Renal mechanisms involved in stress-induced antinatriuresis and antidiuresis in rats

Adrenal response of male rats exposed to prenatal stress and early postnatal stimulation

Stress in pregnant rats caused by chronic immobilization alters the pattern of secretion of corticosterone and modifies the hypothalamic-pituitary-adrenal axis (HPA) of the fetus. Early postnatal handling, however, may reverse the effects of increased secretion of corticosterone. We investigated the effects of prenatal stress and postnatal handling on the activity of the HPA axis of male offspring of stressed female rats. Male 90-day-old rats from four groups were investigated: prenatally stressed animals without postnatal handling, prenatally stressed animals with postnatal handling, unstressed control animals with postnatal handling, and unstressed control animals without postnatal handling. After sacrifice, the adrenal glands were weighed to determine the adrenal-somatic index. Apoptosis was evaluated by TUNEL assay and active caspase-3 expression. We found that the adrenal gland cortex:medulla ratio increased in animals with prenatal stress and that eventually the stress caused apoptosis. Handling newborns to simulate maternal activity ameliorated some of the negative effects of prenatal stress.

Neuroendocrine changes and natriuresis in response to social stress in rats

Sympathetic activation is detected by the tachycardic, hypertensive and hyperthermic responses during social conflicts in rodents and primates. Sympathetic nervous system activation promoting sodium retention has long been recognized to play a significant role in the development and maintenance of salt-sensitive hypertension. The objective was to investigate neuroendocrine activation and renal sodium excretion in response to chronic social stress. Male Wistar rats were subjected to social stress in accordance with the resident-intruder paradigm. Intruder rats were subjected to social confrontation once daily for 6 days. After the last confrontation, plasma corticosterone and urinary catecholamines were determined to assess the neuroendocrine activation. Plasma aldosterone, plasma and urinary creatinine, Na(+) , K(+) and urinary volume were also measured. Chronic social stress increased the urinary norepinephrine, dopamine and plasma corticosterone levels, with no changes in epinephrine levels. On the other hand, high plasma aldosterone levels and low urinary sodium excretion without differences in creatinine clearance were observed. In conclusion, social stress had a strong antinatriuretic effect, which is coincident with noradrenergic and corticoadrenal activation and an increase in plasma aldosterone levels. Activation of these factors may promote sodium retention, which has long been recognized to play a significant role in the development and maintenance of hypertension.

Immobilization stress responses in adult rats exposed in utero to immobilization

The present study investigated the influence of immobilization prenatal stress on adult male rats, with the same postnatal stress, on the immune parameters and its relation with plasma corticosterone (COR) and glucose levels. To study the immunity parameters, profiles of the leucocytes, size of spleen and number of the mononuclear cells of this organ were determined. Basal levels of COR and glucose were higher in prenatally stressed animals. When the adult animals were exposed to immobilization stress, COR increased but the increase was less than that for the control group, and glucose was equal in both groups. Although postnatal acute stress decreased the number of leucocytes and lymphocytes and increased the number of neutrophils, the effect was lower in prenatally stressed animals; for that reason, the ratio neutrophil/lymphocyte increased less. The number of mononuclear cells were higher in the spleen of prenatally stressed animals. This effect was probably due to retention of blood lymphocytes in the spleen. There seemed to be an alteration in the redistribution of leucocytes, both in basal conditions and under postnatal stress. The alteration of the immunological function may be partly due to an alteration in the functionality of the hypothalamic–pituitary–adrenal axis, which was hyperactive in basal conditions but appeared to suffer habituation to the same stress.

Renal effects of plant-derived oleanolic acid in streptozotocin-induced diabetic rats

Previous studies from our laboratories indicate that the anti-diabetic effects of Syzygium cordatum (Hochst.) [Myrtaceae] leaf extract in streptozotocin-induced diabetic rats may be attributed in part to mixtures of triterpenes, oleanolic acid (3ss-hydroxy-olea-12-en-28-oic acid, OA) and ursolic acid (3ss -hydroxyl-urs-12-en-28-oic acid, UA). For the bioactive compounds to have potential in diabetes management, they should alleviate or prevent complications of diabetes mellitus, kidney function, and cardiovascular disorders. This study was, therefore, designed to assess whether S. cordatum leaf derived OA influenced renal function evaluated by the ability to increase urinary Na(+) outputs parameters and creatinine clearance (Ccr) of streptozotocin (STZ)-induced diabetic rats. Extraction and fractionation of S. cordatum powdered leaf ethyl acetate-solubles (EAS) yielded mixtures of OA/UA and methyl maslinate/methyl corosolate. Recrystallization of OA/UA mixture using ethanol afforded OA, the structure of which was confirmed by NMR spectroscopy ((1)H & (13)C). Acute effects of OA on kidney function and mean arterial blood pressure (MAP) were investigated in anesthetized rats challenged with hypotonic saline after a 3.5-h equilibration for 4h of 1 h control, 1.5 h treatment, and 1.5 h recovery periods. OA was added to the infusate during the treatment period. Chronic effects of OA were studied in individually caged rats treated twice daily with OA (60 mg/kg, p.o.) for five weeks. By comparison with respective control animals administration, OA significantly increased Na(+) excretion rates of non-diabetic and STZ-induced diabetic rats without affecting urine flow, K(+) and Cl(-) rates. At the end of five weeks, OA treatment significantly (p < 0.05) increased Ccr in non-diabetic (2.88 +/- 0.14 vs. 3.71 +/- 0.30 ml/min) and STZ-diabetic rats (1.81 +/- 0.32 vs. 3.07 +/- 0.16 ml/min) with concomitant reduction of plasma creatinine concentration (n = 6 in all groups). OA also caused significant decreases in MAP in non-diabetic and STZ-induced diabetic rats. These findings suggest that OA may have beneficial effects on some processes associated with renal derangement of STZ-induced diabetic rats.

