Evaluation of soft tissue response to a poly(urethane urea)

Variations in the performance of vascular prostheses constructed of polyurethanes, and some evidence which suggested that these variations could be due not to the properties of the polymer itself, but to differences in the cellular response to the various microstructures of porous polyurethanes require investigation. Experiments were performed to evaluate quantitatively the extent of the cell behaviour adjacent to a series of polyurethane samples. It was shown that, with Biomer, a polyurethane urea, the profile of cell behaviour as a function of distance from the implant surface and of time following implantation, the response of cells in general and macrophages in particular, varied considerably with different internal microstructure. This supports the suggestion that the cellular response to different structures and susceptibility to degradation are related.

Immune response in biocompatibility

Biocompatibility is concerned with the interactions that occur between biomaterials and host tissues. As foreign objects in that host tissue these materials may initiate several types of response. It has often been postulated that the immune response, by which the host normally defends itself against invasion by foreign organisms, can be involved in the response to biomaterials. This review discusses the mechanisms by which this could occur and the evidence that suggests the immune response is indeed of significance in biocompatibility.

Mechanisms of biodegradation of implantable polymers

This paper is concerned with the mechanisms by which polymers degrade following implantation in the body. The possibility that enzymes, free radicals and other active species are involved in this degradation is discussed.

Quantitative assessment of the tissue response to implanted biomaterials

The tissue response to a small number of polymeric biomaterials was studied using monoclonal antibodies specific for certain inflammatory cell types, to develop a reliable and accurate method for the quantitative evaluation of biocompatibility. The sites of antibody binding were identified using an avidin-biotin staining procedure and the sections evaluated using a computer-aided image analysis system. The staining technique successfully demonstrated both polymorphonuclear leucocytes and macrophages in tissue samples containing polymeric biomaterials. The image analysis system facilitated the measurement of up to 30 cell-related parameters and allowed a large number of cells to be analysed.

Relationship between chemotaxis and complement activation by ceramic biomaterials

This paper examines the relationship between complement activation by ceramic biomaterials and chemotaxis. Complement activation was examined by both neutrophil polarization (a technique which has previously been used to examine chemotaxis) and immunoelectrophoresis assays. The results suggest that at increasing serum concentrations of both calcium hydrogen phosphate and coral (calcium carbonate) powder, the quantity of C3 activation increased, as did the quantity of serum-derived chemotactic factors. In the case of tricalcium phosphate powder, the quantity of C3 activation and the neutrophil polarization response to serum were similar for serum levels between 20 and 80 mg/ml. Complement C3 was not activated in serum incubated with calcium hydrogen phosphate powder and serum incubated with this material was not chemotactic for neutrophils.

Neutrophil polarization and immunoelectrophoresis assays in the study of complement activation by biomaterials

The neutrophil polarization assay, a technique used to measure chemotaxis, was adapted to examine complement activation. Complement activation in serum which had been incubated with metallic and polymeric biomaterials was examined using the neutrophil polarization assay and immunoelectrophoresis assay. In agreement with previous publications, nylon activated the complement cascade, but PTFE did not. The neutrophil polarization assay was found to be the most sensitive technique for examining complement activation by endotoxin but the immunoelectrophoresis assay is the technique most sensitive for detecting complement activation by cobalt powder. In both assays, complement activation was not detected in serum incubated with chromium powder. However, serum incubated with silver and nickel powder stimulated neutrophils to polarize indicating that these powders may activate complement.

Vitrectomy for premacular fibroplasia. Prognostic factors, long-term follow-up, and time course of visual improvement

Two hundred seventy eyes with premacular fibroplasia consecutively treated by pars plana vitrectomy and membrane peeling were reviewed. This study is among the largest series with long-term follow-up reported to date. Visual improvement of two or more lines was achieved in 43% of eyes at 6 to 12 months, in 54% at 1 to 2 years, in 60% at 2 to 3 years, and in 58% at 3 to 5 years. Overall, complications occurred in 34 eyes (13%). Cataract progression after vitrectomy was noted in 106 (57%) of phakic eyes at 3 to 5 years, and 43 of these eyes underwent subsequent cataract extraction. Mean time to best visual acuity after vitrectomy was slightly less than 1 year for all eyes unless they had cataract worsening with subsequent cataract extraction (1.9 years). Significant factors affecting visual outcome were: preoperative lens status, visual acuity before vitrectomy, duration of preoperative symptoms of distortion and/or blurred vision, and the occurrence of intraoperative complications.

