[The effect of increasing ventral movement on the small solutes transport during peritoneal dialysis]

OBJECTIVE

To investigate whether the small solutes transport and the efficiency of peritoneal dialysis can be improved through ventral movement.

METHODS

Eighteen continuous ambulatory peritoneal dialysis (CAPD) patients and 6 male New Zealand rabbits peritoneal dialysis models were observed. Through self and pre-post control, we compared the concentration ratio of the solutes in effluent dialyste(D) to the solutes in plasma(P), mass transfer area coefficient and the drained volume.

RESULTS

The animal experiments showed that the D/P value for BUN was different prominently when comparing the vibration and non-vibration groups in 45 min and 60 min separately(P < 0.05). On the contrary, no obvious difference existed between the two groups when comparing the D/P values for protein and drained volume. The clinical study showed: D/P value for BUN at the 2 and 4 hr and D/P value for creatinine at the 2 hr increased obviously either in the low or high frequency group when compared with the control group(P < 0.01, P < 0.01, P < 0.05, respectively). D/P for protein and drained volume had no difference compared with the control group(P > 0.05).

CONCLUSION

The ventral movement and vibration could efficiently increase the transport of small solutes such as BUN and creatinine while had no influence on the transport of large molecular solutes such as protein and the ultrafiltration volume. It suggested that increasing the movement of CAPD patients can improve the efficiency of peritoneal dialysis.

[Effects on simvastatin in continuous ambulatory peritoneal dialysis patients with hyperlipidemia]

The therapeutic effects of simvastatin on hyperlipidemia and its protective effects on residual renal function (RRF) in continuous ambulatory peritoneal dialysis (CAPD) patients with hyperlipidemia were observed. Forty-seven CAPD patients were randomly divided into two groups, the treatment group and control group. The treatments of two groups were the same except that the treatment group patients were additionally given simvastatin 20 mg.d-1. The results were that, after 12-week treatment, the total cholesterol (TC), triglyceride (TG), low density lipoprotein (LDL), and apoprotein B100 (ApoB100) in the treatment group significantly decreased, but high density lipoprotein (HDL) and apoprotein A1 (ApoA1) significantly increased compared with the control group (all P < 0.05); one year later, RRF of patients of both groups all decreased but there was no significant difference between them. The results suggest that simvastatin can effectively normalize lipidemia, but has no protective effect on RRF in CAPD patients.

["Bu-yang huanwu tang" inhibited the pathogentic process of atherosclerosis induced by cholesterol-rich diet in rabbits]

BACKGROUND AND OBJECTIVE

"Bu-yang huanwu tang", a decoction of Chinese herbs widely used in the treatment for cardio- and cerebro-vascular diseases, has been demonstrated to be able to inhibit platelet adhesion and aggregation, to lower blood lipids, to regulate vascular tone from animal experiments. The aim of this study is to determine whether this decoction inhibits the pathogentic process of atherosclerosis induced by cholesterol-rich diet in rabbits.

METHODS

Three groups of rabbits received the following different diets for 9 weeks: 1. standard diet; 2. atherogenic diet(standard diet plus 1% cholesterol and 3.3% fat); 3. atherogenic diet plus this decoction(5 g.kg-1.d-1). Plasma lipids, 6-keto-PGF1 alpha, endothelin levels were detected and the histological atherosclerotic changes were evaluated.

RESULTS

This decoction inhibited the progression of aortic and abdominal aortic intimal plaques and reduced aortic intimal thickening.

CONCLUSION

The anti-atherogenic mechanism might be related to the decrease of plasma cholesterol and triglycerides and the increase of PGI2. The facts suggest that "Bu-yang huanwu tang" has antiatherogenic and antithrombotic effects.

[Revision of the biological significance of the contact system]

Current concept of blood coagulation is divided into two stages: an "initiation" stage which is handled by tissue factor pathway, and an "augmentation" stage handled by intrinsic pathway beginning in factor XI. Recent studies have demonstrated that the contact system is a modulator for vascular biology with vascular tone regulation, anticoagulant, profibrinolytic, antiadhesive and proinflammatory functions. Changes of contact system are associated with sepsis, thrombosis, etc.

