Figure 17. Diagram showing the regulatory mechanisms of androgen production by theca interstitial cells. The principal endocrine regulators of androstenedione production are LH, insulin, and lipoproteins. The LH receptor/cAMP/PKA signaling pathway leads to the induction of specific genes (broken lines) in the androstenedione biosynthetic pathway. Insulin receptor/protein tyrosine kinase (PTK) signaling can cause marked increases in this response. Lipoproteins are potent stimulators of theca androgen production by virtue of their ability to increase intracellular cholesterol which in turn is transferred to P450C22 via StAR. (Erickson, GF. Normal regulation of ovarian androgen production. Semin Reprod Endocrinol 11:307, 1993. Reproduced with permission from Thieme Medical Publishers.)