Cell proliferation in the wool follicles of fleeceweight selected and control Romney rams

Abstract

Two year old Romney rams from the Massey University fleeceweight-selected (FW) and control (C) lines, five from each line, were given arterial catheters into a branch of the deep circumflex artery on each side of the sheep, to permit local infusion into patches of skin on each lateral abdominal flank. One side of each sheep was infused with saline to give a direct FW v. C comparison, while the other side was infused with low levels of either growth hormone, thyroxine, prolactin or insulin for 4 days. At the end of the infusion period, biopsy samples were taken from each flank for measurement of follicle activity, particularly bulb cell proliferation using intracutaneous injections of 5-bromo-2'-deoxyuridine (BrDU). After a period of recovery, the saline and treated sides were reversed and another series of infusions were performed and biopsies undertaken. Wool from the FW sheep had greater fibre length growth rate and fibre diameter than the C wool (P < 0.05). This was associated with larger follicle bulbs (P < 0.05) and greater numbers of BrDU labelled cells (P < 0.05) in the bulbs of the FW skin. In a restricted number of samples from two sheep, where BrDU was successfully given as repeated intracutaneous injections into the same site (one at 72 h and one at 6 h prior to biopsy), 55-60% of the numbers of BrDU cells in a section of bulb appeared in a section of the shaft of the same follicle. When converted to three dimensions, the efficiency of labelled bulb cell movement into the shaft was 30-40%. Hormonal infusions showed few significant effects with the restricted numbers of animals in each treatment. Thyroxine reduced the size of follicle bulbs (P <0.05) and the numbers of labelled bulb cells in skin from the infused area.