Photoperiodic dependence of seasonal changes in pituitary content of melanocyte-stimulating hormone.

In the Siberian hamster the pituitary content of bioassayable MSH has been shown to be seasonally variable, being greater during the long days of spring and summer than during the short days of autumn and winter. Similar changes in the pituitary content of both bioassayable MSH and immunoreactive alpha MSH can be induced by transfer of animals between artificial light photoperiods of appropriate duration.