triiodothyronine--reverse and Acromegaly

To study whether high growth hormone (GH) milieu may counteract fasting-induced changes in thyroid hormone economy, we measured basal and TRH-stimulated TSH concentrations as well as thyroxine (total, TT4 and free, FT4), total triiodothyronine (TT3) and total reverse T3 (TrT3) before and after a 6-day fast in 6 healthy men and in 8 patients with acromegaly. Baseline values for all parameters were similar in both groups. Fasting induced similar increases in TT4 and TrT3 concentrations and a similar decline in TT3 concentrations in both groups. The TT3/TT4 and TrT3/TT4 ratios changed identically in both groups. We conclude that high GH is incapable of altering fasting-induced changes in thyroid hormone economy.

Topics: Acromegaly; Fasting; Growth Hormone; Humans; Male; Thyroid Function Tests; Thyroid Hormones; Thyrotropin; Thyroxine; Time Factors; Triiodothyronine; Triiodothyronine, Reverse

The pulsatile secretion of TSH was studied in eight patients with active acromegaly before treatment and after 1 month of therapy consisting of the sc infusion of 300 micrograms octreotide/day. Mean GH levels decreased from 37.1 +/- 7.2 to 5.2 +/- 1.4 mU/L (P = 0.002). Insulin-like growth factor-I levels decreased from 82.9 +/- 8.8 to 37.8 +/- 9.8 nmol/L (P less than 0.01) and normalized in five of the eight patients. In one patient TSH levels were undetectable before and during octreotide therapy. In the other seven patients, Cluster analysis revealed 11.9 +/- 0.8 pulses/24 h, with a mean pulse width of 81 +/- 4.6 min, a mean pulse height of 1.33 +/- 0.42 mU/L, and a mean pulse increment of 0.36 +/- 0.12 mU/L. During octreotide therapy these pulse parameters remained unchanged. Pulse height and amplitude increased significantly during the night (i.e. from 2000-0800 h) in both untreated and treated patients. The acrophase was unchanged by therapy. During therapy T3 levels decreased from 2.05 +/- 0.17 nmol/L to 1.44 +/- 0.08 nmol/L (P = 0.001), while rT3 levels increased from 0.14 +/- 0.02 nmol/L to 0.19 +/- 0.03 nmol/L (P less than 0.05). Plasma T4 levels remained unchanged. From these studies we conclude that the TSH pulse generator is unchanged in active acromegaly and apparently unaffected by chronic octreotide infusions.

Topics: Acromegaly; Circadian Rhythm; Female; Growth Hormone; Humans; Insulin-Like Growth Factor I; Male; Middle Aged; Octreotide; Periodicity; Thyroid Gland; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

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.

Topics: Acromegaly; Adult; Circadian Rhythm; Growth Hormone; Humans; Hypothalamus; Insulin-Like Growth Factor I; Male; Prolactin; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Measurement of the free serum concentration, the 24-h urinary excretion and the renal clearance of T4, T3, 3,3',5'-tri-iodothyronine (rT3), 3',5'-diiodothyronine (3',5'-T2) and 3,3'-di-iodothyronine (3,3'-T2) was performed in 13 patients with active acromegaly and in 18 healthy controls. The acromegalic patients had normal serum levels of the free iodothyronines, whereas the urinary excretion of T4 and T3 was increased approximately two-fold in the patients with acromegaly. The creatinine clearance, reflecting the glomerular filtration rate (GFR), was increased in the acromegalic patients, in median 133 ml/min versus 87 ml/min (p less than 0.01) in the controls. Compared to the creatinine clearance the clearance of T3 and 3,3'-T2 was higher (p less than 0.01) in acromegalics as well as in controls. The patients with acromegaly had higher renal clearance of T4 and T3 than controls, in median 81 ml/min versus 33 ml/min, and 269 ml/min versus 137 ml/min, respectively (p less than 0.01). These differences were not due to changes in creatinine clearance. The renal clearance of 3',5'-T2 tended to be enhanced in acromegalic patients (8.2 ml/min versus 3.9 ml/min, p less than 0.10), both before and after correction for creatinine clearance. The data suggest that in acromegaly, as in normal condition, iodothyronines are subject to both glomerular filtration and active tubular transport mechanisms. Further, active acromegaly results not only in increased GFR, but also in changes of the net tubular transport in favour of secretion of at least T4 and T3, and possibly also of 3',5'-T2.

Topics: Acromegaly; Adult; Aged; Diiodothyronines; Female; Humans; Kidney; Male; Middle Aged; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Topics: Acromegaly; Female; Growth Hormone; Humans; Hyperthyroidism; Menopause; Methimazole; Middle Aged; Prednisolone; Prolactin; Propylthiouracil; Thyrotropin; Thyrotropin-Releasing Hormone; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse