Episodic Gonadotropin Secretion: INTRODUCTION
Proper gonadal function in birds depends on gonadotropins secreted from the pituitary gland in an appropriate manner. That LH secretion is distinctly pulsatile is generally well known, but the overall pattern and control of FSH secretion is not well understood in birds. The hypothalamus, in turn, controls the secretion of LH and, most likely, FSH by the pulsatile secretion of GnRH into the portal circulation of the pituitary.
The pattern of LH secretion in intact male chickens appears to be episodic, with a frequency of 0.3 to 0.7 pulses/ h. However, LH concentrations in plasma have been shown to be depressed over time as a result of the handling associated with repeated blood sampling. Moreover, it has been demonstrated that no pulses of LH were recorded when LH concentrations were minimal because of handling.
In the male turkey, LH pulses were identified only when baseline levels of LH and testosterone were low. In this situation, the pulse frequency ranged from 0.12 to 0.32 pulses/h and occurred during both the photophase and sco-tophase of the 14L:10D photoperiod. In the male Japanese quail, LH pulse frequency ranged from 0.25 to 0.42 pulses/h during a long day (20L:4D) photoperiod.
Testosterone is secreted by Leydig cells in response to LH challenges (for review, see ), and concentrations tended to rise as cockerels attained adulthood compared to young birds. Pulsatile secretion of testosterone closely followed LH pulses when serial blood samples were taken every 5-10 min in turkeys. To the best of our knowledge, no reports in the literature concern the pulsatile secretion of testosterone in male chickens. Similarly, no reports describe patterns of FSH secretion in frequent samples from domestic avian species.
Several techniques have been used to obtain frequent samples from birds based on cannulation of a wing artery or the jugular vein. The cannulation procedure might induce stress in the birds because of the technique itself or because of the effect of handling. The monitoring of adrenal cortex activity, as indicated by changes in circulating corticosteroid, along with behavior have been the classical measures of a given stress response. Corticosterone is the main corticosteroid in avian plasma, and it has long been used as an indicator for the degree of relative stress in chickens. The present experiment was conducted to evaluate acute changes in gonadotropin secretion, testosterone, and corticosterone in unrestrained birds with jugular cannulas and free access to feed and water.