Outcome and cost analysis of scheduled versus emergency scleral buckling surgery

Conventional wisdom holds that a retinal detachment of recent onset should be regarded as a surgical emergency. A delay in surgery may result in an extension of detachment for patients with an attached macula and a worse visual outcome for patients with a detached macula. However, the potential disadvantages of performing surgery on an emergency basis must be weighed against the risks of delaying surgery; disadvantages include a greater frequency of operative complications resulting from fatigue factors among the operating personnel, an increased anesthetic risk due to inadequate time to assess and stabilize coexisting medical problems, and higher hospital costs. In this retrospective study covering 4 1/2 years, we compared the risks, benefits, length of hospitalization, and costs of scleral buckling surgery for retinal detachments performed as an emergency procedure or on the day following admission. After a 15% random selection from 884 consecutive operations, 48 emergency procedures were compared with 89 scheduled procedures. Patients selected for emergency surgery had better visual prognoses than scheduled patients. The potential for risk of systemic complications was not a reason for postponing surgery. None of the 18 patients with an attached macula experienced macular involvement while awaiting scheduled surgery. There were no differences between emergency and scheduled patients in ocular or systemic complications, rate of reattachment, rate of decreased visual acuity following surgery, visual outcome adjusted for prognosis, or, since 1985, length of hospital stay. Cost was greater for patients having emergency surgery, because of a difference in pay scales for support personnel.

The mechanical and microscopic aspects of the deformation and fracture of a poly (ether urethane-urea) spun arterial prosthesis

The mechanical properties of a microporous, electrostatically spun poly (ether urethane-urea), used in the construction of arterial prostheses, have been examined, with particular reference to anisotropic, crack initiation processes and preconditioning. The results demonstrate considerable anisotropy in relation to samples derived from circumferential and longitudinal directions of the tube wall structure related to the spinning process. There is also a considerable difference in crack initiation on inner and outer surface of the arterial wall, again related to the processing conditions. The results provide an important contribution to an understanding of structure-property relationships in microporous arterial prosthesis.

The clinical wear of three posterior composites

The wear of three posterior composites and two amalgams was assessed clinically and measured on replica models. For the composite restorations abrasion was measured as the depth of enamel exposed at the cavity margin. Attrition was measured for all materials as the depth of surface wear determined by laser interfereometry. For the posterior composites the mean abrasion was: Clearfil 79.2 microns, Occlusin 175.9 microns and P-30 96.1 microns. The corresponding values for attrition were: 153.4 microns, 205.9 microns and 255.5 microns, respectively. The attrition of the two amalgams was: New True Dentalloy 120.8 microns, Solila Nova 115.3 microns. Therefore, attrition was greater than abrasion and the attrition of the three composites was greater than that of the two amalgams. Abrasion was affected by local factors, including the marginal contour of the restoration, whereas attrition was largely a function of the properties of the material itself. These findings indicate that composites should not be considered as a direct alternative to amalgam, especially in patients with high occlusal stress.

Retained intraocular foreign bodies and endophthalmitis

Retained intraocular foreign bodies (IOFBs) are associated with endophthalmitis in approximately 7 to 13% of cases. The role of prompt surgical removal of the foreign body along with the use of intravitreal antibiotics in reducing this figure is uncertain. Retained IOFBs presenting to The Medical College of Wisconsin between July 1986 and June 1989 were reviewed. A total of 27 cases were evaluated and surgically treated. None of the 27 cases presented with or developed clinical signs of endophthalmitis, yet bacterial cultures of the removed intraocular material were positive in seven cases (foreign body in 5 cases, the aqueous fluid and the vitreous fluid in 1 case each). All eyes presenting within 24 hours of injury underwent immediate surgery (average, 4.5 hours after presentation). Of the seven eyes with positive intraocular cultures, all had pars plana vitrectomy removal of the IOFB and three of these eyes received intravitreal antibiotics at the time of surgery over concern of a high risk of infection. Two of these eyes eventually grew out the Bacillus sp. All eyes received subconjunctival antibiotics and postoperative topical and systemic antibiotics. Even after the positive cultures, no signs of clinical infection developed in any of the eyes. All seven eyes retained excellent visual acuity of 20/70 or better at an average of 10 months' follow-up. Follow-up ranged from 1 to 31 months. Prompt surgical intervention, the use of intravitreal antibiotics in high-risk-type injuries, and the possible use of vitrectomy surgery may reduce the incidence and severity of endophthalmitis.

