Abstract
Hyperosmotic challenges trigger a hypertensive response and natriuresis mediated by central and peripheral sensors. Here, we evaluated the importance of the carotid bodies for the hypertensive and natriuretic responses to acute and sub-chronic NaCl load in conscious rats. Male Wistar rats (250–330 g) submitted to bilateral carotid body removal (CBX) or sham surgery were used. One day after the surgery, the changes in arterial blood pressure (n = 6–7/group) and renal sodium excretion (n = 10/group) to intravenous infusion of 3 M NaCl (1.8 mL/kg b.w. during 1 min) were evaluated in non-anesthetized rats. Another cohort of sham (n = 8) and CBX rats (n = 6) had access to 0.3 M NaCl as the only source of fluid to drink for 7 days while ingestion and renal excretion were monitored daily. The sodium balance was calculated as the difference between sodium infused/ingested and excreted. CBX reduced the hypertensive (8 ± 2 mmHg, vs. sham rats: 19 ± 2 mmHg; p < 0.05) and natriuretic responses (1.33 ± 0.13 mmol/90 min, vs. sham: 1.81 ± 0.11 mmol/90 min; p < 0.05) to acute intravenous infusion of 3 M NaCl, leading to an increase of sodium balance (0.38 ± 0.11 mmol/90 min, vs. sham: -0.06 ± 0.10 mmol/90 min; p < 0.05). In CBX rats, sub-chronic NaCl load with 0.3 M NaCl to drink for 7 days increased sodium balance (18.13 ± 4.45 mmol, vs. sham: 5.58 ± 1.71 mmol; p < 0.05) and plasma sodium concentration (164 ± 5 mmol/L, vs. sham: 140 ± 7 mmol/L; p < 0.05), without changing arterial pressure (121 ± 9 mmHg, vs. sham: 116 ± 2 mmHg). These results suggest that carotid bodies are important for the maintenance of the hypertensive response to acute hypertonic challenges and for sodium excretion to both acute and chronic NaCl load.
Highlights
In order to maintain body fluid homeostasis, behavioral, neuroendocrine, and cardiovascular adjustments are triggered during hyperosmotic challenges (Fitzsimons, 1998; AntunesRodrigues et al, 2004; Antunes et al, 2006)
By measuring Na+ intake and excretion, we found no significant difference in the sodium balance in sham rats during sub-chronic salt load compared to water intake
The present results show that carotid body removal (CBX) reduced sodium excretion to acute intravenous NaCl infusion in about 23%, whereas the excretion during sub-chronic challenge was impaired in 30% in conscious CBX rats
Summary
In order to maintain body fluid homeostasis, behavioral, neuroendocrine, and cardiovascular adjustments are triggered during hyperosmotic challenges (Fitzsimons, 1998; AntunesRodrigues et al, 2004; Antunes et al, 2006). Acute NaCl load increases arterial pressure and renal sodium excretion (Hatzinikolaou et al, 1981; McKinley et al, 1992; Schoorlemmer et al, 2000; Antunes et al, 2006; Silva et al, 2013). The increase in arterial pressure in response to hypertonic NaCl infused intravenously is a consequence of the elevation of total peripheral resistance (Garcia-Estan et al, 1989) due to a vasoconstrictor effect mediated by both sympathetic nervous system and vasopressinergic mechanisms (Antunes et al, 2006). The beneficial effects of the pressor response to acute NaCl load is not fully understood, the increase in arterial pressure may elevate the tissue perfusion, including for the kidneys, which contributes to enhance glomerular filtration rate and urinary sodium (Na+) loss. Oxytocin released in response to high Na+ plasma induces natriuresis (Landgraf et al, 1988; Huang et al, 1995) and the reduction in renal sympathetic activity (Weiss et al, 1996; Pedrino et al, 2008) contributes to the renal vasodilation (Pedrino et al, 2008) and natriuresis (Johns et al, 2011)
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