Effect of nigericin and varying potassium concentrations on the prolactin-stimulated synthesis of milk fat in explants of mammary alveolar tissue from rabbits

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Abstract
The possible role of K+ as a 'second messenger' for prolactin was investigated. Explants obtained from mammary glands of pseudopregnant rabbits were cultured (a) in media with varying potassium concentrations and (b) in the presence of the potassium-specific ionophore, nigericin. The explants were examined histologically and the rate of protein synthesis was measured to determine the viability of the tissue. Increase in the rate of fatty acid synthesis in the presence of prolactin was used as a marker of prolactin stimulation. At low K+ concentrations prolactin-stimulated fatty acid synthesis decreased with the decrease in K+ concentration of the media, whereas there was no similar trend in the rate of protein synthesis. Nigericin (0·01–0·1 μmol/l) inhibited fatty acid synthesis and protein synthesis in the presence or absence of prolactin without significantly affecting tissue K+ content. The mechanism of nigericin inhibition is hence unclear and the results do not provide support for K+ as a 'second messenger' for prolactin.