HORMONAL DEPENDENCE OF THE EFFECTS OF METABOLIC ENCEPHALOPATHY ON CEREBRAL PERFUSION AND OXYGEN UTILIZATION IN THE RAT

Previous studies have demonstrated that in adult rats with chronic hyp onatremia, both symptoms of encephalopathy and mortality largely depen d upon the gender of the animal and the presence of elevated plasma le vels of vasopressin (AVP). Since effects of AVP on blood vessels may b e Fender dependent, the present study was designed to compare the effe cts of chronic (4 days) hyponatremia on cerebral blood flow (CBF), cer ebral oxygen consumption (CMRO(2)), and cerebral perfusion index (CPI) in adult male and female rats. CBF (intra-arterial Xe-133 injection m ethod) and CMRO(2) (arteriovenous difference of cerebral oxygen conten t x CBF) were measured in normonatremic and hyponatremic (hyponatremia induced with 140 mmol/L, glucose and either AVP or desmopressin [dDAV P], plasma sodium=100 to 110 mmol/L) adult rats of both genders. The C PI was assessed from magnetic resonance imaging of the transit of magn etic susceptibility contrast agent through the brain. Female rats with AVP-induced chronic hyponatremia had a 36% decrease in CBF and a 60% decrease in CMRO(2). In male animals, both parameters were not differe nt from control values. AVP-induced hyponatremia resulted in a 45% dec rease in CPI in female rats, but hyponatremia induced with dDAVP did n ot affect CPI in either male or female rats. Chronic (4 days) administ ration of AVP did not affect CPI in either male or female normonatremi c rats. When rats with AVP-induced chronic hyponatremia were pretreate d with estrogen, the CPI in males was not different from that in femal es. Our results demonstrate that during AVP-induced chronic hyponatrem ia in female rats, there is significant depression of both oxygen util ization and blood flow in the brain.