Age-Related Changes in Prolactin Cell Percentage and Serum Prolactin Levels in Intact and Neonatally Gonadectomized Male and Female Rats

Abstract

Electron microscopically the percentages of various pituitary cell types were calculated at 30 and 90 days of age. Prolactin cell percentage was more at 90 days of age than at 30 days in both intact male and female rats. No sexual difference was observed in the percentage of prolactin cells at 30 days of age, but at 90 days female pituitaries contained more numerous prolactin cells than male ones. Neonatal ovariectomy did not affect the prolactin cell percentage at 30 days of age, while it lowered the percentage at 90 days. Neonatal orchidectomy did not affect the prolactin cell percentage at both 30 and 90 days of age. Mitotic prolactin cells were more frequently observed in intact female rats at estrus than in intact male rats at 90 days of age. These results show the presence of the sexual difference in the proliferation of prolactin cells. Serum prolactin levels increased with age in intact male and female rats. In neonatall·y gonadectomized male and female rats the serum prolactin levels failed to increase at 60 and 90 days of age. In general conclusion, the changes in serum prolactin levels are in line with the changes in prolactin cell population during postnatal development.

Sexually Dimorphic Effects of Aging on Rat Somatotropes and Lactotropes

“…In old female rats, which often bear PRL-secreting tumors (Kovacs et al, 1977;Berkvens et al, 1980), the plasma PRL level (Cocchi etal., 1986;Meites, 1986) and number of lactotropes (Takahashi and Kawashima, 1982;Chuknyiska et al, 1986) are increased. Although the inhibitory activity of the tuberoinfundibular dopaminergic system is comparably reduced in both sexes, plasma PRL levels of old male rats remain within a normal range (Forman et al, 1981;Cocchi etal., 1986).…”

Increase in Pit-1 mRNA Is Not Required for the Estrogen-Induced Expression of Prolactin Gene and Lactotroph Proliferation.

“…It is possible, however, that a change in the Pit-1 mRNA level in lactotrophs could not be observed following short term estrogen treatment, because Pit-1 is expressed not only in lactotroph cells but also in other types of hormone producing cells in the anterior pituitary, and the lactotroph cell population is less than 10% in the pituitary of male rats [20]. An increase in lactotroph cell population was therefore achieved by the chronic estrogen treatment.…”

Intrapituitary Regulatory System of Proliferation of Mammotrophs in the Pituitary Gland

“…Mammotrophs are the most actively proliferating cells in rat and mouse pituitaries (Shirasawa and Yoshimura, 1982;Takahashi and Kawashima, 1982;Takahashi, 1992;Takahashi, 1995). In adult female rats the mitotic activity of mammotrophs is higher during estrus than during any other stage of the estrous cycle (Takahashi et al , 1984;Oishi et al , 1993).…”

“…This high proliferation of mammotrophs depends upon ovaries or ovarian estrogen, since ovariectomy decreased the high mitotic activity observed during estrus, while estrogen replacement increased mitotic activity. This sexual difference in mitotic activity is thought to lead to the sexual difference in mammotroph number (Takahashi and Kawashima, 1982;Sasaki and Iwama, 1988).…”

“…This review describes the actions of growth factors produced within the pituitary gland and shows the intrapituitary regulatory system involved in controlling pituitary functions. Of the several types of pituitary cells, the proportion of mammotrophs differs between males and females (Takahashi and Kawashima, 1982), and changes during pregnancy and lactation (Haggi et al , 1986). In addition, the regulation of mammotroph proliferation has been well studied compared to other types of anterior pituitary cells; therefore this study focuses on the proliferation and differentiation of mammotrophs.…”