 1973). However, at even higher oral doses, >25.0 mg/kg, Δ9-tetrahydrocannabinol had no effect on the paw swelling produced by carrageenan (Kosersky et al., 1973). Thus, it would be important to determine if anandamide also shares the ability to inhibit bronchoconstriction and inflammation as well.
In this study, we evaluated the ability of anandamide to modify pulmonary function and ventilation. In addition, we examined the capability of anandamide to prevent or reverse the prolonged airway constriction and pulmonary inflammation produced by the divalent cationic ionophore A23187 (6S-[6α(2S*,3S*),8β(R*),9β,11α]-5-(methylamino)-2-[[3,9,11-trimethyl-8-[1-methyl-2-oxo-2-(1H-pyrrol-2-yl)ethyl]-1,7-dioxaspiro[5.5]undec-2-yl]methyl]-4-benzoxazolecarboxylic acid). This agent is a nonimmunological stimulus which causes the release of bronchoconstrictor and pro-inflammatory substances that are thought to be important in the pathophysiology of asthma (Salari et al., 1985; Sautebin et al., 1985). Inhalation or intravenous delivery of A23187 has been reported to induce bronchospasm in monkeys (Patterson et al., 1979), guinea pigs (Ho and Esterman, 1979; Stengel et al., 1987; Misawa et al., 1989) and cats (Kriseman et al., 1986). These studies and others (Stengel and Silbaugh, 1989; Stengel et al., 1991) have suggested that cyclooxygenase and/or lipoxygenase metabolites of the arachidonic acid cascade, as well as cholinergic and histaminergic mechanisms are involved in the airway obstructive and proinflammatory effects of A23187. To our knowledge, this is the first report describing the in vivo pulmonary responses of anandamide.
Section snippets
Animals
Barrier-maintained, male outbred Hartley guinea pigs were obtained from Charles River Breeding Laboratories (Portage, MI, USA) and were housed in stainless steel, ventilated rack cages. Animal room temperature was maintained at 22–24°C with a relative humidity of 30–70% and a daily light–dark cycle (0600–1800 h light). Food (Purina Guinea Pig Chow, 5025) and water were provided ad libitum. Guinea pigs weighed 328–492 g. Our experimental procedures were approved by our Animal Care and Use
Effect of anandamide on pulmonary function and ventilation
During the 15-min period when increasing doses of anandamide were administered to conscious guinea pigs, no changes were observed in VT, f, Cdyn and RL of animals which received anandamide versus those which received vehicle (Fig. 1). A similar lack of a difference was found comparing ELGV and W/D values of anandamide-treated and vehicle-treated animals (Table 1). Anandamide by itself did not produce any changes on the pulmonary responses measured.
Reversal of A23187-induced airway constriction
The duration of aerosol exposure required to
Discussion
Our results clearly show that anandamide did not produce any adverse effects on pulmonary mechanical and ventilatory parameters in conscious guinea pigs. The observation that anandamide did not alter basal airway responses or reverse an ongoing airway obstruction when administered intravenously suggests that this agent is not acting directly to relax guinea pig airway smooth muscle. However, anandamide appears to possess modest anti-inflammatory properties in A23187-challenged animals.
Acknowledgements
This study was presented in part at the Experimental Biology 95™ meeting in Atlanta, GA, from April 9–13, 1995.
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