Changes in plasma and extracellular fluid volume during long-term treatment with alpha-methyldopa in 11 thiazide-treated patients with essential hypertension.
In eleven patients with essential hypertension, plasma volume (T-1824) (PV), extracellular fluid volume (82Br-distribution space) (ECFV), blood pressure (BP) and the ratio plasma to interstitial fluid volume (PV/IF) have been determined three times before treatment, after more than two months of thiazide treatment and after three and six months of combined thiazide-alpha-methyldopa (AMD) therapy. During combined treatment, PV/IF showed a significant increase, whereas PV and ECFV did not change significantly. Compared to values during thiazide therapy, PV and PV/IF increased, whereas ECFV was unchanged. BP was reduced significantly after thiazide treatment and showed a further significant fall when AMD was added. Based on the results and a review of the literature, it is concluded that AMD acts by interfering with the normal sympathetic activity, thereby producing a reduced venomotor tone and increased venous capacity. The concomitant reduced venous return of blood to the heart is suggested to contribute to the antihypertensive effect of AMD by means of a decreased cardiac output.
D000368:Aged; D001794:Blood Pressure; D001835:Body Weight / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D002740:Chlorothiazide / Q000494:pharmacology / Q000627:therapeutic use*; D003864:Depression, Chemical; D004359:Drug Therapy, Combination; D005110:Extracellular Space / Q000187:drug effects*; D005260:Female; D006801:Humans; D006973:Hypertension / Q000188:drug therapy*; D008297:Male; D008750:Methyldopa / Q000494:pharmacology / Q000627:therapeutic use*; D008875:Middle Aged; D010953:Plasma Volume / Q000187:drug effects*; D013268:Stimulation, Chemical; D013997:Time Factors
D008750:Methyldopa; D002740:Chlorothiazide