A new perspective on adiposity in a naturally obese mammal

• Published in: American journal of physiology: endocrinology and metabolism Vol. 281; no. 6; pp. E1347 - E1351
• Main Authors: Ortiz, Rudy M, Noren, Dawn P, Litz, Beate, Ortiz, C. Leo
• Format: Journal Article
• Language: English
• Published: Legacy CDMS 01.12.2001
• Subjects: Adipose Tissue - anatomy & histology; Adipose Tissue - physiology; Animals; Body Composition - physiology; Body Weight - physiology; Female; Humans; Hydrocortisone - metabolism; Leptin - metabolism; Life Sciences (General); Male; Obesity - pathology; Obesity - physiopathology; Seals, Earless - metabolism; Space life sciences; Non-Nasa Center; Nasa Discipline Regulatory Physiology; NASA Discipline Regulatory Physiology; Non-NASA Center
• ISSN: 0193-1849; 1522-1555
• DOI: 10.1152/ajpendo.2001.281.6.e1347

Department of Biology, University of California, Santa Cruz, Santa Cruz, California 95064 Many mammals seasonally reduce body fat due to inherent periods of fasting, which is associated with decreased leptin concentrations. However, no data exist on the correlation between fat mass (FM) and circulating leptin in marine mammals, which have evolved large fat stores as part of their adaptation to periods of prolonged fasting. Therefore, FM was estimated (by tritiated water dilution), and serum leptin and cortisol were measured in 40 northern elephant seal ( Mirounga angustirostris ) pups early (<1 wk postweaning) and late (6-8 wk postweaning) during their natural, postweaning fast. Body mass (BM) and FM were reduced late; however, percent FM (early: 43.9 ± 0.5, late: 45.5 ± 0.5%) and leptin [early: 2.9   ± 0.1 ng/ml human equivalents (HE), late: 3.0 ± 0.1 ng/ml HE] did not change. Cortisol increased between early (9.2 ± 0.5 µg/dl) and late (16.3 ± 0.9 µg/dl) periods and was significantly and negatively correlated with BM ( r  = 0.426; P  < 0.0001) and FM ( r   = 0.328; P  = 0.003). FM and percent FM were not correlated ( P   > 0.10) with leptin at either period. The present study suggests that these naturally obese mammals appear to possess a novel cascade for regulating body fat that includes cortisol. The lack of a correlation between leptin and FM may reflect the different functions of fat between terrestrial and marine mammals. body composition; cortisol; fat mass; obesity; pinnipeds