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Biomedical subjects

R L Clark

Publications and source records attributed to R L Clark.

At least 73 records · Page 4Linked to original sources
PubMed1989

Retirement responses to social security changes.

Workers often retire at an age later than the age at which they accept Social Security benefits. This study employed a life-cycle model of individual utility to examine the effects of Social Security provisions on the timing of benefit acceptance and retirement. The behavioral responses of older workers are estimated with a two-equation logit model using data from the Retirement History Study. The results indicate that the legislated increase in the age of eligibility for full Social Security benefits beginning in the 21st century will have relatively small effects on the ages of retirement and benefit acceptance. The mandated decrease in the earnings test tax also is predicted to have only a small effect on the behavior of older persons.

Actuarial Analysis↗
PubMed1989

Streptococcal antigen-induced dislocation and dysplasia of the hip in newborn rats. Radiologic and histologic evaluation of a model of congenital dislocation of the hip.

Dislocation of the hip developed in 62% of newborn rats with streptococcal antigen-induced synovitis. Age at the time of the induction of synovitis is critical since dislocation is not observed in older rats. Synovitis with distention and laxity of the joint capsule is most likely responsible for the hip dislocation. Although congenital dislocation of the hip in children is not mediated by an inflammatory process, the current model of dislocation of the hip in rats is similar in being critically age-dependent, and associated with ligamentous laxity. Our model may be helpful in studying this important clinical entity.

Age Factors↗
PubMed1989

Disappearing breast calcifications.

Seventeen patients aged 47-67 years had 20 foci of disappearing breast calcifications. Firm compression was used to obtain craniocaudal and oblique mediolateral views of each patient. The authors categorized calcifications according to shape, size, number, position, and likelihood of benignity or malignancy. The right breast was the site of disappearing calcifications more often than the left. The most common configuration of disappearing calcifications was round or oval. All calcifications but one were found in dense glandular areas of the breast. Dense glandular tissue within 1 cm of the border with the stroma was the most common location. Only one of 20 foci suggested malignancy. The disappearance of breast calcifications is uncommon but probably not rare.

Aged↗
PubMed1989

Influence of the rate of infusion on cyclosporine nephrotoxicity in the rat.

The effect of the rate of infusion of single and multiple doses of cyclosporine (CsA) on renal function was evaluated in Sprague-Dawley rats. CsA was dissolved in cremophore (Crem) or Tween 80 (Tween) and infused over consecutive 10-min periods at doses of 10, 20, 30 and 40 mg/kg. CsA-Crem and CsA-Tween produced similar and progressive changes in MAP, RBF, and RVR. By the end of the infusion, the mean values (% of control) of MAP (122 +/- 16% and 131 +/- 22%), RBF (56 +/- 11% and 66 +/- 20%), and RVR (222 +/- 38% and 232 +/- 134%) were significantly different from their respective preinfusion values. Infusion of Crem alone resulted in renal vasodilation at low doses and renal vasoconstriction at high doses. Vasoconstriction was not produced by infusion of Tween alone. In addition, animals were treated with vehicle alone (Gp 1), CsA 10 mg/kg/day by injection (Gp 2), or CsA 20 mg/kg/day by i.v. infusion over 4 hr (Gp 3), and were studied at 1 week. Systemic toxicity was greater with the 4-hr infusion as judged by an increase in MAP. The mean values of MAP were 107 +/- 8 (Gp 1), 101 +/- 13 (Gp 2), and 135 +/- 5 mm Hg (Gp 3; p less than 0.05). However, renal function was less severely affected with the 4-hr infusion. The mean values of CIn were 434 +/- 99 (Gp 1), 298 +/- 101 (Gp 2; p less than 0.05), and 425 +/- 114 microL/min/100 g BW (Gp 3); and the mean values for RBF were 2.72 +/- 0.74 (Gp 1), 2.08 +/- 0.17 (Gp 2; p less than 0.05), and 3.35 +/- 0.61 mL/min/100 g BW (Gp 3), respectively. Microangiograms showed marked abnormalities in the intrarenal perfusion pattern in the rats injected with CsA, 10 mg/kg BW. In rats infused over 4 hr with CsA, 20 mg/kg BW, the microangiographic pattern was normal. These studies demonstrate that the acute hemodynamic effects of CsA are directly related to the rate of infusion. Furthermore, the renal toxicity which follows repetitive injection of CsA can be minimized or avoided by administering CsA as a slow infusion. In addition to the total dose administered, the rate of infusion is an important determinant of nephrotoxicity.

Animals↗
PubMed1988

Urothelial microvascular response to chronic renal inflammatory disease.

