Fine-structural heterogeneity and morphologic changes in rat pituitary prolactin cells after estrogen and testosterone treatment

Effects of Estradiol on Histological Parameters and Secretory Ability of Pituitary Mammotrophs in Ovariectomized Female Rats

Objective

Estrogen replacement therapy remains current as a therapeutic approach to treat menopausal symptoms and may significantly affect hormone-producing cells in the female pituitaries. The aim of this study was to examine the histological parameters of pituitary mammotrophs and prolactin secretion after chronic estradiol treatment in ovariectomized adult female rats, reflecting premature menopause.

Materials and Methods

In this experimental study, adult female Wistar rats were divided into non-ovariectomized (C), ovariectomized (OVX) and estradiol-treated ovariectomized (OVX+E) groups. Estradiol dipropionate [0.625 mg/kg body mass per day] was administered for four weeks, while the C and OVX groups received vehicle alone. Mammotrophs were identified by the peroxidase-antiperoxidase (PAP) immunohistochemical procedure, while prolactin concentrations were measured by the non-isotopic two-step assay (Delfia) method. Comparison of the differences between groups was performed using one-way analysis of variance (ANOVA) and Tukay (honest significant difference) HSD test.

Results

Ovariectomy caused significant (P<0.05) decreases in mammotroph optical density (OD), volume density (V_V) and number per mm² by 29, 27 and 34%, respectively, in comparison with the C females. In the OVX+E group, significant (P<0.05) increases in OD, cell volume, V_Vand number of mammotrophs per mm² by 181, 15%, 5.8-fold and 5.2-fold, respectively, were observed when compared to OVX animals. The serum prolactin concentration in OVX females was significantly (P<0.05) decreased by 14% in comparison to the C group, while in OVX+E females, prolactin levels were significantly (P<0.05) increased by 53% compared to the OVX controls.

Conclusion

Estradiol supplementation in ovariectomized females is followed by stimulatory histological and secretory changes of the mammotrophs. These results could serve as indicators of possible prolactinome development upon estradiol application in premature menopausal subjects.

In vitro immunoblockade of VIP inhibits the proliferation of pituitary prolactin cells

VIP is a peptide synthesised in the pituitary gland and is involved in the stimulation of prolactin secretion. However, to date it has not been determined whether VIP is able to regulate the proliferation of pituitary prolactin-producing cells, like other factors involved in the regulation of prolactin such as estradiol or dopamine. The aim of the present study was to address whether VIP is involved in regulating the proliferation of pituitary prolactin-secreting cells. Thus, we performed an in vitro study on monolayer cultures of rat pituitary cells, neutralising the possible paracrine effect of VIP by immunoblockade of the peptide and later determining the degree of proliferation of prolactin-secreting cells. The effects of immunoblockade were validated by determining the levels of VIP in the culture media, which were decreased (P < 0.01), and modifications in the patterns of the immunohistochemical reaction to prolactin-positive cells. Immunoblockade of VIP decreased the proliferation of pituitary prolactin-positive cells at all antibody concentrations analysed, mainly between 3 and 12 h (P < 0.01). Moreover, immunoblockade decreased the sizes of the cellular and nuclear areas, except at 1 h, at which point it only decreased the nuclear area of prolactin-positive cells. The results obtained suggest that-in the same way as it regulates the secretion of the hormone-VIP could be involved in regulating the proliferation of prolactin cells, like estradiol or dopamine.

