Blood pressure variability and urinary electrolyte excretion in normotensive adults.

The principal aim of the present study was to determine the relationship of ambulatory blood pressure (BP) to urinary electrolyte excretion in normotensives. Twenty-five young adults underwent ambulatory BP and heart rate monitoring while collecting urine over 24 h. The correlations of 24 h urine sodium excretion and the ratio of sodium/potassium excretion with systolic BP in the laboratory (r = 0.12 and 0.24), ambulatory awake (r = 0.11 and 0.24), and ambulatory asleep (r = 0.24 and 0.31) settings were all in the positive direction but not significant. However, 24 h sodium excretion did correlate significantly and positively with awake and asleep ambulatory systolic (r = 0.45 and 0.41, P < .05) and diastolic (r = 0.42 and 0.43, P < .05) coefficients of variability. Thus, in normotensives on an unlimited diet, 24 h urinary sodium was more closely related to ambulatory BP variability than to BP level.

Intrinsic sympathomimetic activity counteracts beta-blocker inhibition of renin activation.

Enzymatically inactive renin (IR) is the predominant circulating form of renin. Sympathetic activity may influence plasma renin activity (PRA) by regulation of the conversion of IR to active renin (AR, PRA). It has been demonstrated previously that beta blockade lowers PRA at least partly through inhibition of this conversion process. The authors hypothesized that beta blockade and intrinsic sympathomimetic activity (ISA) would have opposing effects on production of AR from its inactive precursor. Eighteen primary hypertensives (12 male, 6 female, mean age 57.7 +/- 2.7) were entered in a placebo-controlled, double-blind crossover study of the effects of equipotent doses of pindolol and propranolol on mean +/- SEM systolic BP, diastolic BP, heart rate, active renin (AR), total renin (TR), inactive renin (IR), and % AR/TR. Drug dose was titrated to achieve a goal DBP of 90 mmHg or less. Active renin was defined as the rate of generation of angiotensin I in 37 degrees C plasma at pH 5.7. Total renin was determined by preincubation of plasma aliquots with 1.5 mg/mL trypsin in the presence of 5 mM benzamadine for one hour at -4 degrees C prior to assay of renin activity. Inactive renin was calculated as TR minus AR. The BP responses achieve by dose titration of propranolol and pindolol were virtually identical at rest, indicating equivalent depressor effects of the two beta blockers. Heart rate and active renin were, however, lowered to a much greater extent with propranolol as compared with pindolol. The lack of significant pindolol-induced fall in % AR/TR suggests that this drug has little net effect on the formation of AR from IR.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship of plasma renin activity to clinic and ambulatory blood pressure in elderly people with isolated systolic hypertension.

Eighty-one untreated elderly patients with clinic-defined isolated systolic hypertension (ISH) and 39 normotensive elderly subjects underwent 24-h ambulatory blood pressure monitoring. Before the ambulatory blood pressure monitoring, EDTA-anticoagulated venous blood was obtained from seated subjects for determination of plasma renin activity. Ambulatory blood pressure and heart rates were determined at 15-30-min intervals by a validated, portable non-invasive technique (Spacelabs 5200). Ambulatory blood pressure variability was defined for each subject as the standard deviation and the coefficient of variation of the ambulatory blood pressure. The mean awake systolic blood pressure was much lower than the clinic-determined value in the ISH group (P less than 0.001), but only slightly so in the normotensive group. Forty-two per cent of the clinic-defined ISH group had mean awake ambulatory systolic blood pressures below the 90th percentile of the normotensive group. A discrepancy between office and ambulatory blood pressures was not associated with blood pressure variability, heart rate or plasma renin activity.

Comparison of office, home and 24-hour ambulatory blood pressures in borderline and mild hypertension.

Clinic/office (casual), home (self), and twenty-four-hour ambulatory (ABP) blood pressure determinations were compared in 32 subjects defined by conventional office criteria as mild or borderline hypertensives. Office diastolic blood pressures (mean 93.1 +/- 5.3 mmHg) were significantly higher than either home (mean 88.9 +/- 7.1 mm Hg) or awake ABP (mean 88.4 +/- 8.4 mm Hg) readings for the total group, as well as for the mild hypertension subgroup (office mean 96.0 +/- 3.5 mm Hg, home mean 91.0 +/- 8.0, awake ABP mean 90.4 +/- 8.8) but not for the borderline subgroup. In the total study group, office diastolic blood pressure (DBP) correlated better with home DBP (r = 0.58, p = 0.0005), than with the awake ABP (r = 0.40, p = 0.02). Home DBP correlated well with awake DBP (r = 0.48, p = 0.006). In subgroup analysis, office DBPs correlated well with home (self) readings for both the mild (r = 0.53, p = 0.03) and the borderline (r = 0.62, p = 0.01) subgroups. When office DBPs were compared with awake ABP DBPs, the correlation coefficient for the mild subgroup was significant (r = 0.49, p = 0.04); this was not the case for the borderline subgroup (r = 0.10, p = NS). Comparison of home (self) DBPs with awake ABP determinations revealed a good correlation for the borderline subgroup (r = 0.63, p = 0.01) but not for the mild subgroup (r = 0.35, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Digoxin-like immunoreactive substance in chronic hemodialysis patients: effect on digitoxin radioimmunoassay.

Digoxin-like immunoreactive substance(s) (DLIS) in the sera of patients with renal insufficiency may confound attempts to monitor serum digoxin levels. We investigated whether DLIS would affect the radioimmunoassay (RIA) for digitoxin. DLIS was detected by RIA in 9 of 38 chronic hemodialysis patients and in none of 25 healthy controls. Digitoxin levels were not elevated in either the control or dialysis group, and false-positive results for digitoxin by RIA were not obtained in any patient with DLIS. It is concluded that DLIS does not interfere with the digitoxin RIA, nor are digitoxin levels spuriously elevated in chronic hemodialysis patients. Digitoxin may be a preferable preparation for digitalis-dependent dialysis patients with DLIS.

The effect of dialysate calcium levels on blood pressure during hemodialysis.

A controlled double-blind prospective study was undertaken of the effect of dialysate calcium levels on BP during hemodialysis. Twenty patients and 240 dialyses were studied using a protocol in which patients underwent alternate hemodialyses with dialysate calcium of 2.5 and 3.5 mEq/L. Dialysate composition was otherwise the same. Mean BPs during dialysis were significantly lower at 1.5, 2.5, and 3.5 hours of dialysis when the lower dialysate calcium was used (P = .007 to .02). However, the difference in BP between the high and low dialysate calcium treatments was clinically minor, with a maximum mean difference (at 1.5 hours) of 4.6 mm Hg. Subgroups of patients with frequent hypotension and low or normal serum calcium did not appear more sensitive to the hypotensive effect of low calcium dialysate. Dialysate calcium levels of 2.5 and 3.5 mEq/L thus differ in their effect on intradialytic BP in a statistically significant, but clinically minor, way. Low calcium dialysate thus may prove useful in the management of patients in whom large amounts of enteric calcium absorption are indicated or unavoidable.