Circulatory effects of splanchnic nerve stimulation in developing swine

Abstract

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.

Intestinal and Femoral Blood Flow Autoregulation in Developing Swine

“…However, this stimulus should also have been effective in the youn ger animals because their intestinal circula tions participate in the same reflexes [9], Our effort to provide additional information on this question through the use of ganglionic blockade with hexaméthonium was limited by the subsequent hypotension that brought the intestinal perfusion pressure below the autoregulatory range in some animals and narrowed the range in others.…”

“…Although pentobarbital is known to depress the heart and ele vate aortic pressure (AoP) in swine [ 1. 18,24], we have shown that the baroreceptor reflexes [4,9] and periph eral vascular constrictor responses [5. 8.…”

“…This artery was separated from surrounding structures by blunt dissection to the site of ganglion and nerve bundles that lie several millimeters from its origin at the aorta. Then a calibrated flow transducer was placed around the vessel to measure mesenteric arterial blood flow (MBF) which supplies the entire small intestine in swine (9). The portal vein was cathcterizcd via a splenic vein in order to record venous pressure (PVP).…”

“…Femoral flow decreased with each decrease in pressure at all ages studied. Control experiments indicated that the observed vascular responses were independent of angiotension-11 activity and were not reflex in origin.Our research on the functional maturation of selected peripheral circulations includes the investigation of both neural [5,6,9] and autoregulatory [7] controls. We have pre viously demonstrated the postnatal timecourse of the development of intestinal and…”

“…femoral circulatory responses to efferent sympathetic nerve stimulation in swine [6,9] and have now examined blood flow autoreg ulation within the same range of postnatal ages using a controlled pressure protocol as in our study on the renal circulation [7], This investigation is the first of its kind for the developing hindlimb and small intestine. Evidence is presented that the capacity for intestinal or femoral blood flow autorcgulation develops later than that for renal blood flow autoregulation in the same species [7] and that, when present, intestinal blood flow autoregulation is more prominent in the jeju num than in the ileum.…”