Effect of nitric oxide on renal autoregulation during hypothermia in the rat

Abstract

Hypothermia-induced reduction of metabolic rate is accompanied by depression of both glomerular perfusion and filtration. The present study investigated whether these changes are linked to changes in renal autoregulation and nitric oxide (NO) signalling. During hypothermia, renal blood flow (RBF) and glomerular filtration rate (GFR) were reduced and urine production was increased, and this was linked with reduced plasma cGMP levels and increased renal vascular resistance. Although stimulation of NO production decreased vascular resistance, blood pressure and urine flow, intravenous infusion of the NO precursor L-arginine or the NO donor sodium nitroprusside did not alter RBF or GFR. In contrast, inhibition of NO synthesis by Nw-nitro-L-arginine led to a further decline in both parameters. Functional renal autoregulation was apparent at both temperatures. Below the autoregulatory range, RBF in both cases increased in proportion to the perfusion ±pressure, although, the slope of the first ascending limb of the pressure-flow relationship was lower during hypothermia. The main difference was rather that the curves obtained during hypothermia levelled off already at a RBF of 3.9 ± 0.3 mL/min then remained stable throughout the autoregulatory pressure range, compared to 7.6 ± 0.3 mL/min during normothermia. This was found to be due to a threefold increase in, primarily, the afferent arteriolar resistance from 2.6 to 7.5 mmHg min mL−1. Infusion of sodium nitroprusside did not significantly affect RBF during hypothermia, although a small increase at pressures below the autoregulatory range was observed. In conclusion, cold-induced rise in renal vascular resistance results from afferent arteriolar vasoconstriction by the autoregulatory mechanism, setting RBF and GFR in proportion to the metabolic rate, which cannot be explained by reduced NO production alone.

Both Underweight and Obesity Are Associated With an Increased Risk of Coronavirus Disease 2019 (COVID-19) Severity

“…Although CRP levels did not tend to be elevated, the underweight group was significantly more likely to develop secondary infections than the other groups. Our findings are consistent with some earlier studies, one of the studies showed that underweight and obese were both independent risk factors for Primary Graft Dysfunction (PGD) and early mortality after lung transplantation (24)(25)(26). Both underweight and obesity may increase the risk of infectionrelated deaths (25).…”

Influence of moderate hypothermia on renal and cerebral haemodynamics and oxygenation during experimental cardiopulmonary bypass in sheep

“…26 Cold-induced reduction in the production of nitric oxide, leading to enhanced tubuloglomerular feedback, has also been suggested to play a role in moderate hypothermiainduced renal vasoconstriction. 24 Although we did not separately record the dose of metaraminol used during moderately hypothermic CPB and the standard procedure to maintain our target MAP, metaraminol is unlikely to have contributed to the reduction in RVC and RBF during moderately hypothermic CPB. This is because metaraminol appears to mainly cause constriction in the extrarenal vasculature.…”

“…The decrease in RVC was likely mediated both by vasoconstriction and increased blood viscosity 17 . For example, in anesthetized rats, moderate hypothermia (28°C) causes renal vasoconstriction 24–26 independent of adrenal medullary secretion of catecholamines and renal sympathetic nerve activity 26 . Cold‐induced reduction in the production of nitric oxide, leading to enhanced tubuloglomerular feedback, has also been suggested to play a role in moderate hypothermia‐induced renal vasoconstriction 24 .…”

“…For example, in anesthetized rats, moderate hypothermia (28°C) causes renal vasoconstriction 24–26 independent of adrenal medullary secretion of catecholamines and renal sympathetic nerve activity 26 . Cold‐induced reduction in the production of nitric oxide, leading to enhanced tubuloglomerular feedback, has also been suggested to play a role in moderate hypothermia‐induced renal vasoconstriction 24 . Although we did not separately record the dose of metaraminol used during moderately hypothermic CPB and the standard procedure to maintain our target MAP, metaraminol is unlikely to have contributed to the reduction in RVC and RBF during moderately hypothermic CPB.…”

Electrolyte handling in the isolated perfused rat kidney: demonstration of vasopressin V2-receptor-dependent calcium reabsorption

“…A recirculating perfusion system, modified from a previously described method ( 13 ), was used with a constant perfusion pressure (90 mmHg) at 37 °C. All parts of the perfusion system up to the kidney were water-mantled and connected to a constant temperature circulating bath, ensuring constant temperature in the renal parenchyma, which is important given that temperature affects kidney function ( 14 ). The kidney was perfused through the renal artery by a computer-controlled peristaltic pump (Minipuls III, Gilson Inc., Middleton, WI, USA).…”