PubMed Health⌕ Search

Biomedical subjects

P Callahan

Publications and source records attributed to P Callahan.

At least 19 recordsLinked to original sources
PubMed2007

The lakes of Titan.

The surface of Saturn's haze-shrouded moon Titan has long been proposed to have oceans or lakes, on the basis of the stability of liquid methane at the surface. Initial visible and radar imaging failed to find any evidence of an ocean, although abundant evidence was found that flowing liquids have existed on the surface. Here we provide definitive evidence for the presence of lakes on the surface of Titan, obtained during the Cassini Radar flyby of Titan on 22 July 2006 (T16). The radar imaging polewards of 70 degrees north shows more than 75 circular to irregular radar-dark patches, in a region where liquid methane and ethane are expected to be abundant and stable on the surface. The radar-dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes, including associated channels and location in topographic depressions. Some of the lakes do not completely fill the depressions in which they lie, and apparently dry depressions are present. We interpret this to indicate that lakes are present in a number of states, including partly dry and liquid-filled. These northern-hemisphere lakes constitute the strongest evidence yet that a condensable-liquid hydrological cycle is active in Titan's surface and atmosphere, in which the lakes are filled through rainfall and/or intersection with the subsurface 'liquid methane' table.

Journal Article↗
PubMed2006

Titan Radar Mapper observations from Cassini's T3 fly-by.

Cassini's Titan Radar Mapper imaged the surface of Saturn's moon Titan on its February 2005 fly-by (denoted T3), collecting high-resolution synthetic-aperture radar and larger-scale radiometry and scatterometry data. These data provide the first definitive identification of impact craters on the surface of Titan, networks of fluvial channels and surficial dark streaks that may be longitudinal dunes. Here we describe this great diversity of landforms. We conclude that much of the surface thus far imaged by radar of the haze-shrouded Titan is very young, with persistent geologic activity.

Journal Article↗
PubMed2006

The sand seas of Titan: Cassini RADAR observations of longitudinal dunes.

The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.

Extraterrestrial Environment↗
PubMed2005

Cassini radar views the surface of Titan.

The Cassini Titan Radar Mapper imaged about 1% of Titan's surface at a resolution of approximately 0.5 kilometer, and larger areas of the globe in lower resolution modes. The images reveal a complex surface, with areas of low relief and a variety of geologic features suggestive of dome-like volcanic constructs, flows, and sinuous channels. The surface appears to be young, with few impact craters. Scattering and dielectric properties are consistent with porous ice or organics. Dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons.

Atmosphere↗
PubMed2005

Effect of steroids and nitric oxide on pituitary hormone release in ovariectomized, peripubertal rats.

The purpose of this study was to determine the effects of the duration of steroid depletion on the steroid-induced luteinizing hormone and prolactin surges in ovariectomized, peripubertal female rats. Additionally, the role of nitric oxide (NO) in mediating the surge responses was determined. Peripubertal, 6-week-old, female Sprague-Dawley rats were ovariectomized. One or three weeks later, animals were injected with 17 beta-estradiol (50 microg, sc) followed 48 h later by progesterone (2.5 mg, sc). Effects of NO were examined by administering L-arginine (300 mg/kg, ip). The response of ovariectomized, adult females to steroid treatment was also determined. One and three weeks after ovariectomy, steroid replacement produced an LH and prolactin surge in peripubertal animals. However, both the magnitude and duration of the LH surge was greater 3 weeks after ovariectomy. While L-arginine significantly enhanced the magnitude of the LH surge 1 week after ovariectomy, by 3 weeks L-arginine caused a decrease in the duration, but not the magnitude of the surge. In contrast, L-arginine did not affect either the magnitude or duration of the prolactin surge one week after ovariectomy, but diminished the magnitude after 3 weeks of steroid depletion. In adults, steroids induced significant increases in both LH and prolactin. These results demonstrate that sensitivity to NO stimulation of LH, but not prolactin secretion, is modulated by the duration of gonadal steroid hormone depletion. The differences in the responsiveness of LH and prolactin to steroid-induced stimulation in peripubertal animals demonstrate that these hormones are regulated by NO through different mechanisms.

Animals↗
PubMed2004

Effects of cyclic steroid hormone replacement on prolactin and luteinizing hormone surges in female rats.

The ability of steroid hormones to produce an LH or prolactin (PRL) surge was determined in rats ovariectomized at 6, 9 or 13 weeks of age and subjected to one, three or six cycles of estrogen and progesterone replacement. Sensitivity to steroid replacement was dependent on the age of the animal at the time of ovariectomy. Repeated cyclic steroid hormone replacement significantly increased the magnitude of the PRL response, but not the LH response, in animals ovariectomized at 6 weeks. The LH response was significantly altered by cyclic steroid replacement only in animals ovariectomized at 13 weeks. These results indicate that the mechanisms involved in the regulation of PRL secretion are influenced by steroid hormone replacement and that cyclic steroid hormone exposure increases the magnitude of the PRL secretory response.

