Dust grains fall from Saturn's D-ring into its equatorial upper atmosphere.

The sizes of Saturn's ring particles range from meters (boulders) to nanometers (dust). Determination of the rings' ages depends on loss processes, including the transport of dust into Saturn's atmosphere. During the Grand Finale orbits of the Cassini spacecraft, its instruments measured tiny dust grains that compose the innermost D-ring of Saturn. The nanometer-sized dust experiences collisions with exospheric (upper atmosphere) hydrogen and molecular hydrogen, which forces it to fall from the ring into the ionosphere and lower atmosphere. We used the Magnetospheric Imaging Instrument to detect and characterize this dust transport and also found that diffusion dominates above and near the altitude of peak ionospheric density. This mechanism results in a mass deposition into the equatorial atmosphere of ~5 kilograms per second, constraining the age of the D-ring.

Chemical interactions between Saturn's atmosphere and its rings.

The Pioneer and Voyager spacecraft made close-up measurements of Saturn's ionosphere and upper atmosphere in the 1970s and 1980s that suggested a chemical interaction between the rings and atmosphere. Exploring this interaction provides information on ring composition and the influence on Saturn's atmosphere from infalling material. The Cassini Ion Neutral Mass Spectrometer sampled in situ the region between the D ring and Saturn during the spacecraft's Grand Finale phase. We used these measurements to characterize the atmospheric structure and material influx from the rings. The atmospheric He/H2 ratio is 10 to 16%. Volatile compounds from the rings (methane; carbon monoxide and/or molecular nitrogen), as well as larger organic-bearing grains, are flowing inward at a rate of 4800 to 45,000 kilograms per second.

Somatotroph hyperplasia. Successful treatment of acromegaly by removal of a pancreatic islet tumor secreting a growth hormone-releasing factor.

A 21-yr-old woman with Turner's syndrome presented with signs and symptoms of acromegaly. The serum growth hormone (GH) (95+/-9.4 ng/ml; mean+/-SEM) and somatomedin C (11 U/ml) levels were elevated, and an increase in GH levels after glucose instead of normal suppression, increase after thyrotropin-releasing hormone (TRH) administration instead of no change, and decrease after dopamine administration instead of stimulation were observed. The pituitary fossa volume was greater than normal (1,440 mm(3)) and the presence of a pituitary tumor was assumed. After tissue removal at transsphenoidal surgery, histological study revealed somatotroph hyperplasia rather than a discrete adenoma. Postoperatively, she remained clinically acromegalic and continued to show increased GH and somatomedin levels. A search was made for ectopic source of a growth hormone-releasing factor (GRF). Computer tomographic scan revealed a 5-cm Diam tumor in the tail of the pancreas. Following removal of this tumor, serum GH fell from 70 to 3 ng/ml over 2 h, and remained low for the subsequent 5 mo. Serum somatomedin C levels fell from 7.2 to normal by 6 wk postoperatively. There were no longer paradoxical GH responses to glucose, TRH, and dopamine. Both the medium that held the tumor cells at surgery and extracts of the tumor contained a peptide with GRF activity. The GRF contained in the tumor extract coeluted on Sephadex G-50 chromatography with rat hypothalamic GH-releasing activity. Stimulation of GH from rat somatotrophs in vitro was achieved at the nanomolar range, using the tumor extract. The patient's course demonstrates the importance of careful interpretation of pituitary histology. Elevated serum GH and somatomedin C levels in a patient with an enlarged sella turcica and the characteristic responses seen in acromegaly to TRH, dopamine, and glucose do not occur exclusively in patients with discrete pituitary tumors and acromegaly. This condition can also occur with somatotroph hyperplasia and then revert to normal after removal of the GRF source. Thus, in patients with acromegaly a consideration of ectopic GRF secretion should be made, and therefore, careful pituitary histology is mandatory. Consideration for chest and abdominal computer tomographic scans before pituitary surgery, in spite of their low yield, may be justified.

Pergolide mesylate: its effects on circulating anterior pituitary hormones in man.

