Dissociation between activation of the hypothalamo-hypophyseal antidiuretic system and the type of diuresis during acute intracranial hypertension. Experimental observation.

Acute cerebral compression by a supra- and infratentorial balloon produced a triphasic pattern of diuresis. The 1st phase was characterized by polyuria associated with five fold increase of plasma (p) antidiuretic hormone (ADH) concentration, decreased urine osmolality in spite of natriuresis and blood pressure elevation. The 2nd phase was characterized by oliguria, a decrease of pADH and reduced urine Na+ concentration, whereas urine osmolality transiently increased. At this stage there was respiratory arrest and fall of blood pressure. The final stage was diabetes insipidus (DI), when EEG activity had disappeared. An increase of serum osmolality mainly occurred during the last DI phase. Serum Na+ concentration fluctuated slightly during the whole period of diuresis. These results present evidence, that the diuresis pattern reflects the hypothalamo-hypophyseal antidiuretic system (HHAS) reaction to acute intracranial pressure (ICP) increase with the vegetative symptoms of cerebral shock.