Hormonal requirement for ovum implantation
Hormonal requirement for ovum implantation varies among the species of animals. The methods attempting to clarify the requirement in each species may be classified as follows:
hormonal replacement therapy after removal of the pituitary or/and the ovaries
hormonal treatment after reduction of specific hormones by its antiserumin vivo
close observation of hormone secretion pattern in early pregnancy
examination of physiological conditions where implantation is delayed and analyze the hormone levels and the receptivity of the target tissues
examination of effects on hormone levels and the receptivity of target tissues of drugs which interfere with implantation. The reported results indicate that both progesterone and estrogen are needed for implantation in rats, mice, and Mongolian gerbils; in other species of animals progesterone alone may be sufficient to induce implantation, although synergistic effect of estrogen appears to be seen in some species such as in the rabbit. It remains to be determined whether the blastocysts of those animals that need only progesterone for implantation have greater ability to produce estrogen than the blastocysts of the animals that need both progesterone and estrogen. Control mechanism of secretion of progesterone and estrogen for inducing implantation may be different in various species. It has been suggested that both leutropin and follicle stimulating hormone are needed for pre-implantation estrogen secretion in the rat, whereas only follicle stimulating hormone is needed in the mouse. In the species where the obligatory delay in implantation is observed, neuroendocrine mechanisms are reported to be involved in controlling the pituitary-ovarian function that causes a delay in implantation.