Pergolide mesylate is a synthetic ergoline with dopamine agonist properties. The endocrine profile was studied in a double blind crossover design in six normal males. Circulating PRL, TSH, GH, LH, FSH, and cortisol were measured in the basal state and after TRH (500 micrograms iv) administration at 4.5, 11.5, and 23.5 h after placebo or pergolide (100 micrograms orally). Pergolide caused suppression of basal PRL from 2-8 ng/ml to less than 2 ng/ml commencing 60 min after administration and persisting throughout the 23.5-h study period. For the three TRH tests, a suppression of peak PRL (mean +/- SEM) response to TRH of 54.6 +/- 5.1 vs. 1.9 +/- 0.5, 45.2 +/- 4.1 vs. 4.5 +2- 0.6, and 34.4 +/- 2.9 vs. 6.9 +/- 1.4 ng/ml, respectively, for placebo and pergolide was noted. Basal TSH levels were unaffected by pergolide, but after pergolide the peak TSH response to the first two TRH challenges was blunted (placebo vs. pergolide: 12.3 +/- 1.2 vs. 6.8 +/- 1.0 and 14.8 +/- 2.0 vs. 9.6 +/- 1.0, respectively); however, the third TSH response (9.8 +/- 1.1 vs. 9.3 +/- 1.2) was not blunted after pergolide. GH secretion was stimulated by pergolide with a consistent pulse observed within 60 min of pergolide administration and an enhancement in the number and amplitude of subsequent GH pulses throughout the 24-h period. Cortisol levels rose after pergolide and returned to levels seen on the control day at 16.5 h. FSH levels were unaffected but LH levels were lowered pergolide. Side effects including nausea, vomiting, and hypotension were observed in all subjects. Pergolide is a potent dopamine agonist with the anticipated endocrine profile and clinical effects; its long duration of actions offers promise of single daily dose therapy for hyperprolactinemia.

Rapid regression of pituitary prolactinomas during bromocriptine treatment.

Therapy for large prolactinomas remains controversial. Surgery is often unsuccessful in restoring endocrine function to normal. However, medical therapy with bromocriptine, a dopamine agonist, not only suppresses PRL levels, but may also lead to a reduction in tumor size. Previous reports have demonstrated radiographic evidence of tumor regression only after 3 or more months of bromocriptine therapy. We have now documented, for the first time, objective evidence of extremely rapid reduction in tumor size in two patients harboring large PRL-secreting pituitary tumors (mean pretreatment serum PRL levels, 2350 and 3900 ng/ml) who were prospectively treated with bromocriptine (7.5 mg/day) in preference to surgical intervention despite marked visual impairment in one of the patients. After 2 and 6 weeks of therapy, respectively, marked reduction in tumor size was demonstrated radiographically in both patients. Headache, visual acuity, and visual fields had improved after only 3 days. Although the mechanism of bromocriptine's antitumor activity is unclear, we believe that a large prospective trial to study the effects of bromocriptine therapy on the size of PRL-secreting macroadenomas is urgently needed to determine whether medical therapy should become the primary modality of treatment to reduce tumor size as well as restore endocrine function.

Fetal tissue typing in anticipation of neonatal heart transplantation.

BACKGROUND: Hypoplastic left heart syndrome is among the most common major congenital cardiac anomalies. Fetuses with this anomaly survive but require either reconstructive surgery or heart transplantation postnatally. CASE: A woman whose fetus was diagnosed with hypoplastic left heart syndrome underwent funipuncture for fetal tissue typing. The fetus then was listed for heart transplantation. Once an ABO-compatible donor heart was procured, the fetus was delivered and immediately underwent transplantation. CONCLUSION: In candidates for neonatal heart transplantation, fetal tissue typing allows the search for an ABO-compatible donor heart to begin earlier. This approach minimizes the morbidity associated with postnatal waiting and allows transplantation to take place while the neonate is less immunocompetent.

Autogenous atrial tunnel for direct cavopulmonary connection in infants and small children.

A technique is described for construction of an autogenous right atrial tunnel for direct cavopulmonary connection in infants and small children requiring Fontan operation. Advantages, in this subset of patients, of this method over others previously described using prosthetic or growth-limited materials are suggested.

Atrially based pericardial tunnel for central pulmonary artery construction.

