CHANGES IN RATIO OF PLASMA TO INTERSTITIAL FLUID VOLUME DURING LONG-TERM ANTIHYPERTENSIVE THERAPY

  • 1 January 1976
    • journal article
    • research article
    • Vol. 87  (5) , 781-791
Abstract
Based on determinations of plasma [volume] (T-1824) (PV) and extracellular fluid volumes (82Br- distribution space) (ECFV), the PV/IF ratio (IF = ECFV-PV) was calculated 3 times with a 1 wk inverval between determinations in untreated patients with essential hypertension. During treatment with hydrochlorothiazide (13 males and 8 females), hydrochlorothiazide-triamterene (5 males and 5 females), hydrochlorothiazide-.alpha.-methyldopa (7 males and 4 females) and propranolol (6 males and 4 females), PV/IF was determined after 2-6 mo. of treatment. PV/IF was significantly reduced during hydrochlorothiazide treatment (.DELTA.PV/IF: -0.011, SD: 0.011, P < 0.001) and propranolol treatment (.DELTA.PV/IF: -0.017, SD: 0.022, P < 0.05), remained unchanged during hydrochlorothiazide-triamterene treatment and increased significantly during hydrochlorothiazide-.alpha.-methyldopa treatment (.DELTA.PV/IF: +0.013, SD: 0.015, P < 0.05). There was a negative correlation between PV/IF and mean blood pressure during hydrochlorothiazide treatment (r: -0.49, n: 21, P < 0.05) and hydrochlorothiazide-triamterene treatment (r: -0.79, n: 10, P < 0.01); no correlation was found during treatment with hydrochlorothiazide-.alpha.-methyldopa or propranolol. Correlation between mean blood pressure and the individual volumes was not observed nor was there any correlation between changes in theparameters investigated. PV/IF probably is more accurately correlated to mean blood pressure than are the individual volumes and, during long-term antihypertensive treatment, PV/IF will reflect changes in the tone of the capacitance vessels and the venous resistance vessels, resulting in a changed equilibrium between the intravascular and the interstitial volumes. The reduction in PV/IF during thiazide and propanolol therapy possibly is related to a relative increase in venoconstrictor sympathetic activity; the increase in PV/IF by .alpha.-methyldopa is caused by decreased sympathetic tone and venodilation.

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