This study examined the metabolic, thermoregulatory and sympathoadrenal response pattern of eight male subjects to repeated bouts of brief cold stress. Water immersion (WI) was used to induce cold stress over a 60 min period on three separate occasions on three successive days. Rectal temperature (T(re)), mean skin temperature (T(sk)) and metabolic rate (VO2) were measured at 10 min intervals throughout WI and for 20 min post-immersion (PI). Blood was drawn and assayed for plasma adrenaline (ADR), noradrenaline (NDR) and cortisol at rest, at the end of immersion and PI. Acute cold stress was induced for each of the three exposures with a reduction in T(re) of approximately 0.63 degrees C (p<0.01) and approximately 1.2 degrees C (p<0.01) at the end of immersion and PI, respectively. T(sk) was reduced for all trials by approximately 6.0 degrees C (p<0.01) at the end of immersion and approximately 3.0 degrees C (p<0.01) at PI. VO2 peaked at 40-50 min of WI to 83%, 58% and 47% above rest for each consecutive trial. Plasma ADR did not show any change (p=0.34) as a consequence of cold stress between trials. Plasma NDR increased at the end of immersion (p<0.01) and remained elevated at PI (p<0.01). Plasma cortisol showed no change for any of the exposure periods. DeltaT(re) was more pronounced for the last exposure and was negatively correlated (r= -0.78, p<0.02) with plasma NDR. The results of this investigation complement previous findings of cold adaptation and suggest a possible adaptive response to repeated brief bouts of cold exposure evidenced by the changing trends in body temperature, metabolic rate and plasma NDR.
ABSTRACT. Accelerating environmental change is perhaps the greatest challenge for natural resource management; successful strategies need to be effective for decades to come. Our objective is to identify opportunities that new environmental conditions may provide for conservation, restoration, and resource use in a globally recognized biodiversity hotspot in southwestern Australia. We describe a variety of changes to key taxonomic groups and system-scale characteristics as a consequence of environmental change (climate and land use), and outline strategies for conserving and restoring important ecological and agricultural characteristics. Opportunities for conservation and economic adaptation are substantial because of gradients in rainfall, temperature, and land use, extensive areas of remnant native vegetation, the ability to reduce and ameliorate areas affected by secondary salinization, and the existence of large national parks and an extensive network of nature reserves. Opportunities presented by the predicted environmental changes encompass agricultural as well as natural ecosystems. These may include expansion of aquaculture, transformation of agricultural systems to adapt to drier autumns and winters, and potential increases in spring and summer rain, carbon-offset plantings, and improving the network of conservation reserves. A central management dilemma is whether restoration/preservation efforts should have a commercial or biodiversity focus, and how they could be integrated. Although the grand challenge is conserving, protecting, restoring, and managing for a future environment, one that balances economic, social, and environmental values, the ultimate goal is to establish a regional culture that values the unique regional environment and balances the utilization of natural resources against protecting remaining natural ecosystems.
This study examined the effect of chronic parathyroidectomy (PTX) in rats on calcium homeostasis in milk and serum and on litter growth rate throughout lactation. Parathyroidectomy was carried out by excision 8 weeks before mating and any animals with evidence of parathyroid regeneration over this time were discarded. Maternal serum and milk samples were collected at days 6, 12 and 20 of lactation and serum samples from the pups were obtained at day 20. Litter growth was measured by weighing the pups daily. Significantly lower concentrations of ionized and total calcium and significantly higher concentrations of phosphate in the serum were found in the PTX animals compared with the sham-operated controls (P< 0·001). The ratio of ionized to total calcium in serum was significantly lower in the PTX group. The mean total calcium concentration in milk was significantly higher at day 6 in the PTX group (P< 0·05) but was not different from the sham-operated group at days 12 and 20. The ratio of milk calcium to percentage milk solids was the same in both groups of animals at all three sampling periods. Litter growth rate was not significantly different in the two groups up to day 5 or from days 12 to 20. It was lower in the PTX group (P< 0·001) between days 5 and 12. The total concentration of calcium in serum from the young was not significantly different in the two groups. It was concluded that parathyroid hormone (PTH) is required for normal maternal calcium homeostasis in serum during lactation and therefore its absence may affect milk homeostasis indirectly for part of lactation. In contrast the concentration of calcium in milk and litter growth rate can be maintained at normal levels in late lactation suggesting that PTH is not an essential hormone in the regulation of calcium levels in milk.
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