AJP - Heart and Circulatory Physiology, Vol 243, Issue 1 113-H122, Copyright © 1982 by American Physiological Society
Circulatory effects of chemical sympathectomy in fetal, neonatal, and adult sheep
K. Tabsh, B. Nuwayhid, S. Murad, E. Ushioda, R. Erkkola, C. R. Brinkman 3rd and N. S. Assali
Circulatory effects of chemical sympathectomy with 6-hydroxydopamine
(6-HD), including changes in vascular sensitivity to neurotransmitters,
were investigated in chronically instrumented unanesthetized fetal,
neonatal, and adult sheep. In all animals acute response to 6-HD consisted
of hypertension and tachycardia, which lasted 2-3 h. Chronic phase of
sympathetic ablation then followed during which arterial pressure and heart
rate of sympathectomized fetus and neonate returned to and remained at
levels observed in intact animals, whereas adult sheep were slightly
hypotensive throughout this period. In all animals supersensitivity of
peripheral circulation to norepinephrine occurred, but only the fetus
exhibited supersensitivity to acetylcholine and isoproterenol. Our
conclusions are as follows: 1) acute phase of chemical sympathectomy in
fetal, neonatal, and adult sheep simulates strong adrenergic stimulation;
2) absence of significant alteration in arterial pressure of fetus and
neonate during the chronic phase of sympathectomy suggests a minor role for
the adrenergic system in the maintenance of resting tone of peripheral
circulation; and 3) on the basis of present and previous data, we postulate
that the supersensitivity of fetal circulation to acetylcholine and
isoproterenol may be secondary to changes occurring in pulmonary vascular
bed.
