[The effect of captopril on the development of adriamycin nephropathy in rats with spontaneous arterial hypertension]

The effects of captopril on morphologic changes and clinical course of adriamycin (ADR) nephropathy in spontaneously hypertensive rats (SHR) were examined. After ADR infections rats were divided into two groups: ADR-C group (n = 20) given captopril (60 mg/kg per day) and ADR group (n = 19) receiving no antihypertensive treatment. SHR were examined every 6 weeks. Captopril normalized systemic blood pressure, but failed to prevent proteinuria. It slowed down renal function deterioration in the early stage of ADR nephropathy (weeks 6 and 12), but at the end of the study both groups had the same degree of renal failure irrespectively of whether blood pressure was well controlled with captopril or hypertension persisted. Captopril slowed down mesangial expansion in the early stages of ADR nephropathy, but at the end of the study there was no statistically significant difference between these two groups. Treatment with captopril also reduced the development of glomerular sclerosis.

Factors affecting the ability of the renal medulla to exert an antihypertensive function

To examine whether changes in renomedullary osmolality and the activity of the renin-angiotensin system may influence the ability of the renal medulla to exert an antihypertensive function, rats were exposed to several manoeuvers. These affected either the medullary osmolality or the renin-angiotensin system (salt or saccharose load, salt depletion, treatment with captopril alone or in combination with salt depletion). A comparison of the antihypertensive capacity of the renal medulla was studied by transplanting renal medullae from the various groups into one-kidney one-clip hypertensive rats. A significant and quantitatively similar reduction in blood pressure was observed in hypertensive rats that received transplants of the medullae from control, salt or saccharose loaded rats and captopril treated rats. In contrast, medullae from salt depleted rats did not affect blood pressure when transplanted into hypertensive animals. The addition of captopril restored the antihypertensive function of renal medulla in salt depleted rats. The results do not support the view that osmolality of the renal medulla regulates its antihypertensive capacity, and suggest that angiotensin II may restrain renomedullary antihypertensive function.

Megakaryocytopoiesis in spontaneously hypertensive rats (SHR)

Bone marrow megakaryocytes and their progenitors were studied in SHR in order to obtain more information about megakaryocytopoiesis in hypertension since it is known that various anomalies of platelet function occur in hypertension. Megakaryocytopoiesis under steady state conditions and following stimulated erythropoiesis and thrombocytopenia was not found to be significantly different in SHR from that in normotensive Wistar controls.

Erythrocytosis in spontaneously hypertensive rats

Spontaneously hypertensive rats (SH) with an increased number of red blood cells (RBC), microcytosis, and normal hemoglobin (Hb) concentration were used to study the effect of different manipulations of the erythron on erythropoietin production and on erythroid progenitor proliferation by bone marrow cells in order to gain insight regarding the regulation of erythropoiesis. The serum erythropoietin (Ep) level was increased in untreated SH rats. After stimulation by either bleeding, hemolysis, or acute hypoxia, both the erythropoietin level and erythroid colony-forming unit (CFU-E) proliferation by bone marrow cells increased in SH rats to levels that were similar to those of normotensive Wistar (W) rats. Exposure to chronic hypoxia induced an increase in Hb concentration in SH rats concomitantly with the increase in RBC. The results obtained in SH rats raise the possibility of a defect in nonEp stimulators of erythropoiesis that may alter Hb synthesis.

The role of the renal medulla in blood pressure control

It is well established that the renal medulla exerts a potent endocrine-like antihypertensive action. The purpose of this paper is to summarize the data that define the extent to which the renomedullary antihypertensive action is involved in blood pressure regulation. It appears that in animals kept under physiological conditions, the renal medulla is not necessary for the maintenance of normotension, since its destruction does not usually result in hypertension. However, in animals exposed to hypertensive stimuli, the presence of renomedullary tissue appears to be the key factor in resisting the increase in blood pressure. Evidence is presented to show that inherited or acquired deficiency of renomedullary antihypertensive function may contribute to the development of various forms of hypertension. It is suggested that inherited differences in the antihypertensive capacity of the renal medulla may account for differing sensitivities of various strains of animals to hypertensive stimuli. Finally, data are presented to show that renomedullary deficiency induced by a decrease in renal perfusion pressure, which could be a consequence of hypertensive damage to renal vessels, may contribute to the increase in blood pressure in various forms of hypertension.

