Clinically important differences in insulin absorption from abdomen in IDDM

Abstract

The absorption of radiolabeled soluble insulin ([ 125I]Actrapid ® Human; 10 U) from subcutaneous injection sites above (120 mm) and below (40 mm) the umbilicus was studied on 2 consecutive days in nine IDDM patients during 180 min. Insulin absorption was measured as disappearance of radioactivity by continuous external monitoring and as appearance of plasma immunoreactive free insulin (IRI). Adipose tissue blood flow (ATBF) was measured concomitantly by the 133Xe-washout technique. Plasma glucose was determined. Prior to the injections the depth of the subcutaneous fat tissue was determined using ultrasound. Significantly less radioactivity remained at the upper site, 42 ± 5 vs. 60 ± 6% after 180 min ( P<0.001). In accordance with this, injection into the site above vs. below the umbilicus resulted in a greater area under curve for plasma insulin, 3306 ± 493 vs. 2357 ± 466 mU/l per min (0–180 min; P < 0.01), and a more pronounced plasma glucose-lowering effect ( P < 0.05). However, ATBF did not differ significantly between the two sites. These data suggest that there are clinically relevant differences in insulin absorption within the abdomen. Thus, insulin injection into the epigastric area causes more rapid insulin absorption resulting in an enhanced plasma glucose-lowering effect than injection into the more conventional site close beneath the umbilicus.