Responses of newborn pig pial arteries to sympathetic nervous stimulation and exogenous norepinephrine.

The purpose of this study was to examine responses of pial arteries of newborn pigs to stimulation of sympathetic nerves and to exogenous norepinephrine. In the cerebral circulation, pial arteries are important resistance vessels. Diameters of pial arteries in anesthetized piglets, aged 1-6 days, were determined using the "closed" cranial window method. Electrical stimulation of the ipsilateral superior cervical ganglion (16 Hz; 2.5 msec; 10 V) reduced pial arterial diameter from 219 +/- 13 microns (mean +/- SEM) to 190 +/- 12 micron (n = 16) (p less than 0.05) without affecting arterial blood pressure. Pial arterial constriction during nerve stimulation was sustained over the 5-min stimulation period. Following cessation of stimulation, diameters returned to control levels. Exogenous norepinephrine in artificial cerebrospinal fluid constricted pial arteries from 149 +/- 19 to 133 +/- 18 microns at 2 X 10(-6) M (p less than 0.05) and from 159 +/- 20 to 123 +/- 16 microns at 2 X 10(-4) M (p less than 0.05) (18 arteries from nine piglets). Pial arterial responses to nerve stimulation and exogenous norepinephrine were not dependent on initial size of the vessels. The results of this study establish the existence of functional sympathetic innervation in the cerebral circulation at birth in pigs.