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G Baker

Publications and source records attributed to G Baker.

At least 19 recordsLinked to original sources
PubMed1992

Detection of calcified atherosclerotic plaque by laser-induced plasma emission.

The use of fluorescence spectroscopy to discriminate atherosclerotic from normal tissue is limited by a lower sensitivity for calcified than noncalcified atherosclerotic plaque (65% vs. 93%, respectively). To evaluate plasma emission as a means to detect calcified plaque, 325 normal and atherosclerotic cadaveric aortic sites were irradiated through a 100-micron silica fiber in blood by a pulsed holmium laser (lambda = 2.1 microns, fluence = 4 J/mm2). A photodiode positioned near the proximal end of the fiber detected plasma emission during a laser pulse. Plasma emission was detected at 0% (0/110) of normal, 0% (0/107) of noncalcified atherosclerotic tissue, and 91% (98/108) of calcified atherosclerotic sites. Spectroscopic analysis confirmed the presence of calcium lines in the plasma emission from calcified atherosclerotic plaque. Although ablative fluences (greater than 3 J/mm2) were required for plasma generation, a single laser pulse ablated only to a depth of 67 +/- 16 microns in normal tissue. In an additional 10 calcified atherosclerotic sites, laser ablation was continued as long as plasma emission was detected. In all cases, plaque ablation was terminated before arterial perforation. Furthermore, the adjunctive use of plasma detection improved the accuracy of fluorescence spectroscopic classification of normal and atherosclerotic tissue. In conclusion, plasma detection has a high sensitivity (91%) and specificity (100%) for calcified atherosclerotic plaque and may be a useful adjunct for laser angioplasty guidance. Furthermore, plasma detection can be implemented both simply and inexpensively.

Aluminum Silicates↗
PubMed1992

Prediction of silicosis and lung cancer in the Australian labor force exposed to silica.

Empirical models for risk, based on recently published epidemiologic data, and simple prediction formulas were used to predict the occurrence of silicosis and lung cancer in the Australian labor force currently exposed to crystalline silica dust. As a result of an 0.9 (range 0.4-1.9)% average lifetime risk, approximately 1010 (range 380-2410) silicosis cases were predicted for the next 40 years among the estimated 136,400 men exposed at current silica dust levels [0.01-0.8 (average 0.094) mg.m-3]. Approximately 630 extra lung cancer cases (95% confidence interval 120-1320) would appear with an average excess risk of 0.5 (interval 0.1-1.1)%, the proportion of silica-induced lung cancer cases being about 15%. Currently 77% of the at-risk labor force is exposed to silica dust levels of < or = 0.1 mg.m-3. With this level as the limit, about 440 (range 140-1210) silicosis cases and 410 (interval 90-780) extra lung cancer cases would occur in 40 years. Adopting this level as the national exposure standard would reduce the risk of silicosis cases by 52% and the excess risk of lung cancer by 36%.

Adult↗
PubMed1992

Selective cutaneous hyperpigmentation in mice following zidovudine administration.

BACKGROUND AND DESIGN: C57BL/6N mice fed zidovudine in their drinking water develop selective hyperpigmentation of the tails and footpads. Zidovudine-fed and identical control mice were observed and sequential biopsy specimens were obtained. Routine light microscopy, electron microscopy, and image analysis of unstained biopsy specimens were used to evaluate the extent, nature, and amount of cutaneous hyperpigmentation. RESULTS: Beginning at day 14 selective hyperpigmentation of the tails and footpads of the mice was noted. Histologic evaluation revealed a gradual increase in melanin, beginning in the lower levels of the epidermis, with eventual pigmentation of the stratum corneum. Electron microscopy demonstrated a sixfold increase in melanosomes in the tail skin of the zidovudine-fed mice. Using image cytometry, melanin was quantitatively shown to increase, paralleling the clinically apparent hyperpigmentation. The hyperpigmentation was reversible on discontinuation of zidovudine. CONCLUSIONS: This animal model parallels the human in developing reversible and selective hyperpigmentation on administration of zidovudine. In this model the increased pigmentation is due to increased numbers of melanosomes within epidermal keratinocytes. Image cytometry may be useful in semiquantitatively studying the pathogenesis of various disorders of hyperpigmentation.

Animals↗
PubMed1991

Multiple in vivo effects of interleukin-3 and interleukin-6 on murine megakaryocytopoiesis.

