Body composition and renal adaptation in the newborn rat

Mouse pup urine as an infant signal

Drops of urine from donors of different ages and sexes were applied to the anogenital regions of 19-day fetuses, killed by freezing, that ordinarily are weak in stimulating parental care. These fetuses were then presented to virgin, naive albino mice (Mus musculus). In Experiment 1, fetuses treated with urine of 6-day-old pups were more stimulating than fetuses treated with water. Differences in contact, picking-up, retrieval, licking and self grooming were significant. The sex of the donor revealed no effect. In Experiment 2, urine from 10-day-old pups was found to be more effective than urine from 4-day-old pups, with different effects on contact and retrieval. Urine from pups was also more effective than urine from adults, because of different effects on contact, picking-up, retrieval, licking and nest building. The effects of urine from adult virgin females differed less from those of pup urine than did the effects of urine from adult males. Compared with the latter the adult female urine had different effects on picking-up, licking and cannibalism. Speculations are made about an infant factor that might be still active in the urine of adult females.

Developmental changes in the rat atriopeptin hormonal system

We undertook a study of fetal synthesis, storage, and release of atriopeptin (AP). Plasma levels of both atriopeptin immunoreactivity (APir) and the NH2-terminal fragment of the prohormone immunoreactivity (NTFir) were very high in the fetus (4 and 20 times the maternal plasma, respectively). However, the atrial content of the AP was low, but surprisingly, ventricular content of AP was quite high (relative to the adult) in the fetus and fell postnatally. Atrial AP messenger RNA (mRNA) increased with postnatal age, whereas ventricular mRNA was extremely high in the fetus and fell rapidly after birth. High fetal plasma peptide levels may derive from the mother since infusion of exogenous atriopeptin 24 into the mother resulted in parallel increases in fetal and maternal peptide levels. Fetal plasma APir and NTFir levels partially reflect the markedly reduced total renal metabolic capacity compared with that of the adult. Plasma levels fell progressively after birth; whereas neonatal atrial content rose substantially. Plasma AP and NTF were simultaneously elevated in both the maternal and fetal circulation after vasopressin injection of the mother. The fetus can also respond to exogenous stimuli (vasopressin or indomethacin--presumably via ductal closure) and promptly release substantial amounts of peptide into its circulation. Thus, it appears that the AP hormonal system is functional during fetal life and responds avidly to increases in intracardiac pressure as does the mature animal.

Postnatal growth and fatty acid synthesis in overgrown rat pups induced by fetal hyperinsulinemia

Fetal hyperinsulinemia in the rat results in increased body weight, lipid content, and enhanced lipogenesis in liver and carcass. The purpose of our study was to determine whether the macrosomia and enhancement of fatty acid (FA) synthesis and/or content persisted postnatally in this animal model. Fetal hyperinsulinemia was produced in Sprague-Dawley rats by injecting fetuses with 2 units of insulin at 20.5 days of gestation. Alternate pups in the same litter were injected with saline. Pups were delivered surgically at 22.5 days of gestation, were weighed daily and sacrificed on day 15. FA content and synthesis rates of liver and skeletal muscle were measured. We found: (1) At birth, insulin-treated pups were 12% heavier than saline littermates, (5.88 +/- 0.14 g v 5.26 +/- 0.14 g, P less than .01); and (2) The enhanced growth associated with prenatal insulin treatment persisted during the suckling period, ie, compared with saline-treated controls, insulin pups were 15.7% heavier at 15 days of age (P less than .01); growth velocity of insulin pups, beginning on day 3, significantly exceeded that of control pups (P less than .05). FA contents of liver and muscle in insulin pups, (62.6 +/- 5.7 mumol/g and 62.7 +/- 13.2 mumol/g) were significantly greater (P less than .05) than in saline littermates (45.1 +/- 5.6 mumol/g and 30.2 +/- 4.7 mumol/g, respectively). We conclude that.(ABSTRACT TRUNCATED AT 250 WORDS)