P#41  Effects of prolactin on under-hair follicle development in mink

Jason Hunt and Jack Rose. Idaho State Univ., Dept of Biol, Sci., Pocatello, USA

In mink, winter anagen is initiated by decreasing photoperiod, and is correlated with reduced serum prolactin (PRL) levels. Inhibition of PRL secretion with melatonin (MEL), or artificially short photoperiod, induces anagen prematurely. Our objectives were to determine: (1). if skin PRL receptor (PRL-R) levels change during natural and artificially induced (MEL & bilateral adrenalectomy, ADX) winter anagen, and (2). if under-hair density was influenced by elevating (haloperidol, HAL) or reducing (MEL) serum PRL levels. Skin PRL-R levels were determined, on July, 27, August 18, Sept 9, and Oct 22, and histological analyses performed on skin samples from Oct 22, to quantify the number of under-hair follicles per follicular bundle type (U-type = under-hairs only, I-type = under-hairs plus one intermediate guard hair, and G-type = under-hairs plus one primary guard hair). Control mink entered winter anagen during mid-Sept and PRL-R levels were unchanged. HAL delayed anagen in two mink while initiating early anagen in one animal. In all HAL-treated mink, PRL-R levels increased on Aug 18, and remained elevated through Oct 22 (P<0.05). MEL induced winter anagen 6-weeks early and PRL-R levels were higher during anagen (Aug 18 & Sept 9) than telogen (July 27 & Oct 22; P<0.05). ADX initiated winter anagen six weeks early and PRL-R levels were unchanged. The number of under hair follicles per bundle in control mink was, U = 19.6 + 2.3, I = 18.0 + 2.0, & G = 15.2 + 1.7. In all groups, the under hair density per bundle was lower in G-type than in U or I-type bundles (P<0.001). ADX increased under-hair density in U-type (22.3 + 1.5) and I-type (19.7 + 2.2) bundles (P<0.01). HAL, reduced under-hair density 53 % in U-type, 57% in I-type and 40% in G-type bundles (P<0.01). We conclude that changes in skin PRL-R levels are not requisite to initiation of winter anagen. Nevertheless, it would appear that increased PRL binding after onset of winter anagen may in part, influence the number of under-hair follicles that develop, supporting the hypothesis that hair density (summer or winter) is determined, in part, through the actions of PRL.