Dependence of the hypertensive effect of chronic vanadate administration on renal excretory function in the rat

The effect of vanadate, an agent that in rats exerts potent vasoconstrictor and diuretic action on blood pressure, cardiac output, total peripheral resistance and plasma and extracellular fluid volume, was investigated in normal rats and in rats with diminished renal excretory function. In normal rats, chronic dietary vanadate did not affect blood pressure, but induced an increase in total peripheral resistance and a decrease in cardiac output, plasma and extracellular fluid volume. In rats with diminished renal excretory function, vanadate increased blood pressure and total peripheral resistance without affecting cardiac output, plasma and extracellular fluid volume. The results indicate that this agent, with predominant vasoconstrictor action, does not cause sustained hypertension unless renal excretory function is diminished.

Pulmonary artery pressure in rats with hereditary platelet function defect

Pulmonary vasoactivity of several biochemical components produced or stored in platelet was the justification for the study of pulmonary artery pressure in fawn-hooded rats (FHR) with hereditary platelet storage pool deficiency. Anesthetized (pentobarbital 35 mg kg-1 i.p.) FHR had higher right ventricular systolic pressure compared with normal Wistar rats (NWR) matched in sex and age (57.7 +/- 6.8 vs. 34.8 +/- 1.2 mm Hg; p less than 0.01). The incidence of higher pulmonary artery pressure (greater than means + 2 SD of NWR) was 68% among FHR. A significant difference was recorded between FHR and NWR in the relative weight of the right ventricle (0.092 +/- 0.021 vs. 0.048 +/- 0.001 g/100 g; p less than 0.05). Rise in pulmonary artery pressure in FHR after 4 weeks of normobaric hypoxia was found to be comparable to that seen posthypoxically in NWR. Morphological consequences of pulmonary hypertension, ranging from moderate medial hypertrophy of small arteries to muscularization of pulmonary arterioles, were recorded in about 50% of FHR with increased pulmonary artery pressure.

Ouabain arrhythmogenicity in hypertrophied right and left ventricle of the rat

Susceptibility to the arrhythmogenic action of ouabain was tested in rats with right ventricular hypertrophy, due to experimental chronic hypoxic pulmonary hypertension, and in spontaneously hypertensive (SH) rats with left ventricular hypertrophy. As parameters of arrhythmogenicity the time-duration of infusion of a solution of ouabain (1 g/100 ml), at a rate of 0.7 mg/kg per minute, was measured until the appearance on the ECG of the first premature ventricular contraction, ventricular tachycardia and cardiac arrest. All three effects of digitalis toxicity (premature ventricular contraction, ventricular tachycardia and cardiac arrest) appeared significantly earlier both in rats with right ventricular hypertrophy, due to chronic experimental hypoxic pulmonary hypertension, and in SH rats with hypertrophy of the left ventricle, as compared to the infusion time of the same solution of ouabain needed to elicit the mentioned toxic effects in control rats without ventricular hypertrophy.

Isometric relaxation of hypertrophied right ventricle in rats

In rats with experimental hypertrophy of the right ventricle due to chronic increase in pressure load -dP/dTmax, a parameter of isometric relaxation, is significantly reduced at a stage of impairment of myocardial function at which the parameter of isometric contractility still remains unaffected.

Effect of chronic vanadate administration on pulmonary circulation in the rat

The effect of prolonged dietary vanadate administration on pulmonary hemodynamics was investigated. Rats treated with vanadate for 2 months developed pulmonary hypertension, as indicated by significantly (p less than 0.001) higher mean and systolic right ventricular pressure. Cardiac output was not affected by vanadate administration, while the calculated pulmonary vascular resistance was found to be significantly (p less than 0.05) higher in rats treated with vanadium. Right ventricular hypertrophy was also noted in vanadium-treated animals. Vanadium treatment did not significantly affect systemic circulation. The results indicate that vanadium administration induces pulmonary hypertension.

