No description available.

The formation of the corpus luteum, its maintenance throughout pregnancy and the secretory activity of this transient endocrine gland receive special emphasis because of its role in the secretion of progesterone. An inadequate luteal phase has been associated with an increased incidence of congenital abnormalities. Anything which interferes with the hormonal environment may lead to fetal death or abnormal embryogenesis. Retinoic acid was administered to mice early in pregnancy to induce neural tube defects. Plasma concentrations were determined by high pressure liquid chromatography. Distribution of the retinoic acid was determined by wholebody autoradiography. The hormonal profile during pregnancy was determined in control and retinoic acid treated dams by specific radioimmunoassay for progesterone and 20 alpha dihydroprogesterone. There was no significant effect of retinoic acid on the hormonal profile of treated dams. This suggests that the teratogenic effects of retinoic acid are not due to a change in the hormonal environment. Progesterone and 20 alpha dihydroprogesterone concentrations were significantly increased on days 10 and 10.5 of pregnancy in both treated and control dams. This is the point when pseudopregnancy would end and pregnancy maintenance comes under the control of luteinizing hormone. The increase in 20 alpha dihydroprogesterone concentration at this point in pregnancy was similar to that observed after the administration of prostaglandin F_2alpha (PGF_2alpha). It seems likely that PGF_2alpha and luteinizing hormone act antagonistically during midpregnancy. Concomitant treatment revealed an interaction resulting in an increased progesterone secretion and the conversion of progesterone to 20 alpha dihydroprogesterone. Hence, PGF_2alpha may be released at the point in pregnancy when luteinizing hormone takes over as the major luteotrophin. Luteinizing hormone thus maintains pregnancy in the mouse in the face of an endogenous PGF_2alpha release.

No description available.

No description available.

Since 1942, when Bittner reported the incidence of non-induced tumors occuring in mice, strains of laboratory mice producing mammary carcinomas have been used as tools in research. Although not ideal for human studies, the histological and morophological similarities of the human and mouse mammary glands make it an excellent model to study the development of breast cancer. This study was performed to develop a rapid and consistent classification system for mouse mammary tissue, and compare various tumors to this system.Laboratory mice from the A and Balb/c strains were utilized in these studies. The three types of tumors developed in these mice were, non-induced, induced, and transplanted. Specimens of these tumors were collected and studied via light and electron microscopy for cellularchanges of tumor cells. These tumors were then classified according to the new system. These various tumors ranged from Class 0, which were normal cells, through gradual cellular changes to a Class IV, which were totally undifferentiated cells. host induced and non-induced tumors were Class III or IV, while the transplanted tumors were Class IV. This system facilitated the classification of mouse mammary tumors.

No description available.

No description available.

Effects of infective stage density, host density and surface area available for transmission on the rate of transmission of the nematode Heligmosomoides polygyrus were investigated in a controlled environment where naive CD1 outbred mice were naturally infected. Within a range of densities of infective larvae (500-6000/cage), randomly spread on damp peat moss, a linear increase was observed in the mean number of fourth stage larvae embedded in the intestinal mucosa per host. As host density increased (1-6 mice/cage), but exposure dose held constant (8000L$ sb3$), the mean number of L$ sb4$ recovered per mouse decreased at a faster rate than expected assuming a constant per capita rate of transmission. In an attempt to interpret the experimental data, mathematical models were generated. Although the inclusion of a death rate of infective larvae dependent on mouse density did improve the fit of the mathematical model based on a constant per capita rate of transmission, the best fit was provided by a model assuming a per capita rate of transmission dependent on mouse density. An independent experiment exploring the impact of surface area available for transmission on the relationship between host density and the rate of infection confirmed the adequacy of the mouse density-dependent per capita rate of transmission hypothesis.

No description available.

The importance of host heterogeneity in generating aggregation was investigated using Heligmosomoides polygyrus (Nematoda) in laboratory mice. The protocol compared parameters of infection between inbred and outbred mice, primary and challenge infections, and gavage and natural exposure, to investigate the relative effects of innate resistance, acquired resistance and behaviour, respectively. The results show that heterogeneity in acquired resistance is the most consistent factor contributing to the variability and aggregation of H. polygyrus. When groups of mice did not acquire resistance, either in certain inbred strains or when mice were immunosuppressed, variability after the challenge was comparable with that after a primary infection. Heterogeneity in host behaviour, particularly in behaviours enhancing skin contact with larvae, frequently increased aggregation above that detected in both primary and challenge infections. Surprisingly, inconsistent results were obtained when inbred and outbred groups of mice were compared. The results suggest that the relative contribution of these three factors is likely to vary spatially and temporally.