Ott's protein osmotic pressure of serum and interstitial fluid in chickens (Gallus gallus): effect of age and gender.

Protein, or colloid, osmotic pressure (COP) is of sufficient magnitude to exert a powerful effect on Starling forces across the capillary wall. Although avian skin lacks active mechanisms for fluid transmission, such as sweating, it is now hypothesized that passive oncotic forces may regulate fluid flow and distribution in the skin and related phenomena. In this study, serum protein profiles, as well as COP in serum (COP(s)) and in suction blister fluid (COP(sbf)), were determined in juvenile, young and adult female and male chickens. For assessing COP, the Ott-Ahlqvist equation was applied. This equation can formulate the effects of multiple serum proteins on COP, according to their molecular mass. The COP values determined in chickens were lower than those previously found in mammals. COP(s) increased with age in males, and was higher in adult males than in adult females. In contrast, COP(sbf) decreased with age in females, although it was better preserved in adult males. The age-dependent decrease in COP was associated with a parallel decrease in the concentration of α(1)-globulin and albumin, and a positive correlation between packed cell volume (PCV) and COP was found. It is concluded that ageing affects Ott's COP around the vessel wall, and that an oncotic mechanism preserves plasma volume. The preservation of COP(sbf) in males suggests better maintenance of the interstitial ground substance. Females seem to lose more of a tissue's COP(s) counteracting force than males, probably as a result of gender-specific changes in the composition of the interstitial matrix. Further studies are required to elucidate the structure and function of avian lymphatics and their role in skin rheology.