Efectos de la selección y de la superovulación en las pérdidas gestacionales de ratonas CF1 / Effects of selection and superovulation on gestational losses in CF1 mice

En un par de líneas de ratones seleccionadas para alto (s') y bajo peso (s), originadas a partir de una población no seleccionada de la cepa CF1 (t), se modificó la estructura ovárica. El diámetro de los folículos ováricos y el número de folículos y de cuerpos lúteos se incrementaron en las hembras de la línea s', sin expresarse en un mayor tamaño de camada al nacimiento, posiblemente, por un aumento de las pérdidas gestacionales. Se probó si los efectos conjuntos de la selección de peso a largo plazo y de la estimulación ovárica incrementaban las pérdidas gestacionales. Se utilizaron dos grupos de hembras por línea: sin y con estimulación ovárica (5UI de eCG y 5UI de hCG). Las hembras se sacrificaron a las 56-72 hs y a los 7 días postservicio y después de la primera parición. Se observaron los números de cuerpos lúteos (CL), embriones (E) y sitios de implantación (SI) y el tamaño de camada al nacimiento (TC). Se estimaron las pérdidas totales (PT) y las pérdidas de cuerpos lúteos (PCL), de embriones (PE) y de fetos (PF). Los promedios de CL, E, SI y TC variaron en el mismo sentido de la selección practicada y fueron significativamente mayores (P<0,05) para las hembras estimuladas, a excepción de TC. La línea s' tuvo un potencial reproductivo superior pero un mayor costo biológico (mayor PT y más tardía) cuando se la comparó con las otras líneas. La estimulación ovárica produjo menores eficiencias reproductivas totales para las tres líneas y pérdidas gestacionales mayores y más tardías, principalmente de SI. Las hembras de la línea no seleccionada (t), no estimuladas, con pesos intermedios, parieron un mayor número de crías, partiendo de un número intermedio de CL, E y SI, con una menor y más temprana mortalidad embrionaria, demostrando ser las más eficientes desde el punto de vista reproductivo y productivo.

The ovarian structure was modified as a consequence of weight selection in a pair of mouse lines selected for high (s') and low weight (s). Lines were founded from an unselected population of CF1 strain (t). The follicle diameter and the number of the ovarian follicles and the corpora lutea were higher in s' females, but they did not reach a larger litter size at birth, may be, by an increase in the gestational losses. In these lines, the co-effects of long-term weight selection and ovarian stimulation were tested to evaluate if they increased gestational losses. Two groups of females per line were employed: without and with ovarian stimulation (5UI of eCG and 5UI of hCG). Females were slaughtered at 56-72hs and at 7 days post-breeding and after first parturition. The number of corpora lutea (CL), embryos (E) and implantation sites (SI), and litter size at birth (TC) were observed. Total losses (PT) and corpora lutea (PCL), embryo (PE) and fetus (PF) losses were estimated. Mean CL, E, SI and TC varied in the same direction of the selection made and they were significantly higher (P<0.05) in stimulated females, though not for TC. Line s' had a higher reproductive potential but a greater biological cost (higher and later gestational mortality) when compared with the other lines. Ovarian stimulation produced lower total reproductive efficiencies for the three lines and higher and later gestational losses, mainly for implantation sites. Females from unselected line (t), without ovarian stimulation, with intermediate weights, bore larger litters, starting from an intermediate number of CL, E and SI, with a lower and earlier embryo mortality, showing to be the most efficient from a reproductive and productive point of view.

Ultrastructural changes in the corpus luteum of Egyptian buffalo-cows during different phases of the oestrous cycle

In this work, the relationship between histological structure of corpus luteum and steroid hormones during estrous cycle of buffalo- cows was studied. Corpora lutea and blood samples were collected from slaughtered animals. The corpora lutea were prepared for a histological examination using electron microscope, while progesterone and estradiol-17 beta were estimated from serum. The results revealed a relation between fine structure of lutein cells and concentrations of progesterone during the same stage of the estrous cycle. The main change which occurred in the cytoplasm of the lutein cells was variation of the number of the secretory granules. After metestrus phase and during the diestrus one, levels of progesterone increased gradually and the cytoplasm of the lutein cells became vacuolated containing lipid droplets, electron dense granules, numerous mitochondria and SER. At estrus phase, a significant sharp decrease of progesterone and a rise of estradiol-17 beta were associated with severe changes in luteal cells of corpus albicans containing numerous lipid droplets of different sizes and empty spaces, followed by a disintegration of the cytoplasm which became cornified