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Biomedical subjects

J A Ramirez

Publications and source records attributed to J A Ramirez.

At least 91 records · Page 5Linked to original sources
PubMed1992

Increased rate of tuberculin skin test conversion among workers at a university hospital.

OBJECTIVES: To summarize the results of an investigation of increased rates of tuberculin skin test conversion in employees at a university hospital. DESIGN: The results of annual tuberculin skin tests performed on all 1,845 hospital employees from 1986 to 1991 were reviewed. SETTING: A 450-bed acute tertiary care university hospital. RESULTS: The rate of tuberculin skin test conversion was 0.35% (standard deviation +/- 0.15) from 1986 to 1989 and increased to 1.7% during 1991. Investigation revealed deviations from the Centers for Disease Control (CDC) guidelines for tuberculosis control, which included the failure to consider tuberculosis as a probable cause of community-acquired pneumonia and the failure to initiate isolation precautions when tuberculosis was suspected. CONCLUSIONS: The epidemic appeared to be secondary to delays in diagnosis and isolation of patients with pulmonary tuberculosis. Future control measures should include isolation of all hospital patients admitted with pneumonia until tuberculosis has been excluded.

Centers for Disease Control and Prevention, U.S.↗
PubMed1992

Bactericidal activity of imipenem compared to erythromycin against intracellular Legionella pneumophila.

Pneumonia is the leading cause of death due to nosocomial infections with mortality ranging from 30 to 70%. Because imipenem has potent in vitro activity against virtually all major causes of nosocomial pneumonia, including P. aeruginosa, S. aureus, members of the family Enterobacteriaceae, and anaerobic organisms, it is used by many physicians as the empirical therapy of choice in severe nosocomial pneumonias. Recognition of Legionella species as nosocomial pathogens has been increasing. The incidence of Legionnaires' disease among patients with nosocomial pneumonia is reported to be as high as 30% (1), but the real prevalence is unknown. Imipenem has bactericidal activity against Legionella in vitro but has not previously been tested for efficacy against intracellular Legionellae.

Cells, Cultured↗
PubMed1991

Serum sex hormone-binding globulin and serum nonsex hormone-binding globulin-bound testosterone fractions in prepubertal boys with chronic renal failure.

We had previously reported that serum sex hormone binding-globulin (SHBG) decreases and serum non-SHBG-bound testosterone (T) and free T increase significantly from infancy to late prepuberty in normal prepubertal children of both sexes. We had also shown an age-related delay in these changes in hypopituitary boys, which was reversed by GH treatment. Stunted growth and delayed puberty are conspicuous features of chronic renal failure (CRF). As another model of delay of growth and development, serum SHBG and serum T fractions were determined in 13 boys with CRF on chronic dialysis. In CRF, mean serum SHBG was significantly higher (99.1 +/- 68.9 nmol/L; P less than 0.05) than in 31 control (C) children of similar ages (66.2 +/- 34.9 nmol/L), while serum non-SHBG-bound T and free T were significantly lower (0.16 +/- 0.12 in CRF vs. 0.24 +/- 0.12 in C and 0.010 +/- 0.005 in CRF vs. 0.016 +/- 0.01 in C, respectively). On the other hand, serum total T (1.31 +/- 0.88 in CRF vs. 1.08 +/- 0.56 in C) and serum insulin-like growth factor-I (IGF-I; 1.06 +/- 0.74 in CRF vs. 1.35 +/- 1.70 in C) were not significantly different. A significant negative correlation between serum SHBG and chronological age as well as a significant positive correlation between serum non-SHBG-bound T and chronological age were found. For a given age, serum SHBG was higher, while serum non-SHBG-bound T was lower in patients with CRF (by analysis of covariance, P less than 0.01). It is postulated that, as has been proposed for hypopituitary boys, this delayed increment in serum T fractions could be responsible for the delay in the onset of puberty reported in CRF. It is known that GH decreases serum SHBG, acting on hepatic cells either directly or through the action of IGF-I. Since it has been suggested that patients with CRF have peripheral resistance to GH or IGF-I, the high levels of SHBG that we have detected in prepubertal boys with CRF could be taken as an additional evidence of this biological resistance.

Adolescent↗
PubMed1991

Glucocorticoids and adrenal androgens in children with end stage renal disease.

