Lipid droplets in the ovine uterus during the estrous cycle: Effects of nutrition, arginine, and FSH

The aim of this study was to evaluate lipid droplet (LD) expression in uteri of FSH-treated or nontreated sheep administered with arginine (Arg) or vehicle (saline, Sal) and fed a control (C), excess (overfed, O) or restricted (underfed, U) diet. In experiment 1, ewes from each diet were randomly assigned to Arg or Sal treatments administered three times daily starting on Day 0 of the first estrous cycle until blood sample and uterine tissue collection at the early- or mid-luteal phase of the second estrous cycle or the late-luteal phase of the first estrous cycle. In experiment 2, ewes were injected twice daily with FSH on Days 13 to 15 of the first estrous cycle, and blood samples and uterine tissue were collected at the early- and mid-luteal phases of the second estrous cycle. Cryopreserved in optimum cutting temperature (OCT) compound, cross-sections of uterine horn were stained with boron-dipyrromethene (BODIPY; marker of LDs) followed by 4′,6-diamidino-2-phenylindole (DAPI) staining and image analysis to determine the proportion (%) of area occupied by LD in luminal epithelium (LE) and endometrial glands (EGs). Control ewes maintained, O ewes gained, and U ewes lost body weight during the experiments. Serum progesterone concentration was not affected by nutritional plane or Arg treatment and was 5.5-fold greater in FSH- than Sal-treated ewes. LDs were detected in LE and superficial EG (close to LE) but not deep EG, or other uterine compartments, and area occupied by LD was greater in LE than in EG. In experiment 1, in LE and EG, area occupied by LDs was greater in C than in O or U; greater in Arg than in Sal; and greater at the late-, less at mid-, and least at early-luteal phases. In experiment 2, in LE and EG, area occupied by LDs was greater at mid- than in early-luteal phase. Comparison of data from FSH-treated and nontreated ewes (e.g., experiment 1 vs. experiment 2) demonstrated that FSH increased the area occupied by LD in LE and EG regardless of diet. Interactions between FSH treatment, stage of the estrous cycle, and plane of nutrition demonstrated that FSH increased the area occupied by LD in LE and EG at the mid-luteal phase in O and U. Thus, LDs are differentially distributed in uterine compartments, and area occupied by LD in endometrium is affected by nutritional plane, Arg or FSH, and stage of the estrous cycle. Such changes in dynamics of LD in the endometrium during the estrous cycle indicate their specific role in uterine functions.