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Effect of Lactation on Short- and Long-term Maternal Cardiac Function in a Mouse Model

Shashika Rodrigo, Dr. Kathy Vincent, Dr. Sandra Herrera, Jamaal Saada, Phyllis Orise, Dr. George Saade, Dr. Massoud Motamedi, Dr. Egle Bytautiene Prewit

University of Texas Medical Branch School of Medicine

Epidemiological studies have shown that lactation is associated with lower rates of maternal cardiovascular disease later in life. Previous research has demonstrated that dams which breastfed their pups had lower blood pressure, fasting glucose and triglycerides than dams who did not breastfeed. These mice lacked oxytocin (Oxt), were unable to eject milk, and thus could not lactate. These mice had similar cardiometabolic phenotypes to those of non-lactating mice. The objective of this study was to investigate maternal cardiac function of age-matched lactating and non-lactating wild type (WT) and total body Oxt knockout mice (Oxt-/-).

Study Design: Five groups of mice were studied: Oxt knockout postpartum (Oxt-/- PP), virgin Oxt-/-, WT lactating (WT L), WT non-lactating (WT NL) and virgin WT mice. Three- to four-month-old female Oxt-/- mice and their wild-type controls (Oxt+/+) were mated with respective males. After delivery WT Oxt+/+ mice were then randomized into WT L and WT NL. In the WT NL group, pups were removed within 24 hours of delivery. Age-matched WT and Oxt-/- virgin mice were studied as a comparison group. Cardiac output (CO), left ventricular ejection fraction (EF), left ventricular E/A ratio (E/A), right and left renal artery Doppler indices (RRI and LRI, respectively), and stroke volume (SV) were determined using small rodent micro-ultrasound. Measurements were collected at baseline and then at two and six months postpartum (PP). Two and six months’ data were normalized to the baseline and analyzed using 1-way ANOVA with multiple comparisons (significance P≤0.05).

Results: While there were variations, there were no significant differences between the groups in EF, E/A, CO, RRI and LRI parameters. Significant differences were observed in the SV parameter. Comparison between two and six months time points within the same groups revealed that in SV in WT L dams at six months was significantly lower when compared to two months data (P=0.01) with no differences in other groups. When WT L and WT NL mice were compared, SV in WT NL group was significantly lower than SV in WT L at two months PP (P=0.046). Among the groups which underwent pregnancy, SV in WT NL and Oxt-/-PP was significantly lower than in WT L at two months PP (P=0.03 and P=0.01, respectively).

Conclusions: Lactation results in beneficial outcome for SV, though it lasts only for a short term. This effect could be mediated by exposure to endogenous oxytocin during lactation.

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