1. We have examined the inter-relationships between erythrocyte sodium content and sodium transport in a group of healthy subjects and in groups of patients with disorders known to change the sodium content of erythrocytes. 2. In the healthy subjects the sodium content of erythrocytes was inversely related to both the permeability of the erythrocyte membrane to sodium (as measured by the unidirectional, ouabain-sensitive, sodium efflux) and the total activity of the sodium pumps (as measured by the rate constant of ouabain-sensitive sodium efflux). There was a correlation between the total activity of the sodium pumps and the membrane permeability to sodium. 3. Changes in the erythrocyte sodium content were due to a decrease in the activity of the sodium pumps (as in hypokalaemia and digoxin treatment), or a decrease in the permeability of the erythrocyte membrane to sodium (as in chronic renal failure) or a reduction of both the membrane permeability and the number of sodium pumps (as in hyperthyroidism or elderly patients). 4. One interpretation of the results in the healthy subjects is that there are two components of sodium influx; one associated with the sodium pumps in what we have called ‘membrane-units’ and the other determined by the ground permeability of the membrane. 5. On the basis of this model we suggest that in the geriatric and hyperthyroid patients there is a reduction in the number of ‘membrane-units’, that in hypokalaemia and during digoxin treatment there is inhibition of the sodium-pump component of the ‘membrane-units’ and that in chronic renal failure there is a decrease in the permeability of the membrane to sodium.

1. The heart-rate changes on standing were studied in 16 elderly patients with idiopathic orthostatic hypotension and compared with those of 20 controls. The mean age of both groups was 78 years, and all were in sinus rhythm. 2. The patients with orthostatic hypotension differed from the control patients in having no early peak in heart rate, and a significantly smaller and slower rise in heart rate within the first 40 s after standing ( P <0.05). 3. It is concluded that there is a failure of the autonomic reflex in elderly patients with orthostatic hypotension, which may contribute towards their symptoms.

1. Total body protein turnover was studied in six elderly patients. 2. During the study they were fed by continuous infusion of a liquid formula through a nasogastric tube. l-[1- 14 C]Leucine and [ 15 N]glycine were infused at a constant rate for 30 h. The labelled glycine was infused into the intragastric line; the labelled leucine was given either by this route or intravenously. 3. The specific radioactivity of free leucine in plasma and the rate of output of 14 CO 2 in expired air both reached a plateau at 10 h, and remained constant until the end of the infusion at 30 h. 4. The 15 N abundance in urinary urea and total N was very similar. In neither was a plateau reached by 30 h but in four out of the six patients the abundance in urinary NH 4 + had attained a plateau by the end of the infusion. 5. Flux rates and rates of protein synthesis were calculated in four ways: (A) from the specific radioactivity of plasma leucine at plateau; (B) from the proportion of dose excreted as 14 CO 2 at plateau; (C) from the final rates of 15 N excretion in urea or total urinary N; (D) from the final or plateau rates of 15 N excretion in urinary NH 4 + . 6. On average, the estimates of synthesis rate obtained by methods B and C agreed closely; those given by methods A and D were lower. Methods A, B and D ranked the individual patients in almost identical order. 7. The comparison of methods makes it possible to examine the validity of the assumptions on which the different methods depend. Method B is probably theoretically the most satisfactory and, of the methods used in this work, probably gives the best estimate of the absolute turnover rate. The other methods can be used for comparative purposes. 8. The results suggest that the rate of protein turnover is reduced in the elderly, compared with younger subjects.