Judging by the amount we spend on cosmetics and anti-aging creams, keeping our skins in tip-top condition is a major concern for some people. Which shouldn't really be a surprise. We need to keep our tightly sealed epidermal barrier in good condition to protect us from damage and disease. Birds, on the other hand, take a much more flexible approach to their skin. Relative to our own pampered hides, bird skins are very plastic and can be modified as climatic conditions change to produce impermeable barriers against cold snaps and permeable barriers when the temperatures rise. How bird skins function as barriers and change in response to climate variation fascinates Liisa Peltonen. Knowing that changes in the skin's barrier properties appear to be correlated with high blood flow, Peltonen and her colleague, Ahti Pyörnilä, decided that they needed to develop a technique for altering skin blood flow if they were to discover the mechanisms that drive plasticity. But it must be non-invasive - even the tiniest pinprick sends blood rushing to the skin - so injecting vascular regulators wasn't an option. It was only when Peltonen picked up a paper about a novel treatment for human patients with impaired circulation in their fingers that she stumbled across a non-invasive alternative that might work for birds: nitric oxide gel(p. 2611).

Nitric oxide is one of those wonderful compounds that seems to regulate almost everything, from our central nervous systems through to vascular tone. But at the time that it occurred to the team to test the effects of nitric oxide on birds, it wasn't clear whether their vascular systems would respond to the gas. And Peltonen and Pyörnilä faced another challenge; how to administer nitric oxide in the least invasive way possible. Fortunately,the medical team had clearly described how they mixed two gels containing sodium nitrite and ascorbic acid to produce the gas and relieve their patients' painful symptoms. Sure enough, when Peltonen mixed samples of KY gel laced with the two compounds she produced tell tail bubbles of nitric oxide. But would the birds' skins respond as well as the human's fingers?

The team decided to test the gel's effects on birds with cold-acclimated impermeable skins, and birds with permeable skins from temperate conditions. Applying the gaseous gel to skin on the bird's backs and chests for 1 min, the team measured the blood flow and found that while blood rushed to the nitric oxide treated skin on the birds' chests, the skin on their backs was relatively unaffected, probably because they lack mechanisms to respond to the gas. And comparing the effects of nitric oxide on both groups, the team found that cold-acclimated birds with a well developed skin barrier registered the highest blood flow rates.

Having discovered a completely non-invasive way of increasing blood flow to localised areas of skin, Peltonen and Pyörnilä are keen to see whether altered blood flow can affect the skin's barrier properties, and track down the mechanisms that drive this remarkable remodelling.

Peltonen, L. M. and Pyörnilä, A.(
). Local action of exogenous nitric oxide (NO) on the skin blood flow of rock pigeons (Columba livia) is affected by acclimation and skin site.
J. Exp. Biol.