D-aspartate localization in the rat pituitary gland and retina

Rat pituitary gland and retina were probed with anti-D-aspartate (D-Asp) antibody previously prepared in this laboratory [Lee et al., Biochem. Biophys. Res. Commun., 231 (1997) 505-508]. D-Asp immunoreactivity (IR) was observed only in the posterior lobe of the pituitary gland of 3-day-old rats, whereas the anterior and posterior lobes were also positive in 3-week and 6-week-old rats, respectively. In the anterior lobe, intense IR was scattered throughout the lobe and the D-Asp-positive cells appeared to be prolactin-containing cells or some other very closely related type of cell. In the retina, D-Asp IR was observed only in the ganglion cell and nerve fiber region of 3-day-old rats. In contrast, during the transient increase in D-Asp levels in 7-day-old rats, D-Asp IR was additionally evident in regions where differentiating bipolar cells had begun to make contact with other types of cells. The functional relevance of D-Asp localization in these tissues is discussed.

Changes in estrogen receptor expression and cell activity of lactotropes in female mink (Mustela vison) pituitary in response to variations in the gonadal steroid environment

This study was undertaken to get new information on the role played by estrogen (E) on the activity of mink lactotropes. Immunocytochemistry for estrogen receptor (ER) and prolactin (PRL) was applied to assess modifications in the protein production that occur as a result of in vivo changes in the gonadal steroid environment. Variations in the functional activity of lactotropes were demonstrated from the ultrastructural characteristics and morphometric parameters (cellular area, numerical density, and secretory granular size). The present study documents the presence of ER in mink lactotropes revealing the ability of E to regulate the expression of ER in the mink pituitary. Furthermore, all morphological and morphometric parameters of lactotropes activity appeared significantly increased in intact females, killed during the mating period, compared with castrated females under the same photoperiodic conditions. Castration thus blocks the stimulatory effect of photoperiod on metabolic activity of mink lactotropes suggesting that E may participate in the photoperiodic regulation of PRL.

Differential effects of estrogen and prolactin on autoimmune disease in the NZB/NZW F1 mouse model of systemic lupus erythematosus

Estrogen and prolactin have been shown to modulate autoimmunity in the NZB/NZW F1 (B/W) mouse model of systemic lupus erythematosus (SLE). However, estrogen stimulates prolactin secretion. The goal of this study was to examine differential effects of estrogen and prolactin in the female B/W mouse model of SLE. B/W females were manipulated to create combinations of low and high concentrations of serum estrogen and prolactin. Hyperprolactinemic mice with either low or high serum estrogen levels had accelerated development of albuminuria at 24 and 32 weeks of age compared to normal and hypoprolatinemic mice. High estrogen/high prolactin mice also had a higher percentage of anti-DNA antibodies compared to mice in the low estrogen/low prolactin and the high estrogen/low prolactin groups. IgG levels were not significantly different between groups. Mean survival was shortest in the high estrogen/high prolactin group (34+/-1.0 weeks) and longest in the high estrogen/low prolactin group (42+/-1.2 weeks; P < 0.05). High levels of serum estrogen were associated with depressed in vitro lymphoproliferation and IL-2 production. This study suggests that high prolactin levels in either high or low serum estrogen states are associated with accelerated autoimmunity in the B/W mouse. This study further demonstrates that high estrogen levels do not accelerate murine SLE when the prolactin-stimulating property of estrogen is suppressed by bromocriptine. Further investigation of hormonal interactions in autoimmunity will provide a better understanding of hormonal immunoregulation and, perhaps, lead to improved clinical application of hormonal immunomodulation.

Ultrastructural and immunocytochemical studies of prolactin-secreting cells in adenohypophysis of the mink (Mustela vison)

