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Original Studies |
Department of Endocrinology (J.H., M.A., E.G., C.H.), Odense University Hospital, DK-5000 Odense C; and Department of Clinical Chemistry (O.K.), Sønderborg Hospital, DK-6400 Sønderborg, Denmark
Address all correspondence and requests for reprints to: Jørgen Hangaard, M.D., Department of Endocrinology, Odense University Hospital, DK-5000 Odense C, Denmark.
This study assessed the controversial role of endogenous opioids and cortisol in the regulation of TSH and PRL secretion in humans. Seven euthyroid male patients with Addisons disease were studied four times, with an interval of 13 months, as follows: 1) during nor-mocortisolism [graduated infusion of hydrocortisone, 0.4 mg/kg, over 19.5 h]; 2) normocortisolism and coadministration of naloxone, at 25 µg/kg·h during the last 6.5 h; 3) hypocortisolism (24 h withdrawal of hydrocortisone, followed by 19.5 h saline infusion); and 4) hypocortisolism plus naloxone administration. The TSH and PRL levels were measured every 15 min, from 08001530 h. A TRH test was performed at 1300 h and 1400 h (10 µg and 200 µg of TRH, respectively). The mean TSH level increased significantly during hypocortisolism, compared with normocortisolism (1.78 ± 0.04 vs. 0.84 ± 0.02 mU/L; P < 0.001). The administration of naloxone suppressed the TSH levels during hypo- and normocortisolism (1.78 ± 0.04 vs. 1.50 ± 0.03 and 0.84 ± 0.02 vs. 0.61 ± 0.02 mU/L, respectively; P < 0.001). During hypocortisolism, the TSH responses to small and high doses of TRH were significantly higher than during normocortisolism (P < 0.02). Naloxone had no effect on the TSH responses to TRH, neither during hypo- nor during normocortisolism. The mean PRL level increased significantly during hypocortisolism, compared with normocortisolism (5.8 ± 0.4 vs. 3.6 ± 0.2 µg/L; P < 0.001), and naloxone induced an increase in PRL levels both during hypo- and normocortisolism (7.1 ± 0.7 vs. 4.7 ± 0.5 µg/L, respectively; P < 0.01). The PRL responses to TRH were similar during hypo- and normocortisolism and without any change during opioid receptor blockade. In conclusion, cortisol suppressed basal TSH and PRL secretion and reduced the sensitivity of the thyrotrophs to TRH, without affecting the PRL response to TRH. Our results suggest that endogenous opioids act at the hypothalamic level to stimulate TSH secretion and to suppress the PRL secretion, but these results argue against an essential role of endogenous opioids in the physiological regulation of TSH and PRL secretion in humans.
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