The in vivo effects of interleukin-3 (IL-3), interleukin-6 (IL-6), and a combination of IL-3 plus IL-6 on murine megakaryocytopoiesis and thrombopoiesis were examined. Human recombinant IL-6 was administered subcutaneously as 14 equal injections of 5,000 units each during a 102-hour period. Murine recombinant IL-3 was given as 8 injections of 80,000 units each during the first 54 hours. Megakaryopoiesis and thrombopoiesis were evaluated 120 hours after initial administration of the cytokines. Platelet levels increased by 20% following IL-3 alone, 35% following IL-6 alone and 61% after administration of both IL-3 and IL-6. Platelet production, as measured by 75Se-selenomethionine incorporation, increased by approximately 120% in animals that had received IL-6 or IL-3 plus IL-6. Megakaryocyte ploidy analysis by two-color flow cytometry showed a shift in the modal ploidy class from 16N to 32N and a significant increase in the frequency of 64N cells only in IL-6 treated animals. Both bone marrow and splenic megakaryocyte colony-forming cells were significantly increased following either IL-3 or IL-6. Bone marrow megakaryocyte size increased 18%, 43%, and 38%, respectively, after administration of IL-3, IL-6, or the combination of IL-3 plus IL-6. Leukocyte counts and hematocrits were unaffected by either cytokine. Additional groups of mice received the same injection schedule as above and the serial effects on peripheral blood cell levels were assessed for 30 days. Platelet levels, which had been elevated by IL-3 or IL-6, fell to control values within 4 days following the last injection. Animals given IL-6 or IL-3 plus IL-6 were subsequently thrombocytopenic relative to controls on days 7 through 9 following cessation of treatment. Temporary 'cycling' of platelet levels was observed for 3 weeks following treatment with IL-6 or the combination of IL-3 plus IL-6. We conclude that IL-6 and to a lesser extent IL-3 stimulate platelet production in vivo and that their combined effects on platelet levels are approximately additive. Following discontinuation of IL-3 or IL-6, the effects are rapidly reversed, presumably by negative feedback mechanisms, resulting in a period of 'rebound thrombocytopenia' in mice that had received IL-6.

Animals↗
PubMed1991

Stimulation of megakaryocytopoiesis in mice by human recombinant interleukin-6.

The in vivo effects of purified human recombinant interleukin-6 (IL-6) on murine megakaryocytopoiesis were examined. IL-6 was administered subcutaneously to Swiss Webster mice, followed by evaluation of bone marrow megakaryocyte ploidy, size and frequency, and median platelet volume 24, 48, and 72 hours after the initiation of IL-6 administration. In addition, bone marrow megakaryocyte morphology was examined using electron microscopy at 72 hours. IL-6 (10,000 U per subcutaneous injection) was administered three times during the first 24 hours, three times during the second 24 hours, and twice during the last 24-hour period. IL-6 bioactivity (10 U/ng) was determined using the IL-6-dependent murine hybridoma cell line B9. Megakaryocyte ploidy distribution, measured by two-color flow cytometry, demonstrated a shift in the modal ploidy class from 16N to 32N and a significant increase in the relative frequency of 64N megakaryocytes 48 and 72 hours (but not 24 hours) after initiation of IL-6 administration (cumulative doses of 60,000 and 80,000 U at 48 and 72 hours, respectively). In addition, ploidy levels were increased in animals that received a cumulative IL-6 dose of only 40,000 U (evaluated after 72 hours). The size of recognizable bone marrow megakaryocytes, determined by the cross-sectional areas of plastic embedded bone marrow megakaryocytes, was increased at the 48-hour (60,000 U IL-6) and 72-hour (80,000 U IL-6) time points. Megakaryocyte frequency, measured by flow cytometry, was unaffected at all time points and doses of IL-6. Median platelet volume, measured by electrical impedance, was not consistently altered by administration of IL-6. Electron microscopic examination of bone marrow megakaryocytes showed an increase in the proportion of megakaryocytes with a wide, peripheral, organelle-deficient zone from 20% +/- 9% (SD) in control animals to 50% +/- 7% (SD) (P less than .02) in animals that received IL-6. No changes were observed in the distribution of the demarcation membranes. IL-6 is a potent stimulator of murine megakaryocytopoiesis, in vivo, and appears to act early in megakaryocyte differentiation.

Animals↗
PubMed1991

Neuraminidase-induced thrombocytopenia in mice: effects on thrombopoiesis.

