No abstract

A B S T R A C T The acute effects of chlorothiazide (CTZ) on total (TSCA) and ionized (SCA2') serum calcium concentrations were studied in three groups of people: (a) eight subjects with normal parathyroid function; (b) six patients with hypoparathyroidism; and (c) two patients with hyperparathyroidism. Most subjects were studied on four occasions; at least 3 days intervened between studies on an individual subject. During each experiment the subject received an i.v. infusion of 5% dextrose in water at 1 ml/min from 8 a.m. to 4 p.m. Additions to the infusions were (a) none; (b) CTZ to deliver 3.33 mg/kg/h; (c) parathyroid extract to deliver 1 U/kg/h; or (d) both CTZ and parathyroid extract at the rates previously indicated. CTZ, when used, was added to the infusion at 10 a.m., parathyroid extract at 8 a.m. When CTZ was infused, the diureticinduced losses of Na and water were replaced by i.v. infusion. In normal subjects 2 h after the start of CTZ infusion, there was a transient increase in SCA +2 which coincided in time of day with a transient decrease in SCA+2 in control experiments. At that time of day SCA+2 was 4.18±0.12 mg/100 ml in control experiments and 4.56±0.08 in experiments with CTZ, P < 0.025. The corresponding values for (TSCA) were 9.32±0.15 and 9.80+0.30, P < 0.01. Such differences were not observed in the group with hypoparathyroidism. In the two patients with hyperparathyroidism, CTZ produced sustained increases in TSCA and SCA+'. In normal subjects and those with hypoparathyroidism, CTZ plus parathyroid extract infusion resulted in sustained increases in both

We found no differences in pH or ionized calcium concentration of serum from blood either collected into evacuated tubes or collected with syringes and separated under oil. Sera can be stored frozen in 1-ml plastic insulin-type syringes for one to three days without significant changes in pH or ionized calcium concentration, whereas storage under oil with or without re-equilibration with CO2 is associated with significant changes in both. Standards prepared with trypsin and triethanolamine give faster electrode response, and their ionized calcium concentrations remain unchanged for 6 h at room temperature. We suggest a not entirely satisfactory control solution of buffered protein, for use in assessing reproducibility of results.