Assessment of renal function in the early stages of nephrotoxicity induced by iodinated contrast media

To determine whether there are early renal function parameters (RFP) which can be monitored to rapidly detect nephrotoxicity induced by contrast media (CM), we observed RFP in 16 patients with normal renal function before and after administration of CM. Forty-eight hours after diatrizoate meglumine administration, blood urea nitrogen (BUN) and serum creatinine (SCr) increased (p < 0.05). In all patients, acute tubular damage was revealed by early urinary RFP. Increases in levels of serum angiotensin-I-converting enzyme (ACE), beta(2)-microglobulin (beta(2)M) and urinary albumin (Alb) were associated with alterations in glomerular function. The changes in early RFP occurred earlier than those of BUN and SCr. The present study demonstrates that serum ACE, beta(2)M, urinary Alb, gamma-glutamyl-transpeptidase and N-acetyl-beta-D-glucosidase are sensitive parameters for the early assessment of subclinical nephrotoxicity induced by CM.

Assessment of urinary endothelin-1 and nitric oxide levels and their relationship with clinical and pathologic types in primary glomerulonephritis

To determine the relationship between the urinary endothelin (ET-1), nitric oxide (NO) levels and the clinical, pathologic types of primary glomerulonephritis (GN) patients, urinary levels of ET-1 and NO were detected in 27 patients with biopsy-proven primary GN and 12 normal controls by radioimmunoassay and by copper-plated and cadmium column reduction assay, respectively. The results showed that urinary ET-1 levels in the patients with primary GN were significantly higher than in normal controls (p < 0.01), while the urinary ET-1 levels in patients with moderate mesangial proliferation GN were significantly higher than those in patients with mild mesangial proliferation GN (p < 0.05). Urinary ET-1 levels in patients whose clinical feature was nephrotic syndrome were found to be higher than in patients whose clinical feature was nephritic syndrome. However, urinary NO levels were to the contrary (p < 0.05). The ratio of ET-1/NO in primary GN patients was significantly higher than that in normal controls, and it positively correlated with the 24-hour urinary excretion of protein. These results suggest that urinary ET-1 levels are related to the proliferation of mesangial cells. The imbalance between ET-1 and NO may be related to the pathogenesis of primary GN and the occurrence of proteinuria.

False-positive 2-[F-18]-fluoro-2-deoxy-D-glucose positron emission tomography studies for evaluation of focal pulmonary abnormalities

Positron emission tomography (PET) with 2-[F-18]-fluoro-2-deoxy-D-glucose (FDG) can demonstrate the glucose metabolism characteristics of a lesion, which may be helpful in differentiating between benign and malignant focal pulmonary lesions. Malignant cells demonstrate higher glucose metabolic activity than benign lesions. However, some inflammatory processes also show significant FDG uptake. We present two cases where high FDG uptake was found in inflammatory lesions in the lungs. The first case was that of a 38-year-old woman with chronic cough for more than 20 years. FDG PET revealed a hypermetabolic lesion with a lesion-to-background ratio of 8.0 at the posterior aspect of the right middle lung. She underwent thoracotomy and tumor resection, and was diagnosed with cryptococcosis. The second case was that of a 72-year-old woman who had pulmonary tuberculosis previously with cavitation in the left lower lobe. She suffered from fever, chills and severe hemoptysis for several days before this admission. FDG PET revealed a hypermetabolic ring at the periphery of the cavity. The lesion-to-background ratio was 7.8. Echo-guided biopsy showed no evidence of malignancy. She was treated with antibiotics and the symptoms subsided gradually. Lung abscess complicating a pre-existing cavity was diagnosed. These two cases substantiate that positive FDG PET results should be interpreted with caution in differentiating benign from malignant pulmonary abnormalities, especially in regions with a high prevalence of granulomatous lesions.

Effects of vitamin C on myocardial mitochondrial function and ATP content in hypoxic rats

AIM

To observe the effects of large dose of vitamin C (Vc) on myocardial mitochondrial function, ATP content, and myocardial structure in acute and chronic hypoxic rats.

METHODS

Rats were exposed to a simulated altitude 4000 m (barometric pressure = 43 kPa) for 3 and 30 d. Vc (0.75 g.kg-1.d-1) was injected i.p. The heart mitochondrial respiratory function were determined by Clark-type O2 electrode; mitochondrial membrane fluidity (MMF) were assayed through fluorescence polarizative method; the contents of ATP, ADP, and AMP in myocardial tissue were measured with HPLC.

