Biology

Endocrinology

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Internal medicine

Hormone

Medicine

Biology of Reproduction

Changing environmental conditions govern adaptive skewing of offspring sex ratio in birds, insects, and in some mammalian species. However, the causes of sex ratio skewing and significance are not well understood. Female mice fed a very high fat (VHF) diet, for example, produce litters that are skewed towards males, while restricting access to this diet to 7 h/day (VHF-R) reduces the fraction of males. Conversely, mice fed a nutritionally balanced but low fat/high carbohydrate (LF) diet produce more daughters than sons. Sex ratio deviation from the expected 0.5 value was not related to the dam weight and no difference in litter size was observed among the dietary groups. Here, we tested whether these diets influence certain metabolic hormones (IGF1, corticosterone, and leptin), and glucose concentrations, thereby possibly altering conditions that might favor either the conception or development of one sex over the other. Experiment 1 used 5-week old mice that were placed permanently on one of three diets: VHF diet (caloric density 5.2 kcal/g; 54 % from lard) ad libitum (VHF, n=11); a restricted VHF diet (VHF-R, n=9) in which the mice had only 7 h access to food during their night; and Purina 5015 (caloric density 4.4 kcal/g; 26 % from fat) ad libitum (5015 Control, n=12), which produces approximately 0.5 offspring sex ratio. After three pregnancies (at 45–48 weeks of age), the mice were sacrificed and serum collected. Experiment 2 consisted of two groups of mice fed continuously from 5 to 17 weeks of age on either the VHF (n=13) or LF (caloric density 3.9 kcal/g; 10% from fat) (n=11) diets. These mice were then sacrificed and serum collected. In the third experiment, mice were fed ad libitum on the VHF (n=6), LF (n=6), or Control (n=4) diets for fifteen weeks beginning at 5 weeks of age. After 5 weeks on the experimental diets, blood glucose concentrations were determined at biweekly intervals over a period of 10 weeks. No differences were detected in serum IGF1 concentrations among the dietary groups in Experiment 1 (636.4 ± 44.3, 642.6 ± 49.0, and 615.6 ± 42.5 ng/ml for VHF, VHF-R, and 5015, respectively) and Experiment 2 (706.2 ± 25.6 and 659.8 ± 27.8 ng/ml for VHF and LF, respectively). Serum corticosterone concentrations were not different between the VHF and VHF-R groups (43.6 ± 6.6 vs 29.8 ± 7.7 ng/ml), but were higher than the controls (9.1 ± 7.7 ng/ml) in Experiment 1. No difference existed between the VHF and LF groups (36.3 ± 11.6 vs 61.6 ± 13.4 ng/ml) in Experiment 2. Leptin concentrations did not differ between the VHF and VHF-R groups (20.7 ± 3.8 vs 24.6 ± 4.9 ng/ml), but were higher than the 5015 and LF groups (9.8 ± 3.5 and 3.2 ± 3.2 ng/ml, respectively). VHF mothers show sex ratio skewing towards males. In contrast, the VHF-R females produce more daughters than sons. Thus, leptin seems unlikely to play a role in offspring sex selection. A significant interaction existed between time and diet (P<0.05) for both blood glucose concentrations and body weight. The overall glucose concentrations, however, did not differ among the three groups suggesting that maternal blood glucose does not influence pup sex ratio. While the blood chemistries displayed differences related to diet, these changes most likely do not provide an explanation for the skewing of offspring sex ratio. Supported by NIH Grant HD 044042. (poster)

EXAMINATION OF METABOLIC HORMONES AND BLOOD GLUCOSE CONCENTRATIONS IN FEMALE MICE ON DIETS THAT FAVOR PRONOUNCED CHANGES IN SEX RATIOS OF PUPS BORN