Differing effects of prolactin on the water content of individual tissues in the rabbit pup at 72 h of age.

We treated neonatal rabbits from birth with exogenous prolactin or the prolactin secretagogue fluphenazine. We compared the hydration at 72 h of skeletal muscle, skin, liver, and brain to that of untreated controls. Treatment did not change the water content of liver. It increased the water content of skeletal muscle, skin, and brain. However, the response to treatment differed among these tissues. In skin and skeletal muscle, the effect of treatment was most apparent in animals whose postnatal weight gain was relatively large. In contrast, treatment increased brain water content in all animals regardless of weight gain. We conclude that much of the early postnatal decrease in skin and skeletal muscle water is due to mobilization of the neonatal tissue water reservoir, and that prolactin appears to regulate that process. Changes in brain water between birth and 72 h of age appear to result from loss of reservoir water and possibly of cerebrospinal fluid offset in part by water accretion due to tissue growth.