Ovine AQP1: cDNA cloning, ontogeny, and control of renal gene expression

The cDNA for the ovine aquaporin 1 (AQP1) was obtained and found to be 97%, 88%, and 85%, respectively, homologous to the bovine, human, and rat AQP1 cDNA. The level of total kidney mRNA expressed as a ratio to glyceraldehyde-3-phosphate dehydrogenase increased sevenfold from 60 days to 140 days of gestation (term=150 days) and reached adult values by 6 weeks after birth. Treatment of pregnant ewes (and their fetuses) at 64 and 74 days of gestation with dexamethasone (0.76 mg/h for 48 h) resulted in a small but statistically significant increase in AQP1 mRNA only in the 74-day fetuses. By immunohistochemistry, it was shown that the increase in AQP1 mRNA with dexamethasone resulted largely from an increase in maturity of the inner zone of the fetal renal cortex (i.e., more tubules) as well as stronger expression of AQP1 in proximal tubules and thin descending limbs of loops of Henle. A similar effect occurred in fetuses infused for 3 days with angiotensin I (6.7 microg/h) in the last third of gestation.