Interaction of angiotensin with exogenous and neurally released norepinephrine on the cat nictitating membrane in vitro.
We have studied the effect of high (1-2.9 X 10(-5) M) and low 1.9 X 10(-9) M) concentrations of angiotensin on the retention and release of 3H-norepinephrine by the cat isolated nicititating membrane preparation in vitro in conjunction with their effect on the contractile responsiveness of the preparation to exogenous norepinephrine and transmural electrical stimulation. Both concentrations of angiotensin made the preparation contract, but only the high concentration affected the retention and spontaneous efflux of 3-H-norepinephrine. Retention was inhibited about 25% only when the preparation was preincubated with the angiotensin for 30 minutes (i.e., before adding 3H-norepinephrine). Under similar conditions cocaine, 2.9 X 10(-5) M, inhibited retention more than 90%. Spontaneous efflux was increased for as long as the high concentration of angiotensin was in contact with the preparation. Under similar conditions, tyramine, 5.7 X 10(-6) M, caused a much greater sustained increase in spontaneous efflux. Transmural stimulation of the preparation caused release of 3H-norepinephrine and frequency-dependent contractions. The contractions were selectively inhibited by phentolamine, 2.7 X 10(-6) M, or bretylium, 2.4 X 10(-5) M. Angiotensin had no effect on this neurally mediated 3H-norepinephrine release and contractile response or on contractions produced by exogenous norepinephrine. Since, as reported previously, angiotensin in vivo strongly inhibits contractile responses of the cat nicitating membrane to both neurally released and exogenous norepinephrine, the present results make it unlikely that such inhibition derives from angiotensin's relatively modest capacity for affecting the disposition of norepinephrine by this effector organ.
D000804:Angiotensin II / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001949:Bretylium Compounds / Q000494:pharmacology; D002415:Cats; D003042:Cocaine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects; D009541:Nictitating Membrane / Q000187:drug effects; D009638:Norepinephrine / Q000378:metabolism / Q000494:pharmacology*; D010646:Phentolamine / Q000494:pharmacology; D013997:Time Factors; D014316:Tritium; D014439:Tyramine / Q000494:pharmacology
D001949:Bretylium Compounds; D014316:Tritium; D000804:Angiotensin II; D003042:Cocaine; D009638:Norepinephrine; D014439:Tyramine; D010646:Phentolamine