Effect of melatonin (MEL) or maternal nutrient restriction on vascularity of the ovine placenta
Objectives were to determine placental vascularity following dietary MEL treatment in a maternal nutrient restriction model. A second experiment was performed to assess MEL receptor dependent modulation in placental vascularity. For Exp. 1, 31 ewes were supplemented with 0 (CON) or 5 mg of MEL per d and allocated to receive 100% (adequate fed; ADQ) of daily nutrient requirements or a 40% restriction in total feed intake (RES) from d 50 to 130 of gestation. Placentomes were collected on d 130 of gestation. For Exp. 2, 14 ewes were fitted with Alzet mini osmotic pumps and infused with vehicle, MEL, or MEL receptor 1 and 2 antagonist (luzindole, LUZ) from d 62 to 90 of gestation. Placentomes were collected on d 90. Placentomes from both Exp. 1 and 2 were fixed, paraffin embedded, and examined for capillary area density (CAD, total capillary area as a proportion of tissue area), capillary number density (CND, total number of capillaries per unit of tissue area), capillary surface density (CSD, total capillary circumference per unit of tissue area), and average cross-sectional area per capillary (APC) for both maternal (caruncular) and fetal (cotyledonary) compartments. For Exp. 1, a MEL x nutritional plane interaction (P = 0.02) was observed for caruncle CAD, which was decreased in MEL-RES vs. CON-RES (0.145 vs 0.269 ± 0.031). A MEL x nutritional plane interaction (P = 0.01) was observed for caruncle APC, which was decreased in MEL-RES vs. all other groups (95.8 vs. 171.7, 195.2, 165.6 ± 18.2 µm2). Cotyledon CND tended to be higher in MEL versus CON, while a tendency (P = 0.06) for a MEL x nutritional plane interaction was observed for cotyledon APC, which was decreased in MEL-RES vs. all other groups (85.9 vs. 122.3, 122.2, 124.9 ± 10.2 µm2). For Exp. 2, LUZ infusion tended (P = 0.08) to increase caruncle CAD (0.171 vs. 0.083 ± 0.026) and APC (129.2 vs. 48.1 ± 23.4 µm2) compared to vehicle infusion. Measurements of cotyledon vascularity were not different (P > 0.10) across infusion treatments. Supported in part by USDA-NIFA-AFRI grant 2011-67012-30683.
Keywords: placenta, sheep, vascularity