Guanethidine Research Articles

Bone mass loss in chronic heart failure is associated with sympathetic nerve activation.

Chronic heart failure causes osteoporosis, but the mechanism remains unclear. The sympathetic nerve plays an important role in both bone metabolism and cardiovascular function. Thirty-six adult male SD rats were randomly divided into the following four groups: sham surgery (Sham) group, guanethidine (GD) group, abdominal transverse aorta coarctation-induced heart failure+normal saline (TAC) group, and TAC+guanethidine (TAC+GD) group. Normal saline (0.9% NaCl) or guanethidine (40mg/kg/ml) was intraperitoneally injected daily for 5weeks. Then, DXA, micro-CT, ELISA and RT-PCR analyses were performed 12weeks after treatment. The bone loss in rats subjected to TAC-induced chronic heart failure and chemical sympathectomy with guanethidine was increased. Serum norepinephrine levels were increased in rats with TAC-induced heart failure but were decreased in TAC-induced heart failure rats treated with guanethidine. The expression of α2A adrenergic receptor, α2C adrenergic receptor, osteoprotegerin (OPG), and osteocalcin in the tibia decreased in the TAC-induced heart failure group, and the expression of β1 adrenergic receptor, β2 adrenergic receptor, receptor activator of nuclear factor-κ B ligand (RANKL), and RANKL/OPG in the tibia increased in the heart failure group. In addition, these changes in gene expression levels were rescued by chemical sympathectomy with guanethidine. TAC-induced chronic heart failure is associated with bone mass loss, and the sympathetic nerve plays a significant role in heart failure-related bone mass loss. The present study supports the hypothesis that heart failure is related to bone loss, and the excessive activation of sympathetic nerves participates in this pathophysiological process. The present study suggests a potential pathological mechanism of osteoporosis associated with heart failure and new perspectives for developing strategies for heart failure-related bone loss.

Sympathectomy Effects on Intra-Abdominal Organ Catecholamine Levels in a Streptozotocin-Induced Diabetic Rat Model.

Diabetes mellitus (DM) is a metabolic disorder whose prevalence has continuously increased worldwide and is associated with dysfunction of the autonomic nervous system and, in particular, that of the sympathetic nervous system (SNS). The objective of this study was to analyze the interaction of DM and the SNS, building a model of sympathectomized diabetic rats to determine alterations in the content of CA (catecholamines) in different intra-abdominal organs. Sympathectomy was conducted with guanethidine (GNT). Additionally, DM was induced with STZ (Streptozotocin). Treatment with GNT decreased norepinephrine (NE) content in all analyzed tissues, with significant differences found in the paraganglia, liver, pancreas, duodenum, and heart compared to the control group. With respect to epinephrine (E), which was only found in the liver, pancreas, and heart, presenting significant differences (p < 0.05) in the heart, a decrease in its concentration was observed for all of the experimental groups with respect to the control. The decrease in dopamine (DA) content due to the GNT-STZ treatment was 30.1% in the heart with respect to the diabetic (STZ) group. The amount of CA in the adrenal medulla indicates the effect of sympathectomy on the GNT group where there was a significant reduction (p < 0.05) of DA. These findings suggest that the elimination of the sympathetic nervous system in diabetic organisms contributed to a decrease in blood glucose; likewise, an alteration in the levels of CA was observed in the different selected organs, possibly attributed to the severity, duration, and pathogenesis of the complications of acute and chronic DM.

The Influence of an Adrenergic Antagonist Guanethidine (GUA) on the Distribution Pattern and Chemical Coding of Dorsal Root Ganglia (DRG) Neurons Supplying the Porcine Urinary Bladder.

