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Biomedical subjects

R Clark

Publications and source records attributed to R Clark.

At least 343 records · Page 19Linked to original sources
PubMed1983

Biochemical activities of T-antigen proteins encoded by simian virus 40 A gene deletion mutants.

We have analyzed T antigens produced by a set of simian virus 40 (SV40) A gene deletion mutants for ATPase activity and for binding to the SV40 origin of DNA replication. Virus stocks of nonviable SV40 A gene deletion mutants were established in SV40-transformed monkey COS cells. Mutant T antigens were produced in mutant virus-infected CV1 cells. The structures of the mutant T antigens were characterized by immunoprecipitation with monoclonal antibodies directed against distinct regions of the T-antigen molecule. T antigens in crude extracts prepared from cells infected with 10 different mutants were immobilized on polyacrylamide beads with monoclonal antibodies, quantified by Coomassie blue staining, and then assayed directly for T antigen-specific ATPase activity and for binding to the SV40 origin of DNA replication. Our results indicate that the T antigen coding sequences required for origin binding map between 0.54 and 0.35 map units on the SV40 genome. In contrast, sequences closer to the C terminus of T antigen (between 0.24 and 0.20 map units) are required for ATPase activity. The presence of the ATPase activity correlated closely with the ability of the mutant viruses to replicate and to transform nonpermissive cells. The origin binding activity was retained, however, by three mutants that lacked these two functions, indicating that this activity is not sufficient to support either cellular transformation or viral replication. Neither the ATPase activity nor the origin binding activity correlated with the ability of the mutant DNA to activate silent rRNA genes or host cell DNA synthesis.

Adenosine Triphosphatases↗
PubMed1983

Histochemical localization of aldehyde dehydrogenase during rat hepatocarcinogenesis.

Significant changes in aldehyde dehydrogenase (ALDH) activity occur during chemically induced rat hepatocarcinogenesis. We have developed a procedure for the histochemical localization of hepatic ALDH which has proven extremely useful as an additional probe for studying changes in this enzyme during hepatocarcinogenesis. Frozen sections of fresh tissue were stained for ALDH using either propionaldehyde-NAD to detect normal liver ALDH or benzaldehyde-NADP to detect tumor ALDH. Histochemically, normal liver ALDH activity is strongly centrilobular with only slight periportal activity and produces a characteristic staining pattern. During hepatocarcinogenesis, ALDH staining patterns in grossly normal liver range from normal-appearing to patterns of distinct, intense focal hepatocyte staining with propionaldehyde-NAD and/or benzaldehyde-NADP. ALDH-positive foci are found both in normal regions of tumor-bearing livers and prior to the appearance of gross neoplasms. Neoplastic nodules and carcinomas possess a wide variety of ALDH staining patterns between and within lesions. Neoplasms with elevated ALDH activity with propionaldehyde-NAD and/or benzaldehyde-NADP, as well as with no detectable ALDH, have been observed. Changes in ALDH can be identified histochemically at a time in hepatocarcinogenesis when other analytical methods cannot detect significant changes. Moreover, considerable heterogeneity in expression of tumor ALDH is demonstrable by histochemistry.

Aldehyde Dehydrogenase↗
PubMed1982

Improvement of insulin secretion but not insulin resistance after short term control of plasma glucose in obese type II diabetics.

Insulin secretion and insulin resistance were examined in seven obese type II diabetics before and after control of plasma glucose levels without weight loss. Control was achieved by regular insulin injection (60-205 U/day in four doses). After 10 days of therapy, plasma insulin and C-peptide responses to oral glucose were significantly improved. Insulin-induced glucose rates, estimated by the glucose clamp technique, averaged 1.08 +/- 0.30 mg/kg. min (mean +/- SEM; n = 7) before treatment and were unchanged (1.08 +/- 0.25) after treatment. These indicate that short term control of plasma glucose improved insulin secretion but not insulin sensitivity. The impaired insulin secretion and insulin sensitivity in type II diabetics appears to be, in part, secondary to metabolic abnormalities associated with hyperglycemia.

Adult↗
PubMed1981

Use of monoclonal antibodies as probes of simian virus 40 T antigen ATPase activity.

We have investigated the ATPase activity of simian virus 40 (SV40) large T antigen by using monoclonal antibodies as specific probes of enzymatic activity. Three hybridoma cell lines secreting anti-T antigen antibodies were derived from mice that were immunized with D2 T antigen, an SV40 T antigen-related protein. Monoclonal antibodies secreted by these hybridomas bind to three distinct T-antigen determinants. In order to bind to T antigen, the three antibodies required amino acid residues coded by the region of the A gene between 0.37 and 0.29 map unit. Two of these antibodies (DL3C3 and DL3C4) strongly inhibited T antigen ATPase activity. The third antibody (DL3C5) only weakly inhibited the ATPase activity possibly by decreasing the affinity of T antigen for ATP. These results demonstrate that the ATPase activity is intrinsic to T antigen and suggest that the ATPase function of T antigen maps on the SV40 A gene between 0.37 and 0.29 map unit. A T antigen-specific ATPase assay capable of detecting low levels of T antigen in crude extracts of SV40 infected cells was developed by using 3C5 to immobilize an active form of the enzyme. These results indicate that monoclonal antibodies can be used as probes of enzyme structure and function.

Adenosine Triphosphatases↗
PubMed1981

The effect of lentinan on fertility and general reproductive performance of the rat.

