Maternal environment and development of high blood pressure in Dahl hypertensive rats

The contribution of the preweanling maternal environment to the development of hypertension was examined using the technique of reciprocal cross-fostering between two inbred rat strains, the Dahl hypertension-sensitive (SS/Jr) rat and the Dahl hypertension-resistant (SR/Jr) rat. Litters of SS/Jr and SR/Jr pups were reared by their natural mother, in-fostered to a dam of the same strain, or cross-fostered to a dam of the opposite strain for the entire preweanling period from postnatal days 1 to 30. At 60 and 100 days of age, one rat from each litter was surgically prepared with an indwelling catheter in the ventral tail artery. One day after surgery, measures of resting mean arterial pressure and heart rate were taken as the animals were resting and undisturbed in their home cages. Body weights were also obtained at 30, 60, and 100 days of age as a measure of general somatic development. Our findings indicate that SS/Jr rats fostered to SR/Jr dams exhibited a significant reduction in resting mean arterial pressure compared with naturally reared or in-fostered SS/Jr rats (P less than 0.01 at 60 days and P less than 0.03 at 100 days). Conversely, arterial pressure of SR/Jr rats did not differ across rearing conditions at either age. Body weights were not significantly affected by cross-fostering in either strain. We conclude from these results that characteristics of the SS/Jr maternal environment interact with the inbred genetic susceptibility of the SS/Jr pup to elicit the full expression of the SS/Jr hypertensive phenotype.