ENDOTHELIN CONCENTRATIONS IN RESPIRATION-RELATED STRUCTURES OF THE MEDULLA DURING THE PERINATAL-PERIOD OF THE RAT

Endothelin-like immunoreactivity (ET-LI) was quantified in the develop ing (foetal and postnatal) rat brain stem and cerebellum using radioim munoassay. The brain stem structures chosen for this study were (a) do rsal medullary region (DMR) including the region of nucleus tractus so litarius where the peripheral chemoreceptor afferents are known to ter minate, (b) ventral medullary region (VMR) where the central chemorece ptors are thought to be located and (c) cerebellum (CER), as a control area. Compared to the prenatal period, significantly elevated concent rations of ET-LI were detected in the early postnatal period and there after the concentrations decreased: DMR and VMR: in comparison to the prenatal concentrations, a two-fold increase was found on the day of b irth which further increased significantly (P < 0.001) on postnatal da y 1 only in the region of DMR; CER: low concentrations of ET-LI were f ound in the early postnatal period which were not significantly differ ent from the prenatal values. No ET-LI could be detected in any of the three regions in the adult rats. The results are discussed in view of the hypothesis that (1) endothelin appears to play an important role in the perinatal period and (2) it is involved in the chemoreceptor pa thway.