Effects of intracerebroventricular administration of adrenoceptor-agonists on the regulation of renal water and electrolytes handling through endocrine, renal and hemodynamic function.

In order to assess the roles of central adrenoceptors in the release of atrial natriuretic peptide (ANP), aldosterone (ALD), vasopressin (AVP) and renin as well as in the regulation of renal and cardiovascular functions, either norepinephrine (NE; 0.07 microgram/kg/min), guanabenz (GB; alpha 2-agonist; 0.4 microgram/kg/min), methoxamine (MET; alpha 1-agonist; 0.4 microgram/kg/min), or isoproterenol (ISO; beta-agonist; 0.07 microgram/kg/min), dissolved in the artificial cerebrospinal fluid (ACSF), was intracerebroventricularly (i.c.v.) administered at a rate of 10 microliters/min for 30 min in anesthetized dogs. In the control study, the drugs were omitted. NE decreased mean arterial pressure (MAP), urinary osmolality (Uosm) and plasma ALD and AVP concentrations, and increased urine flow (UF). GB increased UF and urinary K excretion without any changes in urinary Na excretion, but decreased plasma ALD and AVP, heart rate, and Uosm without changes in MAP. ISO decreased MAP and plasma ALD, and increased Na and K output, renal plasma flow and UF with decreased Uosm. MET and ACSF failed to affect any of these parameters. Glomerular filtration rate, plasma ANP concentration and renin activity did not change in any of the studies. The present results suggest that central alpha 2- and beta-adrenoceptors may attenuate ALD and/or AVP release without changes in ANP and renin release, and decrease blood pressure, thereby causing a diuresis and natriuresis.