A two-stage technique for intraoperative fluid-gas exchange following pars plana vitrectomy

We describe herein a two-stage technique of intraoperative fluid-gas exchange following pars plana vitrectomy. The first stage is a complete fluid-air exchange using an air pump and intraocular linear suction. The air pump then maintains the intraocular pressure at the desired level during adjunctive procedures, such as laser endophotocoagulation. The second stage is an air-gas mixture exchange in which the desired gas, premixed in air to the desired final intraocular concentration, is manually flushed through the eye. This technique allows the attainment of an accurate concentration of intraocular gas if the air-gas mixture exchange is complete. In vitro and in vivo experiments in aphakic human eyes demonstrated that an effectively complete air-gas mixture exchange occurs with a 25-mL flush volume. This result compares favorably with the theoretical prediction derived from a "pharmacokinetic approximation" equation.

Modulation of growth in retina-derived cells by extracellular matrices

Intravitreal membranes from patients with proliferative vitreoretinopathy (PVR) consist partly of retinal glial (RG) and retinal pigment epithelial (RPE) cells surrounded by varying amounts of extracellular matrix (ECM). The contribution of the ECM to the growth of PVR membranes is unknown. This study was undertaken to determine if proliferation in cultured RPE and RG cells is affected by different substrates, including some ECM materials which have been identified in PVR membranes. Substrates tested included type I collagen, basement membrane Matrigel, and poly-D-lysine, as well as uncharacterized cell type-specific matrices deposited by cultured RPE and RG cells. Proliferation was quantified by 3H-thymidine incorporation and radioautography 24 hours after plating and by cell counts after 14 days in the presence of serum. Relative to uncoated culture plastic, growth of RPE cells was inhibited by Matrigel, enhanced by poly-D-lysine, and unaffected by type I collagen. In contrast, growth in RG cells was inhibited by type I collagen and unaffected by the other substrates. Analysis of the timing of DNA synthesis after plating suggested that the substrates which affected RPE growth did so by altering the fraction of cycling cells rather than the cell cycle time. For the cell-derived matrices, heterotypic matrix (matrix produced by the other retinal cell type) enhanced the growth of both RPE and RG. The results suggest that the ECM may modify the growth of cells contributing to PVR membranes. Of note is that the cell-derived matrices reciprocally stimulated growth of RG and RPE cells, cell types which may interact in PVR membranes.

Clearance of experimental vitreous hemorrhage after panretinal cryotherapy is related to macrophage influx

We investigated the effect of panretinal cryotherapy on blood clearance and on the inflammatory cellular response in rabbit eyes with experimental vitreous hemorrhage. Eyes treated with cryotherapy demonstrated less extensive vitreous opacity and more rapid clearance of blood than untreated eyes. The peak inflammatory cellular response measured by counts or radiolabeled cells in the optic nerve was 2.5 times greater in the cryotherapy-treated eyes. Panretinal cryotherapy may promote the clearance of vitreous hemorrhage by stimulating the influx of increased numbers of phagocytic inflammatory cells.

