Mechanisms associated with subnormal luteal function

Mechanisms associated with subnormal luteal function are reviewed with particular reference to sheep and cattle. Since the corpus luteum is a continuation of follicular maturation, mechanisms during both the follicular and luteal phase have been considered. During the follicular phase, extrafollicular and intrafollicular events are important for adequately preparing follicular cells for luteinization and secretion of progesterone (P4). Mechanisms which alter the microenvironment of the preovulatory follicle may impair the ability of follicular cells to subsequently secrete P4 and result in subnormal luteal function. During the luteal phase, secretion of P4 is probably dependent upon a balance between luteotropic and luteolytic stimuli. Subnormal luteal function may be due to an inadequate luteotropic stimulus and(or) an inability of luteal tissue to respond to a luteotropic stimulus. Additionally, a premature luteolytic stimulus may be involved in reduced luteal function. Specifically, premature luteolysis may result from an increased or premature release of a luteolysin or perhaps an increased responsiveness of luteal tissue to a luteolysin.