After weaning, pups of the northern elephant seal Mirounga angustirostris undergo a 2–3 month fast, during which time they abstain from drinking seawater and are able to maintain their water balance by conserving the water liberated from oxidation of their large fat stores. During the fast, plasma o...
| Other Authors: | |
|---|---|
| Format: | Text |
| Language: | English |
| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.615.3075 http://jeb.biologists.org/content/206/16/2795.full.pdf |
| Summary: | After weaning, pups of the northern elephant seal Mirounga angustirostris undergo a 2–3 month fast, during which time they abstain from drinking seawater and are able to maintain their water balance by conserving the water liberated from oxidation of their large fat stores. During the fast, plasma osmolality and volume remain unaltered, indicating osmotic homeostasis and water balance (Castellini et al., 1990; Costa and Ortiz, 1980; Ortiz et al., 1996, 2000). Whether or not vasopressin (VP) is responsible for mediating this conservation of body water is not yet well established, especially since circulating VP concentrations remain relatively low and unchanged (Ortiz et al., 1996, 2000, 2002b). The lack of an increase in plasma [VP] during the prolonged fasting period in northern elephant seal pups may be anomalous among mammals because abstinence from water generally induces an elevation in circulating [VP]. For example, in dogs, water deprivation induces an increase in circulating [VP] (Claybaugh, 1976; Wade et al., 1983), thereby helping to abate the potential imbalances in water and electrolyte homeostasis. The lack of a fasting-induced increase in plasma [VP] in seal pups therefore suggests that fasting pups may be highly sensitive to low concentrations of VP or that pups maintain water balance via other unexamined mechanisms. The primary action of VP is to facilitate the reabsorption of solute-free water from the collecting duct of the kidney, and this action may be associated with the reabsorption of urea (Klein et al., 1997). A number of studies provide compelling evidence that tubular water resorption is mediated via VP in seals. Fasting northern elephant seal pups infused with hypertonic saline exhibited chronically elevated plasma VP concentrations. Furthermore, excreted [VP] was elevated and negatively correlated with free water clearance (CH2O), and positively correlated with excreted cAMP levels, suggesting that VP mediated tubular water reabsorption (Ortiz et al. |
|---|