Colloid osmotic pressure in young analbuminemic rats

Colloid osmotic pressure (COP) was measured in plasma and interstitial fluid (subcutaneous wick) from 8 to 75 days of age in Nagase analbuminemic rats (NAR) and control Sprague-Dawley rats (SDR). In all animals plasma COP (~10 mmHg at 8 days of age) increased during growth. In the female NAR the rise in nonalbumin proteins was so large that at 75 days the plasma COP was not lower than in the SDR; whereas in male NAR a difference of ~4 mmHg remained. Interstitial COP increased with aging in the SDR, but not in the NAR. This resulted in equal transcapillary COP gradients in 75-day-old male and female SDR and male NAR (~11-12 mmHg) but a somewhat larger gradient in the female NAR (~14 mmHg). Blood pressure and plasma volume were not low in the NAR. Extracellular fluid volume (as a percentage of body weight) was similar in all groups and decreased with age. Clearances of ⁵¹Cr-labeled EDTA and ¹²⁵I-labeled hippuric acid were decreased in young (45 day) NAR vs. young SDR, but not at 75 days of age. In conclusion, NAR are able to maintain a normal transcapillary COP gradient, and do not display signs of abnormal volume regulation during early development.