ROLES OF MELATONIN AND PROLACTIN IN TESTICULAR CRUDESCENCE IN MINK (MUSTELA-VISON)

Peripubertal male mink (Mustela vison) were treated with prolactin, me latonin or antibodies against melatonin to determine the effects of al tered circulating concentrations of prolactin and melatonin throughout one season of testicular development. Treatment began on 1 October an d continued until 4 March. Administration of 0.5 mg ovine prolactin da y(-1) by minipump increased the circulating concentration of prolactin for the duration of the study and increased serum concentrations of L H. This treatment had no effect on the testosterone concentration or o n testis size. Neither chronic treatment with melatonin throughout the period of crudescence nor passive immunization against melatonin for 79 days affected the circulating concentrations of prolactin, LH, test osterone or testis size. These results show clearly that, unlike in ot her seasonally breeding species, prolactin does not play a significant role in testis growth in the mink. Administration of melatonin to mal e mink in October did not affect testis growth, presumably because the melatonin signal that cues photoperiodic events had already been rece ived. Administration of antibodies against melatonin did not affect an y of the features measured suggesting that melatonin may have neural b ut not peripheral effects. Further support for this view can-be found in the absence of an influence of melatonin on testis growth or on the plasma concentration of testosterone.