This investigation aimed to identify, by the double immunogold procedure, the ultrastructural characteristics of prolactin (PRL) cells in the mink. Such cells showed a marked pleomorphism and had a close topographic relationship with growth hormone cells. A common morphological characteristic of PRL cells in all stages of mink development was the presence of round secretory granules, in contrast to changes in the ultrastructural characteristics of PRL cells with physiological state and photoperiod. Thus PRL cells in prepubertal, pubertal, and sexually inactive adult mink, killed under a short-day photoperiod, showed little development of the organelles but a significantly increased cytoplasmic electron density. In sexually active mink and in lactating females under long-day conditions, PRL cells had a highly developed cytoplasmic organelle structure consisting mainly of rough endoplasmic reticulum. The morphometric study demonstrated that the mean diameter of the secretory granules similarly varied in both sexes. Pubertal mink had PRL cells with smaller secretory granules (female 74.1 +/- 0.6 nm, male 80.4 +/- 1.7 nm), whereas adult mink killed under a long-day photoperiod presented PRL cells with larger secretory granules (female 194.5 +/- 2.2 nm, male 203.3 +/- 1.7 nm). The changes in the ultrastructural characteristics of PRL cells during the annual cycle suggest a photoperiodic influence upon these cells. In addition the heterogeneity in ultrastructural characteristics and storage characteristics of PRL in some adult mink may suggest a varying metabolic role for PRL under certain, as yet not fully characterized, conditions.

Possible involvement of folliculo-stellate cells in the differentiation of muscle fibers during monolayer culture of pituitary cells

A major objective of the present study was to examine the possibility that non-granular folliculo-stellate (FS) cells in the rat anterior pituitary are involved in the myogenesis that occurs during pituitary cell culture. Enzymatically dissociated anterior pituitary cells were fractionated by use of the Percoll gradient method. The proportion of FS cells was 5.8% on average before cell fractionation. After employing the Percoll gradient procedure, FS cells were enriched to a ratio of 12.2%. Three of five cell fractions were separately cultured, and the incidence of striated muscle fibers was quantitatively investigated. There was a good correlation between the numbers of muscle fibers and the proportions of FS cells in the fractions obtained from the Percoll gradient. These results suggest that FS cells are the cells that transform into striated muscles in pituitary monolayer cultures.

Different ultrastructural localization of VIP and prolactin in anterior pituitary cells of rats chronically treated with estrogen

In the present study we investigated the effect of a long-term estrogen treatment on the intracellular distribution of VIP immunoreactivity in pituitary prolactin cells using double-labeling immunocytochemistry. With the use of pre-embedding ABC method it was found that VIP immunoreactivity was associated with the outer surface of membrane-bound organelles, and was not found in secretory granules. However, prolactin immunoreactivity demonstrated by postembedding immunogold technique was mainly associated within the secretory granules of the same cells. The discrepancy between our and Hsu et al.'s results (1989), who observed VIP immunoreactivity in secretory granules of human anterior pituitary cells, may be owing to the overstimulation of VIP cells by estrogen. It is possible that estrogen treatment depleted the VIP content of the secretory granules and enhanced the cytosolic VIP. The appearance of an alternative form of VIP in estrogen-treated rats with preferential distribution in the cytosol cannot be excluded.

Development and heterogeneity of prolactin cells

Prolactin (PRL) is synthesized in pituitary cells called mammotrophs (PRL cells). Ample evidence demonstrates that the PRL cell population consists of structurally and functionally heterogeneous PRL cells. Multiple variants of PRL molecules are found in various species. Prolactin cells may be divided into various subtypes in the rat and mouse. Secretory activities differ among the PRL cell population. These heterogeneities may reflect various phases of the maturation process of PRL cells, or the integrated outcome of various functional differences in PRL cells. To clarify the significance of heterogeneities among PRL cells, we present updated reports on the differentiation, proliferation, and development of PRL cells, and discuss factors responsible for the functional differences in PRL cell population. The age-related alteration in PRL secretion in the rat is summarized, because it is one of the most important aspects of the developmental changes in PRL cells. A mammosomatotroph, which secretes growth hormone and PRL, is found in various species. Prolactin cells and somatotrophs are derived from the same lineage. The possible relationship among PRL cells, somatotrophs, and mammosomatotrophs is discussed.

