The embryonic metabolism of nitric oxide and its interrelation with postembryonic development in chicken (Gallus gallus domesticus L.) and quails (Coturnix coturnix L.)

The embryonic development is accompanied by the intense synthesis of nitric oxide (NO). Many processes of the embryogenesis (e.g. tissue differentiation, apoptosis) were found to be NO-dependent. However, due to the difficulties related to the control of NO metabolites in living tissues the physiological effects of NO have been studied by the indirect methods exclusively, via the effects of the inhibitors of NO synthesis or the effects of NO donor compounds and arginine as the precursor in the NO biosynthesis. But this does not allow us to establish the mechanism of the relationship between the observed effect and the metabolism of nitric oxide. Myogenesis is also considered NO-dependent since arginine, NO-synthase inhibitors, and NO donors were reported to affect the development of muscles. However, these effects are quite contradictory. The lack of data on the relationship between nitric oxide metabolism and these effects does not allow us to suggest in detail the role of NO in myogenesis and the mechanism of its influence on muscle development. And the lack of understanding of this mechanism does not allow the use of nitric oxide to correct the animal development. In this study we are presenting a pioneer view on the interrelationships of embryonic NO metabolism with the features of the postembryonic body development in different poultry species determined with the use of highly sensitive and highly specific enzymatic sensor for determination of the NO metabolites. The study was aimed at the determination of interrelationships between the intensities of embryonic NO synthesis and its oxidation and embryonic and postembryonic body growth in poultry and at the evaluation of possible application of these interrelationships for the enhancement of meat productivity. The experiments were performed in 2017-2019 on different breeds of chickens and quails. It was found that the intensity of embryonic NO synthesis is similar within any given poultry species. In most cases no significant differences between the breeds (p > 0,05). This was determined by the total concentration of all NO metabolites in the embryo. However, the intensity of embryonic NO oxidation to nitrate can vary drastically. Differences between embryos of egg and meat breeds, lines and crosses on this indicator reach several orders of magnitude. In the embryos of egg breeds, there is mainly an accumulation of nitric oxide in the so-called donor compounds. By the end of embryogenesis, their concentration reaches several hundred of micromoles. In meat breed embryos NO is mainly oxidized to nitrate. The variance of the intensity of embryonic NO oxidation within a given breed does not exceed 10-15 %. This oxidation was found to occur predominantly in the embryonic muscle tissues. The intensity of NO oxidation is similar for endogenous (synthesized by embryos) and exogenous (injected in ovo) NO donors. The injections of inhibitors of NO synthesis decreased the embryonic concentration of total NO metabolites while the NO donors to nitrate ratio was not affected. These effects suggest that the intensity of NO oxidation to nitrate is directly correlated with certain features of embryonic tissues. Therefore, it can be considered as a biochemical marker of these features. It correlates with meat productivity and is an indicator inherent to a given to a given to a given breed. It is not sex-linked and does not depend on the layer age, nutrition, etc. Thus, it can be regarded as a highly sensitive and highly specific genetically preconditioned marker. The 2-fold increase or decrease of embryonic concentration of oxidized NO (by the intraembryonic injections of NO donors or inhibitors of NO synthesis, respectively) did not significantly affect the postnatal body growth rate. The exact mechanism of the embryonic NO oxidation and the interrelationships of the latter with the development of muscular tissues are still to be elucidated.