Anzai N, Kawahara K
Department of Physiology, Kitasato University School of Medicine, Sagamihara, 228-8555, Japan.
Jpn J Physiol. 1998 Jun;48(3):181-7. doi: 10.2170/jjphysiol.48.181.
The present study was designed to investigate whether the limited capacity for concentrating urine in neonatal rats is associated with an immature ability to regulate serum osmolality. During milk deprivation, the percent of reduction in body weight per 10 h (mean +/- SE) was 4.3 +/- 0.2, 3.7 +/- 0.1, 4.8 +/- 0.2, and 6.0 +/- 0.1% in 4-, 7-, 10-, and 14-d-old rats, respectively (n = 23-24, each age). The osmolality of urine increased to 718 +/- 12 (4 d), 741 +/- 28 (7 d), 792 +/- 20 (10 d), and 1,203 +/- 41 mosmol/kg H2O (14 d). Free-water absorption (TcH2O) promptly increased after deprivation of milk: It significantly increased from 2.3 +/- 0.3 (0-4 h) to 3.4 +/- 0.1 (4-7 h) (4 d), from 3.1 +/- 0.3 to 4.1 +/- 0.3 (7 d), from 3. 6 +/- 0.4 to 5.2 +/- 0.3 (10 d), and from 5.0 +/- 0.4 to 7.9 +/- 0.7 microliter/min/100 g (14 d). The raised values were maintained at the later period of dehydration. Thus serum osmolality was unchanged throughout dehydration: 287 +/- 1.0 (7 d) and 292 +/- 0.9 mosmol/kg H2O (14 d). On the other hand, the level of serum sodium concentration slightly but significantly increased (r = 0.61) when the body weight reduction was higher than 5% of the control (14-d-old rats). These results indicate that neonatal rats of 4-14 d control their serum osmolality by reabsorbing free water in the kidney during the 10 or 12 h of milk deprivation.
本研究旨在探讨新生大鼠浓缩尿液能力有限是否与调节血清渗透压的能力不成熟有关。在剥夺乳汁期间，4日龄、7日龄、10日龄和14日龄大鼠每10小时体重减轻的百分比（平均值±标准误）分别为4.3±0.2%、3.7±0.1%、4.8±0.2%和6.0±0.1%（各年龄组n = 23 - 24）。尿液渗透压分别升至718±12（4日龄）、741±28（7日龄）、792±20（10日龄）和1203±41 mosmol/kg H₂O（14日龄）。剥夺乳汁后，自由水重吸收（TcH₂O）迅速增加：4日龄时从2.3±0.3（0 - 4小时）显著增加至3.4±0.1（4 - 7小时），7日龄时从3.1±0.3增加至4.1±0.3，10日龄时从3.6±0.4增加至5.2±0.3，14日龄时从5.0±0.4增加至7.9±0.7微升/分钟/100克。升高的值在脱水后期维持不变。因此，在整个脱水过程中血清渗透压保持不变：7日龄时为287±1.0 mosmol/kg H₂O，14日龄时为292±0.9 mosmol/kg H₂O。另一方面，当体重减轻高于对照组（14日龄大鼠）的5%时，血清钠浓度水平略有但显著升高（r = 0.61）。这些结果表明，4 - 14日龄的新生大鼠在剥夺乳汁10或12小时期间，通过在肾脏中重吸收自由水来控制其血清渗透压。
