LEFT-VENTRICULAR NOREPINEPHRINE AND EPINEPHRINE KINETICS AT BIRTH IN LAMBS

Little is known about the changes in the left ventricular (LV) kinetic s of the catecholamines norepinephrine and epinephrine occurring at bi rth and their relationship to perinatal alterations in LV function and whole-body catecholamine kinetics. To address this issue, whole-body and LV catecholamine kinetics (radiotracer dilution methodology) and f etal LV output and myocardial blood flow (radioactive microspheres) we re measured in chronically instrumented near-term fetuses and in the s ame animals 1 and 4 hours after birth. Between fetal and 1-hour lambs, LV external work increased 115% (P<.005); carotid arterial plasma nor epinephrine concentration, 148% (P<.01); carotid arterial plasma epine phrine concentration, 546% (P<.005); LV norepinephrine spillover, a me asure of LV sympathetic activity, 4.1-fold (P<.005); LV epinephrine sp illover, 3-fold (P<.05); total-body spillover of norepinephrine, 52% ( P<.025); and total-body spillover of epinephrine, 460% (P<.005). Arter ial catecholamine concentrations and total-body catecholamine spillove rs were unchanged between 1- and 4-hour lambs, but LV external work fe ll (P<.05) to a level still 77% greater than in fetal lambs (P<.005); LV norepinephrine spillover returned to near-fetal levels, and LV epin ephrine spillover became undetectable. These results suggest that (1) a transient increase in LV sympathetic activity occurs at birth and ma y contribute to the immediate postnatal augmentation of LV performance , (2) organ differences in the pattern of sympathetic activation occur at birth, and (3) birth-related increases in LV sympathetic activity are accompanied by release of epinephrine from the heart.