THE NORADRENERGIC INNERVATION OF THE RAT THYMUS DURING PREGNANCY AND IN THE POST-PARTUM PERIOD

The noradrenergic innervation of the rat thymus during pregnancy and t he post partum period was examined by a sucrose glyoxylic acid method for catecholamines, and by high pressure liquid chromatography. Fluore scent nerves decreased in number throughout pregnancy when there was a n overall loss in thymic weight due to cortical involution. These chan ges are maximal by parturition. There was a dramatic increase in nerve s between d 21 of pregnancy and d 1 after parturition, especially in t he capsule and around blood vessels in the connective tissue septa. Th e neonates were removed at parturition and thymic weight was rapidly r egained. The increased numbers of nerves remained throughout this post partum period. Noradrenaline levels in the thymus altered in a simila r pattern throughout pregnancy and the post partum period, but did not parallel thymic weight changes. The mean noradrenaline concentration in the virgin thymus was 1063 +/- 107 pg/mg protein. Levels remained s imilar during early pregnancy and increased significantly at d 16. Vir gin levels were regained by d 21. Values peaked after parturition but rapidly decreased over the next 3 days, and remained at or below virgi n levels to d 28 except for a transient rise at d 10 post partum. Adre naline values were consistently below detection levels. This study sho ws that there are variations in both nerves visualised, and in neurotr ansmitter (noradrenaline) content in the thymus during the course of p regnancy and the post partum period. Thus thymic function could be inf luenced by central events (levels of catecholamines in peripheral bloo d) as well as local events mediated by transmitter changes in nerves.