Abstract
In order to determine whether endogenous dopaminergic tone has any role in the diurnal variation in TSH secretion, the 24-h secretory pattern of TSH and the TSH response to a dopamine antagonist, metoclopramide (MCP), were evaluated in normal women (n=4) and in hyperprolactinemic-amenorrheic women with pituitary microadenoma (n=6). TSH concentrations expressed as percent deviation from the 24-h mean significantly differed with respect to time of day in normal women and hyperprolactinemic women. They were significantly higher during the night (2000-0700h) than during the daytime (0800-1900h). Whereas MCP administration induced no significant changes in serum TSH levels in normal women, it significantly increased serum TSH levels in hyperprolactinemic women. Thus, the diurnal variation in TSH secretion was demonstrated in hyperprolactinemic women with pituitary microadenoma in the face of an increased dopaminergic inhibition of TSH secretion. The present study did not provide evidence that the diurnal pattern of TSH secretion is related to the endogenous dopaminergic tone.
