Over the last three years we have carried out studies on the urine output of both
sodium and
dopamine in five different ethnic groups: whites, Ghanaians, Zimbabweans, Iranians and Thais.
Sodium was measured by ion specific
electrode and
dopamine by HPLC with electrochemical detection (using
epinine as an internal standard). In several groups
salt loading studies were also carried out. The five ethnic groups differed substantially with regard to the correlation between their urinary
sodium and
dopamine outputs. Three groups (whites, Thais and Zimbabweans) showed a strong positive correlation (P less than .001) and this may reflect their traditionally
salt rich diet. In two groups (Ghanaians and Iranians) there was no correlation and this may reflect a
salt scarce environment. Taken together with our previously reported studies showing that normotensive Ghanaians do not mobilize
dopamine on
salt loading, this would suggest that certain ethnic groups are predisposed to develop
hypertension on
salt loading--that is, they are '
salt sensitive.' This genetic trait may have passed from the West Coast of Africa, with the slaves, to America and the Caribbean. Other workers have reported deficiencies in
vasodilator systems in the American black, such as
dopamine,
kallikrein and the renal
prostaglandins. These defects may lead to the nosologic entity of 'low
renin'
hypertension, well described in American blacks, and could open up avenues of
therapy based either on DA1 activators (such as
fenoldopam) or on renal
prodrugs (such as
gludopa).