Previous studies to examine the effects of thrombocytopenia on thrombopoiesis have generally utilized immune-mediated platelet depletion. We have developed a nonimmune model to exclude the possibility that adverse immune-mediated effects have been misinterpreted as the physiological response to stimulation of thrombopoiesis. Thrombopoiesis was examined in mice after induction of thrombocytopenia with a single injection of the nonimmunologic agent neuraminidase (Ndase). Utilizing electron microscopy, we examined platelets and megakaryocytes (MK) obtained 8, 12, 24, 48, 72, 96, and 120 hr after administration of Ndase. Eight to 48 hr after induction of acute, severe thrombocytopenia (mean platelet count less than 50,000/microliters), the medians of the platelet sectional area distributions, as measured morphometrically, were significantly greater than the median platelet sectional area of pooled controls. The maximum median value for platelet sectional area was observed at 24 hr. The largest platelets in these samples contained more profiles of endoplasmic reticulum and Golgi cisternae, and a lower concentration of surface-connected canalicular system, as compared with normal platelets. By 72 hr post-injection of Ndase, virtually all platelets exhibited normal size and organelle complement. Mean platelet volumes, determined by electrical impedance analysis, paralleled the serial changes in platelet sectional areas. MK frequency and ploidy, measured by two-color fluorescence activated flow cytometry, were unchanged 12 and 24 hr following Ndase. At 48 hr, total MK frequency increased significantly (P less than 0.01) from 0.11% to 0.17%, and MK ploidy distribution shifted with a reduction in 16N MK (P less than 0.005) and an increase in 32N MK (P less than 0.01). MK ploidy was maximally altered from normal at 72 hr with increased 32N MK frequency (32.0%, P less than 0.001) and increased 64N MK frequency (2.4%, P less than 0.005). Morphologic and morphometric examination of MK at all time points did not reveal detectable changes from normal in cytoplasmic appearance or size, respectively. Therefore, we have demonstrated marked alterations of morphology and size of platelets, and of MK ploidy, using this nonimmunologic model. These studies further support our previous observations that megakaryocyte ploidy and platelet volume are independently regulated in response to depletion of the circulating platelet mass, and they show that these changes are not dependent upon the mechanism of thrombocytopenia.

Animals↗
PubMed1991

Albino gene dosage and retinal decussation patterns in the pigmented ferret.

We have examined the retinal decussation patterns in pigmented ferrets that were either wild-type sable or heterozygous with one albino gene. Unilateral injections of horseradish peroxidase were made into the optic tract and labeled ganglion cells visualized in retinal wholemounts. In both wild-type and heterozygous ferrets, those ganglion cells in the temporal retina with the largest cell bodies projected only to the contralateral side of the brain. The total number of ipsilaterally projecting ganglion cells did not differ with the genotype of the animal. The numbers ranged from 5471-6759 cells. Unlike the cat, there is no difference in retinal decussation patterns in wild-type sable ferrets and heterozygous ferrets carrying one albino gene.

Albinism↗
PubMed1991

Treatment of anovulation due to polycystic ovarian syndrome by laparoscopic ovarian electrocautery.

Our experience of ovarian electrocautery for the treatment of polycystic ovarian syndrome (PCOS) in ten women is described. We found that nine responded favourably, either ovulating spontaneously or becoming more responsive to ovulation induction. There was a significant and persistent fall in serum testosterone levels, and a transient fall with subsequent rise in inhibin. We recommend that laparoscopic ovarian electrocautery is considered as an alternative to ovulation induction with gonadotrophins, in women with PCOS who fail to respond to clomiphene citrate.

Adult↗
PubMed1991

An animal model for the study of azidothymidine-induced hyperpigmentation.

Mice fed azidothymidine demonstrated dramatic hyperpigmentation of their tails. Histologic examination demonstrated large quantities of melanin pigment throughout the entire epidermal layer. Control mice had scant melanin pigment localized to the basal layer. Our findings demonstrate that the mouse is a useful model for the investigation of drug-induced hyperpigmentation.

Animals↗
PubMed1990

A comparison of vaginal ultrasonic-guided and laparoscopic retrieval of oocytes for in vitro fertilization.

A retrospective analysis was undertaken to compare the less invasive technique of vaginal ultrasonic-guided oocyte retrieval with the standard laparoscopic technique. We have shown that the outcome of the transvaginal technique with respect to oocytes harvested, fertilization rate, and pregnancy rate is comparable with the laparoscopy technique. We have also shown that 9 clinicians with little previous expertise in ultrasound have been able to incorporate this technique into a busy and successful in vitro fertilization unit.

Female↗
PubMed1990

Splenic thrombopoiesis after bone marrow ablation with radiostrontium: a murine model.

