Dopaminergic-opioidergic interaction is reflected by changes in pituitary hormone secretion in patients with...

In a randomized, double-blind crossover study 13 untreated patients with mild essential hypertension were exposed to submaximal bicycle exercise. Sixty minutes before ergometry 10 mg metoclopramide or placebo, and 10 min before exercise 0.4 mg naloxone or placebo, were given intravenously. Plasma adrenocorticotrophic hormone, beta-endorphin and cortisol levels increased significantly after ergometry, whether performed after placebo, naloxone, metoclopramide or metoclopramide + naloxone treatment. However, only naloxone administration potentiated plasma adrenocorticotrophic hormone, beta-endorphin and cortisol responses to workload. Plasma levels of adrenocorticotrophic hormone, beta-endorphin and cortisol were 45 +/- 14 pg/ml, 6.2 +/- 1.2 pmol/l and 141 +/- ng/ml, respectively, after ergometry, when performed after placebo, but these values were increased to 61 +/- 10 pg/ml, 11.4 +/- 2.8 pmol/l and 207 +/- 22 ng/ml, respectively, after naloxone treatment. This naloxone-induced potentiation of hormonal release was blocked by metoclopramide pretreatment, suggesting a close interaction between dopaminergic and opioidergic mechanisms, regulating hormonal responses to physical exercise.