Prolactin profiles of pregnant, lactating and non-mated female mink (Mustela vison).

This study was part of an experiment on energy metabolism in pregnant and lactating female mink (Mustela vison). Ten mated and three non-mated female mink were kept in metabolic cages in the laboratory from immediately after mating until the kits were three to four weeks old. Consecutive energy balance experiments with periods each of one week duration, including a 22 h respiration experiment (only three with females that were not mated) were performed, and weekly blood samples were collected for determination of plasma concentrations of thyroid hormones, prolactin, insulin and glucose. Prolactin profiles of pregnant and lactating females had a biphasic pattern: there was an increase in April, a decline immediately before parturition, and peak values were recorded in early May, usually when the females were in the first week of lactation. In females that were not mated plasma concentrations of prolactin did not rise above basal concentration. These females also exhibited a delayed spring moult, and had a lower feed intake. In addition, plasma profiles of thyroid hormones of mated and non-mated animals were different; concentrations of thyroid hormones decreased in April to early May, but the decrease started earlier and was most pronounced in pregnant female mink. These data indicate that prolactin secretion in female mink is regulated by photoperiod, but that other endocrinological events during pregnancy may also be involved.