Effects ofHypoxis hemerocallidea(Fisch. & C.A. Mey.) [Hypoxidaceae] Corm (African Potato) Aqueous Extract on Renal Electrolyte and Fluid Handling in the Rat

Current biomedical evidence suggests that Hypoxis hemerocallidea (Fisch. & C.A. Mey.) [Hypoxidaceae] (African Potato [AP]) corm extract may be useful in the management of type 2 diabetes mellitus. However, more recent reports have also indicated that certain herbal extracts attenuate the deterioration of kidney function in diabetes mellitus. Accordingly, this study investigated the effects of short- (acute) and long-term (chronic) administration of H. hemerocallidea corm aqueous extract (APE) on renal fluid and electrolyte handling in male Wistar rats. Acute effects of APE were investigated in separate groups of anesthetized rats challenged with a continuous jugular infusion of 0.077 M NaCl at 9 mL x h(- 1). After a 3.5-h equilibration period, consecutive 30-min urine collections were made over the subsequent 4 h of 1-h control, 1.5-h treatment, and 1.5-h recovery periods for measurements of urine flow, Na+, and K+ excretion rates. To establish the effects of acute APE, the extract was added to the infusate at doses of 90, 180, or 360 microg x h (-1) in separate groups of rats during the treatment period. For chronic studies, individually caged rats were administered twice with APE (30 mg x kg (-1) PO) every third consecutive day at 09h00 and 17h00 for 5 weeks. Control rats received distilled water (3 mL x kg(-1)). Urine volume and total urinary outputs of creatinine, Na+, and K+ were determined from 24-h samples. Acute infusion of APE produced a dose-dependent, significant (p < 0.01) decrease in urine flow, K+, and Na+ excretion rates. Chronic APE treatment significantly reduced urinary Na+ output between weeks 2 and 5, without affecting either urine flow or K+ excretion rates. When compared with control animals, APE significantly reduced GFR (2.54+/-0.09 mL x min (-1) vs. 1.52+/-0.02 mL x min (-1)) and increased plasma creatinine concentration (55 +/- 3 micromol x L(-1) vs. 68 +/-6 micromol x L(-1)). The results from this study suggest that the H. hemerocallidea corm aqueous extract may impair kidney function.

Effects ofFicus thonningii(Blume) [Morarceae] Stem-Bark Ethanolic Extract on Blood Glucose, Cardiovascular and Kidney Functions of Rats, and on Kidney Cell Lines of the Proximal (LLC-PK1) and Distal Tubules (MDBK)

Previous observations indicate that Ficus thonningii (Blume) [Moraceae] stem-bark extracts may be useful in the control of diabetes mellitus. Accordingly, we investigated in some experimental animal paradigms the effects of F. thonningii stem-bark ethanolic extract (FTE) on renal and cardiovascular functions as complications of diabetes. Oral glucose tolerance tests were conducted in separate groups of non-diabetic and STZ-treated diabetic rats given glucose load (0.86 g x kg(-1), p.o.) after 18-h fast, followed by various FTE doses (60, 120, and 240 mg x kg(-1)). Rats treated with deionized water (3 mL x kg(-1) p.o.), or metformin (500 mg x kg(-1) p.o.) acted as untreated and treated positive controls, respectively. Blood glucose was monitored at 15-min intervals for the first hour, and hourly thereafter for 3 h. Acute effects of FTE on kidney function and mean arterial blood pressure (MAP) were investigated in anaesthetized rats challenged with hypotonic saline after a 3.5-h equilibration for 4 h of 1 h control, 1.5 h treatment, and 1.5 h recovery periods. FTE was added to the infusate during the treatment period. Chronic effects of FTE were studied in individually caged rats treated daily with FTE (120 mg x kg(-1), p.o.) for five weeks. Cytotoxicity of FTE was assessed by dye-reduction colorimetric (MTT) assay on MDBK and LLCPK1 kidney cell lines exposed for 24 h, 48 h, and 72 h to graded concentrations of the extract. Myocardial contractile performance was evaluated on rat isolated atrial muscle strips. FTE, like metformin, decreased blood glucose levels in non-diabetic and STZ-diabetic rats. Both acute and chronic FTE treatments did not affect renal function. In vitro studies demonstrated that FTE increased MDBK cell metabolic activity by an average of 15% (72 h), and LLCPK1 mirrored the controls. Acute intravenous infusion of FTE reduced the MAP from 119 +/- 1 mmHg to 98 +/- 4 mmHg. The MAP also was reduced throughout the five-week experimental study period. FTE also produced concentration-dependent, negative inotropic and chronotropic effects on rat isolated, electrically driven left-, and spontaneously beating right-, atrial muscle preparations. Our experimental findings suggest that FTE possesses reno- and cardio-protective effects in diabetes mellitus.

