Is Clonidine-Induced Diuresis Mediated by Atrial Natriuretic Factor?*

The effect of intracerebroventricular (ICV) administration of clonidine on urine output, urinary sodium excretion, urinary cGMP, and plasma immunoreactive atrial natriuretic factor (IR-ANF) was studied in conscious, normally hydrated rats. Clonidine treatment evoked a significant dosedependent increase in urine output. A 20-fold elevation was noted after the highest clonidine dose (2 μg/rat). The observed diuresis was accompanied by enhanced sodium excretion, which with the highest dose (2 μg) of clonidine increased from 1.6 ± 0.36 to 39.4 ± 10.5 meq/liter (P < 0.001). Plasma IR-ANF rose from 30.7 ± 8.8 to 113.3 ± 32.3 pg/ml plasma 5 min after the 0.5 lig clonidine dose (P < 0.05), and urinary cGMP excretion was augmented from 8.49 ± 4.29 to 27.7 ± 5.0 pmol/min 1 h after 0.5 ng clonidine (P < 0.05). Pretreatment with peripherally administered anti-ANF serum abolished the diuretic effect of intracerebroventricularly administered clonidine; urine output decreased from 1.49 ± 0.41 to 0.42 ± 0.21 ml/h. The ur...