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Biomedical subjects

R K Sharma

Publications and source records attributed to R K Sharma.

At least 577 records · Page 32Linked to original sources

Signal transduction: regulation of cAMP concentration in cardiac muscle by calmodulin-dependent cyclic nucleotide phosphodiesterase.

The bovine heart calmodulin-dependent phosphodiesterase can be phosphorylated by cAMP-dependent protein kinase, resulting in a decrease in the enzyme's affinity for calmodulin. The phosphorylation of calmodulin-dependent phosphodiesterase is blocked by Ca2+ and calmodulin and reversed by the calmodulin-dependent phosphatase. The dephosphorylation is accompanied by an increase in the affinity of the phosphodiesterase for calmodulin. The CaM-dependent phosphodiesterase isozymes of heart and brain are regulated by calmodulin, but the affinity for calmodulin are different. Furthermore, the bovine heart CaM-dependent phosphodiesterase isozyme in stimulated at much lower Ca2+ concentration than the bovine brain isozymes. Results from this study suggest that the activity of this phosphodiesterase is precisely regulated by cross-talk between Ca2+ and cAMP signalling pathways.

3',5'-Cyclic-AMP Phosphodiesterases↗

Purification and characterization of the 180-kDa membrane guanylate cyclase containing atrial natriuretic factor receptor from rat adrenal gland and its regulation by protein kinase C.

The original concept that cyclic GMP is one of the mediators of the hormone-dependent process of steroidogenesis has been strengthened by the characterization of a 180-kDa protein from rat adrenocortical carcinoma and rat and mouse testes. This protein appears to have an unusual characteristic of containing both the atrial natriuretic factor (ANF)-binding and guanylate cyclase activities, and appears to be intimately involved in the ANF-dependent steroidogenic signal transduction. In rat adrenal glands we now demonstrate: 1) the direct presence of a 180-kDa ANF-binding protein in GTP-affinity purified membrane fraction as evidenced by affinity cross-linking technique and by the Western blot analysis of the partially purified enzyme; 2) that the enzyme is biochemically and immunologically different from the soluble guanylate cyclase as there is no antigenic cross-reactivity of 180-kDa guanylate cyclase antibody with soluble guanylate cyclase; 3) in contrast to the soluble guanylate cyclase, the particulate enzyme is not stimulated by nitrite-generating compounds and hemin; and 4) protein kinase C inhibits both the basal and ANF-dependent guanylate cyclase activity and phosphorylates the 180-kDa guanylate cyclase. These results reveal the presence of a 180-kDa protein in rat adrenal glands and support the contention that: (a) this protein contains both the guanylate cyclase and ANF receptor; (b) the 180-kDa enzyme is coupled with the ANF-dependent cyclic GMP production; (c) the 180-kDa enzyme is biochemically distinct from the nonspecific soluble guanylate cyclase; and (d) there is a protein kinase C-dependent negative regulatory loop for the operation of ANF-dependent cyclic GMP signal pathway which acts via the phosphorylation of 180-kDa guanylate cyclase.

Adrenal Cortex Neoplasms↗

Management of hereditary retinal degenerations: present status and future directions.

Research on hereditary retinal degenerations has considerably improved our understanding of these disorders, although much remains to be learned about the exact mechanism involved in the pathogenesis. The advent of recombinant DNA technology will refine diagnostic capabilities, which have so far been based on the manifestations of the disease to localization of the molecular defects. The correlation of the molecular defects with the phenotype of the disease will result in better prognostic counseling for patients. In certain forms of retinitis pigmentosa, such as Refsum disease, gyrate atrophy of the choroid and retina, and abetalipoproteinemia, exact biochemical defects have been identified and specific treatments have been applied with some success. In other forms of retinitis pigmentosa, various investigations have suggested the possibilities of arresting the progress of degeneration by means such as the use of growth factors and controlling apoptosis. Efforts to alter the expression of the mutated gene or to introduce a normal gene into the genome are in their infancy, but results are encouraging. Vitamin A has been tried in patients with retinitis pigmentosa, and the results demonstrate statistically significant beneficial effects of this vitamin, suggesting that the course of the disease can be decelerated to some extent. Another interesting research area with potential for therapeutic application is the replacement of the retinal pigment epithelium or the degenerated neural retina by transplantation of the respective cell types. Clinical trials are being conducted both with retinal pigment epithelium and neuroretinal transplants.

