Endocrine Mechanisms of Parturition

Abstract

Intrauterine growth and development follow an orderly sequence of critical phases that influence the several organ systems of the fetus differently at various times. Thus, placental growth and differentiation precede major growth of the fetus. The fetus develops in utero until capable of an indepen­ dent existence outside the uterus. In some mammals, for example the goat, cow, rat, and rabbit, progesterone production by the corpus luteum (CL) of pregnancy continues throughout gestation (51, 61,82-84,193,194,195, 196). In other species, the placenta gradually takes over this role (12, 25, 37, 83, 84, 118, 119, 127, 152, 208). Estrogens are also produced by the ovary and placenta during gestation (4,11,25,31,38,53,84,119,120,136, 156, 169). In the primate species the fetal and maternal adrenals provide precursors for placental estrogen synthesis (87, 164, 169, 175). Other hor­ mones, such as placental lactogen (PL) (chorionic somatomammotrophin) and chorionic gonadotrophin are necessary for normal maternal, placental, and fetal metabolism (51,88,90, 120,201). PL is produced by the syncytio­ trophoblast of the placenta and is a hormone of fetal origin. Thus, both fetal and maternal endocrine factors are of importance in the mechanisms that maintain the pregnant state. The process of parturiton also involves fetal and maternal factors whose role is to remove or supplant these maintenance mechanisms.