Proceedings of The Physiological Society

University of Cambridge (2004) J Physiol 555P, PC17


Impact of dietary sodium on haeme-oxygenase distribution in rat kidneys

X.C. Wu and Edward J. Johns*

Department of Physiology, The Medical School, Birmingham, UK and * Department of Physiology, University College Cork, Republic of Ireland

The haemoxygenase enzyme isoforms (HO-1 and HO-2) generate carbon monoxide locally in vascular smooth muscle cells and may be important in regulating vessel tone and at this level may interact with nitric oxide (NO). There have been conflicting reports as to the contribution of the HO enzymes to salt-induced hypertension which has been hindered by the diversity in the duration and degree of dietary salt loading as well as to changing production of NO. The aim of the present study was to evaluate the effect of a short period of a modest elevation in dietary salt intake on HO-1 and HO-2 expression in different regions of the kidney with NO present and following its blockade and relate them to functional responses.

Male Wistar rats (0.3 ± 0.01 kg) were maintained on a normal rat diet but were given either tap water, saline (140 mmol NaCl), saline plus L-NAME (2.77 ± 0.7 mg/day) or water plus L-NAME to drink for a 7-day period. From day 4 to 7 fluid intake and output was estimated and creatinine clearance measured and used to calculate glomerular filtation rate (GFR). On day 7 the animals were anaesthetized (1 ml of chloralose/urethane, 16.5/250 mg, I.P.), blood pressure measured from a femoral artery, a blood sample collected and following an anaesthetic overdose to kill the rats, the kidneys were harvested. The kidneys were separated into cortex and medulla and HO-1 and HO-2 evaluated by Western blotting. Means ± S.E.M. were subjected to ANOVA and significance taken at P < 0.05.

Blood pressure in the normal rats (n = 9) was 103 ± 6 mmHg, but was increased by 24 % (P < 0.01) and 13 % in the rats maintained on saline plus L NAME and water plus NAME, respectively. GFR (n = 7), at 2.73 ± 0.38 ml min-1 kg-1 in the rats given water to drink, was similar in the rats given saline or L-NAME to drink but was decreased by 18 % (P < 0.05) in the rats on saline plus L-NAME. Analysis of the Western blots demonstrated that HO-2 was similar in both cortex and medulla and was not affected by any treatment. HO-1 was present to a higher degree in the cortex than medulla, giving a densitometric rato of 1.73 = 0.20 (n = 10). Drinking saline decreased the medullary expression of HO-1, such that the cortex to medulla ratio increased to 2.40 = 0.19 (P < 0.05) but L-NAME given to the animals receiving either saline or water, normalized the ratio (1.81 = 0.28 and 1.89 = 0.31, respectively).

These findings demonstrated that one week of saline intake depressed medullary but not cortical expression of HO-1 and that this appeared to be related and dependent upon the NO synthase activity. The exact way in which the HO-1 and NOS systems interact in response to the raised salt intake is unclear at present.

Where applicable, experiments conform with Society ethical requirements