Animals↗

Chronic hepatitis C virus infection in renal transplant: treatment and outcome.

BACKGROUND: Chronic hepatitis C virus (HCV) infection is a common cause of liver disease in post-renal transplant period and causes poor patient and graft survival. We analyzed the effects of antiviral therapy using ribavirin monotherapy or ribavirin in combination with interferon (IFN)-alpha in our kidney transplant recipients with chronic hepatitis C. METHODS: Total of 14 patients received antiviral therapy, all of whom had stable graft function, raised aminotransferases and positive HCV viremia at the start of treatment. Eight patients received ribavirin alone for a period of six months to two yr, in doses of 400-800 mg daily. Five patients received IFN-alpha therapy for a period of two months to 1.5 yr, in doses of 1.5 million units daily or three million units thrice weekly with ribavirin. One patient received pegylated IFN 50 microg once weekly in combination with ribavirin. The response was seen in terms of biochemical and virological improvement at the end of study period. RESULTS: In patients treated with ribavirin alone (n = 8), mean alanine aminotransferase (ALT) levels before and after treatment were significantly different (198.4 +/- 147.6 and 104.8 +/- 66.5 IU/L respectively; p < 0.05). ALT levels normalized completely in three patients at the end of treatment, improved in three patients and deteriorated in two. Only in one of eight patients on ribavirin alone, HCV-RNA became negative after six months of treatment while in the rest (n = 7) HCV-RNA continued to be positive. In subjects on IFN plus ribavirin (n = 6), the mean ALT levels decreased significantly (from 280.2 +/- 114.9 IU/L at baseline to 71 +/- 49 IU/L at end of therapy; p < 0.05). Two patients had sustained remission (33.3%) on IFN plus ribavirin (persistently negative HCV-RNA), two patients relapsed after initial remission and in two patients treatment was stopped after two months because of graft dysfunction. Totally four patients developed graft dysfunction at some time during the course of IFN therapy (66.6%), but it was discontinued in only two (33.3%). All patients regained normal creatinine levels after discontinuation of IFN, although one patient developed chronic allograft nephropathy as shown by kidney biopsy. Four patients in IFN group developed leucopenia. Two patients developed severe anemia one of whom required blood transfusion and one developed severe flu-like syndrome requiring stoppage of therapy. CONCLUSION: Ribavirin monotherapy in renal transplant recipients with chronic hepatitis C infection results in good biochemical response but is not associated with virological clearance. IFN in combination with ribavirin is effective in two-thirds of patients after a minimum therapy of six months, but it is poorly tolerated, results in graft dysfunction in significant number of patients, and relapse can occur after stopping treatment.

Adult↗

Expression of nitric oxide synthase during the development of RCS rat retinas.

Nitric oxide (NO) has been reported to be both neurodestructive and neuroprotective in the central nervous system and could possibly play an important role in neurodegenerative disorders. On the assumption that NO synthesis may influence degenerative processes in the retina, we have examined the development and distribution of nitric-oxide-synthase(NOS)-immunoreactive cells in developing Royal College of Surgeons (RCS) rat retinas, which is an animal model for retinal degeneration. An antibody against constitutive neuronal NOS was used for immunocytochemistry on RCS rat retinas from postnatal (PN) days 3, 7, 10, 14, 35, 70 and 281 and compared with that in the normal rats of PN days 3, 7, 10, 14, 54 and adults. Immunoreactive cells were not seen in PN 3 retinas but were distinctly seen in the PN 7 retina along with a plexus in the inner plexiform layer. In both groups (normal and RCS rats) a distinct sublayering of the plexus in the inner plexiform layer could be seen at PN 10, which became more distinct at PN 14. The immunoreactive cells were detected also in the oldest retina examined, which was PN 281 in the case of RCS rats. In both groups, certain amacrine cells, certain bipolar cells and certain horizontal cells were found to be immunoreactive. In conclusion, the developmental timetable of the NOS immunoreactivity was identical in the normal and the RCS rat retinas. The NOS-immunoreactive cells persisted in the RCS retinas even when the retina had degenerated extensively. Abnormalities with the inducible isoforms of NOS cannot be ruled out from this study. We conclude that the chronological and qualitative development of the constitutive neuronal NOS immunoreactivity is normal in RCS rat retinas.

Animals↗

Developmental expression of GABA(A) receptors in retinal transplants.

gamma-Aminobutyric acid (GABA) has transiently been found in certain retinal cells during development, and thus it has been suggested that besides its role as an inhibitory neurotransmitter, it also plays a role during the development of the retina. Further it has been suggested that this developmental role of GABA is mediated through GABA(A) receptors. Retinal cell transplants are being tried for the treatment of degenerative retinal disorders. Even though the donor tissue continues to proliferate, to develop and to differentiate after transplantation, its development is not entirely normal. Various neurotransmitters have been found in retinal transplants, but the receptors, which are needed for their action, have not been demonstrated. It was therefore of interest to see the expression of GABA(A) receptors during the development of the transplants. Embryonic day (E) 15 rabbit retinas were transplanted into the eyes of adult rabbits. Transplants were allowed to survive for various times so that the grafts attained the equivalent ages of (donor age + survival time) E 19, 21, 26, 29 and postnatal (PN) day 2, 5, 9, 19 and 95. On formaldehyde-fixed cryostat sections of the transplant tissue immunohistochemistry was performed. Antibodies against the alpha(1) and beta(2/3) subunits of the GABA(A) receptors were used to demonstrate these receptors. No immunoreactivity was detected in transplants of ages E 19 and 22. The GABA(A) receptor beta(2/3) subunit first appeared in E 29 transplants, whereas the GABA(A) receptor alpha(1) subunit was first detected at PN 2. At these ages faint immunoreactivity was detected in certain plexiform layers in the transplants. In older ages the immunoreactivity increased and also appeared in certain cells lying in between the rosettes along with the plexiform layers that are equivalent to the inner and the outer plexiform layers of the normal retina. The development of the GABA(A) receptor alpha(1) and beta(2/3) subunit immunoreactivity compared well with that during the development of the normal retina. The results suggest that GABA present in the retinal transplants can exert its action through its receptors.

Animals↗

Cell proliferation in retinal transplants.

The MIB-1 antibody against a nuclear protein Ki-67 was used to study the proliferation of cells in the rabbit retinal transplants. Fragmented pieces of embryonic day 15 rabbit retinas were transplanted into the subretinal space of adult rabbits and allowed to survive for different times. Fragmented donor tissue starts organizing in rosettes 1 day after transplantation. The transplanted cells continue to proliferate in the host eye and their pattern of proliferation resembles that of normal developing retina, suggesting that the factors responsible for the proliferation pattern are preserved after transplantation. The dividing cells in metaphase line up in the luminal layers of the rosettes. Certain cells become postmitotic in the regions corresponding to the inner retina first, followed by the cells in the luminal layers of rosettes. Cells in the regions between the rosettes, corresponding to the inner nuclear layer, presumably the Müller cells, proliferate significantly for the equivalent age of postnatal day 2. Few cells in these regions proliferate for at least the equivalent age of postnatal day 11 in transplants. There is a layer of nonproliferating, degenerating cells in the transplant situated close to the host retina. However, some cells in this layer, situated at the host-graft interface, proliferate. These cells proliferate for a long time possibly indicating gliosis.

Animals↗

Soluble substituted poly-p-phenylenes--a new material for application in light-emitting diodes: synthesis and characterization.

Poly-p-phenylenes have attracted a great deal of attention with respect to their applications in displays, light-emitting devices, and batteries. However, the polymer poly-p-phenylene obtained by the Kovacic method is insoluble and intractable. The present study reports the preparation of soluble poly(p-phenylenes) by polymerization of derivatives of benzene in the presence of a specific aromatic nuclei. The resultant copolymer so obtained is soluble in common organic solvents such as chloroform and toluene. Preliminary studies have indicated that the polymer shows orange photoluminescence and electroluminescence when a potential of 7-10 V is applied to the device.

Chloroform↗

Effect of centrifuge speed, refrigeration medium, and sperm washing medium on cryopreserved sperm quality after thawing.

