Effect of age on the secretory activity of different layers of preovulatory follicles in laying hens

Abstract

Age-related deterioration in female fertility is mainly associated with a decrease in the number and quality of ovarian follicles, which, in turn, leads to various endocrine disorders. In the present work, the steroidogenic activity of theca and granulosa layers from preovulatory follicles of laying hens of different ages was studied in vitro. Young hens aged 32-33 weeks with a long egg clutch and hens aged 74-76 weeks with a short egg clutch were used in the experiments. The granulosa and theca layers were isolated from the two largest preovulatory follicles F1 and F2 and cultured separately for 18 h. After culture, the concentration of sex steroid hormones in the media was determined by ELISA. The production of progesterone by the granulosa layer was 1.5-2.0 times higher in reproductively aged layers than in young layers. Concurrently, the secretory activity of granulosa cells increased with the development of follicles from the F2 stage to the F1 stage only in aged birds (from 74.0±7.5 to 97.0±10.9 pmol/mg tissue, P<0.05). Furthermore, testosterone production by the theca layer in aged hens was 2.0-2.8 times higher than that in young hens, but did not change significantly with the growth of follicles in birds of both groups. At the same time the ability of theca cells to secrete estradiol-17β was 1.6-2.3 times lower (P<0.001) in F1 than in F2 follicles, regardless of the age of the birds. The findings indicate that the processes associated with ovarian aging modulate the steroidogenic activity of follicular cells in laying hens, with the age-related reduction in the egg clutch being related to an increase in the basal production of progesterone and testosterone in the two largest preovulatory follicles.