Steroid control of gonadotropin secretion and ovarian function in heifers.

The failure of anti-steroid treatments to induce multiple ovulations in cattle in a repeatable way, prompted us to examine the role of the gonadal steroids in the control of gonadotropin secretion in this species. A better understanding of the control of gonadotropin secretion in the cow would assist in the development of treatments to control prolificacy. Groups of six heifers were implanted with one of three sizes of estradiol (E2) implant on day 9 of a synchronized estrous cycle, and five control heifers received empty implants. All heifers were ovariectomized during the luteal phase of the subsequent estrous cycle and given progesterone-releasing intravaginal devices (PRID). Blood samples were taken every 10 min for 12 h with PRIDs and for 6 h after PRID withdrawal, for the measurement of LH and FSH concentrations. The two larger implant sizes (increasing E2 concentrations to 7.4 and 18.7 pg/ml plasma during the luteal phase of the cycle) decreased ovulation rate, the number of large follicles, and luteal weight. After ovariectomy, the three implant sizes produced E2 concentrations comparable with those during the luteal and follicular phases of the estrous cycle and at estrus (1.5, 4.4, and 10.5 pg/ml, respectively). E2 alone decreased mean LH and FSH concentrations and LH pulse amplitude, whereas progesterone alone reduced mean gonadotropin concentrations and LH pulse frequency. Only in the presence of progesterone did E2 decrease LH pulse frequency. Steroid concentrations which mimicked those of the luteal and follicular phases of the cycle produced luteal- and follicular-phase patterns of LH and FSH secretion. These results confirm that E2 and progesterone are important regulators of gonadotropin secretion in cattle, and question the role of inhibin in this respect.

The effect of cross-linking agents on the impact resistance of a linear poly(methyl methacrylate) denture-base polymer.

Eight different cross-linking agents were added to the monomer component of a linear poly(methyl methacrylate) denture-base resin in various concentrations, and their effect on the impact resistance of the cured polymer studied. The cross-linking agents were chosen to provide a range of cross-linking chain lengths and degrees of chain flexibility. When tested under oral conditions, the polymers cross-linked with long and flexible chains did not show the marked reduction in impact resistance found in polymers cross-linked with shorter and stiffer cross-linking chains. It seems likely that by replacing EGDMA in denture-base resins with a cross-linking agent such as PEG 600 DMA, one could use a higher concentration with a consequent improvement in solvent resistance.

Impact testing of denture base polymers.

Acrylic resin has been the denture base material of choice since its initial production in 1936, due to its aesthetic properties and ease of processing. It would be desirable, however, to have a material which is also unbreakable under clinical conditions. A wide range of materials has been suggested for use as denture base materials. The impact resistance of a polysulphone denture base polymer has been compared with that of a linear poly(methyl methacrylate) and four rubber-methacrylate denture base polymers. When tested under oral conditions, the polysulphone material had an impact resistance about twice as high as the best rubber-methacrylate and about four times as high as ordinary poly(methyl methacrylate).

A history of dental polymers.

The disadvantages of the use of vulcanite as a denture base material prompted the development of a wide range of thermoplastic polymers as alternatives to vulcanite. Heat-cured acrylic resin materials are the most widely used polymeric denture base materials at present, but research into further improvements in denture base materials continues.

Technical considerations of therapeutic plasma exchange as a nephrology nursing procedure.

In the past, therapeutic plasma exchange (TPE) has had limited appreciation and lacked acceptance as a treatment modality. Jokingly, it has been referred to as a procedure looking for a disease because of seemingly broad historical applications to practice. In current clinical practice, TPE has earned its place as an aggressive therapeutic modality for treating a wide spectrum of diseases and/or syndromes. The acceptance of TPE has coincided with changes in equipment, technology, and the emergence of highly qualified professionals involved in performing the treatments. This article will describe these variables related to nephrology nurses becoming more involved in the use of TPE.

A clinical project to evaluate reuse of a CAPD disconnect system minicap as a safe, effective practice.

The current health care environment is being driven by approaches to health care services that focus on quality and at the same time cost-effectiveness. With this in mind, a clinical project was designed to investigate the possibility of reusing the disconnect minicap as a safe, effective clinical practice. During a two-phase project, continuous ambulatory peritoneal dialysis (CAPD) disconnect caps were purposely touch contaminated and cultured before and after povodine iodine was instilled in the minicap. During the second phase of the project a simulated peritoneal effluent system was constructed and fluid cultures obtained. The specimen analyses demonstrated negative reports of the minicap after dwelling in povidine iodine and fluids after reuse of the minicap. The pilot project opens an area of research for nephrology nurses that could potentially lead to cost savings in the provision of care for patients with chronic renal failure.

Density-gradient sedimentation in silica sols. Anomalous shifts in the banding densities of polystyrene "latex" beads.

When polystyrene "latex" beads are centrifuged to equilibrium in gradients of Nalcoag 1030, Nalcoag 1034A and Ludox 130M, which are commercial formulations of colloidal silica, the beads at densities that may be markedly lower or higher than the bulk density. Addition to the gradient of small amounts of certain polymers restores the banding densities towards the expected value. These findings closely mimic previously observed "density shifts" of biological particles. A possible model for this anomalous behavior is discussed.