Hypertension in SHR rats: contribution of maternal environment

The role of the maternal environment in the development of hypertension in spontaneously hypertensive (SHR) rats was evaluated using the technique of reciprocal cross fostering. Litters of SHR and Wistar-Kyoto (WKY) normotensive pups were either reared by their natural mothers, in fostered to mothers of the same strain, or cross fostered to mothers of the opposite strain shortly after birth. Litters were weaned at 21 days of age, at which time all pups were weighed. At 18-20 wk of age, resting mean arterial blood pressures (MAP) and heart rates were determined for male subjects from the six groups (2 strains X 3 rearing conditions) via an indwelling tail artery catheter. At weaning, SHR animals weighed less than WKY animals. SHRs fostered to WKY mothers were significantly heavier than control SHRs, and WKYs fostered to SHR mothers were significantly lighter than WKY controls at weaning. These body weight differences were also evident in adulthood. Cross fostering SHR pups to normotensive WKY mothers resulted in a dramatic reduction in resting MAP measured in adulthood. Conversely, cross fostering WKY pups to SHR mothers had no measurable effect on adult resting MAP. We propose that an interaction between characteristics of the SHR maternal environment and a genetic susceptibility in SHR pups is essential in triggering the full expression of the hypertensive phenotype in this animal model of human essential hypertension.