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Biomedical subjects

R Johnson

Publications and source records attributed to R Johnson.

At least 451 records · Page 25Linked to original sources
PubMed1987

Regulation of lens cyclic nucleotide metabolism by Ca2+ plus calmodulin.

Adenylate cyclase activity was identified in membranes isolated from bovine lens fiber cells. Basal activity, in the presence of microM Ca2+ was stimulated by either sodium fluoride, guanosine 5'-[alpha,beta-imido]triphosphate (Gpp(NH)p), or forskolin; ethylene glycolbis(2-aminoethylether) tetraacetic acid (EGTA) markedly inhibited both the basal activity and the extent of stimulation by these agents. Exogenous calmodulin enhanced the Ca2+-dependent stimulation of adenylate cyclase activity. In the presence of optimal concentrations of Ca2+ plus calmodulin, adenylate cyclase activity was approximately 15 times greater than that in the presence of EGTA. Adenylate cyclase activity was not stimulated by a number of potential agonists that included carbachol, serotonin, prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), adenosine, isoproterenol epinephrine, dopamine, and phenylephrine. The presence of the Ns and Ni guanine nucleotide regulatory complexes was indicated by two observations: Cholera toxin catalyzed the adenosine diphosphate (ADP) ribosylation of a number of lens membrane proteins, including a 46,500-dalton component (likely the alpha-subunit of Ns), and Pertussis toxin catalyzed the ADP ribosylation of a single 41,000-dalton lens membrane component (likely the alpha-subunit of Ni). However, that Gpp(NH)p did not inhibit either the forskolin-activated or the calmodulin-activated adenylate cyclase activities does not indicate a role for Ni in regulating this enzyme. Both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) phosphodiesterase activities were identified in a supernate fraction derived from bovine lens. The cAMP phosphodiesterase activity appeared to be predominantly the low Km form of the enzyme. The cGMP phosphodiesterase activity, which was Ca2+-dependent, was partly inhibited maximally by 7 microM R24571, indicating its probable calmodulin dependence.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1987

Long-term studies in prevention of food allergy: patterns of IgG anti-cow's milk antibody responses.

Over the past 7 years we have enrolled several hundred families in a study of the prophylaxis of atopic allergy. Initially, control and study patients were at different institutions, but more recently a true double-blind random assignment to control or study group has been instituted. Nevertheless, all of the infants from these highly atopic families can be utilized to obtain the data reported; that is, the rate of change of IgE levels, the appearance of food sensitization (food-specific IgE), the signs and symptoms of atopic allergy diseases and the changes in cow's milk-specific IgG antibody during the first 2 years of life. Some aspects of the first three of these parameters have been presented in the eight references to this paper, but only preliminary data on the use of IgG anti-cow's milk antibody as a measure of compliance has been available. In this paper an analysis is presented of the various patterns of IgG antibody levels in the first 60 infants of the over 200 who have been studied to date. Both the age of onset and the subsequent changes in the foregoing immunologic measurements provide fundamental data with which to measure the success rate of any prophylactic or therapeutic regimen and may improve our capacity to predict the future course of infants and children with a strong familial tendency to allergy.

Animals↗
PubMed1987

Institution-specific versus published in vitro antimicrobial susceptibility data in making formulary decisions.

The results of susceptibility testing of 549 isolates of gram-negative organisms to 17 antimicrobial agents were compared with published reports of the sensitivity of those organisms to those agents. All gram-negative bacilli isolated from cultures obtained from hospitalized patients during a three-month period were preserved for antimicrobial sensitivity testing. Standard Kirby-Bauer disk diffusion susceptibility tests were performed using 17 broad-spectrum antimicrobial agents that either were included in the hospital formulary or were being considered for inclusion. Organisms were recorded as being sensitive or resistant to each drug, and the results were compared with the published results of in vitro sensitivity studies. When the results of actual antimicrobial sensitivity testing varied from published results, the discordant results were assigned a ranking of 1 to 4 based on the percentage difference. In 34 of 77 drug-organism pairs tested, the results of susceptibility testing differed by more than 10% cumulative susceptibility from published values; 26 of these represented instances in which the results of actual testing were at least 10% less than published values. For seven of the antimicrobial agents that were being considered for inclusion in the hospital formulary, results indicating unexpectedly suboptimal activity against institutional pathogens were a determinant in eliminating the agents from further consideration. In vitro testing of antimicrobial susceptibility of local pathogens can be a better method of predicting the susceptibility of such pathogens to new antimicrobial agents than relying on published susceptibility data. Pharmacy and therapeutics committees should consider testing prevalent institutional pathogens for susceptibility to all antimicrobial agents that are proposed additions to the formulary.

