The Effect of Melatonin or Maternal Nutrient Restriction on Cell Proliferation in the Ovine Placenta

Our objectives were to assess melatonin receptor dependent modulation of placental cell proliferation following treatment with either melatonin, luzindole (melatonin receptor 1 and 2 antagonist), or vehicle. In addition, a second study was conducted to assess placental cell proliferation following dietary melatonin treatment in a maternal nutrient restriction model. For the first experiment, 14 primiparous ewes were fitted with Alzet mini osmotic pumps attached to a catheter and infused with vehicle, melatonin, or luzindole from d 62 to 90 of gestation. Ewes were euthanized and placentomes collected for analysis at the end of the 4 week infusion. For the second experiment, 31 primiparous ewes were supplemented with 5 mg of melatonin per d (MEL) or no melatonin (CON) and allocated to receive 100% (adequate) or 60% (restricted) of their nutrient requirements from d 50 to 130 of gestation. On d 130 of gestation, ewes were euthanized and placentomes were collected for analysis. Placentomes from both experiment 1 and 2 were examined for percentage of proliferating cells using an immunofluorescence assay. A Ki-67 mouse monoclonal antibody was used to stain proliferating cells within each tissue section and was compared to non-proliferating cells stained with DAPI to determine the percentage of proliferating cells within each sample. Total RNA, DNA and protein was also analyzed within each sample. For experiment 1, cell proliferation in the cotyledon and caruncle was not affected (P \u3e 0.30) by vehicle, melatonin or luzindole infusions. Dietary melatonin supplementation from mid to late gestation may impact cotyledon cell proliferation; however chronic infusion of melatonin or luzindole did not change proliferation in either the cotyledon or caruncle. Treatment did not alter the concentrations of RNA, DNA, protein (P . 0.15), or the ratio of RNA:DNA and the ratio of protein:DNA (P . 0.17). For experiment 2, there was no melatonin supplementation by nutritional plane interactions (P \u3e 0.50) on cellular proliferation in either the cotyledon or caruncle. There was a tendency (P = 0.08) for melatonin supplemented ewes to have an increased percentage of proliferating cells in the cotyledon; however, this effect of melatonin was absent (P \u3e 0.30) in the caruncle. Nutritional plane did not alter cellular proliferation in either the cotyledon (P \u3e 0.70) or caruncle (P \u3e 0.50). There was no effect of nutritional plane or melatonin treatment on the concentration of DNA or protein (P . 0.21) in caruncular tissue. However there was an interaction on RNA (P = 0.02) in caruncular tissue which may be due to an increase in gene expression following melatonin treatment. There was no effect of treatment or nutritional plane on DNA, RNA, protein (P . 0.20) as well as no effect on RNA:DNA or protein:DNA (P . 0.25). In summary, melatonin may alter placental growth in ewes with IUGR; however, this needs further investigation