Aim:
The patterns of qualitative and quantitative changes in the microvascular network in the skin of adult male white rats under of nalbuphine administration.

Material and methods:
The research employed methods such as vascular bed injection, skin section clearing, and microscopic imaging using an MBI-1 microscope. Morphometric analysis of the microcirculation vessels was conducted, and statistical processing of the results was performed using specialized software.

Results:
The nalbuphine significantly impacted the morphological state of the white rat’s skin after two weeks of administration, with the initial changes occurring in the blood vessel plexuses. In the injected skin samples, both arterioles and capillaries were dilated, with the diameter of the subpapillary arteriolar network significantly increasing to 28.62±1.07 μm (control – 22.24±0.73 μm), and the diameter of intrapapillary capillary loops expanding to 6.20±0.11 μm (control – 5.91±0.26 μm). Arterioles exhibited tortuosity. After four weeks, the loops of the vascular plexus lost their delicate, lace-like structure, with microaneurysms in arterioles and sacculations in venules becoming evident. After six weeks of opioid exposure, significant structural alterations were observed in the blood vessels of the skin. Capillaries became obliterated, with some destroyed, and this process was accompanied by hemorrhages. The density of intrapapillary capillary loops decreased significantly to 59.0±2.0 (control – 79.60±2.078), while the trophic activity index increased to 39.490±1.307 μm (control – 27.172±1.143 μm),

Conclusions:
Morphometric analysis of the morphological state of the vascular plexuses in the skin clearly illustrates the relationship between quantitative and qualitative changes in the structural organization of the microcirculation network under opioid exposure.