Chronic hyperprolactinemia reduces peripheral beta-adrenergic responsiveness in male rats

The MtTW15 prolactin (PRL) secreting adenoma elevated serum PRL concentrations over controls within 5 weeks after tissue implantation. This treatment resulted in a significant reduction of peripheral beta-adrenergic responsiveness as assessed by three different parameters. Isoproterenol-induced thirst was significantly attenuated in the MtTW15 rats. The decrease in the thirst response was proportional to the increase in serum PRL. Unanesthetized heart rates of both groups were not significantly different before isoproterenol was administered. However, following administration of the beta-adrenergic agonist the heart rate response in rats with elevated PRL was significantly attenuated when compared to the controls. Elevation of serum PRL virtually abolished the elevation of tail skin temperature response associated with administration of isoproterenol. Collectively, these results suggest hyperprolactinemia reduces peripheral beta-adrenergic responsiveness; however the mechanism for this reduced response remains to be elucidated.