Abstract
SUMMARY Nidation may be induced on the evening of L3 in hypophysectomized pregnant rats by subcutaneous injection of proteolytic enzymes, protein precipitants, and by acidic extracts of rat hypothalamus, cerebral cortex, heart, liver and spleen. With the exception of the protein precipitants, these materials apparently stimulated the ovary to release sufficient oestrogen for nidation provided that exogenous progesterone was available. Similarly, implantation could be induced (on L9) by extracts of adenohypophysis, hypothalamus, cerebral cortex or trypsin in hypophysectomized pregnant rats in delayed nidation. However, a single injection of blood serum from male or female rat donors was ineffective. The assumption is made that specific gonadotrophins from the pituitary are not the only factors able to cause release of oestrogen from the ovary.
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