Although guanethidine (GUA) was used in the past as a drug to suppress hyperactivity of the sympathetic nerve fibers, there are no available data concerning the possible action of this substance on the sensory component of the peripheral nervous system supplying the urinary bladder. Thus, the present study was aimed at disclosing the influence of intravesically instilled GUA on the distribution, relative frequency, and chemical coding of dorsal root ganglion neurons associated with the porcine urinary bladder. The investigated sensory neurons were visualized with a retrograde tracing method using Fast Blue (FB), while their chemical profile was disclosed with single-labeling immunohistochemistry using antibodies against substance P (SP), calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase activating polypeptide (PACAP), galanin (GAL), neuronal nitric oxide synthase (nNOS), somatostatin (SOM), and calbindin (CB). After GUA treatment, a slight decrease in the number of FB+ neurons containing SP was observed when compared with untreated animals (34.6 ± 6.5% vs. 45.6 ± 1.3%), while the number of retrogradely traced cells immunolabeled for GAL, nNOS, and CB distinctly increased (12.3 ± 1.0% vs. 7.4 ± 0.6%, 11.9 ± 0.6% vs. 5.4 ± 0.5% and 8.6 ± 0.5% vs. 2.7 ± 0.4%, respectively). However, administration of GUA did not change the number of FB+ neurons containing CGRP, PACAP, or SOM. The present study provides evidence that GUA significantly modifies the sensory innervation of the porcine urinary bladder wall and thus may be considered a potential tool for studying the plasticity of this subdivision of the bladder innervation.

The Influence of an Adrenergic Antagonist Guanethidine on the Distribution Pattern and Chemical Coding of Caudal Mesenteric Ganglion Perikarya and Their Axons Supplying the Porcine Bladder.

This study was aimed at disclosing the influence of intravesically instilled guanethidine (GUA) on the distribution, relative frequency and chemical coding of both the urinary bladder intramural sympathetic nerve fibers and their parent cell bodies in the caudal mesenteric ganglion (CaMG) in juvenile female pigs. GUA instillation led to a profound decrease in the number of perivascular nerve terminals. Furthermore, the chemical profile of the perivascular innervation within the treated bladder also distinctly changed, as most of axons became somatostatin-immunoreactive (SOM-IR), while in the control animals they were found to be neuropeptide Y (NPY)-positive. Intravesical treatment with GUA led not only to a significant decrease in the number of bladder-projecting tyrosine hydroxylase (TH) CaMG somata (94.3 ± 1.8% vs. 73.3 ± 1.4%; control vs. GUA-treated pigs), but simultaneously resulted in the rearrangement of their co-transmitters repertoire, causing a distinct decrease in the number of TH+/NPY+ (89.6 ± 0.7% vs. 27.8 ± 0.9%) cell bodies and an increase in the number of SOM-(3.6 ± 0.4% vs. 68.7 ± 1.9%), calbindin-(CB; 2.06 ± 0.2% vs. 9.1 ± 1.2%) or galanin-containing (GAL; 1.6 ± 0.3% vs. 28.2 ± 1.3%) somata. The present study provides evidence that GUA significantly modifies the sympathetic innervation of the porcine urinary bladder wall, and thus may be considered a potential tool for studying the plasticity of this subdivision of the bladder innervation.

Role of Calcitonin Gene-Related Peptide in Cooling-Induced Hemodynamic Perturbations in Rats: Investigation by Spectrum Analysis

Calcitonin gene-related peptide (CGRP) and its receptors are widely distributed in the nervous and cardiovascular systems as a potent vasodilator; however, the underlying mechanisms of action of CGRP on cardiovascular regulation, such as cooling-elicited hemodynamic perturbation (CEHP), are still unclear. We used spectral and crossspectral analyses to explore such questions in this study. Conscious rats were pretreated with the CGRP antagonist CGRP_(8-37)-only, or following the removal of sympathetic influences using hexamethonium (HEX) or guanethidine (GUA) and then subjected the treated rats to a stressful cooling trial (CS). Cardiovascular indices were monitored via an implanted telemetric device throughout the experiment. The analyses included measurements of blood pressure (BP), heart rate (HR), cardiovascular variabilities (BPV, HRV), coherence linkage at very-low, low and high frequency regions (VLF: 0.02 to 0.2 Hz, LF: 0.2 to 0.6 Hz, and HF: 0.6 to 3.0 Hz), and dicrotic notch (Dn). Key findings of the hemodynamic indices and spectral changes in efferent sympathetic oscillations (LF) and myogenic oscillations (VLF) in comparison with the control vehicle were demonstrated: (I) under resting condition, CGRP_(8-37)- only increased the BP, HR and powers of VLF_(BPV), LF_(BPV). In contrast, the effects of CGRP_(8-37)-only were generally diminished or further reduced when the rats were pretreated with HEX or GUA. (II) Under CS condition, CGRP_(8-37)-only increased the HR but attenuated the power of LF_(BPV), converted the negative correlation (NC) into positive correlation (PC) for VLF_(HRV) with VLF_(BPV) (VLF pair) and LF_(HRV) with LF_(BPV) (LF pair). On the other hand, when pretreated with sympathetic removals, both HEX+CGRP_(8-37) and GUA+CGRP_(8-37) generally abolished the control coolinginduced pressor and tachycardia, attenuated or further reduced the effects of CGRP_(8-37)-only on VLF_(BPV), VLF_(HRV) and LF_(BPV). In addition, HEX+CGRP_(8-37) generally persisted the CGRP_(8-37)-only effect of PC for VLF and LF pairs, but GUA reversed the PC of VLF pair back to a NC tendency. Furthermore, cross-spectral analyses indicated that throughout the experiment, CGRP8-37-only enhanced the coherence linkage between BPV and HRV at the LF region but weakened that at the HF region. HEX+CGRP_(8-37) abolished the CGRP_(8-37)-only effect on the LF region but GUA+CGRP_(8-37) persisted the CGRP_(8-37)-only effects. Taken together, our results indicate that CGRP is dependent on the status of intrinsic sympathetic tonus to exert its function on cardiovascular regulation.

