Acute Pressure Natriuresis and Na+ Transporter Regulation More Robust in Female vs. Male Sprague Dawley Rats
Authors: McFarlin Brandon E. , Ralph Donna Lee , McDonough Alicia A. 
Published: April 2020

Increased effective circulating volume (ECV) or vasoconstriction can increase blood pressure (BP). Elevated BP triggers pressure natriuresis (P‐Nat) and diuresis which is fundamental for restoring ECV homeostasis.
In males (M), increasing BP by acute vasoconstriction (acute‐HTN) drives transporters to retract to the base of the microvilli (NHE3) or sub‐apical pools (NaPi2, NCC) facilitating natriuresis.
Females (F) at baseline excrete a saline load more rapidly than M, and NHE3 is localized to the base of the microvilli as NHE3‐P (inactivation) suggesting that F at baseline resemble M during acute‐HTN. These observations drive our
AIM to determine mechanisms governing the acute P‐Nat response in F Sprague Dawley rats.

METHODS

Rats (225–290 g, n=5/group) were anesthetized with Inactin. BP was raised by arterial constriction of celiac, mesenteric and abdominal aorta, or sham surgery for 35 min. BP was measured via carotid artery cannula and urine was collected over 5‐min intervals. Na+, K+ and Li+ were assessed by flame photometry; lithium clearance (CLi) measured to estimate volume flow from PT. Kidneys were dissected into cortex and medulla for immediate homogenization or surface fixed for immunohistochemistry (IHC). Transporters’ abundance was assessed by semi‐quantitative immunoblotting.

RESULTS

At baseline mean arterial pressure (MAP, mmHg) was higher in M (105 ± 3) than F (91 ± 5), p=0.04. M and F exhibited similar urine output (UV: M = 0.05 ± 0.1 and F = 0.07 ± 0.02 ml/5min), UNaV (M = 0.008 ± 0.003 and F = 0.013 ± 0.005 ml/5min), CLi (M = 0.42 ± 0.09 and F = 0.42 ± 0.08 ml/min/kg) and Na+ clearance (CNa: M = 0.04 ± 0.02 and F = 0.08 ± 0.03 ml/min/kg).
During acute‐HTN (BP increased to 128 ± 3 mmHg in M and F) UV increased 15‐fold in F (to 1.0 ± 0.2 ml/5min, p=0.01) and 6‐fold in M (to 0.3 ± 0.1 ml/5min, p=0.08). UNaV increased 12‐fold in F (to 0.16 ± 0.02 mmol/5min, p=0.004) and 6‐fold in M (to 0.05 ±0.03 mmol/5min, ns). Volume flow from the PT (CLi) increased 9‐fold in F (to 4.0 ±0.7 mmol/min/kg, p=0.02) and 5‐fold in M (to 2.1 ± 0.5 mmol/min/kg, p=0.07). CNa increased 13‐fold in F (to 1.1 ± 0.1 mmol/min/kg, p=0.003) and 6‐fold in M (to 0.2 ± 0.1 mmol/min/kg, p=ns). These changes culminated in a leftward shift in renal function curves in F vs. M (p<0.0001).

Transporters’ responses to acute‐HTN. By IHC, NHE3 remained localized at the base of the microvilli in F. Transporter profiles in acute‐HTN, normalized to controls, were significantly altered in F vs. M (p<0.0001 by ANOVA). F exhibited 29% greater PT NHE3‐P (inactive), and 22–24% less NHE3, and NKCC2‐P in mTAL. M exhibited 14% less NKCC‐P in mTAL, 30% higher cTAL NKCC2 and 36% higher CCD ENaC (full length). The mTAL transporter kinase SPAK‐P decreased in both M and F by 34 – 43%, respectively. Associated with these differences, P‐Nat reduced MAP more in F than M (115 ± 5 in F and 123 ± 5 in M) by 35 min.

CONCLUSIONS

Females exhibit more robust pressure natriuresis than males evident in leftward shift in renal function curves. Greater CLi in F vs. M maybe mediated by increased PT NHE3‐P/NHE3 ratio (less active). Greater CNa in F than M maybe mediated by the larger reductions in mTAL Na+ transporters’ activation and SPAK‐P in F. These results shed further light on the “female advantage” to resist hypertension and cardiovascular disease.

Support or Funding Information

NIH NIDDK DK083785