UNLABELLED: We studied the effects of chronic renal failure on the pituitary-cortisol axis and adrenal androgen function in 26 patients (16 male and 10 female), aged 6.5 to 22.5 years (mean 14.5). Ten patients were prepubertal, 8 pubertal, and 8 post-pubertal. All of them were on chronic hemodialysis. Pubic hair development was delayed in 56% of the patients. Serum cortisol was increased in 15 out of the 26 patients. Serum delta 4-androstenedione was high in 11 out of 15 patients in Tanner's stage I or II and in 1 out of 11 patients in Tanner's stage III, IV or V (p less than 0.01). Serum cortisol was elevated in 10 out of 12 patients with high serum delta 4-androstenedione and in only 5 out of 14 with normal delta 4-androstenedione (p less than 0.02). Serum dehydroepiandrosterone sulphate was normal in 22 patients and elevated in 4 males. There was a significant inverse correlation between bone age and serum cortisol (r: -0.59; p less than 0.005) and a significant positive correlation between bone age and serum dehydroepiandrosterone sulphate (r: 0.45 p less than 0.01). Serum ACTH was normal. A reduction by 50% in cortisol and 78% in dehydroepiandrosterone sulphate was found after dexamethasone suppression, but delta 4-androstenedione did not suppress after dexamethasone. After ACTH stimulation test cortisol increased by 50% and delta 4-androstenedione by 80%. CONCLUSIONS: The increased levels of cortisol and delta 4-androstenedione with partial resistance to dexamethasone suggest that these patients have a hypothalamic-pituitary dysfunction similar to that found in Cushing's disease or in chronic stress. The difference in the responses of delta 4-androstenedione and dehydroepiandrosterone sulphate observed is consistent with the existence of different mechanisms of control for these two steroids.

Adolescent↗
PubMed1989

ATP-sensitive K+ channels in a plasma membrane H+-ATPase mutant of the yeast Saccharomyces cerevisiae.

A mutant in the plasma membrane H+-ATPase gene of the yeast Saccharomyces cerevisiae with a reduced H+-ATPase activity, when examined at the single-channel level with the patch-clamp technique, was found to exhibit K+ channels activated by intracellular application of ATP. In the parent strain, the same channel, identified by its conductance and selectivity, is not activated by ATP. This activity in the mutant is blocked by the ATPase inhibitor N,N'-dicyclohexylcarbodiimide. ADP and the ATP analog adenosine 5'-[gamma-[35S]thio]triphosphate do not activate the channel. These findings suggest a tight physical coupling between the plasma membrane ATPase and the K+ channel.

Adenosine Triphosphate↗
PubMed1987

Hormonal profile in pubertal females with chronic renal failure: before and under haemodialysis and after renal transplantation.

The effects of chronic renal failure on the hypothalamic-pituitary-ovarian axis in 25 girls, aged 9.1 to 20.9 years (mean 13.8) were studied. Twelve patients on conservative treatment (group A) had serum creatinine values between 176.8 and 1502.8 mumol/l; 9 patients were on haemodialysis (group B); and 12 patients had received a renal transplant (group C). Tanner stage of breast development was delayed relative to chronological age in 5 out of 18 patients. Serum oestradiol was normal or low when related to pubertal stages in all groups. Serum LH was elevated in group A and B patients, but normal in group C patients. Serum FSH was elevated in 6 out of the 21 patients in group A plus B, and in 2 out of the 12 patients in group C. Serum PRL was elevated in 12/12, 6/8, and 4/11 patients in group A, B, and C respectively. After GnRH administration to 4 patients in group A, 3 showed delayed or absent gonadotropin response; all 4 patients studied in group C showed normal gonadotropin response. The data indicate a decreased E2 secretion, abnormal gonadotropin and PRL levels and a blunted gonadotropin response to GnRH in girls with chronic renal failure. These results seem to indicate an alteration of the hypothalamic-pituitary unit that can be reversed after successful renal transplantation.

Adolescent↗
PubMed1986

The effect of diffusion on the trapping of membrane-bound receptors by localized coated pits.

Localized coated pits are considered in the primary steps of receptor-mediated endocytosis. According to the pit reinsertion mechanism, we have modified our previous kinetic model and studied the effect of diffusion on the trapping rate constant (k+). Using experimental data for low density lipoprotein (LDL) receptors on fibroblast cells, we found that the binding of receptors to coated pits is not totally diffusion controlled. For example, the process is less than 78% diffusion controlled if receptors are not allowed to escape the coated pits. However, due to the large uncertainties in the experimental parameters, a diffusion-controlled process cannot be ruled out. The greatest differences between localized and random reinsertion were found when the escaping rate constant (k-) is much greater than the rate constant for invagination of the pits (lambda 1). Under this condition, k+ for localized reinsertion is no less than 39% diffusion controlled, while k+ for random reinsertion shows no diffusion effect at all.

