To study the diuretic effect of vasopressin on AqF, Viggiano et al.
21 investigated the effect of intranasally applied desmopressin, a synthetic antidiuretic hormone (1-desamino-8-D-arginine vasopressin) with a higher ratio of diuretic-to-pressor activity than natural vasopressin,
38 on AqF in patients with neurogenic diabetes insipidus lacking AVP. They observed a slightly higher aqueous humor formation rate with desmopressin. However, they also found a change in plasma osmolality with and without desmopressin and concluded, therefore, that AVP does not play a significant role in AqF regulation. Wallace et al.
16 reported that intravenously applied desmopressin caused an increase in aqueous humor formation rate in rabbits without altering the systemic blood pressure. Niederer et al.
39 studied the effect of lysine-vasopressin, cortisol, and prolactin on aqueous humor production in rabbits using a radioactive tracer. They concluded that vasopressin most likely reduced aqueous humor production by acting directly on the ciliary epithelium, as decreased outflow facility seemed unlikely, since Nagasubramanian
40 measured increased outflow facility after intracameral vasopressin injection. In contrast, Cole and Nagasubramanian
19,20 detected an increase of active ion transport by measuring transepithelial short-circuit current in in vitro preparations of the ciliary body and reported an increase in IOP after blocking endogenous vasopressin by ethanol and intravenously infusing Pitressin, a mixture of arginine-vasopressin and lysine-vasopressin. Therefore, they hypothesized that vasopressin would increase aqueous humor production. In the late 1970s, Nagasubramanian
41 stated that, at physiological levels, vasopressin can stimulate active sodium transport into the eye with the tendency to raise IOP and suggested that the hormone plays a role in maintaining homeostasis in terms of limiting diurnal variations in aqueous humor formation and IOP due to body hydration. However, in a clinical trial performed by Becker and Christensen,
12 vasopressin was applied topically and caused not only a decrease in IOP, but also a suppression of AqF by 60% ± 5%. The present study confirms the AqF-lowering effect of vasopressin and indicates that the mechanisms are dose-dependent.