Inhibitory effects of electrical stimulation of thalamic nucleus submedius on the nociceptive responses of spinal dorsal horn neurons in the rat

The aim of the present study is to examine whether stimulation of the thalamic nucleus submedius (Sm) exerts an inhibitory influence on the long latency responses (C-responses) of the spinal cord dorsal horn neurons evoked by noxious cutaneous electrical stimulation, in an attempt to provide electrophysiological evidence for involvement of the Sm in modulation of nociception. Single unit extracellular recordings from the dorsal horn neurons were obtained with glass micropipettes in pentobarbital-anesthetized rats. A total of 71 nociceptive neurons, including 61 wide dynamic range (WDR) and 10 nociceptive specific (NS) neurons, were studied in 29 rats. Electrical stimulation of either ipsilateral or contralateral Sm markedly suppressed the C-responses in most (75%, 53/71) of these neurons, and facilitated the responses in only a few neurons. In general, the inhibitory effect was dependent on both the stimulus intensity and the length of stimulus train, and the stimulus threshold for the inhibition to be elicited was about 50 microA when a 300-ms train of 0.2-ms pulses at 200 Hz was used. The inhibitory effect outlasted the Sm stimulation about 500 ms. Inhibition of C-responses could also be produced by stimulation of the dorsal hypothalamic area (DA). On the other hand, stimulation of the structures in the medial thalamus surrounding Sm had no obvious influences on the C-responses of the dorsal horn neurons. The findings of this study provided further support for the hypothesis that Sm may be implicated in the descending modulation of nociception.

Homomeric interactions between transmembrane proteins of Moloney murine leukemia virus

We have studied homomeric interactions between transmembrane proteins (TM) of the Moloney murine leukemia virus envelope using the Saccharomyces cerevisiae two-hybrid system. TM interacts strongly with itself but not with various control proteins. Deletional and mutational analyses indicated that the putative leucine zipper motif in the extracellular domain of TM is essential and sufficient to mediate the binding. The first three repeats of the leucine zipper-like motif are the most important in mediating the interaction. The TM-TM interaction detected in this system may play a role in several stages of viral replication.

Brain 'ouabain' mediates sympathetic hyperactivity in congestive heart failure

In congestive heart failure (CHF), endogenous compounds with ouabainlike activity (OLA) may contribute to the maintenance of the circulatory homeostasis by peripheral as well as central effects. In the present study, we assessed changes in peripheral (plasma and left ventricle) and central (pituitary, hypothalamus, pons, and cortex) OLA in two animal models of CHF and determined whether brain OLA mediates sympathetic hyperactivity in CHF. Cardiomyopathic hamsters with their controls were studied at 9 months of age for tissue OLA. Rats were studied 4 weeks after acute coronary artery ligation for tissue OLA and sympathetic activity. In both models, left ventricular end-diastolic pressure was markedly increased. CHF was associated with significant increases in both plasma and tissue OLA in both models. In the brain, the most marked (twofold to threefold) increases occurred in the hypothalamus. In vitro, all OLA measured could be blocked by antibody Fab fragments (Digibind). Conscious rats with CHF showed elevated plasma catecholamines and enhanced responses of mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) to air stress and to intracerebroventricular (ICV) injection of the alpha 2-adrenergic receptor agonist guanabenz compared with sham-operated rats. ICV administration of the Fab fragments did not change resting RSNA or responses to air stress at 1 hour. However, 18 hours after injection of the Fab fragments, resting RSNA levels had significantly decreased compared with the control values, and plasma catecholamine levels had decreased to control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of electrical stimulation of thalamic nucleus submedius area on the rat tail flick reflex

This study in lightly anesthetized rats found that unilateral electrical stimulation delivered to the ventral part of the thalamic nucleus submedius (Sm), the thalamic reuniens nucleus (Re) and the hypothalamic dorsal area (DA) markedly depressed the TF reflex, and this inhibitory effect increased following increasing stimulation intensity. Stimulation in the dorsal part of Sm did not produce any or only slight depression of the TF reflex. Furthermore, an ipsilateral electrolytic lesion of the ventrolateral orbital cortex (VLO) eliminated the unilateral Sm-evoked inhibition, but not the inhibition elicited by Re and DA and contralateral Sm stimulation. Finally, after bilateral electrolytic lesions of the ventrolateral periaqueductal gray (PAG) the DA and Re and contralateral Sm-evoked inhibitions were also eliminated. The results suggest that the Sm plays an important role in modulation of nociceptive inputs, and this role of Sm is mediated by the VLO and leads to activation of the PAG descending inhibitory system and depression of the nociceptive inputs at the spinal cord level.

[The roles of thalamic nucleus submedius in nociception and pain modulation]

Recent studies on the roles of thalamic nucleus submedius (Sm) in nociception and pain modulation were reviewed in this article in combination with own our works. Results of these studies showed that Sm may be involved in effective-motivational aspects of pain, and that Sm-VLO-PAG may constitute a pathway of nociceptive modulation which may depress the nociceptive inputs at the spinal cord level via the brain-stem descending inhibitory system, thereby mediate a negative feedback regulation of pain.

