Objective: To explain a role of nitric oxide synthesis in physiological regulation of hypothalamic-pituitary hormonal axis. Design: Review article. Settings: Department of Pathological Physiology, 1st Faculty of Medicine, Charles University in Prague. Conclusion: Both inducible and constitutive nitric oxide synthase is expressed in hypothalamic nuclei (mainly in nucleus supraopticus and paraventricularis) and in adenohypophysis, too. Its product, nitric oxide, is involved in both expression and release control of hormones as corticotropin-releasing hormone, gonadotropin-releasing hormone, vasopressin, and oxytocin. The role of NO in prolactin, luteinizing and growth hormone regulation is less clear. On a peripheral level, NO can both mediate or antagonize some hormonal effects, e. g. organ specific vasodilatory effect of vasopressin.

        Key words: cyclic guanosine monophosphate, hypothalamus, nitric oxide, nitric oxide synthase, pituitary gland.