Retinal vascular reactivity to norepinephrine and angiotensin II in normals and diabetics.

Retinal arterial vasoconstriction induced by an infusion of angiotensin II or norepinephrine was investigated in eight normal controls (N), nine diabetics without retinopathy (DNR), and 10 diabetics with retinopathy (DR) by color fundus photographs taken before and after the infusions. Image analysis was done by a semiautomated computerized microdensitometer using a videoscanner. Normal controls and diabetics without retinopathy had a significant reduction in diameter compared with diabetics with retinopathy, who failed to constrict arterioles in response to either vasopressor. The mechanism of this phenomenon is unclear. Semiautomated computerized microdensitometry is reproducible and appears to be a sensitive technique to evaluate the vascular reactivity of the retinal vasculature.

Reproducibility of the densitometric analysis of fluorescein angiograms.

Computer-aided operator-interactive densitometry was applied to assess the reproducibility or retinal-fluorescein angiograms. To achieve this, the fundus camera images of glass tubings of various diameter filled with fluorescein of varying concentrations were subjected to densitometric analysis. These studies were carried out repeatedly at 9-micrometer and 29-micrometer scanning resolutions by three observers and thus the inter- and intra-operator errors could be estimated. The scanned data were analyzed as both optical densities and intensities for some of the measurements. In both analyzing modes good linearity was obtained when the densitometric response was plotted against tubing diameter for various concentrations. To determine the reproducibility of transit time and retinal circulation time analyses, a randomly selected patient's angiogram was repeatedly analyzed by three observers and compared. From these data the inter- and intra-operator errors were also determined for successive frames and the reproducibility of the area under the dye dilution curves for both arteries and veins was computed. The overall densitometric reproducibility was found to be good; however, practical usefulness of the retinal circulation time remains to be established.

The determination of glycosylated hemoglobins in rats using high pressure liquid chromatography.

Glycosylated hemoglobins (GHb) or fast hemoglobins (FH) are minor components of hemoglobin that so far have been quantified in men, monkeys, and mice, and they are elevated in diabetic subjects of all these species. Since the rat is a useful model for experimental diabetic studies, hemolysates from streptozotocin-induced diabetic rats were analyzed for FH fractions using a high pressure liquid chromatography method. In a long-term study (3 mo), the maximal increment of the FH fractions was achieved after 5 wk of diabetes (from 5.67% +/- 0.41% SD to 10.80% +/- 0.74%) supporting the notion that the biosynthesis of these compounds occurs continuously during the lifespan of the red cell. In a short-term study, however, an elevation of the FH by 11% after 2 days and by 26% after 6 days of diabetes was noticed suggesting that a rapid increase of the FH may occur in relation to rapid changes of the glucose level.

Insulin resistance and monoclonal gammopathy.

Two maturity-onset diabetic patients developed severe insulin resistance during the course of monoclonal gammopathies. One patient had Waldenström macroglobulinemia and the other had multiple myeloma with IgA gammopathy. The maximum insulin binding capacity (MIBC) was 121 U/liter and 54.7 U/liter, respectively, during insulin resistance. The clinical courses of insulin resistance paralleled the activity of the monoclonal gammopathies (MG) with the insulin resistance disappearing after the monoclonal gammopathies were controlled. Six other diabetic patients with concurrent insulin resistance and monoclonal gammopathies are reviewed.