Role of Efferent Sympathoadrenal Effects in Cooling-Induced Hemodynamic Perturbations in Rats: An Investigation by Spectrum Analysis.

Cold stress may produce hemodynamic perturbations but the underlying mechanisms are still not clear. Spectral analysis was used in this study to explore that sympathoadrenal activation could be involved in mechanisms of hemodynamic perturbations to cooling. Conscious rats after treatment with a control vehicle (saline) compared with withdrawal of sympathetic influences by ganglion blocker hexamethonium (HEX) or chemical sympathectomy guanethidine (GUA) were challenged by stressful cooling as acute immersing all four extremities in ice water (4 ± 2°C) for 10 min. Plasma nitric oxide (NO) and the appearance of Dichroitic notch (DN) were measured in comparison between treatment groups throughout the experimental course. Hemodynamic indices were telemetrically monitored, and variability of blood pressure and heart rate (BPV; HRV) were assessed over a range of frequencies: very-low frequency (VLF: 0.02-0.2 Hz), low frequency (LF: 0.2-0.6 Hz), high frequency (HF: 0.6-3 Hz), normalized (n)LF, nHF, ratio LF/HF of HRV (LF/HF(HRV)), and total power (TP: ≤3 Hz). Results showed that the concomitant reciprocal changes of spectral powers existed between frequencies of BPV and HRV to the stressful cooling (i.e. VLF(BPV) versus VLF(HRV), LF(BPV) versus LF(HRV), and nLF(BPV) versus nLF(HRV)) which contribute to the underlying mechanisms of sympathetic efferent influences and myogenic cardiovascular responsiveness. Furthermore, compared with the control vehicle in the stressful cooling, HEX restrained the increase of the pressor, tachycardia and VLF(BPV), except that VLF(HRV) was reduced. GUA abolished pressor, however, restrained the increase of the tachycardia, VLF(BPV) and LF(BPV). In addition, GUA reversed the downward tendency of nLF(BPV) into an upward tendency and attenuated both nLF(HRV) and LF/HF(HRV). DN was virtually undetectable after HEX management but was apparently noticeable after GUA management. Finally, the increase of plasma NO after cooling was diminished after HEX or GUA management. Taken together, these results substantiate that the spectral changes during stressful cooling are highly relevant to the efferent sympathetic rhythmicity and subsequent NO production.

Role of Beta-Adrenoceptors in Cooling-Evoked Hemodynamic Perturbations of Rats: Investigation by Spectral Analysis

