The Tohoku Journal of Experimental Medicine
Online ISSN : 1349-3329
Print ISSN : 0040-8727
ISSN-L : 0040-8727
Enhanced Prolactin Secretion in Patients with Primary Hypothyroidism during Thyroid Replacement
SHUICHI SATOKUNIHIKO HANEWATSUSHI SASAKIYASUYUKI SHIMIZUOSAMU MURAKAMIHIROSHI FUKAZAWATOSHIRO SAKURADASHINTARO SAITOKAORU YOSHINAGA
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1984 Volume 144 Issue 4 Pages 425-431

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Abstract

SATO, S., HANEW, K., SASAKI, A., SHIMIZU, Y., MURAKAMI, O., FUKAZAWA, H., SAKURADA, T., SAITO, S. and YOSHINAGA, K. Enhanced Prolactin Secretion in Patients with Primary Hypothyroidism during Thyroid Replacement. Tohoku J. exp. Med., 1984, 144 (4), 425-431 - Thyroid hormones are known to exert some influence on prolactin (PRL) secretion indirectly via the hypothalamic dopaminergic system and directly at the level of pituitary gland. In order to study the effect of thyroid hormones on the activity of hypothalamic dopamine neurons, lactotrophs and thyrotrophs, we administered increasing doses of thyroid hormones to patients with primary hypothyroidism, and examined the changes of basal PRL, TSH and PRL responses to a dopamine receptor blocker (sulpiride). Among 24 patients with primary hypothyroidism, hyperprolactinemia was observed in 10 cases (18.0-236ng/ml, mean±S.E. 58.6±20.0ng/ml), while elevated TSH levels were observed in all of them (6.6-972μU/ml, mean±S.E. 231.4±53.9μU/ml). There was a significant negative relationship between plasma T3 or T4 levels and basal plasma TSH levels (p<0.05), whereas a poor correlation was observed between the thyroid hormones and basal plasma PRL levels (r=-0.25, p>0.05). Following the administration of gradually increasing doses of thyroid hormones, plasma PRL showed paradoxical and transient increases, while plasma TSH decreased steadily. Plasma PRL response to sulpiride also became exaggerated during the treatment. The elevated basal PRL level and the enhanced response to sulpiride turned to be within the normal range when the patients became euthyroid by treatment. These results may indicate that thyroid hormones stimulate not only hypothalamic dopaminergic activity, but also the lactotroph activity in a long term hypothyroid state. Regarding the paradoxical elevation of basal PRL, one can postulate that the activation of lactotroph by a small dose of thyroid hormone may be able to overcome the hypothalamic dopaminergic inhibition.

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