Effects of dehydration and salt-loading on hypothalamic vasopressin mRNA level in male and female rats.

Experiments were carried out on 9- to 11-week-old male and female Sprague-Dawley rats. Dot-blot analysis and 3'-end digoxigenin-labeled 26mer oligonucleotide probe were used in the investigation of vasopressin (AVP) mRNA level in the hypothalamus of male and female rats. The normal hypothalamic AVP-mRNA level in males was 48% higher than that in females (P < 0.05). Plasma osmolality was also higher in males than in females (P < 0.05). In dehydrated rats, the hypothalamic AVP-mRNA level was 2.47 and 1.98 times in females (P < 0.001) and males (P < 0.01), respectively, as much as in their normal controls; the difference in hypothalamic AVP-mRNA level between dehydrated females and males was statistically insignificant. Plasma osmolality was higher in dehydrated females than in dehydrated males (P < 0.01). In salt-loaded rats, hypothalamic AVP-mRNA level was 2.47 and 2.17 times in females (P < 0.001) and males (P < 0.01), respectively, as much as in their controls. The difference in hypothalamic AVP-mRNA level between salt-loaded males and females was not statistically significant. Plasma osmolality in salt-loaded females was also higher than that in salt-loaded males (P < 0.001). These findings indicate that there is sex difference in hypothalamic AVP mRNA level and plasma osmolality under normal conditions; during dehydration and salt-loading AVP mRNA level increases and the difference in AVP mRNA level between males and females becomes insignificant.