Local inhibition of nitric oxide temporarily stimulates aldosterone secretion in conscious sheep in vivo

A method to attenuate pneumoperitoneum-induced reductions in splanchnic blood flow

OBJECTIVE

To determine if increasing nitric oxide bioactivity by inclusion of ethyl nitrite (ENO) in the insufflation admixture would attenuate pneumoperitoneum-induced decreases in splanchnic perfusion.

SUMMARY BACKGROUND DATA

Organ blood flow is reduced during pneumoperitoneum and can contribute to laparoscopy-associated morbidity and mortality. Previous attempts to control such decreases in flow have been ineffective.

METHODS

Laser-Doppler flow probes were placed on the liver and right kidney of anesthetized pigs. After a baseline recording period, animals were insufflated to a final intraperitoneal pressure of 15 mm Hg. Group one received CO2 (standard practice), whereas group 2 received CO2 plus 100 ppm ENO. Insufflation was maintained for 60 minutes and then the abdomen was manually deflated; monitoring was continued for another 60 minutes.

RESULTS

CO2 insufflation (n = 5) cut liver blood flow in half; liver flow remained at this level throughout the postinsufflation period. Inclusion of 100 ppm ENO (n = 6) attenuated both the acute and prolonged blood flow decreases. Statistical modeling of the data showed that, on average, liver blood flow was 14.3 U/min higher in the ENO pigs compared with the CO2 group (P = 0.0454). In contrast, neither treatment significantly altered kidney blood flow (P = 0.6215).

CONCLUSION

The data indicate that ENO can effectively attenuate pneumoperitoneum-induced blood flow decreases within the peritoneal cavity. The result suggests a novel therapeutic method of regulating hemodynamic changes during laparoscopic procedures.

NO Synthase Inhibition Increases Aldosterone in Humans

To test the hypothesis that NO influences aldosterone production in humans, we examined the effect of N G -nitro- l -arginine methyl ester ( l -NAME) on aldosterone concentrations in the presence and absence of the NO precursor l -arginine (3 g TID) and the angiotensin-converting enzyme inhibitor ramipril (10 mg QD). Ten normal subjects were given l -NAME (66 μg/kg per min for 30 minutes) or vehicle in random order on separate days during placebo and after randomized, double-blind treatment with l -arginine, ramipril, or l -arginine plus ramipril. Infusion of l -NAME significantly increased systolic blood pressure (all P <0.05) and decreased heart rate (all P ≤0.02) during all 4 treatment arms. After placebo pretreatment, serum aldosterone was significantly higher during l -NAME infusion than during vehicle (6.6±1.7 versus 3.3±0.5 ng/dL; P =0.045). Combined treatment with l -arginine plus ramipril abolished this effect. There was no effect of l -NAME on plasma renin activity (PRA; P =0.297) or angiotensin II concentrations ( P =0.537). However, there was a significant interactive effect of l -NAME and time on serum potassium ( P =0.039). There was a significant linear relationship between PRA and aldosterone concentration after vehicle infusion ([aldosterone]=3.9·PRA+1.9; r 2 =0.476; P =0.027) and l -NAME infusion ([aldosterone]=7.2·PRA+3.1; r 2 =0.457; P =0.032), and the intercepts of these lines were different ( P =0.029). There was a significant linear relationship between serum potassium and aldosterone during l -NAME ([aldosterone]=8.2 · [potassium]−28.9; r 2 =0.609; P =0.008) but not during vehicle ( P =0.313). These data suggest that endogenous NO modulates aldosterone synthesis in humans.

Chronic administration of nitric oxide reduces angiotensin II receptor type 1 expression and aldosterone synthesis in zona glomerulosa cells

Acute nitric oxide (NO) inhibits angiotensin II (ANG II)-stimulated aldosterone synthesis in zona glomerulosa (ZG) cells. In this study, we investigated the effects of chronic administration of NO on the ANG II receptor type 1 (AT1) expression and aldosterone synthesis. ZG cells were treated daily with DETA NONOate (10(-4) M), an NO donor, for 0, 12, 24, 48, 72, and 96 h. Chinese hamster ovary (CHO) cells, stably transfected with the AT1B receptor, were used as a positive control. Western blot analysis indicated that AT1 receptor expression was decreased as a function of time of NO administration in both CHO and ZG cells. ANG II binding to its receptors was determined by radioligand binding. NO treatment of ZG cells for 96 h resulted in a decrease in ANG II binding compared with control. The receptor density was decreased to 1,864 +/- 129 fmol/mg protein from 3,157 +/- 220 fmol/mg protein (P < 0.005), but the affinity was not changed (1.95 +/- 0.22 vs. 1.88 +/- 0.21 nM). Confocal Raman microspectroscopy and immunocytochemistry both confirmed that the expression of AT1 receptors in ZG cells decreased with chronic NO administration. In addition, chronic NO administration also decreased the expression of cholesterol side-chain cleavage enzyme in ZG cells and inhibited ANG II- and 25-hydroxycholesterol-stimulated aldosterone synthesis in ZG cells. This study demonstrates that chronic administration of NO inhibits aldosterone synthesis in ZG cells by downregulation of the expression of both AT1 receptors and cholesterol side-chain cleavage enzyme.