Guanethidine-induced Sympathectomy Research Articles

Maturation of sympathetic neurotransmission in the rat heart. IV. Effects guanethidine-induced sympathectomy on neonatal development of synaptic vesicles, synaptic terminal function and heart growth.

Sympathetic nerve input has been proposed to regulate cardiac growth and differentiation. In the present study, this hypothesis was tested by giving the neurotoxic adrenergic neuron blocking agent, guanethidine (50 mg/kg, s.c.), daily to rats for 21 consecutive days to produce long-term peripheral sympathectomy in neonatal rats. Ontogeny of the sympathetic nerve terminal was measured by the ablity of synaptic vesicle preparations to take up radiolabeled norepinephrine, and heart growth in the sympathectomized animals was monitored by organ weight as well as by RNA and protein synthesis. Guanethidine treatment produced a massive sympathectomy, as synaptic vesicle development was totally arrested; the functional consequence of this treatment was confirmed by the attenuation of chronotropic responses to tyramine, a drug which acts by displacement of norepinephrine from the noradrenergic terminal. Despite the clear-cut effectiveness of guanethidine to prevent formation of functional sympathetic innervation of the heart, no significant alterations in heart growth or RNA and protein synthetic capabilities were observed in the developing rats. These results suggest that the presence of sympathetic innervaton is not obligatory for normal growth of the heart to occur.

Effects of guanethidine-induced sympathectomy on cell proliferation in the progenitive compartments of the neonatal mouse incisor

Treatment of mice with guanethidine sulphate every 48 h from birth until 14 days produced a 64.2 and 68.0 per cent reduction in perikarya of the superior cervical and coeliac ganglia, respectively, at 15 days after birth and 78.9 and 81.3 per cent at 30 days. The growth rate of mice between 21 and 30 days after birth was significantly reduced. At 15 and 30 days after birth, [ 3H]-thymidine was injected into control and sympathectomized mice, and labelling indices for the inner enamel epithelium, outer enamel epithelium, stratum intermedium, stellate reticulum, odontoblasts, and pulp and periodontal ligament fibroblasts determined from autoradiographs. A statistically significant decline in labelling index was found in the inner enamel epithelium, stellate reticulum, and odontoblast cell populations at 30 days as compared to 15 days in controls. Sympathectomized mice demonstrated a significant decline in labelling index in the inner enamel epithelium, stratum intermedium, odontoblasts, and pulp fibroblasts at 30 days as compared to 15 days. The sympathetic nervous system, therefore, has only a minimal role in regulation in incisor eruption and cellular proliferation. The effect of sympathectomy on the stratum intermedium and stellate reticulum may be due to increased tissue pressure resulting from loss of vasoconstrictive sympathetic control.

Crypt cell renewal and chemical sympathectomy in the pre-closure ileum of the neonatal rat.

The present study was designed to analyze the effect of guanethidine-induced sympathectomy on ileal crypt cell proliferation before neonatal closure to macromolecular absorption (pre-closure ileum). The present experiments demonstrated an alteration of the crypt cell generation cycle (T<sub>C</sub>) in the pre-closure ileum (15 days after birth) with guanethidine treatment. Percent labeled mitoses measurements for 15-day-old rats indicated a lengthening of T<sub>C</sub> from 18.1 to 23.0 h with the elongation primarily due to alteration of T<sub>G1</sub> (pre-DNA-synthetic gap period) and T<sub>S</sub> (DNA-synthetic period). Mitotic and labeling indices and the amplitude of the circadian rhythm in mitotic activity were significantly depressed in guanethidine-treated rats.

Pattern of crypt cell proliferation in the pre- and post-closure ileum of the neonatal rat: effects of sympathectomy.

The present experiments were designed to investigate ileal crypt cell division before and after neonatal closure to macromolecular absorption by measurements of mitotic index, labelling index, colchicine-induced estimation of mitotic rate (mitoses/cell/hour) and crypt depth and villus height on postnatal days 15--23. In addition, the effects of the sympathetic nervous system on crypt cell proliferation were analyzed by guanethidine-induced sympathectomy. Guanethidine treatment resulted in at least a 70% reduction in superior cervical and coeliac perikarya at 15 days after birth. All cell proliferative indices demonstrated a rather constant rate of cell division in the ileal epithelium between 15 and 17 days after birth with a sudden burst of mitotic activity on day 18. The mitotic rate of control rats increased from day 18 to 23 with 3-week-old rat demonstrating a faster rate of ileal crypt cell proliferation than adult rats. The ileal crypt depth more than doubled between 15 and 23 days while the height of the villus column increased slowly but steadily (36%) during the period of this study. Cell division is inhibited by guanethidine-induced sympathectomy although there is still an acceleration of mitosis in the post-closure period. The relationship of sympathectomy and ileal crypt cell proliferation is discussed and compared to hormonal effects on closure and related developmental events.

