Increased spillover and reduced clearance both contribute to rise in plasma catecholamines after birth in lambs. Smolich, Joseph J., Helen S. Cox, Graeme Eisenhoferc, and Murray D. Eslerb. Institute of Reproduction and Development, Monash University, Clayton, Victoria, Australia; Baker Medical Research Institute, Prahran, Victoria, Australia; Clinical Neuroscience Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, U.S.A.
APStracts 2:0347H, 1995.
By combining blood flow and catecholamine kinetic data, we defined the inter-relationship between changes in plasma levels, total body spillover and total body clearance of norepinephrine and epinephrine occurring with birth. Fetal lambs were instrumented under general anaesthesia at 133-134 days gestation (term = 147 days) with arterial, peripheral venous and left atrial catheters. One week later, fetal norepinephrine and epinephrine kinetics were measured using isotope dilution methodology and systemic blood flows obtained with radioactive microspheres. Measurements were repeated in newborn lambs 1 and 4 hours after cesarean section delivery. Between fetal and 1 hour lambs, 1) systemic output fell from 505 +/- 26 to 339 +/- 16 ml x min-1 x kg-1 (P &LT 0.005): 2) systemic plasma norepinephrine concentration increased from 995 +/- 97 to 2,424 +/- 324 pg x ml-1 (P &LT 0.005) and plasma epinephrine concentration from 40 +/- 9 to 329 +/- 50 pg x ml-1 (P &LT 0.005); 3) norepinephrine total body spillover rose from 161 +/- 20 to 262 +/- 48 ng x min-1 x kg-1 (P &LT 0.01) and epinephrine total body spillover from 5.4 +/- 0.9 to 31.1 +/- 6.4 ng x min-1 x kg-1 (P &LT 0.005); 4) norepinephrine total body clearance decreased from 160 +/- 13 to 105 +/- 9 ml x min-1 x kg-1 (P &LT 0.005) and epinephrine total body clearance from 144 +/- 12 to 91 +/- 7 ml x min-1 x kg-1 (P &LT 0.005). Systemic blood flow and catecholamine data were similar in 1 and 4 hr lambs, and values at these time points were therefore pooled to define the relation between perinatal changes in catecholamine plasma levels, spillover and clearance. Between fetal and newborn lambs, plasma norepinephrine rose by 1,375 +/- 207 pg x ml-1, of which 604 +/- 119 pg x ml-1 (44%) resulted from increased norepinephrine total body spillover and 771 +/- 160 pg x ml-1 from reduced norepinephrine total body clearance. In the same interval, plasma epinephrine rose by 292 +/- 30 pg x ml-1, of which 123 +/- 18 pg x ml-1 (42%) was due to increased epinephrine total body spillover and 169 +/- 19 pmol x ml-1 to reduced epinephrine total body clearance. These findings indicate that 1) sympatho -adrenal activity increases with birth; 2) increased total body spillover and reduced total body clearance contribute a similar portion of the plasma norepinephrine and epinephrine surge at birth. 

Received 16 March 1995; accepted in final form 4 August 1995.
APS Manuscript Number H253-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.