Corpora lutea in superovulated ewes fed different planes of nutrition

The corpus luteum (CL) is an ovarian structure which is critical for the maintenance of reproductive cyclicity and pregnancy support. Diet and/or diet components may affect some luteal functions. FSH is widely used to induce multiple follicle development and superovulation. We hypothesized that FSH would affect luteal function in ewes fed different nutritional planes. Therefore, the aim of this study was to determine if FSH-treatment affects (1) ovulation rate; (2) CL weight; (3) cell proliferation; (4) vascularity; (5) expression of endothelial nitric oxide (eNOS) and soluble guanylate cyclase (sGC) proteins; and (6) luteal and serum progesterone (P4) concentration in control (C), overfed (O), and underfed (U) ewes at the early- and mid-luteal phases. In addition, data generated from this study were compared to data obtained from nonsuperovulated sheep and described by Bass et al. Ewes were categorized by weight and randomly assigned into nutrition groups: C (2.14 Mcal/kg; n = 11), O (2xC; n = 12), and U (0.6xC; n = 11). Nutritional treatment was initiated 60 d prior to day 0 of the estrous cycle. Ewes were injected with FSH on day 13-15 of the first estrous cycle, and blood samples and ovaries were collected at early- and mid-luteal phases of the second estrous cycle. The number of CL/ewe was determined, and CL was dissected and weighed. CL was fixed for evaluation of expression of Ki67 (a proliferating cell marker), CD31 (an endothelial cell marker), and eNOS and sGC proteins using immunohistochemistry and image analysis. From day 0 until tissue collection, C maintained, O gained, and U lost body weight. The CL number was greater (P < 0.03) in C and O than U. Weights of CL, cell proliferation, vascularity, and eNOS but not sGC expression were greater (P < 0.001), and serum, but not luteal tissue, P4 concentrations tended to be greater (P = 0.09) at the early- than mid-luteal phase. Comparisons of CL measurements demonstrated greater (P < 0.01) cell proliferation and serum P4 concentration, but less vascularity at the early and mid-luteal phases, and less CL weight at the mid-luteal phase in superovulated than nonsuperovulated ewes; however, concentration of P4 in luteal tissues was similar in both groups. Thus, in superovulated ewes, luteal cell proliferation and vascularity, expression of eNOS, and serum P4 concentration depend on the stage of luteal development, but not diet. Comparison to control ewes demonstrated several differences and some similarities in luteal functions after FSH-induced superovulation.