1. Current evidence suggests that the antidiuretic hormone (ADH) and changes in sodium balance influence renal prostaglandins (PGs). To separate these two mechanisms, the effect of sodium loading on the urinary excretion of PGE2 and PGF was studied in female Brattleboro rats with diabetes insipidus (DIHO) and compared with that in female, age matched, heterozygous Long Evans controls (LEHE).

2. Ten DIHO and ten LEHE rats had a normal sodium intake. In ten DIHO rats a 0.16% NaCl solution was supplied instead of drinking water for either 8 days (n = 5) or 14 days (n = 5). In two groups of LEHE rats, sodium loading was obtained with a 0.80% NaCl solution for the same study periods. Urine PGs were measured by radioimmunoassay in three 24 h urine collections for each rat.

3. Urine PGs were significantly increased in the 8 day loaded but not in the 14 day loaded LEHE rats. In DIHO rats, a non-significant increase in both PGE2 and PGF was present after 8 days of sodium loading, while PGE2 and the E/F ratio were decreased after 14 days of salt loading.

4. The findings suggest that the natriuresis induced by sodium loading in the rat may be mediated in part by increased production of PGs. In addition, it seems that ADH plays a role in this response.

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