Vascular reactivity to angiotensin and noradrenaline in rats maintained on a sodium free diet or made hypertensive with desoxycorticosterone acetate and salt (DOCA/salt).

The pressor response to angiotensin II (ATII) and to noradrenaline (NA), as well as the response of vascular beds (hindquarter and kidney) isolated and perfused with Krebs' solution, and the contractions of strips of thoracic aortae, portal veins to the same agents were measured in animals and organs taken from rats maintained on a sodium free diet or made hypertensive with DOCA/salt and in several groups of controls. The myoptropic effects of ATII and of 5HT were compared in stomach fundi. The main purpose of the study was to find out how a reduction or an increase of total body sodium and the associated changes of renin production can influence the vascular response to angiotensin and to catecholamines. Reduction of sodium in the diet was accompanied by no changes or a decrease of the responses of isolated vascular beds and tissues to ATII and NA; the pressor effect of ATII was also reduced, while that of NA was definitely increased. Treatment with DOCA/salt and the resulting hypertension were accompanied by an increased vascular response to ATII in vivo, to ATII and NA in the isolated hindquarter, while the other preparations (the perfused kidney, the thoracic aorta and the stomach fundus) showed a decreased response specific for ATII (in the kidney and the aorta) and to both ATII and 5HT (in the stomach). The responses of the portal vein to ATII and NA were unchanged. These results are discussed in relation to the changes of renin production, occuring in the two experimental conditions, and with respect to the various mechanisms currently considered for explaining the changes of vascular reactivity in hypertension.