Antidiuretic hormone secretion and urine flow in aged catheterized patients.

Repeated measurements of urine flow, every 10 min, and plasma ADH levels, every 20 min, were done in six aged, supine catheterized patients for seven hours. Orthogonal spectral analysis revealed 80 to 130 ultradian rhythms in urinary osmolality and in Na+ and K+ concentrations, but not in the flow of urine that fluctuated rapidly. Plasma ADH levels were constant, ranging from 0.5 pg/ml to 1.5 pg/ml, without evidence for pulsatile episodic secretion.