Apparent role of melatonin and prolactin in initiating winter fur growth in mink.

A study was conducted to determine the effects of exogenous melatonin and bromocriptine (CB-154), an inhibitor of prolactin synthesis and secretion, on the induction of winter fur growth in mink. Melatonin (10 and 120 mg) was administered to mink (N = 5/group) via silastic implants inserted sc over the scapular area during the last week of June 1985. Treatment of mink (N = 5) with CB-154 alone or in combination with 10 mg melatonin (N = 5) consisted of daily sc injections of 2 mg of the drug in sterile saline from June 25 through July 30. Control animals (N = 5) did not receive injections of vehicle or sham implants. Administration of CB-154 alone or in combination with 10 mg melatonin, as well as 120 mg melatonin alone, initiated growth of the winter fur significantly earlier than that of controls or mink treated with 10 mg melatonin (P less than 0.05). These data suggest that inhibition of prolactin secretion by melatonin is requisite for induction of molt of summer fur and growth of winter fur of mink.