AJP - Regulatory, Integrative and Comparative Physiology, Vol 241, Issue 3 130-R135, Copyright © 1981 by American Physiological Society
Role of sympathetic system in morphine-induced mydriasis in rat
M. C. Wallenstein
The effects of three doses (5, 30, and 60 mg/kg) of morphine on pupillary
diameter (PD) were studied in rats that were either normal,
neurotransmitter antagonist pretreated, guanethidine pretreated, cervical
sympathectomized, or adrenalectomized. Morphine produced a dose-dependent
increase in PD and exophthalmos. In addition, the PD concurrently underwent
fluctuations. alpha-Adrenergic antagonists blocked both mydriasis and
exophthalmos, whereas a beta-adrenergic antagonist had no significant
effect. This suggested a role for the sympathetic nervous system. However,
cervical sympathectomy or guanethidine pretreatment only partially blocked
the increase in PD or exophthalmos. Adrenalectomy also partially blocked
the mydriasis and exophthalmos. Adrenalectomy combined with guanethidine
pretreatment completely blocked morphine-induced mydriasis but no
exophthalmos. Thus, the results suggest that both direct sympathetic
innervation and hormonal action from the adrenals are involved in
morphine-induced mydriasis in the rat.