Aim: Rapid immersion of a rat’s limbs into 4°C water, a model of cooling stress (CS), can elicit hemodynamic perturbations (CEHP). We have reported that CEHP is highly relevant to the sympathetic activation. This study identifies the role of β-adrenoceptors in CEHP. Method: Conscious rats were pretreated with the β-adrenoceptor blockade propranolol, (PRO)-only, or following the removal of sympathetic influences using hexamethonium (HEX) or guanethidine (GUA), and then they were subjected to a 10-min CS trial. Cardiovascular indices were monitored via an implanted telemetric device throughout the experimental course. The analyses included measurements of systolic blood pressure (SBP); heart rate (HR); cardiovascular variability (BPV; HRV); spectral coherence at very-low, low, and high frequency regions (VLF: 0.02-0.2 Hz, LF: 0.2-0.6 Hz, and HF: 0.6-3.0 Hz); total power (TP); and dicrotic notch (Dn). Results: Compared with the vehicle control under the resting (PreCS) and CS conditions respectively, the PROonly (a) increased the powers for VLFBPV, LFBPV, HFBPV, HFHRV, and TPBPV but decreased the power for VLFHRV, the LF/ HF ratio, the Dn under PreCS; (b) increased the powers for LFHRV, HFHRV, and TPHRV, decreased the powers for LFBPV, HFBPV, and TPBPV, the LF/HF ratio, and the Dn, and converted the original negative correlation into positive correlation for VLFHRV with VLFBPV under CS; and (c) weakened the spectral coherence at all frequency regions between BPV and HRV throughout the experimental course. Compared with the control vehicle under PreCS and CS, there were more decreases of SBP (under CS) and HR (under PreCS and CS) after the GUA+PRO than the other interventions (PROonly and/or HEX+PRO). In addition, the effect on spectral powers of the PRO-only was generally altered when the rats were pretreated with HEX or GUA throughout the experimental course. Significance: Our findings suggest that PRO may exert vascular effects which are dependent on the sympathetic vasodilator tone. Intact sympathetic efferent pathways are required for the inhibition of CEHP by PRO. Besides, the effects of HEX+PRO versus GUA+PRO indicate a functional role of adrenal medulla to release epinephrine to react the cooling stress.

Evidence for the involvement of peripheral β-adrenoceptors in delayed liquid gastric emptying induced by dipyrone, 4-aminoantipyrine, and antipyrine in rats

Dipyrone (Dp), 4-aminoantipyrine (AA), and antipyrine (At) delay liquid gastric emptying (GE) in rats. We evaluated adrenergic participation in this phenomenon in a study in male Wistar rats (250-300 g) pretreated subcutaneously with guanethidine (GUA), 100 mg·kg−1·day−1, or vehicle (V) for 2 days before experimental treatments. Other groups of animals were pretreated intravenously (iv) 15 min before treatment with V, prazosin (PRA; 1 mg/kg), yohimbine (YOH; 3 mg/kg), or propranolol (PRO; 4 mg/kg), or with intracerebroventricular (icv) administration of 25 µg PRO or V. The groups were treated iv with saline or with 240 µmol/kg Dp, AA, or At. GE was determined 10 min later by measuring the percentage of gastric retention (%GR) of saline labeled with phenol red 10 min after gavage. %GR (mean±SE, n=8) indicated that GUA abolished the effect of Dp (GUA vs V=31.7±1.6 vs 47.1±2.3%) and of At (33.2±2.3 vs 54.7±3.6%) on GE and significantly reduced the effect of AA (48.1±3.2 vs 67.2±3.1%). PRA and YOH did not modify the effect of the drugs. %GR (mean±SE, n=8) indicated that iv, but not icv, PRO abolished the effect of Dp (PRO vs V=29.1±1.7 vs 46.9±2.7%) and At (30.5±1.7 vs 49±3.2%) and significantly reduced the effect of AA (48.4±2.6 vs 59.5±3.1%). These data suggest activation of peripheral β-adrenoceptors in the delayed GE induced by phenylpyrazolone derivatives.

TCT-441: Peri-adventitial Renal Artery Delivery of Guanethidine Monosulfate Attenuates Renal Nerve Function: Preclinical Experience and Implication for Resistant Hypertension

TCT-441: Peri-adventitial Renal Artery Delivery of Guanethidine Monosulfate Attenuates Renal Nerve Function: Preclinical Experience and Implication for Resistant Hypertension

The Development of a Sensitive High-performance Liquid Chromatographic Method for the Analysis of Guanethidine*

A rapid and sensitive HPLC method has been developed for the quantitative analysis of guanethidine and N-oxide in biological fluids. A reverse-phase HPLC method was employed, using an ODS stationary phase, with 55% 0·15 M HCl and 45% methanol as mobile phase. The guanidino compounds were derivatized by reaction with 9,10-phenanthraquinone and detected by UV spectrophotometry at 320 nm. Sensitivity to 3 μg mL−1 was demonstrated. We believe this to be the first reported method to employ UV detection for the analysis of guanethidine.