RESULTS

After administration of Vc, the ATP content was increased from 35 +/- 3 mg.g-1 to 53 +/- 3 mg.g-1 in acute hypoxic rats (P < 0.01), from 42 +/- 4 mg.g-1 to 48 +/- 3 mg.g-1 in chronic hypoxic rats (P < 0.01); Pa, O2 was increased from 7.2 +/- 1.4 kPa to 9.5 +/- 1.2 kPa in acute hypoxic rats (P < 0.01); mitochondrial respiratory control rate (RCR) was increased from 2.1 +/- 0.6 to 4.7 +/- 0.5 in acute hypoxic rats (P < 0.01), and from 3.3 +/- 0.7 to 4.5 +/- 0.6 in chronic hypoxic rats (P < 0.01); MMF was increased in acute and chronic hypoxic rats (P < 0.05); the degree of myocardial necrosis in vitamin C preventive rats was attenuated as compared with those of acute hypoxic rats.

CONCLUSION

Vc is effective on improving myocardial energy metabolism and protecting against myocardial structural injury in hypoxic rats.

[Heat shock response induces resistance to hydrogen peroxide and increases synthesis of interleukin-6 in rat astrocyte in vitro]

Cell viability and cell membrane disruption of rat astrocyte after heat shock response (HSR) were assessed by the analysis of MTT reduction and lactate dehydrogenase (LDH) release. We studied whether HSR would modulate the susceptibility of astrocyte to H2O2-induced oxidative stress. Cell viability was assessed by reduction of MTT. HSR in 43 degrees C water bath for 30 min decreased H2O2 toxicity (P < 0.01) to astrocyte. HSR induced decrease in H2O2 (50 mumol/L) toxicity was also shown by the reduction in the release of LDH, which was a marker of cell membrane disruption. The result also showed that prior to the incubation in 43 degrees C water bath for 30 min strongly increased IL-6 release 6 h (P < 0.05) after HSR. The above data suggest that the enhanced release of IL-6 from astrocyte may be one of the mechanisms underlying the cell protective effect induced by HSR.

In vitro-in vivo relationship of oral extended-release dosage forms

PURPOSE

A method to establish the in vitro-in vivo relationship of oral extended-release products is proposed.

METHODS

The approach utilizes incremental amounts of drug released and absorbed within defined time intervals, to construct a chi2 distributed variable for testing in vitro-in vivo similarity.

RESULTS

A case study is used to demonstrate that the similarities between incremental values of in vivo absorbed and in vivo dissolved fractions are distinguishable for different dissolution profiles despite naturally significant linear correlations between cumulative in vivo absorbed and in vitro dissolved fractions (with different dissolution tests) of an oral extended-release product.

CONCLUSIONS

The method enables investigators to compare different in vitro dissolution profiles of an oral extended-release product to find an optimized dissolution profile to be the surrogate of the in vivo release process of the product.

Preventive and therapeutic effects of nitrendipine on hypoxic right ventricular hypertrophy

AIM

To assess whether nitrendipine (Nit) can be used to prevent and treat the hypoxic right ventricular hypertrophy (RVH).

METHODS

Rats were exposed to a simulated altitude of 5000 m (barometric pressure = 54 kPa) for 30-60 d. Nit (10-20 mg.kg-1.d-1) was administered via gavage. The therapeutic efficacy was evaluated with right ventricular weight index (RVWI), right ventricular systolic pressure (RVSP), and myocardial ultrastructure.

RESULTS

Chronic intermittent hypoxia for 30 d (8 h.d-1) resulted in an increase of RVSP and RVWI as well as in the changes of RV myocardial ultrastructure. As the hypoxic time was prolonged to 60 d, RVWI and RVSP were not further augmented. Nit (20 mg.kg-1.d-1, i.g.), when administered from the beginning of hypoxia, reduced RVSP (8.1 +/- 1.1 vs 6.0 +/- 1.0 kPa, P < 0.05) and RVWI (1.014 +/- 0.012 vs 0.915 +/- 0.049 mg/g body weight, P < 0.05). After development of hypoxic RVH, Nit (20 mg.kg-1) also decreased RVSP (7.9 +/- 1.0 vs 6.2 +/- 0.8 kPa, P < 0.05) and RVWI (1.02 +/- 0.13 vs 0.88 +/- 0.12 g/kg body weight, P < 0.05). Myocardial blood flow was increased and myocardial ultrastructure became nearly normal in rats treated with Nit.