Murine platelet production is normally supported by high-ploidy bone marrow megakaryocytes without significant contribution from splenic megakaryocytes with predominantly low-ploidy levels. We produced sustained bone marrow ablation using radiostrontium, and examined the processes by which splenic platelet production is initiated and maintained in the absence of bone marrow function. Bone marrow hematopoiesis, measured by total nucleated cell number and viability, megakaryocyte colony-forming cells, and granulocyte-macrophage colony-forming cells, was rapidly ablated in mice by using yttrium 90-free strontium 90. Platelet count declined from normal (1224 x 10(3)/microliters) to a nadir (98 x 10(3)/microliters) 11 days after 90Sr, and then rose to a stable level (705 x 10(3)/microliters) on days 20 through 115. Peripheral leukocyte concentration decreased rapidly and remained below 25% of normal in contrast to hemoglobin levels, which were minimally lowered. Mean spleen weight rose rapidly after 90Sr to 66% above normal. Splenic megakaryocyte frequency, measured by two-color fluorescence-activated flow cytometry, rose from basal levels (0.09% +/- 0.06%) to 0.15% +/- 0.07% (p less than 0.001), total spleen nucleated cells fell to 71% of normal, and the absolute number of spleen megakaryocytes was unchanged. Total spleen megakaryocyte colony-forming cells were not significantly increased above normal whereas total spleen granulocyte-macrophage colony-forming cells increased abruptly after day 13 to 10 times normal levels. Splenectomy after hematopoietic recovery from 90Sr bone marrow ablation resulted in a rapid decline of platelet levels, followed by death. Although the spleen became the sole site of platelet production, the splenic megakaryocyte ploidy distribution was only minimally changed from normal, and the modal ploidy class remained 2N. In contrast to experimental thrombocytopenia in mice with intact bone marrow, in which megakaryocyte ploidy is increased, thrombocytopenia associated with sustained bone marrow ablation does not result in upward regulation of splenic megakaryocyte ploidy as a compensatory mechanism.

Animals↗
PubMed1990

Regulation of platelet heterogeneity: effects of thrombocytopenia on platelet volume and density.

We have examined the effects of variable degrees of acute thrombocytopenia on platelet levels, mean platelet volume (MPV), and buoyant density after induction of thrombocytopenia by platelet antiserum (PAS) in mice with or without spleens. Mice were studied serially 10-16, 36, 48, 60-64, 84, 108, 144, 180, 228, 276, 348-360, 372, and 516 h after PAS treatment. MPV and platelet count (PC) x 10(6)/microliters for normal intact mice (n = 136) were 4.7 +/- 0.3 fl (SD) and 1.69 +/- 0.52 (SD), respectively. Twelve hours after PAS-induced severe thrombocytopenia (PC less than 0.05 x 10(6)/microliters), MPV increased significantly (p less than 0.01) to 6.4 fl, was maximal at 36 h (8.2 fl), remained elevated until 144 h following PAS treatment, and then returned to normal. Platelet density decreased significantly (p less than 0.05) 64 h after PAS treatment and returned to normal at 144 h. Hematocrits of repeatedly bled intact control mice decreased from 45% to 30%, accompanied by thrombocytosis (maximal PC 2.24 x 10(6)/microliters) without significant changes in either MPV or platelet density. Moderate thrombocytopenia (PC 0.1-0.2 x 10(6)/microliters) in intact mice produced significantly (p less than 0.05) increased MPV, at 5.7 fl 12 h after PAS treatment, with a peak MPV of 7.6 fl (p less than 0.001) at 36 h; MPV returned to normal at 84 h. Platelet density decreased (p less than 0.001) 12 h after PAS treatment and returned to baseline at 228 h. Control splenectomized mice (n = 185) had an MPV of 5.0 fl +/- 0.7 fl and a PC of 2.14 +/- 0.6 x 10(6)/microliters. Comparably severe and moderate thrombocytopenia in splenectomized mice produced alterations in platelet count, MPV, and density similar to those in intact mice, although maximal MPV and the degree of rebound thrombocytosis after severe thrombocytopenia were more marked in splenectomized mice. In response to reduction of the platelet mass in both intact and splenectomized mice, MPV increased in proportion to the severity of thrombocytopenia, occurred as early as 4 h after induction, and persisted during early rebound thrombocytosis. Previous observations that megakaryocyte ploidy did not shift until 48 h after onset of thrombocytopenia confirm that both initial and maximal changes in MPV in response to this stimulus are regulated by processes other than alterations of megakaryocyte DNA levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Measurement of megakaryocyte frequency and ploidy distribution in unfractionated murine bone marrow.

