Fractional reduction of somatostatin concentration interacted with rat growth hormone releasing hormone to titrate the magnitude of pulsatile growth hormone and prolactin release in perifusion

Growth hormone (GH) pulses in vivo are associated with increased hypothalamic portal growth hormone releasing hormone (GH-RH) concentration and can be prevented by GH-RH antisera. GH pulses are also associated with prior reduction of portal somatostatin (SRIF) concentrations, although SRIF antisera do not abolish GH pulses. In vitro, pulses of GH-RH as well as SRIF withdrawal are followed by pulses of GH release; the presence of GH-RH enhances post-SRIF GH release. We asked four questions: (1) During combined GHRH-SRIF exposure in vitro, must SRIF withdrawal be complete to produce a pulse of GH release, or is there a threshold diminution of SRIF which permits it? (2) When pulsatile GH release does occur, is it an all-or-none phenomenon, or is it titratable by fractional reduction of SRIF? (3) Does varying the GH-RH concentration while administering SRIF systematically alter GH release in response to fractional SRIF reduction? (4) Given a small but distinct effect of GH-RH on release of stored prolactin (PRL) in this system, does fractional SRIF reduction alter PRL release in parallel? Rat pituitary tissue whose hormone stores had been prelabeled with tritium was perifused for 120 min in combined 25 nM SRIF and 3 or 10 nM rat GH-RH (rGH-RH). Then, while maintaining rGH-RH concentrations, the SRIF concentration was left unchanged (control) or was reduced to 20, 15, 10, 5, or 0 nM for 60 min. Release of stored rGH and rPRL was assessed by immunoprecipitation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of polymerase chain reaction and Chlamydiazyme for the detection ofChlamydia trachomatis in clinical specimens

An attempt was made to improve laboratory diagnosis ofChalmydia trachomatis and to validate the Abbott Chlamydiazyme confirmatory test used at present by comparing the polymerase chain reaction (PCR) procedure and the Abbott enzyme immunoassay. A total of 275 routine clinical specimens representing a range of positive and negative findings by Chlamydiazyme were retested by PCR. The procedures demonstrated 99 % concordance for specimens with optical density (OD) readings above the Chlamydiazyme cut-off of 0.1, but PCR was confirmed to be significantly more sensitive (p<0.025) for specimens with OD values between 0.05 and 0.09. Specimens in this range should be retested routinely by PCR.     

Epidemiologists in the United States: an assessment of the current supply and the anticipated need

We provide 1985 estimates of the work force of epidemiologists in the United States, the number of graduates from training programs in epidemiology, and a projection of the future need for these health professionals. Our methods included a search of mailing lists from professional organizations, mail contact with graduate training programs, telephone interviews with experts, and a review of job announcements in professional journals. The study indicates that the current work force of epidemiologists in the United States is estimated to include 4,600 persons, more than half of whom are physicians; most epidemiologists are located in either a state with a major federal public health agency or one with a large population; and programs in epidemiology graduate an average of 475 persons with one or two years of master's level education and approximately 80 with doctoral-level education each year. After considering the factors that influence the supply of epidemiologists, we project a substantial need for more epidemiologists in the future than current sources will provide.     

Physiological evidence that periodontal collagen in the rat exists as fibres prior to histological fixation

The hypothesis that the collagen in the periodontal membrane forms a thixotropic gel in life and that the arrangement seen in histological preparations is a fixation artifact was tested by comparing the effects of various agents on the position of teeth in isolated unfixed mandibles and on the length of bundles of rat tail tendon collagen. Changing from Ringer solution to deionized water produced a reversible shortening of fibres and extrusion of teeth. Sucrose solutions produced irreversible lengthening and intrusion. Glutaraldehyde generally produced no length changes in the fibres or movements of the teeth but made both the fibres and teeth unresponsive to further changes of solution. Six mandibles in Ringer solution were heated in 5 °C increments to 70 °C. Between 60 and 65 °C (denaturation temperature of soft tissue collagens) the incisor extruded by 60 ± 15 (SD) μm. This extrusion did not occur in mandibles that had been stored in formalin. These results are consistent with at least part of the periodontal collagen existing as obliquely oriented fibres before fixation. This orientation is such that contraction of the fibres could produce an eruptive force.     

Stability of regional cerebral glucose metabolism in the normal brain measured by positron emission tomography

Cerebral glucose utilization (LCMRGI) was measured using the [18F]fluorodeoxyglucose method with PET in two groups of ten healthy young volunteers, each scanned in a resting state under different methodological conditions. In addition, five subjects had a second scan within 48 hr. Mean hemispheric values averaged 45.8 +/- 3.3 mumol/100 g/min in the right cerebral hemisphere and 47.0 +/- 3.7 mumol/100 g/min in the left hemisphere. A four-way analysis of variance (group, sex, region, hemisphere) was carried out on the results using three different methods of data manipulation: (a) the raw values of glucose utilization, (b) LCMRGI values "normalized" by the mean hemispheric gray matter LCMRGI value, and (c) log transformed LCMRGI values. For all analysis techniques, significantly higher LCMRGI values were consistently seen in the left mid and posterior temporal area and caudate nucleus relative to the right, and in the right occipital region relative to the left. The coefficient of variation of intrasubject regional differences (9.9%) was significantly smaller than the coefficient of variation for regions between subjects (16.5%). No differences were noted between the sexes and no effect of repeat procedures was seen in subjects having multiple scans. In addition, inter-regional LCMRGI correlations were examined both in values from the 20 normal subjects, as well as in a set of hypothetical "abnormal" values. Results were compared with those reported from other PET centers; despite certain methodological differences, the intersubject and inter-regional variation of LCMRGI is fairly constant.     

Evaluation of three substitutes for Percoll in sperm isolation by density gradient centrifugation

Silane-coated silica particle solutions (ISolate(TM) and PureSperm)TM)) and iodixanol (OptiPrep(TM)) were compared to polyvinylpyrrolidone (PVP)-coated silica particles (Percoll(TM)) in their efficacy to recover spermatozoa by gradient centrifugation for use in assisted reproductive procedures. Efficacy was assessed in terms of percentages of sperm recovery, sperm vitality and motility, normal sperm morphology and normal sperm chromatin condensation. No significant difference was found in the recovery of spermatozoa for men with both normal sperm counts and oligozoospermia, between PVP-coated and silane-coated particle solutions. Iodixanol had significantly lower sperm recovery compared to the other products. Sperm vitality, progressive motility, normal morphology and normal chromatin condensation did not differ significantly between any of the sperm isolation products.