COMPARISON OF LACTOTROPE SUBTYPES OF NEONATAL AND ADULT MALE-RATS - PLAQUE ASSAYS AND PATCH-CLAMP STUDIES

We examined the differences in lactotrope number and function between pituitary cultures from neonatal (10-day-old) and adult male rats. Bas al hormone release was measured with the reverse hemolytic plaque assa y. Whole cell Ba2+ currents through Ca2+ channels were recorded from i dentified prolactin (PRL) secretors with the patch-clamp technique. La ctotropes were classified in two groups according to the relative amou nt of PRL released: small-plaque (SP) secretors accounted for 6% of al l cells in both neonatal and adult pituitary cultures, whereas large-p laque (LP) secretors comprised 13% of the adult pituitary cells but we re scarce in cultures from neonates. Simultaneous plaque assays for PR L and growth hormone (GH) showed that in adults as well as in neonates the number of SP and LP secretors was similar to the number of lactos omatotropes (PRL cells that also release GH) and classical lactotropes (PRL-only cells), respectively. Ba2+ current density at positive memb rane potentials was markedly higher in adult LP secretors than in neon atal or adult SP lactotropes. We conclude that the appearance of LP se cretors constitutes a major postnatal change within the rat lactotrope population. These cells present a large activity of high-threshold Ca 2+ channels in the plasma membrane, release PRL at high basal rates, a nd may correspond to classical lactotropes. The results further sugges t that neonatal lactotrope-like cells persist during development and g ive place to adult SP secretors.