Role of norepinephrine in the rabbit ganglionectomy response

Superior cervical ganglionectomy (SCG) produced delayed mydriasis and ocular hypotension in rabbits. Norepinephrine (NE) was lost from the iris-ciliary body exponentially with onset of about 11 h. NE in aqueous humor peaked at twice control levels (from 7 to 14 ng/ml) at 16.5 h and subsequently declined to below control levels by 24 h. Intracameral administration of radiolabeled NE (150 ng) to control eyes resulted in a calculated outflow of 1.6 microliter/min, comparable to that seen with fluorescein (1.7 microliter/min). NE administered to ganglionectomized eyes (26 h after surgery) resulted in a calculated outflow of 3.1 microliter/min. These results suggest that mydriasis following SCG may be due to NE released from degenerating sympathetic nerve endings. However, NE concentration in the aqueous humor appears inadequate to produce the delayed increase in outflow observed in rabbits after SCG.