Pharmacological and Functional Characterization of Novel EP and DP Receptor Agonists: DP1 Receptor Mediates Penile Erection in Multiple Species

Abstract

Introduction Despite the widespread use of prostaglandin E1 as an efficacious treatment for male erectile dysfunction for more than two decades, research on prostanoid function in penile physiology has been limited. Aim To characterize the pharmacological and physiological activity of novel subtype-selective EP and DP receptor agonists. Methods Radioligand binding and second messenger assays were used to define receptor subtype specificity of the EP and DP agonists. Functional activity was further characterized using isolated human and rabbit penile cavernosal tissue in organ baths. In vivo activity was assessed in rabbits and rats by measuring changes in cavernous pressure after intracavernosal injection of receptor agonists. Main Outcome Measures Receptor binding and signal transduction, smooth muscle contractile activity, erectile function. Results In organ bath preparations of human cavernosal tissue contracted with phenylephrine, EP2- and EP4-selective agonists exhibited variable potency in causing relaxation. One of the compounds caused mild contraction, and none of the compounds was as effective as PGE1 (EC50 =0.23 µM). There was no consistent correlation between the pharmacological profile (receptor binding and second messenger assays) of the EP agonists and their effect on cavernosal tissue tone. In contrast, the DP1-selective agonist AS702224 (EC50 =29 nM) was more effective in relaxing human cavernosal tissue than either PGE1, PGD2 (EC50 =58 nM), or the DP agonist BW245C (EC50 =59 nM). In rabbit cavernosal tissue, PGE1 and PGD2 caused only contraction, while AS702224 and BW245C caused relaxation. Intracavernosal administration of AS702224 and BW245C also caused penile tumescence in rabbits and rats. For each compound, the erectile response improved with increasing dose and was significantly higher than vehicle alone. Conclusions These data suggest that AS702224 is a potent DP1-selective agonist that causes penile erection. The DP1 receptor mediates relaxation in human cavernosal tissue, and stimulates pro-erectile responses in rat and rabbit. Thus, rabbits and rats can be useful models for investigating the physiological function of DP1 receptors.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2Receptors (EP1–4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

“…Human corpus cavernosum produces all major PGs, including PGE 2 , PGD 2 , PGF 2 α , PGI 2 , and TxA 2 ( Khan et al, 1999 ), and expresses their receptors, like EP1, EP2, EP3-type I, EP3-type II, EP4, and DP ( Brugger et al, 2008 ). There is no sufficient data showing their expression in rodent corpus cavernosal tissues.…”

Extended Release Niacin-Laropiprant in Patients with Hypercholesterolemia or Mixed Dyslipidemias Improves Clinical Parameters

“…This suggests that PGD 2 has an important role to play in the regulation of sleep and wakefulness, and this appears to be at least partially a DP1 mediated effect 87. The DP1 receptor has also been shown to mediate the erectile response in a number of species, including humans One possible concern with DP1 anatgonists must therefore be impotence, which may already be of concern in patients with cardiovascular disease 89. Another issue which may have particular relevance for diabetics is the observation that, in a mouse model, overexpression of PGDS led to an increase in PGD 2 production in adipocytes.…”