Age Factors↗
PubMed2000

Multisite evaluation of a new diabetes self-test for glucose and glycated protein (fructosamine).

BACKGROUND: In diabetes management, the true average blood glucose is best obtained using glycated protein tests that give the average blood glucose over a previous time window of either weeks (fructosamine tests) or months (glycated hemoglobin tests). Until now, glycated protein tests have only been available as laboratory tests and have therefore been underutilized in diabetes management. Recently, a fructosamine self-test for use by diabetes patients at home was cleared for marketing by the U.S. Food and Drug Administration (FDA). We have studied the performance of this test in three geographically distinct diabetes clinics to confirm the performance and accuracy of both glucose and fructosamine testing with this device. This new self-testing system has the potential to improve glycemic control dramatically in patients with diabetes, including those patients with type 2 diabetes using oral drug therapy. METHODS: Three geographically different sites (San Diego, CA, Tallahassee, FL, and Minneapolis, MN) were selected for the study. Sixty male and 56 female adult patients, with both type 1 (59) and type 2 (57) diabetes, were selected for participation in the study (total patients = 116). Fingerstick puncture capillary blood glucose was tested using the YSI Model 1500 and the Duet Glucose test. A fingerstick puncture capillary blood test was also tested with the Duet GlucoProtein (fructosamine) test strip in duplicate. For fructosamine comparison, a venipuncture blood sample of ethylene diaminetetraacetic acid (EDTA) plasma was collected and tested using the Roche Unimate laboratory test. RESULTS: The glucose test gave excellent correlation to the reference laboratory method (r = 0.98) and the GlucoProtein test gave a correlation of 0.72 compared to the laboratory method. The bias of both tests compared to the laboratory tests was 10% or less at all concentrations. Error grid analysis of the glucose test showed that 97.5% of test results were in the accurate zone and 2.5% were in the clinically neutral or benign errors zone. Analysis of fructosamine test results using a two-by-two grid yielded sensitivity of 100%, specificity of 92% and accuracy of 94%. CONCLUSIONS: The Duet Glucose Control System is accurate for both measuring glucose and GlucoProtein (fructosamine) using a fingerstick blood sample. This new testing system has the potential to provide useful information to both healthcare specialists in their office and also to patients at home to help them achieve better long-term glucose control and avoid the potential acute and chronic complications of diabetes.

Adolescent↗
PubMed2000

Immunoneutralization of endogenous opioid peptides prevents the suckling-induced prolactin increase and the inhibition of tuberoinfundibular dopaminergic neurons.

Previous studies have shown that the endogenous opioid peptides, acting at specific opiate receptor subtypes, are involved in the suckling-induced prolactin secretory response. The prolactin increase elicited by suckling is due, at least in part, to an inhibition of tuberoinfundibular dopaminergic (TIDA) neurons in the hypothalamus. We investigated the effects of immunoneutralization of dynorphin, leu-enkephalin and met-enkephalin on the suckling-induced prolactin increase and on the activity of the TIDA neurons in lactating female rats between days 7 and 12 postpartum. Rats were injected into the right lateral ventricle with antiserum specific for one of these three peptides. Control rats were administered equal amounts of immunoglobulin proteins. Suckling produced a profound and significant increase in prolactin levels, as well as a decrease in DOPA accumulation in the median eminence of lactating rats. Administration of immunoglobulin concentrations of up to 3.6 microg did not inhibit the prolactin secretory response to the suckling stimulus and did not prevent the suckling-induced inhibition of TIDA neurons. Antisera to all three endogenous opioid peptides abolished the suckling-induced prolactin increase and prevented the inhibition in DOPA accumulation in the median eminence. Thus, the endogenous opioid peptides, dynorphin, leu-enkephalin and met-enkephalin, are essential for the prolactin secretory response to suckling and inhibition of TIDA neuronal activity is at least one of the mechanisms of action utilized by these peptides.

Animals↗
PubMed1998

Orphanin FQ stimulates prolactin and growth hormone release in male and female rats.

Intracerebroventricular administration of Orphanin FQ (5.5, 55 or 550 pmol) caused a dose-related increase in prolactin secretion in both male and female rats and stimulated GH secretion in males. The magnitude of the prolactin secretory response was greater in females than in males. These effects of OFQ on prolactin and growth hormone release are the same as the stimulatory effects of the endogenous opioid peptides.

Analysis of Variance↗
PubMed1997

Immunoneutralization of beta-endorphin blocks prolactin release during suckling without affecting tuberoinfundibular dopaminergic neural activity.

