Age-related changes in the secretion of LH in vivo and in vitro in infantile and prepubertal Holstein bull calves

Abstract

The objectives of this study were (i) to determine whether age-related changes in the secretion of LH are associated with alterations in secretory activity or numbers of gonadotrophs, and (ii) to determine whether gonadotrophs obtained from the pars distalis and pars tuberalis undergo similar age-related changes in function. Blood samples were collected from Holstein bull calves every 15 min for 12 h at < 1, 12, and 42 weeks of age (n = 5 per age group) to characterize the secretion of LH. Calves were killed 3-5 days later. The pars distalis and pars tuberalis were enzymatically dispersed into suspensions of single cells. Cells from the pars distalis were (i) extracted with 0.01 mol NaHCO3 l-1, (ii) fixed for immunocytochemical analysis, and (iii) cultured in six-well plastic plates at a density of 500,000 cells per well in media containing 2.5% homologous calf serum for 18 and 72 h. Cells from the pars tuberalis were cultured as for pars distalis cells. As expected, LH pulse frequency increased (P < 0.01) between one and 12 weeks of age and then declined. The percentage of cells from the pars distalis containing immunoreactive LH averaged 8.4%, and did not change with age. The mass of the pars distalis and the total number of cells recovered increased with age (P < 0.05); consequently, the number of gonadotrophs recovered also increased. The initial content of LH of pars distalis cells changed with age and was greatest at 12 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)