Elevated ambulatory blood pressure in microalbuminuric IDDM patients is inversely associated with renal plasma flow. A compensatory mechanism?

Abstract

Objective: To evaluate the relationship between renal function, ambulatory blood pressure (AMBP), and glycemic control in microalbuminuric IDDM patients compared with normoalbuminuric patients.

Research design and methods: Nineteen male patients (age 33 +/- 6 years) with slight microalbuminuria (UAE 20-70 micrograms/min) were compared with 19 normoalbuminuric (UAE < 15 micrograms/min) age-matched (33 +/- 6 years) male patients. Through constant infusion technique, 125I-iothalamate marked the glomerular filtration rate (GFR), and 131I-hippuran marked effective renal plasma flow (RPF). AMBP was measured by oscillometric technique (Spacelabs 90202).

Results: The microalbuminuric group had higher daytime systolic AMBP (132 +/- 11 vs. 125 +/- 7 mmHg, P < 0.05) and a poorer glycemic control (HbA1c 9.5 +/- 1.5 vs. 8.2 +/- 1.3%, P < 0.01). GFR (135 +/- 22 and 135 +/- 17 ml/min) and RPF (598 +/- 112 and 542 +/- 98 ml/min) were similar in the two groups. In the microalbuminuric group, daytime systolic AMBP was inversely correlated to both RPF (r = -0.77, P < 0.005) and GFR (r = -0.53, P = 0.02). HbA1c and GFR correlated positively in the microalbuminuric group (r = 0.47, P < 0.04). In contrast, the normoalbuminuric patients exhibited no such associations.

Conclusions: IDDM patients with moderate microalbuminuria have elevated AMBP and a strong negative association between AMBP and RPF. This leaves several possibilities of interpretation. Primary blood pressure increase (of unknown origin) may induce morphological changes leading to reduction in renal function. Alternatively, blood pressure increase early in the course of incipient nephropathy may represent a compensatory mechanism, initially aiming at preservation of renal function, but later becoming maladaptive.