Effects of thalamic nucleus submedius lesions on the tail flick reflex inhibition evoked by hindlimb electrical stimulation in the rat

Bilateral electrolytic lesions of the thalamic nucleus submedius (Sm) facilitated the TF reflex and attenuated the antinociception evoked by hindlimb electrical stimulation with high intensities in lightly anaesthetized rats. However, the antinociception produced by low intensity hindlimb stimulation was unchanged, except that the after-effect was reduced. The results show that the Sm is probably involved in pain modulation and plays an important role in mediation of the antinociception elicited by high intensity peripheral stimulation.

Harvey ras (H-ras) point mutations are induced by 4-nitroquinoline-1-oxide in murine oral squamous epithelia, while squamous cell carcinomas and loss of heterozygosity occur without additional exposure

Tumorigenesis is a multistep genetic process requiring several somatic mutations for neoplastic transformation. These mutations appear to be sequential, random, and independent events. However, we find linked, nonrandom ras mutations occurring during 4-nitroquinoline-1-oxide-induced tumorigenesis months after exposure to the carcinogen had ceased. The carcinogen had been topically applied to the oral cavity of CBA mice for 4 to 16 weeks. Dysplasia developed after 24 weeks, and carcinoma in situ and squamous cell carcinoma developed after 28 weeks. H-ras mutations were detected in 13 of 25 tissue specimens (10 of 14 invasive carcinomas and 2 of 4 carcinoma in situ, 1 of 5 dysplastic tissue, and 0 of 2 normal tissues). Approximately one-half of the tumors had G to A point mutations at codon 12 of the cellular H-ras proto-oncogene on mouse chromosome 7. None had codon 11, 13, or 61 mutations. Loss of heterozygosity occurred in 5 of 14 invasive cancers. Larger invasive squamous cell carcinomas consistently lost the wild-type allele, whereas preneoplastic lesions and small tumors were heterozygous for ras. This suggests a causal relationship between carcinogen treatment, H-ras activation, and initiation of tumorigenesis. The wild-type allele in mouse chromosome 7 is lost with the progression of tumorigenesis long after exposure to the carcinogen. Thus, loss of heterozygosity of the ras gene appears to occur without multiple carcinogen-induced mutations, i.e., as a result of a cascade of events induced by an earlier ras mutation.

Posttransplantation plasma cell dyscrasias

BACKGROUND

Lymphoproliferative disorders that occur in patients receiving cyclosporine for immunosuppression after solid organ transplantation typically are B-cell neoplasms associated with Epstein-Barr virus (EBV), which may be polyclonal or monoclonal in origin. Although these tumors may have partial B-cell differentiation, (manifested as plasmacytoid features), terminal differentiation to plasma cells that secrete a monoclonal immunoglobulin is rare. The case of a patient who developed a posttransplantation lymphoproliferative disorder that was composed of multiple plasmacytomas located in the abdomen and urinary bladder after liver transplantation is presented. The patient also had high levels of an immunoglobulin-G kappa monoclonal paraprotein.

METHODS

The plasmacytoma was examined for the presence of EBV by both polymerase chain reaction and in situ hybridization, and the possibility of a codon-12 mutation in the ras gene was investigated by digestion of DNA amplification products with the HpaII-restriction endonuclease.

RESULTS

Epstein-Barr virus genomes were demonstrated by DNA amplification of sequences in the long, internal, direct repeat region, and in situ hybridization showed expression of EBV RNA transcripts that annealed to an EBER-1 probe. Immunohistochemistry showed clonally restricted expression of kappa light chains but failed to reveal evidence of expression of the latent membrane protein 1 encoded by EBV. Mutations of codon-12 in the H-ras gene were not detected.

CONCLUSIONS

Resolution of the tumor and the paraprotein after radiation and reduction of immunosuppression indicates that terminal plasmacytic differentiation does not necessarily portend an unfavorable prognosis, even in a clonal lesion.

Effects of enalapril versus losartan on regression of volume overload-induced cardiac hypertrophy in rats

BACKGROUND

The role of nonhemodynamic cardiac trophic mechanisms differs not only between different models of cardiac hypertrophy but also within the same model for development versus maintenance of cardiac hypertrophy. Our previous studies pointed to a major role for the renin-angiotensin system (RAS) as a cardiac trophic stimulus in the remodeling of the heart in response to volume overload by aortocaval shunt or minoxidil treatment.

METHODS AND RESULTS

In the present study, we evaluated the effects of blockade of the RAS by the angiotensin-converting enzyme inhibitor enalapril and the angiotensin II receptor blocker losartan on left ventricular (LV) and right ventricular mass and LV dilation in relation to changes in central hemodynamics during the maintenance of minoxidil and aortocaval shunt-induced cardiac hypertrophy. Both blockers similarly decreased LV end-diastolic pressure (LVEDP) and LV peak systolic pressure, whereas cardiac output remained unchanged in both models of volume overload. This suggests a major contribution of improved LV performance and decreased afterload to the decrease in cardiac preload by the two blockers rather than decreased venous return. Both blockers reversed LV hypertrophy in parallel to their effects on LVEDP in both models of volume overload. In minoxidil-treated rats, the extent of reversal in LV mass and dilation by the two blockers was similar to "spontaneous regression" after discontinuation of minoxidil treatment.

