PRL and GH cells in the adenohypophysis of adult mice were studied with immunohistochemistry and stereological morphometry by light and electron microscopy. We compared findings for males and females. In female mice, most PRL-immunoreactive cells (43% of all parenchymal cells) and most GH-immunoreactive cells (33% of all parenchymal cells) were classical PRL cells (type I PRL cells) or GH cells (type I GH cells), respectively. Besides these classical types of cells, we found PRL- and GH-immunoreactive (type II PRL and GH) cells that contained small (approximately 100-200 nm in diameter) and round secretory granules. However, in female mice type II PRL or GH cells accounted for less than 3% of all parenchymal cells, as was also true for type II GH cells in the males. The percentages of type I and type II PRL cells in male mice were about the same (approximately 10% of all parenchymal cells). Only a few mammosomatotropes (0-0.6% of all parenchymal cells) were found in the mouse adenohypophysis of either sex. All mammosomatotropes were type II cells; none were PRL or GH cells of the classical type. This immunohistochemical study confirmed our previous findings by conventional electron microscopy that there are marked sex differences in the proportions of PRL and GH cells in the adult mouse adenohypophysis; PRL cells are more abundant in the female mice, and GH cells are more abundant in the males.

Epithelial cell proliferation and apoptosis during morphogenesis of the murine palatal rugae (PR) were examined histochemically by using anti-bromodeoxyuridine (BrdU) and the terminal deoxynucleotidyl transferase-mediated UTP nick-end-labelling (TUNEL) technique. Formation of the PR rudiment was observed as an epithelial placode in fetuses at 12.5 days post-coitus (dpc). During the PR formation, BrdU-positive cells were detected mainly in the epithelium of the interplacode and interprotruding areas in fetuses administered BrdU maternally at 2 h before killing. TUNEL-positive cells were detected only at the epithelial placode area in 12.5-14.5 dpc. At 16.5-18.5 dpc, the BrdU-positive cells were decreased in number in the epithelial cells at the interprotruding area of the PR. Only a few TUNEL-positive cells were observed in the protruding area of the PR at 16.5 dpc. These results suggest that cell proliferation and apoptosis in the palatal epithelium are involved spatiotemporally in the murine PR morphogenesis.

Adult female mice of the DDY/S strain were used to study the distribution of PRL or GH cells and the vasculature of the anterior pituitary lobe. Electron microscopy was used to quantify PRL or GH cells in horizontal sections. Most parenchymal cells were either PRL or GH cells, and both types of cells were present in all regions. The densities of PRL cells in the rostral and caudal areas were significantly greater than that of GH cells. The density of GH cells was greater in the anterolateral wings. Thus, the spatial differences in concentrations of PRL and GH cells were reversed. The vasculature was studied with scanning electron microscopy of vascular casts and with stereoscopy of pituitary glands injected with India ink. The adenohypophysis was supplied by long and short portal vessels. The long portal vessels originated from the primary capillary plexus on the median eminence and the upper portion of the pituitary stalk, and they supplied rostral regions of the adenohypophysis. Most of the short portal vessels connected caudal areas of the anterior lobe with the posterior lobe, crossing the surface of the intermediate lobe. The blood in the short portal vessels may flow from the posterior lobe toward the anterior lobe. Thus, within the rostral and caudal areas, which are supplied by long and short portal vessels, respectively, PRL cells predominated; the anterolateral wings where GH cells predominated were far from these regions. These data suggest that the anatomical pattern of the blood supply may account in part for the spatial distribution of PRL and GH cells.

We have examined alterations in the hypothalamo-pituitary GH-somatic growth axis and the hypothalamo-pituitary LH-ovarian axis in a line of transgenic ICR mice expressing human GH (hGH) under the influence of the whey acid protein promoter. Transgenic female mice weighed twice as much as control females and were infertile. The size of the anterior pituitary (AP) was 1/3 that of the controls. In transgenic mice, acinar cells in the mammary and mandibular glands displayed hGH-immunoreactivity, and plasma hGH was detected by radioimmunoassay. In the medial basal hypothalamus (MBH) of transgenic females, the immunoreactive-GHRH level was decreased (P<0.01). There was a corresponding reduction in the number of GHRH-immunoreactive neurons in the arcuate nucleus (ARC) and in the immunostaining of GHRH nerve terminals in the median eminence. The level of somatostatin (SRIH) in the MBH was increased (P<0.05), and SRIH-immunoreactive neurons in the periventricular nucleus (PeV) were increased in size and number in transgenic mice. The MBH level of LHRH in transgenic animals was greater (P<0.01) than in controls, although there was no apparent difference in the number of LHRH-immunoreactive neurons or in LHRH level in the preoptic area. There are fewer SRIH- and LHRH-immunoreactive neurons in the ARC in transgenic mice. Cells in the AP for GH, PRL, and LH were fewer in transgenic mice. The ovary suffered disturbance of follicular development and of corpora lutea formation. These results demonstrate that chronic overproduction of hGH may profoundly affect the organization of the GHRH/SRIH-GH-somatic growth axis and the LHRH-LH-ovarian axis due to reduction of GHRH-, SRIH- and LHRH-neurons in the ARC and increase of SRIH-neurons in the PeV.