A. M. Balaszczuk

Nitric oxide and thyroid gland: modulation of cardiovascular function in autonomic-blocked anaesthetized rats.

We have previously reported that acute administration of NG‐nitro‐l‐arginine methyl ester (l‐NAME) increases the mean arterial pressure (MAP) and heart rate (HR) in autonomic‐blocked (CAB) anaesthetized rats. In the present study we examined whether thyroid and adrenal glands are involved in these pressor and chronotropic responses. Sprague‐Dawley rats were studied after bilateral vagotomy and ganglionic blockade with hexamethonium (10 mg kg−1), and stabilization of MAP with infusion of phenylephrine (PE) (6 μg kg−1 min−1). The rats were divided into groups: L, CAB; PE, CAB + PE bolus (6 μg kg−1); L‐TX, thyroidectomy + CAB; L‐AX, adrenalectomy + CAB; TX, only thyroidectomy; C, CAB. L, L‐AX and L‐TX groups received a bolus of l‐NAME (7.5 mg kg−1). Triiodothyronine (T3), thyroxin (T4) and thyrotropin (TSH) levels were measured in L and L‐TX rats before and after l‐NAME administration. Reduced nicotamide adenine dinucleotide (NADPH) diaphorase activity was determined in heart and aorta of the TX group. The pressor response induced by l‐NAME was similar in all groups. l‐NAME‐induced‐tachycardia was associated with this rise in MAP. Adrenalectomy did not modify this chronotropic response, but it was attenuated by thyroidectomy. Thyroidectomy by itself decreased the circulating levels of T3 but it had no effect on the plasma levels of T4 and TSH. L and L‐TX groups showed similar levels of circulating T4 and TSH, meanwhile the plasma level of T3 decreased in the L group. Nitric oxide synthase (NOS) activity in atria as well as in aorta was greater in the TX group compared with C. When autonomic influences are removed, the thyroid gland modulates intrinsic heart rate via a mechanism that involves, at least in part, the nitric oxide pathway.

Effects Of L-Arginine And Furosemide On Blood Pressure And Renal Function In Volume-Expanded Rats

1. The aim of the present study was to investigate the effects of L‐arginine (L‐Arg) on blood pressure and water and electrolyte excretion in control and extracellular fluid volume‐expanded rats (10% bodyweight with 0.9% NaCl) and to determine whether diuretic treatment with furosemide (FUR) can be optimized by the administration of L‐Arg in this model.

Effects of dopamine and nitric oxide on arterial pressure and renal function in volume expansion

1.u2002The aim of the present study was to investigate the role of dopamine (DA) in the hypotensive and renal effects of l‐arginine during extracellular fluid volume expansion (10% bodyweight).

Nitric oxide synthase blockade and body fluid volumes

The influence of chronic nitric oxide synthase inhibition with N G-nitro-L-arginine methyl ester (L-NAME) on body fluid distribution was studied in male Wistar rats weighing 260-340 g. Extracellular, interstitial and intracellular spaces, as well as plasma volume were measured after a three-week treatment with L-NAME (approximately 70 mg/kg per 24 h in drinking water). An increase in extracellular space (16.1 +/- 1.1 vs 13.7 +/- 0.6 ml/100 g in control group, N = 12, P<0.01), interstitial space (14.0 +/- 0.9 vs 9.7 +/- 0.6 ml/100 g in control group, P<0.001) and total water (68.7 +/- 3.9 vs 59.0 +/- 2.9 ml/100 g, P<0.001) was observed in the L-NAME group (N = 8). Plasma volume was lower in L-NAME-treated rats (2.8 +/- 0.2 ml/100 g) than in the control group (3.6 +/- 0.1 ml/100 g, P<0.001). Blood volume was also lower in L-NAME-treated rats (5.2 +/- 0.3 ml/100 g) than in the control group (7.2 +/- 0.3 ml/100 g, P<0.001). The increase in total ratio of kidney wet weight to body weight in the L-NAME group (903 +/- 31 vs 773 +/- 45 mg/100 g in control group, P<0.01) but not in total kidney water suggests that this experimental hypertension occurs with an increase in renal mass. The fact that the heart weight to body weight ratio and the total heart water remained constant indicates that, despite the presence of high blood pressure, no modification in cardiac mass occurred. These data show that L-NAME-induced hypertension causes alterations in body fluid distribution and in renal mass.