CONCLUSIONS

These results indicate that in contrast to the development phase of cardiac hypertrophy, the RAS does not contribute to the maintenance of volume overload-induced cardiac hypertrophy in these two models via direct cardiac trophic effects. The RAS, however, maintains cardiac hypertrophy indirectly by contributing to the persistence of high filling pressures.

[Descending pathways mediating the effect of stimulating cerebral peduncle on the spinal nociceptive transmission in the rat]

The descending pathways for the effects of stimulation of cerebral peduncle (CP) on the nociceptive neurons of spinal cord dorsal horn were analyzed by subtotal spinal cord lesions in anesthetized rats. Inhibition was the predominant effect of CP stimulation on the C-fiber elicited nociceptive responses of dorsal horn neurons, in 30.7% of such neurons, the inhibition was preceded by some initial excitation. In most neurons the inhibitory effect was mediated by both dorsal funiculus (DF) and dorsolateral funiculus (DLF), that of DF usually predominated. It seemed that DLF played a more important role than DF. However, the excitatory effect was mediated by DF alone. Since in the rat the corticospinal tract (CST) is situated in the DF, the results suggest that cerebral cortex can modulate spinal nociceptive transmission not only by the CST, but also through a relay in some supraspinal structure(s) sending descending fibers into the DLF.

Exploration of requirements for peptide binding to HLA DRB1*0101 and DRB1*0401

The individual amino acid contacts responsible for peptide binding to DRB1*0101 and/or DRB1*0401 were defined using a quantitative binding assay. The differential contribution of each amino acid in two well studied T cell determinants, HA307-319 and RMBP 90-102, was delineated by comparing the IC50 values of analogues of varying length. This analysis confirmed the importance of a hydrophobic amino acid located near the amino-terminus for binding to both alleles and revealed that the contribution of the carboxyl-terminal amino acids differed between DRB1*0101 and DRB1*0401. Taking advantage of previous experiments demonstrating that all of the residues could be replaced with alanine, with the exception of the key hydrophobic amino acid, simplified analogues composed of polyalanines were used to prove 1) optimal binding depended on the position of the hydrophobic side chain relative to the amino- and carboxyl-termini; 2) aromatic amino acids were superior to aliphatic side chains at this position; and 3) a significant amount of free energy of binding arises from hydrogen bonding between the class II binding site and the amide bonds of the ligand. The role of each carbonyl and amide nitrogen was measured by assaying analogues containing reduced peptide bonds or N-methyl amino acids. Serine, but not glycine, could be used as a framework amino acid for peptide ligands, indicating that the beneficial aspects of these simplified structures was the combination of retaining the correct orientation of the peptide bonds, the restriction of the conformational freedom by limiting the possible phi/psi angles of the peptide, and avoidance of deleterious side-chain contacts. Collectively, these data were consistent with the peptide binding in a nonrepeating conformation with the vast majority of the free energy of binding arising from hydrogen bonds with the peptide backbone and a single, key hydrophobic side chain interacting in a conserved pocket in both DRB1*0101 and DRB1*0401.

Exploration of requirements for peptide binding to HLA DRB1*0101 and DRB1*0401

The individual amino acid contacts responsible for peptide binding to DRB1*0101 and/or DRB1*0401 were defined using a quantitative binding assay. The differential contribution of each amino acid in two well studied T cell determinants, HA307-319 and RMBP 90-102, was delineated by comparing the IC50 values of analogues of varying length. This analysis confirmed the importance of a hydrophobic amino acid located near the amino-terminus for binding to both alleles and revealed that the contribution of the carboxyl-terminal amino acids differed between DRB1*0101 and DRB1*0401. Taking advantage of previous experiments demonstrating that all of the residues could be replaced with alanine, with the exception of the key hydrophobic amino acid, simplified analogues composed of polyalanines were used to prove 1) optimal binding depended on the position of the hydrophobic side chain relative to the amino- and carboxyl-termini; 2) aromatic amino acids were superior to aliphatic side chains at this position; and 3) a significant amount of free energy of binding arises from hydrogen bonding between the class II binding site and the amide bonds of the ligand. The role of each carbonyl and amide nitrogen was measured by assaying analogues containing reduced peptide bonds or N-methyl amino acids. Serine, but not glycine, could be used as a framework amino acid for peptide ligands, indicating that the beneficial aspects of these simplified structures was the combination of retaining the correct orientation of the peptide bonds, the restriction of the conformational freedom by limiting the possible phi/psi angles of the peptide, and avoidance of deleterious side-chain contacts. Collectively, these data were consistent with the peptide binding in a nonrepeating conformation with the vast majority of the free energy of binding arising from hydrogen bonds with the peptide backbone and a single, key hydrophobic side chain interacting in a conserved pocket in both DRB1*0101 and DRB1*0401.