The effect of immunoneutralization of beta-endorphin on the suckling-induced prolactin increase and on the activity of the tuberoinfundibular dopaminergic (TIDA) neurons was determined in lactating female rats between days 8 - 12 post-partum. Two antisera were used in the immunoneutralization studies. Both were specific for beta-endorphin, exhibiting little cross reactivity with met- or leu-enkephalin or dynorphin. Antisera to beta-endorphin completely abolished the suckling-induced prolactin increase indicating that this endogenous opioid peptide is involved in this response. Suckling significantly inhibited DOPA accumulation in the median eminence and antiserum to beta-endorphin did not prevent this inhibition. Additionally, 5-endorphin antiserum significantly reduced TIDA neural activity even in pup-deprived dams. These results indicate that beta-endorphin is involved in the prolactin secretory response to suckling but that inhibition of TIDA neuronal activity is not its mechanism of action. Other possible mechanisms are discussed.

Animals↗
PubMed1997

Effects of age and gender on the AII-induced stimulation of prolactin release and inositol phosphate accumulation in rat anterior pituitary cells in vitro.

The stimulatory effects of Angiotensin II (AII) on prolactin secretion and inositol phosphate accumulation were examined in dispersed anterior pituitary cells collected from young (3-4 month), mature (7-8 month) and old (18-20 month) male and female rats. Physiological doses of AII (0.01-10 nM) stimulated prolactin release from cells collected from mature female rats only. This effect was antagonized by pretreatment with Saralasin, an AII receptor antagonist. Significant accumulation of the inositol phosphates was observed in cells obtained from the mature, female donors and this increase preceded the prolactin response. Although there was a small increase in total inositol phosphate accumulation in cells obtained from the old female rats, this was transient and did not coincide with a similar increase in prolactin release. These results indicate that pituitary sensitivity to AII stimulation is related to the age and the gender of the donor animal. The physiological role of pituitary AII needs to be examined in sexually mature female animals.

Aging↗
PubMed1997

Relationship between tolerance/intolerance of ambiguity and perceived environmental uncertainty in hospitals.

1 Many variables may contribute to a nurse's perceptions when working in a changing health care environment, especially in the field of psychiatry. 2 While this study did not find a relationship between tolerance for ambiguity and perceived environmental uncertainty in hospitals, age and educational background appear to be variable, which may warrant further study as ultimately impacting nursing. 3 Research which explores those personality variables which underlie perception would assist nurse administrators in designing interventions, opening new lines of communication, and increasing sensitivity to individual nurse's need in these changing times.

Adult↗
PubMed1996

Inhibition of tuberoinfundibular dopaminergic neural activity during suckling: involvement of mu and kappa opiate receptor subtypes.

Previous studies have shown that mu (mu) and kappa (kappa) opioid antagonists inhibit suckling-induced prolactin release. Prolactin responses elicited by pup suckling or opioid administration are mediated, at least in part, by suppression of dopamine (DA) release from tuberoinfundibular dopaminergic (TIDA) neurons in the hypothalamus. We examined the effects of the mu opiate receptor antagonist, beta-funaltrexamine (beta-FNA), and the kappa opiate receptor antagonist, nor-binaltorphimine (nor-BNI) on the activity of TIDA neurons in lactating rats. TIDA neuronal activity was determined by measuring DOPA accumulation in the caudate putamen (CP) and median eminence (ME). The effects of opioid antagonist treatment were determined in pup-deprived (low circulating prolactin levels) or pup-suckled rats (high circulating prolactin levels). The accumulation of 5-hydroxytryptophan (5-HTP) in the medial preoptic area (MPOA), the anterior hypothalamus (AH) and the median eminence (ME) was quantified as an index of serotonergic activity in the same animals for comparative purposes. In vehicle treated rats, suckling caused a significant and selective decrease in DOPA accumulation in the ME. beta-FNA (5 micrograms, i.c.v.) pretreatment significantly increased DOPA accumulation in the ME of pup-deprived and pup-suckled rats. beta-FNA pretreatment also prevented the suckling-induced suppression of DOPA accumulation in the ME. In contrast to the actions of beta-FNA, pretreatment with nor-BNI (8 micrograms, i.c.v.) did not significantly affect the activity of the TIDA neurons in pup-deprived or pup-suckled rats. Suckling alone did not alter 5-HTP accumulation in any of the brain regions examined, and neither opioid antagonist had appreciable effects on 5-HTP accumulation. These results demonstrate that the EOP tonically inhibit the TIDA neurons in both pup-deprived and pup-suckled, post-partum female rats by acting through the mu, but not the kappa, opiate receptor subtype. Furthermore, the suckling-induced inhibition of TIDA neurons is also mediated through the EOP acting at mu, but not kappa opioid receptors.

