Aumento na ingestão de sódio durante as fases pós-natais induz aumento de pressão arterial na fase adulta
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Data
2014-03-31
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Universidade Federal de Goiás
Resumo
Changes in plasma sodium concentration have led to adjustment mechanisms in
order to restore their physiological conditions. The behavioral adjustments consist in the
regulation of water and sodium intake. Among the vegetative adjustments, we highlight
changes in renal sympathetic activity, blood pressure, renal blood flow (RBF) and renal
vascular conductance (RVC). Experimental evidence has demonstrated increase of blo od
pressure of the adult offspring from mothers with high sodium diets during pregnancy.
Although these studies had demonstrated the importance of prenatal phases in
hypertension development, there has been no evidence of the effects of high sodium diets
during postnatal phases in relation to hypertension. Thus, in the present study, we
evaluated the effects of sodium overload during childhood on cardiovascular and
behavioral parameters in adulthood. That way, 21 days after birth, we have offered to the
experimental group, hypertonic solution (NaCl 0.3 M) and food ad libitum for 60 days. The
control rats were maintained with tap water and food ad libitum. Afterwards, both groups
were maintained with tap water and food during 15 days (recovery). Later, we per formed
chronic cannulation of right femoral artery to record baseline mean arterial pressure (MAP)
and heart rate (HR) in unanesthetized animals. In the experimental group, we observed
increases in basal MAP (118.3 ± 2.7 mmHg) and HR (398.2 ± 7.5 bpm), compared with the
control group (98.6 ± 2.6 mmHg; 365.4 ± 12.2 bpm). Baroreflex index was diminished in
experimental group in relation to control group by phenylephrine infusions ( -1.24 ± 0.2
bpm·mmHg
-1
vs. -1.83 ± 0.04 bpm·mmHg
-1
, respectively) as by sodium nitroprusside
infusions (0.85 ± 0.22 bpm·mmHg
-1
vs. 2.12 ± 0.2 bpm·mmHg
-1
, respectively). The
baseline values of MAP, HR, RBF, RVC and renal sympathetic nerve activity (RSNA) in
anesthetized animals were evaluated. MAP and HR of experimental group (124.4 ± 3.0
mmHg; 437.9 ± 10.5 bpm) were significantly higher than control group (102.4 ± 2.4 mmHg;
375.2 ± 15.4 bpm). The baseline values of RBF (control: 3.4 ± 0.4 ml·min
-1
; experimental:
3.9 ± 0.2 ml·min
-1
), RVC (control: 0.0288 ± 0.0044 ml·(min·mmHg)
-1
; experimental: 0.0336
± 0.0012 ml·(min·mmHg)
-1
) and RSNA (control: 0.0300 ± 0.0095 V and 89.5 ± 3.67
spikes·s
-1
; experimental: 0.0351 ± 0.0109 V and 78.1 ± 4.89 spikes·s
-1
) were similar
between the groups. Ex vivo cardiovascular function in adulthood was also evaluated. It
has been observed that animals treated with sodium overload during the postnatal period
showed reduction of vascular endothelium-independent relaxation and also an increase in
intraventricular diastolic pressure during the cardiac reperfusion. Furthermore, after the
recovery period, the animals were submitted to osmotic challenge. The cardiovascular
adjustments induced by acute hypernatremia were evaluated. It was observed that in the
control animals, the infusion of hypertonic saline evoked a transient increase in MAP (Δ
9.2 ± 2.2 mmHg ), transient bradycardia (Δ -18.9 ± 7.9 bpm) and sustained increases in
RBF (Δ 37.7 ± 6.9 % of baseline ) and RVC (Δ 50.0 ± 4.4 % of baseline, 60 min after
infusion). However, in the experimental rats, hypertonic saline infusion caused a transient
increase in MAP, higher than observed in control animals (Δ 18. 7 ± 1.7 mmHg, after 10
min) and sustained bradycardia (Δ -25.0 ± 10.2 bpm, after 60 min). The increases in RBF
(Δ 30.8 ± 11.0% of baseline, after 60 min) and RVC (Δ 27.9 ± 12.3 % of baseline, af ter 60
min) were lower than the observed in the control group. Later, we performed tests of
water and sodium intake induced by furosemide (10 mg·kg
-1
bw, sc). In test-induced
drinking, the hypertonic 0.3 M sodium intake was reduced in experimental animals
compared to the control group (7.8 ± 1.1 ml vs. 12.1 ± 0.6 ml, respectively). Alt ogether, the
results of the present study show that changes in hidromineral homeostasis, in postuterine phases, affect the behavioral and cardiovascular adjustments induced by sodium
depletion and hypernatremia. Furthermore, they show that a high -sodium diet during the
postnatal period alters baroreflex sensitivity and BP, in adulthood, compromising the
cardiac relaxation after ischemia and endothelium-independent vasorelaxation .
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MOREIRA, Marina Conceição dos Santos. Aumento na ingestão de sódio durante as fases pós-natais induz aumento de pressão arterial na fase adulta. 2014. 49 f. Dissertação (Mestrado em Biologia) - Universidade Federal de Goiás, Goiânia, 2014.