
Originally Posted by
gdevine
A. Wayne Meikle
Division of Endocrinology, University of Utah School of Medicine, Endocrine Testing Laboratory ARUP, Salt Lake City, Utah
ABSTRACT
Thyroid hormone deficiency affects all tissues of the body, including multiple endocrine changes that alter growth hormone, corticotrophin, glucocorticoids, and gonadal function. Primary hypothyroidism is associated with hypogonadotropic hypogonadism, which is reversible with thyroid hormone replacement therapy. In male children follicle-stimulating hormone (FSH) is elevated and associated with testicular enlargement without virilization. Men with primary hypothyroidism have subnormal responses of luteinizing hormone (LH) to gonadotropin-releasing hormone (GnRH) administration and normal response to human chorionic gonadotropin (hCG). Free testosterone concentrations are reduced in men with primary hypothyroidism and thyroid hormone replacement normalizes free testosterone concentrations. In men with primary hypothyroidism, prolactin is not consistently elevated (except in men and children with longstanding severe primary hypothyroidism), but prolactin declines following thyroid hormone replacement therapy. Thyroid hormone is known to affect sex hormone-binding hormonal globulin (SHBG) concentrations. Men with hyperthyroidism have elevated concentrations of testosterone and SHBG. Thyroid hormone therapy in normal men may also duplicate this elevation. In addition estradiol elevations are observed in men with hyperthyroidism, and gynecomastia is common in them as well. In contrast to patients with primary hypothyroidism, men with hyperthyroidism exhibit hyperresponsiveness of LH to GnRH administration and subnormal responses to hCG. Radioactive iodine therapy (RAI) of men treated for thyroid cancer produces a dose-dependent impairment of spermatogenesis and elevation of FSH up to approximately 2 years. Permanent testicular germ cell damage may occur in men treated with high doses of RAI. RAI commonly increases serum concentrations of FSH and LH while reducing inhibin B levels without affecting serum concentrations of testosterone. Thus, radioiodine therapy transiently impairs both germinal and Leydig cell function that usually recover by 18 months posttherapy.
Testicular dysfunction in men with primary hypothyroidism; reversal of hypogonadotrophic hypogonadism with replacement thyroxine.
Donnelly P, White C.
Source
Royal Prince Alfred Hospital, Camperdown; Liverpool District Hospital; Prince of Wales Hospital, Sydney, Australia.
Abstract
OBJECTIVE:
Primary hypothyroidism can cause disturbances in normal gonadal function. The aim of this study was to investigate the relationship in men between hypogonadism and primary hypothyroidism and the extent to which free and total testosterone levels rose after introduction of replacement thyroxine.
DESIGN:
Paired study of patients in a hypothyroid and thyroxine treated state.
PATIENTS:
Ten men with primary hypothyroidism.
MEASUREMENTS:
Free and total testosterone, gonadotrophin and prolactin levels before and after thyroxine replacement therapy.
RESULTS:
Low free testosterone levels (161 +/- 62 pmol/l) demonstrated at the time the men were hypothyroid rose significantly with the commencement of thyroxine replacement (315 +/- 141 pmol/l; P < 0.001). Gonadotrophin levels were not elevated consistent with hypogonadotrophic hypogonadism. Hyperprolactinaemia, which can occur in primary hypothyroidism and cause hypogonadotrophic hypogonadism, was not present in the majority of these patients. However a reduction in prolactin level was evident with thyroxine replacement and a rise in free testosterone levels.
CONCLUSION:
This suggests an effect of hypothyroidism on gonadotrophin secretion at the level of the hypothalamus-pituitary, either directly or through modulation of prolactin secretion. Low free testosterone may also be a contributing factor to some of the symptoms and signs of hypothyroidism in men.