Effect of norgestomet on peripheral levels of progesterone and estradiol-17beta in beef cows

Peripheral levels of progesterone and estradiol 17beta were quantified in 27 cycling cows following administration of a single Hydron ear implant (G. D. Searle and Co.) containing 2, 4 or 6 mg norgestomet or controls which received no implant. Implants were inserted subcutaneously in the ear on day 15 of the estrous cycle (day of estrus = day 0) and removed 9 days later. The 4 mg (seven of seven cows) and 6 mg (six of six cows) implants suppressed estrus; however, three of eight cows in the 2 mg group exhibited estrus prior to implant removal. The 6 mg implant group had a significantly longer interval from implant removal to estrus than either the 2 or 4 mg group. Failure to detect differences in the rate at which progesterone declined indicated norgestomet treatment did not affect normal corpus luteum regression. Estradiol levels rose at a similar rate approaching estrus in all treatments. There was no indication of increased endogenous estradiol levels due to norgestomet treatment.     

Ascorbate both activates and inactivates bleomycin by free radical generation.

The chemotherapeutic agent bleomycin (BLM) is activated by reducing agents to break isolated DNA. Paradoxically, these same reducing agents protect cellular DNA from BLM damage. To resolve this paradox, we have examined the reaction of FeIIIBLM with DNA in the presence of ascorbate. As expected, ascorbate augments FeIIIBLM-induced DNA damage. However, when ascorbate is added to FeIIIBLM prior to exposure to DNA, a redox-inactive BLM is produced in a reaction that generates the ascorbyl radical. This reaction occurs in both ascorbate-supplemented buffer and unsupplemented plasma. In buffered solution, this reaction was found to be stoichiometric; for each mole of BLM present, 6.9 mol of ascorbate was oxidized and 4.7 mol of oxygen was consumed. Iron was found to serve only as a catalyst for the reaction. These data suggest that both activation of BLM and the generation of redox-inactive BLM occur via the same reaction and that BLM-induced DNA damage depends upon BLM reaching DNA prior to its interaction with reducing agents.     

Displacement sensors in the honeybee pollen basket

The mechanical importance of different groups of corbicular setae to the formation and maintenance of the pollen load was established through ablation experiments. The neurophysiological characteristics of corbicular setae were investigated and it was found that there are three types of response to mechanical displacement of individual setae. At least some of the anterior corbicular setae behave as linear displacement sensors and are capable of measuring the size of the forming pollen load during foraging.