Water and Salt Excretion after Intravenous Salt Load in Hypertensive Subjects

Water loading and restriction in essential hypertension

Blood pressure, plasma arginine vasopressin (AVP), and renal excretory responses to short-term water loading (oral load of 20 ml/kg body weight over 30-45 minutes) were compared in 10 normotensive and 13 mild to moderately essential hypertensive subjects. In addition, we examined the renal concentrating ability of an additional group of 10 normotensive subjects and 12 hypertensive subjects in response to a 24-hour water restriction and intranasal administration of 10 micrograms of [1-deamino,8-D-arginine]vasopression. The hypertensive subjects exhibited both an exaggerated diuresis and natriuresis to the water load. At 20- and 60-minutes after water loading, hypertensive subjects had excreted 34 and 55% of the load, respectively, compared with 15 and 35% in normotensive subjects. Mean blood pressure rose significantly in both groups and hypertensive subjects exhibited a greater rise of systolic blood pressure (16 mm Hg) than normotensive subjects (8 mm Hg) 20 minutes after water loading. The maximum diuresis and natriuresis corresponded to the period in which the rise of blood pressure was greatest. The hypertensive subjects diluted and concentrated their urine as well as normotensive subjects did, indicating normal renal responsiveness to AVP. Plasma Na, osmolality, and AVP decreased similarly in both groups after water loading and rose similarly in the two groups after water restriction. This finding suggests that osmotic responsiveness of AVP is not altered in hypertensive subjects. In conclusion, the data suggest that the exaggerated renal response to water loading could be explained by the greater rise of blood pressure in hypertensive subjects rather than by altered AVP responses.

Effect of a simple deconditioning procedure on the diuretic and natriuretic response of hypertensive patients to a hypertonic salt load

The increased diuretic and natriuretic response of hypertensive patients to an intravenous salt load was modified toward normal by a deconditioning procedure which consisted in repeated exposure to the external situation of the test without, however, infusing any fluid into the vein. After this deconditioning, ratios between amounts of urine and sodium excreted in the first and the second 90-minute period of the test and the total 3-hour quantity of urine excreted were significantly reduced, but blood pressure was not changed. The response of normotensive patients to the same deconditioning was modified in the same direction but to a much smaller extent. It is suggested that the increased diuretic and natriuretic responses of hypertensive patients to an intravenous salt load are similar to the hyperreactive pressor and diuretic responses of these patients when exposed to stimuli that seem threatening to them, and that these responses are caused (at least in part) by hyperreactivity of the central nervous system to the external situation of the test.

INCREASED SENSITIVITY OF A VOLUME-REGULATING MECHANISM IN THE PRE-HYPERTENSIVE STATE; STUDIES IN NORMOTENSIVE WOMEN AFTER TOXEMIA OF PREGNANCY

Normotensive women after toxemia of pregnancy reacted to the infusion of reconstituted human plasma with a water diuresis, whereas control subjects exhibited an antidiuretic response. The latter was probably due to the presence of antidiuretic material in the infused plasma, whereas the water diuresis, which has also been found in hypertensive subjects, can be explained as the manifestation of an increased sensitivity of a volume-regulating mechanism in the hypertensive as well as in the "pre-hypertensive" state.