Effect of chlorpromazine on sympathetic neuroeffector transmission in the rabbit isolated pulmonary artery and aorta

The effects of chlorpromazine on sympathetic neuroeffector transmission have been studied in the rabbit isolated pulmonary artery and aorta. 2. Chlorpromazine (10(-8)-10(-5) M), prazosin (10(-9)-10(-7) M) and phentolamine (3 x 10(-8)-3 x 10(-5) M) decreased the contractions of pulmonary artery evoked by electrical field stimulation (150 pulses; 3 Hz). The rank order of inhibitory potency (ID50) was prazosin greater than chlorpromazine greater than phentolamine. 3. Rauwolscine (3 x 10(-9) M-4 x 10(-6) M) enhanced the neurogenic response by up to 201%. However, higher concentrations (6 x 10(-6)-3 x 10(-5) M) reduced the contractions evoked by transmural stimulation. 4. The inhibitory effect of prazosin (10(-6) M) was reversible, while that of chlorpromazine (10(-8) M) was not. 5. Chlorpromazine (10(-8)-10(-4) M), desmethylimipramine (3 x 10(-9)-10(-5) M), cocaine (10(-7)-3 x 10(-4) M) and phentolamine (10(-5)-3 x 10(-4) M) reduced the accumulation of [3H]-noradrenaline ([3H]-NA, 10(-8) M) by aorta. The rank order of inhibitory potency (ID50) was: desmethylimipramine greater than chlorpromazine greater than cocaine greater than phentolamine. Prazosin (10(-7)-10(-5) M) and rauwolscine (10(-8)-10(-4) M) did not reduce [3H]-NA accumulation. 6. Chlorpromazine (10(-8)-10(-6) M) and prazosin (3 x 10(-9)-10(-7) M) antagonized the contractions of aorta evoked by exogenous noradrenaline (10(-9)-3 x 10(-4) M) and phenylephrine (10(-9)-3 x 10(-3) M). The pA2 values for chlorpromazine on the alpha 1-adrenoceptors were 8.24 (noradrenaline) and 8.27 (phenylephrine). The corresponding values for prazosin were 8.64 and 8.57, respectively. 7. It is concluded that chlorpromazine and prazosin are potent inhibitors of postsynaptic alpha 1-adrenoceptors. Chlorpromazine and phentolamine, unlike prazosin and rauwolscine, are also inhibitors of Uptake.