Suppression of parathyroid hormone secretion by aluminum

The effect of aluminum on parathyroid hormone secretion was examined using collagenase-dispersed bovine parathyroid cells. An increase in the medium aluminum concentration over the range of 0.5 to 2.0 mM, in low calcium medium, progressively inhibited the secretion of radioimmuno-assayable hormone. At 2.0 mM aluminum hormone secretion was inhibited by 68% while high medium calcium, without aluminum, maximally inhibited parathyroid hormone secretion only 39%. Individually, 2.0 mM aluminum or 2.0 mM calcium inhibited isoproterenol-stimulated hormone secretion by 43%. Either metal suppressed basal and isoproterenol-stimulated cyclic AMP levels of the parathyroid cells. That the inhibitory effect of aluminum on parathyroid hormone secretion was not due to an irreversible toxic effect was demonstrated by a restoration of normal secretion when cells were returned to 0.5 mM calcium medium without aluminum. The incorporation of [3H]leucine into total cell protein, parathyroid secretory protein, proparathyroid hormone, or parathyroid hormone was not affected by aluminum. The secretion of radiolabeled protein was, however, inhibited by aluminum. These results suggest that aluminum does not affect protein biosynthesis of the parathyroid cell or the conversion of proparathyroid hormone to parathyroid hormone. Aluminum appears to directly affect the secretion of protein from dispersed parathyroid cells.

Analysis of Stomach Contents of Dugongs From Queensland

Quantitative analysis of samples of the stomach contents of 95 north Queensland dugongs, Dugong dugon, (63 from the Townsville area, 30 from the Mornington Island area and 2 from the Torres Strait area) and one dugong from south Queensland indicates that the diet of most consisted almost entirely of seagrasses of all available genera. Halodule was found in 95% of stomachs, followed by Halophila (89%). Cymodocea (61%) and Thalassia (39%). Seagrass rhizomes were present in all stomachs examined including that of a newborn calf. The generic composition of the stomach contents probably reflects that of the seagrass beds in the areas where the dugongs were captured and is not necessarily indicative of discrimination in selecting food. Non-epiphytic algae occurred in 51% of the stomachs, usually in small amounts. When seagrasses were abundant, dugongs appeared to eat algae often but only in very small amounts (<2% of food volume). Dugongs do not appear to be well adapted to utilize algae as food and probably usually consume them incidentally with seagrasses. Many of the dugongs which drowned in the shark nets near Townsville in the year after a cyclone had severely damaged the seagrass beds in the area, had eaten more of the seagrasses Cymodocea and Thalassia, less of the seagrasses Halodule and Halophila, and more algae than animals which died in other years.

Retinal changes in Himalayan climbers

Changes in the fundus of the eye were studied in 15 members of a mountaineering expedition to Dhaulagiri, Nepal (elevation, 8,167 meters [26,795 ft]). Retinal photographs were taken at sea level and at 5,883 meters (19,300) after each climber had descended from his highest point. Five Nepali Sherpas and an additional American climber who came to the base camp late in the climb were also studied. Vascular engorgement with tortuosity, a 24% increase in arterial diameter, and a 23% increase in venous diameter were observed. Retinal hemorrhages were seen in five American climbers (33%), but in none of the Sherpas. The high incidence is striking, but the cause is unknown. We suggest that the hypoxic vasodilatation makes retinal vessels more vulnerable to sudden rises in intravascular pressure.