Prolactin and TSH secretion in functional tests in patients with primary hypothyroidism and hyperprolactinemia

It was previously proposed that hyperprolactinemia in primary hypothyroidism is caused by enhanced release of hypothalamic TRH leading to elevation of both TSH and prolactin levels. Since the dopaminergic system is involved in regulation of prolactin and TSH secretion, we attempted to evaluate the origin of hyperprolactinemia in patients with primary hypothyroidism using tests with metoclopramide, a dopaminergic blocker (10 mg, i.v) and TRH. Two groups of patients were examined: 20 women with primary hypothyroidism and normal prolactin levels (group A) and 10 women with primary hypothyroidism and hyperprolactinemia (mean basal prolactin level 1514.8 + 300.8 mIU/ml). Prolactin reaction in metoclopramide test in group A was markedly increased vs. control group (1131 and 776%, respectively). In group В prolactin reaction in metoclopramide test was blurred (299%), similarly as in patients with microprolactinomas. We came to a conclusion that hyperprolactinemia in patients with primary hypothyroidism is unlikely to be caused by excessive TRH release, but possibly by the presence of subclinical microadenoma which manifests by the hypothyroid state or, possibly, by disturbed dopaminergic regulation of prolactin and TSH secretion in patients with primary hypothyroidism.

Metoclopramide test in the diagnosis of isolated hypogonadotrophic hypogonadism

The responses of serum prolactin (Prl) to metoclopramide and LH and FSH to GnRH were studied simultaneously in 9 boys with hypogonadotrophic hypogonadism (HH), 7 boys with constitutional delay of puberty (D) and 15 controls. Metoclopramide increased the Prl levels in all groups. The boys with HH had lower Prl responses than the controls, whereas the boys with D had similar responses to the controls. Of the 9 boys with HH, 8 had subnormal Prl responses, 3 subnormal LH and none subnormal FSH. A metoclopramide test is clearly more sensitive than a GnRH test in differentiating HH and D and appears to make the differentiation between these two conditions clearer.