P2 subtypes

Two different types of P-adrenoceptors have been characterized and categorized as P - and P2-subtypes. The P -receptors are associated primarily with the cardiac muscle, whereas the P2-subtype is located peripherally. Selective P -blockers include practolol (121) and (122), atenolol (123) and (124), and betaxolol (125) and (126). 

Fisher, J. L. and Macdonald, R. L. (1997) Single channel properties of recombinant GABAa receptors containing y2 or 8 subtypes expressed with ai and p2 subtypes in mouse L929 cells../. Physiol. 505, 283-297. 

Driessen B, Bultmann R, Goncalves J, Starke K (1996) Opposite modulation of noradrenaline and ATP release in guinea pig vas deferens through prejunctional (l-adrenoccptors evidence for the P2 subtype. Naunyn-Schmiedeberg s Arch Pharmacol 353 564-71 Drukarch B, Stoof JC (1990) D2 dopamine autoreceptor selective drugs do they really exist Life Sci 47 361-76... 

The paradigm used by Ahlquist for classifying receptors based on their pharmacological characteristics (i.e., rank order of potency of agonists) was further developed by Lands and colleagues with the subdivision of the P-adrenergic receptors into pr and P2-subtypes (12). The pradrenergic receptor, the dominant receptor in heart and adipose tissue, was equally sensitive to epinephrine and... 

The majority of P-ARs were of the P2-AR subtype not only in the rat myometrium but also in the endometrial and serosal epithelia of the uterus. Specific labeling was also observed in glandular elements (74). It was also shown that the majority of P-ARs were of the P2-AR subtype in the smooth muscle layers as well as in the epithelium. The latter localization suggests a role for epinephrine or norepinephrine ontheoviductal epithelium (75). It was found that most receptors were of the P2-subtype in rat testis, with the greatest density of receptors found in interstitial cells and some specific labeling over the seminiferous tubules (76). 

ADRENOCEPTOR AGONIST Selective for the p2 Subtype, also with activity as a (peripheral D,) DOPAMINE RECEPTOR AGONIST. Therapeutically, it can be used in HEART FAILURE treatment. Dopram doxapram. 

Hexopar inositol nicotinate nicotinic acid, hexoprenaline [ban, inn] (hexoprenaline hydrochloride [jan]) is a P-ADRENOCEPTOR agonist selective for the P2-subtype that therapeutically can be used as a BRONCHODIIATOR in ANTIASTHMATIC treatment, hexoprenaline hydrochloride hexoprenaline. hexuronic acid ascorbic acid, hexylcaine [inn] (hexylcaine hydrochloride [usan]) is an ester series LOCAL ANAESTHETIC, used by topical application for the local relief of pain, hexylcaine hydrochloride hexylcaine. hexylresorcinol [usan] is a urinary ANTISEPTIC and an ANTHELMINTIC. It inhibits melanosis (blackspot) in shrimps, and is used as a food additive for prevention of enzymic browning in shrimps and fruits, hexyltheobromine pentifylline. 

Pulmadil ") is a p-ADRENOCEPTOR AGONIST selective for the P2-subtype. Therapeutically, it can be used as a BRONCHODILATOR in ANTIASTHMATIC treatment. 

The J3 receptor antagonists are the next most common topical medical treatment. There are two classes of topical J3 blockers. The nonselective ones bind to both j3j and p2 receptors and include timolol, levobunolol, metipranolol, and carteolol. There is one pj-selective antagonist, betaxolol, available for ophthalmic use. It is less likely to cause breathing difficulty than nonselective 15 blockers, but it is less efficacious than the nonselective j5 blockers since the j5 receptors of the ciliary body epithelium and ocular blood vessels are 75—90% p2 subtype. The molecular basis of 15 blockade leading to decreased aqueous production and reduced lOP is uncertain. 

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