Leptin Is Involved in Vascularization of Developing Luteal Tissue.

Abstract

Over half of idiopathic miscarriages are attributed to corpora luteal (CL) defects. Defective luteal tissue typically arises from aberrant luteal development, which commonly results in a decrease in progesterone production. Numerous factors have been identified in the regulation of luteal development including improper vascularization of the developing CL. Several different angiogenic regulators have been identified as playing an important role in vascularization of luteal tissue including vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF-2), and angiopoietin 1 (Ang-1). All three factors stimulate vascular growth in non-ovarian tissues where they are regulated by various growth promotants including leptin. Leptin is an important metabolic hormone known to have both reproductive and angiogenic properties. Previously, we reported that the expression of both leptin and its receptor is highest in the early stage of the luteal phase and that VEGF, FGF-2, and Ang-1 expression are upregulated by leptin in early, developing luteal tissue. Furthermore, it was determined that blocking ovarian leptin changed luteal vascular morphology and significantly altered the number of large luteal cells present in a day 15 CL. Collectively, the evidence suggests that leptin may be involved in angiogenesis of developing luteal tissue. Therefore, it is hypothesized that ovarian leptin is involved in the vascularization of the developing CL. Eleven cycling crossbred does of similar age were randomly allocated to one of four treatment groups: Control [C; saline in 2.5U heparin (vehicle) only; n=3], rabbit anti-leptin antibody + saline [AL+S; AL antibody (1:10 dilution) in vehicle + vehicle only; n=3], saline + leptin [S+L; vehicle + leptin (1ug, ovine leptin) in vehicle; n=2), and rabbit anti-leptin antibody + leptin (AL+L; in vehicle; n=3). Females were checked twice daily for classical, behavioral estrus and on day 10 of the 3rd estrous cycle does were synchronized (PGF2a administration) for the surgical insertion of a 7-day osmotic infusion pump-catheter apparatus, in apposition to each ovarian hilus, 48 hr post injection (day 0; estrus). Catheter and pump apparatus infused the first treatment (vehicle, anti-leptin, or leptin) over a period of 3 days followed by the second treatment (vehicle, anti-leptin, or leptin) over a period of 4 days, at a flow rate of 0.5 μl/hr. On day 8, ovaries were surgically removed for CL collection and analysis. Gross morphology of CL tissue was recorded and either snap frozen in liquid nitrogen for mRNA analysis or paraffin embedded for microscopic evaluation. Blood samples were collected via jugular venipuncture, from day 0 until day 8 for analysis of serum progesterone during the infusion period. Data was analyzed using MIXED procedures of SAS. Luteal tissue from the S+L and AL+L treatment was underdeveloped but highly vascular. Moreover, progesterone production was low (P<0.05) in all treatment groups compared to the control group. Although luteal expression of VEGF and FGF2 did not differ, Ang-1 was significantly lower (P<0.05) in all treatments compared to the control group. Collectively, the evidence supports the supposition that leptin appears to be involved in vascularization of the developing CL. This research was funded by NIH-NIGMS-MBRS Award #1SCGM095443-01.