Cryopreservation and subsequent thawing of semen for assisted reproductive procedures decreases sperm motility; motility further reduces when the cryoprotectant medium is removed because of the osmotic shock and centrifugation done to prepare the sperm. To compare motility and thus pregnancy rates, this study examined the effects of adding an additional refrigeration medium and three different centrifugation speeds for sperm preparation. Semen samples from 16 healthy normal volunteers were obtained by masturbation after 48 h of abstinence. Sperm motility and other motion characteristics were analyzed with a computer-assisted semen analyzer before freezing, after thawing, and after centrifugation. Each sample was divided into 6 aliquots and frozen using the liquid nitrogen vapor method. After thawing, human tubal fluid (HTF) with 5% human serum albumin was added to 3 aliquots, and refrigeration medium (identical to freezing medium without glycerol) was added to the remaining 3 tubes for each specimen. The tubes containing the two media were then washed by centrifugation at 100 g, 300 g, and 500 g for 10 min. Aliquots with refrigeration medium did not significantly differ from those with HTF for percent motility, curvilinear velocity, straight-line velocity, and amplitude of lateral head displacement at any centrifugation speed. Motile sperm count was significantly greater only at 100 g and 300 g for refrigeration medium (p = .02 and .01) and HTF (p = 0.001); at 300 g, average path velocity in refrigeration medium aliquots (p = .01) and linearity in HTF (p = .01) were greater. The results indicated that the reduction in motility and other motion characteristics probably cannot be overcome by changing factors such as the sperm preparation medium or centrifugation speed. More effective cryopreservation techniques or preparation methods that eliminate centrifugation need to be developed.

Centrifugation↗

Influence of artificial stimulation on unprocessed and Percoll-washed cryopreserved sperm.

The ability of pentoxifylline and 2-deoxyadenosine to stimulate sperm motility and motion characteristics was assessed in unprocessed and processed (Percoll-separated) cryopreserved specimens. Specimens from 12 healthy volunteers were obtained, and the motion characteristics were analyzed; half the sample was immediately cryopreserved and the other was washed using the Percoll gradient technique. To study stimulation, samples were thawed and divided into four aliquots: One was used as a control, and the others were incubated with 2.5 mM 2-deoxyadenosine, 2.5 mM pentoxifylline, or 5.0 mM pentoxifylline for 60 min. Sperm characteristics were analyzed on a sperm motion analyzer at 0 and 60 min incubation. In both unprocessed and processed samples, percentage motility improved significantly after stimulation with 2-deoxyadenosine or pentoxifylline (p = .003 or p = .0002, respectively); other characteristics improved to varying extent after 2-deoxyadenosine or pentoxifylline stimulation. Comparison after stimulation revealed that sperm motion characteristics in the unprocessed specimen were similar to sperm motion characteristics in the processed group.

Cryopreservation↗

Effect of peritoneal fluid from endometriosis patients on sperm motion characteristics and acrosome reaction.

OBJECTIVE: To determine whether peritoneal fluid from women with endometriosis contributes to infertility by impairing sperm motion and functional characteristics. METHODS: Women with endometriosis (n = 20) underwent laparoscopy for infertility or pelvic pain. Patients undergoing tubal ligation served as controls (n = 14). Peritoneal fluid was aspirated from women with endometriosis, or from women undergoing laparoscopic tubal ligation. Sperm motility, motion characteristics and acrosome reaction were assessed following incubation with peritoneal fluid. RESULTS: Sperm motility, motion characteristics, and acrosome reaction did not differ significantly between the two groups after 3, 5, or 24 hours of incubation with peritoneal fluid. CONCLUSIONS: Sperm motion or functional characteristics showed no significant impairment when sperm from normal donors were incubated with peritoneal fluid from patients with endometriosis. It is unlikely that peritoneal fluid in these patients contributes to infertility.

Acrosome Reaction↗

Bancroftian filariasis in Namrup tea estate, district Dibrugarh, Assam.

Filariasis survey in a randomly selected tea estate of district Dibrugrah revealed 6.7% infection of Wuchereria bancrofti in labour population with microfilaria (mf) rate of 7.6% in males and 5.9% in females. The mf rate increased progressively with the age which however, dropped in 31-40 age group of males and in 41-50 age group of females. Chronic filariasis diseases rate was 2.7%. The involvement of genitals in manifesting chronic filariasis was significantly higher than of the lower extremities. Infection and infectivity rates in the vector mosquito, Culex quinquefasciatus were 6.1% and 4.6% respectively with mean L3 load per infective mosquito of 8.5. Drains, land, peridomestic ditches were chief breeding habitats of Cules quinquefasciatus in the tea estate.

