Developmental Profile of Prolactin Cells in the Anterior Pituitary of Postnatal Rats during the Lactational Stage

Abstract

Changes in prolactin (PRL)-, growth hormone (GH)- and PRL/GH-containing cells in the anterior pituitary of pre- and postnatal male and female rats were determined using immunocytochemistry with double fluorescent antibodies. The pituitary glands from a fetus on Day 20 of gestation and pups on Days 0, 1, 4, 7, 12, and 20 of the postnatal period with sex distinction were monodispersed and subjected to immunocytochemistry. Following immunostaining, the three types of cells described above were counted (i.e., only PRL-, only GH-, and both PRL and GH-positive cells in a visual field of microscope). Anterior pituitaries and blood were obtained from pups on Days 0, 1, 4, 7, 12, and 20 after birth and pooled with sex distinction, and bioactive PRL levels in the anterior pituitary and serum were measured using an Nb2 rat lymphoma cell bioassay. Double fluorescent-labeled immunocytochemistry was able to distinguish reliably between PRL-, GH-, and PRL/GH-containing cells. The PRL cells increased rapidly after parturition to 4 days of age and after 12 days of age in both genders. The latter increase was involved in the remarkable increase of PRL/GH-containing cells, which were first found at term and remained at low levels until 12 days of age. The weight and PRL level of the anterior pituitary increased in both sexes throughout the lactational stage, but the levels in female rats at 20 days of age were significantly greater than those of male rats. Serum PRL concentration remained at low levels except on Day 0. The present results demonstrate that the development of PRL-containing cells in postnatal rats during the lactational period is activated with two distinct stages, at term to Day 4 and after Day 12, and the development in the latter stage is involved with sexual dimorphism.

Expression of retinaldehyde dehydrogenase 1 in the anterior pituitary glands of adult rats

“…In the rat pituitary gland, the number of PRL-producing cells increases rapidly after P3 (Taniguchi et al 2001) or P4 (Yamamuro et al 1999). On the other hand, immunoreactivity for S-100 protein appears on P6 in the marginal layer cells and on P10 in the FS-cells, and the number of FS-cells increases thereafter (Shirasawa et al 1983).…”

Landmarks in the development of the female reproductive system

“…Gonadotropes acquire the capacity to respond to the stimulatory action of estradiol on LH and FSH secretion probably after menarche (Dierschke et al, 1974;Reiter et al, 1974;Presl et al, 1976; Yamamuro et al, 1999) but prolactin levels remain low until the prepubertal period Natagani et al, 2000).…”

“…Prolactin has a luteotropic role in rats. The prolactin content and prolactin-containing cells of the anterior pituitary increase with postnatal age (Watanobe and Takebe, 1987;Yamamuro et al, 1999) but prolactin levels remain low until the prepubertal period Natagani et al, 2000). Prolactin is not luteotropic in monkeys or humans .…”

Triiodothyronine Expands the Lactotroph and Maintains the Lactosomatotroph Population, Whereas Thyrotrophin‐Releasing Hormone Augments Thyrotroph Abundance in Aggregate Cell Cultures of Postnatal Rat Pituitary Gland

“…All hormonal cell types in the rat are present at E16–18 but their number is still relatively low, being only approximately 20% of the cells at E18 (7). The absolute and proportional number of differentiated cells rapidly increases thereafter with rates different according to cell type and age (8), but knowledge about the mechanisms underlying these phases of development and growth are limited. There are estimates that, during late‐foetal and early postnatal periods, up to one‐third of the hormonal cells are produced by mitosis of already differentiated cells (9–13).…”