Renal function in suckling and fasting pups of the northern elephant seal

Abstract

Elephant seals fast for prolonged periods without access to water. This is made possible, in part, by reductions in urine production. However, the mechanisms involved in reducing urine production are not understood. In this study, Ž . Ž . glomerular filtration rate GFR was measured in five northern elephant seal pups Mirounga angustirostris via the inulin clearance technique. Measurements were made during day 9 and day 18᎐22 of nursing and the second and eighth week of the postweaning fast. Plasma aldosterone and cortisol concentrations, quantified by radioimmunoassay, were measured in eight other weanlings during the second and eighth week of the fast. Mean GFR was 79.3" 29.3 mlrmin during the early suckling period and 78.2" 17.1, 89.8" 52.7, and 80.4" 12.2 mlrmin during the late suckling, early fasting and late fasting periods, respectively. Differences between nursing and fasting were insignificant, possibly because reduced protein oxidation during suckling and rapid recruitment of protein for tissue synthesis obviated the need for postprandial hyperfiltration. Alternatively, maintenance of GFR during fasting may facilitate urea concentration by compensating for reductions in the fractional excretion of urea. It is further hypothesized that aldosterone is primarily responsible for mediating renal water reabsorption in this system. ᮊ

Lipolysis and glycerol gluconeogenesis in simultaneously fasting and lactating northern elephant seals

“…1). Similar variations have been observed in isotope clearance curves obtained in elephant seals and are believed to be due to selective ischemia associated with brief bouts of apnea (23). Curve fitting was therefore necessitated to determine the plateau SA either via best fit of the data points or through extrapolation of the curve fit to equilibration values.…”

Angiotensin II and Aldosterone Increase with Fasting in Breeding Adult Male Northern Elephant Seals (Mirounga angustirostris)

“…Mean aldosterone concentrations from nursing and postnursing adult female harp seals (300 pg/mL) were similar to those reported here during the late period ( pg/mL) and for lactating adult 254 ‫ע‬ 39 female northern elephant seals (380 pg/mL; D. E. Crocker, unpublished data). In elephant seal pups, mean aldosterone concentrations increased from 200 to 1,500 pg/mL during the first 7 wk of the postweaning fast (Ortiz et al 2000(Ortiz et al , 2002a(Ortiz et al , 2002b(Ortiz et al , 2003Houser et al 2001), representing a 7.5-fold increase, whereas the increase in fasting adult males over a comparable duration was only 1.7-fold. An age-related change in the sensitivity of aldosterone response to fasting may be but one potential explanation for the discrepancy in the degree of change of aldosterone between pups and adults.…”

“…0.05 commercially available kits for Ang II and AVP (Phoenix Pharmaceuticals, Belmont, CA) and aldosterone (DPC, Los Angeles). Each assay had been validated previously for use with northern elephant seal samples (Zenteno-Savin and Castellini 1998; Ortiz et al 2000Ortiz et al , 2002aOrtiz et al , 2002bOrtiz et al , 2003Houser et al 2001). For measurements of Ang II and AVP, separate 1.0-mL aliquots were extracted using C18 columns (Prep-Sep, Fisher Scientific, Fair Lawn, NJ) as previously described (Zenteno-Savin and Castellini 1998).…”

Adrenal sensitivity to stress is maintained despite variation in baseline glucocorticoids in moulting seals

“…Hormones were assayed using commercially available radioimmunoassay (RIA; cortisol and aldosterone from Siemens, Inc., Washington, DC, USA; and rT 3 from Alpco, Inc., Salem, NH, USA) or enzyme immunoassay (EIA) kits (ACTH from Alpco, Inc.). All kits have been previously validated for northern elephant seals (cortisol, Ortiz et al , 2001 ; aldosterone, Ortiz et al , 2000 ; Houser et al , 2001 ; and ACTH and rT 3 , Ensminger et al , 2014 ). The responses of glucose and lactate were measured in serial samples using a dedicated autoanalyser (YSI, 2300; Yellow Springs Inc., Yellow Springs, OH, USA).…”