Adolescent↗

Comparison of three sperm preparation media.

OBJECTIVE: In assisted reproduction, spermatozoa must be effectively separated from seminal plasma to undergo capacitation, a prerequisite for fertilization. Percoll was recently withdrawn from the American market because of safety concerns. The purpose of this study was to evaluate the quality of sperm separated by two different sperm washing media, and compare these results to sperm quality after separation on a Percoll (Perwash) gradient. MATERIALS AND METHODS: Semen samples from 10 normozoospermic men were compared after separation on three media: Perwash, a Percoll-type medium (Conception Technologies, La Jolla, CA), ISolate (Irvine Scientific, Santa Ana, CA), and SpermFertil (Embryotech Laboratories, Wilmington, MA). Semen characteristics examined were: sperm count, percentage motility, curvilinear velocity, lateral head displacement, percentage recovery of motile sperm, viability, hypo-osmotic swelling, and penetration in bovine cervical mucus. Sperm morphology was scored using World Health Organization and Kruger's strict criteria. The motility of the sperm was examined at one-hour intervals for three hours to determine which method produced samples with the longest period of motility. RESULTS: Total motile sperm count, motility, curvilinear velocity, and percentage of normal morphological forms as determined by the WHO method were significantly lower in specimens prepared by SpermFertil than in ISolate or Perwash specimens (P < .05). Tail abnormalities were significantly more frequent in specimens prepared by SpermFertil than in ISolate and Perwash specimens (P < .001). Percentage recovery of motile sperm was significantly higher in ISolate and Perwash specimens than in SpermFertil specimens (P < .05). Semen characteristics were similar in specimens prepared with ISolate and with Perwash. At all time intervals, sperm motility was higher in ISolate and Perwash specimens than in SpermFertil specimens (P < .001). CONCLUSION: Sperm samples separated with a SpermFertil column have poorer sperm quality in several respects than samples prepared with ISolate or Perwash. This finding and the similarity between ISolate and Percoll procedures suggests that ISolate is a good alternative to Percoll-type media to prepare sperm for assisted reproduction.

Analysis of Variance↗

Acute renal failure in an intensive care unit in India--prognostic factors and outcome.

We prospectively analyzed 70 consecutive patients who developed acute renal failure (ARF) in the intensive care unit (ICU) during a six year period to define prognostic factors and outcome. Age, sex, preexisting chronic diseases, systemic infections, number of organs failing during the disease course, need and mode of renal replacement therapy (RRT), and length of stay in ICU were recorded. Analysis of factors in survivors (n=7, Gp A) and nonsurvivors (n=63, Gp B) was done by univariate and multivariate analysis. The mean age of patients was 28.6 years. Forty nine (70%) patients developed ARF following surgery, whereas 21 (30%) developed ARF in a medical setting. Cardiovascular surgery (39) and pancreatic surgery (7) were important causes in the surgical group, whereas in the medical group acute pancreatitis (11) was the main causative factor. One patient had ARF only, while in the rest, other organs were also involved. In more than 80% of these patients, organ failure and sepsis were present before the onset of ARF. Fifty two (74.3%) patients required dialytic support. The overall mortality was 90%. Number of organs failing, (1.5 +/-9 in Gp A vs 3.6 +/- 8 in Gp B), presence of systemic infection (1 in Gp A vs 55 in Gp B), prolonged stay in ICU (3.7 +/- 1.1 days in Gp A vs 8.0 +/- 5.4 in Gp B) and need for RRT (2 in Gp A vs 50 in Gp B) correlated with the mortality. Using multiple logistic regression analysis, only multiple organ failure (3 or more) correlated with the mortality. We conclude that multiple organ failure is a poor prognostic factor in patients with ARF in the setting of the ICU.

Acute Kidney Injury↗

Captopril for prevention of contrast-induced nephropathy in diabetic patients: a randomised study.

