Differences of desensitization and hypersensitization between alpha 1A- and alpha 1B-adrenoceptors in rat isolated...

To study the differences of the agonist-induced desensitization and the reserpinization-induced hypersensitization between alpha 1A- and alpha 1B-adrenoceptors (AR) mediated vasoconstriction.

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 alpha 1-AR since the perfusing Krebs solution contained propranolol 1 mumol . L-1 and yohimbine 0.1 mumol . L-1 to block beta- and alpha 2-AR. CCRC for NE was made, preparations were pretreated with CEC 50 mumol . L-1 for then washed, and CCRC for NE was repeated. After i.p. reserpine 4 mg . g-1 i.p., 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.

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 alpha 1-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.

Alpha 1B-AR mediated vasoconstriction is easier to be desensitized, while alpha 1A-AR mediated vasoconstriction is easier to be hypersensitized in rats.