Translocation of protein kinase C isozymes in rat pituitary lactotroph-enriched cell cultures by substance P: effects of sex and age

Abstract

It is generally accepted that the phospholipid and calcium-dependent enzyme protein kinase C (PKC) plays a significant role in secretion of hormones from anterior piuitary cells. The present study was undertaken to study age and sex-related changes in 1. levels of immunoreactivity of PKC isozymes and 2. distribution of immunoreactivity of PKC isozymes after stimulation with substance P (SP) in rat lactotroph-enriched cell cultures. The α, β, δ and ζ isozymes were present in both sexes and at all ages. There was a sex-specific differential regulation of the different PKC isozymes as a function of sexual maturation. In male rats there was an up-regulation of the α isozyme throughout the sexual development, while the β subtype showed a small, but significant decrease in immunoreactivity with increasing age. In female rats, on the other hand, the β species was up-regulated with increasing age while the other subtypes remained constant. The concentration of the δ and ζ isozymes was unaffected of sex and age. Stimulation of lactotroph-enriched cell cultures with substance P (SP) resulted in translocation of the α and β isozymes from the soluble to the particulate fraction while the δ and ζ species were left unchanged independently of age and sex. However, a decrease in responsiveness was observed in adult male rats, although a significant degree of translocation of α and β species was still detected. On the basis of these results it is suggested that in lactotroph-enriched cell cultures basal levels of PKC subtype immunoreactivity and distribution of immunoreactivity of PKC isozymes after SP challenge might be regulated as a function of sex and age.