The long term objective of the experiments in this project is to discover which aspects of differential FSH and LH release are regulated directly at the level of the anterior pituitary gland itself. Three in vitro setups will be used: (a) a dynamic perifusion apparatus using dispersed cells; (b) a dynamic perifusion apparatus using pituitary fragments; (c) a static, dispersed pituitary cell culture. These set-ups will permit contrast of dynamic vs static GnRH input-gonadotrope-output relations as well as contrast of dynamic control in the absence (dispersed) and presence (pituitary fragments)) of cell-cell connections. We will measure LH and FSH in the medium and in the pituitary gland, as well as pituitary GnRH receptor levels.
Specific Aim 1 is to examine FSH and LH secretory rates in response to variations in intensity, duration and/or frequency of GnRH input, frequently cited as accounting for differences in the secretion rates of the two gonadotropins. Donors will be intact males and intact females at each cycle stage.
Specific Aim 2 is to determine the effect of in vitro treatment with gonadal steroids and folliculostatin on FSH and LH secretion in basal and GnRH-stimulated pituitaries. The literature is contradictory on the site(s) of gonadal negative feedback; our models will enable us to probe for interactions between these feedback factors and a dynamic GnRH signal, at the level of the pituitary gland itself.
Specific Aim 3 is to determine the effect of in vivo increases or decreases in gonadal feedback in donor males and females on the secretory activity in vitro of their pituitaries.
Specific Aim 4 is to determine whether the anterior pituitary gland itself is an important site of interaction of glucorticoids on differential regulation of LH and FSH secretion rates. In vivo, castrated male rats pretreated with cortisol show a suppressed LH response to GnRH, but the FSH secretory response to GnRH is normal, and pituitary FSH stores are increased, suggesting that glucocorticoids could be an important probe in the search for the site of differential FSH regulation. This finding could not be replicated in a static, dispersed pituitary cell culture.
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