Role of alpha-1 adrenoceptor subtypes mediating constriction of the rabbit ear thermoregulatory microvasculature
✍ Scribed by Zhongyu Li; William P. Silver; L. Andrew Koman; Jack W. Strandhoy; Eileen Rosencrance; Stan Gordon; Thomas L. Smith
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 724 KB
- Volume
- 18
- Category
- Article
- ISSN
- 0736-0266
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✦ Synopsis
An acute in vivo preparation of the microvasculature of the rabbit ear was used to evaluate the functional role of alpha, (al)-adrenoceptor subtypes in thermoregulatory microcirculation. The effect of al-adrenoceptor subtype blockade on phenylephrine-induced vasoconstriction was assessed with the alA, alB, and alD-adrenoceptor-selective antagonists 5-methyl-urapidil M ) . chloroethylclonidine (1 0-j M ) , and X-[2-[4(2-methoxyphenyl)-l-piperazinyl]ethyl]-8-azaspirol[4.S]decane-7,9-dione dihydrochloride (BMY7378) (10-6 M ) , respectively. The results demonstrated that pretreatment of the ear microvasculature with 5-methylurapidil or BMY7378 shifted the phenylephrine concentration-response curve rightward and significantly changed the log of the phenylephrine concentration, causing half-maximum stimulation (EC,,) in arterioles (p < 0.05). BMY7378 shifted the phenylephrinc concentration-response curve of the arteriovenous anastomoses about 100-fold rightward (p < 0.05). All three a,-adrenoceptor antagonists eliminated the vasoconstrictive effects of phenylephrine on venules. The results indicate that the ear microvasculature has a heterogenous distribution of ul-adrenoceptor subtypes. The alA and alD-adrenoceptor subtypes appear to have a greater influence on constrictive function in arterioles, whereas the alD-adrenoceptor is the dominant constrictor of arteriovenous anastomoses. In general, the al-adrenoceptor does not play a major vasoconstrictor role in venules. Chloroethylclonidine, an irreversible alB-adrenoceptor antagonist, induced contractile responses in the ear microvasculature, probably due to its a2-adrenoceptor agonist effects. This study extended our understanding of the adrenergic receptor control mechanisms of a cutaneous thermoregulatory end organ characterized by two parallel perfusion circuits providing nutritional and thermoregulatory functions.