CONCLUSION

Nit prevented and lessened the hypoxic right ventricular hypertrophy.

Pharmacokinetics of oral extended-release dosage forms. I. Release kinetics, concentration, and absorbed fraction

In this study, we derive pharmacokinetic models for oral extended-release (OER) drug products with defined in vivo release kinetics (IVRK) and a compartmental system. Fitting the model to clinical data, we were able to examine the correlation between released and absorbed fractions. Furthermore, we found that absorbed fractions of OER products can be expressed by absorption rate and release duration only. The expression is unchanged in different compartmental systems with the same IVRK, implying that the IVRK drives the pharmacokinetic system of an OER product. The apparent absorption rate constant of an OER product can be estimated by solving an implicit equation using observed concentrations. We also propose a new method for calculating absorbed fractions, which is more accurate than Loo-Riegelman method. Ultimately, these methods may permit optimally designed OER products.

Pulmonary delivery of free and liposomal insulin

The effects of oligomerization and liposomal entrapment on pulmonary insulin absorption were investigated in rats using an intratracheal instillation method. The results indicated that both dimeric and hexameric insulins can be rapidly absorbed into the systemic circulation, producing a significant hypoglycemic response. Intratracheal instillation of insulin in two different oligomerized states has not resulted in any significant difference in the duration of hypoglycemic effect. However, the initial hypoglycemic response (first 10 min) obtained from intratracheal administration of 25 IU/kg hexameric insulin appears to be slower than that from the 25 IU/kg dimeric insulin, thereby suggesting that hexameric insulin may have a lower permeability coefficient across alveolar epithelium than the dimeric insulin. Intratracheal administration of insulin liposomes (dipalmitoylphosphatidyl choline:cholesterol, 7:2) led to facilitated pulmonary uptake of insulin and enhanced the hypoglycemic effect. Nevertheless, similar insulin uptake and pharmacodynamic response were obtained from both the physical mixture of insulin and blank liposomes and liposomally entrapped insulin.

Cerebellar stimulation modulates thalamic noxious-evoked responses

Parafascicular (PF) neurons responding to noxious stimuli and focal electrical stimulation of midbrain, diencephalon, and hypothalamic nuclei, which send projections to PF, modulates the PF spontaneous and noxious-evoked responses. Some cerebellar efferents ascend to PF. This investigation attempted to study the effect of cerebellar stimulation on spontaneous and noxious-evoked PF neuronal activity in rats. It was observed that 26% (73/280) of PF neurons responded to a noxious stimulus. The PF neuronal population exhibits two cell types according to their response pattern following the noxious stimulus. One type of PF neurons were excited (n = 53) and were classified as nociceptive-on cells. The second type of PF neurons responded to noxious stimulus by a decrease in the ongoing firing rate (n = 20) and were classified as nociceptive-off cells. The responses of these two types of nociceptively identified cells were tested following cerebellar lateral nucleus stimulation (Lat.N.S.) utilizing several current intensities. Lat.N.S. with lower intensities (0.1-0.2 mA) elicited suppression of both spontaneous and nociceptive-evoked discharges of the nociceptive-on neurons, although higher intensities (0.4-0.6 mA) elicited excitation on both discharges of this type of neuron. In contrast, Lat.N.S. induced a monophasic intensity-dependent suppression of both the spontaneous and the nociceptive-evoked discharges of the nociceptive-off neurons. The results indicate that Lat.N.S. modulates the nociceptive-evoked responses of PF neurons. The possible role and related pathways of cerebellum in modulating noxious input were discussed.