Arterial hypertrophy and pressor responsiveness during development of hypertension in spontaneously hypertensive rats

BACKGROUND

In contrast to studies in isolated blood vessels, results from whole-animal studies are ambiguous regarding differences in pressor responsiveness between spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats, possibly related to the measurement of blood pressure instead of total peripheral resistance (TPR) and to differences in compensatory mechanisms.

OBJECTIVE AND DESIGN

We evaluated responses of blood pressure and TPR to two doses of the alpha 1-agonist phenylephrine during the development of hypertension and cardiovascular hypertrophy in SHR aged 8-26 weeks compared with age-matched WKY rats before and after ganglionic blockade. At 16 weeks of age more-complete dose-response curves to the alpha 1-agonist methoxamine were also constructed.

RESULTS

Over the age range studied, the SHR developed marked hypertension, related to a significant rise in TPR, and concomitantly significant cardiac hypertrophy, as well as hypertrophy of the mesenteric arterial bed. The blood pressure responses to phenylephrine were diminished in the SHR compared with the WKY rats at all ages studied, but this effect was significant only in the absence of ganglionic blockade. TPR responses were significantly less in the SHR than in the WKY rats, both with and without concomitant ganglionic blockade. In contrast, both blood pressure and TPR responses to low doses, but not higher doses, of methoxamine were enhanced in the SHR compared with the WKY rats.

CONCLUSION

These results indicate that the development of hypertension in SHR in vivo is associated with variable changes in blood pressure and TPR responses to alpha 1-receptor stimulation, depending on the alpha 1-agonist employed.

Dietary sodium stimulates ouabainlike activity in adrenalectomized spontaneously hypertensive rats

Both the adrenal glands and the hypothalamus have been proposed to produce compound(s) with ouabainlike activity (OLA). To evaluate the contribution of the adrenal glands, 4-wk-old spontaneously hypertensive rats (SHR) were sham operated or adrenalectomized. The adrenalectomized SHR were given daily injections of corticosterone and aldosterone. Subsequently, rats were randomized to control or high (8%) dietary Na+, and after 2.5 wk, blood pressure and OLA in plasma, hypothalamus, and pituitary were evaluated. Hypertension developed somewhat less in adrenalectomized vs. sham-operated SHR. On control Na+ intake, adrenalectomy caused only minor decreases in circulating and central OLA. Adrenalectomy did not prevent the 50-90% increases in plasma, hypothalamus, and pituitary OLA caused by high Na+ intake for 2.5 wk. These findings are consistent with the concept that, at least in SHR, the central nervous system may represent the major source of both central and peripheral OLA.

The renin-angiotensin system and volume overload-induced cardiac hypertrophy in rats. Effects of angiotensin converting enzyme inhibitor versus angiotensin II receptor blocker

BACKGROUND

The degree of cardiac hypertrophy is not only load dependent: Among other factors, the renin-angiotensin system may play a role in the regulation of cardiac myocyte growth.

METHODS AND RESULTS

To evaluate the role of the renin-angiotensin system in volume overload-induced cardiac hypertrophy, we assessed: 1) the time course of changes in cardiac hemodynamics, cardiac anatomy, and plasma and cardiac renin activity in response to volume overload induced by two sizes of abdominal aortocaval shunt and 2) the effects of chronic treatment with an angiotensin converting enzyme inhibitor (ACEI) versus an angiotensin II receptor blocker on hemodynamics and cardiac hypertrophy. Drug treatment started 3 days before shunt surgery. An increase in left ventricular end-diastolic pressure (LVEDP) and the development of right ventricular (RV) and left ventricular (LV) eccentric hypertrophy in response to volume overload occurred within the first week after induction of the shunt. Plasma renin activity (PRA) and cardiac renin activity peaked shortly after induction of the shunt. During the chronic phase, LVEDP and PRA decreased somewhat but remained significantly elevated up to 7 weeks after shunt surgery. Cardiac renin activity returned toward normal within 4 weeks after surgery. Treatment with the ACEI enalapril caused only a modest decrease in LV internal diameter but did not affect increases in LV and RV weights in response to volume overload despite a major decrease in LVEDP after chronic treatment. In contrast, treatment with the angiotensin II receptor blocker losartan, which had similar effects on cardiac and peripheral hemodynamics, prevented dilation of the LV after 7 days and attenuated the dilation of the LV after 28 days. Moreover, increases in LV and RV weights were significantly attenuated by losartan.

CONCLUSIONS

The development of volume overload-induced cardiac hypertrophy is associated with significant increases in PRA and cardiac renin activity shortly after induction of an aortocaval shunt. Whereas the two blockers of the renin-angiotensin system decreased LVEDP to a similar extent, only the angiotensin II receptor blocker blunted the hypertrophic response of the heart to volume overload, which is indicative for other than hemodynamic determinants of the cardiac hypertrophic response. One trophic factor may be cardiac angiotensin II generated via an angiotensin II-forming enzyme resistant to ACEI and possibly activated by cardiac volume overload.

