It has been established that nitric oxide (NO) is a
universal mediator, mediating smooth muscle tone
and participating in tissue differentiation processes,
apoptosis, and immune response [1]. The lactation
process is also accompanied by intense generation of
nitric oxide by the enzyme NO synthase contained in
mammary gland tissues [2]. Nitric oxide is a short
lived compound, rapidly oxidizing to a number of
nitro and nitroso compounds. Nitrate and nitrite are
the end products of its oxidation in aqueous solutions
[1]. Milk, according to the data of various investiga
tors, in health can contain tens and hundreds of
micromoles of nitrate as well as several micromoles of
nitrite [3–5]. Milk also contains Snitrosothiols
(RSNO), which are also metabolites of shortlived
NO and are regarded as its physiological depot [4]. In
connection with this, a number of theoretical and
practical problems arise. First, how does the presence
in milk of NO metabolites, especially nitrite, and its
safety as a food product combine? It is known that
milk contains lactoperoxidase, effectively oxidizing
nitrite to toxic nitrogen dioxide [4]. The toxicity of
nitrate is due to its capacity for reduction to nitrite by
bacterial enzymes and xanthine oxidase [3]. Second, is
there a interrelation between the state of the mammary
gland and composition of nitro and nitroso com
pounds of milk? It should be noted that nitrite can be
produced also by leukocytes [3]. Third, what is the
physiological role of the presence in milk of physiolog
ical NO donors, primarily Snitrosothiols?