Effect of Oligopeptides-Homologues of the Fragment of ACTH15-18 on Morphogenetic Markers of Stress in the Adrenal Glands on the Model of Acute Cold Injury in Rats.

Objectives: Aim of the current study was to evaluate the stress-protective effect of oligopeptides-homologues of the adrenocorticotropic hormone (ACTH) fragment 15-18 on morphogenetic signs of stress reaction of the adrenal glands under acute cold exposure (CE) in rats.

Materials and methods: The acute cold stress was reproduced by placing random-bred male rats in a freezer at a temperature of -18°C for 2 hours. The peptides-homologous of ACTH_15-18 acetyl-(D-Lys)-Lys-Arg-Arg-amide (KK-1) and acetyl-(D-Lys)-Lys-(D-Arg)-Arg-amide (KK-5) and the reference medicine (Sema) were administered intranasally in a dose of 20 mg/kg 30 minutes before and after CE. Rectal temperature was measured before and 10 min after CE. Zona glomeruloza, zona fasciculata, zona reticularis, and the area of cells and nuclei of adrenocorticocytes of the zona fasciculata were measured.

Results: KK-1 significantly prevented structural changes in the adrenal cortex and medulla and stabilized the secretory activity of glucocorticoid-producing cells. However, the congestion of the capillaries of the zona fasciculata and zona reticularis remained in some locations. Zona fasciculata cells had a marked tendency to decrease, and the area of nuclei significantly decreased (p<0.05) recovering the width to control animals' markers. KK-5 had a more marked recovery of the adrenal glands (a greater saturation of cytoplasm of adrenocorticocytes of zona glomerulosa and zona fasciculata). The number of chromaffin cells at rest was increased in the adrenal medulla. KK-5 statistically significantly normalized both the area of cells (p<0.05) and the area of nuclei (p<0.05) of the zona fasciculata, unlike KK-1, which reliably restored only the marker of the nuclei area. Some morphometric parameters of acute stress hypertrophy remained in the adrenal glands of rats receiving Sema.

Conclusion: KK-1 and KK-5 prevented the manifestation of acute stress reactions in the adrenal cortex of rats. KK-5 had a more marked stress-protective effect compared with the peptide KK-1. Both study substances exceeded the reference medicine Sema. KK-5 is a promising stres-sprotector and frigoprotector.