Severe experimental uraemia does not decrease the population of rat pituitary somatotrophs

BACKGROUND

Growth hormone (GH) secretion by the anterior pituitary has been shown to be depressed in severely uraemic rats. Changes in the population of pituitary somatotrophs might be partially responsible for this decrease.

METHODS

To analyse the population of pituitary somatotrophs in severe uraemia, immunocytochemical detection and quantification of GH-producing cells were carried out on paraffin sections from young rats either 5/6 nephrectomized, sham-operated fed ad libitum or sham-operated pair-fed with the nephrectomized animals.

RESULTS

Nephrectomized rats were severely uraemic and growth retarded. The overall cell density (total pituitary cells/mm2) was higher in 5/6 nephrectomized animals in comparison with the two sham-operated groups. Thus, although the percentage of GH cells was slightly lower in nephrectomized than in control rats, no difference in either the density (cells/mm2) or the cross-sectional area of GH cells was found among groups.

CONCLUSIONS

These results suggest that severe experimental uraemia interferes with the maturation process of the pituitary gland and support the contention that differences in either the number or the size of pituitary somatotrophs cannot explain the reduced GH secretion previously reported in severely uraemic rats.

Expression of argyrophilic nucleolar organizer regions (AgNORs) in the harderian gland of male and female hamsters during postnatal development

The expression of argyrophilic nucleolar organizer regions (AgNORs) was studied in the different secretory cell types of the Harderian gland of male and female Syrian hamsters during postnatal development. Mean AgNOR area was calculated for each cell type in paraffin sections from 7-, 14-, 21-, 28-, 45- and 90-day-old animals. AgNOR content was similar in male type I-cells and in female cells, decreasing in both cell types from the 7th to the 14th day, increasing afterwards at the 21st day, and remaining at relatively stable levels from that point to the end of the study. AgNOR content of male type II-cells was greater than in other cell type studied, and was greater in 45- and 90-day-old animals than in 28-day-olds. Changes of AgNOR content in type I-cells of male and female hamsters during the first two weeks seem to be related to changes in proliferative activity while metabolic activity might be responsible for changes taking place later on. Our results also support that male type I- and type II-cells have a different biological behaviour and that type II-cells are far from being degenerating cells.

Severe uremia depresses the ability of perifused rat pituitary cells to secrete growth hormone in response to growth hormone releasing hormone

To examine whether growth hormone (GH) secretion is impaired by chronic renal failure (CRF) and to gain some insight into the influence of uremia itself and associated malnutrition, the GH secretory response of dispersed anterior pituitary cells perifused with GH-releasing hormone (GHRH) was investigated in 5/6 nephrectomized (UREM, N = 15) and three groups (N = 15 each) of normal renal function, sham-operated rats under three different nutritional conditions: fed "ad libitum" (SAL), pair-fed with a diet similar to the UREM group (SPF), and pair-fed with a diet similar to the UREM group in terms of protein ingestion but calorically supplemented up to intake of SAL group (SPF+). Ten days after nephrectomy, UREM rats had severe CRF, as shown by much higher (P < 0.0001) serum urea nitrogen concentrations (X +/- mean +/- SE) than sham groups (59 +/- 6 versus 8 +/- 0, 9 +/- 0, and 5 +/- 0 mmol/L, respectively), and they were growth retarded, as shown by lower gains (P < 0.0001) in weight (13.5 +/- 2.5 versus 62 +/- 2.1, 20.5 +/- 1.9, and 50.4 +/- 1.0 g) and length (2.9 +/- 0.2 versus 5.8 +/- 0.1, 3.6 +/- 0.1, and 5.6 +/- 0.1 cm). Perifusion studies showed similar basal GH secretory rate (ng/min/10(7) cells) in the four groups. A fixed sequence of progressively increasing GHRH doses resulted in a lower overall mean GH secretion in UREM rats (15.8 +/- 1.6 ng/min/10(7) cells), as compared with SAL (50.8 +/- 9.0 ng/min/10(7) cells, P < 0.01), SPF (33.0 +/- 3.3 ng/min/10(7) cells, P < 0.05), and SPF+ (49.4 +/- 5.1 ng/min/10(7) cells, P < 0.01) groups. Analysis of dose-response curves showed that the maximal secretory response was produced by the same concentration of GHRH (10 nM) in the four groups and was lower (P < 0.01) in UREM than SAL and SPF+ rats (34.9 +/- 5.0 versus 115.7 +/- 28.4 and 98.9 +/- 9.8 ng/min/10(7) cells). The concentration of GHRH that caused the half of maximal effect was identical, close to 1 nM, in the four groups of animals. This study provides direct evidence that the ability of pituitary cells to secrete GH in response to GHRH is depressed in severe CRF. The lower secretory capacity of pituitary gland is only partly dependent on caloric malnutrition associated with CRF. Data of dose-response curves suggest that decreased GH secretion may be related to a lesser number of pituitary receptors for GHRH.

