REDUCED AVAILABILITY OF MILK AFTER CENTRAL INJECTIONS OF CORTICOTROPIN-RELEASING HORMONE IN LACTATING RATS

Corticotropin-releasing hormone (CRH) plays a major role in activating the pituitary-adrenal axis in stress; its central application may therefore be expected to mimic stress. Since stress reportedly disrupts lactation, experiments were designed to study the effects of CRH administration upon the transfer of milk from rat mothers to their pups and to examine some of the possible underlying physiological mechanisms. CRH was administered intracerebroventricularly to primiparous rats on the 8th day of lactation immediately prior to being reunited with 8 of their overnight-separated pups. Changes in litter weights were measured for a period of up to 4 h as an index of milk procurement by the young (milk transfer); a qualitative assessment of maternal behaviour was also made. Treatment of dams with 0.1-1 nmol CRH resulted in a dose-dependent reduction in the amount of milk obtained by the pups. Conscious mothers treated with CRH initially showed intense behavioural activation; these events (mainly hyperlocomotion and grooming) in the mother resulted in reduced opportunities for nipple attachment by the pups and, thus, milk transfer. On the other hand, milk transfer was also significantly reduced in urethane-anaesthetized mothers treated with CRH, indicating that behavioural activation cannot have been the sole factor underlying the CRH-induced inhibition of milk transfer in awake dams. Although oxytocin (OT) release is stimulated by a variety of stressors, the possibility of an inhibitory effect of CRH upon OT secretion and/or disruption of the reflex are serving milk ejection was considered. The peripheral administration of OT (100 mU/rat s.c.) did not, however, surmount the inhibitory actions of CRH upon milk transfer. In view of other reports that CRH may in fact enhance OT secretion, it is tentatively proposed that the inability of exogenously administered OT to facilitate milk transfer might be related to the known effects of centrally applied CRH upon the autonomic nervous system.