Distribution of lactotroph subpopulations in different regions of the rat pituitary

In this study, we examined the distribution of lactotrophs in different regions of pituitaries of ovariectomized (OVX) rats either untreated or treated with estradiol, progesterone or a combination of estradiol and progesterone. Anterior pituitaries were cut into inner and outer zones. Each of these regions was enzymatically dispersed and the resulting cells subjected to density sedimentation through a discontinuous Percoll gradient. The light and heavy cell subpopulations obtained were compared with cells not subjected to Percoll (unseparated cells). Cell numbers were determined and prolactin positive cells were assessed by immunocytochemistry. In OVX rats, the percentage of lactotrophs in the unseparated cell fraction of the outer zone was significantly (P < 0.05) lower than that in the inner zone. Estradiol increased the percentage of PRL cells in all cell populations, but the effect on inner zone light cells was significantly less than on any other type of cells. Progesterone given alone did not affect the percentage of lactotrophs in pituitary compared to untreated OVX rats nor did it alter the effects of estradiol. When the number of lactotrophs was calculated, the unseparated cells of inner and outer zone were equivalent except in the untreated OVX group where there was a significantly greater number of lactotrophs in the outer zone. In untreated OVX rats there was an equal distribution of lactotrophs between light and heavy cells in both inner and outer zones. Estradiol significantly increased the number of PRL cells in both zones and the effect was greater in the heavy cell fractions especially in the outer zone. In contrast, progesterone decreased the number of PRL positive cells in both zones and across cell types, but this effect was most pronounced in the outer zone. Progesterone also decreased the total pituitary cell number and this effect was greater than could be accounted for by the decrease in lactotroph numbers. We conclude that, except in untreated OVX rats, the numbers of lactotrophs in inner and outer zones are similar. The results also indicate that estradiol and progesterone can significantly alter the proportion and/or numbers of PRL positive cells within pituitary zones and may also affect cells that are not identified as PRL positive.

Morphofunctional study on prolactin-producing cells of the anterior pituitaries in adult male rats following thyroidectomy, thyroxine treatment and/or thyrotropin-releasing hormone treatment

An immunoelectron-microscopic and morphometric study was carried out on the anterior pituitary prolactin (PRL) cells of adult male Wistar rats treated with a combination of thyroidectomy and administration of L-thyroxine (T4) and/or synthetic thyrotropin-releasing hormone (TRH) in order to clarify the effects of changes in the hypothalamus-pituitary-thyroid axis on the ultrastructure and function of PRL cells. After thyroidectomy, PRL cells underwent atrophy and hypofunction of their cell organelles, but these changes tended to be restored to their normal level by T4 treatment. On the other hand, the administration of TRH to intact rats produced hypertrophy and hyperfunction in the PRL cells, although this treatment had no effect on the PRL cells of thyroidectomized rats. However, treatment with a combination of T4 and TRH had a strong effect and led to hypertrophy and hyperfunction in the PRL cells of thyroidectomized rats. Serum and pituitary PRL levels were measured by radioimmunoassay (RIA) for a comparison with the morphological results. They correlated well with the morphological changes. These results indicate that TRH stimulates PRL secretion in the presence of thyroid hormone, and that the thyroid hormone plays an important role in the basic maintenance of PRL cell function and its reactivity to TRH.

Measurement of prolactin release and cytosolic calcium in estradiol-primed lactotrophs

We have developed a perifusion system that can measure both changes of cytosolic free calcium concentration [Ca2+]i and prolactin release simultaneously from cultured lactotrophs. This model incorporated a commonly-used perifusion system to a spectrofluorometer. Indo-1 loaded cells were injected into Sephadex G-150 matrix in the cuvette at a site where the emitting light of the fluorometer projects. During perifusion periods, the perifusate was collected in a fraction collector, while optical density of the emitting light at 405 nm was recorded. The [Ca2+]i was calculated based on an ionomycin and Mn2+ quenching technique. As expected, TRH (1 mumol/l) stimulated prolactin release from cultured lactotrophs in this system. We further observed that prolactin releases as induced by TRH and ionomycin were not proportional with changes of the [Ca2+]i, suggesting that changes of [Ca2+]i is not the sole final pathway of intracellular transduction systems for prolactin release.

