Use of tritiated water for measurement of 24-hour milk intake in suckling lean and genetically obese (ob/ob) mice
1979
Rath, Elizabeth A. | Thenen, Shirley W.
A non-invasive method of measuring milk intake of suckling mice over a 24-hour period under physiological conditions was used to determine whether genetically obese (ob/ob) mice are hyperphagic at 10 and 15 days of age. Lactating dams were injected with tritiated water which equilibriated with body water in 30 minutes. Constant specific activity of the tritiated water was maintained over 24 hours by provision of it in drinking water. Tritium accumulation in pups was proportional to milk intake. Pups were removed from dams after 24 hours, weighed and blood samples assayed for 3-H content. Body water content was computed from body weight. Milk composition on days 10 and 15, analyzed volumetrically and gravimetrically had 68 to 69% water content; 20% lipid content on day 10 and 17% on day 15. Mean milk intake at 10 days was 0.96 ml. At 15 days, intake decreased with increasing litter size. Using this method, it is established that under physiological conditions ob/ob mice, identified at 4 to 5 weeks of age, do not have increased milk consumption at either 10 or 15 days of age, and thus do not exhibit hyperphagia prior to the increase in circulating insulin concentrations or adipose cell size.
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