Dorothee M. Gaumann

Intrathecal somatostatin, somatostatin analogs, substance P analog and dynorphin A cause comparable neurotoxicity in rats

Rats chronically implanted with intrathecal catheters received intrathecal injections (10 microliters followed by 10 microliters saline flush) of either saline (n = 5), somatostatin (100 micrograms, n = 10), the somatostatin analog BIM 23003 (100 micrograms, n = 5), the somatostatin analog SMS 201-995 (100 micrograms, n = 5), the substance P analog [D-Pro2, D-Trp7,9] SP (10 micrograms, n = 10), or dynorphin A (1-17) (20 nmol, n = 8). These doses (somatostatin, substance P and dynorphin A) were selected based on previous studies in which they caused significant motor deficits. Effects on thermal cutaneous nociception, behavior, motor function and spinal cord histopathology were evaluated. All peptides caused severe neurotoxicity, evidenced by flaccid hind leg paralysis and lumbar spinal neuronal degeneration, which was accompanied by an inflammatory reaction in meninges and spinal gray matter. Histopathological changes had developed within 24 h after injection of somatostatin, substance P analog and dynorphin A, showing mild to severe neuronal degeneration and mild inflammatory responses in spinal cord and meninges. Significant antinociceptive effects, due to severe neurotoxic effects, were only observed following intrathecal injection of SMS 201-995 and the substance P analog. Potential neurotoxic mechanisms of the different peptides are discussed.

Adrenal vein catecholamines and neuropeptides during splanchnic nerve stimulation in cats.

Splanchnic nerve stimulation in bursts at low (5 Hz) and high (50 Hz) frequency (30 V, 1 msec; train duration 1 sec; train rate 0.5/second) was employed in 10 cats under halothane anesthesia, during 10-minute periods, while blood samples were concurrently collected from the adrenal vein and femoral artery for the measurement of norepinephrine (NE), epinephrine (EPI), dopamine (DA), Met-enkephalin (ME), neuropeptide Y (NPY), peptide YY (PYY) and neurotensin (NT). In Group I (n = 5), splanchnic nerve stimulation was initially applied at 5 Hz followed after 20 min by a 50 Hz stimulus, while in Group II (n = 5) the stimulation sequence was reversed. Adrenal vein and femoral artery plasma levels of catecholamines and neuropeptides were not significantly affected by the stimulation sequence, while a significant decrease in blood pressure response was observed in Group II during the 5 Hz stimulation as compared to Group I, indicating desensitization. Splanchnic nerve stimulation at 5 Hz caused a preferential increase in adrenal vein NE (9-fold) versus EPI (7-fold) levels as compared to baseline, while 50 Hz stimulation led to further comparable increases in NE (5-fold) and EPI (6-fold) levels. Significant increases in adrenal vein DA and neuropeptide levels were only observed during 50 Hz stimulation, with DA showing a 5-fold, ME a 2.6-fold and NPY a 3-fold increase as compared to 5 Hz stimulation, and NT a 3.6-fold increase as compared to baseline. Present findings indicate different dynamics in the movement of catecholamines and neuropeptides from the adrenal.

Effects of hemorrhage and opiate antagonists on adrenal release of neuropeptides in cats

Concurrent levels of methionine-enkephalin (ME), neuropeptide Y (NPY), peptide YY (PYY), neurotensin (NT), vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK) and bombesin (BMB) were measured in adrenal vein (AD), femoral vein (FV) and femoral artery (FA) under baseline conditions and during hypotensive hemorrhage (HTH) in halothane anesthetized cats (Group II, n = 6) and compared to a non-bled control group (Group I, n = 6). Five cats (Group III) received an IV bolus of naltrexone (1 mg/kg) followed by a continuous infusion prior to induction of HTH. A blood volume loss of approximately 40% evoked a selective increase in AD levels of ME, NPY, PYY and NT. No differences in regard to hemodynamics and pattern of neuropeptide levels were observed between Group II and Group III. Administration of naloxone (1 mg/kg, IV) in Group I and Group II at the end of the experiment led to a significant increase in MABP in both groups but did not evoke changes in neuropeptide levels. We conclude that adrenal neuropeptide release during hypotensive hemorrhage is not modulated by actions on opiate receptors in the halothane anesthetized cat.

Sympathetic stimulating effects of sufentanil in the cat are mediated centrally

The hemodynamic and adrenal secretory response to sufentanil (25 micrograms/kg i.v.) was evaluated during halothane anesthesia in 3 groups of cats: group I, n = 5, control; group II, n = 4, naloxone pretreatment (3 mg/kg i.v.); and group III, n = 5, acute spinal transection at T3-4. Administration of sufentanil in intact cats (group I), caused a significant increase in mean arterial blood pressure and adrenal vein plasma levels of norepinephrine, epinephrine, dopamine, and Met-enkephalin. These effects were abolished in naloxone-pretreated cats (group II). Following spinal transection (group III), sufentanil evoked a significant increase in blood pressure and heart rate, but no change in adrenal hormone levels. Intraventricular injections of sufentanil suggest that these sympathetic stimulating effects are mediated at central sites in proximity to the lateral and third ventricle.

