627: The effect of lactation on long-term cardiovascular function

Abstract

Epidemiological studies are inconsistent regarding the long-term maternal cardiovascular outcomes after pregnancy and lactation, especially when compared to never pregnant women. Moreover, human studies are confounded by many factors. Our objective was to investigate the effects of pregnancy and lactation on the long-term maternal vascular function in mice. 2-3 month old female B629SF2/J mice were bred and allowed to deliver. They were randomized into lactating (L, n=10-16) and non-lactating (NL, n=10-12) groups. At 6 months post partum, L and NL groups and age-matched virgins (VG, n=7-9) underwent blood pressure (BP) measurements via tail cuff. Mice were sacrificed, and carotid and mesenteric arteries were excised for in-vitro vascular reactivity studies using small vessel wire myograph. After a stabilization period, responses to single dose of potassium chloride (KCL, 60mmol/L) and concentration-response curves (CRC) to acetylcholine (Ach), sodium nitroprusside (SNP), isoproterenol (ISO), phenylephrine (PE) and thromboxane (TBX) were obtained. The BP measurements, maximal effect (Emax), and area under the curve (AUC) were analyzed using the 1-way ANOVA and Kruskal-Wallis test as appropriate (significance: P<0.05). At 6 months post partum, the L mice had significantly lower systolic, diastolic, and mean BP than both NL and VG groups (P=0.03 for all). BP measurements were lower in NL when compared to VG mice, though not significantly. Relaxation responses to SNP and ISO in carotid artery were significantly higher in L groups as compared to NL (SNP Emax P=0.03, AUC P<0.001; figure; ISO Emax P=0.01, AUC P=0.04) and to VG mice (SNP AUC P<0.001). These responses were not significantly different between NL and VG groups. All other comparisons were not significantly different. Pregnancy independently improves long term cardiovascular function, but the most benefit is derived when pregnancy is followed by lactation.