Rhythms in urine flow are not correlated with rhythmic secretion of antidiuretic hormone (ADH) in well hydrated men

Repeated measurements of urine flow, every 10 min, and plasma ADH levels, every 20 min. were done in 7 healthy, normal young adults who consumed constant amounts of fluids and urinated voluntarily, and in 6 supine catheterized patients. Normal subjects who were hyperhydrated, stood up every 10 min. to urinate and then returned to a semirecumbant position. Catheterized patients who were also hyperhydrated assumed similar test procedure excluding postural changes. Variance spectra revealed significant ultraradian rhythms of about 100 ± 40 min/cycle in the flow of urine, in urine osmolality, sodium and potassium excretion as well as in plasma ADH levels, in normals, but all these rhythms were neither correlated nor phase locked to rhythms in ADH levels. In the supine patients, significant ultraradian rhythms in urinary osmolality, sodium and potassium excretion were observed, but not in the flow of urine that fluctuated rapidly. Plasma ADH levels were constant, ranging from 0.5 to 1.5 pg/ml, without evidence for pulsatile episodic secretion. The finding that despite the hyperhydrated state plasma ADH levels in normal controls ranged between 0.5 to 15.0 pg/ml, suggests that in humans orthostasis is a powerful stimulus for ADH secretion. It is also suggested that there are different control mechanisms responsible for urine flow and solute excretion.