Lentinan, a polysaccharide [(1 leads to 3)-beta-D-glucan], at 0.01, 0.10 or 1.0 mg/kg/day, was administered i.v. once daily to male rats for 9 weeks and to females for 2 weeks before mating. Some animals continued to be treated until they were killed during gestation: others were killed on day 21 post partum. Selected animals of the F1 generation were retained without further treatment, to provide F2 offspring. Reactions to treatment were generally dose-related and included bruising and cutaneous lesions of the tail and swelling and discolouration of the pinnae. In males given 1.0 mg/kg/day there was a clear evidence of gonadal damage and impairment of reproductive capacity; this effect was less marked at 0.1 mg/kg/day and much reduced at 0.01 mg/kg/day. However, the reproductive performance of the selected F1 pups did not appear to have been affected by the treatment of the F0 parents at any dosage. In animals of both sexes there was a dose-related enlargement of the spleen, with evidence of macrophage infiltration.

Abnormalities, Drug-Induced↗
PubMed1981

The effect of lentinan on pregnancy of the New Zealand white rabbit.

Lentinan at 0.1, 0.3 and 1.0 mg/kg/day was administered i.v. to the New Zealand White rabbit, once daily, on days 6--18 of gestation. There were no significant treatment-related effects of post implantation loss, mean litter size and weight, mean foetal weight or the incidence of minor skeletal or visceral anomalies.

Abnormalities, Drug-Induced↗
PubMed1981

The effect of lentinan on the in utero embryonic and foetal development of the rat and on postnatal development of the F1 offspring.

Lentinan, a polysaccharide [(1 leads to 3)-beta-D-glucan], at 0.10, 1.0 or 5.0 mg/kg/day was administered i.v. to rats once daily from day 6 until, and including, day 17 of pregnancy. Some animals were killed on day 20 of gestation, others were killed on day 21 post partum. Selected animals of the F1 offspring were retained without further treatment, to provide F2 offspring. Reactions to treatment were generally dose-related and included swelling and discolouration of the pinnae, with occasional cutaneous lesions of the tail and swelling of the hind feet. Spleen weight was increased at all dosages. Litter characteristics at day 20 of pregnancy, including the incidence of abnormality, were not affected by treatment. For dams allowed to litter, mean pup weights were slightly increased, with slight acceleration of some physiological markers before weaning. There was no evidence that treatment of the F0 parents affected the reproductive performance of the F1 offspring.

Abnormalities, Drug-Induced↗
PubMed1981

The effect of lentinan on the in utero foetal development of the rat and on postnatal development of the F1 offspring.

Lentinan, a polysaccharide [(1 leads to 3)-beta-D-glucan], at 0.1, 1.0 and 5.0 mg/kg/day was administered i.v. to rats once daily from day 15 of pregnancy to day 21 post partum. All animals were allowed to deliver their young and selected animals of the F1 generation were retained without further treatment, to provide F2 offspring. Reactions to treatment were generally dose-related and included bruising of the tail and swelling and discolouration of the pinnae. Animals at 5.0 mg/kg/day sometimes showed swollen hind limbs and cutaneous lesions of the tail. Mean spleen weight in females was increased at all dosages, more so at 1.0 and 5.0 mg/kg/day. There was no evidence of an adverse effect on litter characteristics, including the pre-weaning development of the F1 offspring, or that treatment of the F0 parents adversely affected post-weaning development and reproductive performance of the F1 offspring.

Abnormalities, Drug-Induced↗
PubMed1980

Serum salicylate levels and right-to-left ductus shunts in newborn infants with persistent pulmonary hypertension.

Although a right-to-left shunt via a patent ductus arteriosus is one criterion for the diagnosis of persistent pulmonary hypertension of the newborn infant, it cannot be demonstrated by simultaneous pre- and postductus arteriosus blood oxygen tensions in many infants with the clinical syndrome. In animals, exposure of the fetal ductus arteriosus to salicylates causes contriction and results in pulmonary hypertension. We postulated that maternal ingestion of salicylates and premature closure of the ductus arteriosus may explain why some infants with PPHN do not have right-to-left ductus shunts. Therefore, we studied serum salicylate levels in six groups of infants: I, normal infants' cord blood (0.73 +/- 0.44 mg/dl, N = 20); Ia, normal infants at 24 to 36 hours of age (0.08 +/- 0.1 mg/dl, N = 5): II, other cardiopulmonary diseases with no right-to-left ductus shunt (2.08 +/- 1.74 mg/dl, N = 26); III, other cardiopulmonary diseases and right-to-left ductus shunt (2.34 +/- 1.70 mg/dl, delta Pao2 70 +/- 71 mm Hg, N = 6); IV, PPHN and right-to-left ductus shunt (1.86 +/- 1.51 mg/dl, delta Pao2 39.6 +/- 58.9 mm Hg, N = 5); V, PPHN without right-to-left ductus shunt (7.77 +/- 5.18 mg/dl, delta Pao2 2.2 +/- 1.5 mm Hg, N = 6). Serum salicylate levels were significantly greater (P less than 0.01) in infants with PPHN without right-to-left ductus shunt, indicating that the ductus arteriosus may have been closed prematurely. No other factor, including serum bilirubin, amikacin, ampicillin, or furosemide levels, could be found to account for the difference in serum salicylate levels. Premature closure of the ductus arteriosus secondary to maternal ingestion of salicylates may be one cause of PPHN and may explain the absence of right-to-left ductus shunting in some infants with the clinical syndrome.

Ductus Arteriosus↗
PubMed1980

Teardrop sign: plain film recognition of ankle effusion.

Ankle effusions may be detected on lateral radiographs by observing a teardrop-shaped density extending anteriorly from the ankle joint along the neck of the talus. The normal and abnormal radiographic appearances of the ankle are discussed and the teardrop sign is identified.

Adipose Tissue↗