Absence of direct regulation of prolactin cells by estradiol-17 beta in rainbow trout (Oncorhynchus mykiss)

The effects of estradiol-17 beta (E2) implants on plasma prolactin (PRL) concentrations, pituitary PRL content and pituitary PRL mRNA levels were examined in rainbow trout (Oncorhynchus mykiss). Intact immature fish treated with 1 mg estradiol-17 beta did not show significant changes in both PRL mRNA levels and pituitary PRL content after 3 days of treatment. In a similar experiment, no changes were observed in plasma PRL levels followed during 7 days. Similarly, lack of estradiol-17 beta effect on plasma PRL levels and on final PRL pituitary content was observed in ovariectomized female rainbow trout treated during 48 days with 25 mg estradiol-17 beta and in mature male fish over a 3-week treatment period. Localization of estradiol receptor (ER) mRNAs in the pituitary was carried out by Northern blot analysis using a full-length rainbow trout estrogen receptor (rtER) cDNA as a probe. The rostral pars distalis of the pituitary which contained mostly PRL cells showed the lower amount of rtER mRNA when compared to other parts of the pituitary. Moreover, two mRNAs of different size (3.5 and 1.4 kb) were detected in different parts of the pituitary. Further hybridization experiments using probes containing part of the rtER cDNA (E domain or C and D domains) indicated that the small-sized mRNA (1.4 kb) probably encodes a truncated ER protein lacking hormone binding domain or an ER-related protein. Thus, only the 3.56 kb mRNA appeared to be involved in the regulation of pituitary function by estradiol. In situ hybridization analysis allowed a more precise localization of this rtER mRNA in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of the mammotroph Golgi complex by the dopamine agonist 2 Br-alpha-ergocryptine (CB-154) in ovariectomized estrogen primed rats

The present study examined the acute effects of 2 Br-alpha-ergocryptine (CB-154, a dopamine agonist) on mammotroph organelles during prolactin (PRL) suppression. Ovariectomized estrogen-primed rats received a single injection (sc) of 0.5 mg CB-154 and the animals were killed at intervals following injection. The anterior pituitary glands were fixed for electron microscopy and immunocytochemistry was used to confirm mammotroph identification. Serum PRL levels were determined by RIA. Following CB-154 administration, serum PRL was significantly (P less than 0.05) reduced within 15 minutes and was suppressed (P less than 0.01) to ovariectomized levels at 2 and 6 hours. A stereological analysis of mammotrophs in the central regions of the anterior pituitary showed that the Golgi complex volume was significantly (P less than 0.05) reduced at 2 hours after CB-154 treatment. However, the Golgi complex volume had recovered by 6 hours post CB-154 injection. In addition, the volumes of the mammotroph cells, the mature secretory granules, and the secondary lysosomes had significantly increased by 6 hours. There were no significant changes in any of the organelles following CB-154 in the mammotrophs from the peripheral regions of the gland. These studies show that the Golgi complex is especially susceptible to acute morphological changes induced by bromocryptine and that the mammotrophs in the central regions are more responsive to CB-154 than those in the peripheral regions.

Fetal development and regulation of pituitary cell types

The ontogenesis of the pituitary gland is considered from anatomical and functional points of view. Embryogenesis of the hypothalamo-pituitary unit involving development of the hypothalamo-hypophyseal portal system is complete during early life as shown in several mammalian species. The ultrastructural characteristics of the different cell types during development are described according to observations made by using immunochemical techniques. The patterns of differentiation of the cell types are reviewed according to studies of pituitary glands from human anencephalic fetuses and encephalectomized rat fetuses as well as in vitro studies of cultured pituitary primordia in synthetic media. The maturation of the neuroendocrine mechanisms controlling the secretion of fetal hormones is also analyzed. During fetal life, the factors implicated in the regulation of pituitary hormone secretion are generally the same as in adults, but the intensity of the response of pituitary cells to their action is variable according to the species, thus reflecting an immaturity in the functioning of certain cell types.

