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Biomedical subjects

R W Lam

Publications and source records attributed to R W Lam.

123 records · Page 7Linked to original sources
PubMed1981

Ontogenesis of beta-adrenergic receptors in the ovine placenta.

Radioligands with high specific activity and high affinity have recently become available to study the beta-adrenergic receptor (BAR). BAR may be important in the placenta for mediating a variety of metabolic and hemodynamic effects of catecholamines including placental hormone synthesis and secretion, placental glycogenolysis, and placental blood flow. Little is known regarding the development of the BAR. We have used the tritiated radioligand dihydroalprenolol to study the ontogenesis of BAR in the fetal and maternal portions of the ovine placenta. The receptor number decreased from 415 fmoles . mg-1 of protein at 120 days' gestation to 226 fmoles . mg-1 at 145 days; this trend was highly significant (r = -0.822, p less than 0.01). Similar changes were noted in the dissociation constant. Downward regulation as a result of fetal neurosympathetic maturation is proposed as an explanation for this observation.

Adrenergic beta-Agonists↗
PubMed1981

Ontogenesis of tissue catecholamines in fetal and neonatal rabbits.

The ontogenesis of tissue catecholamine concentrations in heart, lung, brown adipose tissue, adrenal and para-aortic chromaffin tissue was assessed in fetal and newborn rabbits using a radioenzymatic assay adapted to perchloric extracts of tissue. Measurements were conducted at 20, 24, 27 and 31 days gestation and at 3 and 7 days of age. Myocardial norepinephrine was detectable at 20 days gestation, the earliest age studied. Lung norepinephrine was not detectable until 24 days gestation. Norepinephrine concentrations in brown adipose were similar to myocardial levels. Adrenal and para-aortic tissue catecholamine content increased significantly between 24 days gestation and 7 days of postnatal age. Epinephrine became the predominant adrenal catecholamine by 24 days gestation. Para-aortic body norepinephrine concentrations always were substantially less than adrenal norepinephrine or epinephrine contents. Epinephrine was undetectable in para-aortic bodies at 20 and 24 days and at 31 days was only 27% of norepinephrine content. Adrenal maturation as reflected by epinephrine content or epinephrine/norepinephrine ratio correlated positively with body weight in the 31 day gestation fetuses. Thus, significant changes in tissue norepinephrine concentrations occur during the developmental time period studied. Parallel maturational changes occur in adrenal and para-aortic chromaffin tissue.

Adipose Tissue, Brown↗
PubMed1977

Thyroid function at birth in infants of 30 to 45 weeks' gestation.

Serum T4 was measured in cord blood of 2,683 infants of gestational ages 30 to 45 weeks and birth weights of 1,460 to 5,250 gm. In addition, serum TBG was measured in 180, and serum TSH in 125 of these infants. Mean serum T4 increased with gestational age from 9.4 microng/dl at 30 weeks to 11.7 at 45 weeks. TBG varied from 3.1 to 11.4 mg/dl but showed no correlation with gestational age. There was a positive correlation between T4 and TBG. Serum TSH levels showed a significant negative correlation with gestational age, decreasing from 15 micronU/ml at 30 weeks to 7 micronU/ml at 45 weeks, while the serum T4/TSH ratio increased from 0.6 to 1.6. The results indicate that cord, T4 varies mainly with TBG, and to a lesser extent with gestational age.

Fetal Blood↗
PubMed1977

The response of newborn sheep to TRH with and without somatostatin.

