Hypertension Watch

AUGUST 10, 2011

Intrarenal Dopamine and Blood Pressure Regulation
Previous studies have suggested that dopamine, in addition to regulating of mood, impulse, and motor function, works inside the kidney to modulate renal function, the renin-angiotensin system, and blood pressure. A study published in July 2011 in the Journal of Clinical Investigation attempts to elucidate the connection between intrarenal dopamine and blood pressure.

Dopamine is produced in the proximal tubule of the kidney via a conversion involving aromatic amino acid decarboxylase (AADC). Researchers engineered knockout mice without the AADC enzyme that were unable to produce kidney-specific dopamine. Other physiologic sources of dopamine remained intact.

Results showed that the mice lacking intrarenal dopamine had significantly elevated mean arterial blood pressure (MAP) at 3 months of age compared with the control group (124 mm Hg and 105 mm Hg, respectively). When fed a high-salt diet, increase in MAP was greater in the knockout mice ( 16 mm Hg) than in the control mice ( 1 mm Hg). The knockout mice also had higher renin expression, a more marked increase in MAP when exposed to exogenous angiotensin II, accelerated damage to their kidneys and vasculature, and a shortened lifespan (15 months, vs 30 months in the control group).

The study’s findings suggest that some people predisposed to hypertension may have differences in their kidneys’ dopamine system that could lead to fluid retention and an increase in blood pressure. They may also be more sensitive to increases in salt intake and benefit more readily from dietary interventions. Drug therapies that modulate and enhance this system may offer novel targets for the treatment of hypertension and kidney disease.

Dietary Proteins Show Promise for Hypertension
A small study indicates there may be a positive link between an increase in dietary protein and lower blood pressure.

The randomized, controlled trial, published online before print July 18, 2001, in Circulation, examined 352 adults with either prehypertension or stage 1 hypertension. Those taking antihypertensive medications were excluded from the trial. The groups were given, in random order, 3 alternating 8-week regimens of powdered supplement packets containing either soy protein (40 g protein), milk protein (40 g protein), or a control containing a complex carbohydrate (0 grams protein), with a 3-week washout period in between each change. Their blood pressure was measured at the beginning and end of each 8-week period to see the individual effects of each dietary change.

During the periods in which they took the high-protein supplements, subjects exhibited statistically significant reductions in their systolic blood pressure compared with that of the carbohydrate supplementation. There was no significant change in diastolic blood pressure. Low-fat dairy has been suggested as a beneficial addition to diet to lower blood pressure, but its benefits were previously attributed to its calcium and potassium content. Because calcium and potassium were kept constant between the 3 supplements, these findings imply that the protein may be the key to the more favorable blood pressure readings.

Discrepancies Reported Between Hypertension Studies in Young Adults
A recent comparison of 2 studies focused on hypertension found significant differences in the incidence of the condition in young adults. An accurate determination of the prevalence of hypertension is of great interest, as hypertension is a known risk factor for coronary heart disease (CHD), the leading cause of mortality in the United States. Two surveys, the 2007-2008 National Longitudinal Study of Adolescent Health, Wave IV (Add Health) and the 2008 National Health and Nutritional Examination Survey (NHANES), were compared in a July 2011 article in the journal Epidemiology.

Independently, both studies recorded whether subjects had been previously diagnosed with hypertension by a health care professional (excluding diagnoses during pregnancy). Certified examiners then obtained multiple blood pressure readings from each participant.

The researchers comparing these 2 trials used data from 14,252 Add Health participants and 733 NHANES participants, who were between the ages of 24 and 32 years. They found that while a self-reported history of hypertension was similar between the 2 studies (11% for Add Health vs 9% for NHANES), the actual prevalence of hypertension varied greatly (19% for Add Health, 4% for NHANES). This discrepancy may indicate that young adults are largely uninformed about their blood pressure status, increasing the need for education and screening.

The significant differences unearthed in this comparison trial illustrate a need for more detailed and controlled surveys to determine accurate prevalence statistics of hypertension in young adults. Because hypertension is a modifiable risk, proper education and timely intervention may prevent CHD progression and other complications.

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