Endocrine Abstracts

In birds similar to mammalian species, the reproductive performance in females deteriorates with age. In the present study, relationships between the growth of preovulatory follicles (PF), reproductive aging and sex steroids were investigated using young hens with long clutch (YLC), old hens with long clutch (OLC) and old hens with short clutch (OSC). 1) hens were killed 1.5 and 14.5 h after assumed ovulation. 2) YLC hens were killed 3.5 h after treatments with LH and/or aminoglutethimide (AG), an inhibitor of steroid synthesis. Volumes of PF (F1-F5) and plasma concentrations of ovarian steroids were determined. 3) Granulosa (GC) and theca cells (TC) from F3 follicles of YLC and OSC hens were exposed in vitro to estradiol-17beta (E₂, 1 ng/ml) and the proliferative activity (PA) of the cells was examined using CellTiter 96 Aqueous One Solution Assay. In YLC and OLC groups, the total follicular volume (TV) rose between 1.5 and 14.5 h after ovulation (YLC: from 31.8±1.3 to 43.2±2.6 ml; OLC: from 35.7±2.0 to 46.4±2.5 ml, P<0.01), negatively correlating with the plasma level of E₂ (P<0.01). By contrast, there was no growth of PF in the middle of the ovulatory cycle in the OSC group, with a positive correlation being present between E₂ and TV (P<0.05). In young hens, AG caused a decline in levels of steroids and a rise in TV, which was associated with a fall in E₂ (r=−0.54, P<0.05). E₂ increased in vitro the rate of viable GC (YLC: from 201 to 250%; OSC: from 175 to 210%, P<0.01) and did not affect PA of TC from both groups. E₂ seems to play a dual role; it stimulates the follicular growth in old hens, whereas it may inhibit the growth of PF in young animals.