Cell Membrane↗
PubMed1986

Phenytoin neuropathy: structural changes in the sural nerve.

Phenytoin has been implicated as a causative agent in peripheral neuropathy, although structural changes in nerve have not been characterized. A 47-year-old man was seen with clinical and electrophysiological signs of peripheral neuropathy after 30 years of phenytoin administration. Despite a modest dose of phenytoin (300 mg/day) blood levels were 31 to 38 micrograms/ml. A sural nerve biopsy showed a loss of large myelinated nerve fibers and a nonrandom clustered distribution of segmental demyelination and remyelination. The latter findings were accompanied by axonal shrinkage. Sixteen months after phenytoin was stopped, the patient's clinical and electrophysiological findings reflected improvement. These data indicate that long-term phenytoin administration can cause a reversible neuropathy characterized by axonal shrinkage and secondary demyelination.

Atrophy↗
PubMed1986

The absorption of dietary phosphorus and calcium in hemodialysis patients.

Absorption of dietary phosphorus plays a critical role in the development of metabolic bone diseases in patients with chronic renal failure. However, phosphorus absorption is difficult to quantitate in dialysis patients because the dialysis treatments complicate metabolic balance studies. Utilizing a recently developed technique which permits measurement of net absorption of dietary constituents after a single meal, we measured phosphorus absorption in dialysis patients. The following observations were made: A.) Following a meal containing approximately 300 mg phosphorus, mean phosphorus absorption in five hemodialysis patients (with severe vitamin D deficiency) was only slightly less than in matched controls (186 +/- 35 vs. 242 +/- 30). B.) After dialysis patients were treated with 1,25(OH)2-D3, phosphorus absorption increased from 186 +/- 35 to 272 +/- 16 mg (P less than 0.025). C.) The effect of three aluminum containing antacids on phosphorus absorption was studied; each slightly reduced the absorption of phosphorus compared to placebo (P less than 0.01), but there was no significant difference between them. D.) Aluminum hydroxide and calcium carbonate each reduced dietary phosphorus absorption to approximately the same extent. Calcium carbonate ingestion was associated with sharply increased calcium absorption. The absorption of dietary phosphorus is influenced only modestly by 1,25(OH)2-D3 and is inhibited to an equal but only modest degree by various aluminum antacids and by calcium carbonate.

Adult↗
PubMed1983

Bone marrow reconstitution of immune responses following irradiation in the leopard frog, Rana pipiens.

The bone marrow of Rana is an important source of cells capable of maintaining individual viability, responding to Concanavalin A (Con A) and producing PFC against sheep erythrocyte (SRBC) antigens. Frog marrow is more effective than the spleen in maintaining life. Radiation destroys the ability of frogs to respond to SRBC immunization (lack of bone marrow and spleen PFC, serum antibody) and bone marrow/spleen cells to respond to Con A, i.e., bone marrow and spleen contain radiation-sensitive cells. Shielding one hind leg during irradiation leads to reconstitution of bone marrow/spleen PFC responses, antibody synthesis and individual viability. Our results suggest that bone marrow is: a) the source of stem cells, and b) the source of mature T- and B- lymphocytes that can recirculate within the immune system.

Animals↗
PubMed1983

Aging changes in lymphopoietic and myelopoietic organs of the annual cyprinodont fish, Nothobranchius guentheri.

The thymus of aging annual, cyprinodont fish, Nothobranchius guentheri and Cynolebias adloffi begins to undergo senescent changes at approximately four months. At this time, the histopathology reveals increased amounts of connective tissue, epithelial cysts and myoid cells, but decreased numbers of thymocytes. At 12 months, of the 50 fish observed at 10 stages from day 15 and 1, 2, 4, 6, 8, 9, 10, 11, 12 months the maximum time of senescence, there was an increased incidence of tumors in the oral cavity, connective tissue, kidney and liver in all 5 fish. At least in the kidney, the malignant transformation was classified as nodular-type histiocytic lymphoma. It is of interest that development of these tumors occurs during peak senescent changes in the thymus, supporting the view that as fish age, accompanied by atrophy of the thymus, the immune system is less vigorous and there is an increase in the incidence of cancer.

Aging↗