Abstract
Hormone-induced adaptations occur in many aspects of maternal physiology during gestation. Before these changes can be initiated, the newly formed blastocyst must signal its presence to the mother. This process is known as the maternal recognition of pregnancy and occurs in all mammalian species, but there are important species differences in how this process is achieved. Because progesterone is essential to support uterine function in pregnancy, a critical step is to maintain the function of the corpus luteum, formed from the freshly ovulated follicle, to sustain progesterone secretion. Humans and other primates have an extended luteal phase during their menstrual cycle, and post ovulatory progesterone secretion continues for a period beyond the time of implantation. Hence, these species use a placenta-derived hormone, human chorionic gonadotropin, to act as a luteotrophic hormone. Commonly used laboratory rodent species, however, have a short luteal phase during their oestrous cycle, and progesterone secretion lasts for only a few hours after ovulation. These species use a mating-induced signal to support corpus luteum function to initiate pregnancy. A unique neuroendocrine reflex initiated by vagino-cervical stimulation during mating induces a pattern of twice-daily prolactin surges that provide luteotrophic support for the first part of pregnancy, maintaining progesterone secretion until implantation can occur. After formation of the placenta, placental lactogens take over as the primary luteotrophic hormones. This chapter reviews the initial processes whereby the establishment of pregnancy is signalled to the maternal endocrine system, sustaining progesterone secretion and enabling subsequent initiation of hormone-induced adaptive changes in maternal physiology and behaviour. In the interests of limiting the scope of the chapter, we have focused on humans and rodents, as the major biomedical research species. We have not attempted to describe the processes in the blastocyst and uterus leading to implantation, which are clearly important for pregnancy but do not have a significant neuroendocrine involvement. Similarly, we have not covered immune interactions between the conceptus and the mother.