Discontinuity of central intrapericardial pulmonary arteries requires reconstruction of a pulmonary artery confluence before cavopulmonary connection, whether this connection be by bidirectional Glenn or Fontan procedure. Reconstruction of the central pulmonary arteries has previously been described using material of poor or no growth potential. A method is described for central pulmonary artery reconstruction that provides growth potential and is based on previous experience with Fontan lateral tunnel construction.

Rapid safe central venous access in children and adults undergoing open cardiac operations.

A technique is described for percutaneous placement of central venous catheters under direct vision in children and adults undergoing open heart operations. The method is reliable, rapid, and safe, and avoids blind attempts at obtaining vascular access.

Surgical treatment for cardiac rhabdomyomas in children.

Cardiac rhabdomyomas are the most common cardiac tumor in children. These tumors may cause obstruction to blood flow, valvular insufficiency, and cardiac arrhythmias. We present two cases of cardiac rhabdomyomas in infants that were managed surgically and review the literature. Without surgical intervention, the prognosis for symptomatic cardiac rhabdomyomas is dismal, with eventual death likely due to heart failure or arrhythmias. As our two cases indicate, surgical treatment may improve this prognosis. Pediatric cardiac rhabdomyomas should be resected when the tumors cause hemodynamic compromise or cardiac arrhythmias.

Herpes simplex encephalitis occurring after chemotherapy, surgery, and stereotactic radiotherapy for medulloblastoma.

Reactivation of latent herpes simplex virus (HSV) in the trigeminal ganglion most commonly gives rise to recurrent herpes labialis and rarely to herpes simplex encephalitis. The mechanisms underlying reactivation of latent trigeminal HSV are complex. Here we report the case history of a 25-year-old woman who developed a fatal, bilateral necrotizing destructive temporal lobe lesion following surgical removal of a cerebellar medulloblastoma and combined radiotherapy and chemotherapy for recurrent tumor. Neuropathologic examination of the brain revealed minimal inflammatory changes, but immunohistochemistry was positive for HSV protein, and HSV deoxyribonucleic acid (DNA) was recovered from formalin-fixed paraffin-embedded brain tissue. The temporal proximity of the surgery, chemotherapy, and radiotherapy to the onset of disease suggests that these factors may have acted as triggers that precipitated conversion of latent HSV to overt HSV.

Microspectrophotometric analysis of respiratory pigments using a novel fibre optic dip probe in microsamples.

A microspectrophotometer system to monitor the reduction of mitochondrial respiratory pigments in cell extracts and permeabilized cells has been developed. The novel optical fibre set-up uses visible spectrophotometry to measure the reduction of mitochondrial electron carriers. The basis of the system is an Ocean Optics S1000 spectrometer, a broadband tungsten based light source, input and output coupling fibre optics and a fibre optic dip-probe which requires less than 20 microl of sample for analysis. The spectral range of the system is from 250 to 850 nm with a spectral resolution of 0.5 nm. Data are presented for the reduction of purified cytochrome c by the reducing agent sodium dithionite and the reduction of cytochrome c by isolated mitochondria using sodium succinate as substrate. Reduction of cytochrome c by digitonin permeabilized cultured mouse cells, C2C12, is also shown. The effect of temperature on cytochrome c reduction in these assays is also demonstrated. The optical design of the probe system is optimized to maintain maximum light throughput and spectral resolution. The key features of the system are small sample size, front-end adaptability, high sensitivity and fast multispectral acquisition which are essential for observing these biological reactions in vivo.

Reduction of neutrophil margination by L-arginine during hypothermic cardiopulmonary bypass in a pig model.

