Bromocriptine suppresses the thyrotrophin response to thyrotrophin releasing hormone during human pregnancy

The safety of bromocriptine in hyperprolactinaemic female infertility: a literature review

The dopamine agonist bromocriptine has been widely used to facilitate pregnancy in hyperprolactinaemic women, with a success rate of 80% in relevant cases. Neither the inappropriate hyperprolactinaemia consequent upon bromocriptine withdrawal after conception nor the relative hypoprolactinaemia caused by treatment throughout gestation appears to affect adversely the course and outcome of pregnancy or the endocrine status of the fetus. No teratogenic effect of bromocriptine has been evidenced in humans, and no disturbances in the physical, psychomotor, and intellectual development of the offspring have been observed. Pituitary-tumor enlargement during closely supervised pregnancies very rarely leads to severe and irreversible complications; both the re-institution of bromocriptine treatment in the event of tumor enlargement and its preventive use throughout pregnancy have been shown to be effective measures. It is interesting, moreover, that a reduction of hyperprolactinaemia, compared with pregestational levels, may be seen after bromocriptine-facilitated pregnancies.

Recovery of serum TSH and thyroid hormones after 3'isopropyl-3,5-diiodo-L-thyronine (DIIP) treatment: absence of inhibiting effect of bromocriptine on TSH secretion and evidence for autoregulation of serum T3 levels

Bromocriptine, because of its dopaminergic activity, could possibly inhibit TSH secretion. This hypothesis was tested in 7 normal male volunteers. Thyroid function was suppressed with the very potent thyromimetic analogue, 3'isopropyl-3,5-diiodo-L-thyronine (DIIP). We wanted to observe, after stopping this treatment, whether the return of serum T3, T4, rT3 and TSH values was influenced by concomitant bromocriptine treatment (5 mg/day). For comparison, the DIIP study was also performed without bromocriptine treatment. In both cases, serum T4 and serum T3, which had decreased by, respectively, 34% +/- 5% and 17% +/- 5%, returned over the same time interval to their initial values. Serum TSH and TRH-mediated TSH secretion were also unaffected by the bromocriptine treatment. DIIP does not interfere in the serum determination of T3, T4 and rT3. During suppression with DIIP serum T3 fell less than serum T4 and returned more rapidly to its initial concentrations. It is concluded that dopaminergic inhibition by bromocriptine, at this dose, is insufficient to alter normal thyroid function. In addition, during suppression and shortly thereafter there is a tendency for the serum T3 levels to be maintained.

The effect of oestrogen (mestranol) on the thyrotrophin response to thyrotrophin releasing hormone in postmenopausal oophorectomised women

The thyrotrophin (TSH) responses to thyrotrophin releasing hormone (TRH) in 16 oophorectomised postmenopausal women on long term treatment with mestranol 24 micrograms daily were compared to those in 16 oophorectomised postmenopausal women on placebo treatment. No significant difference between the groups was found in either basal TSH levels or the TSH response to TRH. It is therefore unlikely that the difference in TSH response to TRH between men and women of reproductive age is due to a direct stimulatory effect of oestrogen in women.

Pharmacological interference with in vitro tests of thyroid function

Numerous drugs may cause changes in the serum concentrations of T4 and of T3. If such alterations are not recognized an incorrect diagnosis may result. In moderate degrees of hypo- and hyperthyroidism thyroid hormone levels may be spuriously normal, or the influence of pharmacological substances may lead to false diagnosis of thyroid disease in euthyroid patients. Since prediction of such alterations remains uncertain, it may be necessary to perform additional investigations when a potential artefact is recognized. On the other hand many pharmacological agents, especially those which interact with neurotransmitters, may influence TSH secretion, too. The TRH-test may show an increase or decreased TSH response, although complete suppression is only rarely seen during high-dose glucocorticoid treatment when low TRH doses are applied. Because of TRH-test gives such wide separation between different clinical states false interpretations are generally less likely than with drug-induced changes in T4 and T3 values.