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Guinea Pig Mammary Gland Milk Content by Isotope Dilution Methods Using ¹⁴¹Ce and ¹⁴C-Polyethylene Glycol-4000¹

Department of Physical Biology, New York State University, Cornell University, Ithaca 14850

ABSTRACT

The use of ¹⁴¹Ce and ¹⁴C-polyethylene glycol-4000 (¹⁴C-PEG) as contained-milk volume indicator labels was tested in the guinea pig mammary gland. Labels in aqueous solution were introduced into the mammary gland, the gland was manipulated periodically during a waiting period, and then samples of milk were serially drawn from the glands with the aid of oxytocin. Neither label penetrated uniformly into all milk compartments. A portion (approximately 10%) of the ¹⁴C-PEG was absorbed during the experimental time of 90 to 115 min and precluded its use as a dilution indicator label in the guinea pig. Ninety eight percent of the ¹⁴¹Ce was recovered from the gland; however, its nonuniform distribution produced an underestimate of the contained-milk volume. A method is described whereby the initial underestimate of milk volume can be corrected. The method is based on a sample of milk taken under conditions of nonuniform dispersion of ¹⁴¹Ce and an estimate of the deviation of the ratio (% of initial milk estimate)/(% of accumulated dose) for total milk from the theoretical value of 1. By this method, ¹⁴¹Ce can yield reliable estimates of the contained-milk content of the guinea pig mammary gland.

¹ This work was supported in part by the U.S. Atomic Energy Commission under Contract AT (301-1)-4039 by a predoctoral fellowship to the senior author.

² Present address: The Lovelace Foundation, Fission Product Inhalation Laboratories, Building 9200, Area Y, Sandia Base, Albuquerque, New Mexico 87115.