Ultrastructural immunocytochemistry of the adenohypophysis in the rat: a review

Immunocytochemistry has made great strides in the morphology of endocrine glands, especially the adenohypophysis, because the localization of hormones can be clearly demonstrated by this method in the microscopic preparations both for light and electron microscopy. In the adenohypophysis, electron microscopic immunocytochemistry is useful for identifying the producer cell of each hormone. The second contribution is its application to the cell biology of secretion mechanisms. The pituitary hormones, their precursors, derivatives, and fragments were artificially synthesized and their antibodies were produced. Using these antibodies the intracellular sites of synthesis, condensation, processing, and sorting were studied under the electron microscope. The ultrastructure of each cell organelle and its alteration due to the changing function was studied. It was proved that the intracisternal granules in the thyroidectomy cells contain thyroid-stimulating hormone (TSH). The trans-Golgi network or GERL contains a peculiar supporting structure, intracisternal skeleton. Transport of secretory granules may be performed in relation to the microtubules, actin, and some related substances. The most frequently observed mode of hormone release in the adenohypophysis is exocytosis. Sometimes multigranular exocytosis occurs. Vesiculation of membrane around the secretory granules often occur inward or outward. The inward vesiculation forms pinocytotic vesicles, through which the membrane material may be retrieved. The outward vesiculation forms vesicle-like fragments of cytoplasm being discarded to the extracellular space. By these mechanisms the surface area of the cell is maintained constantly.

Effects of drugs on pituitary fine structure in laboratory animals

Although an increasing number of chemicals are reported to affect endocrine glands, only a few studies are dealing with their toxic effect on pituitary. The drugs can induce lesions acting directly on endocrine cells or indirectly by interfering with the regulation of their endocrine activities. Some drugs stimulate pituitary cell proliferation leading to hyperplasia and tumor formation; other chemicals have an inhibitory effect on adenohypophysial cells; and only one drug, hexadimethrine bromide, has been found to induce pituitary necrosis. Although complex toxicologic studies have been carried out on many chemicals, the mechanism of action of most drugs is not completely elucidated and further studies are necessary to establish structure function correlations.

The effect of chronic apomorphine treatment on the ultrastructure of the prolactin cells and on plasma prolactin levels in young and aged male Wistar rats

Effects of two doses of apomorphine on the plasma prolactin (PRL) levels and on the ultrastructure of PRL cells in young and aged male Wistar rats were investigated. In young and aged control rats no significant differences were found between the plasma PRL levels. Immunocytochemical staining with anti-r-PRL revealed significant differences between young and aged control rats; in young rats the number of PRL cells with polymorphic granules exceeded the number of cells with round granules, whereas in aged rats almost exclusively cells with round granules were found. In young rats, chronic treatment with a low dose (0.01 mg/kg/day) of apomorphine did not result in a significant change in plasma PRL level or cell morphology. However, high dose (0.25 mg/kg/day) of apomorphine resulted in a significant decrease in plasma PRL levels, a decrease of number of cells with polymorphic granules and an increase of cells with round granules. The occurrence of PRL cells with round granules and plasma levels was negatively correlated. In aged rats, apomorphine (0.01 or 0.25 mg/kg/day) treatment did not affect plasma levels nor did it affect the distribution of the cell types. We conclude that in young rats PRL cells are sensitive to apomorphine and that their ultrastructure reflects a phase of the secretory cycle. In aged rats, the cells appear to have lost their sensitivity to apomorphine. The fact, that the distribution over the different cell types in control aged rats is similar to that of the apomorphine-treated young rats, suggests a strong influence of endogenous dopamine on PRL cell physiology in the aged rat.

