Infradian rhythms in urinary growth hormone excretion

All studies of urinary GH excretion in normal and disordered growth have revealed marked day to day (infradian) variation. We used serial overnight urinary GH estimations as an indirect measure of endogenous GH secretion in eight normal prepubertal children (aged 3.6-7.3 yr) over 90-365 days to determine whether longer term rhythms in GH output could exist. This study constitutes a first step in examining the potential relationship between GH excretion and growth. Urinary GH was measured by immunoradiometric assay after dialysis, expressed as the total amount excreted (nanograms per night) or as the GH/creatinine ratio (nanograms per mmol), and assessed by pulse counting techniques and time-series analysis. Variability in urinary GH excretion (median coefficient of variation, 46%) was significantly greater than creatinine (median coefficient of variation, 25%; P = 0.003). Additionally, there was marked month by month variation in baseline urinary GH in all children. High frequency pulses of urinary GH wer...