Sodium loading and renal prostaglandins in old rats.

1. Previous studies have shown that altered synthesis of prostaglandins (PGs) in the kidney of ageing rats contributes to impaired Na conservation during sodium deprivation. In the present study, we wished to assess whether the disturbance of prostaglandin synthesis also affects the response to sodium loading in old rats. 2. We measured the urinary excretion of thromboxane B2 (TXB2), 6-keto PGF1 alpha (6KPGF1 alpha) and PGE2 in young (3-4 months) and old (20-21 months) rats after 24, 48 and 72 h of Na loading. In a separate protocol, we measured prostanoid synthesis by isolated glomeruli, cortical homogenates, medullary and papillary slices from young and old rats in basal conditions and after 15 days of dietary Na loading. 3. Young and old rats excreted similarly the Na load. The urinary excretion (U) of TXB2 and 6KPGF1 alpha were unchanged during Na load in young rats. U6KPGF1 alpha, which was significantly higher in old rats and UTXB2 which also tended to be elevated, decreased in old rats with Na loading. Sodium loading was associated with a transient increase of UPGE2 in young, but not in old rats. 4. TXB2 synthesis was increased in all portions of the kidneys of old rats. 6KPGF1 alpha production was elevated in glomeruli and cortex and that of PGE2 in cortex. In medulla and papilla only TXB2 synthesis was enhanced. 5. Sodium loading did not significantly change prostanoid synthesis in the kidneys of young rats. In old rats, glomerular and cortical TXB2 decreased whereas medullary and papillary 6KPGF1 alpha increased.(ABSTRACT TRUNCATED AT 250 WORDS)