Pulmonary biotransformation of insulin in rat and rabbit

In vitro biodegradation of insulin in rabbit and rat lung homogenates was investigated. Insulin can be sequentially metabolized into two primary fragments in rabbit lung homogenate by an aminopeptidase. The amino acid sequences of the fragments were found to be the des-Phe-InsulinB1 (Metabolite I) and des-Phe-Val-InsulinB1-2 (Metabolite II). However, only the former metabolite (Metabolite I) was identified in the rat lung homogenate. The km and Vm values associated with rabbit lung homogenate were 0.29 +/- 0.14 mM and 16.4 +/- 6.9 microM/hr/mg protein, respectively, whereas those for a rabbit lung preparation containing both microsomes and cytosol were 0.22 +/- 0.07 mM and 17.9 +/- 5.4 microM/hr/mg protein, respectively. The km and Vm associated with the cytosolic fraction of rabbit lung were 0.32 +/- 0.16 and 20.6 +/- 6.1 microM/hr/mg protein, respectively. The results indicate that the lung aminopeptidase may be a cytosolic enzyme. The degradation of dimeric insulin in the lung homogenate was faster than that of hexameric insulin due to the difference in collision frequency between the enzyme and insulin aggregates. The major metabolites in the lungs reportedly retain almost the same bioactivity of insulin, suggesting that the pulmonary route of insulin delivery will not adversely affect its hypoglycemic activity.

Comparison of inhibitory potency by nonpeptide angiotensin II receptor antagonists PD123177 and DuP 753 on proximal nephron and renal transport

The nonpeptide angiotensin II receptor antagonists, DuP 753 and PD123177, have been recently proposed to efficiently discriminate between two receptor subtypes. Because angiotensin II uses two signaling systems to control transport in the proximal tubule, the hypothesis was entertained that angiotensin-regulated proximal reabsorption might be transduced through two receptor subtypes and, therefore, have two components, sensitive to either DuP 753 or PD123177. Using in vivo microperfusion in the rat, a maximally effective dose of PD123177 (60 or 120 mg/kg, i.v.) had a powerful inhibitory effect on transport in the S1 proximal tubule, significantly (P less than .001) reducing bicarbonate absorption by 50% (360 +/- 4 to 179 +/- 8 peq/mm.min), chloride absorption by 38% (211 +/- 1 to 131 +/- 4 peq/mm.min) and sodium and water absorption by 32% (5.7 +/- 0.1 to 3.9 +/- 0.5 nl/mm.min). These results were only slightly different than previously reported effects on proximal solute and water absorption by DuP 753 (10 mg/kg). The two drugs demonstrated virtually no additivity in their transport inhibitory effects. Although downstream reabsorptive elements compensate for the powerful action of PD123177 in the earliest segment of the nephron, we also showed, using free-flow micropuncture and clearance techniques, that PD123177 induces a substantial diuresis, natriuresis and chloruresis, again similar in magnitude to DuP 753. These results suggest PD123177 has diuretic potency roughly equivalent to that of DuP 753, but do not lend support to the simple thesis that there are two separately acting receptor-signal transduction systems in the proximal tubule for angiotensin II.

The herpes simplex virus 1 gene encoding a protease also contains within its coding domain the gene encoding the more abundant substrate

The herpes simplex virus 1 open reading frames UL26 and UL26.5 are 3' coterminal. The larger, UL26 open reading frame encodes a protein approximately 80,000 in apparent molecular weight and contains the promoter and coding sequence of the UL26.5 gene, which specifies a capsid protein designated infected cell protein 35. The larger product contains in its entirety the amino acid sequence of the smaller protein. We report that the UL26 gene encodes a protease which catalyzes its own cleavage and that of the more abundant product of UL26.5. By inserting the coding sequence of an epitope to a cytomegalovirus monoclonal antibody and homologs of the immunoglobulin G binding domain of staphylococcal protein A into the 3' termini of the coding domains of the two open reading frames, we identified both products of the cleavage and determined that the cleavage site is approximately 20 amino acids from the carboxyl termini of both proteins.

