Aust. J. Bioi. Sci., 1981,34, Quantitative and qualitative changes in the microvasculature of the corpus luteum of the guinea pig during cyclical luteal regression were studied by light and electron microscopy. During luteal regression, between day 12 of the oestrous cycle and day 1 of the next cycle, there was a reduction in the extent of the luteal capillary bed as measured both by 'hit' counts and by differential counts of all nucleated cells. Luteal cells made up a constant proportion of :::::: 60 % of the luteal tissue area up to day 1 of the next cycle, but had increased as a proportion of all nucleated cells by that stage. Both fibroblasts and macrophages increased in number and in area occupied during luteal regression. Ultrastructural changes in capillaries during luteal regression included, an increased incidence and degree of protrusion of endothelial cells into the lumina of small blood vessels, and degeneration and death of many endothelial cells. In spite of the widespread presence of endothelial cell degeneration, most small vessels retained a continuous lining of apparently viable endothelium. It is concluded that in this species there is a rapid and substantial reduction in the luteal capillary bed, which commences during the early stages of luteal regression, and a mechanism is proposed by which the capillary bed may be reduced while retaining its integrity.
The duration of pseudopregnancy in rats was increased to 15\ m=. \ 9\ m=+-\ 3\ m=. \ 4 days (control 12\m=.\5 \ m=+-\ 0\ m=. \ 7)following surgical separation of the posterior parts of the uterine horns from their cervical attachments. Under these conditions, the uterine horns became distended with fluid. The uterine walls were stretched and thin, but appeared otherwise undamaged. Deciduoma formation was readily induced in distended horns but the presence of deciduomata did not further prolong the duration of pseudopregnancy.
Summary. Transection of the uterine horns near to their cervical ends (posterior uterine section) led to a prolongation of pseudopregnancy from 13\m=.\1\m=+-\0\m=.\16 (control) to 14\m=.\9\ m=+-\ 0\m=.\24 days (P<0\m=.\001). This was significantly greater than the prolongation following transection of the uterine horns one third of the way from the uterotubal junction to the uterine bifurcation (14\m=.\0 \ m=+-\ 0\m=.\16 days, P<0\m=.\01).When unilateral ovariectomy was accompanied by contralateral posterior uterine section, the prolongation of pseudopregnancy ( 14\ m=. \ 5\ m=+-\ 0\m=.\20 days, control 12\m=.\8\ m=+-\ 0\m=.\25 days, P< 0\m=.\001) was greater than when accompanied by ipsilateral posterior uterine section (13\m=.\7 \ m=+-\ 0\m=.\20days, P<0\m=.\02).These results indicate a quantitative and a unilateral component in the effects of uterine section, and support the hypothesis that prolongation of pseudopregnancy following posterior uterine section is brought about by the same mechanism as that following hysterectomy.
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