Aminoglycosides↗
PubMed1986

Echocardiographic diagnosis and intravenous digoxin management of fetal tachyarrhythmias and congestive heart failure.

Fetal echocardiography now affords an accurate clinical diagnosis of nonimmune fetal hydrops secondary to fetal tachyarrhythmias and/or certain types of congenital heart disease. Individual case reports of the treatment of tachyarrhythmias have been reported that use various drugs, including digoxin, propranolol hydrochloride, procainamide hydrochloride, and digoxin plus verapamil hydrochloride. We found no report of intrauterine treatment of congestive heart failure due to congenital heart disease with sinus rhythm. The seven cases presented herein include five cases of isolated supraventricular tachycardia, one with supraventricular tachycardia and myocardial tumors, and one of congenital heart disease with congestive heart failure. Maternal treatment with digoxin converted tachyarrhythmia to sinus rhythm in all six fetuses, and resolved the hydrops in the fetus with congenital heart disease. Premature delivery was avoided in five of the seven cases with favorable outcome in six of the cases. In five mothers who were given oral digitalization, the fetuses had delayed (three to 35 days) response to therapy. Two mothers were treated intravenously and the fetus responded to therapy in less than 24 hours. Because of problems possibly related to poor absorption and/or rapid clearance of digoxin, the intravenous route of administration should be used as the best way to achieve adequate therapeutic levels in the fetus.

Atrioventricular Node↗
PubMed1986

Elevated serum calcium and osteocalcin levels from calcitriol in preterm infants. A prospective randomized study.

The hypothesis of this study was that pharmacologic doses of calcitriol (1,25-dihydroxyvitamin D3) would result in elevated levels of serum osteocalcin, the major noncollagenous bone protein, and calcium in infants of very low birth weight (less than 1500 g). Twenty-four infants of very low birth weight but of the appropriate weight for gestational age were matched in 250-g weight ranges and randomized into calcitriol treatment and control groups on the first day after birth. Treated infants received 4 micrograms/kg of calcitriol intravenously on entry and on the second and third study days. Controls did not receive calcitriol. Four infants from each group were hypocalcemic (serum calcium level, less than 7.0 mg/dL [less than 1.75 mmol/L]) on entry (five to 20 hours after birth) to the study. Seven infants received calcium replacement; data analyses with and without these infants were similar. Of the remaining 17 infants, eight were in the treatment group and nine were in the control group. Calcitriol significantly increased serum calcium and osteocalcin concentrations on days 2, 3, and 4 after birth compared with the control group. None of eight treated infants manifested hypocalcemia after calcitriol vs eight of nine controls. There were no acute changes in heart rate, respiratory rate, systolic blood pressure, or urinary calcium loss nor were there changes at the infusion site, but the diastolic blood pressure increased with treatment. Although high doses of calcitriol may elevate serum calcium concentrations in infants of very low birth weight, we suggest that the long-term or subtle biologic effects of high doses of calcitriol remain to be studied and that its routine use not be recommended at present.

Calcitriol↗
PubMed1986

Intestinal atresia and stenosis: a review comparing its etiopathogenesis.

Two theories were proposed originally to describe the development of congenital intestinal atresia. The theory of imperfect recanalization, the theory of vascular insufficiency, and studies which have been performed to validate each of these theories were reviewed. Specific causes of the development of vascular insufficiencies in different species were reviewed if literature was available. In utero vascular accidents have been incriminated as the major cause of congenital intestinal atresia distal to the duodenum. There was relatively little evidence to show that intestinal atresia is inherited in any species. Duodenal atresia may be caused by either an embryologic defect for which there is some evidence of inheritance or by a vascular accident. The pathogenic mechanism for intestinal atresia may be similar in most species.

Animals↗