Rebleeding in experimental traumatic hyphema treated with intraocular tissue plasminogen activator

Tissue plasminogen activator has recently been shown to enhance the clearance of experimental nontraumatic hyphema in animals. However, hyphema in human eyes usually results from ocular trauma, and rebleeding is a serious complication. Hemorrhage is also a potential complication of fibrinolytic therapy. We assessed the incidence of rebleeding in an animal model of surgically induced traumatic hyphema after intracameral injection of tissue plasminogen activator (25 micrograms) or physiological saline. Eight eyes were each treated with tissue plasminogen activator or physiological saline at 10 minutes, 24 hours, 48 hours, or 72 hours after injury. Controls were 8 eyes with hyphema but no intracameral injection. No eyes treated with physiological saline (total, 32 eyes) or control eyes rebled. In contrast, the incidence of rebleeding from the injury site in eyes treated with tissue plasminogen activator was 88% (7/8) at 10 minutes, 75% (6/8) at 24 hours, 50% (4/8) at 48 hours, and 0% (0/8) at 72 hours after injury. Treatment of traumatic hyphema with tissue plasminogen activator prior to healing of damaged vascular endothelium may contribute to rebleeding.

Intraocular foreign bodies in young people

The authors examined 104 patients with penetrating ocular injuries and retained intraocular foreign bodies. Nineteen patients (18%), with 20 injured eyes, were aged 18 years or younger. Fifty percent of eyes in the young people (10/20) achieved a final visual acuity of 20/30 or better and 65% (13/20) achieved 20/100 or better. Young people were significantly more likely than adults to be injured as a result of a projectile weapon or explosion (P less than 0.001). They also had a greater incidence of an initial visual acuity worse than 5/200 (P less than 0.001), which was statistically associated with a greater incidence of hyphema (P = 0.002), retinal detachment (P = 0.022), and uveal prolapse (P = 0.082). Although the distribution of final visual acuity was not significantly different between young people and adults, the latter tended to have poorer visual outcome after adjusting for initial visual acuity (P = 0.01).

Posterior segment manifestations of ocular trauma

Nonpenetrating or blunt ocular trauma, orbital trauma and systemic trauma may cause a variety of posterior segment abnormalities. Blunt ocular trauma may cause damage to the retina (commotio retinae), retinal pigment epithelium (retinal pigment epithelial edema), choroid (choroidal rupture) and optic nerve (optic nerve evulsion) alone or in combination. Traumatic macular holes and retinal detachment or dialysis may also occur after blunt ocular trauma. Trauma to the orbital tissues adjacent to the globe can cause concussive forces with damage to multiple structures within the eye (chorioretinitis sclopetaria). Systemic trauma may result in diffuse retinopathy (Purtscher's retinopathy, shaken baby syndrome) or localized retinal abnormalities (whiplash retinopathy, fat embolism syndrome). Alterations in intravascular (Valsalva retinopathy) or intracranial pressure (Terson's syndrome) due to a variety of causes may result in preretinal or vitreous hemorrhage and associated visual loss. The purpose of this report is to review each of these entities of traumatic posterior segment abnormalities.

Magnetic resonance imaging of juxtapapillary plaques in cadaver eyes

Adequate treatment of juxtapapillary melanomas with episcleral plaque brachytherapy using lower energy radiation sources may be difficult because of uncertainties regarding the relationship of the plaque to the optic nerve and tumour base. We obtained magnetic resonance images of a dummy plaque placed in a juxtapapillary location in cadaver specimens. Although it is possible to place a plaque in close association with the optic nerve sheath, a tissue barrier exists which may prevent actual contact between the plaque and nerve. Posterior tilting of the plaque may also occur. Because of these uncertainties regarding plaque placement, juxtapapillary melanomas should be considered a distinct subgroup when evaluating the efficacy of radioactive plaque brachytherapy in the treatment of choroidal melanoma.

Long-term follow-up of acute multifocal posterior placoid pigment epitheliopathy

Eleven patients with acute multifocal posterior placoid pigment epitheliopathy were followed up for 47 to 175 months (mean 106 months). Seven of 18 affected eyes (39%) developed progressive mild alterations in the retinal pigment epithelium. Seventeen eyes (94%) had a final visual acuity of 20/30 or better. One eye with progressive retinal pigment atrophy involving the fovea lost visual acuity from 20/25 to 20/60.

Visualization of the spatial distribution of silver in histological sections

The distribution of silver surrounding silver-containing implant devices can be clearly demonstrated using an autometallographic technique originally described by Danscher.

