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The autocrine and paracrine role of the insulin-like growth factors (IGFs) and epiderrnal growth factor (EGF)-related peptides in pig ovary are reviewed. For convenience, each of these regulatory systems is divided into several interactive components: regulated expression of the growth factors, growth factor reception at the cell surface and intracellular action of the growth factors. In addition, the concept of regulated bioavailability and targeting of growth factors in the extracellular space is developed as an important control locus and area for future study. With regard to the 1GF system, these components include two ligands — IGF-1 and -II, both expressed in the porcine ovary —and the possibility of three receptors. IGF-I and the type I IGF receptor appear to be the most important in stimulating ovarian function and amplifying hormone action. In addition, the 'set-point' of the ovarian 1GF system may be determined by the activity of several IGF-binding proteins (IGFBPs). At least four of these proteins are expressed in the pig ovary. Studies of their regulation and action in ovarian cells indicate that they can function as antagonists to FSH and the IGFs. However, preliminary evidence suggests a more dynamic model in which these proteins may direct the site and timing of IGF effects. There are fewer data on the EGF system. At least four EGF-related peptides are expressed in pig ovaries, but insufficient information is available to predict their physiological regulation. These peptides are potent mitogens for ovarian cells. Their steroidogenic effects are more variable, apparently depending on the level of differentiation of target cells as well as the presence or absence of critical co-factors. Differential targeting and activation of these peptides can be predicted from their primary structure. However, few data are yet available to substantiate these mechanisms in the ovary. The data in each of these areas suggest a pivotal role for these systems in ovarian function. However, control of these systems in vivo will be required to confirm this hypothesis.

The role of insulin-like growth factors and epidermal growth factor-related peptides in intraovarianregulation in the pig ovary