POLE OF VAGAL NERVE ACTIVITY DURING SUCKLING - EFFECTS ON PLASMA-LEVELS OF OXYTOCIN, PROLACTIN, VIP, SOMATOSTATIN, INSULIN, GLUCAGON, GLUCOSE AND OF MILK SECRETION IN LACTATING RATS

The aim of this study was to investigate the role of vagal nerve activ ity for the release of oxytocin, prolactin and gastrointestinal (GI) h ormones during suckling as well as for the secretion of milk in lactat ing rats. We have therefore performed experiments on vagotomized lacta ting rats. The animals were decapitated and trunk blood was collected from nonsuckling rats and from suckling rats in connection with milk e jection. Oxytocin, prolactin, vasoactive intestinal polypeptide (VIP), somatostatin, insulin, glucagon and glucose levels in plasma were mea sured by RIA-technique. In addition, maternal weight as well as the we ight of the litters were recorded 7 d after vagotomy. As expected, oxy tocin and prolactin levels rose in response to suckling in sham-operat ed controls. In vagotomized animals the suckling-induced increase of o xytocin was blocked and prolactin levels were significantly decreased. VIP levels in plasma increased following suckling in sham-operated an imals and failed to respond after vagotomy. In contrast, somatostatin levels that rose significantly in sham-operated rats were even more si gnificantly raised in vagotomized animals. In addition, insulin but no t glucagon levels were increased by suckling. The insulin response, ho wever, persisted after vagotomy. Interestingly, suckling was followed by a lowering of blood-glucose levels in vagotomized, but not in sham- operated animals. The vagotomized rats ate as much and increased in we ight as sham-operated rats during the 7 d of vagotomy. The litters of vagotomized rats, however, gained significantly less weight in compari son with control litters. In conclusion, this study shows that vagal n erve activity is of importance for the release of oxytocin, prolactin, vasoactive intestinal polypeptide and somatostatin during suckling. I n addition, vagal nerve activity was found to be of fundamental import ance for adequate milk secretion, since litters of vagotomized rats in creased in weight less than litters of sham-operated operated animals.