Influence of high dietary sodium intake on the functional subtypes of alpha-adrenoceptors in the renal cortical vasculature of Wistar-Kyoto rats

1 Increased renal vascular resistance is one renal functional abnormality that contributes to hypertension, and alpha(1)-adrenoceptors play a pivotal role in modulating this renal vascular resistance. This study investigates the functional contribution of alpha(1)-adrenoceptor subtypes in the renal cortical vasculature of Wistar-Kyoto rats on a normal sodium diet (WKYNNa) compared with those given saline to drink for 6 weeks (WKYHNa). 2 The renal cortical vascular responses to the adrenergic agonists noradrenaline (NA), methoxamine (ME) and phenylephrine (PE) were measured in WKYHNa and WKYNNa rats either in the absence (the control phase) or presence of chloroethylclonidine (CEC), an alpha(1B)-adrenoceptor antagonist, 5-methylurapidil (5-MeU), an alpha(1A) antagonist, or BMY7378, an alpha(1D) antagonist. 3 Results showed a greater renal cortical vascular sensitivity to NA, PE and ME in the WKYHNa compared with WKYNNa rats (P < 0.05). Moreover, 5-MeU and BMY7378 attenuated adrenergically induced renal cortical vasoconstriction in WKYHNa and WKYNNa rats; this response was largely blunted in CEC-treated WKYHNa rats (all P < 0.05) but not in CEC-treated WKYNNa rats. 4 The data suggest that irrespective of dietary sodium content, in Wistar-Kyoto rats alpha(1A)- and alpha(1D)-subtypes are the major alpha(1)-adrenoceptors in renal cortical vasculature; however, there appears to be a functional involvement of alpha(1B)-adrenoceptors in the WKYHNa rats.

Loss of alpha2B-adrenoceptors increases magnitude of hypertension following nitric oxide synthase inhibition

Vascular alpha(2B)-adrenoceptors (alpha(2B)-AR) may mediate vasoconstriction and contribute to the development of hypertension. Therefore, we hypothesized that blood pressure would not increase as much in mice with mutated alpha(2B)-AR as in wild-type (WT) mice following nitric oxide (NO) synthase (NOS) inhibition with N(omega)-nitro-l-arginine (l-NNA, 250 mg/l in drinking water). Mean arterial pressure (MAP) was recorded in heterozygous (HET) alpha(2B)-AR knockout mice and WT littermates using telemetry devices for 7 control and 14 l-NNA treatment days. MAP in HET mice was increased significantly on treatment days 1 and 4 to 14, whereas MAP did not change in WT mice (days 0 and 14 = 113 +/- 3 and 114 +/- 4 mmHg in WT, 108 +/- 0.3 and 135 +/- 13 mmHg in HET, P < 0.05). MAP was significantly higher in HET than in WT mice days 10 through 14 (P < 0.05). Thus blood pressure increased more rather than less in mice with decreased alpha(2B)-AR expression. We therefore examined constrictor responses to phenylephrine (PE, 10(-9) to 10(-4) M) with and without NOS inhibition to determine basal NO contributions to arterial tone. In small pressurized mesenteric arteries (inner diameter = 177 +/- 5 microm), PE constriction was decreased in untreated HET arteries compared with WT (P < 0.05). l-NNA (100 microM) augmented PE constriction more in HET arteries than in WT arteries, and responses were not different between groups in the presence of l-NNA. Acetylcholine dilated preconstricted arteries from HET mice more than arteries from WT mice. Endothelial NOS expression was increased in HET compared with WT mesenteric arteries by Western analysis. Griess assay showed increased NO(x) concentrations in HET plasma compared with those in WT plasma. These data demonstrate that diminished alpha(2B)-AR expression increases the dependence of arterial pressure and vascular tone on NO production and that vascular alpha(2B)-AR either directly or indirectly regulates vascular endothelial NOS function.