TY - JOUR
T1 - Effects of experimentally induced mild hyperthyroidism on growth hormone and insulin secretion and sex steroid levels in healthy young men
AU - Lovejoy, Jennifer C.
AU - Smith, Steven R.
AU - Bray, George A.
AU - Veldhuis, Johannes D.
AU - Rood, Jennifer C.
AU - Tulley, Richard
N1 - Funding Information:
From the Pennington Biomedical Research Center and Louisiana State University School of Medicine. Baton Rouge, LA: and the University of Virginia Health Sciences Center and National Science Foundation Center for Biological Timing, Charlottesville. VA Submitted December 10. 1996: accepted June 25. 1997. Supported by a gram from the National Aeronautics and Space Administration t NAG 9-714). Address reprint requests ro Jennifer C. Lovejoy, PhD. Pennington Biomedical Research Center 6400 Perkins Rd Baton Rouge, LA 70808-4124. Copyright © 1997 by W.B. Saunders Company 0026-0495/97/4612-0009503.00/0
PY - 1997
Y1 - 1997
N2 - Although triiodothyronine (T3) exerts major regulatory actions in both animals and humans, most clinical studies of T3 administration have been relatively short-term. The present study examined the effects of more than 2 months (63 days) of low-dose T3 treatment on overnight pulsatile growth hormone (GH) secretion, short-term insulin secretion, and of sex steroid levels in seven healthy, lean men studied at an inpatient metabolic unit. At baseline, there were strong correlations between sex hormone-binding globulin (SHBG) and several measures of GH production, including total GH production (r = .99), GH interburst interval (r =-.75), and GH mass (r = .82). SHBG was also inversely correlated with basal insulin secretion (r = -.74). There was a 42% increase in serum levels of total testosterone (18.5 ± 1.3 to 26.3 ± 1.8 nmol/L, P = .005) and a 150% increase in SHBG (18.0 ± 2.2 to 44.9 ± 7.0 nmol/L, P = .008) following T3 treatment. Estradiol and free testosterone levels were unchanged by treatment, although free testosterone decreased from 142.8 ± 18.4 to 137.3 ± 19.5 pmol/L. T3 treatment significantly reduced the GH interburst interval (P < .05) and produced slight increases in the measures of GH secretion. There were no statistically significant effects of T3 treatment on insulin secretion, although insulin peak amplitude, mass secreted per burst, and total production all decreased. We conclude that experimentally induced T3 excess in healthy men produces significant and sustained changes in sex hormone levels and GH secretion. Furthermore, there are strong associations between SHBG and both GH and insulin secretion independent of thyroid hormone excess that require additional study.
AB - Although triiodothyronine (T3) exerts major regulatory actions in both animals and humans, most clinical studies of T3 administration have been relatively short-term. The present study examined the effects of more than 2 months (63 days) of low-dose T3 treatment on overnight pulsatile growth hormone (GH) secretion, short-term insulin secretion, and of sex steroid levels in seven healthy, lean men studied at an inpatient metabolic unit. At baseline, there were strong correlations between sex hormone-binding globulin (SHBG) and several measures of GH production, including total GH production (r = .99), GH interburst interval (r =-.75), and GH mass (r = .82). SHBG was also inversely correlated with basal insulin secretion (r = -.74). There was a 42% increase in serum levels of total testosterone (18.5 ± 1.3 to 26.3 ± 1.8 nmol/L, P = .005) and a 150% increase in SHBG (18.0 ± 2.2 to 44.9 ± 7.0 nmol/L, P = .008) following T3 treatment. Estradiol and free testosterone levels were unchanged by treatment, although free testosterone decreased from 142.8 ± 18.4 to 137.3 ± 19.5 pmol/L. T3 treatment significantly reduced the GH interburst interval (P < .05) and produced slight increases in the measures of GH secretion. There were no statistically significant effects of T3 treatment on insulin secretion, although insulin peak amplitude, mass secreted per burst, and total production all decreased. We conclude that experimentally induced T3 excess in healthy men produces significant and sustained changes in sex hormone levels and GH secretion. Furthermore, there are strong associations between SHBG and both GH and insulin secretion independent of thyroid hormone excess that require additional study.
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U2 - 10.1016/S0026-0495(97)90142-6
DO - 10.1016/S0026-0495(97)90142-6
M3 - Article
C2 - 9439537
AN - SCOPUS:0031452617
VL - 46
SP - 1424
EP - 1428
JO - Metabolism: Clinical and Experimental
JF - Metabolism: Clinical and Experimental
SN - 0026-0495
IS - 12
ER -