Neuronal Control of Salt Sensitivity: Role of Sensory and Sympathetic Nerves

18 Neonatal degeneration of capsaicin-sensitive sensory nerves renders a rat responsive to a salt load with an increase in blood pressure and a decrease in natriuretic response (Wang, et al, Hypertension 1998;32:649-653). To test the hypothesis that the sympathetic nervous system contributes to the development of salt sensitive hypertension induced by sensory denervation, newborn Wistar rats were given 50mg/kg capsaicin and/or 80mg/kg guanethidine s.c.. Control rats were treated with vehicle. After the weaning period, male rats were grouped as the following and given high sodium diet (4%) for 2 weeks: capsaicin and guanethidine co-administration (CAP-GUA), capsaicin only (CAP), guanethidine only (GUA), and vehicle control (CON). Norepinephrine concentrations in the atrium were significantly lower in CAP-GUA and GUA than in CON rats (p

Structural changes and in situ aortic pressure-diameter relationship in long-term chemical-sympathectomized rats.

This study determined the effects of long-term chemical sympathectomy with guanethidine (GN) on the mechanical properties and composition of the distal abdominal aorta in Wistar rats. GN was daily administered for 3 mo (3M-GN, from 1 to 12 wk), 5 wk (5W-GN, from 7 to 12 wk), and 8 days (8D-GN, from 11 to 12 wk). All experiments were performed at 12 wk of age to avoid age differences at examination. We used a high-resolution echo-tracking system to determine in situ, in the systolic-diastolic range, the aortic diameter-, compliance-, and distensibility-pressure curves in anesthetized rats. We observed an equivalent significant fall in the tyramine pressor response in all conscious GN-treated rats. Blood pressure was not affected by sympathectomy after 8 days and 5 wk of treatment but was significantly reduced in 3M-GN rats. Chronic sympathetic denervation increased aortic diameter and compliance in 8D-GN rats, compared with those obtained at the same distending pressure in control rats, suggesting vascular smooth muscle relaxation. In contrast, in 5W-GN and 3M-GN rats, the distensibility pressure-curves were significantly shifted toward lower levels of distensibility and pressure, indicating a decreased aortic distensibility at the same level of arterial pressure. Sympathectomy produced a significant reduction in the content of elastin, one of the most distensible components of the arterial wall in 5W-GN and 3M-GN rats. These results suggest that intact sympathetic nerves are necessary to maintain normal functional and structural properties of large arteries in rat. The reduction in aortic distensibility, in long-term sympathectomized rats, could have resulted from complex interactions between local aortic denervation, change in the set point of distending pressure, and changes in aortic smooth muscle tone and/or wall composition.

Effects of nitric oxide on human and canine prostates

Objectives To determine whether nitric oxide (NO) is a mediator of prostatic smooth muscle activity. Methods Pharmacologic experiments using electrical field stimulation (EFS) were performed on strips of human and canine prostate. Results EFS alone elicited frequency-dependent contractions in preparations of human and canine prostates. The greatest contractile activity was achieved at 30 Hz. In the presence of 10 −5 M guanethidine (GUA) and 2 × 10 −1 M atropine (ATR), EFS elicited relaxation of canine prostate strips relative to baseline tension. A weak biphasic response consisting of initial relaxation and subsequent contraction relative to baseline tension was observed in the human prostate strips exposed to similar conditions. The smooth muscle activity observed in the presence of GUA plus ATR was attributed to nonadrenergic, noncholinergic (NANC) nerve transmission. 10 −4 M L-N G-nitroarginine methylester (NAME) significantly increased EFS-elicited NANC smooth muscle activity both in human and canine prostates. L-arginine, 10 −2 M, reversed the effect of L-NAME in human and canine prostates. Sodium nitroprusside, 10 −4 M, a donor of NO, caused relaxation of both human and canine prostates. The mean magnitude of the relaxant response/cross-sectional area in human prostate (2.64 ± 0.4 g/cm 2) was significantly greater than in the canine prostate (1.09 ± 0.17 g/cm 2) ( P < 0.005). Conclusions These results provide compelling evidence that NO plays a role in mediating contractile function of human and canine prostates.

Is ovarian adrenergic innervation essential to gonadal function in adult rats?