Adrenal medullary secretion with splanchnic stimulation in spinal cats

This project was undertaken to determine whether previously observed adrenal medullary hyperactivity that developed following high spinal cord transection in the cat could be explained by increased sensitivity of the synapse between the splanchnic nerve and chromaffin cell. The splanchnic nerve was stimulated in acute (2-3 h; n = 7) or chronic (61-64 days; n = 7), spinally transected (T3) cats that were decerebrate and unanesthetized. Mean arterial blood pressure and adrenolumbar venous blood flow were significantly greater in the chronic animals. Stimulation (30 V; 1 ms pulses) was applied at 3 Hz and 30 Hz to deliver the same number of pulses within 3 min. Adrenal medullary secretion (ng/min) of epinephrine (EPI), norepinephrine (NE), dopamine, neuropeptide Y (NPY), [Met]enkephalin (ENK), and encrypted [Met]enkephalin was determined at baseline and in relation to both patterns of stimulation. With near threshold (3 Hz) stimulation, the following differences were observed between groups: (1) secretion of EPI, NPY, and ENK was significantly greater in the chronic than in the acute animals; and (2) preferential secretion of NE was elicited in the acute animals. These observations suggest that there may be some facilitation of the splanchnic nerve--chromaffin cell synapse that occurs over time following high thoracic spinal cord transection. However, it is likely that central, spinal mechanisms also contribute to adrenal medullary hyperactivity.

Electroencephalographic and behavioral assessment of intracerebroventricular somatostatin and a substance P analogue

Chronically implanted rats were injected either with somatostatin (SST) lumbar intrathecally (i.t.) (100 micrograms, n = 5), into the fourth ventricle (3 micrograms, n = 5; 10 micrograms, n = 6; 30 micrograms, n = 5) or into the lateral ventricle (10 micrograms, n = 6; 30 micrograms, n = 6), or received an injection of the substance P (SP) analogue, [D-Pro2, D-Trp7,9]SP into the fourth ventricle (0.3 micrograms, n = 2; 1 micrograms, n = 4; 3 micrograms, n = 4; 10 micrograms, n = 1) or lateral ventricle (3 micrograms, n = 3). A dose-dependent EEG depressant effect was observed following fourth and lateral ventricular injections of SST and of the SP analogue. Acute death due to respiratory depression was observed following i.t. and fourth ventricular injection of SST, and fourth ventricular injection of the SP analogue. Prominent motor behavior (barrel rotation, circling, cranial stereotypies) was observed, without signs of EEG seizure activity, following intraventricular injection of both drugs. Present findings indicate neurotoxic effects of SST and SP analogue at the cerebral level.

Effects of hemorrhage and naloxone on adrenal release of methionine-enkephalin and catecholamines in halothane anesthetized dogs

Concurrent levels of methionine-enkephalin and catecholamines in adrenal vein, femoral vein and femoral artery were measured under baseline conditions and during graded hemorrhage in halothane anesthetized dogs and compared to a non-bled control group. Naloxone was administered in both groups at the end of the experiment. Normotensive hypovolemia with a remaining blood volume of 76% led to a moderate decrease in mean arterial blood pressure from baseline and a 15- to 20-fold increase in norepinephrine, epinephrine and dopamine, and a 5-fold increase in enkephalin in the adrenal vein. Subsequent induction of hypotensive hypovolemia with a remaining blood volume of 51% resulted in a profound drop in blood pressure and evoked a further increase in the level of catecholamines (40- to 50-fold from baseline) and enkephalin (8-fold from baseline) in the adrenal vein. In the control group only a 3- to 4-fold increase from baseline in adrenal vein hormone levels was observed over time. Naloxone administration at the end of the experiment, led to a 2- to 6-fold further increase in hormones at the 3 collection sites in both groups of dogs. Joint calculation of the partial correlation coefficients for the influence of preceding blood volume and blood pressure, and concurrent blood volume and blood pressure on hormone secretion in the adrenal vein revealed that these variables explained the variation in hormone levels between 56 and 92% during normotensive hypovolemia and 62-83% during hypotensive hypovolemia. In one dog with bilateral adrenalectomy, hemorrhage was poorly tolerated, and naloxone administration did not lead to increased systemic plasma levels of catecholamines and enkephalin or improved hemodynamics. In the hemorrhage group, molar ratios of norepinephrine/epinephrine in the adrenal vein showed a significant increasing trend during the experiment. Findings in these experiments support the idea of differential monoaminergic and enkephalinergic regulation in adrenal medullary cells.

Effect of acute and chronic spinal transection on evoked secretion of adrenal medullary catecholamines in the cat

Eight cats were spinally transected at T3. After an acute (0-5 days) or chronic (15-37 days) period, animals were rendered decerebrate and the effects of visceral (bladder distention) and somatic (sciatic nerve stimulation) stimuli were examined. Epinephrine, norepinephrine and dopamine levels were measured in plasma collected from the left adrenolumbar vein; heart rate and blood pressure were continuously monitored. In chronic animals both visceral and somatic stimuli most frequently evoked prominent increases in blood pressure and the secretion of adrenal medullary catecholamines; the same stimuli caused little change in these parameters in acute animals. These data indicate that a condition similar to the clinical syndrome of autonomic hyperreflexia may be elicited in the chronic spinally transected cat, and that this condition is accompanied by a notable activation of the adrenal medulla.

Cryptic Met-enkephalin in adrenal and portal vein during splanchnic artery occlusion shock in cats

Adrenal vein (AD), portal vein (PV), and femoral artery (FA) plasma levels of immunoreactive (IR) Met-enkephalin pentapeptide (ME) and extended ME-IR forms, obtained after sequential incubation of plasma with trypsin and carboxypeptidase B, were examined in 4 cats during splanchnic artery occlusion shock at baseline (S1), during early shock (S2), late shock (S3), and after naloxone (1 mg/kg, i.v.) administration (S4). Early shock (S2) led to a significant increase in levels of extended and fully processed Met-enkephalin IR at all 3 collection sites (AD, PV, FA) without a change in proportional levels of extended Met-enkephalin IR to the pentapeptide IR (ME). Naloxone administration during late shock (S4), however, resulted in a disproportionate increase (150-fold from baseline) in adrenal vein plasma levels of extended Met-enkephalin IR forms, as compared to ME IR (23-fold). In contrast, no changes in plasma levels occurred in PV and FA.