Morphofunctional study of mammotropic cells following intraventricular administration of met-enkephalin

An ultrastructural and morphometric study was carried out on the adenohypophyseal mammotropic cells of rats treated intraventricularly with an acute dose (150 micrograms) of Met-enkephalin. In the female rats, clear features of cellular hyperactivity appeared after opioid administration. The changes affected the Golgi complex, the rough endoplasmic reticulum, the mature and immature secretory granules and the images of exocytosis. Such changes did not appear when naloxone was administered before the opioid, and naloxone induced an increase in the numerical density of lysosomal dense bodies with lipoid inclusions. In the male animals, administration of an identical dose of Met-enkephalin caused only a few significant changes, similar to those observed in the controls. It is concluded that Met-enkephalin administered intraventricularly causes evident modifications in the mammotropic cells of female rats whereas such changes in the male animals are not significant.

Inhibitory effect of cabergoline on the development of estrogen-induced prolactin-secreting adenomas of the pituitary

Cabergoline 1-[(6-allylergolin-8 beta-yl)carbonyl]-1-[3-(dimethylamino) propyl]-3-ethylurea is a recently developed ergot derivative with a long-lasting dopamine agonist action. We now studied the ability of cabergoline to counteract the development of a prolactin-secreting tumor (prolactinoma) induced in female rats by long-term administration of high doses of estrogens. The effect of cabergoline was compared to that of bromocriptine. Cabergoline (0.6 mg/kg p.o.) had a marked and sustained prolactin-lowering effect in freely moving female rats, its effect still being present 3 days after a single dose. Bromocriptine, at a dose 5-fold higher (3 mg/kg s.c.), induced a strong and short-lasting prolactin inhibitory effect which, however, had completely disappeared 24 h post-injection. Intermittent administration of cabergoline (0.6 mg/kg p.o. every 3 days), starting from the first day of estrogen treatment, completely counteracted the development of the prolactinoma, as judged by the weight of the pituitary and the stimulating effect of estrogens on plasma prolactin and mitotic rate and DNA synthesis of pituitary cells. These effects of cabergoline were shared by a 5-fold higher dose of bromocriptine (3 mg/kg s.c.) given daily. The potent anti-tumorigenic effect of cabergoline, coupled to a sustained prolactin-lowering effect, the most prolonged ever seen with an ergot derivative, makes cabergoline a most suitable drug for the treatment of human macroprolactinomas.

Immuno-electron-microscopic study of the prolactin cells in the pituitary gland of male Wistar rats during aging

Prolactin cells were identified by means of immunocytochemistry with protein-A gold as a marker on ultrathin sections of the pituitary gland of young (3-4 months), middle-aged (16-19 months), and aged (26-30 months) male Wistar rats. Point-counting volumetry revealed that the prolactin (PRL) cell-volume density in middle-aged rats was significantly increased in comparison to the volume densities in young and aged rats. Within the PRL-cell population, four types of PRL cells were distinguished on the basis of the shape and size of their secretory granules. During aging, dramatic changes occurred in the relative volumes of the four cell types. The volume percentage of cells with round granules (type I, granule diameter 150-250 nm, and type IIA, granule diameter 250-350 nm) increased from +/- 30% in young rats to +/- 90% in old rats. The volume percentage of cells with round and polymorphic granules (type IIB; granule diameter 350-400 nm and type III; granule diameter 500-600 nm) decreased from +/- 70% in young rats to +/- 7% in old rats. Age-related changes in serum PRL levels were not found. It is concluded that although during the life span of the male Wistar rat considerable changes in PRL-cell volume densities and in the ratios of PRL-cell types occur serum, PRL levels remain more or less constant.

