The effect of remifentanil on propofol requirements to achieve loss of response to command vs. loss of response to pain.

When providing total intravenous anaesthesia, careful selection of end-points is required in titrating dose to effect during induction. Although propofol and remifentanil have predominantly different pharmacodynamic effects, they are seen to interact in achieving loss of consciousness and analgesia. To highlight these differences, we performed a double-blind, randomised controlled trial, comparing one group of patients receiving propofol alone (n = 42) with another group receiving remifentanil plus propofol (n = 46) as a target-controlled infusion of remifentanil (Minto; 3 ng.ml-1 ). Propofol was also titrated using a target-controlled infusion (Marsh effect model) to produce loss of response to tactile and vocal stimuli, and subsequently to loss of response to pain. The effect-site concentration of propofol at which 50% of patients lost tactile/verbal response was 2.9 µg.ml-1 in the propofol only group and 2.4 µg.ml-1 in the remifentanil with propofol group. In contrast, loss of pain response occurred at 4.4 µg.ml-1 in the propofol group, and 2.7 µg.ml-1 in the remifentanil with propofol group, with correspondingly lower bispectral index values. Judicious use of analgesia in total intravenous anaesthesia can have a propofol-sparing effect and potentially minimise the suppression of brain electrical activity. .

Transcription termination at the thr attenuator. Evidence that the adenine residues upstream of the stem and loop structure are not required for termination.

The Escherichia coli thr operon attenuator has a structure similar to other Rho-independent terminators. The DNA sequence immediately 5' to the termination site is dG+dC-rich and contains a region of dyad symmetry that, when transcribed into RNA, encodes a hairpin structure in the transcript. It also contains a stretch of 9 consecutive dA-dT residues immediately distal to the region of dyad symmetry which encode uridine residues at the 3' end of the terminated transcript. In addition, the thr attenuator has a stretch of 6 dA-dT residues immediately upstream of the region of dyad symmetry which encode 6 adenines. These adenines could potentially pair with the distal uridines to form a hairpin structure extended by as much as 6 A-U base pairs. In this report we have examined the role of the upstream adenines in transcription termination. We used templates that specify mismatches or create new base pairs in the potential A-U secondary structure of the transcript as well as templates that delete segments of the A residues upstream of the hairpin. We conclude that A-U pairing is not required for efficient transcription termination at the thr attenuator. This conclusion is likely to apply to other Rho-independent terminators that contain hairpin-proximal dA-dT residues.

Controlling Cotton's Insect Pests: A New System.

Cotton is more heavily treated with insecticides than any other crop in the United States. In southern Texas, this heavy treatment resulted in insecticide- resistant strains of major pests which almost destroyed the industry in the late 1960's and early 1970's. An integrated insect control program based on new short-season cotton varieties and traditional cultural practices has restored production in the area. The new system has been widely implemented because it produces greater net returns by reducing the use of insecticides, fertilizer, and irrigation.