Free and polymerized tubulin in cultured bone cells and Chinese hamster ovary cells: the influence of cold and hormones

A low pH method of liposome-membrane fusion (Schneider et al., 1980, Proc. Natl. Acad. Sci. U. S. A. 77:442) was used to enrich the mitochondrial inner membrane lipid bilayer 30-700% with exogenous phospholipid and cholesterol. By varying the phospholipid-to- cholesterol ratio of the liposomes it was possible to incorporate specific amounts of cholesterol (up to 44 mol %) into the inner membrane bilayer in a controlled fashion. The membrane surface area increased proportionally to the increase in total membrane bilayer lipid. Inner membrane enriched with phospholipid only, or with phospholipid plus cholesterol up to 20 mol %, showed randomly distributed intramembrane particles (integral proteins) in the membrane plane, and the average distance between intramembrane particles increased proportionally to the amount of newly incorporated lipid. Membranes containing between 20 and 27 mol % cholesterol exhibited small clusters of intramembrane particles while cholesterol contents above 27 mol % resulted in larger aggregations of intramembrane particles. In phospholipid-enriched membranes with randomly dispersed intramembrane particles, electron transfer activities from NADH- and succinate-dehydrogenase to cytochrome c decreased proportionally to the increase in distance between the particles. In contrast, these electron- transfer activities increased with decreasing distances between intramembrane particles brought about by cholesterol incorporation. These results indicate that (a) catalytically interacting redox components in the mitochondrial inner membrane such as the dehydrogenase complexes, ubiquinone, and heme proteins are independent, laterally diffusible components; (b) the average distance between these redox components is effected by the available surface area of the membrane lipid bilayer; and (c) the distance over which redox components diffuse before collision and electron transfer mediates the rate of such transfer.     

Efficacy of intermittent or continuous administration of GnRH in inducing ovulation in early and late seasonal anoestrus in the Père David's deer hind (Elaphurus davidianus)

Père David's deer hinds were treated with GnRH, administered as intermittent i.v. injections (2.0 micrograms/injection at 2-h intervals) for 4 days, or as a continuous s.c. infusion (1.0 micrograms/h) for 14 days. These treatments were given early (February-March) and late (May-June) in the period of seasonal anoestrus. The administration of repeated injections of GnRH increased mean LH concentrations from pretreatment values of 0.54 +/- 0.09 to 2.10 +/- 0.25 ng/ml over the first 8 h of treatment in early anoestrus, and from 0.62 +/- 0.11 to 2.73 +/- 0.49 ng/ml in late anoestrus. The mean amplitude of GnRH-induced LH episodes was greater (P less than 0.01) in late (4.03 +/- 0.28 ng/ml) than in early (3.12 +/- 0.26 ng/ml) anoestrus, but within each replicate (early or late anoestrus), neither mean LH episode amplitude nor mean plasma LH concentrations differed significantly between the four periods of intensive blood sampling. On the basis of their progesterone profiles, 6/12 hinds had ovulated in response to treatment with injections of GnRH (1/6 in early anoestrus and 5/6 in late anoestrus), and oestrus and a preovulatory LH surge were recorded in all of these animals. Oestrus and a preovulatory LH surge were also recorded in one other animal treated in early anoestrus in which progesterone concentrations remained low. The mean times of onset of oestrus (91.0 +/- 1.00 and 62.4 +/- 0.98 h) and of the preovulatory LH surge (85.8 +/- 3.76 and 59.4 +/- 0.25 h) both occurred significantly earlier (P less than 0.001) in animals treated in late anoestrus. Continuous infusion of GnRH to seasonally anoestrous hinds resulted in an increase in mean plasma LH concentrations, but this response did not differ significantly between early (2.15 +/- 0.28 ng/ml) and late (2.48 +/- 0.26 ng/ml) anoestrus. Ovulation, based on progesterone profiles, occurred in 2/7 hinds in early anoestrus and in 4/6 hinds in late anoestrus. Oestrus was detected in all except one of these hinds. The mean time of onset of oestrus occurred earlier in animals treated in late anoestrus (66.2 +/- 0.32 h and 46.7 +/- 0.67 h, P less than 0.01). The administration of GnRH, given either intermittently or continuously, will induce ovulation in a proportion of seasonally anoestrous Père David's deer. However, more animals ovulate in response to this treatment in late than in early anoestrus (75% compared with 23%).     