Renal pelvocaliceal mucosal opacification has been observed clinically in patients with inflammatory disease. We studied the microvascular changes that might be responsible for this finding using barium injection and microradiographic studies of 20 human kidneys excised due to infection. There were six patients with staghorn calculi and chronic pyelonephritis, four with pyohydronephrosis, eight with acute and chronic pyelonephritis, and two with xanthogranulomatous pyelonephritis. The microangiograms correlated with severity of inflammation. In mild cases, slight vessel hypertrophy involved the terminal arterioles and arteries supplying the urothelium. In severe cases, there was marked neovascularity with feeding vessel hypertrophy and mucosal thickening. Our studies demonstrate that abnormal pelvocaliceal vascularity is responsible for the findings seen on urography and angiography of inflammatory disease.

Angiography↗
PubMed1988

Needle localization biopsy of occult lesions of the breast. Experience in 199 cases.

From January 1980 through June 1986, 199 percutaneous needle localizations for clinically occult breast lesions were performed at North Carolina Memorial Hospital. A retrospective analysis of the medical records, mammograms, operative notes, and pathology reports was undertaken to evaluate the success of this procedure. In our series, biopsy was prompted by abnormal calcifications in 27.1% of lesions, occult masses in 37.2%, and by a combination of occult masses and microcalcification in 35.7%. Overall, we had a yield of positive biopsies for cancer of 16.3%, with the yield improving from 12.3% in the earlier years of our study, to 18.7% in the latter years. Of the cancer cases detected, 89.7% were stage I. The localization procedure was successful in 95.9% of the cases. Analysis of our eight failures, along with a review of the literature, shows the major reasons for failure to be incomplete removal of areas with multiple calcifications, dislodgement of the needle, and problems resulting from lack of communication between the radiologist and surgeon. We conclude that the failure rate is low, the yield good, and needle localization a worthwhile procedure for localizing nonpalpable occult lesions.

Adult↗
PubMed1987

Molding of the uterus following intrauterine contraceptive device removal: documentation by hysterosalpingography.

Intrauterine contraceptive devices (IUDs) distort the uterine cavity. We report 2 cases of endometrial molding demonstrated by hysterosalpingography (HSG) following removal of an IUD. Other processes may cause filling defects in the uterine cavity including inflammatory synechiae (Asherman's syndrome), tuberculosis, endometrial hyperplasia, and polyps. Whenever filling defects are seen, the history of IUD usage should be determined.

Adult↗
PubMed1987

Interactions between caffeine and adenosine agonists in producing embryo resorptions and malformations in mice.

Caffeine has previously been demonstrated to be teratogenic in mice, causing primarily limb reduction defects and cleft palate. To investigate the possibility that the mechanism of caffeine teratogenesis is related to its central stimulant activity, which is thought to result from its activity as an adenosine antagonist, the effects of the stable adenosine agonists L-phenylisopropyladenosine (L-PIA) and chloroadenosine on caffeine teratogenicity were examined. It was found that these adenosine analogs have embryolethal effects when administered intraperitoneally on Days 11 and 12 of gestation at extremely low dosages (minimal effect levels of 1 and 10 mumol/kg, respectively). Caffeine at dosages as low as 129 mumol/kg ip protected against the embryolethal effects of 5 mumol/kg L-PIA if administered simultaneously with L-PIA but not if administered 30 to 60 min after L-PIA. The maternotoxicity of either of the adenosine agonists or caffeine alone was ameliorated by coadministration of the other, particularly when the molar excess of caffeine was approximately 20-fold. These results suggest that the embryotoxicity and maternotoxicity of the adenosine agonists and the maternotoxicity of caffeine are mediated by binding to adenosine receptors. When coadministered with teratogenic dosages of caffeine (1160 to 1290 mumol/kg), L-PIA and chloroadenosine at dosage levels of 1 to 100 mumol/kg did not prevent and in some cases potentiated the teratogenic effects of caffeine. This lack of protection by L-PIA and chloroadenosine suggests that adenosine receptors are not the primary site of action for caffeine-induced teratogenicity. The embryolethal effects of L-PIA and chloroadenosine and the teratogenicity of caffeine occurred only at maternotoxic dosages. However, an analysis of the correlation structure indicates that the embryotoxicities of L-PIA and caffeine were not secondary to maternotoxicity as measured by body weight change.

2-Chloroadenosine↗
PubMed1987

Effect of acetylation on arthropathic activity of group A streptococcal peptidoglycan-polysaccharide fragments.

