AJP - Heart and Circulatory Physiology, Vol 248, Issue 1 69-H74, Copyright © 1985 by American Physiological Society
Circulatory effects of splanchnic nerve stimulation in developing swine
N. M. Buckley, P. Brazeau, I. D. Frasier and P. M. Gootman
The relative maturity of immediate intestinal circulatory responses to
efferent splanchnic nerve stimulation for 20 s was tested in 34 piglets (1
day-1 mo old) under pentobarbital anesthesia (15-30 mg/kg). Aortic
pressure, heart rate, and superior mesenteric arterial flow (measured by
electromagnetic flow transducers) were recorded simultaneously. Intestinal
vascular resistance was calculated as mean aortic pressure/mean arterial
flow. Resistance increased in most animals during experimental inhibition
of the carotid sinus baroreceptor reflex. Transection of the splanchnic
nerve decreased mesenteric resistance in all animals. Nerve stimulation at
2 Hz was not effective in all of the youngest animals; at 3 Hz, mesenteric
resistance increased in all animals. The latency of this response was
shorter at each increase in stimulation frequency. The aortic pressure rise
associated with splanchnic nerve stimulation was greater with each increase
in frequency. This rise was attenuated or absent after adrenalectomy and
during postganglionic fiber stimulation. The vasoconstrictor effect of
splanchnic nerve stimulation was attenuated after alpha-adrenergic receptor
blockade with phentolamine in a dose (0.25-0.75 mg/kg) that blocked
vasoconstrictor effects of norepinephrine (0.5 micrograms/kg). We conclude
that alpha-adrenergic mechanisms are functional, although not mature, and
that sympathetic vasoconstrictor tone is present in the intestinal
circulation of swine at birth.
