An investigation of the relationship between oestradiol and mineralisation of red deer (Cervus elaphus) antlers : A thesis submitted in partial fulfilment of the requirements for the degree of Master of Applied Science at Lincoln University

Abstract

Two studies were carried out to determine the mode of action of oestradiol (E₂) on terminal mineralisation of red deer (Cervus elaphus) antlers. The first study aimed to localise oestrogen receptors (ER) to specific regions of the antler. Partially grown antlers were removed from red deer stags, the skin was peeled off and tissue samples were taken as follows: tip (containing undifferentiated mesenchymal tissue and cartilage), periosteum from the shaft, cartilage (including some perichondrium), calcified cartilage, bone. Binding capacity and affinity (Ka) ER were measured by a radio receptor assay and results were calculated from Scatchard plots. High affinity ER (Ka 1.3-3.4 x 10¹⁰/M) were detectable in all antler tissues except for bone, with periosteum > tip > cartilage > calcified cartilage with respect to receptor capacity (range 12-74 fmol/mg protein). These results indicate regional differences between tissues within the antler. The presence of ER in non-calcified tissues indicates the possibility of an indirect action of Bi on mineralisation of antler bone rather than a direct effect on the bone cells. The second experiment investigated whether E₂ had a local effect on antler mineralisation. Silastic tubing containing 0, 0.1, 1, 10 or 100 mg E₂ was surgically implanted into the 6 week old antlers of stags (n=2) next to the periosteum. Contralateral antlers received empty implants. Implants were left in place for 4 weeks, then antlers were amputated and changes in bone structure were monitored by histological and biochemical methods. Plasma osteocalcin and alkaline phosphatase (AP) concentrations increased over the antler growing period and decreased significantly (p<0.01) with antler amputation, suggesting local production of these compounds in the antler. Macroscopic examination of antlers showed that one stag treated with a 1 mg implant and both stags treated with either 10 or 100 mg E:z implants had increased mineralisation of antler bone adjacent to the implantation site. This zone of mineralisation extended proximally (towards the base) following vascular channels, but not distally (towards the tip) in the antler. Ash content increased (p<0.01) and percentage of intraosseous space decreased (p<0.01) with increasing concentrations of E₂ . Slight changes in these parameters were also detected for some doses of E₂ in the contralateral antler suggesting further spread of E₂ or secondary factors from the implantation site at higher doses. These results show that cartilaginous and fibrous tissues within the antler contain ER and that E₂ causes mineralisation of antler bones by a direct effect on this organ. The relationship between these findings awaits resolution and it is suggested that antlers may prove to be useful model organs for studies on the physiology of bone mineralisation.