Hormone responses to a bolus injection of thyrotropin releasing hormone (TRH) were studied in 8 newborn lambs between 6 and 19 hours of age. The effect of a bolus injection and 45 min infusion of somatostatin (SRIF) on these responses was studied in 2 other animals. Serial measurements of serum TSH, prolactin, triiodothyronine (T3) and thyroxine (T4) were conducted for 2 to 6 h in all animals. Mean baseline T4 and T3 concentrations were 12.6 microng/dl and 221 ng/dl, respectively, both significantly higher than values in fetal or adult animals. These high values were due to the events of parturition. In spite of the high baseline T4 and T3 levels, there were rapid and significant increases in both TSH and prolactin concentrations in response to TRH alone. The TSH response evoked further increments in serum T3 and T4 concentrations observed at 30 min and 60 min, respectively, both subsequently increasing progressively through 6 h. During the 45 min period of SRIF infusion, the TSH T4 and T3 responses to the zero time TRH injection were minimal. However, after discontinuing SRIF, late increases in TSH, T4 and T3 were observed. The results indicate that the hyperiodothyroninemia characteristic of the newborn period does not block the response to exogenous TRH, whereas the inhibitory effect of exogenous SRIF is observed in the newborn as in the adult. The increased endogenous TRH secretion presumably responsible for the neonatal TSH surge may be overriding the negative feedback effect of thyroid hormones.

Animals↗
PubMed1977

Radioimmunoassay for free and conjugated urinary metanephrine.

We describe a convenient and specific radioimmunoassay for urinary metanephrine, in which we used an antiserum generated in rabbits by injecting with synephrine conjugated to bovine serum albumin as described by Grota and Brown [Endocrinology 98, 615 (1976)]. The antiserum is specific for metanephrine and epinephrine. Epinephrine cross reaction is minimized to 1% by adding 2 ng of epinephrine to each assay tube. Incubation time is 12 h. The sensitivity of the assay is 40 pg. Within-and between-assay coefficients of variation are 7.0 and 9.7%, respectively. We assayed first-voided morning urine and 24-h urine specimens from 15 normal subjects before and after acid hydrolysis, to assess total and free metanephrine concentrations. Mean (+/-SD) total and free urinary metanephrine excretion were 17 +/- 11 and 3.5 +/- 1.0 micrograms/24 h in these subjects; corresponding values for the morning specimens were 13.4 +/- 8.3 and 3.5 +/- 1.5 micrograms/liter, respectively.

Adult↗
PubMed1975

Thyroid hormone metabolism in amniotic and allantoic fluids of the sheep.

Amniotic and allantoic fluid samples were obtained at the time of uterotomy from healthy pregnant ewes at various time during gestation. In most instances maternal and fetal blood was collected simultaneously. Serum thyroxine (T4) and triiodithyronine (T3) and free T4 were measured in most samples. To determine whether conjugastes of T4 were presented in amniotic and allantoic fluids. T4 was measured before and after 24-hr acid hydrolysis. T4 and T3 turnover from amniotic fluid were measured using kinetic methods after intravenous or intraamniotic fluid injection of radiolabeled hormones. T3 was unmeasurable less than 15 ng/100 ml) in amniotic and allantoic fluids as well as in most fetal serum samples. T4 levels in amniotic fluids were low before 120 days of gestation (0.17 +/- 0.03 mug/100 ml; mean and SEM) concentration between 124 and 152 days was 0.33 +/- 0.03 mug/100 ml. T4 concentrations in allantoic fluid were relatively high before 120 days (0.57 +/- 0.1 mug/100 ml) and did not increase with progression of the pregnancy...

Allantois↗
PubMedDate not supplied

Seasonal mood symptoms in bulimia nervosa and seasonal affective disorder.

Mood and appetite disturbances are commonly found in bulimia nervosa and seasonal affective disorder (SAD). To investigate seasonality of mood symptoms, we administered the Seasonal Pattern Assessment Questionnaire (SPAQ) to 38 consecutive bulimic patients, 38 age- and sex-matched SAD patients, and 25 age- and sex-matched normal controls. The SPAQ is a reliable, retrospective, self-rated questionnaire that assesses seasonal changes in mood, sleep, weight, and social activity. The SAD patients had significantly higher Global Seasonality Scores (GSS) than the bulimic patients, who had higher scores than the control group (F = 78.6, df = 2.98, P less than .0001). Forty-two percent of bulimics met case-finding SPAQ criteria for SAD, compared with none of the control group (chi 2 = 14.1, df = 1, P less than .0005). These data suggest that a significant number of unselected bulimic patients have seasonal mood symptoms as severe as that seen in SAD. We propose that a common neurobiologic abnormality, such as serotonergic dysfunction, may underlie the common symptoms found in bulimia and SAD.

