Results

 

Fig. 4  (A): Mean (± S.E.) serum prolactin concentrations, and (B): Mean guard hair length from March 4 to May 6. Mink (N=4/group) were  treated with haloperidol, melatonin or as controls on Feb 20 and     depilated over the dorsal surface on March 4.

BRIEF EXPLANATION (Fig 4): Altering serum PRL levels to values significantly above or below those of control mink results in earlier onset of anagen in both guard and under hair follicles following depilation. This suggests that mink hair follicles may exhibit a seasonally influenced bi-phasic response to PRL, and supports the hypothesis that, PRL stimulates onset of  summer anagen but inhibits winter anagen.

 


Fig.5 (A): Underhair density, and (B): diameter for G, I and U bundle types of   mink treated as described in Fig 4 and analyzed by light microscopy.  Each bar represents the mean (± S.E.). Bundles with symbols are significantly  different from the same bundle-type at  p<0.01



Table 1: Underhair diameter, cross-sectional area, and ellipticity ratio (major axis ÷ minor axis) for mink treated as described in Fig. 4, and analyzed using  Scion Image software.  Because there was no difference among bundle  types (G,U & I), the data were pooled for statistical analysis. Groups were different at P<0.05 (* ) or P<0.01 (** ).


BRIEF EXPLANATION (Figs 5,6 & Table 1):  Increasing serum PRL levels (HAL group) resulted  in fur with reduced underhair density, but fibers of greater diameter for all three bundle types (P<0.01). In contrast, mink with undetectable serum PRL concentrations (MEL group) developed fur with increased underhair density, but with fibers of smaller diameter for all three bundle types (P<0.01). We hypothesize that during the summer, PRL targets (perhaps directly)  a subset of underhair follicles for activation and development to a larger size. In support of this hypothesis, Champion and Robards (2000) reported that the cross-sectional area of secondary-type hair fibers in sheep, (analogous to underhairs of mink), increased during the summer and decreased during the winter.



Table 2  G-type (top) and I-type (bottom) guard hair diameter, cross-sectional area, ellipticity ratio (major axis ÷ minor axis) and density for mink treated as described in Fig. 7. Groups were different at P<0.05 (* ) or P<0.01 (** ).

BRIEF EXPLANATION (Table 2): The cross-sectional area of G-type guard hair fibers in HAL-treated mink was greater than controls or MEL-treated mink. Both hair fiber diameter and cross-sectional area of I-type guard hairs were reduced in MEL-treated mink. The diameter and cross-sectional area of I-type fibers in HAL-treated mink, although not different from controls tended to be larger. There was no effect  of HAL or MEL on guard hair (G & I) density or ellipticity, suggesting that PRL effects hair density primarily through its actions on underhair type follicles.

EXPERIMENT TWO
 

Fig. 7    Underhair density (A) and diameter (B) for G, I and U hair follicle bundle     types.  Mink  (N=4/group) were treated as CON, HAL or MEL on Feb 13,  2001.  Skin samples were collected while the animals were in summer (April     24) or winter (September 29) anagen.


Table 3   Underhair diameter, cross-sectional area (AREA) and ellipticity ratio for mink in     spontaneous summer (TOP) and winter (BOTTOM) anagen, following treatments as  described in Fig.7. There were no difference among bundle types (G,U & I), and  the data were pooled for statistical analysis. Groups were different at P<0.01.



 
Table 4    G-type & I-type guard hair diameter, cross-sectional area (AREA), ellipticity and  density for mink in summer  (TOP) and winter (BOTTOM) anagen. Mink were  treated as described in Fig. 3. Groups were different at P<0.01.

BRIEF EXPLANATION (Fig 7, Tables 3 & 4): Serum PRL levels in HAL-treated mink increased 6 weeks earlier than controls, and yet only 2  mink entered anagen earlier than controls (4 weeks), while the remaining two mink entered anagen the same time as controls (Larson et al., 2003). Underhair diameters (G,U & I) were greater than controls, while underhair density (I & U) was less than controls (P<0.01). The diameter of G-type fibers was greater in HAL-treated mink.  When analyzed by Scion software, the cross-sectional areas of both G and I type guard hairs were greater than controls. There were no effects of HAL on guard hair (G or I) density or ellipticity.

    Serum PRL levels were undetectable in MEL-treated mink and none of these animals grew the summer fur (Larson et al., 2003). These mink subsequently entered winter anagen at the same time (early September) as controls even though serum PRL levels were less than controls. Both underhair density and diameters in MEL-treated mink were not different from controls. It was surprising that underhair diameters were not different between summer and winter anagen for controls (Table 3). Even more perplexing, both the cross-sectional area and diameter of guard hairs (G & I) in MEL-treated mink were greater than controls.  There was no effect of MEL on guard hair (G or I) density or ellipticity during development of winter anagen.





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