Effect of environmental salinity changes on the secretory activity of prolactin cells in ocular pituitary transplants in Poecilia latipinna (teleostei)

Abstract

Observations were made on plasma sodium levels and on the pituitary prolactin cells in Poecilia latipinna in one-third seawater ( 1 3SW ) and at various times up to 7 days after transfer to freshwater (FW). The pattern of adjustment of plasma sodium, an initial fall during the first 16–18 hr followed by restoration to normal FW levels at 3 and 7 days, was similar in both normal fish and in fish with the pituitary gland autotransplanted to the anterior chamber of the eye. In both groups the prolactin cells displayed histological signs of progressive increase in activity from 6 hr onwards. However, both plasma sodium values and prolactin cell nuclear area indicated that prolactin secretion in FW was rather lower in the autotransplants than in the in situ gland, although probably about normal in fish adapted to 1 3SW . It is suggested that this may indicate some partial inhibition of the prolactin cells by catecholamines in the eye tissues. Our main conclusion is that P. latipinna prolactin cells in vivo can be activated by reduced environmental salinity in the absence of hypothalamic connexions, and that the time-course of this activation follows closely the pattern in intact fish.