Somatotropin: Effects on Ovarian Function in Swine and Transgenic Mice

IN SITU GENE EXPRESSION OF OVARIAN STEROIDOGENIC ENZYMES IN bGH-TRANSGENIC AND NON-TRANSGENIC MICE. Cao WG, Danilovich NA, Hausler CL, Bartke A, and Winters TA. Departments of Animal Science, Food and Nutrition, and Physiology, Southern Illinois University, Carbondale, IL.

Steroid hormone production is an indicator of ovarian follicle health and status. The objective of this study was to determine the expression of three ovarian steroidogenic enzyme genes [cytochrome P450 cholesterol side chain cleavage enzyme (P450scc), 17-alpha-hydroxylase (17a-OH), and 3-beta-hydroxysteroid dehydrogenase (3b-HSD)] in two lines of transgenic mice expressing bovine growth hormone (bGH) and their non-transgenic littermates. Female PEPCK-bGH and MT-bGH transgenic mice and non-transgenic littermates (4 groups; n=6/group) were sacrificed at proestrus. Ovaries were collected, sectioned and processed for in situ hybridization (ISH) with specific 35S-cRNA probes to P450scc, 17a-OH, and 3b-HSD. Silver grains over ISH ovarian sections, indicating transcription, were quantified using an image analysis system (Optimas 5.2, Redmond, WA). Granulosa cells (n=54) were analyzed from the three largest follicles for each animal, and means separated using a series of paired t-tests. Number of grains per cell were 84, 85, and 53% higher (P<0.05) than controls for P450scc, 17a-OH, and 3b-HSD, respectively, in PEPCK-bGH-transgenics; and 75, 69, and 55% higher (P<0.05) than controls for P450scc, 17a-OH, and 3b-HSD, respectively, in the MT-bGH transgenics. Steroidogenic gene transcription was not different between the two transgenic lines. These results indicate that chronic GH exposure significantly increases the steroidogenic capacity of murine ovarian follicles, potentially contributing to the increased ovulation rates in these animals. Supported by the Illinois Council on Food and Agricultural Research, the SIU-C University Priorities and Interdisciplinary Initiative Program, and the National Institute of Child Health and Human Development.

IN SITU OVARIAN FOLLICLE APOPTOSIS IN bGH-TRANSGENIC AND NON-TRANSGENIC MICE. Danilovich NA, Cao WG, Bartke A, and Winters TA. Departments of Animal Science, Food and Nutrition, and Physiology, Southern Illinois University, Carbondale, IL.

Apoptosis is the underlying mechanism for ovarian follicle atresia in mammals. A decrease in follicle apoptosis could result in an increase in ovulation rate. The objective of this study was to determine the level of apoptosis in transgenic mice expressing bovine growth hormone (bGH) and their non-transgenic littermates. Female PEPCK-bGH transgenic mice (n=10) and non-transgenic littermates (n=8) were sacrificed at early proestrus. Ovaries were collected, sectioned, and processed using a non-radioactive in situ apoptosis assay kit (Oncor, Gaithersburg, MD). Follicles were microscopically classified and counted by size and level of apoptosis, and means separated using a series of paired t-tests. Overall, the percentage of all follicles containing apoptotic cells was lower (P<0.05) in the transgenic (28.6) vs. controls (51.3). The percentage of transgenic follicles undergoing heavy apoptosis was lower (P<0.05) vs. control in large and medium antral follicles, but not different in small preantral follicles. The percentage of healthy large preovulatory follicles was also higher (P<0.05) in the transgenic (7.3) vs. controls (4.3). These results indicate that chronic GH exposure significantly decreases follicle apoptosis, and thus atresia in murine ovarian follicles, probably contributing to the increased ovulation rates in these animals. Supported by the Illinois Council on Food and Agricultural Research, the SIU-C University Priorities and Interdisciplinary Initiative Program, and the National Institute of Child Health and Human Development.