Submitted on December 4, 2006
Accepted on January 23, 2008
Interactions between subtotal nephrectomy and salt: effects on blood pressure and renal function in pregnant and non-pregnant ewes
Karen Jane Gibson1*, Amanda Catherine Boyce1, Clare L Thomson1, Sarah Chinchen1, and Eugenie Ruth Lumbers1
1 Department of Physiology and Pharmacology, School of Medical Sciences, The University of New South Wales, Sydney, New South Wales, Australia
* To whom correspondence should be addressed. E-mail: k.gibson{at}unsw.edu.au.
The effects of high salt intake on blood pressure and renal function were studied in 9 subtotally nephrectomised pregnant (STNxP) and 7 intact pregnant (IntP) ewes in late gestation, and in 8 subtotally nephrectomized non-pregnant (STNxNP) and 7 intact non-pregnant (IntNP) ewes. STNxP had higher mean arterial pressures (P<0.02) and plasma creatinine levels (P<0.001) than IntP. High salt (0.17 M NaCl as drinking water for 5 days) did not change blood pressure in either STNxP or IntP. STNxNP had higher mean arterial pressures (P=0.03) and plasma creatinine levels (P<0.001) than IntNP. In STNxNP, blood pressure increased with high salt intake and there was a positive relationship between diastolic pressure and sodium balance (r=0.497, P=0.05). This relationship was not present in IntNP, STNxP or IntP. Because high salt intake did not cause an increase in blood pressure of STNxP ewes, it is concluded that they were protected by pregnancy from further rises in blood pressure. The observed increase in GFR (P<0.03) and depression of fractional proximal sodium reabsorption (P=0.003) which occurred in STNxP, but not in STNxNP, in response to high salt may have contributed to this protection. As well, the increased production of vasorelaxants in pregnancy may selectively protect against the occurrence of salt sensitive hypertension in pregnancy.
