Role of Renal Nerves in Renal Responses to Acute Volume Expansion During Pregnancy in Rats

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Abstract
To examine the role of the renal nerves in renal responses to acute volume expansion (VE) at Days 17-19 of pregnancy in rats, the diuretic and natriuretic responses to acute VE were measured from intact and denervated kidneys. One group of pregnant rats (Pregnant 1) was treated with the same amount of VE (1 ml/min for 15 min) as age -and sex-matched virgin control rats, and a second group of pregnant rats (Pregnant 2) was treated with a VE corrected for the higher body weight (presumably expanded blood volume) normally observed in late pregnancy (1.38 ml/min for 15 min). Urine flow and sodium excretion were measured before and after VE from innervated and denervated kidneys in anesthetized (Inactin) rats. Mean arterial pressure was not significantly different among the groups. During VE, the increments in urinary flow (UV) rate and sodium excretion (UNaV) from the innervated kidneys of Pregnant 1 rats were significantly smaller (26.5% for UV and 17.0% for UNaV) than those from the innervated kidneys of virgin rats. Although the UV and UNaV were greater in the Pregnant 2 group than in the Pregnant 1 group, these differences were not statistically significant. However, the values were still significantly smaller than those observed in the control group (39.1% for UV and 52.8% for UNaV). Urine flow and sodium excretion from the denervated kidneys of pregnant rats (both groups) were not significantly different from those of denervated kidneys of control rats. These results demonstrate that the reduced diuresis and natriuresis observed during acute volume expansion in pregnant rats may be due to the contribution of tonic renal nerve activity during the third week of pregnancy.

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