Changes in serum angiotensin-converting enzyme in acutely starved non-obese patients. A possible dissociation between angiotensin-converting enzyme and the thyroid state.

We investigated changes in the serum angiotensin-converting enzyme, as an index of thyroid hormone action, before, during and after fasting in 15 non-obese, hospitalized patients. Serum angiotensin-converting enzyme decreased significantly from 14.6 +/- 1.1 U/l before fasting to 13.2 +/- 1.1 U/l on the 5th day (P less than 0.05, N = 15) during fasting, and to 10.6 +/- 1.0 U/l on the 10th day (P less than 0.05, N = 8). The serum TSH and T3 levels decreased significantly to below the normal range, and the serum T4 level decreased gradually during fasting, whereas free T4 (Amerlex) changed slightly, but within normal range. Although re-feeding did not lead to any reduction in the serum TSH, T3, or T4 level, the serum angiotensin-converting enzyme further decreased to 8.7 +/- 0.9 U/l on the 5th day of re-feeding compared with that on the 10th day of fasting (P less than 0.01, N = 8). There was a delay in the re-elevation of serum angiotensin-converting enzyme following a rise in serum T3. No correlations were found between serum angiotensin-converting enzyme levels and thyroid hormone levels throughout the study period. It is concluded that a significant reduction in the serum angiotensin-converting enzyme level occurs under a 'low T3' state during acute starvation, although there is no clear association between serum angiotensin-converting enzyme and thyroid hormone levels.