Changes in hair growth (7)
Method III
Both club and growing hairs were plucked just prior to wounding in 12 follicles
in four rats. Two subsequently failed to produce emergent vibrissae. As shown
in Table 3, of the remaining follicles, five produced longer hairs; three had fibres
of equivalent length to their controls; and two manufactured shorter fibres.
Therefore, in close agreement with method II, half of the damaged follicles had
formed longer hairs in Gl. Moreover, the mean length increase of 14-8 % was
also near to that attained by Gl follicles in the previous method.
Effect of plucking alone
Following plucking, hair production was terminated in all twenty follicles.
Sixteen new whiskers were seen between 7 and 17 days, and four between 27 and
55 days, but none of the plucked follicles produced Gl vibrissae longer than their
controls.
Method IV
In three rats where 19 follicles were damaged above the bulb region, 3
follicles failed to produce emergent whiskers. The Gl fibre lengths for the
remaining 16 follicles revealed no hairs of longer than control length. Four
whiskers were shorter than their controls, while the remaining twelve were
equivalent in length.
Normal whisker length
Vibrissa length measurements agreed with all previous investigations in that
a distinct anteroposterior gradient of increasing fibre size was observed. Apart
from the top horizontal row, the lengths could all be divided into discrete nonoverlapping
groups representing vertical rows. The range of length displayed
within these groups was similar to that found on male Wistar rats by Ibrahim & Wright (1975).
Paired length measurements carried out to determine normal differences in
club length between whiskers in identical positions on either side of the face
revealed a margin rarely exceeding 2 mm, or about 4 % for the hairs of length
normally used experimentally. Ibrahim & Wright (1975) also found that vibrissae
grew synchronously within the same margin. These authors showed that for the
first three postnatal cycles, whiskers underwent a stepwise increase in length
before levelling off. Age-related length differences were confirmed in the current
work, and it was for this reason that 6-month-old rats, whose whisker lengths had
stabilized, were used for all experimental procedures.
Follicle wounding
As four operational procedures were performed, the reasoning behind the use
of these different techniques will be briefly considered.
Using the method I procedure it was apparent that apart from inflicting injury
in situ, cellular material was being lost from the bulb region of many follicles. To
overcome any influence this loss of bulbar material might have on subsequent
hair growth, method II was employed. As damage with these two methods was
inflicted on both the epidermal matrix and the dermal papilla, method III was
devised. It has already been shown that plucking of growing vibrissae removes
a high proportion of epidermal matrix with no stimulatory effect on whisker
length (Oliver, 1965; Ibrahim & Wright, 1978), and plucking procedures in this
study confirmed these findings. Thus in method III, which acted as a quasi
control, the removal of club and growing hairs prior to wounding meant that
damage was essentially restricted to the dermal papilla alone (Jahoda & Oliver,
1984). The method IV control procedure was designed to show the effects on
whisker growth of damage above the bulb region.
The present experiments confirmed the recuperative powers of vibrissa
follicles following injury, with over 90 % of them manufacturing external fibres
after being wounded. However, the most striking result was the confirmation of
consistent increases in hair length (Oliver & Jahoda, 1981). This effect was
manifested by some 10 % of follicles after method I operations, where a complex
response included production of over 33 % short hairs. However, following
methods II and III, in which no loss of cellular material from the capsule
occurred, some 50 % of postoperative vibrissae were longer than expected. This
Hair growth changes following vibrissa wounding 91
effect persisted into the second postoperative generation. In contrast, none of
the follicles wounded distal to the bulb region produced longer than expected
hairs. Recently, Ibrahim & Wright (1982) observed the formation of a single long
vibrissa fibre following lower follicle regeneration. They have also shown whisker
length increases of the same degree as in the present experiments following
exposure of adult mice to high levels of testosterone (Ibrahim & Wright, 1983).
What is intriguing about the present results is that they specifically implicate the
dermal papilla in the production of longer hairs.
Hair length, which was employed as the primary measure of follicle activity,
is the product of the rate of fibre growth, and the duration of fibre production.
Where changes in these two parameters occurred they were consistent for all
wounding methods. Growth rate when affected was reduced. Therefore longer
whisker production was exclusively due to increases in the duration of growth.
This effect was especially demonstrated in the results from methods II and III
where more longer hairs were produced despite the increased number of follicles
showing reduced growth rates. Interestingly, where experimental follicles
produced hairs of normal length, this could either reflect the absence of wounding
effects, or (as in ten method I follicles) be the result of increases in duration
of growth and reductions in growth rate anulling each other.
Increased duration of hair growth has only rarely been demonstrated experimentally.
Therefore it is noteworthy that when Hale & Ebling (1975) elicited this
phenomenon through the action of propylthiouracil on rat pelage hairs, it was
associated with a reduction in growth rate. At the same time treatment with
thyroxine caused hairs to grow faster, while reducing the length of the growing
period. Likewise in the present study a balance between the two altered
parameters could negate any effect on fibre length. Indeed a major point to
emerge from these findings is that factors which control growth rate appear to be
independent of those which determine the duration of growth. Interestingly
vibrissa length increases produced through the influence of testosterone involved
longer growth periods, but unaffected growth rates (Ibrahim & Wright, 1983).
The hair growth cycle can be divided into three basic stages; anagen, the
growing phase; catagen, the period of follicle regression; and telogen, when
epidermal proliferation and hair growth is arrested. The mechanisms which
control the repeated initiation and termination of the adult hair cycle represent
the principal enigmas of hair growth. The timing of this cycle is astonishingly
consistent for individual vibrissa follicles, and Oliver (1965) has noted the
relationship between the order of hair replacement in adult follicles, and the
sequence of vibrissa follicle development in embryos. The same author (Oliver,
1980) has proposed a control system based on an active mesenchymal element
which would both initiate growth, and maintain it through a growing period. It
was suggested that follicle behaviour might be governed by stimuli from the
papilla, therefore reflecting some 'intrapapillary cycle of events'. This infers that
the dermal papilla of each follicle starts off with an internal mechanism regulating
the timing of the cycle, perhaps derived from embryonic regulatory mechanisms.
While the current results were in accordance with the above ideas to the extent
that stimulation of the dermal papilla by wounding appeared to be primarily
responsible for the production of longer fibres, the question as to why papilla
injury should affect the duration of the growing period remains unresolved.
Nevertheless, a histological study offers a reasonable explanation for some
aspects of follicle behaviour after injury (Jahoda & Oliver, 1984).
We would like to thank Mr Bruce Pert and Mademoiselle Yolande Bouvat for their expert
technical assistance. This work was supported by a Medical Research Council studentship.
Labels: hairloss, hairlosssolution, hairlosstreatment