Plasma inactive renin in patients with hyperthyroidism

Effect of L-thyroxine on serum angiotensin converting enzyme activity in sheep

The effect of L-thyroxine on serum angiotensin converting enzyme activity using a sheep model was examined. Following two weeks of L-thyroxine treatment, the activity of serum angiotensin converting enzyme was increased from 6.92 U/ml to 8.65 U/ml (s.e.m. = 0.40, n = 13, P less than 0.01). Discontinuation of L-thyroxine treatment resulted in lowering the activity of serum angiotensin converting enzyme within three weeks to values close to those observed during the control period. It was concluded that L-thyroxine modulates serum angiotensin converting enzyme activity. The sheep is an appropriate animal model for the study of the factors that control serum angiotensin converting enzyme activity.

Comparison of serum angiotensin-converting enzyme in Graves' disease, toxic nodular goiter, and other thyroid conditions

Angiotensin-converting enzyme (ACE) was measured in plasma of patients with Graves' disease and with toxic nodular goiter, as well as in their treated counterparts and in normal controls. A significant elevation of ACE levels and a positive correlation between ACE, thyroxine, and triiodothyronine levels was found in both groups of thyrotoxicosis. Parallel fluctuations of triiodothyronine and ACE levels, albeit with a certain lag of the latter, was observed in patients in whom multiple measurements were taken. ACE levels, which were also determined in hypothyroid patients and in patients with euthyroid goiter on suppression therapy, were in the same range as normal controls and as in treated thyrotoxic patients. We conclude that the pathogenesis of thyrotoxicosis does not play a role in ACE elevation but that increased thyroid hormone seems to induce elevation of ACE. ACE elevation in thyrotoxicosis may constitute an integral part of the renin-angiotensin axis.

Electrolyte excretion in 12-hour urine and in spot urine. Relationship to plasma renin activity and aldosterone concentration in older children

Plasma renin activity (PRA) and urinary electrolyte excretion were measured in 137 healthy children aged 6 to 14 years. Plasma aldosterone concentration (PAC) was measured in 52 of the children. Nocturnal 12-hour urine was collected in 110 of the children. Spot urine was collected on two occasions, once just before lying down, once after 90-min supine rest in another 27. Na/K ratio and fractional Na excretion rate (FENa) in 12-hour urine showed a significant inverse correlation with PRA or PAC. Na excretion (mmol/min, mmol/mmol creatinine), Na/K ratio and FENa in the spot urine following 90 min in a supine position showed a significant inverse correlation with PRA or PAC, but they failed to show a significant relationship to PRA or PAC in the spot urine preceding supine rest. A spot urine after 90 min in the supine position is collected easily and hence most appropriate to study the relationship between Na excretion and PRA or PAC clinically.