Metergoline inhibition of thyrotrophin and prolactin secretions in primary hypothyroidism

Activity of the hypothalamic-pituitary-thyroid axis during exposure to cold

It seems clear from the studies reviewed here that there is adequate evidence to support the concept of a biphasic response of the thyroid gland to cold as first postulated by Moll et al. (1972). The initial response to acute exposure to cold begins at the level of the hypothalamus as a result of either neural stimuli from skin and other areas and/or blood of somewhat lower than normal temperature reaching the hypothalamus (Andersson et al., 1963). As a result, the secretion of norepinephrine and/or dopamine may increase, and serotonin and/or somatostatin may decrease. The net result of these is an increase in the release of TRH from the hypothalamus. This, in turn, stimulates the cascade for the release of TSH from the anterior pituitary gland and thyroid hormone from the thyroid gland. Moll et al. (1972) postulated the lack of a feedback limb in this acute phase, and, indeed, this may be the case. It is possible, however, that certain hormones, such as somatostatin, norepinephrine, T3, and T4 could act in the capacity of feedback inhibitors. Additional experiments will be required to assess this possibility. The transitional link between the acute (less than 1 day) and chronic (greater than 1 day) phases of the response of the thyroid gland to cold could be T4 itself. An increase in the concentration of T4 in plasma has been reported to increase peripheral deiodination of T4 to T3 by kidneys and liver of rats. There are no studies at present to indicate that hepatic conjugation can be increased by elevation of plasma levels of T4 and T3. If it can, these responses would provide adequate reasons as to why peripheral metabolism of thyroid hormones increases during chronic exposure to cold. The time-course for these changes to occur needs to be studied in greater detail to establish the sequence of events following acute exposure to cold. The latter may also increase urinary excretion of T4 and T3 in man, but not the rat. This suggests that another aspect of exposure to cold needing additional study is measurement of the binding affinities of T4 and T3 for their transport proteins during exposure to cold as compared to affinities prior to exposure to cold. If binding affinities are reduced, the amount of free hormones would increase and, consequently the likelihood of being excreted into urine and conjugated by the liver would also increase.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Effects of long-term treatment with metergoline in patients with idiopathic oligospermia

The effect of metergoline, an ergoline derivative with antiserotonin as well as dopaminergic properties, was studied in forty-five male patients with idiopathic oligospermia. Metergoline treatment (6 mg daily for 5 months) had no demonstrable effect on spermatogenesis; moreover, it did not influence the serum levels of LH, FSH, testosterone and oestradiol although it significantly reduced prolactin levels. It is concluded that, in all likelihood, serotonin plays little or no part in the pathogenesis of idiopathic oligospermia and that pharmacological reduction of normal prolactin levels has no therapeutic effect on this disease.