Quantitative bioassay of luteinizing hormone releasing activity in the quail hypothalamus during photostimulated sexual development

Abstract

A quantitative bioassay using dispersed chicken pituitary cells was employed to measure luteinizing hormone releasing activity in pooled hypothalamic extracts from groups of quail during photostimulated sexual development. Levels of releasing activity with 95% confidence limits were expressed in terms of microlitres of a standard hypothalamic extract (CS). LH releasing activity was measurable in the hypothalamus of male and female quail reared under both short and long photoperiods. Using an approximate conversion factor from CS, levels ranged between 5.1 and 13.3 ng synthetic LH-RH/mg basal hypothalamic tissue. Dramatic increases in LH secretion seen after transfer to photostimulatory daylengths were not associated with any large changes in hypothalamic LH releasing activity. Several significant fluctuations in levels of releasing activity were observed but these could not readily be correlated with changes in plasma LH levels. Combined data from four experiments show that the mean concentration of releasing activity was just significantly higher in groups of birds receiving 7 or more long days than in short day quail and birds receiving fewer than 7 stimulatory photoperiods ( P < 0.05). This difference represents a 30% increase in releasing activity in long-term photostimulated quail. Castration did not alter LH releasing activity during one 5-week experiment, although a group of castrated birds maintained on long days for 1 year showed the highest level of releasing activity found in any quail.