[Effects of stimulation of SI cortex and cerebral peduncle on the nociceptive responses of spinal dorsal horn neurons in the rat]

Single spinal dorsal horn neurons were recorded extracellularly with glass micropipettes, and the effect of stimulation of SI cortex or cerebral peduncle (CP) was observed on the long latency discharges (C-fiber evoked response) of the wide dynamic range (WDR) neurons induced by intense electrical skin stimulation. Inhibition was the predominant effect of SI cortex stimulation on the C-fiber evoked responses of WDR neurons. The effect of CP stimulation was similar to that of SI cortex stimulation, except that the former was much more effective than the latter. The inhibition lasted a period of time varying from 400 ms to more than 10 min after CP stimulation in different neurons. Systemic naloxone had no significant effect on the inhibition produced by CP stimulation. Systemic methysergide reduced or eliminated the inhibition in a part of the neurons tested, suggesting that 5-HT, but not opioid peptides, is involved partially in mediation of the descending inhibitory effect originating from the cortex.

Dietary sodium restriction and pressor responsiveness to tyramine in spontaneously hypertensive rats

OBJECTIVE

To determine in vivo whether in young spontaneously hypertensive rats (SHR) dietary sodium restriction decreases adrenergic transmitter release from the sympathetic nerve terminal.

DESIGN

Dietary sodium restriction was initiated in young and mature SHR and Wistar-Kyoto (WKY) rats, and subsequently changes in pressor responsiveness to norepinephrine and to the indirectly acting sympathomimetic tyramine were determined in relation to their effects upon plasma catecholamines.

RESULTS

In young SHR sodium restriction for 3-6 weeks prevented the development of hypertension, whereas in mature SHR sodium restriction did not affect blood pressure. Sodium restriction caused modest decreases in pressor responsiveness to the exogenous alpha-agonist, not different in young and mature SHR compared with WKY rats. In contrast, sodium restriction markedly inhibited pressor-responses to tyramine in young SHR and WKY rats, but not at all in mature rats. Tyramine increased plasma norepinephrine 5-10-fold. However, sodium restriction did not affect this response. The pressor response to tyramine was related to increases in total peripheral resistance, with minimal changes in cardiac output, and could be blocked by alpha 1-receptor blockade in rats on either control or low-sodium diets.

CONCLUSIONS

These results show that sodium restriction causes only a small decrease in the pressor response to norepinephrine, but a more marked inhibition of the pressor response to tyramine in young SHR and WKY rats without affecting the plasma norepinephrine response to tyramine. These results suggest that dietary sodium can indeed affect presynaptic functions in vivo, but that plasma norepinephrine responses to tyramine may not reflect changes in arterial norepinephrine release, or that sodium restriction affects a co-transmitter rather than norepinephrine release per se.

Dietary sodium and the antihypertensive effect of nifedipine in spontaneously hypertensive rats

To assess the interaction of dietary sodium and the antihypertensive response to a calcium antagonist, spontaneously hypertensive rats (SHR) were given a diet of regular or increased (120 v 342 mumol Na+/g food) sodium intake from 4 until 16 weeks of age. Nifedipine was added at 10 weeks of age. This level of sodium intake did not enhance the development of hypertension in SHR. In rats with the regular sodium intake, nifedipine caused only a minor decrease in blood pressure. In contrast, with increased sodium intake nifedipine caused a marked antihypertensive response, preventing the rise in blood pressure occurring between 10 and 16 weeks of age. This enhanced response was associated with a diminished blood pressure fall from ganglionic blockade. These results indicate that modest increases in sodium intake enhance the blood pressure response to a calcium antagonist possibly by potentiating its inhibitory effects on sympathetic activity.

A method for rapid screening of recombinant proteins for recognition by T lymphocytes

A simple, cost-effective method is described that allows rapid screening of recombinant protein sequences for their ability to stimulate T cells. Individual microcultures of E. coli each expressing a gene product or peptide sequence fused to protein A are grown in 96-well plates. Following lysis of the bacteria, the fusion peptide is readily captured with immobilized immunoglobulin in tissue culture wells. No further purification is required. T lymphocytes plus appropriate antigen-presenting cells are added directly to the wells and assayed for proliferation. The DNA in bacteria from wells stimulating T cell proliferation is then sequenced. The technique allows rapid mapping of T cell epitopes by facilitating screening of truncation mutants without extensive purification. Described here is a further application of the technique to study monosubstituted analogues of a known T cell epitope.

Role of the deep mesencephalic nucleus in the antinociception induced by stimulation of the anterior pretectal nucleus in rats

The present study showed that the inhibitory effect on the tail-flick reflex (TF) of stimulating the deep mesencephalic nucleus (DpMe) was very similar to that produced by stimulation of the anterior pretectal nucleus (APtN). An electrolytic lesion of the ipsilateral DpMe greatly reduced the inhibitory effect of APtN stimulation on the TF. Furthermore, activating the neuronal cell bodies in DpMe but not the fibers of passage by microinjection of L-glutamate into this area was also shown to elicit inhibition of TF. On the other hand, inhibiting the neuronal cells in DpMe by microinjection of gamma-aminobutyric acid produced a marked reduction in the APtN-induced inhibition of TF, which was comparable to that produced by DpMe lesions. It is suggested that the APtN-induced antinociception is, at least in part, mediated via a relay through the DpMe.

