Circadian and pulsatile thyrotropin release in treated acromegalics

We studied the 24-h TSH profiles of 16 treated male acromegalic patients (age range 26-68 yr) in clinical and biochemical remission. Eight had undergone transsphenoidal surgery, the others surgery and pituitary irradiation. Blood samples were taken at 20-min intervals; circadian rhythms were established by cosinor analysis, pulsatile release with the Cluster programme. All patients, except one irradiated subject, were euthyroid. TSH reserve was diminished preoperatively in 7 subjects and at the time of the profile study in 10 subjects, one of whom was biochemically hypothyroid. A significant circadian rhythm was present in 14 subjects and absent in the hypothyroid patient. The acrophase occurred at 2.46 +/- 0.51 h in nonirradiated patients and at 3.37 +/- 0.38 h in irradiated patients (NS). About 10 TSH pulses/24 h (range 6-13) were detected; there was no significant difference between irradiated and non-irradiated patients. With cross-correlation techniques synchronous release of TSH and PRL was demonstrated in 7 out of 8 nonirradiated patients in contrast to only 2 of the irradiated patients. This study demonstrates a qualitatively normal TSH secretion pattern for treated acromegalic patients, but the absolute TSH levels are clearly low compared with published data on normal subjects. The present findings can be explained by a diminished TSH cell mass; in addition radiation therapy causes a disturbance at the hypothalamic level, as indicated by the loss of synchronism between TSH and PRL release.