Effect of acute nitric oxide synthase inhibition in the modulation of heart rate in rats

Acute nitric oxide synthase inhibition with N G-nitro-L-arginine methyl ester (L-NAME) on chronotropic and pressor responses was studied in anesthetized intact rats and rats submitted to partial and complete autonomic blockade. Blood pressure and heart rate were monitored intra-arterially. Intravenous L-NAME injection (7.5 mg/kg) elicited the same hypertensive response in intact rats and in rats with partial (ganglionic and parasympathetic blockade) and complete autonomic blockade (38 +/- 3, 55 +/- 6, 54 +/- 5, 45 +/- 5 mmHg, respectively; N = 9, P = NS). L-NAME-induced bradycardia at the time when blood pressure reached the peak plateau was similar in intact rats and in rats with partial autonomic blockade (43 +/- 8, 38 +/- 5, 46 +/- 6 bpm, respectively; N = 9, P = NS). Rats with combined autonomic blockade showed a tachycardic response to L-NAME (10 3 bpm, P<0.05 vs intact animals, N = 9). Increasing doses of L-NAME (5.0, 7.5 and 10 mg/kg, N = 9) caused a similar increase in blood pressure (45 +/- 5, 38 +/- 3, 44 +/- 9 mmHg, respectively; P = NS) and heart rate (31 +/- 4, 34 +/- 3, 35 +/- 4 bpm, respectively; P = NS). Addition of L-NAME (500 micro M) to isolated atria from rats killed by cervical dislocation and rats previously subjected to complete autonomic blockade did not affect spontaneous beating or contractile strength (N = 9). In vivo results showed that L-NAME promoted a tachycardic response in rats with complete autonomic blockade, whereas the in vitro experiments showed no effect on intrinsic heart rate, suggesting that humoral mechanisms may be involved in the L-NAME-induced cardiac response.

HEMORRHAGIC SHOCK: NITRIC OXIDE SYNTHASES ACTIVITY AND ITS ASSOCIATION WITH CAVEOLIN-1 IN RAT HEARTS: PP.22.409

Nitric oxide synthases (NOS) are involved in many aspects of cardiovascular homeostasis including regulation of blood pressure and heart rate (HR). Objectives: (i) to investigate the role of NO pathway in the cardiovascular adjustment in hemorrhaged rats (bleeding: 20% of the volemia) (ii) to study a relationship between caveolin-1 and NOS in this experimental model. Methods: Groups of animals (n = 10/age group): S = sham, H = hemorrhaged rats, S+L-NAME (1 mg/kg iv and 0.5 mg/kg.h iv = 100 fÝl/h), H+L-NAME. We evaluated in the left ventricle the NOS activity (NADPH-d technique), eNOS expression (Western blot) and coimmunoprecipitation analysis of caveolin-1 and eNOS (Immunofluorescence) at 60 and 120 min of bleeding. Analysis of variance (ANOVA) followed by the ad hoc Bonferroni test was used for multiple comparisons. The 5% probability level was used as a criterion for biological significance. Results: L-NAME restored the hypotension induced by hemorrhage. Blood loss decreased heart rate in the first stage increasing at 60 and 120 min. L-NAME blunted this effect. Left ventricle histochemical NOS activity increased at 60 and 120 min (21% and 45%, respectively). eNOS protein levels increased in left ventricle at 60 min without changes at 120 min compared with S group. eNOS exhibited a diffuse staining pattern throughout the ventricle cell and is significantly associated with caveolin-1 in S group. Meanwhile, at 60 min of bleeding a dissociation of caveolin-1 and eNOS was observed. The binding of caveolin-1 with eNOS is partially restored at 120 min. Conclusions: The involvement of NO pathway on cardiovascular parameters occurs in an isoform-specific and time dependent manner after blood loss. This response would be influenced by direct protein interactions between the eNOS and it regulatory protein, caveolin-1 in hemorraghed rat.