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Influence of Oxytocin on Diffusion of Sulfonamides from Plasma into Bovine Milk^{1, 2,}

Department of Veterinary Physiology and Pharmacology and the Department of Animal Science, University of Minnesota, St. Paul

ABSTRACT

An attempt was made to characterize the lag period seen between the appearance of sulfonamides in plasma and milk after systemic administration. Experiments were devised to test the hypothesis that the major part of the lag period may be due to improper milk sampling techniques.

One hundred milligrams per kilogram of sulfamethazine or sulfacetamide were given to four cows, as a single intravenous dose. Milk and plasma samples were taken simultaneously for a 36-hr period. Cows receiving sulfamethazine also received oxytocin before each milk sampling. One week later this experiment was repeated; however, oxytocin was used to withdraw milk in the sulfacetamide treated cows.

A comparison of the oxytocin treated cows with the untreated cows showed that oxytocin treatment reduced the lag period seen between the appearance of peak concentrations in the plasma and milk. Milk-to-plasma ultrafiltrate ratios for both sulfamethazine and sulfacetamide were found to agree much closer with theoretically calculated ratios for passive diffusion when oxytocin was used to completely evacuate the gland at each sampling. However, a lag still remained between theoretical and actual milk-to-plasma ratios after oxytocin treatment.

It was concluded that one intravenous dose with oxytocin could not be used as effectively as constant intravenous infusion techniques to study the mechanism of transport of organic acids into bovine milk.

¹ Scientific Journal Series Paper no. 6109, Minnesota Agricultural Experiment Station.

² Supported by Grant no. EF-00481-03, National Institute of Health.