Uptake and retention of 3H-estradiol by gonadotrophs and lactotrophs in the pituitary glands of the guinea pig, hamster and gerbil

Nuclear uptake and retention of 3H-estradiol by luteinizing hormone (LH) and prolactin (PRL) cells was examined in three species of rodents (guinea pigs, hamsters and gerbils) using the combined techniques of immunocytochemistry and autoradiography. Castrated animals were injected with 3H-estradiol and decapitated 1.5 h later. The pituitary glands were processed for thaw-mount autoradiography followed by conventional immunocytochemical staining for LH and PRL. 3H-estradiol accumulated in more than 80% of the anterior pituitary cells in the gerbils, while only 33 and 22% of the cells accumulated 3H-estradiol in the hamsters and guinea pigs, respectively. A varying percentage of immunoreactive LH and PRL cells in all three species were found also to contain binding sites for estradiol. Some LH and PRL cells in hamsters and guinea pigs and only some in PRL cells of gerbils were found to be devoid of grains. Quantitative analysis revealed that the number of grains per nucleus differed considerably from cell to cell. LH cells of guinea pigs accumulated much larger amounts of 3H-estradiol than did the PRL cells, while the LH cells in the hamsters and gerbils accumulated only slightly more 3H-estradiol than the PRL cells. These results confirm the previous observations in rats and baboons that demonstrated tremendous species differences in percentage of cells in the anterior pituitary gland that accumulated 3H-estradiol. Also, these data suggest that there are functionally heterogeneous cell types among the LH and PRL cells in hamsters, guinea pigs and gerbils as has been previously demonstrated in rats and baboons.

Prolactin cells of female rats treated with the carcinogen 7,12-dimethylbenz(A) anthracene (DMBA) in vivo. An ultrastructural study

Pituitary prolactin (PRL) cell microadenomata developed in females of a strain of Sprague-Dawley rats (SD1) following intragastric treatment with the carcinogenic hydrocarbon 7,12-dimethylbenz(a) anthracene (DMBA). Similar treatment of another strain of Sprague-Dawley rats (SD2) resulted in mammary tumour development but no PRL cell microadenomata. In SD1 strain rats morphologically distinct populations of PRL cells appeared after DMBA treatment, one composed of cells characterised by abundant, organised but very dilated RER and with large hormone storage granules, 500-600 nm in diameter (P1). The other cell type had electron-dense cytoplasm, narrow organised arrays of RER and moderately large, pleomorphic granules (P2). Both cell types appeared active with large Golgi and prominent nucleoli. P2 cells were most numerous 2 months after DMBA treatment but had virtually disappeared at 6 months and microadenomata were common at 8 months. PRL cells of SD2 rats were uniform in morphology, characterised by only moderate accumulations of RER, pleomorphic hormone storage granules, large Golgi and prominent nucleoli, and showed no close resemblance to either P1 or P2 cells of SD1 strain rats. It is possible that the morphological variations which developed in SD1 PRL cells may represent changes in responsiveness to factors controlling PRL cell secretion and proliferation and which may be pertinent to microadenoma development.

Estradiol induces a shift in cultured cells that release prolactin or growth hormone

The process by which estradiol induces an increase in the percentage of prolactin cells in the rat pituitary requires clarification. In this study the effect of estradiol treatment on growth hormone and prolactin cells in monolayer cultures of male rat pituitaries was assessed by use of reverse hemolytic plaque assays. Treatment of cultures with 17 beta-estradiol (10 nM) for 6 days elevated significantly (P less than 0.01) the percentage of all cells in culture that released prolactin without affecting the percentage of growth hormone secretors. However, by sequentially assaying single cells for growth hormone and prolactin, we found that estradiol caused a marked increase (P less than 0.01) in the proportion of individual cells that released both growth hormone and prolactin and a commensurate decrease in the proportion that released growth hormone alone. These results demonstrate that estradiol acts directly on cultures of male pituitary cells to shift the proportions of cells that released growth hormone, prolactin, or both hormones and indicate that estradiol may convert cells that release only growth hormone to those that release both growth hormone and prolactin.