Abstract
SUMMARY: The administration of 1-α-methylallylthiocarbamoyl-2-methylthiocarbamoyl hydrazine (ICI 33828) to lactating rats in doses ranging from 5 to 40 mg. daily resulted in a marked inhibition of litter growth. When oxytocin (1 i.u. twice daily) was administered in addition to ICI 33828 (5 mg. or 20 mg. daily) the depression in litter growth rate was largely overcome. Histological studies indicated that the mammary glands of the treated mothers were secreting, but that the pups were unable to obtain the available milk without exogenous oxytocin. It is suggested that ICI 33828 acts on the hypothalamus by blocking the release of oxytocin and possibly enhancing the release of prolactin.