Insulin aggregation in aqueous media and its effect on alpha-chymotrypsin-mediated proteolytic degradation

Self-association of zinc-insulin monomers into dimers and hexamers may lead to enhanced protection of the peptide from proteolytic degradation. The present study has been undertaken to investigate the relationship, if any, between the rate of enzymatic degradation of insulin by a protease, alpha-chymotrypsin, and the extent of insulin aggregation in aqueous solutions. Insulin solutions (0.6 mg/ml) containing varying proportions of dimer and hexamer were obtained by adding ethylene diamine tetraacetic acid (EDTA) within a concentration range of 0.005 to 0.040 mM. As the EDTA concentration was increased above 0.040 mM, a complete dissociation of hexamers to dimers occurred and the rate of enzymatic degradation reached its maximum. The overall first-order rate constants appeared to be linearly related to the square of EDTA concentrations. The apparent first-order rate constants for dimer and hexamer degradation obtained from a linear plot of rate constant versus EDTA squared concentration were found to be 0.02800 +/- 0.00065 and 0.00798 +/- 0.00075 min-1, respectively. Two major insulin degradation products were also detected and the kinetics of product appearance agreed well with the disappearance kinetics of insulin. The results indicated that the degradation of insulin dimers by alpha-chymotrypsin is about 3.5 times faster than the degradation of the hexamer. The second-order dependency of degradation rate on EDTA concentration might be due to the fact that insulin hexamers contain two zinc ions which are sequestered by two EDTA molecules. Chelation of zinc ions by EDTA lead to hexamer deaggregation to dimers as was evidenced from a circular dichroism study.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of DuP 753 on proximal nephron and renal transport

We used the nonpeptide angiotensin II receptor antagonist DuP 753, which lacks the agonist and kinin/prostaglandin-inducing properties of saralasin and captopril, respectively, to examine the role of endogenous angiotensin II in regulating transport in the proximal convoluted tubule (PCT) and whole kidney. During in vivo microperfusion in the Munich-Wistar rat, a maximally effective dose of DuP 753 (10 mg/kg, intravenously) powerfully inhibited absorption of bicarbonate (370 +/- 3 to 200 +/- 9 pEq/mm.min, P less than .001), chloride (214 +/- 3 to 105 +/- 9 pEq/mm.min, P less than .001), and water 5.2 +/- 0.1 to 2.8 +/- 0.2 nL/mm.min, P less than .001) in the S1 subsegment of the PCT. DuP 753 was significantly more effective than captopril (3 mg/kg, intravenously) in inhibiting sodium chloride transport and is the most potent diuretic ever described in this segment. Consistent with the axial decline of angiotensin II receptor density in the PCT, DuP 753 was a less effective transport inhibitor in the S2 subsegment of the PCT, similar to captopril. Using free-flow micropuncture and clearance techniques, though inhibition in the earliest segment of the nephron is partially compensated by downstream reabsorption, DuP 753 induces a substantial diuresis, natriuresis, and chloruresis. In conclusion, DuP 753 markedly decreases S1 PCT fluid and electrolyte absorption, indicating that endogenous angiotensin II exerts significant tonic support of proximal transport in vivo.

The promoter, transcriptional unit, and coding sequence of herpes simplex virus 1 family 35 proteins are contained within and in frame with the UL26 open reading frame

The herpes simplex virus 1 (HSV-1) genome specifies an abundant capsid protein which in denaturing gels forms multiple bands designated family 35 proteins (D.K. Braun, B. Roizman, and L. Pereira, J. Virol. 49:142-153, 1984). Nucleotide-sequencing studies have assigned the coding sequences of these proteins to the open reading frame UL26 (D.J. McGeoch, M.A. Dalrymple, A.J. Davidson, A. Dolan, M.C. Frame, D. McNab, L.J. Perry, J.E. Scott, and P. Taylor, J. Gen. Virol. 69:1531-1574, 1988). IN studies reported here, a series of plasmid constructs containing deletions or insertions of an alpha 4 promoter or of a sequence encoding a cytomegalovirus epitope reacting with a mouse monoclonal antibody revealed the following: the open reading frame previously designated UL26 encodes two proteins which share amino acid sequences, and each coding domain is contained in its own transcriptional unit that terminates at a common, unique poly(A) site. On the basis of the transcription initiation site (+1), it was predicted that the UL26 open reading frame encodes a protein of 635 amino acids, and a protein with an apparent molecular weight of approximately 75,000 has been identified. The second transcriptional unit, designated UL26.5, predicted to specify a protein of 329 amino acids, encodes the family 35 proteins; it is transcribed by an mRNA which initiates at approximately nucleotide +1000 of the UL26 transcription initiation site and is translated from the methionine initiation codon located at position +1099 of the UL26 transcriptional unit. The DNA fragment comprising the sequences downstream of the HpaI cleavage site (+832 of UL26) contains both the promoter and the coding sequence of family 35 proteins and is both competent and efficient in expressing the proteins in transfected cells superinfected with HSV-1 or HSV-2.

