Diurnal variation in the levels of antidiuretic hormone in the elderly.

The secretion of antidiuretic hormone (ADH) and the serum osmolality were measured at 4-h intervals throughout a 24-h period in 69 healthy elderly volunteers. In male subjects the concentrations of plasma ADH were always twofold higher than in female subjects. The normal diurnal rhythm, with increased ADH secretion during the night, was not seen in this group of elderly subjects, with the exception of elderly men who did not urinate during the night, in whom a substantial increase in plasma ADH levels occurred. In as many as 25% of all the ADH measurements performed (n = 455) ADH was not detectable by the method used. The lack of a definite diurnal rhythm in most of the elderly subjects could to some extent explain the increased diuresis during the night in the elderly.