Aim: 

The skin circulation is very important for newborn rats, because they do not have a hair coat. The fraction of cardiac output going to the skin decreases during development from 18% at the age of 9 days to 7% at the age of 64 days (Stulkova 1977). However, the mechanisms providing this difference are still not well understood. We hypothesized that changes of endothelial function in skin feed arteries may be responsible for the relative decline of cutaneous blood flow during development.

Methods: 

We studied isometric contraction of saphenous arteries from young (1–2-week-old) and adult (2–3 months) rats. The saphenous artery is a muscular-type artery supplying mainly the cutaneous vascular bed. The responses to methoxamine (MX, 1adrenoceptor agonist) and U46619 (thromboxane A2 analogue) were studied. For comparison of mRNA expression we used qPCR.

Results: 

The contractile responses of young arteries were prominently weaker compared to adult. However, removal of the endothelium as well as inhibition of NO-synthase using L-NNA completely eliminated this difference. Moreover, L-NNA caused an increase of basal tone of the arteries in young, but not in adult animals, indicating spontaneous NO release from the endothelium. Further, we found a 2-fold higher expression of eNOS in young saphenous arteries compared to adult. Importantly, smooth muscle sensitivity to NO-donors did not differ between the two groups.

Conclusion: 

The endothelium of saphenous arteries in young rats spontaneously produces NO. NO decreases the resistance of feed arteries and thereby increases blood flow in the skin. In adult saphenous arteries this mechanism is not present.

References: 

(1) Stulkova, B. 1977. Biol. Neonate 32, 119–124.