Reduced lecithin: cholesterol acyltransferase (LCAT) and Na+, K+, ATPase activity in diabetic patients.

OBJECTIVE: To investigate the plasma concentrations of lecithin:cholesterol acyltransferase (LCAT EC 2.3.1.43) and erythrocyte membrane Na+, K+, ATPase and the correlation of these parameters in diabetes mellitus. DESIGN AND METHODS: Na+, K+, ATPase was measured with spectrophotometric method and LCAT with radioactive method in 19 patients with insulin-dependent diabetes mellitus (IDDM), in 20 with non-insulin-dependent diabetes mellitus (NIDDM) and in 20 healthy volunteers as the control group. RESULTS: Compared with the control group, plasma LCAT concentrations were found to be decreased in both of the patient groups (p < 0.01 for both). Erythrocyte membrane Na+, K+, ATPase activities were higher in the controls than both in the NIDDM and IDDM groups (p < 0.01 and p < 0.001, respectively). There were significant correlations between LCAT and Na+, K+, ATPase in IDDM (r = 0.82, p < 0.001) and in NIDDM (r = 0.74, p < 0.001). In order to investigate the effect of cholesterol (C) and lysophosphatidylcholine (LPC) on Na+, K+, ATPase activity, this enzyme's activity was determined in erythrocyte membranes obtained from diabetic subjects after in vitro incubation with increasing concentrations of LPC and C (2-10 microM). Enzymatic activity was significantly reduced by in vitro C at increasing concentrations but significantly increased by in vitro LPC at increasing concentrations. CONCLUSIONS: From these data, it is to be concluded that the decrease in Na+, K+, ATPase activity in diabetes might be due to decreased LCAT concentrations and that may explain the development of atherosclerosis in diabetics.

The influence of calcium infusion on serum prolactin in hyperprolactinemic women.

This study investigated the influence of calcium on serum prolactin (PRL) in hyperprolactinemic and healthy women. Previous studies have shown an inhibitory effect of Ca2+ on serum PRL, related to the degree of hypercalcemia. Serum PRL levels were measured by immunoradiometric assay (IRMA) in subjects before and one hour after 1375 mg Ca2+ injection. Serum PRL level was significantly decreased by calcium injection in hyperprolactinemic women (89.2 +/- 29.1 and 63.3 +/- 35.8 ng/ml; p < 0.01) while it was not significant (p > 0.05) in women with normal PRL levels (12.6 +/- 5.1 ng/ml and 11.3 +/- 4.0 ng/ml). These results indicate that acute alterations in serum calcium levels affect PRL secretion in hyperprolactinemic women.