Hypotensive effect of heparin on experimental chronic pulmonary hypertension in rats

Daily heparin injections (300 mg s.c.) during four weeks of hypoxic exposure resulted in a smaller rise in pulmonary artery pressure as compared with otherwise nontreated rats exposed to the same regimen of hypoxia. Heparin treatment did not significantly affect the systemic arterial pressure of the hypoxic rats. In spite of the different pressure load of the right ventricle after hypoxia in treated and control rats, there was no difference in parameters indicative of the degree of right ventricular hypertrophy between these two groups of hypoxic rats. This finding suggests that the difference in pressure load between the two groups of hypoxic rats occurred late in the course of hypoxic exposure.

Platelets in rats with chronic normobaric hypoxic pulmonary hypertension

A study of the platelet count in rats exposed to normobaric hypoxia for 4 weeks revealed that hypoxia alone, without any change in barometric pressure, considerably reduced the number of thrombocytes. In order to elucidate the mechanism of hypoxic thrombocytopenia, the survival and recovery of 51Cr-labelled platelets were tested. The survival and recovery of platelets from hypoxic rats injected into normoxic recipients were normal. However, when 51Cr-labelled platelets from normoxic rats were injected into a hypoxic recipient, the survival was found to be normal but the recovery of those platelets was lower than in the normal rat. This finding suggests that the reduction of platelet counts in normobaric hypoxia may be due to the platelets' partial sequestration.

Separate and combined use of verapamil, aspirin and captopril in experimental chronic pulmonary hypertension

In Wistar rats, rendered pulmonary hypertensive by chronic confinement in normobaric "hypoxic cages", impairment of transmembrane transport of calcium by Verapamil and blockage of the action of Angiotensin I converting enzyme by Captopril when applied simultaneously did not show an additive effect in reducing the rise of pulmonary artery pressure and decreasing the augmentation of right ventricular mass. Similarly, the action of Verapamil together with decrease of prostaglandin synthetase activity by Aspirin showed no additive effect. Although in this way the results of the present study failed to give substantial support to the idea of the existence of several mediators of hypoxic pulmonary vasoconstriction, they by no means deny this possibility.

Hemodynamic effects of two ergot derivatives in the conscious spontaneously hypertensive rat

The effect of acute and chronic administration of two ergot derivatives, dihydroergosine (DHESN) and ergosinine (ESNN), on blood pressure, heart rate, cardiac output and total peripheral resistance was studied in conscious spontaneously hypertensive rats. Acute administration of either DHESN or ESNN (50-100 micrograms/kg) resulted in prompt and significant (p less than 0.01) decrease of both blood pressure and heart rate, which lasted for more than 12 h. The decrease in blood pressure was due to reduction in total peripheral resistance, as cardiac output remained unchanged. Prolonged treatment (50 micrograms/kg, i.p., every second day for 12 days) with either DHESN or ESNN significantly (p less than 0.01) decreased blood pressure. In chronically treated rats, total peripheral resistance was found to be decreased while no changes in cardiac output and heart rate were observed. The results indicate that both DHESN and ESNN are potent antihypertensive agents, due to their vasodilator effects. The hypotensive effect of DHESN could be partially blocked by haloperidol, but not by yohimbine. Both, DHESN and ESNN antagonized the effect of phenylephrine on blood pressure.

A sex difference in the hemodynamic effects of chronic normobaric hypoxia in rats

The packed cell volume was higher and the increase in systolic pressure in the right ventricle, as an indication of systolic pressure in the pulmonary artery, was smaller in female rats previously exposed for 4 weeks to normobaric hypercapnic hypoxia, as compared to males treated in the same way. Gonadectomy performed in male rats either on the first day of life or after maturation did not have a significant influence on circulatory reaction to chronic normobaric hypoxia. Female rats in permanent estrus and those with ovariectomy had larger posthypoxic hypertrophy of the right ventricle as indicated by higher values for right/left ventricular weight ratio and relative weight of the right ventricle, than untreated controls.

