PITUITARY EXPRESSION OF PROTEIN-KINASE-C ISOTYPES DURING EARLY DEVELOPMENT

Protein kinase C (PKC) is a critical regulator of signal transduction and cell function in many tissues, including pituitary, Although PKC i nfluences pituitary hormone secretion in adults, its role in determini ng characteristic perinatal patterns of hormone secretion and synthesi s is not known, and the expression of major PKC isotypes in perinatal pituitary is poorly defined. We therefore determined the developmental , cell-specific expression of the major PKC isotypes, using Western an alysis and double label immunohistochemistry, in pituitaries of perina tal and mature rats. Expression of specific PKC isotypes was strikingl y age-dependent. Pituitary expression of PKC alpha was particularly hi gh in neonates and declined significantly with age, with levels in adu lt rats approximately half those of neonates as assessed by Western an alysis, Similarly, immunohistochemistry indicated that PKC alpha was l ess abundant in adult than in neonatal pituitaries; the most intensely staining cells of both age groups were identified as somatotrophs and gonadotrophs. In contrast to PKC alpha, pituitary expression of PKC e psilon increased approximately two-fold with advancing age as assessed by Western analysis; this age-dependent pattern was confirmed by immu nohistochemistry. Perinatal pituitaries expressed PKC epsilon in some somatotrophs and in all gonadotrophs, whereas PKC epsilon expression w as limited to gonadotrophs in the mature pituitary, Pituitary expressi on of PKC beta II, delta, and zeta did not differ with age, and PKC ga mma was not detected in pituitaries of any age group. These results in dicate that expression of PKC isotypes within the pituitary is develop mentally regulated in a cell-specific and isotype-specific manner, and are consistent with the concept that PKC contributes to the regulatio n of pituitary function during early development.