Captopril attenuates proteosynthesis in the aorta and decreases endothelaemia in rabbits with aortic insufficiency

The effect of the angiotensin converting enzyme (ACE) inhibitor, captopril, on proteosynthesis in the aorta, acetylcholine-stimulated aortic relaxation and endothelaemia (circulating endothelial cells) was investigated in rabbits with aortic insufficiency. The animals were studied 28 days after experimental intervention. Cardiac volume overload stimulated proteosynthesis in the aorta as reflected by increased ribonucleic acid (RNA) concentration and [14C] leucine incorporation into proteins of the aorta. Moreover, the number of endothelial cells in the blood was increased. The administration of captopril starting from the second day of the haemodynamic overload, partially prevented the increase both in aortic proteosynthesis and in endothelaemia. Despite these alterations, the relaxing ability of the aorta to acetylcholine was not changed either by the haemodynamic overload or by captopril. We conclude that the increase of proteosynthesis in the aorta and of endothelaemia in the early period of chronic cardiac volume overload in rabbits were partially prevented by chronic captopril treatment. Neither aortic insufficiency nor captopril changed the acetylcholine-induced relaxation of the aorta.

The effect of ambroxol on the vascular reactivity in the rabbit

Experiments were designed to determine whether ambroxol, a drug used for the treatment of respiratory disorders, affects the basal tension and/or contractions due to adrenergic stimuli in the isolated rabbit portal vein and pulmonary artery. Ambroxol in concentrations of 10(-6)-10(-4) mol/l produced a concentration-dependent increase in basal tension, but a decrease in spontaneous mechanical activity of portal vein. The same concentrations of ambroxol failed to influence basal tension of pulmonary artery. However, when the vessel tone was increased by exogenous noradrenaline, ambroxol elicited concentration-dependent contractions also in this vessel. Moreover, ambroxol in the concentration of 10(-5) mol/l significantly enhanced vascular contractions due to both exo- and endogenous noradrenaline. The results suggest that ambroxol, in biologically relevant concentrations, may influence or even induce vascular contractions to adrenergic stimuli. Their expression, however, depend on the type of vascular smooth muscle. (Fig. 7, Ref. 25.)

Restriction of nitric oxide rather than elevated blood pressure is responsible for alterations of vascular responses in nitric oxide-deficient hypertension

The responsiveness of isolated high-pressure (aorta, renal artery) and low-pressure vessels (pulmonary artery) was compared during systemic hypertension induced by chronic inhibition of nitric oxide synthesis by NG-nitro-L-arginine methyl ester (L-NAME) in rats. L-NAME (40 mg/kg/day) was given to animals in their drinking water. After 4 weeks of L-NAME treatment, systolic blood pressure increased by 37% as compared with that in the control group. Chronic L-NAME treatment resulted in significant reduction of endothelium-dependent relaxation to acetylcholine (10(-8) to 3 x 10(-6) mol/l) in both types of vessels. The reduced relaxation was not influenced by acute pretreatment with indomethacin (10(-5) mol/l), however, it was further reduced by acute pretreatment with additional L-NAME (10(-4) mol/l). L-arginine (10(-4) mol/l) improved the reduced relaxation. Endothelium-independent relaxation to sodium nitroprusside (10(-9) to 10(-6) mol/l) was unaffected by L-NAME treatment. beta-adrenoceptor-mediated relaxation to isoprenaline (10(-8) to 3 x 10(-6) mol/l) was also not influenced by chronic L-NAME treatment. Similar alterations in the responsiveness of high- and low-pressure vessels indicate rather the decisive role of nitric oxide restriction than that of elevated blood pressure in their development.

Remodelling and functional alterations of the rabbit coronary artery in volume overloaded heart

OBJECTIVE

The aim was to study the contractility of the conduit coronary artery to vasoactive agents in developing and established volume overload cardiac hypertrophy and to compare it with structural alterations in the artery.

METHODS

Aortic valve insufficiency in rabbits was used to produce a volume overloaded heart. One month (developing hypertrophy), and four months (stabilised hypertrophy) after inducing aortic insufficiency, the isometric contraction of the coronary artery to acetylcholine, serotonin, and potassium chloride was recorded. For transmission electron microscopy, the coronary arteries were perfused via the ascending aorta with glutaraldehyde fixative under constant pressure. The point counting method was used for quantitative evaluation. Semithin sections were used to determine the geometry (ie, the inner diameter and wall thickness) of the coronary artery by light microscopy.

RESULTS

A significant increase in heart weight and heart weight to body weight ratio was found after one month and four months of volume overload. Concentration-response relations of the coronary artery to all three agents were shifted to the right; in developing hypertrophy the shift was non-significant, in stabilised hypertrophy it was significant. The contractions were weakened by up to one fifth of the control values. An associated increase in wall thickness of the coronary artery was found, due to a significant expansion of the intercellular space. The internal diameter did not change significantly. Ultrastructural findings (an increase of the area occupied by organelles in myocytes) suggested a transition from "contractile" to more "synthetic" type of smooth muscle cells.

CONCLUSIONS

In cardiac hypertrophy due to volume overload, the structure of the coronary arteries reflects the long term haemodynamic alterations, particularly through an increase in the non-cellular component. In parallel, the contraction efficiency to vasoactive drugs decreases markedly.

Contractility of the rabbit abdominal aorta 4 days after endothelium denudation

The purpose of this study was to evaluate contractility of the rabbit abdominal aorta 4 days after de-endothelialization by balloon catheter. The isometric tension of ring-segments in response to vasoactive agents was monitored. A significant enhancement of contraction to noradrenaline and serotonin was found in aortas 4 days after endothelium denudation as compared with controls with endothelium. The enhancement, however, did not differ from that found already in acutely denuded vessels (immediate denudation). No significant difference in contractility to potassium chloride was found in either group of denuded preparations as compared with controls. The sensitivity to all three vasoactive agents (EC50) was not influenced by denudation. These results indicate that changes in the contractility of denuded vessels are predominantly a consequence of lacking the endothelium as a producer of endothelium-derived relaxing factor. The access of mitogens to the media does not seem to interfere with the magnitude of contraction 4 days after denudation.

[The effect of cadmium on neuromuscular transmission in rabbit blood vessels]

Influence of cadmium on contractions of isolated v.portae of a rabbit, elicited by transmural nerve stimulation and by exogene norepinephrine, has been studied. Low concentrations of cadmium (10(-6) mol/l) potentiated contractions of the vessels in response to transmural nerve stimulation but they did not influence the magnitude of response to norepinephrine. Higher concentrations of cadmium (10(-5) - 10(-4) mol/l) inhibited contractions of v.portae elicited by both adrenergic stimuli. The results indicate that the effect of cadmium on contractions induced by transmural nerve stimulation is realized predominantly pre-synaptically, probably by influence on homeostasis of calcium in the nerve ending. Potentiation of responses of v.portae indicates a mechanism by which ions of cadmium could contribute to the development of hypertension.