The early development of diabetes insipidus passes through 3 phases in rats on constant diet after electrolytic interruption of the supraoptic tracts in the hypothalamus. Immediately postoperatively, there is a burst of overdrinking with rapid weight gain and polyuria. The interphase then supervenes: weight is lost, the urine becomes more concentrated and scant. The large discrepancy between fluid intake and urine output characteristic of the first phase narrows. Approximately six days postoperatively, water turnover rises abruptly, weight gain resumes, and water intake exceeds urine volume by a value roughly twice that of the intact animal. Total solute excretion decreases during the initial burst of polyuria and rises to a peak at the end of the interphase. These fluctuations appear to parallel urea output. The changes in water turnover are unaccompanied by major alterations in the ratio between urinary potassium and sodium, can be suppressed by vasopressin, are unaltered by ACTH administration and persist after adrenalectomy. They thus appear to be solely due to fluctuations in amounts of vasopressin reaching the circulation.

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