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The Possible Vascular Regulation of Luteal Function

The corpusluteum is oneofthe most unique structures that exist inmam- mals. This endocrine gland appears out of"primordiallike" cells, grows to maturity, and then completely disappears, at least functionally. All this occurs in a period quite limited when compared with the functional life ofthe ovary itself. The fleeting quality ofthe gland has been commented upon by Rothchild (i): "This ephemerality is one of the most distinctive features ofthe corpus luteum and may be a clue to the nature ofits activity and the way this activity is regulated." The manner in which the corpus luteum is regulated has intrigued repro- ductive physiologists for several decades (fig. i). The role ofthe hypo- thalamus has been described at length, as have several routes for feedback control ofgonadotropin release originating from the ovary. It is generally accepted that the anterior pituitary is controlled by releasing factors or in- hibiting factors which are liberated from various centers in the hypo- thalamus and reach the pituitary by way of the specialized portal blood system connecting these two areas. Each pituitary gonadotropin has its hypothalamic factor—a releasing factor for follicle stimulating hormone (FSH) and luteinizing hormone (LH) each and an inhibiting factor for prolactin, at least in the rat. The FSH released is thought to be responsible for follicular maturation and estrogen secretion. The LH induces ovulation and luteinization of the granulosa cells which undergo hypertrophy and hyperplasia until the mature corpus luteum is formed. This corpus luteum is the source of progesterone. The estrogens and progestogens, besides priming the uterus for reproductive processes, also feed back on the hypo- thalamus and pituitary to regulate gonadotropin release. It is also known