Background. Along with hydrogen sulfide and carbon monoxide, nitrogen monoxide (NO) has earned a reputation as a powerful vasodilator. NO is synthesized from L-arginine by a group of enzymes called NO synthases (NOS). NOS catalyzes the conversion of L-arginine into L-citrulline and NO. There are three isoforms of NOS that are often described based on their expression in tissues: 1) neuronal NOS (nNOS), 2) inducible NOS (iNOS), and 3) epithelial NOS (eNOS). NO is a vital molecule involved in a number of signaling functions in the kidney and can be released by a variety of kidney cells, including endothelial and mesangial cells as well as podocytes. Podocyte damage mediated by antibodies against podocyte antigens deposited under glomerular visceral epithelial cells is called membranous nephropathy. Cell-free cryopreserved biological agents (CfBA) have attracted our attention as potential means for the treatment of patients with membranous nephropathy, in particular, cryoextract of human placenta, cryoextract of porcine spleen and mesenchymal stem cell-conditioned medium (MSC-CM). The purpose of the study was to assess the effect of cryoextracts of placenta (CEP) and spleen (CES), as well as MSC-CM on the state of NOergic system of the kidneys of rats with autoimmune membranous nephropathy. Materials and methods. Research on the effectiveness of CfBA in autoimmune nephritis (AIN) was conducted on 42 male rats. AIN was reproduced according to the method of W.R. Heymann et al. The studied drugs were administered to rats from the day 60 of the experiment. CfBA were injected intramuscularly with an interval of 2 days (total of 5 injections) on the day 60, 62, 64, 66 and 68 of the experiment, respectively. NOS activity was evaluated by the spectrophotometric method based on the amount of oxidizable NADPH2. The content of stable NO metabolites was determined by the spectrophotometric method according to the modified Griess test. Results. It was found that the development of AIN in rats was accompanied by an imbalance of NOS activity in renal tissues. The activity of iNOS was increased statistically significantly (р < 0.001) by 83.3 %. The concentration of stable NO metabolites in the blood of rats with AIN increased statistically significantly (p = 0.008) by 68.2 %, which was 4.5 times higher than an increase in total NOS activity. A decrease in the activity of iNOS was noted against the background of using the investigated CfBA. Our study demonstrated the most pronounced increase in the activity of constitutional Ca2+-dependent NOS isoforms (nNOS on eNOS) against the background of MSC-CM administration. Conclusions. Depending on the ability to normalize iNOS hyperactivity (percentage compared to the indicators of untreated rats with AIN), it is advisable to place the studied CfBA in the following sequence: MSC-CM (54.5 %; p < 0.001) > CES (36.4 %; p = 0.008) > CEP (31.8 %; p = 0.04). According to the ability to eliminate inhibition of constitutive NOS activity in renal tissues (percentage compared to the indicators of untreated rats with AIN), it is advisable to place them in the following sequence: MSC-CM (57.9 %; p = 0.05) > CEP (42.4 %; p = 0.015) > CES (21.2 %; p = 0.02). By the ability to normalize the content of stable NO metabolites in the blood (percentage compared to the indicators of untreated rats with AIN), it is advisable to place the studied CfBA in the following sequence: MSC-CM (41.3 %; p = 0.018) > CES (25.2 %; p = 0.1) > CEP (4.9 %; p = 0.7).