Chronic arterial vasodilation, central hemodynamics, and cardiac hypertrophy in spontaneously hypertensive rats

To determine the possible contribution of cardiac volume overload in the failure of arterial vasodilators to induce regression of left ventricular hypertrophy (LVH), we evaluated in spontaneously hypertensive rats (SHRs) the changes in central hemodynamics caused by treatment with hydralazine or minoxidil. Cardiac output measured by the thermodilution technique and filling pressures were measured in conscious, freely moving rats. Increases in cardiac output were observed after 1 day of treatment, and persisted during chronic treatment; ganglionic blockade did not affect this increase. However, the LV end-diastolic pressure and right atrial pressure of SHRs were not increased by hydralazine or minoxidil. Minoxidil increased the LV weight, and decreased the LV wall thickness to LV internal radius ratio, whereas hydralazine did not change these parameters. We conclude that in SHRs changes in filling pressures do not represent the primary stimulus for the persistence or progression of cardiac hypertrophy during chronic arterial vasodilation.

Electrohydraulic-clamshell heart with energy converter inside the compliance reservoir

Two new ideas on the electrohydraulic actuation of blood pumps have been combined. The first idea was to put the energy converters that propel the hydraulic fluid inside the compliance reservoir instead of having them separate. Compactness of the device and better cooling of the energy converter by the surrounding fluid are two major advantages of this approach. Secondly, we put the pumping membrane inside a clamshell that fits over a soft ventricle (1). The ventricle can be implanted first, after which the shell is slid over it. These two ideas have resulted in devices described in this paper. Preliminary in vitro and in vivo data are presented.

Dietary sodium restriction and the development of two-kidney, one-clip hypertension in young versus adult rats

To determine the effects of moderate versus severe dietary sodium restriction on the development of 2-kidney, 1-clip (2K,1C) hypertension, young male Wistar rats were placed on diets containing 9, 26, or 101 (control) mumol sodium/g food. Three days later, a solid silver clip (i.d. 0.20 mm) was placed on the left renal artery and diets were continued up to 6 weeks. Adult rats received a 0.25-mm clip. In young clipped rats receiving the 101 mumol/g diet, blood pressure (BP), plasma renin activity (PRA), and BP response to captopril were increased as early as 1 week after clipping and increased further over time. Moderate sodium restriction (26 mumol sodium/g) led to only a slight delay in the development of hypertension; the levels of BP and PRA, the BP response to captopril, and the extent of cardiac hypertrophy achieved by 6 weeks were not different between the 2K, 1C rats receiving 26 or 101 mumol sodium/g. Sodium restriction to 9 mumol/g decreased rate of growth and completely prevented the rise in BP and in left ventricular weight. At 3 and 6 weeks the severely sodium-restricted rats had significantly higher PRA levels than the 2K, 1C control group. However, the BP response to captopril was attenuated relative to the other hypertensive groups. In adult rats, this level of sodium restriction had a small, but significant effect on body weight, but still prevented the increase in BP and in left ventricular weight. In conclusion, dietary sodium restriction can prevent the development of 2K,1C hypertension in both young and adult rats, but only if the restriction is severe. This effect may relate to a marked reduction in the pressor effectiveness of the renin-angiotensin system by low sodium intake per se or by associated metabolic or other changes.

Inactivity of acrylonitrile epoxide to modify a Ha-ras DNA in a non-focus transfection-transformation assay

The transforming potential of acrylonitrile epoxide (ANO) was tested in a modified NIH3T3 transfection-transformation assay. This involves a new ras construct obtained by ligating a human c-Ha-ras-1 proto-oncogene to the pSV2neo mammalian vector. The new plasmid was allowed to react with ANO or an established carcinogen in vitro, and the modified ras DNA transfected into NIH 3T3 cells. The transfectants are subjected to triple selections: G418 (neomycin) resistance, low serum growth, and limit dilutions. The end points are scored by cell growth kinetics and monolayer saturation density. In using this protocol, the EJ tumor ras plasmid was the positive control, and anti-benzo[a]pyrene-7,8- dihydrodiol-9,10-epoxide (anti-BPDE) and N-methyl-N-nitrosourea were found to be positive in yielding transformants. Although ANO-modified ras gave rise to two G418R clones, both were scored negative due to their normal growth rate and monolayer density similar to the negative controls. Southern blot analysis of anti-BPDE transformant DNA revealed a fragment of 411 bp, indicating a ras mutation at codon 11 or 12. However, both the ANO clones showed the wild-type band of 355 bp by the same method.

Concept of a soft, compressible artificial ventricle under evaluation

This study was designed to compare the relative merits of soft and rigid artificial ventricles. A cascade mock circulation was used to measure cardiac output under different circumstances. The data show that these soft air driven ventricles show a Starling's-like response over a wider range of filling pressures than identical, but rigid, ventricles. Compression of soft ventricles by high intrathoracic pressures was simulated in vitro. Air pressures up to +20 mm Hg did not seriously affect soft ventricles. Cardiac tamponade was simulated by compressing the ventricle in a closed fluid compartment. Tamponade became severe when volume reduction of the ventricle rose to 60 ml. Hemolysis caused by soft and rigid ventricles was tested in a blood bag set-up and was 48-82% higher in the rigid ventricle, depending on the driving conditions. Possibly, this could be explained by the authors' finding that rigid ventricles showed a 20% higher intraventricular dP/dtmax value than soft ventricles. Soft ventricles were implanted in three calves as a total artificial heart (TAH). Implantation without quick connectors was easy because the surgeon could easily fold and compress the ventricles. No physiological complications of softness were observed. Blood damage in the animals was low (less than 5 mg/dl). The authors conclude that soft ventricles show distinct surgical and functional advantages over rigid ventricles.