Movements and associations of ribosomal subunits in a secretory cell during growth inhibition by starvation

In Chironomus tentans salivary gland cells, the cytoplasm can be dissected into concentric zones situated at increasing distances from the nuclear envelope. After RNA labeling, the newly made ribosomal subunits are found in the cytoplasm mainly in the neighborhood of the nucleus with a gradient of increasing abundance towards the periphery of the cell. The gradient for the small subunit lasts for a few hours and disappears entirely after treatment with puromycin. The large subunit also forms a gradient but one which is only partially abolished by puromycin. The residual gradient which which is resistant to the addition of the drug is probably due to the binding of some large ribosomal units to the membranes of the endoplasmic reticulum (J.-E. Edstrom and u. Lonn. 1976. J. Cell Biol. 70:562-572, and U. Lonn and J.-E. Edstrom. 1976. J. Cell. Biol. 70:573-580). If growth is inhibited by starvation, only the puromycin-sensitive type gradient is observed for the large subunit, suggesting that the attachment of these newly made subunits to the endoplasmic reticulum membranes will not occur. If, on the other hand, the drug-resistant gradient is allowed to form in feeding animals, it is conserved during a subsequent starvation for longer periods than in control feeding animals. This observation provides a further support for an effect of starvation on the normal turnover of the large subunits associated with the endoplasmic reticulum. These results also indicate a considerable structural stability in the cytoplasm of these cells worth little or no gross redistribution of cytoplasmic structures over a period of at least 6 days.     

Intrauterine deposition of calcium on copper-bearing intrauterine contraceptive devices.

Copper-bearing intrauterine contraceptive devices (IUDs) removed after various times in utero were examined by scanning electron microscopy and x-ray microanalysis of the elements present. As time in utero increased these devices became increasingly calcified. This calcification may limit the release of copper from the devices and decrease the specific contraceptive effectiveness of copper over an enert plastic device. Conversely, any teratogenic effects attributable to the copper may decrease with time in utero and depend on the extent of calcification. Even though the amount of copper in the device is not significantly diminished after two years, devices should not remain in situ for over two years because calcium accumulation probably prevents further diffusion of copper. Calcification can begin as early as six months after insertion. Consequently a careful review of the amount of time a copper-containing IUD should be left in situ should be undertaken.     

New Record Folder for Use in General Practice

A new concept for filing medical records in general practice is described, based on an A4-size folder; in experimental use in 40 practices doctors were generally in favour of the new system.     

Evidence that the seasonally breeding Bennett's wallaby (Macropus rufogriseus rufogriseus) does not exhibit short-day photorefractoriness

Adult female Bennett's wallabies (N = 6) were maintained in artificial winter solstitial daylengths commencing 3 weeks before the winter solstice for 16 or 42 weeks. Such treatment effectively prevented the normal establishment of seasonal reproductive quiescence with animals continuing to exhibit reproductive cycles beyond the time of the normal termination of the breeding season. Animals maintained in natural photoperiods or simulated natural changes in daylength after the winter solstice all entered reproductive quiescence by early February. In the Bennett's wallaby, therefore, the breeding season does not terminate as a result of refractoriness to short daylengths. Our results indicate that the relatively small increases in photoperiod shortly after the winter solstice provide the environmental signal responsible for initiating the onset of seasonal reproductive quiescence which normally occurs 5-8 weeks after the solstice. These results contrast with the effect of fixed artificial summer solstitial daylengths on the onset of the breeding season in which breeding begins spontaneously at the normal time of year as a result of long-day photorefractoriness.