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Title: Renal sodium-dopamine relationship and the effects of sodium loading on natriuretic and hormonal responses in Chinese
Author: Chan, Thomas Yan Keung
ISNI:       0000 0001 3527 128X
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2001
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Dopamine (DA) is an important intrarenal natriuretic, vasodilatory substance in the body. In my work, my main objective was to establish whether Chinese have an efficient renal DA system that will enable them to handle a salt load effectively without showing an increase in blood pressure (BP). A reduction in sympathetic nervous system activity, which is reflected by a fall in urinary free noradrenaline (NA) output, and enhanced renal kallikrein production, as indicated by increased urinary kallikrein output, may also contribute to the natriuretic response to salt loading. The relative importance of these two mechanisms in sodium homeostasis in Chinese were also studied. In my studies, urinary free DA and NA were measured by HPLC with electrochemical detection. If DA is an important intrarenal natriuretic substance in Chinese and dietary sodium is the major determinant of its intrarenal synthesis, there should be a positive correlation between 24-hour urinary sodium and free DA outputs even under basal conditions. There should be a marked and sustained increase in urinary free DA output during the natriuretic response to salt loading. Their renal DA system should also be sensitive to small and gradual increases in oral salt intake. In my first cross-sectional study, 89 normotensive subjects (BP < 140 mmHg) with (5 M, 25 F, aged 48.3 +/- 1.3 years) or without (21 M, 38 F, aged 43.4 +/- 2.0 years) a family history of hypertension and 24 hypertensive patients (8 M, 16 F, aged 45.5 +/-1.7 years, systolic BP >160 and/or diastolic BP > 95 mmHg) were recruited in 1989-1991. There was a positive correlation between 24-hour urinary sodium and free DA outputs in normotensives without a family history of hypertension (r=0.42, p < 0.001). However, such a relationship was not seen in normotensives with a family history of hypertension (r=0.22, p0.5). In my second cross-sectional study, 85 normotensive subjects (BP < 120/80 mmHg) with (14 M, 13 F, aged 39.1 +/-1.4 years) or without (23 M, 35 F, aged 42.1 +/-1.2 years) a family history of hypertension and 47 hypertensive patients (25 M, 22 F, BP > 140/90 mmHg).were recruited in 1996-1998. A positive correlation between 24-hour urinary sodium and free DA outputs was seen in both normotensives (r=0.57, p=0.004 and r=0.36, p=0.006) and hypertensives (r=0.44, p=0.002). Variations in findings between these two studies could be in part due to differences in the inclusion criteria (BP and its measurement), recruitment method and subject characteristics (age, body weight, BP levels and salt intake). Hypertensives in the second study were slightly younger and had less severe hypertension than hypertensives in the first study. Perhaps, a positive urinary sodium-free DA relationship is seen only in the earlier stages or when the hypertension is less severe. In the second study, hypertensives had a higher 24-hour urinary free DA output than normotensives. This hyperdopaminergic response may represent an early antihypertensive compensatory mechanism.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral