RELATIVE ABUNDANCE OF LARGE WHALES AROUND SOUTH GEORGIA (1979–1998)1

To assess large-whale stocks following the cessation of land-based South Georgia whaling in 1965, we report three independent sighting databases: a cruise in 1997, observations from Bird Island (NW of South Georgia) between 1979 and 1998, and mariner sightings between 1992 and 1997. All species were rare, with sightings of southern right whales being the most common event. Two right whales photographed off South Georgia matched animals known from Peninsula Valdés, Argentina, a population known to be growing at 7%per annum. In contrast, blue and fin whales appeared to be less abundant. A single blue whale mother-calf pair was observed off the Shag Rocks in February 1997. Extirpation of animals from this particular feeding ground is the most likely reason for ongoing low numbers of all species. Other factors may include competition for krill by traditional predators such as penguins and seals and more recently by humans, an unusually high rate of natural mortality, habitat change such as alteration in sea ice coverage, and/or the impact of ongoing whaling. The history of this critical area of large-whale habitat and this report demonstrate the need for improved, consistent longterm monitoring of population trends for these depleted stocks.     

Irreversible inactivation of mammalian Δ5-3β-hydroxysteroid dehydrogenases by 5, 10-secosteroids. Enzymatic oxidation of allenic alcohols to the corresponding allenic ketones

Novel 4,5-allenic 3β-hydroxy-5,10-secosteroids have been synthesized by sodium borohydride reduction of the corresponding conjugated allenic 3-oxo-5, 10-secosteroids. The secosteroid allenic alcohols are substrates for bovine adrenal and human placental Δ⁵-3β-hydroxysteroid dehydrogenases, and the resulting electrophilic conjugated allenic ketones are shown to inactivate these dehydrogenases in a time-dependent manner. Inactivated enzyme did not recover activity after filtration through Sephadex G-25. In contrast, the secosteroid allenic alcohols were not oxidized at C-3 by the bacterial 3β(and 17β)-hydroxysteroid dehydrogenase from $\text{P. testosteroni}$, nor did the corresponding allenic ketones inactivate this enzyme when incubated directly.     

Vitamin A enhances forelimb regeneration in juvenile leopard frogs Rana pipiens

The effect of retinoids on forelimb regeneration in the leopard frog, Rana pipiens, was examined by the topical application of a concentrated solution of vitamin A palmitate to the amputated left limb stumps of 30 froglets. This treatment resulted in the enhancement of regeneration; regenerative outgrowths of experimental frogs were more frequent, larger in size, and had improved morphology compared to their untreated control counterparts. We conclude that vitamin A palmitate, topically administered in concentrated dosages, exerts a positive effect on the regenerative capacity of Rana pipiens.     

The process of epithelial cell attachment to glass surfaces studied by reflexion contrast microscopy

The process of attachment was studied in primary mouse kidney epithelial cell cultures by means of reflexion contrast microscopy, a method developed for studying the cell membrane-substrate relationship. The first in a series of events is simple adherence to the substrate, called close contact. This phenomenon is associated with the greatest extension of lamellar cytoplasm and the fewest number of cell nuclei/unit area. The nuclei of such cells are in close contact with the bottom portion of the cell membrane. Approx. 24 h after planting, as the cultures become more crowded, cells develop a different kind of attachment to the substrate—focal contacts—that are correlated with a decrease in lamellar cytoplasm. Cells detached from the substrate after close contact formation readily reattach, while cells detached after formation of focal contacts do not reattach. After incubation for periods greater than 5 days, the dense cultures degenerate and cells lose their attachment to the glass surface.