Adrenoceptor agonists pharmacological effects

Tocolysis. The uterine relaxant effect of P2-adrenoceptor agonists, such as terbutaline or fenoterol, can be used to prevent premature labor. Vasodilation Ltillmann, Color Atlas of Pharmacology (... 

The adverse effects of adrenoceptor agonists are primarily extensions of their pharmacologic effects in the cardiovascular and central nervous systems. 

Phenylephrine is a sympathomimetic aj adrenoceptor agonist capable of producing mydriasis in some species by iris dilator muscle contraction. In the horse, topical application of a 10% solution has been shown to have no effect on the pupil diameter in the normal eye. However, 10% phenylephrine in combination with topical atropine is reported to be useful in reversing pupillary spasm in some stubborn cases of anterior uveitis, although there is no pharmacological evidence to support any additive mydriatic effect when the two agents are used together. 

The U2 agonists produce a spectrum of pharmacological effects, some of which are attributable to central effects and others to their action on peripheral receptors in target tissues. Within the CNS, tt2 adrenoceptors mediate sedation, analgesia and decreased output from the sympathetic nervous system. The peripheral effects of 02 agonists include vasoconstriction and impaired insulin release. 

England G C, Clarke K W, Goossens L 1992 A comparison of the sedative effects of three a2-adrenoceptor agonists (romifidine, detomidine and xylazine) in the horse. Journal of Veterinary Pharmacology and Therapeutics 15 194-201... 

Sams R, Pizzo P 1987 Detection and identification of ketamine and its metabolites in horse urine. Journal of Analytical Toxicology 11 58-62 Sarazan R D, Starke W A, Krause G F et al 1989 Cardiovascular effects of detomidine, a new U2-adrenoceptor agonist, in the conscious pony. Journal of Veterinary Pharmacology and Therapeutics 12 378-388... 

These very different sets of potencies indicated that two distinct adrenoceptor types are likely to be associated with each set of pharmacological effects. Set A effects could be blocked by adrenergic blockers available in 1948 (dibenamine, ergot alkaloids). These were named as a/p/ia-adrenoceptors Set B effects, where IPR was the most potent agonist, was then said to interact with era-adrenoceptors. In fact, IPR was found to be devoid of any a-agonist effects. Ahlquist s work also established that NE possessed primarily a-adrenoceptor activity, while EP acted on both types of receptors. 

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