Urogenital System

The male and female rat reproductive organs are basi­cally similar to those of the mouse. Adult female rats develop cyclic uterine infiltrates of eosinophils in response to estrogen, which can be misconstrued as abnormal. During proestrus, the uterus is filled with clear fluid (Fig. 2.3), which is normal. Rats have 3 pairs of pectoral and 3 pairs of inguinal mammary glands. As in the mouse, mammary tissue extends throughout much of the subcutis of the sides and necks of rats. Proteinuria is normal in rats, due to tubular produc­tion of alpha globulins. Proteinuria due to loss of serum proteins is not normal (see “Chronic Progressive Nephropathy”).