[Relationship between exposure to stress and development of hypertension]

The relationship between stress and hypertension has long been a topic of debate. Until recently, no animal (nor physical) model existed which incorporated these two parameters together, hence accurate assessments of their interactions were postulations, at best. The borderline hypertensive rat (BHR) is an animal model in which arterial hypertension will ensue only when the rat is subjected to a chronic stressor. Therefore, this animal model offers an opportunity to study the physiological consequences of a given stressor on the entire organism during the course of the development of hypertension. The cardiovascular and humoral effects of chronic exposure to a physiological stressor on the BHR, at rest and during exposure to an acute and novel stress, have been examined and are presented in this paper. The involvement of the central nervous system in the regulation of this stress induced hypertensive state has been hypothesized to play a major role in the regulation of the stress and hypertensive relationship. Of particular importance are the endogenous opioids and their influence on the maintenance of homeostasis during periods of physiological stress. The localization of the endogenous opioid enkephalin in the paraventricular nucleus of the hypothalamus (PVN), an important brain region in the regulation of the stress response further substantiates the involvement of the opioid system during stress induced hypertension. Immunohistochemical data on the localization of ENKergic fibers in the PVN and other brain regions are similarly discussed in this paper.