The recent studies have shown that noradrenalin, the principal endogenous alpha-adrenergic agent, inhibits the antidiuretic action of antidiuretic hormone in human subjects and animals. These reports demonstrated that the infusion of noradrenalin into man and animals increased urine volume and free water clearance without significant changes of renal plasma flow, glomerular filtration rate and sodium excretion.
These findings indicate that noradrenalin could inhibit the antidiuretic effect of vasopressin without changes of renal hemodynamics and this inhibition was due to a direct effect of noradrenalin at the renal tubular level. The beta-adrenergic stimulating drug, isoproterenol, is known to cause antidiuresis which is indistinguishable from that induced by vasopressin.
It is also known that propranolol, beta-adrenergic blocking agent, abolishes isoproterenol induced antidiuretic effect, but not that of vasopressin.
To clarify the mechanism by which adrenergic agents alter water excretion and the action of antidiuretic hormone, water was infused with combination of these drugs and its blocking agent into unanesthetized rabbit.
Twenty rabbits were infused with 2.5% dextrose solution until water diuresis was maintained, and then simultaneous administration of pitressin (20 pU/kg/min), pitressin (20 pU/kg/min) plus noradrenalin (0. 5 pg/kg/min), pitressin (20 pU/kg/min) plus noradrenalin (0. 5pg/kg/min) plus inderal (3pg/kg/min) were performed for 80 minutes intervals respectively.
During experiments urine volume, inulin clearance, osmolar clearance, free water clearance and sodium excretion were measured for four consecutive specimens every twenty minutes respectively.
The results were as follows
(1) Water diuresis was inhibited and free water was reabsorbed by pitressin.
(2) Fitressin induced antidiuresis was inhibited and free water was excreted by noradrenalin.
(3) Inderal, beta-adrenergic blocking agent, maintained the effect of noradrenalin on pitressin
induced antidiuresis and free water was excreted.
(4) Inulin clearance, osmolar clearance, urine osmolarity and sodium excretion were not altered
by pitressin, noradrenalin or inderal.
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