RESUMPTION OF LACTATION BY SUCKLING IN LACTATING RATS AFTER REMOVAL OF LITTERS

Abstract

SUMMARY Foster litters were given to lactating rats whose own litters had been removed 3, 5 or 9 days previously. Lactation was restored in all groups by this re-suckling procedure within a relatively short period. The restoration of lactation became more difficult as the interval between the removal of the original litters and the application of the foster litters increased. Changes in the nucleic acid content of the mammary gland after re-suckling were investigated in the rats whose litters were removed for 3 days before re-suckling. Both the DNAP content of the gland and its weight increased steadily in proportion to the length of the period of re-suckling, so that a fairly constant DNAP concentration was maintained in the tissue. The RNAP content and the RNAP:DNAP ratio, on the other hand, increased abruptly at about the time when milk secretion was initiated by re-suckling. The DNAP content continued to increase even after the onset of restored milk secretion. These results suggest that milk secretion after re-suckling began before full restoration of the tissue structure and that growth of the glandular tissue took place concurrently with milk secretion.