Measurement of megakaryocyte frequency, ploidy distribution, and maturation stage have been complicated by the low frequency of megakaryocytes in either bone marrow or spleen. Due to harsh labeling conditions, previous studies utilizing flow cytometry have not quantified cell recovery or megakaryocyte frequency. We have modified our two-color fluorescence-activated cytometric technique in order to identify megakaryocytes in unfractionated murine bone marrow with a fluoresceinated cell surface immunologic probe (heterologous polyclonal platelet antiserum) and to selectively measure megakaryocyte DNA content with propidium iodide using isosmolar conditions. Under these conditions, total nucleated cell recovery from unfractionated normal murine bone marrow, after all preparative procedures, averaged 68.0% +/- 5.0% (SD) with 93.5% +/- 2.0% DNA staining efficiency. Mean megakaryocyte frequency (n = 30) was 0.14% +/- 0.04%. Using both our previously described gating technique with single parameter analysis and our modified dual parameter technique, the modal megakaryocyte ploidy class was 16N. Low ploidy megakaryocytes, 2N and 4N, constituted 9.8% and 10.8%, respectively, of the total megakaryocyte population. Analysis of the megakaryocyte population with respect to cell surface fluorescence intensity demonstrated that the dimly fluorescent population contained an increased proportion of lower ploidy class cells (2N + 4N + 8N) compared with brightly fluorescent cells, which contained an increased proportion of higher ploidy cells (16N + 32N). Our modifications of the two-color technique yielded improved recovery of total nucleated bone marrow cells from unfractionated bone marrow and provided more precise measurements of megakaryocyte frequency and ploidy than previously available.

Animals↗
PubMed1988

Treatment-independent pregnancies after cessation of gonadotropin ovulation induction in women with oligomenorrhea and anovulatory menses.

Life-table analysis was performed for the cumulative spontaneous pregnancy rate (CSPR) of 56 patients with oligomenorrhea and anovulatory cycles who had been treated with gonadotropin for ovulation induction between 1963 and 1985. Twenty-seven had at least one spontaneous pregnancy, giving rise to a CSPR of 66.4% (95% confidence limit [CL] 42.4% to 90.4%) at 115 months for the first spontaneous pregnancy, which is significantly lower than the cumulative induced pregnancy rate (CIPR) of 88.6% at 23 months for the first course of gonadotropin therapy (P less than 0.0001). This fertility potential was not affected by the baseline estrogen and follicle-stimulating hormone levels, diagnosis, result of gonadotropin therapy, and age and menstrual pattern during exposure to spontaneous pregnancy by Cox regression analysis. More multiple births occurred in the induced pregnancies than in the spontaneous pregnancies (P = 0.005).

Anovulation↗
PubMed1988

Artificial insemination with cryopreserved donor semen: a decade of experience.

Ten years' experience of artificial insemination with cryopreserved donor semen for 1023 courses in 783 women resulting in 572 pregnancies is reported. A simple approach with multiple inseminations timed on the basis of cycle length, temperature charts, mucus symptoms and signs was used. The life table pregnancy rate was 61% after 12 cycles of treatment and 75% after 24 cycles. Women had a significantly higher rate of pregnancy in second and subsequent courses of treatment, and the pregnancy rate for treatment beyond 12 cycles was significantly less successful. Women over 35 years of age were significantly less successful.

Counseling↗
PubMed1988

Rate responsive pacing using a minute ventilation sensor.

Minute ventilation, the product of respiratory rate and tidal volume, correlates directly with oxygen consumption, cardiac output, and heart rate. An implantable pacemaker has been developed which allows variation in pacing rate in response to measured changes in minute ventilation. This single chamber system measures transthoracic impedance between the tip electrode of a standard bipolar lead and the pulse generator case. Low amplitude current pulses (1 mA for 15 microseconds) are generated each 50 msec between the the ring electrode and the case. In the adaptive mode, the pulse generator calculates a rate response factor or slope after maximal exercise. This slope, which describes the relationship between pacing rate and minute ventilation together with the pacing rate limits are the only programmable rate responsive features. Minute ventilation rate responsive systems have been implanted in 12 patients (8 females, 4 males), of mean age 63 years. Indications were His bundle ablation (6), acquired complete heart block (4), and sick sinus syndrome (2). At post-implant exercise testing, pacing rate rose within the first minute. Peak rate and time to upper rate were dependent on workload. After exercise, pacing rate remained at peak for up to 2 minutes before a gradual fall to resting rate. Comparative studies of the minute ventilation and the activity sensor pacing systems in the same patients confirmed that the minute ventilation system more closely parallels normal sinus response to activity. The minute ventilation rate responsive pacing system is simple to programme, no special lead is required and the system is highly physiologic.

Aged↗