Effects of SQ 14.225, an orally active inhibitor of angiotensin-converting enzyme, on hypoxic pulmonary hypertension and right ventricular hypertrophy in rats

Treatment with SQ 14.225, an inhibitor of the enzyme converting angiotensin I to angiotensin II and lowering of plasma renin activity by dietary salt overload, significantly decreased hypertrophy of the right ventricle in chronically hypoxic rats. The smaller degree of right ventricular hypertrophy registered in hypoxic rats with suppressed activity of the renin-angiotensin system was proportional to the decrease in hypoxic pulmonary hypertension noted in these animals. Lowering of pulmonary hypertension in chronically hypoxic rats by suppression of the renin-angiotensin system is consistent with the idea that angiotensin II may be involved in eliciting hypoxic pulmonary vasoconstriction. Inhibition of converting enzyme also lowered the systemic arterial pressure in hypoxic rats, but this finding could not be taken as evidence for the role of the renin-angiotensin system in homeostatic control of blood pressure in normal animals, since the plasma-renin activity in hypoxic rats is increased and the blood pressure higher than in rats kept under normoxic conditions.

Decreased pulmonary pressor response to acute hypoxia in chronically hypoxic rats

The pulmonary vascular response to an acute hypoxic stimulus was examined in rats which were kept for 4 weeks in a hypoxic environment and compared to that of rats kept in a normoxic environment. To this end, the effects of breathing gas mixtures containing 7, 21 an 100% O2 on right ventricular systolic pressure (RVPs), cardiac output (Q) and calculated pulmonary vascular resistance (PVR) in chronically hypoxic (CH) rats and rats kept in a normoxic environment (N) were examined. During breathing of 21% O2 RVPs, Q, and PVR were all higher in CH than in N rats. Breathing a gas mixture containing 7% O2 had no effect on systemic blood pressure, heart rate or Q, in both CH and N rats. When compared to breathing of 21% O2, the RVP and PVR remained unchanged in CH rats breathing 7% O2, while both variables significantly (p less than 0.01) increased in N rats. The presented data indicate that the reaction of the pulmonary vasculature to an hypoxic challenge is decreased in CH rats.

Effect of isoproterenol on blood pressure and heart rate in different phases of the oestrous cycle

The effects of a beta-adrenergic agonist, 1-isoproterenol, on heart rate and systemic blood pressure were examined in female rats in different phases of the oestrous cycle. In addition, the effect of isoproterenol on the same variables was studied in ovariectomized rats and ovariectomized rats treated with either oestradiol or progesterone. To this end, heart rate and blood pressure were monitored for 10 min after i.v. injection of isoproterenol (80 micrograms/kg). After isoproterenol injection, the heart rate was found to be significantly (p less than 0.05) higher in rats in the prooestrous phase of the cycle than in rats in the metaoestrous phase. Furthermore, isoproterenol induced a significantly (p less than 0.05) greater increase in heart rate in ovariectomized rats treated with oestradiol, than in ovariectomized otherwise nontreated animals or ovariectomized rats treated with progesterone. No difference in blood pressure response to isoproterenol was observed between the groups. The results indicate that oestrogens modify cardiovascular response to a beta-adrenergic stimulator, possibly by affecting beta-adrenergic receptors in the heart.