We studied the relative importance of ovarian innervation during different phases of female rat sexual development, 30, 40, 45 and 60-day-old. Chemical sympathectomy was promoted by long term postnatal treatment with guanethidine (GD), an adrenergic neuron blocking agent. The sympathectomized rats exhibited delayed puberty and alterations in estrous cycle. Reduced circulating E2, LH and Prl levels at 30 days of age were observed, besides decreased steroidal secretory responsiveness to gonadotropins in vitro. On the other hand, normal pituitary secretory responsiveness to LHRH in vivo and plasma gonadotropin concentrations were observed in 60-day-old rats. These data reinforce the view that ovarian sympathetic innervation contributes to the regulation of the prepubertal development of the ovarian functions.

The suprachiasmatic nucleus controls the circadian rhythm of heart rate via the sympathetic nervous system

The mammalian suprachiasmatic nucleus (SCN) controls a wide variety of circadian behavioral and physiological processes. The specific motor output pathway(s) by which these diverse processes are controlled are unknown. The only established motor output of this system is the regulation of pineal melatonin synthesis via the sympathetic nervous system. It is therefore possible that other peripheral circadian rhythms are regulated similarly. To address this issue, body temperature (BT), general activity (GA), wheel-running activity (WR), and heart rate (HR) were recorded in laboratory rats, and the effects of SCN lesion (SCNX) and of pharmacological sympathectomy with guanethidine (GUAN) on these multiple circadian rhythms were determined. The SCNX abolished circadian patterns in all motor outputs, whereas sham animals showed robust rhythms in all measures. In contrast, guanethidine, which depleted peripheral but not central catecholamine content, selectively reduced HR circadian rhythmicity. Other rhythms (BT, GA, and WR) were unaffected. These results suggest that the SCN influences some peripheral targets via circadian regulation of the sympathetic nervous system, and other circadian outputs are regulated via different, unknown pathways.

Neonatal guanethidine treatment alters endoneurial but not dorsal root ganglion perfusion in the rat

In previous work, we suggested that there were differences in vasoregulation between dorsal root ganglia (DRG) and the endoneurium of peripheral nerve trunks. To investigate symphatetic control of both microvessel beds, we compared local perfusion in the sciatic nerve endoneurium and lumbar DRG of adult Sprague-Dawley rats treated from neonatal day 5 with guanethidine monosulfate to induce adrenergic sympathectomy. Control rats were injected with normal saline. Local blood flow and microvascular resistance were measured using microelectrodes sensitive to the clearance of hydrogen. Guanethidine-sympathectomized rats had higher sciatic endoneurial blood flow and lower endoneurial microvascular resistance than saline-injected controls. In contrast, DRG blood flow was not increased by sympathectomy and was comparable to control value despite the hypotension induced by sympathectomy. The results that sympathetic control of local blood flow and may be less apparent in DRG than endoneurium and that local autoregulation may protect DRG from hypotension.

Evidence for an adrenergic innervation of the adrenal cortical blood vessels in rats.

The aim of this study was to investigate the blood flow in the adrenal cortex of the rat. Relative changes in the adrenal cortical blood flow were continuously measured by Laser Doppler flowmetry in 33 chloralose-anaesthetized artificially ventilated rats during electrical stimulation (1 ms, 5 V) of the left great splanchnic nerve (LGSN), which conveys both pre- and post-ganglionic nerve fibres to the adrenal gland. Laser Doppler flux (LDF) was decreased and regional resistance (RR) was increased by augmenting nerve stimulation at increasingly higher frequencies (2, 4, 8, 20 and 40 Hz). The decrease in LDF, when compared to pre-drug stimulations at 4 Hz was partially or totally inhibited by the adrenergic blocking agents trimethaphan (TRIM), guanethidine (GUA) and alpha 1-blockade with prazosin (PRAZ). Furthermore, both the decrease in LDF and the increase in RR were either completely or partially blocked by stimulation at 40 Hz after TRIM-treatment and GUA-treatment. It is concluded that the adrenal cortex in the rat is innervated by post-ganglionic adrenergic nerve fibres, which are involved in the regulation of blood flow in the adrenal cortex.

Modulation of non-adrenergic non-cholinergic inhibitory transmission in rat duodenum: role of opiates and 5-hydroxytryptamine.

