Prejunctional modulation of norepinephrine release in the human iris-ciliary body.
OBJECTIVE
To characterize the prejunctional mechanisms that control the impulse-evoked release of norepinephrine in the isolated, superfused human iris-ciliary body.


METHODS
Human iris-ciliary body tissue segments were preincubated with 3H-norepinephrine, superfused and electrically-stimulated in vitro to evoke the discharge of 3H-norepinephrine. The effects of prejunctional modulators on evoked 3H-norepinephrine overflow were evaluated.


RESULTS
Stimulation-evoked (but not spontaneous) 3H-norepinephrine release was inhibited by alpha 2-adrenergic, muscarinic, dopaminergic, neuropeptide Y, and prostaglandin agonists and was enhanced by angiotensin II. Agonist-induced effects on 3H-norepinephrine overflow were blocked by selective antagonists, where available. Yohimbine and atropine alone enhanced 3H-norepinephrine output, suggesting that prejunctional alpha 2-adrenergic and muscarinic receptors undergo tonic activation by endogenously released neurotransmitters.


CONCLUSIONS
Human ocular sympathetic nerves express inhibitory alpha 2-adrenergic, muscarinic, dopaminergic, prostaglandin, and neuropeptide Y receptors and facilitatory angiotensin II receptors that control the impulse-evoked release of 3H-norepinephrine. These receptors may be useful targets for pharmacologic manipulation of the adrenergic system in vivo.
Jumblatt
J E
JE
Department of Ophthalmology and Visual Sciences, Kentucky Lions Eye Research Institute, Univ. of Louisville School of Medicine.
Ohia
S E
SE
Hackmiller
R C
RC
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002924:Ciliary Body / Q000294:innervation*; D004558:Electric Stimulation; D006801:Humans; D007498:Iris / Q000294:innervation*; D008875:Middle Aged; D009638:Norepinephrine / Q000378:metabolism*; D011941:Receptors, Adrenergic / Q000378:metabolism; D011945:Receptors, Angiotensin / Q000378:metabolism; D017476:Receptors, Neuropeptide Y / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000378:metabolism*
D011941:Receptors, Adrenergic; D011945:Receptors, Angiotensin; D017476:Receptors, Neuropeptide Y; D009638:Norepinephrine