Responses of iris blood flow to stimulation of the cervical sympathetic in the rabbit

Abstract

o (1) The effects of α- and β-blocking agents (phentolamine and propranolol) on the responses of iris vessels to stimulation of the cervical sympathetic in albino rabbits were studied. Vascular responses were expressed in terms of percentage changes of vascular heat dissipation ( Cole and Rumble, 1970 ). (2) Using square wave stimulation at 21 Hz there was a linear relationship of vascular response to stimulus intensity and the action of the antagonists was shown by alterations in the slope of the stimulus/response line. (3) Phentolamine given by close arterial infusion, intravitreal injection or transcorneal iontophoresis markedly diminished the response to sympathetic stimulation but propranolol had little or no effect. In further experiments the log dose response curves to exogenous noradrenaline and isoprenaline showed the action of noradrenaline to be enhanced 24 hr after superior cervical ganglionectomy whilst the isoprenaline response was unchanged. (4) The experiments with blocking agents suggested the β-receptor sites subserved little or no part in the response to sympathetic stimulation. The ganglionectomy experiments indicate that sites in the iris responsible for isoprenaline uptake are either absent or extraneuronal.