Effects of prolonged dopamine infusion on anterior pituitary function in normal males.

The influence of a 48-h dopamine (DA) infusion (5-7.5 micrograms/kg.min) on serum PRL, TSH, LH, FSH, and GH values was determined in six normal adult males. Sustained suppression of serum PRL to 78% (P less than 0.01) below baseline levels during DA was followed by an acute rebound of 319% (P less than 0.01) 4 h after stopping DA. Similarly, TSH decreased by 44% during DA but had a more gradual and sustained rebound of 41% (P less than 0.01) over a 36-h period. While both serum LH and FSH initially dropped by 25% (P less than 0.001) and 10% (P less than 0.05), a gradual escape occurred during the DA infusion, followed by rebounds of 23% (P less than 0.01), respectively. A brief rise in serum GH levels occurred with DA treatment, followed by a return to baseline. Subsequently, oscillatory spikes continued throughout the DA infusion but were significantly decreased (P less than 0.01) after stopping DA. Thus, DA administration initially produced a reduction in serum PRL, TSH, LH and PSH while stimulating GH release. PRL and TSH showed a sustained inhibition, whereas LH and FSH progressively escaped after a lesser degree of suppression by DA. The rebound after DA withdrawal probably reflected the discharge of hormone synthesized and stored during DA administration. The inverse relationship between the nadir of inhibition and the peak rebound values (r = 0.92) supports this hypothesis. Clearly, the patterns of serum LH, FSH, and GH values differ with acute and chronic DA administration. These differences are of potential importance in interpreting dopaminergic influences on anterior pituitary function.