Ovarian activity in the intact or hypophysectomized pregnant mouse

Abstract

Various parameters of ovarian activity were determined for the intact or hypophysectomized pregnant mouse, as a baseline to establish the nature of luteotropic hormones in this species.Seventeen per cent of White Swiss mice with a vaginal plug were not pregnant at subsequent stages of gestation. The greatest number of failures occurred between days 12 and 15 of pregnancy, coinciding with the temporary absence of antral follicles and regressive changes in the vaginal epithelium. This suggests that there is a period of transient hormonal imbalance before full placental function is established, which is responsible at this time for the peak in embryonic mortality.Two periods of luteal growth were apparent between days 1 and 4 and 10 to 14 of pregnancy. The first histologic evidence of luteal regression occurred at day 16, correlating with renewed squamous cell proliferation of the vaginal mucosa.There were no significant differences in the number of ova shed on day 1 of pregnancy (11.0 f 0.5 ova) and the subsequent number of embryonic swellings at any stage. Gestation in intact pregnant mice lasted 18 days (n = 2) or 19 days (n = 36).The number of young counted late on day 1 post partum (9.1 & 0.5) was significantly less than the number of embryonic swellings as a result of maternal cannibalism.Hypophysectomy on day 1 of pregnancy led to rapid histologic degeneration of the corpus luteum. In this feature, the mouse resembled the hamster rather than the rat. Day 10 of pregnancy represented the earliest time at which, at least in some animals the pituitary could be removed and pregnancy continue. Following hypophysectomy from day 11 on, luteal activity, continuation of pregnancy, fetal and placental weight and vaginal histology were comparable to intact, pregnant mice. This is similar to the hypophysectomized rat in the latter half of pregnancy but differs from the situation in the hamster.On the basis of the present findings and results jn the folbwing paper, it appears likely that the mouse placenta, in addition to secreting a prolactin-like hormone, also produces other gonadotropins.

Plasma Progesterone, FSH and LH Levels Associated with Implantation in the Mouse

“…The low levels of progesterone found in the present study on days I and 2 also agree with the indirect biological evidence of Finn and Martin (1969) that progesterone secretion does not begin until around 48 h p.c. It also fits the histological evidence of Choudary and Greenwald (1969) showing that development of luteal cells starts on day 2 but fully developed luteal cells are not recognizable until day 3. Neither McCormack and Greenwald (1974) nor Murr et al (1974b) showed the sharp rise and fall of progesterone early on day 4; this may be because they took samples only once a day or it may reflect differences in the strains of mice used in the investigations.…”

History of Maternal Recognition of Pregnancy

“…Deansely ( 1966 ) noted that the maintenance of adequate amounts of progesterone was required for pregnancy in rodents. Morphological changes in CL of pregnant mice were reported by Choudary and Greenwald ( 1969 ) to be associated with a shift from dependency on maternal prolactin, to day 6 of pregnancy, to LH on days 9 and 10 of pregnancy and then placental "luteotrophins" for the remainder of pregnancy which was consistent with other published results (Newton and Beck 1939 ;Cerruti and Lyons 1960 ). However, more recent reviews provide clarity to mechanisms for pregnancy recognition in rodents (see Soares et al 2007 ;Ben-Jonathan et al 2008 ).…”

Evolution of NMRI Mice Ovaries and Corpora lutea during Pregnancy: Morphologic and Morphometric Study

“…During the estrous cycle in mice, an in crease of CL volume has been observed at metestrous for some newly formed CL and at diestrous 2 for degenerating CL [7], In the rat during pregnancy, CL volume increases 3 times between DIO and 17 [5], 6 times be tween D1 and 15 [2] and 2.6 times between D8 and 16 [3], In the mouse during pregnan cy, the maximum diameter of CL has been observed at D18 [9] and at D14 [11], In our study, a 10-fold increase has been observed between DO and 18.5 for CL volume of type I. This observation suggests a strong rela tionship between pregnancy and ovarian lu teal function.…”

“…Newly formed CL are small and slightly basophilic, whereas the old CL are large and eosinophilic [6,7], with regressive signs [9,11]. During pregnancy in mice, old CL were reported to disappear between DIO and D12 of gestation [9], after D14 [11], and after D15 [8],…”

“…Only new CL formation and evolution are well known during the estrous cycle [7,9] and during pregnancy [9][10][11]. The evolution of all CL during pregnancy has not yet been clearly described.…”