Temporal changes in LH and testosterone and their relationship with the first antler in red deer (Cervus elaphus) stags from 3 to 15 months of age

Abstract

ABSTRACT Blood samples were taken from six tame red deer stags at 3–15 months of age once a month from a jugular catheter every 30 min for 24 h to investigate hormonal secretion during puberty and during growth of the pedicle and first antler. All plasma samples were analysed for LH and testosterone concentrations and the resultant data were analysed using the PULSAR pulse detection routine. In addition each stag was injected with gonadotrophin-releasing hormone (GnRH; 20 ng/kg body weight) after the above samples had been taken and the bleeding regimen was continued for a further 2 h. Body weight, antler size and status (i.e. whether the stags had a pedicle or antler) were also recorded. The pulsatile secretion of LH could be considered to have occurred in three phases. The first of these was one of development, with the LH pulse frequency increasing to 8 pulses/24 h, the second a phase of regression, with a decrease in LH pulse frequency to 2 pulses/24 h, and finally a second phase of development characterized by increased LH pulse frequency to 12 pulses/24 h. Testosterone secretion generally followed the same pattern. During the period before the permanent bony pedicles grew, there were less than five LH pulses/24 h. When the pedicles were growing, LH and testosterone pulsatile secretion increased but the pulse frequency of both hormones fell during velvet antler growth. However, the overall mean testosterone level did not significantly decrease between the growth stages (2·74 and 2·29 nmol/l respectively) although mean testosterone plasma rose during pedicle growth and fell during velvet antler growth. Both hormone plasma concentrations increased dramatically, and testosterone was particularly high (11·82 nmol/l), at the time of antler cleaning. All stags responded to exogenous GnRH by secreting LH and testosterone in all sampling periods. The LH response to GnRH increased during pedicle growth and fell during antler growth before rising again in autumn as the breeding season approached. Testosterone responses largely paralleled those of LH except that they remained high in early antler development. The results are consistent with the following hypotheses. (1) Pedicle initiation is caused by increased plasma level of testosterone stimulated by increasing LH pulse frequency and (2) testosterone is stimulatory for pedicle growth but not necessarily so for velvet antler growth. Journal of Endocrinology (1991) 131, 467–474