Contrast-induced nephrotoxicity is an important cause of hospital-acquired acute renal insufficiency. Different modalities have been used to prevent contrast induced-nephrotoxicity namely saline infusion, mannitol, furosemide, calcium channel blockers, atrial natriuretic factor and dopamine infusion with variable success. The possible role of medullary ischaemia mediated by renin angiotensin system in genesis of contrast-induced nephrotoxicity prompted us to investigate the role of captopril (a sulfhydryl group containing angiotensin-converting enzyme inhibitor) in its prevention. Seventy-one patients of diabetes mellitus undergoing coronary angiography were included in the study. Patients randomised to receive captopril, received the drug in a dose of 25 mg thrice a day for three days, starting one hour prior to angiography while the patients in the control group underwent angiography in a routine manner without receiving captopril. Following angiography, patients in the control group developed a significant increase in serum creatinine and blood urea nitrogen levels, as compared to those who received captopril. Contrast-induced nephrotoxicity (i.e. a rise of 0.5 mg/dL in serum creatinine) developed in 29 percent of the control group. Administration of captopril reduced the risk of development of contrast-induced nephrotoxicity by 79 percent. Glomerular filtration rate as measured by Tc DTPA renal scanning prior to and 24-72 hours following angiography demonstrated a mean fall of 9.6 ml/min in the control group while those in the captopril group had a mean increase of 13 ml/min in glomerular filtration rate. We conclude that abnormalities of renal perfusion possibly mediated by renin angiotensin system are responsible for development of contrast-induced nephrotoxicity. Administration of the angiotensin-converting enzyme inhibitor, captopril, offers protection against development of contrast-induced nephrotoxicity.

Acute Kidney Injury↗

Cryopreservation of human spermatozoa: comparison of TEST-yolk buffer and glycerol.

OBJECTIVE: Comparison of human sperm motility, morphology, and sperm membrane integrity using two cryoprotective media, Test-yolk buffer with glycerol and glycerol alone. METHODS: Semen samples from 10 healthy donors were divided and frozen with either glycerol or a combination of glycerol and TEST-yolk buffer. Semen characteristics were evaluated before freezing and after thawing. Motility was measured at 0, 60, 120, and 180 minutes post-thaw following removal of the cryoprotectant (post-wash). RESULTS: Percentage of motile sperm decreased significantly compared to prefreeze values in both groups. Post-thaw motility following removal of the freezing media was higher in specimens that were frozen in TEST-yolk buffer compared to those frozen in glycerol at 0 minutes (P = 0.004). Similarly, specimens cryopreserved in TEST-yolk buffer had higher sperm motility compared to aliquots that were frozen in glycerol at 180 minutes (P = 0.013). The percentage of normal sperm forms was significantly higher post-wash and post-thaw in specimens that were cryopreserved in TEST-yolk buffer (P = 0.04). CONCLUSIONS: Sperm cryopreserved in TEST-yolk buffer had significantly better motility, morphology, and sperm membrane integrity than sperm preserved in glycerol alone.

Buffers↗

Pefloxacin in steroid dependent and resistant idiopathic nephrotic syndrome.

Children with nephrotic syndrome who are either steroid dependent or resistant are difficult to manage. Ten children (age 8-14 years, mean 13.2 years) with idiopathic nephrotic syndrome (5 steroid dependent, 5 steroid resistant) formed the study group. All of them had received a course of cyclophosphamide at least six months previously and were now given pefloxacin in the dose of 200mg to 400mg twice daily (mean dose 2-4.6mg/kg/daily) for 4 to 8 weeks. They did not get steroid along with pefloxacin. After a mean follow up period of 18 weeks (12-20 weeks), 7 patients were in remission (2 complete, 5 partial), while 2 patients did not show any response; one patient discontinued pefloxacin within 2 weeks of start of therapy due to nausea and vomiting. One patient developed arthralgia and another discoloration of nails. There was a significant reduction in proteinuria after pefloxacin therapy (pre-3.6+/-2.02gm/24h; post 1.9+/-1.8gm/24h, p<0.006), and side effects were minimal and reversible. Thus for the subgroup of idiopathic nephrotic children who are steroid dependent or resistant and do not respond to a course of cyclophosphamide, pefloxacin could be helpful in inducing remission.

Adjuvants, Immunologic↗