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The primary blood supply to the uterus is the uterine artery, a major branch of the hypogastric or internal iliac artery. In the fetus this same hypogastric artery gives rise to the umbilical artery, which delivers nearly 50% of the cardiac output to the placenta. This fact is mentioned in order to stress the remarkable capability of this particular portion of the vascular system to accommodate a tremendous increase in blood flow during pregnancy. The uterine arteries descend for a short distance (about 4 cm) after dividing from the hypogastric (internal iliac) artery. In the base of the broad ligament, the uterine artery progresses medially, crossing anterior to the ureter about 2 cm lateral to its division into the cervicovaginal artery and the ascending uterine artery at the level of the supravaginal portion of the cervix. The ascending branch runs a tortuous course along the lateral margin of the uterus, providing a major branch to the upper portion of the cervix and eight to 24 arcuate branches to the uterus1 (Fig. 1). The tortuosity of the uterine artery as it traverses the broad ligament and as it ascends the uterus is directly related to the woman′s parity. The arteries of parous women assume a much more convoluted and tortuous course.

In many animal species as well as in women, the function of the corpus luteum appears to be regulated by both luteotropic and luteolytic factors. The limited accessibility to well-defined human tissue has impaired studies on the human corpus luteum, and most knowledge, therefore, is based on extrapolations from measurements of steroids in the ovarian vein blood, or in the systemic circulation. Since a countercurrent system carrying steroids and prostaglandins (PGs) from the uteroovarian vein to the ovarian artery has been demonstrated both in animals (1) and in women (2), an intraovarian hormonal environment is created different from that of the periphery. This local milieu appears to be important for follicular development, ovulation and corpus luteum formation and function, which can be regarded as a dynamic sector within the ovary. However, there exists also a more static compartment, represented by primordial follicles and stromal cells. In the following, we will focus the discussion upon factors regulating the corpus luteum function during its life span. Crudely, these influences can be divided into distant factors, e.g., gonadotropins, and local factors, represented by PGs and catecholamines. Since we recently reviewed the gonadotropic regulation of human corpus luteum function (3), the current presentation will be restricted to the above-mentioned local factors. The intimate interrelation between these two regulatory systems, however, must be kept in mind.

The uteroplacental arterial system is rather similar in various species (see Lundgren, 1957; Reynolds, 1963; Moll and Kunzel, 1971; Egund and Carter, 1974; Del Campo and Ginther, 1972). As shown for man and guinea pig in Figure 1, the uterine artery and the ovarian artery provide a dual arterial supply. From their anastomosis, the uterine arcade, segmental parametrial (mesometrial) off-shoots arise, divide in one or several branches and enter the uterus. These branches are short and barely accessible in the human but long and easily accessible in rodents. Inside the uterine wall the arteries form a network of arcuate (circumferential) arteries which gives rise to the coiled arteries, i.e., the radial arteries (in the strict sense) in the myometrium and the spiral arteries in the endometrium, part of which supply the placenta. There are differences in the extent to which the various components are involved in the control of uteroplacental blood flow; the basic anatomical pattern, however, is the same in the different species.

The luteolytic effect of prostaglandin F2α (PGF2α) was first reported in rats by Pharriss and Wyngarden in 1969 (18). Since that time this prostaglandin has been found to have a similar effect in many mammalian species, including monkeys, but not humans (16). Prostaglandin F2α has been shown to have a physiological role as a luteolytic hormone in the sheep (17). It is produced in high concentrations by the uterus at the end of the estrus cycle and is transferred from the uteroovarian vein to the ovarian artery by a countercurrent mechanism (17).