Effects of labor contractions on catecholamine release and breathing frequency in newborn rats

Abstract

Plasma catecholamines in newborn rats (0-2 hr old) were analyzed following vaginal birth, cesarean section with simulated labor contractions, or cesarean section without labor contractions. Upon delivery, pups were exposed to key elements of the rat's natural birth process, that is, umbilical cord occlusion, tactile stimulation, and cooling. Only pups exposed to actual or simulated labor showed an immediate rise in norepinephrine and epinephrine. Initial postpartum respiratory frequencies were higher in vaginal than in cesarean delivered pups and, in all groups, inversely correlated with catecholamine titers, suggesting respiratory distress or transient tachypnea at lower catecholamine levels. These findings establish a rat model for analyzing effects of labor on neonatal adaptive response during the transition from prenatal to postnatal life.

Figure 1

Ambient postpartum temperature in relation to time since birth (in minutes) for blood collection and respiratory sampling in vaginal, compressed, and noncompressed pups.

Figure 2

Postpartum plasma norepinephrine titers (M ± SEM in pg/100 μl plasma) following either vaginal birth (V), cesarean birth with compressions (C), or cesarean birth with no compressions (NC) at 0, 5, 30, 60, 90, and 120 min postpartum. Pups in the V and C conditions were significantly different from pups in the NC condition at 0 min postpartum. *p < .05.

Figure 3

Postpartum plasma epinephrine titers (M ± SEM in pg/100 μl plasma) following either vaginal birth (V), cesarean birth with compressions (C), or cesarean birth with no compressions (NC) at 0, 5, 30, 60, 90, and 120 min postpartum. Pups in the V and C conditions were significantly different from pups in the NC condition at 0 min postpartum. *p < .05.

Figure 4

Respiratory movements of rat pups (M ± SEM) at time 5, 30, 60, 90, or 120 min following either vaginal birth (V), cesarean birth with compressions (C), or cesarean birth with no compressions (NC). Pups in the V condition were significantly different from pups in the C and NC conditions at 5 min postpartum. *p < .05.