Results of vitrectomy for diabetic traction retinal detachments using the en bloc excision technique

En bloc excision is a technique in which fibrovascular diabetic membranes and the posterior hyaloid are separated from the retina as a single unit. In a consecutive series of 69 eyes with diabetic traction retinal detachment treated with this technique, initial retinal reattachment was accomplished in 100% (69/69) of the eyes. With a minimum of 6 months' follow-up, the retina remained completely attached in 83% (57/69) of eyes, while the macula was attached in 88% (61/69) of eyes. Final visual acuity was 5/200 or better in 71% (49/69) of eyes. While current surgical techniques allow a high rate of anatomic success in the repair of diabetic traction retinal detachment, visual results remain limited by irreversible alterations in retinal function.

A model for biocompatibility and its evaluation

Concepts of biocompatibility have changed radically in recent years. This paper describes these new concepts and the present knowledge of the components and mediators of biocompatibility and leads to the development of a model for the explanation and rationalization of these phenomena. Of particular importance is the question of the assessment or evaluation of biocompatibility. The paper concludes with comments on the need for a schedule of biocompatibility assessment procedures to take into account this new thinking.

The spatial resolution of protein adsorption on surfaces of heterogeneous metallic biomaterials

This study was designed to examine the heterogeneity of the adsorption of proteins onto metallic materials. The materials studied included pure Ag, Au, and Ti and sintered Ag 10% Ti and Ag 10% Ta. The distribution of the protein adsorption was studied using I-125 labeled albumin detected by microautoradiography. The surface morphology of the specimens was examined in the scanning electron microscope prior to exposure to the protein solution. A heterogeneous distribution in albumin adsorption was observed over the Ag surface. Similar regions were observed over parts of the mixed metal specimens, but superimposed on this pattern were distinct regions of very low protein adsorption which appeared to correlate closely with the regions of Ti or Ta observed in the scanning electron microscope. A uniform distribution of adsorbed albumin was observed on the Au and Ti, with Au giving a much denser microautoradiograph than Ti. This work demonstrates that variations in the protein adsorption to heterogeneous materials can be observed on a microscopic scale.

Resolution of an apparent choroidal melanoma

A 67-year-old white woman had a lesion that clinically, echographically, and angiographically appeared to be consistent with choroidal melanoma. At follow-up examination 2 months later, the lesion had clinically completely resolved. A limited choroidal hemorrhage simulating a choroidal melanoma is postulated.

Modulation of steroid affinity for the androgen receptor by sucrose

The effects of sucrose on androgen binding to its receptor were investigated. Sucrose decreased the rate of thermal inactivation of unoccupied and occupied androgen receptor (AR) and the rates of [3H]5 alpha-dihydrotestosterone [( 3H]DHT) dissociation from both activated and nonactivated AR complexes. Binding of [3H]DHT to AR in vivo, or in intact cells at 37 degrees C, caused reduction of [3H]DHT dissociation from cytosolic and nuclear complexes, as compared to in vitro labeled receptor complexes. Further, exposure of these complexes to sucrose at 0 degrees C caused an additional reduction of dissociation rates. Thus, the decrease of [3H]DHT dissociation induced by sucrose is independent of the reaction that reduces DHT dissociation from activated and transformed AR. Sucrose also reduced the ability of mersalyl acid to inactivate AR complexes. This effect of sucrose was markedly diminished in the presence of 2M urea. Sucrose did not significantly affect the association rate, sedimentation properties, or nuclear binding ability of AR complexes, but it did decrease the equilibrium dissociation constant. Other monosaccharides and disaccharides also stabilized AR. These data suggest that sucrose induces conformational changes in the steroid binding domain of androgen receptor, thereby reducing the rates of inactivation, steroid dissociation, and the accessibility of sulfhydryl groups to mersalyl.

Echographic verification of radioactive plaque position in the treatment of melanomas

Visualization of the position of an episcleral plaque in relation to the underlying choroidal melanoma during the early radiation treatment period reconfirms accurate plaque location and may help assure optimal treatment. We used high-resolution B-scan echography to confirm the position of the episcleral plaque in 16 consecutive cases of choroidal melanoma. The technique is most useful for well-defined tumors as small as 3 mm in height whose anterior border does not extend beyond the ora serrata.