5-Hydroxytryptophan↗
PubMed1994

Multiple opiate receptor subtypes are involved in the stimulation of growth hormone release by beta-endorphin in female rats.

The growth hormone (GH) secretory response to beta-endorphin and the involvement of opiate receptor subtypes in this response were determined in diestrous female rats. The involvement of the mu (mu), delta (delta) and/or kappa (kappa) site was determined by administering specific antagonists for each of these sites prior to beta-endorphin. beta-Funaltrexamine (1 or 5 micrograms) was administered to block mu sites, ICI 154,129 (5 or 25 micrograms) blocked delta sites and nor-binaltorphimine (8 micrograms) blocked kappa sites. The ability of these antagonists to block GH secretion following intravenous morphine administration was also determined. The opiate antagonists and beta-endorphin were administered into the lateral ventricle. A dose-response study for beta-endorphin indicated that 0.5 micrograms beta-endorphin was the minimum stimulatory dose for GH release, producing an approximately 4-fold increase in circulating levels of GH; lower doses of beta-endorphin did not stimulate secretion. All three antagonists were capable of blocking the stimulatory effects of beta-endorphin. These results provide evidence that all three opiate receptor subtypes are involved in the stimulatory effect of beta-endorphin on GH release.

Animals↗
PubMed1993

Morphine induced analgesia is attenuated in post-partum lactating rats.

The analgesic effects of morphine administration were determined in post-partum, lactating female rats, as well as in intact, cycling females during the diestrous stage of the estrous cycle. All doses of morphine (2.5, 5 and 10 mg/kg, iv) produced a significant analgesic response in both post-partum and diestrous females using the hot water tail immersion latency test. However, the analgesic response in the post-partum females was significantly less than during diestrus at all doses tested. In addition, pretreatment with the mu 1 specific antagonist, Naloxonazine, significantly blunted the analgesic response in diestrous females, but did not significantly affect analgesia in post-partum females. These results indicate that morphine is less effective in producing analgesia in post-partum females. The mu 1 opiate receptor site does not appear to be involved in the analgesia produced during the post-partum period.

Analgesia↗
PubMed1993

Opiate receptor subtype involvement in the stimulation of prolactin release by beta-endorphin in female rats.

The prolactin secretory response to beta-endorphin and the involvement of opiate receptor subtypes in this response was determined in both diestrous and postpartum, lactating female rats. The involvement of the mu-, delta- and/or kappa-site was determined by administering specific antagonists for each of these sites prior to beta-endorphin. beta-Funaltrexamine (beta-FNA, 1 or 5 micrograms) was administered to block mu-sites, ICI 154,129 (5, 10 or 25 micrograms) blocked delta-sites and nor-binaltorphimine (norBNI, 8 micrograms) blocked kappa-sites. The ability of beta-FNA and ICI 154,129 to block prolactin secretion following morphine administration was also determined. A dose response study for beta-endorphin indicated that beta-endorphin, at doses as low as 25 ng, was a potent stimulus for prolactin release producing an increase in prolactin that mimicked the suckling-induced prolactin increase. In addition, all three antagonists were capable of antagonizing the stimulatory effect of beta-endorphin in both diestrous and postpartum female rats. These results indicate that beta-endorphin is a potent stimulus for prolactin secretion and that these three opiate receptor subtypes interact to produce its stimulatory effect on prolactin release.

Animals↗
PubMed1992

Effects of immobilization stress on tuberoinfundibular dopaminergic (TIDA) neuronal activity and prolactin levels in lactating and non-lactating female rats.

The effects of immobilization stress on the prolactin secretory response and on the activity of the tuberoinfundibular dopaminergic (TIDA) neurons were determined in intact, virgin female rats on the morning of diestrus or proestrus and in post-partum, lactating female rats. The virgin females exhibited a significant increase in circulating levels of prolactin which was evident by 1 minute and persisted during the immobilization (5 minutes). In contrast, the prolactin secretory response in lactating females was significantly attenuated compared to non-lactating animals. The activity of the TIDA neurons was not altered by the 5 minutes of stress. Even after 30 minutes of immobilization, TIDA neuronal activity was not affected in either the lactating or cycling females. These data suggest that the cycling female rat is capable of a prolactin secretory response to the stressor without inhibition of TIDA neuronal activity. It seems likely that prolactin releasing factors mediate this response. In contrast, stress did not produce a similar prolactin increase during lactation. It seems likely that, during lactation, the pituitary is not sensitive to releasing factors unless the TIDA neurons are inhibited. There appear to be differences in the sensitivity of the pituitary depending on the physiological state of the model employed.

Animals↗