Effects of LPS Endotoxemia on Cardiovascular Parameters and Plasma Nitric Oxide of Ovariectomized Rats

Abstract

Females of reproductive age have a more active immune system than males, but influence of sex hormones on cardiovascular system have been controversial. The cardiovascular responses of ovariectomized female rats compared with females in estrus phase after immunological challenge with LPS infusion and nitric oxide production have not yet been elucidated. Wistar rats, eight weeks after being subjected to ovariectomy (OVX) or false-OVX (Sham), had their femoral artery and vein catheterized. Cardiovascular parameters were recorded in conscious rats for 2 hours after LPS injection (5 mg / kg, IV), previously treated with saline or L-NAME (10mg / kg). Plasma samples were collected for measurement of nitrite (NO2) by Griess method. LPS promoted four distinct phases in mean arterial pressure (MAP) of the sham group, with hypotension within 10 minutes (DMAP = -27.5 ± 6 mmHg, n = 8). OVX rats did not show this initial drop (DMAP = -4.4 ± 4 mmHg, n = 7); and pretreatment with L-NAME did not alter the pattern of response to LPS. After 2 hours of LPS injection, NO2 plasma levels were higher in OVX (29±0,9 µM, n = 9 versus 21 ± 2µM, n = 9) and group treated with L-NAME prevented this rise (19 ± 1uM, n = 8 versus 14 ± 2 µM, n = 4). Female rats in estrus decrease more pressure to LPS in the first minutes compared to ovarietomized rats. Blockade of NOS did not alter the decrease in MAP, so it is possible that other mediators participate in the hypotension induced by endotoxemia in female rats.