Temporal Patterns of Circulating Hormones as Assessed by Continuous Blood Sampling

Definition of rhythms and mean daily levels of GH, TSH, LH, FSH and testosterone has been obtained by a continuous blood sampling technique using a double lumen catheter and measurement of integrated plasma levels by sensitive and precise radioligand assays in 9 healthy young adults (7 males and 2 females). In each subject, sequential continuous blood samples of 3–4 hr duration were obtained over a 24-hr period of near normal activity. Growth hormone rises in samples coincident with sleep onset in the males, a circadian rhythm of TSH levels (peak at midnight, nadir in the afternoon) and no significant time related changes of LH and FSH levels in the whole group or of testosterone in the males were found.