The perinatal rat: body weight, hematocrit and regional changes in heart weight and lactate dehydrogenase isozyme composition and activity.

Body weight (BW), hematocrit (Hct), heart weight (HW) and cardiac lactate dehydrogenase (LDH) activity and isozyme pattern were studied in the perinatal rat. BW increased linearly, from 5 days before birth till 10 days after birth, while Hct increased from 30 to 34% within 1 day of birth. HW increased in step with BW.