Enhanced prolactin secretion in patients with primary hypothyroidism during thyroid replacement.

Abstract

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 (18.0-236 ng/ml, mean +S.E. 58.6+20.0 ng/ml), while elevated TSH levels were observed in all of them (6.6-972,uU/ml, mean ±S.E. 231.4+53.9,aU/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. primary hypothyroidism ; thyroid hormone ; prolactin ; sulpiride ; dopaminergic regulation

The effect of sex hormones on bone metabolism of the otic capsule – an overview

“…Since these all areas concerned with endolymph absorption, absence of pendrin results in endolymphatic hydrops (Royaux et al, 2003). Pendred's syndrome is typically associated with hypothyroidism, and so prolactin levels could be expected to be elevated (Sato et al, 1984), but this has not been an issue of discussion in the literature. On the other hand, there may yet be some uncovered role of prolactin given the fact that, in the mammary gland, prolactin actually stimulates the pendrin-iodide transporter which is essential for iodide uptake into milk (Rillema and Hill, 2003).…”

Contemporary management of prolactinomas

“…Hyperprolactinemia can occur in approximately 20 to 30% of patients with primary hypothyroidism. 58,114,126,136 Severe primary hypothyroidism results in elevated thyrotropin-releasing hormone levels, causing mild-to-moderate elevations in serum prolactin, which can lead to thyrotroph hypertrophy and pituitary hyperplasia. This situation can sometimes be misdiagnosed as a prolactinoma; therefore, it is important to obtain the concentration of thyroid-stimulating hormone to rule out primary hypothyroidism.…”