Role of the renal medulla in the resistance of rats to salt hypertension

The role of the renal medulla in the sensitivity of rats to the hypertensive stimulus of salt overload was investigated in a strain of rats shown to be resistant to salt hypertension. Rats were divided into four groups: I -2/3 nephrectomy (medulla left intact); II - unilateral nephrectomy plus dissection of the medulla of the remaining kidney (UNDRM);III - UNDRM plus renomedullary autotransplantation; IV - UNDRM plus renocortical autotransplantation. Two weeks after surgery all rats were given 1% NaCl solution instead of drinking water, and the blood pressure was measured every week for 6 weeks. The blood pressure, although increased, was significantly lower in groups I and III than in the other two groups throughout the period of salt loading. Renal excretory function was similarly altered in all rats, as indicated by similar plasma creatinine concentrations. The results indicate that antihypertensive activity of the renal medulla may account for the high resistance of the described rat substrain to salt hypertension.

Dynamics of regression of right ventricular hypertrophy in rats with hypoxic pulmonary hypertension

Normobaric hypoxia caused a significant increase in right/left ventricular weight ratio in rats, a reliable indicator of hypertrophy of the right ventricle, already after 1 week of intermittent hypoxic confinement 7 days after termination of a 4-week hypoxic exposure the right/left ventricular weight ratio was significantly lower compared to the values immediately after hypoxic treatment. 8 weeks of sojourning in a normoxic environment were not sufficient to normalize the right ventricular systolic pressure and right/left ventricular weight ratio. It is concluded that changes in the right ventricular mass in rat is a fast reaction to the changes in pressure load.

Plasma renin activity and hypertrophy of the right ventricle in hypoxic rats

A NaCl load in chronically hypoxic rats abolished the increase in plasma renin activity occurring in rats exposed to hypoxia of the same degree and duration but with normal NaCl intake. The parallel reduction in hypoxic hypertrophy of the right ventricle in NaCl-loaded rats could be considered as indirect evidence supporting the view that renin may be involved in the development of heart hypertrophy.

Effects of verapamil and aspirin on experimental chronic hypoxic pulmonary hypertension and right ventricular hypertrophy in rats

Rats made hypoxic by confinement in hypoxic cages for 4 weeks developed pulmonary hypertension and right ventricular hypertrophy. Treatment with Verapamil or aspirin reduced both chronic hypoxic pulmonary hypertension and the hypertrophy of the right ventricle. The antihypertensive effect of Verapamil is explained by the involvement of the transmembrane calcium flux in pulmonary vascular smooth muscle in the hypoxic vasoconstrictory response. Part of the antihypertensive effect of inhibition of prostaglandin synthesis is attributed to a decrease in packed cell volume produced in hypoxic, aspirin treated rats.

The mechanism of renomedullary antihypertensive action: haemodynamic studies in hydronephrotic rats with one-kidney renal-clip hypertension

1. The protective action of the renal medulla was studied in one-kidney renal-clip hypertension in rats with unilateral hereditary hydronephrosis and almost complete atrophy of the medulla of the affected kidney. 2. Rats were unilaterally nephrectomized. The first group had a normal kidney remaining, and the animals from the second and third groups were left with a hydronephrotic kidney and received renomedullary and renocortical autotransplants respectively. Two weeks later all rats were made hypertensive by placing a silver clip (0.2 mm) on the renal artery. 3. From the fourth day after clipping until the end of the experiment blood pressure was found to be significantly (P less than 0.01) lower in rats with medullary transplants than in the other groups. No differences in renal excretory function, plasma volume and plasma renin activity were found between the groups either before or during development of hypertension (5 and 21 days after clipping). Early in the course of hypertension (5 days) cardiac output was significantly (P less than 0.05) lower in the rats with medullary transplants than in the other groups, although an increase in plasma volume was noted in all three groups. At that time no difference in total peripheral resistance was found between the groups. 4. The results are consistent with the hypothesis that the renomedullary antihypertensive substance(s) mitigates hypertension by preventing a hypertensive haemodynamic response to sodium/volume overload.

Resistance of a substrain of Wistar rats to salt hypertension

Male rats of the Wistar substrain, in which 2/3 nephrectomy was performed, did not develop hypertension when placed on a high salt intake, while rats of the Long-Evans substrain become hypertensive under the same conditions. The described substrain of Wistar rats represents a useful experimental model for studying the mechanism of resistance to the hypertensive stimulus of salt overload.