1. We studied the effects that lesions produced in the paraventricular and suprachiasmatic nuclei and intervening periventricular area had on 24 h mean circadian blood pressures in Dahl salt-sensitive and -resistant rats and their sham-operated controls. We measured blood pressures while the animals were on a low salt diet and after 1, 5 and 13 weeks of 8% NaCl diet.

2. Salt-sensitive rats with lesions had lower blood pressures than salt-sensitive sham-operated controls at all points of the study. In contrast, identical lesions in salt-resistant rats produced a transient pressor response to the diet. Twenty-four hour mean heart rate, determined after 13 weeks of 8% NaCl intake, was low only in salt-sensitive rats with lesions. Sodium intake and excretion per kg of body weight, as well as plasma sodium concentrations, were similar in all groups.

3. We conclude that the anteromedial hypothalamic area, which includes the paraventricular nucleus, the suprachiasmatic nucleus and the intervening periventricular area, participates in the development of Dahl hypertension. We suggest that a multifactorial mechanism is involved: (a) the facilitatory role of this region in ACTH release, (b) this region's participation in the baroreceptor reflex via vasopressinergic efferents to the nucleus of the tractus solitarius, and (c) the roles of the paraventricular and suprachiasmatic nuclei in the regulation of salt and water balance.

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