Relation between apelin-36 and arginine vasopressin in male rats subjected to water deprivation and volume expansion

ABSTRACT

The closed anatomical localization in supraoptic and paraventricular nuclei and tissue distribution of apelin-36 and arginine vasopressin [AVP] suggest a role for the peptide apelin-36 in body fluid homeostasis and regulation of AVP release. However, conflicting reports make the precise role of apelin-36 remains to be clarified. To investigate the effect of water deprivation and acute volume expansion on plasma and brain tissue levels of apelin-36 and AVP in an attempt to clarify the interaction between the two peptides in control of body fluid homeostasis. The study was conducted on 40 male albino rats divided into 4 groups. Group I 10 control rats, group II 10 rats subjected to 24h-water deprivation [WD], group III 10 rats subjected to 48h-WD and group IV 10 rats subjected to acute volume expansion 10% of body weight by infusion of isotonic saline over 40 minutes. The following parameters were measured in all rats; plasma and brain tissue apelin -36 and AVP, plasma Na[+] and K[+] concentrations, urinary excretion rates of Na[+] and K[+] and urine flow rate per minute. Hematocrite value and plasma protein concentrations were measured to investigate the state of dehydration and hydration. Water deprivation induced significant decrease in plasma apelin-36 level associated with an increase in its brain tissue contents. This was mirrored by increased plasma AVP level and decreased brain tissue content. The reverse was detected after acute volume expansion. Moreover, increased apelin-36 concentration in plasma after acute VE was associated with diuresis and natriuresis. A significant negative correlation was detected between plasma as well as brain tissue concentrations of both apelin-36 and AVP. Apelin-36 may be implicated in the control of body fluid homeostasis and exerts opposite action to AVP in this regard. Furthermore it may be an inhibitor of AVP and the two peptides may play complementary roles in maintenance of water balance