Nitric oxide generation by L-arginine (2 mg/kg/min) infusion during cardiopulmonary bypass (CPB) increases blood flow to all organs and reduces cytokine induced organ damage by reducing the level of marginating neutrophils (Ns). The N-trapping in the oxygenator (OX), arterial filter (AF), cardiotomy reservoir (CR), and N-margination were quantified with indium 111 labeled autologous neutrophils (INN) in nine groups of 40 Yorkshire pigs (30-35 kg). Cardiopulmonary bypass (180 min or 90 min CPB, 90 min reperfusion) was carried out at 2.5-3.5 L/min and at two temperatures (18 degrees C, 28 degrees C). The INN (650-780 microCi) was administered intravenously 15 mins before CPB. All pigs received heparin systemically (activated coagulation time > 400 secs); CPB was instituted with a roller pump, OX (Univox 1.8 m2), AF (0.25 m2), and CR (BCR-3500, Bentley Lab, Irvine, CA). The INN distribution in the device (OX, AF, CR) and organs was imaged with a gamma camera and measured with an ion chamber and a gamma counter. The LA infusion decreased N-trapping, estimated as the percent of injected INN (mean +/- standard deviation), in OX from control (2.7 +/- 2.02)% to (0.94 +/- 0.29)%, and margination in lung from control (48 +/- 4)% to minimal levels (23 +/- 2)% (p < 0.01). In the CPB reperfusion group, a beneficial effect was observed at LA low dose and toxicity of higher N-margination at 15 mg/ kg/min. Neither CPB temperature nor Leumedin affected N-margination significantly.

Emboli from an extraluminal blood flow hollow fiber oxygenator with and without an arterial filter during cardiopulmonary bypass in a pig model.

The effect of an arterial filter on visceral emboli was quantified with autologous indium-111 labeled platelets (INPLT) during cardiopulmonary bypass (CPB) in Yorkshire pigs. Biodistribution of INPLT was determined in 12 control pigs (30-35 kg, unoperated control [n = 6] and sham operated control [n = 6]). CPB was carried out with (n = 6) and without (n = 6) an arterial filter in 12 pigs at a flow rate of 2.5-3.5 L/min. Platelets labeled with In-111 tropolone (650-780 microCi) were injected intravenously 24 hr before CPB. All pigs were systemically heparinized (activated coagulation time > 400 sec); CPB was instituted with a roller pump, an extraluminal blood flow oxygenator (Bentley Univox, 1.8 m2), and an arterial filter (0.25 m2) and continued for 3 hr. Platelet kinetics, pooling, and counts were monitored by a Geiger probe and a Coulter counter. The thrombi in the oxygenator and arterial filter and emboli in viscera and brain were imaged with a gamma camera and measured with an ion chamber and gamma counter. Percentage of INPLT (mean +/- SD) in organs, tissues, and components of the circuit in four groups of pigs was calculated. Flow cytometry with antibodies to CD61 (GPIIIa) and CD62P (GMP-140: control) of porcine platelets was carried out with blood samples taken before, during, and after CPB for estimation of circulating platelet aggregates and platelet microparticles. Pulmonary, renal, cardiac, and cerebral emboli in pigs undergoing CPB with and without a filter were similar (p < 0.1). The amount of filter adherent thrombi was small (0.04 +/- 0.01%); oxygenator adherent thrombus in both groups was similar (p < 0.1). Emboli were found in the cerebral medulla, hippocampus, and posterior cerebral cortex in both groups. During CPB, the arterial filter functioned minimally as a trap for platelet thrombi detached from the oxygenator and circulating emboli. Flow cytometry of blood demonstrated the shift of equilibria from single platelets to platelet aggregates and microparticles during CPB and their gradual reversal to single platelets after CPB; the loosely adherent emboli disaggregated and further shifted these equilibria to single platelets and smaller aggregates, probably through the action of endogenous nitric oxide and prostacyclin. The emboli were trapped in organs and tissues and microparticles were sequestered by the reticuloendothelial system.

Operant conditioning of mental retardates' visual monitoring.

To study improvement of visual monitoring of retardates, specialized training methods backed up by incentives were used. The extent to which these training techniques might be expected to produce results which would generalize to those situations in which the retardate was required to monitor without the increased signal rate and knowledge of results was explored. Subjects were 8 female mental retardates with IQs from 38 to 69. Detection of an aperiodic pattern change during pre-training was compared with final performance after 4 training sessions. During training, the task difficulty was increased until during the final training session it approximated the test conditions. Immediate knowledge of results was given for correct detections and false positive responses. Tokens were given to the subjects, based on the scores at the end of the session. After the final session these tokens were exchanged for prizes. As predicted, training under these conditions significantly enhanced the retardates' performance and transferred to the condition with no knowledge of results.