THE EFFECTIVENESS OF ALPHA-2-ADRENOCEPTOR ACTIVATION INCREASES FROM THE DISTAL TO THE PROXIMAL PART OF THE VEINS OF CANINE LIMBS

• Type: Article in International Scientific Journal
• Date: 1990

Authors

GUIMARAES, S (Author) Other; José Pedro Nunes (Author) FMUP

Journal

Title: British Journal of Pharmacology

Vol. 101

Pages: 387-393

ISSN: 0007-1188

Publisher: Wiley-Blackwell

Indexing

ISI Web of Knowledge - 16 Citations

Scopus - 17 Citations

Other information

Authenticus ID: P-001-RFP

Abstract (EN): 1. The effectiveness of ¿1- and ¿2-adrenoceptor activation was compared at different levels of the saphenous and cephalic vein of the dog in vitro. 2. Helically cut strips were used to determine concentration-response curves to phenylephrine, noradrenaline, UK-14,304 (5-bromo-6-(imidazoline-2-ylamino)-quinoxaline) and B-HT 920 (2-amino-6-allyl-5,6,7,8-tetra-hydro-4H-(thiazo)-4,5-d-azepine). The effect of prazosin and yohimbine on these curves was also studied. 3. At the distal level, the maximum response to UK-14,304 amounted to 33 and 50% of those to noradrenaline in the saphenous and cephalic vein, respectively, while at the proximal level the maximum response to UK-14,304 amounted to 72 and 78% of those to noradrenaline, in the saphenous and cephalic vein, respectively. 4. In both vessels, the results obtained with B-HT 920 were very similar to those for UK-14,304. 5. The pD2 values for UK-14,304- which were identical at the three levels of both vessels - and the pA2 values for the antagonism exerted by either prazosin or yohimbine against the responses to UK-14,304 indicate that the ¿2-adrenoceptors are identical at the different levels of both vessels. 6. These results show that the effectiveness of ¿2-adrenoceptor stimulation increases from the distal to the proximal regions of canine limb veins. Apparently, this is due to a greater density of ¿2-adrenoceptors in the proximal regions. 7. Yohimbine is much more potent against phenylephrine distally than proximally in both vessels. However, after 30 nM phenoxybenzamine - a concentration which eliminates the vast majority of ¿1-adrenoceptors without affecting ¿2-adrenoceptors - yohimbine became equally potent at both levels, suggesting that the difference existing before phenoxybenzamine depended on ¿1-adrenoceptors. Hence it is concluded that ¿1-adrenoceptors in distal and proximal portions may differ.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 7