Several reports have shown that average plasma GH concentrations in insulin-treated and in juvenile diabetics are elevated in respect to normal values: these findings have been alternatively attributed to an increased pituitary GH secretion or to a lower GH catabolism induced by the disease.
To reinvestigate the problem we studied GH kinetics in twentyfour diabetics using 125I-GH. The patients were all normal in body weight and their fasting blood sugar did not exceed 190 mg. per 100 ml.; fourteen normal subjects were included as a control group.
After single injection of the tracer, the plasma disappearance curve of labeled hormone was obtained. Starting from this curve, metabolic clearance rate (MCR), fractional catabolic rate (FCR), initial distribution volume (IDV), and total distribution volume (TDV) were computed; MCR and plasma concentration of endogenous GH in plasma samples were used to estimate the amount of hormone irreversibly lost during the experiment (IHL240).
The major points that result from the comparison of the values obtained in diabetic patients with those in the normal group are: MCR values in diabetics do not differ from those found in normals (63.6 ± 19.6 and 64.6 ± 24.3 ml./min./m.2 respectively*). The higher plasma concentrations of endogenous GH in diabetics together with a normal MCR, yield hormone loss values (IHL240) significantly larger than normal (46.4 ± 29.5 μg/240 min. as compared to 23.7 ± 24.5) thus indicating that an increased GH secretion is present in diabetics.
TDV, fairly constant in normals, (5.8 ± 0.9 L./m.2) tends to decrease in diabetic patients as the disease progresses; in fact the values of TDV are significantly reduced (P<0.005) in long-term diabetics (>10 yrs. of disease) while TDV of short-term diabetics (<10 yrs.) does not differ from the normal value (4.6 ± 1.16 L./m.2 and 5.8 ± 0.9 L./m.2, respectively).