Endogenous digoxin-like immunoactivity in subjects with diabetes mellitus and hypertension.

The serum concentrations of digoxin-like immunoactivity (DLIA) were measured in 99 patients: 20 healthy volunteers (HV), 15 patients with insulin-dependent diabetes mellitus (IDDM), 14 patients with non-insulin-dependent diabetes mellitus without hypertension taking oral hypoglycemic (OHA) agents (NIDDM/-HT), 11 patients with NIDDM without hypertension taking insulin (NIDDM/-HT+INS), 12 NIDDM patients with hypertension taking OHA (NIDDM/+HT), nine NIDDM patients with hypertension taking insulin (NIDDM/+HT/+INS), 10 patients with essential hypertension with normal insulin levels (HT/-HI), and in eight patients with essential hypertension with hyperinsulinemia (HT/+HI). The numbers (%) of subjects with DLIA levels above the detection limit of the assay used (> 0.1 nmol/L) were, in the NIDDM/-HT group, 12/14 (85.7%) and in the NIDDM/+HT group, 9/12 (75%), significantly higher (P < .05) than in the HV (7/20; 35%), IDDM (3/15; 20%), and HT/-HI groups (2/10; 20%). The number and percentage of subjects with DLIA levels above the detection limit in the HT/+HI group was six of eight (75%), significantly (P < .05) higher than in the IDDM and HT/-HI groups, and tended to be higher than in the HV group (P < .055). Means and SD of serum DLIA levels (nmol/L) in the NIDDM/-EH (0.18/0.09) and NIDDM/+EH (0.19/0.15) groups were significantly higher (P < .05) than in the HV (0.09/0.07), IDDM (0.05/0.05), and EH/-HI (0.06/0.06) groups. DLIA levels in the HT/+HI group (0.15/0.12) were significantly higher (P < .05) than in the IDDM and HT/-HI groups. The percentage of DLIA levels above the detection limit, as well as the mean and SD of DLIA in the NIDDM group taking OHA, did not differ from those in subjects taking insulin. In all subjects studied (n = 99), DLIA correlated with C-peptide (r = 0.30; P < .01) and glomerular filtration (GF) (r = -0.21; P < .05). After exclusion of insulin-treated patients, DLIA correlated significantly with plasma glucose (PG; r = 0.25; P < .05), immunoreactive insulin (IRI; r = 0.41; P < .001), C-peptide (r = 0.27; P < .05), and GF (r = -0.26; P < .05) (n = 64). Correlation of DLIA with IRI (r = 0.33; P < .05; n = 38) also persisted after exclusion of patients taking insulin and those with DLIA levels below the detection limit. Similarly, DLIA also correlated with C-peptide (r = 0.64; P < .05) and IRI (r = 0.70; P < .05) in the subgroup of 10 patients with the highest levels of DLIA (> 0.25 nmol/L). None of the sera (n = 15) with different DLIA concentrations (0.0-0.38 nmol/L) exhibited K-pNPPase (Na+-K+-ATPase) inhibitory activity. In conclusion, this work demonstrated elevated serum DLIA in NIDDM and HT/+HI patients, and its correlation with IRI and GF. However, due to the fact that the chemical nature and biologic properties of DLIA are still a matter of debate, it is too early to speculate whether the elevation of DLIA is just a secondary result associated with HI and reduced GF, or whether it also has pathophysiologic consequences. Nevertheless, in both cases the elevated concentrations of substances with DLIA and their interference with antidigoxin antibodies may affect therapeutic monitoring of digitalization in NIDDM and HT/+HI patients. Also, the elevated DLIA could subclassify these patients. The significance of such subclassifications (pathophysiologic, therapeutic, or prognostic), however, will need further investigation.

[Membrane-associated acetylcholinesterase in the sarcotubular system of skeletal muscles]. / Membránovo asociovaná acetylcholínesteráza zo sarkotubulárneho systému kostrového svalu.

Isolated membranes of the sarcotubular system of the skeletal muscle of the rabbit exhibit acetylcholinesterase activity. The activity of the enzyme depends on the intactness of the vesicles, it increases with time and after the action of detergents, suggesting that the enzyme may be bound to the membranes in a latent occluded form. The optimal conditions of the hydrolytic reaction were determined to be at the protein concentration of 35-40 micrograms/ml. The most suitable pH for acetylcholinesterase activity was found to be in the mildly alkaline region of pH = 8.0. The dependence of the activity of the enzyme on the concentration of the substrate displayed a hyperbolic course, the reciprocal dependence according to Lineweaver and Burk yielded the values KM = 0.69 mmol.l-1 and Vmax = 1.99 mumol/mg/h. The observed properties of acetylcholinesterase from the sarcotubular system show that the enzyme is associated with these membranes and after the action of detergents it has a well measurable activity.