Results and prognostic factors in penetrating ocular injuries with retained intraocular foreign bodies

Of 105 eyes with ocular injuries involving retained intraocular foreign bodies, 63 (60%) had a final visual acuity of 20/40 or better; 20 (19%) were 20/50 to 5/200; and 15 (14%) were worse than 5/200. Six eyes (6%) were enucleated. The extent of visual recovery was limited in selected cases by the characteristics of the initial injury. Multivariate analysis was used to identify prognostic factors. Predictive of a good visual outcome (greater than or equal to 20/40) were: (1) initial visual acuity better than 20/40 and (2) the need for only one or two operations in the treatment of the injury. Predictive of a poor visual outcome (less than 5/200) were: (1) initial visual acuity worse than 5/200 and (2) a wound 4 mm or longer in length, independent of wound location. The visual outcome in this series of patients was compared with other large series of intraocular foreign bodies reported before the development of vitreous microsurgical techniques. The percentage of patients with a visual outcome of 20/40 or better has remained the same, whereas the incidence of enucleation has diminished.

Albumin adsorption on metal surfaces

Studies of adsorption kinetics, desorption and adsorption isotherms concerning the interaction between albumin and a range of metal and metal oxides were undertaken in vitro. Three distinct types of behaviour concerning the adsorption of albumin on to metal surfaces were identified. Some metals adsorb considerably greater amounts of protein than might be expected from surface energy alone and it is suggested that electrostatic forces could be responsible for this phenomenon.

Intraocular Echinococcus multilocularis

Alveolar hydatid disease, caused by the organism Echinococcus multilocularis, is a potentially lethal helminthic infection. After initial hepatic infestation, the organism may spread locally and hematogenously to distant sites. Death occurs secondary to hepatic failure, local extension into vital structures, or metastasis to the brain or lungs. A 67-year-old male Alaskan Eskimo developed decreased visual acuity secondary to a choroidal mass in the right eye eight years after an initial diagnosis of alveolar hydatid disease and four years before the development of symptomatic cerebral metastasis. A pathologic examination disclosed characteristic parasitic membranes involving the posterior pole of the right eye. To our knowledge, this is the first report of ocular involvement in alveolar hydatid disease.

The enzymatic degradation of polymers in vitro

Specimens of 14C-labeled poly(ethylene terephthalate), nylon 66, and poly(methyl methacrylate) have been synthesized and exposed, in vitro, to a number of enzyme solutions. Poly(ethylene terephthalate) was found to be affected by esterase and papain, although in different ways, but not by trypsin or chymotrypsin. Nylon 66 was unaffected by esterase but degraded by the other three. Poly(methyl methacrylate) was not affected by any of these enzymes. This indicates that some nominally stable polymers are susceptible to degradation by enzymes under some circumstances. The amount of degradation is small, but could have significant sequelae should it be reproduced in vivo.

Evulsion of the retina associated with optic nerve evulsion

We examined two patients with optic nerve evulsion as well as nasal peripapillary retinal and retinal pigment epithelial evulsion after ocular trauma. Fluorescein angiography demonstrated an intact peripapillary choriocapillaris, loss of peripapillary retina and retinal pigment epithelium, and complete disruption of retinal perfusion. We have postulated a mechanism for traumatic peripapillary retinal evulsion involving severe anterior displacement and abduction of the globe that may explain how the disruptive force was transmitted to the nasal retinal nerve fiber layer. We have provided a clinical correlation with magnetic resonance imaging of the optic nerve and globe of a normal individual.

The effect of environmental aging on the fracture toughness of dental composites

The effect of aging four commercially-available dental composites in water or ethanol at 37 degrees C for periods of up to 28 days was assessed by measuring changes in the materials' plane-strain fracture toughness (KIC). The results, obtained by means of a mini Short Rod Fracture Toughness Test specimen design, suggest that while water aging does not produce significant changes in KIC, aging in ethanol does cause significant increases in fracture toughness for three of the four dental composites studied. In view of previously-reported loss of wear resistance for dental composites aged in ethanol solutions, the present study emphasizes the difficulties in using fracture toughness to predict wear properties.