Purified group A streptococcal peptidoglycan-polysaccharide (PG-PS) fragments were either de-O-acylated, or acetylated and then de-O-acylated to yield N-acetylated PG-PS. Native PG-PS was poorly degraded, N-acetylated PG-PS was extensively degraded, and de-O-acylated PG-PS was only slightly degraded by hen egg white lysozyme. N-acetylated PG-PS was also extensively degraded by human lysozyme and partially degraded by rat serum or rat liver extract. After a single intraperitoneal injection of rats with a sterile, aqueous suspension, all PG-PS preparations induced acute arthritis. The acute arthritis induced by N-acetylated PG-PS was significantly more severe than that induced by native PG-PS; that induced by de-O-acylated PG-PS was of intermediate severity. After the acute reaction, rats injected with native PG-PS developed chronic relapsing erosive synovitis which remained severe for the duration of the experiment (83 days). In contrast, joint inflammation induced by N-acetylated PG-PS resolved within 6 weeks with little evidence of recurrent disease. Chronic arthritis induced by de-O-acylated PG-PS was of intermediate severity. In another assay of arthropathic activity, the arthritis in all rat ankle joints, which had been injected directly with native PG-PS, could be reactivated 3 weeks later by the intravenous injection of a small dose of PG. In contrast, only 50% of the joints initially injected with de-O-acylated PG-PS and none of the joints injected with N-acetylated PG-PS could be reactivated. These studies support the concepts that the resistance of PG-PS to muralytic digestion is crucial for chronic arthropathic activity and that the nature and degree of PG acetylation are important molecular determinants of the phlogistic activities of PG-PS polymers.

Acetylation↗
PubMed1987

Evaluation of temazepam and diphenhydramine as hypnotics in a nursing-home population.

Seventeen nursing home residents with sleeping problems were enrolled in a randomized, double-blind, crossover trial of temazepam 15 mg, diphenhydramine (DPH) 50 mg, and placebo. Each drug was given for five consecutive nights with a 72-hour washout period between drugs. Subjects were assessed three times weekly with tests of psychomotor and cognitive function and four times weekly with observer sleep diaries and morning sleep questionnaires. Three subjects failed to complete the study. By report of the subjects, DPH resulted in shorter sleep latency than did placebo (t = 2.77, p less than 0.05). On the fifth night, use of DPH was associated with longer duration of sleep than temazepam (t = 2.88, p less than 0.05). No significant difference in tests of neurologic function was noted although, compared with placebo, subjects performed more poorly on seven of eight tests while taking temazepam and five of eight tests while taking DPH. Several instances of daytime hypersomnolence were noted in subjects taking temazepam and DPH, but none in subjects given placebo.

Aged↗
PubMed1987

The evaluation of gross hematuria in anticoagulated patients: efficacy of i.v. urography and cystoscopy.

To determine the efficacy of investigating gross hematuria in anticoagulated patients, records were reviewed of 24 patients who had gross hematuria while being treated with warfarin for various thromboembolic disorders. All had IV urography, and half had cystoscopy. Sources of bleeding were found in seven (29%) of 24 patients by IV urography and in five (42%) of 12 patients by cystoscopy. Abnormalities considered responsible for bleeding included renal stones (four), transitional cell carcinoma (one), calcified renal mass (one), lymphoma (one), bladder tumors (two), hemorrhagic cystitis (two), and a bleeding prostate tumor (one). Additionally, an enlarged prostate was the only abnormal finding in five patients. If an enlarged prostate is considered a source of bleeding, the workup that included both IV urography and cystoscopy identified a cause of bleeding in 17 (71%) of 24 patients. The results suggest that IV urography and cystography are warranted in patients who take anticoagulants and who have gross hematuria.

Adult↗
PubMed1987

The effects of ionizing radiation on the pulmonary vasculature of intact rats and isolated pulmonary endothelium.

We studied the effects of ionizing radiation on the morphology of the pulmonary circulation using an in vivo rat model and an in vitro pulmonary artery endothelial cell model. Gamma radiation was given as either an acute (30 Gy) or fractionated (5 X 6 Gy) dose to one hemithorax of rats. An acute 30-Gy dose delivered resulted in a 70% decrease in pulmonary arterial perfusion, using technetium-99m microaggregated albumin (99mTc-MAA), in the irradiated lung by 2-3 weeks after irradiation. Pulmonary microradiographs, using a barium sulfate perfusion method, obtained 2-3 weeks after irradiation demonstrated widespread loss of capillary filling and segmentation of the vessels. Histologic examination demonstrated intact capillaries, suggesting that the alterations in pulmonary perfusion were at the precapillary level. Similar abnormalities in lung perfusion and morphology were found after delivery of fractionated doses of radiation, but the onset of the changes was delayed, occurring 4-6 weeks postirradiation. Using cultured pulmonary endothelial cell monolayers, cell sloughing and retraction from the surface substrate were observed within 24 h after in vitro delivery of 30 Gy. Similar findings occurred in monolayers given fractionated doses (5 X 6 Gy) of radiation 2-3 days after the final dose. The in vivo animal and in vitro endothelial cell models offer a useful means of examining the morphologic alterations involved in radiation lung vascular damage.

Animals↗
PubMed1986

Bladder mucosal tears during voiding cystourethrography in chronic renal failure.

We report 6 patients with chronic renal failure who developed contrast intravasation/extravasation during voiding cystourethrography. Two patients underwent cystoscopy and were noted to have diffuse mucosal tears, but had normal-appearing bladder mucosa on follow-up inspection. None of the patients experienced symptoms or clinical sequelae. Pathophysiological changes in the chronically unused bladder which predispose it to mucosal injury are considered.

Adolescent↗