Adult↗
PubMedDate not supplied

The validity of atypical depression in DSM-IV.

Atypical depression has been included in the DSM-IV as an episode specifier of major depressive episodes and dysthymia. This report will review evidence for the clinical validity of atypical depression using operational criteria for the validation of clinical syndromes. English language articles between 1969 and March 1996 were found using a computerized and manual reference search and were selected according to the following criteria: (1) primary research, (2) definition of atypical depression, which includes depression and not anxiety alone, and (3) relevance of data for validation of atypical depression. Studies were evaluated on Kendall's six criteria for establishing clinical validity. There are supporting data for diagnostic validity of atypical depression in the criteria of clinical description and differential treatment response, with atypical depression having a superior response to monoamine oxidase (MAO) inhibitors compared to tricyclic antidepressants. There is still only limited support for the validity of atypical depression in the criteria of pathophysiology, points of rarity with other similar diagnoses, distinctive course and outcome, and genetics. Based on the current evidence, atypical depression is a useful diagnostic concept, particularly for predicting differential drug response, but further research is required to conclusively demonstrate its validity as a clinical syndrome.

Antidepressive Agents↗
PubMedDate not supplied

Differential response of ovine placental lactogen levels in maternal and fetal circulations following single umbilical artery ligation in fetal sheep.

We investigated circulating maternal and fetal serum concentrations of ovine placental lactogen (oPL) following single umbilical artery ligation (SUAL) at 108 to 114 days' gestation. Ovine placental lactogen was isolated and purified from placental cotyledons, and a radioimmunoassay developed using previously described methods. Intrauterine growth retardation (IUGR) was manifest as increasing fetal brain-to-liver weight ratio with increasing duration of survival following SUAL. During the first five to seven days following SUAL, circulating oPL levels in ewes with SUAL fetuses were significantly reduced when compared with levels in ewes with control fetuses. In contrast, oPL levels in SUAL fetuses were significantly increased above levels in control fetuses for the first five to seven days following surgery. Fetal ovine growth hormone levels were elevated in SUAL fetuses, while ovine prolactin levels were similar in the two groups. IUGR was associated with mild fetal acidosis and fetal plasma CAT levels which were similar in SUAL and control fetuses. No correlation was found between fetal pH or CAT and fetal oPL levels. These findings are consistent with the view that circulating levels of oPL in the mother are related to the mass of functioning trophoblast. Elevated fetal oPL levels following SUAL may result from acute placental ischaemia with alterations in placental lactogen secretion at the maternofetal interface.

Animals↗
PubMedDate not supplied

Pitfalls of rare earth imaging: conquering the three Ps.

Rare earth technology has become the standard in radiographic imaging, but misapplication and insufficient comprehension of the variables of usage create practical problems. Special problem areas are pediatrics, portable radiography and phototimed exposures. These problems, as well as possible solutions, are addressed in this article.

Humans↗
PubMedDate not supplied

The influence of film-screen color sensitivity and type of measurement device on kVp measurements.

Three methods for evaluating radiographic kVp were studied: the Wisconsin Test Cassette, the Noninvasive Evaluator of Radiation Outputs (NERO), and the Dynalyzer. The Dynalyzer kVp readings were the highest and were followed by NERO and cassette readings in descending order. By film type, the cassette readings ranged from Kodak OG (green sensitive), TMG (green sensitive), XK (blue sensitive), and XRP (blue sensitive) in descending order. The results show that there is significant variation between the methods.

Color↗
PubMedDate not supplied

Chemical substance use among R.T.s in Georgia.

This article describes the results of a survey on the prevalence of chemical substance use by radiologic science professionals. The sample population was a random selection of registered radiographers, nuclear medicine technologists, radiation therapists and diagnostic medical sonographers in Georgia. Prevalence rates of 11 major drug categories among this population are presented and compared with prevalence rates among the general U.S. population, both nationally and regionally. Results showed that the study group had higher use rates than the general population for some drugs, such as analgesics and stimulants, and lower use rates for other drugs, including tobacco, tranquilizers and sedatives. Significant associations regarding drug use also are reported. Implications include the need for increased drug education and increased attention to customized employee assistance programs.

Adolescent↗