Salt & Hypertension & Diabetes

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Lay Summary Project Title: Does habitual low dietary sodium intake augment the response to angiotensin receptor blockade and thiazide therapy in hypertensive patients with type 2 diabetes and elevated albumin excretion rate? Rationale: One of the complications of type 2 (adult) diabetes and high blood pressure (BP) is diabetic kidney disease. In this disorder, the kidneys leak protein (albumin) into the urine and in early stages this is known as microalbuminuria. In some patients this progressively worsens, leading to kidney failure. Some groups of blood pressure lowering medications also lower the blood pressure in the kidneys. This protects against kidney damage by slowing the progression of the protein leakage into the urine. The effectiveness of these groups of blood pressure tablets is reduced when the salt intake in the diet is high. Aims of this study: To determine if the effectiveness of the antihypertensive drug telmisartan, alone, and in combination with the drug hydrochlorothiazide, is increased by a low dietary salt (sodium chloride) intake, and if there is an additional beneficial effect on kidney function; In this study, participants with type 2 diabetes, high blood pressure and early diabetic kidney disease (microalbuminuria) will be recruited. Two groups will be compared - those who usually have a high salt intake in their diet versus those who usually have a low salt intake in their diet, as determined by previous urine sodium test results. All patients will take antihypertensive medication to control their blood pressure called verapamil, prazosin and methyldopa, these medications do not interfere with the test results. The participants will continue their usual diet and dietary salt intake throughout the study, however they will take salt and placebo capsules at various times during the study to look at the effects of additional salt intake on blood pressure and kidney function in patients with high versus those with low dietary sodium intake. Participants: The participants (n=32) includes men and non-pregnant women aged 20-80, with type 2 diabetes, high blood pressure, early diabetic kidney disease and a high or low dietary salt intake. Study Design and Procedures: Cross-over double blind study design. The study involves 12 scheduled visits over 28 weeks. The study consists of 3 phases: Two 8 week phases separated by a 6 week washout. Patients commence on verapamil ± prazosin ± methyldopa therapy and this is maintained throughout the 28 study period. The effect of telmisartan will be studied in each 8 week phase, and a thiazide will be added at week 4 to 8. The effect of salt or placebo will be examined in the last 2 weeks of each 4 week cycle. During the study, a total of approximately 210 ml (10 tablespoons) of blood will be collected. Potential side effects: There are potential side effects of blood pressure lowering medications however as all the patients have high blood pressure, they will be on blood pressure lowering medications. This study involves exposure to a very small amount of radiation during nuclear medicine MAG 3 tests to look at kidney function. This has been approved by the radiation research subcommittee. Provision of test results: Participants (and their general practitioner with their consent) will have access to all laboratory tests and when the final study report is produced by the investigator, this will be forwarded to study participants in lay terms.

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