Differences in the nyctohemeral secretion of TSH and PRL in healthy euthyroid men.

The circadian rhythm of TSH, PRL and cortisol was studied in 21 healthy euthyroid men in a normal sleep/wake cycle. Higher nyctohemeral (22.00 h till 6.00 h) levels of TSH as compared to diurnal (8.00 h till 22.00 h) levels were observed in 14 out of 21 men (Group A). In the remaining 7 volunteers the nyctohemeral and diurnal TSH-levels (Group B) were the same. In Group A, the nyctohemeral PRL-surge was also higher than in Group B (p < 0.01). The nyctohemeral area under the curve (AUC) of both TSH and PRL were significantly higher in Group A than in Group B (p < 0.05 and p < 0.001 respectively). The mean diurnal concentrations of TSH and PRL were, however, similar in both groups. Therefore, an impairment of the nyctohemeral TSH-surge can occur in healthy men usually combined with a reduced nyctohemeral PRL-surge. An impairment of nyctohemeral TSH-surge is thus not confined to patients with thyroid diseases.