In rat duodenal segments in vitro, electrical field stimulation induced a TTX-sensitive relaxation in the presence of atropine and guanethidine. A correlation between the amplitude of the evoked response and stimulus frequency was observed. Opioid peptides DAGO, DPDPE and DYN caused a dose-dependent increase in the amplitude of the response to EFS. Naloxone shifted to the right the dose-response curves for each opioid peptide significantly enhancing the ED50 values. The amplitude of the response to EFS was enhanced, dose-dependently, also in the presence of 5-HT. Such an effect induced by 5-HT was prevented by 5-HT receptor desensitization, but persisted unchanged after naloxone pretreatment. Opioids failed to affect the response to EFS after 5-HT receptor desensitization. Results suggest that in rat duodenum opioids modulate NANC inhibitory neurotransmission, indirectly the release of 5-HT.

Normal blood flow but lower oxygen tension in diabetes of young rats: microenvironment and the influence of sympathectomy.

Studies of rats with experimental streptozotocin (STZ)-induced diabetes at 4 months have identified sciatic nerve trunk oligemia and hypoxia, but it is uncertain how early these abnormalities develop or which develops first. We studied young (4-week-old) rats after 6 or 16 weeks of STZ-induced diabetes (or after citrate buffer injection in controls) by recording multi-fiber conduction in three different nerve territories and by measuring sciatic endoneurial blood flow (NBF) and oxygen tension (PnO2) at end point. To evaluate the impact of sympathectomy on this diabetic model, separate animal groups were treated for 5 weeks with guanethidine monosulfate given at the onset of diabetes (group 1, end point 6 weeks) or after 6 weeks of diabetes (group 2, end point 16 weeks). Diabetes was associated with deficits in sensory and motor caudal conduction and increased resistance to ischemic conduction failure (RICF). NBF was comparable to control animals at both time points and was within the published normal range of NBF. In contrast, oxygen tensions were shifted to lower values in diabetic animals. Sympathectomy was associated with blunting of the RICF increase in group 2 but worsened caudal sensory conduction despite evidence of modest improvement in sciatic nerve oxygenation. Our findings support the concept that neuropathy occurs early in diabetes and that hypoxia develops before oligemia. Sympathectomy did not benefit this diabetic model.

Guanethidine-Mediated Destruction of Ovarian Sympathetic Nerves Disrupts Ovarian Development and Function in Rats*

Immunosympathectomy produced by treatment of newborn rats with antibodies to nerve growth factor (NGF) delays ovarian development and disrupts estrous cyclicity. While these alterations have been ascribed to loss of sympathetic neurons innervating the ovary, the treatment also causes partial loss of ovarian sensory innervation. The present experiments were undertaken to determine if selective interference with ovarian noradrenergic/sympathetic action would result in alterations of ovarian development similar to those caused by NGF antibodies (NGF Ab). We have used two approaches to disrupt catecholamine action on ovarian cells: 1) inhibition of beta-adrenoreceptors by local delivery of receptor blockers to the ovaries of juvenile rats; and 2) elimination of the sympathetic innervation by long term postnatal treatment with guanethidine (GD), an adrenergic neuron blocking agent. When GD is administered chronically it produces an autoimmune-mediated destruction of peripheral sympathetic nerves, without affecting cholinergic or sensory neurons. Of the receptor blockers tested, FM-24, a nonreversible antagonist, resulted in a sustained 70% decrease in available receptors throughout the 10-day period studied. In spite of this, the timing of puberty, assessed by the age at vaginal opening and first ovulation, was not delayed, suggesting that activation of the remaining receptors by an intact innervation suffices to maintain a normal noradrenergic influence. GD treatment initiated at the end of the first week of postnatal life and maintained for three weeks slowed the juvenile-peripubertal rate of body growth, delayed the time of vaginal opening and first ovulation, and disrupted subsequent estrous cyclicity, but did not affect the animals' fertility. The ovaries of GD-treated rats exhibited a striking loss of sympathetic (norepinephrine and neuropeptide Y) nerves but a normal sensory innervation (represented by fibers containing calcitonin gene-related peptide). The concentration of beta-adrenoreceptors in granulosa cells was reduced, suggesting follicular immaturity. Direct assessment of this inference by morphometric analysis of the ovaries revealed that follicular development was retarded. The progesterone and estrogen response of juvenile ovaries to gonadotropins in vitro were also reduced. At this time, circulating LH levels were slightly decreased, but neither LHRH content in the median eminence nor the LHRH response to prostaglandin E2 in vitro were affected.(ABSTRACT TRUNCATED AT 400 WORDS)