Unique resistance to guanethidine-induced chemical sympathectomy of spontaneously hypertensive rats: a resistance overcome by treatment with antibody to nerve growth factor.

The chronic administration of high doses of guanethidine to rats produces complete destruction of the peripheral sympathetic nervous system. In a study of the effect of guanethidine-induced sympathectomy on the development of hypertension is spontaneous hypertensive rats (SHR, Okomoto strain), only a partial sympathectomy could be produced as assessed by biochemical parameters (tyrosine hydroxylase activity in ganglia and tissue norepinephrine concentrations) and by evaluation of response to stimulation of vasomotor outflow in pithed rat preparations. Other strains of rats (Sprague-Dawley, American Wistar, Kyoto Wistar) were uniformly sensitive to guanethidine sympathectomy. The resistance to guanethidine was not due to a lower accumulation of guanethidine in the neurons of SHR. Addition to the guanethidine treatment of low doses of antibody to nerve growth factor (NGF), which itself produced only a modest sympathectomy, resulted in an almost complete sympathectomy. SHR did not become hypertensive when sympathectomized by combined guanethidine-anti NGF. These results show that the sympathetic neurons of SHR differ from those of other strains with respect to sensitivity to guanethidine cytotoxicity and suggest the possibility of a role for NGF in that altered responsiveness.

Reinnervation following guanethidine-induced sympathectomy of adult rats

The reinnervation of various tissues by autonomic neurons has been studied in adult rats which had been sympathectomized by chronic guanethidine treatment (30 or 60 mg/kg/day for 8--15 weeks). In the heart, iris, ileum, mesentery, vas deferens and epididymis, fluorescence histochemistry reveals an almost complete disappearance of adrenergic fibres which is very longlasting. Even after 63 weeks few fluorescent fibres can be seen in these tissues and the density of innervation is not increased by incubation in alpha-methylnoradrenaline. The superior cervical ganglion represents an exception; large numbers of fluorescent fibres but few fluorescent ganglion cells were apparent during recovery. Axon counts carried out by electron microscopy on the vas deferens showed that after recovery for one year the number of axons was similar to that of controls; however, the pattern of innervation was abnormal, small granular vesicles were rarely seen and there was little uptake of 5-hydroxydopamine. On the basis of this evidence and of some pharmacological data it is suggested that there is a limited reinnervation by adrenergic axons accompanied by a great increase in the number of non-adrenergic, possibly cholinergic, axons.

Analysis of intestinal cell proliferation after guanethidine-induced sympathectomy. I. Stathmokinetic, labelling index, mitotic index, and cellular migration studies.

Guanethidine-induced sympathectomy in the rat during the neonatal period (injection of 20 microgram/g body weight every 48 h from day of birth until day 14) produces an absolute reduction in the number of sympathetic ganglion cells, but no significant alteration of body weight. Superior cervical ganglia show 79.8% fewer cell bodies at 15 days and 92.3% at 45 days; coeliac ganglia exhibit an 81.0% reduction at 15 days and 89.6% at 45 days in guanethidine-treated rats as compared to normal controls. The sympathetic ganglion cells that remain after treatment have an abnormal morphological appearance with distended mitochondria and depletion of endoplasmic reticulum. Sympathectomy produces a prolongation of the generation cycle time (Tc) as measured by the colchicine-induced mitotic arrest technique, and a decrease in labelling, mitotic, and migration indices. In addition, sympathectomy suppresses the amplitude of the circadian rhythm in mitotic activity. The general suppression of this activity in the intestinal epithelium is more pronounced in the jejunum and ileum than in the duodenum. Variation in the effectiveness of sympathectomy on the inhibition of intestinal cell proliferation may be related to segmental differences in cell proliferation, to segmental differences in innervation, and/or to segmental variation in the effectiveness of guanethidine.