A new approach to the modeling and control of postoperative pain

The objective of this paper has been to explore contributions which the technology of control engineering can make to the relief of postoperative pain. A human-operated, closed-loop, analgesic drug injection system has been designed to alleviate chronic pain. In this system, a patient presses a button when pain relief is required. A computer interfaces the button to the patient's drug injection pump. A patient pain model has been developed to describe the dynamics of the human physiological and psychological responses to chronic pain. A pharmacokinetic model of analgesia is also included. The pain model has been validated by adjusting its parameters so that its behavior mimics actual button-pressing records of self-administered analgesia. A modified Smith delay compensator and IPFM controller are used to compensate for the inherent nonlinearity of the system and to obtain the high performance required. The results of this simulation study are promising. The nonlinear patient pain model represents a contribution to the description of the dynamics and quantification of pain. The control algorithms proposed have shown, through modeling studies, an improvement in the performance of self-administered analgesia systems. The simulated patients obtained good pain relief without excessive button-pressing, and without undesirable high concentrations of opioids being observed. The SDC/IPFM controller architecture has been found to be robust in the presence of pain noise and pharmacokinetic plant parameter changes.

Proximal nephron and renal effects of DuP 753, a nonpeptide angiotensin II receptor antagonist

The purpose of these studies was to quantitatively assess the role of endogenous angiotensin II activity in controlling transport in the proximal convoluted tubule (PCT) and whole nephron. We used the nonpeptide angiotensin II receptor antagonist DuP 753, which lacks the agonist and kinin/prostaglandin-inducing properties of saralasin and captopril, respectively. During in vivo microperfusion in the Munich-Wistar rat, we found that DuP 753 had a powerful inhibitory effect on bicarbonate (370 +/- 3 to 200 +/- 9 pEq/mm.min, P less than 0.001), chloride (214 +/- 3 to 105 +/- 9 pEq/mm.min, P less than 0.001), and water (5.2 +/- 0.1 to 2.8 +/- 0.2 nl/mm.min, P less than 0.001) absorption in the S1 subsegment of the PCT. At maximally effective doses, DuP 753 (10 mg/kg i.v.) was significantly more effective than was captopril (3 mg/kg i.v.) in inhibiting sodium chloride transport in the S1 PCT. DuP 753 is the most potent diuretic ever described in this segment. Consistent with the axial decline of angiotensin II receptor density in the PCT, DuP 753 was a less effective transport inhibitor in the S2 subsegment of the PCT, similar to captopril. Though downstream reabsorptive elements partially compensate for the action in the earliest segment of the nephron, we also showed using free-flow micropuncture and clearance techniques that DuP 753 induces a substantial diuresis, natriuresis and chloruresis. In conclusion, the marked decrease in S1 PCT fluid and electrolyte absorption induced by DuP 753 indicates that endogenous angiotensin II exerts significant tonic support of proximal transport in vivo.

Effects of intracellular calcium on proximal bicarbonate absorption

Using in vivo microperfusion in the proximal convoluted tubule (PCT) of the Munich-Wistar rat, we assessed the impact of raising intracellular calcium concentration on bicarbonate transport and its regulation by angiotensin II. Luminal perfusion with the calcium ionophore A23187 caused a dose-dependent increase in S1 PCT bicarbonate absorption, with a maximal change of 60 peq.mm-1.min-1. Subsequent addition of phorbol ester (PMA) after A23187 further increased transport but to a level no higher than previously shown with PMA alone, and A23187 was nonstimulatory when added after PMA. These results suggest that intracellular calcium affects the same pathway as protein kinase C in stimulating proximal acidification. Pretreatment with A23187 (+/- PMA) attenuated by approximately one-third the bicarbonate absorptive response in the S1 PCT usually observed after angiotensin II administration. A23187 had similar actions, but of smaller magnitude, in the S2 PCT. In conclusion, a rise in intracellular calcium increases bicarbonate absorption in the S1 and S2 PCT in vivo.