Development of a new inflow valve for a 20cc semisoft ventricle: preliminary results

We remodeled and tested our semisoft 20cc ventricle and made a new bileaflet flap inflow valve. Housings, bases, outflow valve, and a newly designed diaphragm were all made by vacuum forming and put together by radiofrequency welding or glue. In vitro, the ventricle produced a cardiac output of 2.5 to 3.0 L/min and showed reliable durability results. Hematological testing showed no important thrombogenicity of the new valve. Cardiac output was higher than expected for the volume of the ventricle, perhaps because of stretching or flow through. Animal experiments with the left ventricular assist device (LVAD) version was done at Ohio State University. Earlier in Utah, we did 20 cc total artificial heart (TAH) implantations and LVAD experiments in lambs and recently in calves with the 60cc TAH version. A soft ventricle is easy to implant and low in production costs.

Soft artificial ventricles for infants and adults, with or without a clamshell

The quick connect system and mechanical disk valves used in total artificial hearts (TAH) are sources of thrombogenesis and blood damage. Our soft TAH, which has no quick connectors, can be squeezed and bent, making it easily implantable, and blood damage is reduced by the use of trileaflet and biflap polyurethane valves. The soft ventricles were made by vacuum forming, after which the pieces were welded together by radiofrequency heat sealing. A rapid clamshell can be pushed and slipped over the soft heart to prevent deformation of the ventricle. Three calves have had the 60 cc soft TAH implanted, both with and without a clamshell. The cardiac outputs were as high as 7 L/min, without a vacuum applied during diastole. Two lambs received the 20 cc TAH (as an acute experiment); it fit and functioned well. One healthy lamb received a 20 cc left ventricular assist device (LVAD) with a pulsating artificial atrium as a survival experiment. The lamb survived for 8 days, after which the device was removed and the lamb returned to the meadow. Thrombosis in the TAH was minimal, and the plasma free hemoglobin values in all the TAH and LVAD experiments were usually lower than 5 mg/dl and often lower than 2 mg/dl.

New polyurethane valves in new soft artificial hearts

This article describes new bistable valves, and introduces a new soft heart that is easy to implant. Earlier, five polyurethane (PU) valves were implanted in the mitral position in sheep. All five survived for 1 year or more, and the valves, although calcified, were intact. Since the opening resistance was somewhat high, valves that are bistable were developed, which means they may be open or closed. These valves have lower opening resistance, and regurgitation is similar to that of mechanical valves. Eight calves have been implanted with a new, soft total artificial heart (TAH). Seven had bistable leaflet valves; the eighth had mechanical (Bicer) valves in the inflow position. Four of the calves were sacrificed after 22 to 43 days. At autopsy, the number of thromboemboli found, particularly in the kidneys, was low compared with previous experiments. None of these animals received anticoagulants other than the heparin given during heart/lung bypass.

The role of aluminum in the pathogenesis of anemia in an outpatient hemodialysis population

Anemia is a well-defined complication of aluminum overload in chronic dialysis patients which may be present before other manifestations of aluminum toxicity are obvious. Causes of anemia in chronic renal failure are multiple, and at the present time there is no marker for aluminum-induced anemia. Deferoxamine (DFO) treatment can correct aluminum-related anemia and microcytosis, but may be associated with side effects. Because of the possible role of aluminum in red blood cells in causing the anemia associated with aluminum overload, we attempted to test red blood cell (RBC) aluminum as a marker for aluminum-associated anemia and to assess the prevalence of aluminum-associated anemia in an outpatient dialysis population. Both random plasma aluminum and RBC aluminum correlated well with the increase in plasma aluminum seen following DFO challenge. However, RBC aluminum was affected less by changes in oral aluminum intake than plasma aluminum. There were strong correlations of RBC and plasma aluminum to corpuscular volume (MCV) in our patients. Moreover, patients within the highest quartile of RBC aluminum had a lower mean MCV (82.1 +/- 1.7 vs 89.6 +/- 1.7, p less than .01) and hematocrit (HCT) (24.3 +/- 4 vs 28.2 +/- 1.5, p less than .05) than those within the lowest quartile. These data suggest that aluminum toxicity is an important cause of microcytic anemia in outpatient hemodialysis patients. Prospective long-term studies are needed to further define the usefulness of RBC aluminum in diagnosing and following hemodialysis patients with aluminum-induced anemia.

