Blood pressure responses to milk ejection in the young rat.

When young rats receive milk ejections from their mothers they exhibit abrupt 30-50% increases in blood pressure. In our first experiment, we recorded, via carotid cannulae, blood pressure and heart rate during natural nursing bouts. Blood pressure changes coincident with behaviorally defined milk ejections were twice as large as the changes associated with other behaviors observed. In addition, the increases in blood pressure during milk ejection were significantly greater when pups were separated from their mothers for 18-20 hours prior to testing. A second experiment showed that these responses were independent of the mother's overt behavior because virtually identical results were obtained when pups received milk from anesthetized dams stimulated to release milk with oxytocin. These results are discussed with regard to possible immediate functions of the response, and long term effects of repeated cardiovascular activation in early development.