On the biodegradation of poly-beta-hydroxybutyrate (PHB) homopolymer and poly-beta-hydroxybutyrate-hydroxyvalerate copolymers

The known biodegradability of PHB in certain biological environments has led to its proposed use as a 'biodegradable' implant material. Monofilaments of PHB homopolymer and two PHV-PHB copolymers have been studied in vivo and in vitro and assessed for changes in mechanical properties and topography. In vivo biodegradation was only observed with PHB when pre-degraded by 10.0 Mrad of gamma-irradiation before implantation. High temperature in vitro hydrolysis suggested that PHV copolymer additions retarded the rate of degradation of PHB. Hydration reactions had most effect on the ultimate tensile properties of the materials. In contrast, the elastic properties appeared to be relatively unaffected.

Binding of (3H)7 alpha,17 alpha-dimethyl-19-nortestosterone (mibolerone) to progesterone receptors: comparison with binding of (3H)R5020 and (3H)ORG2058

The binding characteristics of (3H)7 alpha,17 alpha-dimethyl-19-nortestosterone [3H)DMNT) to progesterone receptors (PgR) of calf uterine tissue cytosol were determined and compared to those of the synthetic progestins (3H)ORG2058 and (3H)R5020. Scatchard plot analysis of the equilibrium binding data showed that (3H)DMNT binds to calf uterine PgR with a KD of 2.35 +/- 1.1 nM. This value is slightly higher than that of (3H)R5020 (KD = 1.16 +/- 0.4 nM) and (3H)ORG2058 (KD = 1.04 +/- 0.65 nM). Analysis of dissociation kinetics showed that (3H)DMNT dissociates much more rapidly from the receptor than the other two ligands. Competition experiments showed that ORG2058 has a lower inhibition constant (Ki) than DMNT. Sucrose density gradient (SDG) analysis of PgR showed that (3H)ORG2058-PgR complexes sediment as 8S, (3H)R5020-PgR complexes sediment as 8S and 4S, and (3H)DMNT-PgR complexes sediment as 8S entities along with dissociated (3H)steroid. These data suggest that (3H)DMNT binds to PgR with lower affinity than (3H)ORG2058 and (3H)R5020. The number of binding sites detected with (3H)DMNT are significantly lower than those measured with (3H)ORG2058.

Life History of Symbiont-Bearing Giant Clams from Stable Isotope Profiles

Stable isotopic and shell-growth banding studies of the symbiont-bearing giant clam Tridacna maxima reveal the existence of two growth phases related to sexual maturity that can be discerned in the shells of extinct and extant mollusks. The changeover from the first to second growth phase at an age of approximately 10 years is accompanied by a decrease in rate of calcification and suggests a reordering of energy priorities between biomineralization and reproduction. The carbon-13 to carbon-12 ratio of Tridacna maxima is systematically depleted relative to symbiont-barren mollusks, making it possible to determine the importance of algal-molluscan symbiosis to the functional morphology and paleoecology of mollusks in the geologic record.

Changes in the sedimentation properties of cytosolic androgen receptors associated with activation in vitro and in vivo

In cell-free systems androgen receptor (AR) labeled with (3H)DHT at 0 degrees C in the presence of 50mM molybdate remains unactivated (less than 3% binding to nuclei) and untransformed (7-8S on sucrose density gradients containing 0.4M KCl and 50mM molybdate). In the absence of molybdate, however, these complexes undergo activation and transformation even at 0 degrees C, albeit, very slowly. Incubation of unactivated, untransformed AR complexes at 18 degrees C, or at 0 degrees C in the presence of 0.4M KCl, greatly accelerated both activation and transformation. Activation and transformation are also associated with formation of high affinity (3H)DHT-receptor complexes as indicated by decreased rates of (3H)DHT dissociation from the receptor. Cytosolic AR complexes labeled with (3H)DHT in tissue slices at 37 degrees C, or in vivo, undergo rapid activation, transformation and nuclear translocation. The data suggest that activation and transformation of cytosolic AR in cell-free systems is associated with changes in the physicochemical properties of AR similar to those occurring upon hormone binding in intact cells and in vivo.