Corticofugal influences of S1 cortex on ventrobasal thalamic neurons in the awake rat

Corticofugal influences on the responses of 39 ventrobasal (VB) thalamic neurons to repetitive stimuli were studied in awake rats by focally suppressing the evoked and spontaneous electrocortical activity of the primary (S1) somatosensory cortex with magnesium or lidocaine plus magnesium. Suppression of the S1 cortex reduced the number of spikes discharged by 19 (66%) of 29 VB units in response to each of 25 electrical stimuli delivered to the medial lemniscus; 9 units were unaffected and 1 showed an increased response to 1-10 Hz stimuli. The responses of 6 (38%) of 16 VB units to electrical somatic stimuli were also reduced following S1 cortical suppression; 9 units were unaffected and 1 showed an increased response to 20-40 Hz stimuli. A comparison of the reduced responsiveness of 5 units studied during medial lemniscal and somatic stimulation did not reveal any additional response attenuation attributable to subthalamic corticofugal influences. We conclude that, in the awake rat, somatosensory transmission to VB thalamic neurons is primarily facilitated by S1 corticothalamic neurons.

Responsiveness of ventrobasal thalamic neurons after suppression of S1 cortex in the anesthetized rat

Corticofugal influences on the responses of ventrobasal (VB) thalamic neurons to repetitive stimuli were studied in anesthetized rats by suppressing primary somatosensory (S1) electrocortical activity with topically applied lidocaine. Effective concentrations of lidocaine were confined to S1 and immediately adjacent cortex and suppressed evoked S1 responses and corticofugal discharges. Suppression of S1 cortex reduced the average number of spikes discharged by 83 VB neurons in response to each of 25 electrical somatic stimuli delivered at frequencies ranging from 1 to 50 Hz. Of 20 units studied both before and after S1 suppression, 14 (70%) showed a similar reduced response to repetitive stimuli. Cortical suppression produced no consistent changes in spontaneous activity, somatic stimulus threshold, response latency, or size of receptive field. There was no significant difference in the effect of cortical suppression on the responsiveness of 8 VB neurons to repetitive medial lemniscal, as compared to somatic, stimuli. We conclude that, in the anesthetized rat, S1 corticofugal activity facilitates somato-sensory transmission to VB neurons and that this facilitation is mediated, at least in part, by corticothalamic neurons.

9-Hydroxyprostaglandin dehydrogenase from rat kidney. Purification to homogeneity and partial characterization

A 9-hydroxyprostaglandin dehydrogenase has been purified from rat kidney to apparent homogeneity. The molecular weight of the enzyme as determined by gel filtration was 33,000. Electrophoresis in sodium dodecyl sulfate gave a value of 34,000 indicating the absence of subunits. The enzyme catalyzes NAD+-specific irreversible oxidation of 15-keto-13,14-dihydro-prostaglandin F2 alpha as well as of 15-keto-PGF2 alpha and PGF2 alpha although at a lesser degree. It does not catalyze the oxidation of 6-keto-PGF1 alpha. The enzyme was sensitive to sulfhydryl inhibitors and was inhibited by prostaglandins, fatty acids, triiodothyroacetic acid, and indomethacin.

Studies on the thromboxane synthesizing system in human platelet microsomes

The thromboxane synthesizing system from human platelets has been characterized by using arachidonic acid and prostaglandin endoperoxide as indirect and direct substrates. The synthesis of thromboxanes from either substrates catalyzed by the microsomal fraction was monitored by measuring the formation of thromboxane B2 immunoreactivity. Both hemoglobin and phenolic compounds were required for the maximal synthesis of thromboxane B2 from arachidonic acid but not from prostaglandin endoperoxide. Studies on the kinetics of the formation of thromboxane B2 from either substrates indicated that the synthesis of prostaglandin endoperoxide intermediate is the rate-limiting step in the overall production of thromboxanes from arachidonic acid. Effect of the microsomal protein concentrations on the rate of formation of thromboxane B2 showed concave upward relationship suggesting the possible involvement of endogenous stimulator(s) in thromboxane synthetase catalyzed reaction. A variety of compounds including sulfhydryl inhibitors, prostaglandin endoperoxide analog, prostaglandin antagonist, N-0164, and N-substituted imidazoles could directly inhibit the thromboxane synthetase, while nonsteroidal antiinflammatory drugs apparently affected the prostaglandin endoperoxide synthetase which catalyzes the synthesis of the immediate precursor of thromboxanes.

Transformation of arachidonate into 6-oxoprostaglandin F1 alpha, thromboxane B2 and prostaglandin E2 by sheep lung microsomal fraction

In the presence of haemoglobin and isoproterenol, the microsomal fraction of sheep lung catalysed the conversion of arachidonate predominantly into thromboxane B2 and to a lesser extent into 6-oxoprostaglandin F1alpha. Very little prostaglandin E2 and prostaglandin F2alpha were formed. If reduced glutathione was added in combination with haemoglobin and isoproterenol, the synthesis of prostaglandin E2 was favoured over that of thromboxane B2 and 6-oxoprostaglandin F1alpha. The identities of these products were confirmed by t.l.c. and by combined g.l.c.-mass spectrometry. These results indicate that microsomal fraction of sheep lung possesses active prostaglandin synthase, prostacyclin synthase and thromboxane synthase activities.