Differences of desensitization and hypersensitization between α(1A)- and α(1B)-adrenoceptors in rat isolated blood vessels

Aim: To study the differences of the agonist-induced desensitization and the reserpinization-induced hypersensitization between α(1A)- and α(1B)-adrenoceptors (AR) mediated vasoconstriction. Methods: The thoracic aortae, mesenteric, and renal arteries of rats were isolated. The cumulative-concentration response-curve (CCRC) of vasoconstriction for NE was recorded. NE activated only α₁-AR since the perfusing Krebs solution contained propranolol 1 μmol · L^-1 and yohimbine 0.1 μmol · L^-1 to block β- and α₂-AR. CCRC for NE was made, preparations were pretreated with CEC 50 μmol · L^-1 for 30 min or preincubated with NE 10 μmol · L^-1 for 1 h then washed, and CCRC for NE was repeated. After ip reserpine 4 mg · g^-1 ip, the rats were killed, the thoracic aortae and renal arteries were taken, CCRC for NE was compared with the corresponding blood vessels in control rats. Results: Pretreatment with CEC caused reductions of the NE-induced maximal constriction by 82.5 ± 3.0% (P < 0.01) and 54.2 ± 9.5% (P < 0.01) in thoracic aortae and mesenteric arteries, respectively, but no effect in renal arteries. Preincubation with NE caused the α₁-AR mediated-vasoconstriction diminished 14.4 ± 5.9, 1.8 ± 0.8 and 7.3 ± 1.8 times in aortae, renal arteries, and mesenteric arteries, respectively. In reserpinized rats, the contraction in renal arteries induced by NE increased by 56%, but showed no change in aortae. Conclusion: α(1B)-AR mediated vasoconstriction is easier to be desensitized, while α(1A)-AR mediated vasoconstriction is easier to be hypersensitized in rats.