Anderson R R
Department of Animal Sciences, University of Missouri, Columbia 65211.
J Dairy Sci. 1992 Jan;75(1):105-10. doi: 10.3168/jds.S0022-0302(92)77744-3.
Milk samples were obtained from lactating albino guinea pigs after 4 to 6 h of separation from their offspring. The samples were collected in 5-ml glass vials and capped immediately. They were transported rapidly to a pH-gas analyzer for measurements of pH, bicarbonate, base excess, and partial pressure of CO2. Eight guinea pigs were sampled daily for 20 d for a total of 160 observations. Analysis of variance indicated animal and day differences. Regression analyses over days revealed equations of best fit to be quadratic, although stepwise trends were observed in the data as well. The quadratic model for pH was Y(pH) = 6.996 - .057X + .002X2, where X was day of lactation (R2 = .54). The model for bicarbonate was Y (-HCO3 in milliequivalents per liter) = 8.896 - .659X + .0202X2 (R2 = .60). For base excess, the model was Y (in milliequivalents per liter) = -22.65 - 1.99X + .069X2 (R2 = .58). The model for partial pressure of CO2 was Y (millimeters of Hg) = 38.63 + 1.06X - .080X2 (R2 = .33). Decreases in pH and bicarbonate were parallel to changes in mammary epithelial cells of guinea pigs in which degeneration of mechanisms responsible for two important ingredients relating to milk volume occur. These have been identified previously as reductions in lactose and potassium. Synthesis of the enzyme carbonic anhydrase with its resultant bicarbonate production may be related in some way to these components of milk secretion.
从与幼崽分离4至6小时后的泌乳白化豚鼠身上采集牛奶样本。样本收集在5毫升的玻璃瓶中，并立即加盖。然后迅速将它们运送到pH气体分析仪，以测量pH值、碳酸氢盐、碱剩余和二氧化碳分压。每天对8只豚鼠进行采样，持续20天，共获得160个观察结果。方差分析表明存在动物和天数差异。对天数进行的回归分析显示，最佳拟合方程为二次方程，不过数据中也观察到了逐步变化趋势。pH值的二次模型为Y(pH) = 6.996 - .057X + .002X²，其中X为泌乳天数(R² = .54)。碳酸氢盐的模型为Y（每升毫当量的 - HCO₃） = 8.896 - .659X + .0202X² (R² = .60)。对于碱剩余，模型为Y（每升毫当量） = -22.65 - 1.99X + .069X² (R² = .58)。二氧化碳分压的模型为Y（毫米汞柱） = 38.63 + 1.06X - .080X² (R² = .33)。pH值和碳酸氢盐的降低与豚鼠乳腺上皮细胞的变化平行，在这些细胞中，与奶量相关的两种重要成分的生成机制发生退化。这些成分先前已被确定为乳糖和钾的减少。碳酸酐酶的合成及其产生的碳酸氢盐可能在某种程度上与乳汁分泌的这些成分有关。
