Paper Information

Title: 

ADRENOCEPTORS MEDIATE CONCENTRATION-DEPENDENT BIPHASIC RESPONSE FOR ISOPROTERENOL AND EPINEPHRINE IN RAT AORTA: A NEW SIGHT ON ADRENOCEPTORS

Type: POSTER
Author(s): FAKHRAEI NAHID*,YOUSEFVAND NAMDAR,DEHPOUR A.R.
 
 *DEPARTMENT OF BIOLOGY, SCHOOL OF SCIENCES, UNIVERSITY OF RAZI, KERMANSHAH, IRAN
 
Name of Seminar: IRANIAN CONGRESS OF PHYSIOLOGY AND PHARMACOLOGY
Type of Seminar:  CONGRESS
Sponsor:  PHYSIOLOGY AND PHARMACOLOGY SOCIETY, MASHHAD UNIVERSITY OF MEDICAL SCIENCE
Date:  2009Volume 19
 
 
Abstract: 

In this study the effects of different doses of isoproterenol and epinephrine on isolated rat aorta, with and without preconstriction of phenylephrine, were compared and investigated. Male wistar rats were used. The thoracic aorta was removed, cut into 3-4 mm rings and mounted in an organ-bath system. Recording of isometric changes in tension was done with a force transducer (AD Instruments TRI202P, Spain) connected via an interface to a computer system. Adrenaline and isoproterenol were administrated separately in a cumulative fashion to obtain concentration-response curve with and without preconstriction of phenylephrine (10-6M). Following attainment of plateau, different adrenoceptors antagonist was added, separately. The results revealed that isoproterenol and epinephrine had a concentration-dependent biphasic response in aortic rings preconstricted with phenylephrine (10-6M). Isoproterenol relaxed phenylephrine-induced contraction but, after maximum relaxation, high concentration of isoproterenol (10-4M), caused a contraction in aortic rings. Isoproterenol at high concentrations (10-5-10-4M), at the basal tone (2g), produced a large contraction. Lower concentrations of epinephrine (10-11-10-7M) produced a small relaxation and contraction was observed with higher concentrations (10-6-10-4M). Epinephrine at basal tone (2g) produced a concentration-dependent contraction. Using different antagonists for identifying the involved receptors in the contraction, we found the main receptor in the contraction induced with high contractions of isoproterenol was a1 adrenoceptor therefore prazosin could almost totally antagonize the contraction. Surprisingly, the other antagonists to some extent, could antagonize the contraction, however, the effect of propranolol (b1 and b2), was more potent than alprenolol (b1). This result demonstrated that a1, b1 and b2 adrenoceptors are involved in the observed contraction. In conclusion, our result indicated that different receptors respond distinct biphasic response in different doses of agonists and these responses are vary in different vascular tension and probably in different vascular beds.

 
Keyword(s): ADRENOCEPTORS, ISOPROTERENOL, EPINEPHRINE, AORTA, RAT
 
Yearly Visit 42   tarjomyar
 
Latest on Blog
Enter SID Blog