Trophic action of sympathetic nerves reduces arterial smooth muscle Ca(2+) sensitivity during early post-natal development in rats.

AIM: A decrease in the Ca(2+) sensitivity of smooth muscle contraction is a hallmark of functional remodelling of blood vessels during development. However, the responsible factors are largely unknown. Here, we tested the hypothesis that the post-natal decline of arterial Ca(2+) sensitivity is the result of trophic effects of sympathetic nerves. METHODS: Contractile responses, intracellular Ca(2+) levels and protein expression profiles were compared in saphenous arteries from young (1- and 2-week-old) and adult rats using wire myography, Ca(2+) fluorimetry and Western blotting respectively. RESULTS: We observed a lower Ca(2+) sensitivity of contractions induced by methoxamine, an agonist of α1 -adrenoceptors, and U46619, an agonist of thromboxane A2 receptors, in arteries from adult as compared to young animals. Post-natal maturation was associated with stronger expression of regulatory proteins mediating Ca(2+) -dependent contraction (myosin light chain kinase (MLCK), myosin targeting subunit (MYPT1) and h-caldesmon) and weaker expression of proteins regulating Ca(2+) -independent contraction (Rho kinase, extracellular-regulated kinases (ERK1/2) and mitogen-activated protein kinases p38 MAPK) in vessels from adult rats. To eliminate the trophic action of sympathetic nerves, we performed lumbar sympathectomy in adult rats. This resulted in higher Ca(2+) sensitivity of agonist-induced contractions in denervated as compared to control arteries. Furthermore, denervated arteries contained less MLCK, MYPT1 and h-caldesmon and more ERK1/2 and p38 MAPK. CONCLUSIONS: Sympathetic denervation reverses developmental changes both in Ca(2+) sensitivity and in the expression of regulatory proteins back to the early post-natal phenotype in the rat saphenous artery. We conclude that trophic effects of sympathetic nerves govern functional remodelling of arteries during early post-natal development.

Effects of chronic hypotension on the adrenergic nervous plexus of the saphenous artery in rats and its regeneration after femoral nerve injury.

The effects of chronic hypotension on the density and intensity of fluorescence (after treatment with glyoxylic acid) of the plexus of adrenergic fibers in the wall of the saphenous artery and on the reinnervation of this vessel were studied in Wistar rats. Regional hypotension in the vascular bed of the hind part of the rats' bodies was induced by stenosis of the abdominal part of the aorta distal to the renal arteries. After four weeks, the saphenous artery was denervated in one limb by resection of a segment of the femoral nerve. In the limb with the nerve lesion, chronic (6-7 weeks) hypotension led to a reduction in the intensity of nerve fiber fluorescence by 20% as compared with normotensive animals (controls), though the density of the nerve plexus did not change. Partial reinnervation of the vessel was observed 2-3 weeks after femoral nerve lesioning. Measures of reinnervation in normotensive and hypotensive rats were no different at two weeks, though at three weeks rats with hypotension showed more complete recovery of innervation.

[Effect of chronic hypotension on the adrenergic nerve plexus of the rat a. saphena and on its regeneration after femoral nerve injury].

The influence of chronic hypotension on density and fluorescence intensity (after glyoxylic acid treatment) of periarterial plexus of nerve fibers in saphenous artery wall and on reinnervation of this vessel was studied in Wistar rats. Regional hypotension in the rat hindquarters vascular system was created by partial occlusion of abdominal aorta distally to the renal arteries. Four weeks later, the segment of femoral nerve was resected in one of the limbs to denervate the saphenous artery. In the limb with intact nerve, chronic (6-7 weeks-long) hypotension resulted in 20% decrease of fluorescence intensity of nerve fibers, as compared to that one in normotensive (control) rats, however the density of the nerve plexus did not change. Partial reinnervation of the vessel occurred in 2-3 weeks after femoral nerve injury. After 2 weeks parameters of reinnervation were similar in hypotensive and normotensive rats, but after 3 weeks hypotensive rats demonstrated more complete restoration of the innervation.

[Elevation of the vascular smooth muscle sensitivity to effects of constrictors after denervation and under decreased blood pressure].

Changes in contractile activity of saphenous artery in normotensive rats and in rats with regional hypotension have been investigated. The abdominal aorta was partially occluded in Wistar rats distally to the renal arteries. Four weeks later, a 5-7-mm segment of the femoral nerve in one hindlimb was resected to denervate the saphenous artery. After two weeks, the isometric contraction of innervated and denervated saphenous artery segments was studied. In normotensive rats, the denervation augmented vessel sensitivity to noradrenaline, phenylephrine, serotonin, and KCl (in the presence of phentolamine). Chronic hypotension also augmented vessel sensitivity to constrictor agonists, whereas denervation did not result in further increase of sensitivity. In glyoxilic acid-stained preparations obtained from hypotensive rats, a reduced intensity of fluorescence of adrenergic fibers was observed. It was assumed that the higher sensitivity of vascular smooth muscle in hypotensive rats is due to functional disturbances of sympathetic innervation.