TY - JOUR T1 - RELEASE OF NOREPINEPHRINE FROM ISOLATED RAT IRIS BY FIELD STIMULATION JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 332 LP - 341 VL - 172 IS - 2 AU - LARS-OVE FARNEBO AU - BERTIL HAMBERGER Y1 - 1970/04/01 UR - http://jpet.aspetjournals.org/content/172/2/332.abstract N2 - The field stimulation-induced release of endogenous norepinephrine (studied by fluorescence histochemistry) and of exogenous H3-norepinephrine was investigated in the isolated rat iris. Isolated irides were incubated with H3-norepinephrine and then superfused with physiologic buffer before they were stimulated for 60 minutes. The stimulation caused a high release of H3-norepinephrine for 15 to 20 minutes which then declined. A slight reduction of the fluorescence intensity in the adrenergic nerves was observed. No release of norepinephrine occurred when Ca++ was excluded from the buffer. Incubation with reserpine phosphate before the superfusion caused a high spontaneous tritium efflux, and this efflux was further enhanced by stimulation. These data confirm earlier in vivo findings that the depletion by reserpine can be influenced by nerve impulses. After reserpine and nialamide pretreatment the norepinephrine taken up into the nerves could not be released by stimulation in spite of a high intraneuronal concentration. One hour after treatment with H44/68 (a potent inhibitor of tyrosine hydroxylase) a higher stimulus-induced depletion of endogenous norepinephrine and a lower release of H3-norepinephrine was found, as compared to the release from irides of untreated rate. It may be that exogenous H3-norepinephrine is not available for stimulus-induced release to the same extent after H44/68 or that the nerves attempt to save as much transmitter as possible. © 1970, by The Williams & Wilkins Co. ER -