Effect of an Oral Water Load on Serum TSH in Normal Subjects, and on TSH and Prolactin Responses to Thyrotropin-Releasing Hormone (TRH) in Patients with Primary Hypothyroidism

Reports of suppression of plasma prolactin (PRL) in humans by water loading led us to examine the effect of a 20 cc/kg water load on serum TSH in 21 normal volunteers. In addition, the effects of a water load on basal and TRH-stimulated TSH and PRL levels were evaluated in seven patients with primary hypothyroidism. The water load had no effect on pasal serum TSH levels in either normal or hypothyroid subjects, and did not alter the TSH response to TRH in hypothyroid subjects. Basal or TRH-stimulated plasma PRL was also unaffected by water loading in the hypothyrpid subjects. These data suggest that a water load of 20 cc/kg does not significantly affect TSH release by the anterior pituitary, and also provide further evidence that water loading does not consistently suppress PRL secretion.