In vitro bromodeoxyuridine-labelling of single cell suspensions: effects of time and temperature of sample storage

The present study was aimed to explore how the in vitro BrdUrd-labelling of rat thymocytes might be affected by both the time elapsed between obtaining the sample and the beginning of the labelling (0, 15, 30 or 60 min) and the effect of the temperature of storage (4 degrees C versus room temperature). Single cell suspensions obtained after in vivo labelling with BrdUrd were used as controls. The S phase fraction was calculated by flow cytometry both according to BrdUrd-immunolabelling and DNA content. Immediate incubation with BrdUrd after the sample was obtained resulted in a slight decrease of the proportion of S phase cells analysed either according to DNA content or to BrdUrd-immunolabelling. Regardless of storage-temperature, the S phase fraction decreased in samples kept for 15 min or more before BrdUrd incubation. No BrdUrd-positive cells were detected in samples stored for 60 min at room temperature. This effect was related to temperature since positive cells were found when the samples were kept at 4 degrees C during the same time period. Our results suggest that during in vitro incubation a relative loss of S phase cells exists and that a delay beyond 15 min between obtaining the sample and the in vitro labelling seriously compromises the results of this technique.

In vivo bromodeoxyuridine (BrdU)-labelling index of rat thymus: influence of different BrdU doses and exposure times as analyzed both in tissue sections and in single cell suspensions

Tissue sections and single cell suspensions of rat thymus were analyzed by flow and image cytometry to study the effects of different doses of bromodeoxyuridine (BrdU) (10, 50 and 100 mg/kg and different labelling periods (15, 30 and 60 min) on the BrdU-labelling index. The proportions of BrdU-labelled cells, as analyzed by flow cytometry, were similar in the different groups of our study. However, the quality of the results was not exactly the same, since when the BrdU dose decreased, the separation between BrdU-positive S-phase cells and both the G0/G1 and the G2/M BrdU-negative cells on a DNA/BrdU histogram became less clear. On the other hand, the proportion of BrdU-labelled cells in tissue sections was greater in the groups of animals that received doses of 100 mg/kg and were killed 15, 30 or 60 min later than in the sections obtained from the remaining groups. Our results show that both dose and exposure time to BrdU may influence the final results when cell proliferation is assessed, the variations obtained clearly depending on the technique used for the immunological detection of BrdU-positive S-phase cells.

Influence of luteinizing hormone-releasing hormone (LHRH) treatment on cellular proliferation in the rat anterior pituitary

This study was designed to gain insight into the action of LHRH on the control of cellular proliferation in the anterior pituitary. The fraction of cells labelled with bromodeoxyuridine (S-phase cells) was studied in cytospin preparations of anterior pituitary cells taken from control male and female rats and from rats treated with daily doses of 2 micrograms/100 g body weight of LHRH (7 days), with doses of 40 micrograms of LHRH given on alternate days for 14 days (7 doses) or, finally, treated with daily doses of 50 ng of busereline acetate (14 days). Treatment with LHRH for 14 days resulted in a significant increase in the fraction of S-phase cells. However, neither the blockade of gonadotrophin secretion with busereline acetate nor its stimulation with LHRH for seven days resulted in a significant change in the proliferative activity of anterior pituitary cells. This action was independent of sex. No significant changes were seen in the proportions of pituitary gonadotrops of the different study groups. Regardless of the treatment-group very few cells doubly-immunostained for BrdU and LH were found. It is concluded that LHRH may stimulate cellular proliferation in the anterior pituitary, but further studies are needed to define which cells are involved in this action.

Evaluation of cellular proliferation in human biopsy samples of lymphoid tissue according to the expression of AgNORs

The proportions of cells with a high expression of AgNORs, as directly assessed under the light microscope, and those of Ki-67-immunoreactive cells were divided into three categories (low, < 25%; intermediate, 25-50%; high, > 50%) and compared to a series of 41 human biopsy samples of lymphoid tissue. Irrespective of histological features a strong correlation was found between both variables (contingency coefficient = 0.8; P < 0.001). It is concluded that direct evaluation of cells with a high expression of AgNORs may serve as an index of proliferative activity in biopsy samples of lymphoid tissue.

Cellular proliferation and/or differentiation can condition modifications in the expression of AgNORs in rat anterior pituitary cells during growth

The expression of argyrophilic nucleolar organizer regions (AgNORs) was studied in the anterior lobe of the hypophysis of 1-, 7-, 14-, 28- and 80-day-old rats. Mean area and numbers of AgNORs per nucleus decreased during this period with a simultaneous increase of both nuclear area and mean AgNOR-particle area. Comparison of our data on AgNOR expression with previously reported data on the proliferative activity and cell maturation and differentiation of anterior pituitary cells during a similar period led us to conclude that, at least in our experimental model, variations in the expression of AgNORs are more related to phenomena of cellular maturation than to proliferative activity.

Expression of silver-stained nucleolar organizer regions is coupled to cell cycle in rat thymic cells

To directly analyze the relationship between the expression of silver-stained nucleolar organizer regions (AgNORs) and cell proliferation, thymic cells from newborn rats were separately sorted at the G0-G1-phase and early-mid and late-mid S-phase of the cell cycle according to their DNA content. Different AgNOR-derived parameters (mean area and numbers of AgNORs per cell and mean AgNOR-particle area) were evaluated after silver staining of cytospins. A linear correlation was observed between the mean area and numbers of AgNORs per cell, both parameters increasing progressively from G0-G1-phase to early-mid and late-mid S-phase. An increase of the mean AgNOR-particle area was also seen between G0-G1 and S-phase but this was not significant along the S-phase. A bias on the selection of S-phase cells linked to intrathymic maturation can be ruled out as S-phase cells labeled with bromodeoxyuridine were found throughout the thymus, and, moreover, the analysis of the frequency distribution of nuclear area did not show a bimodal pattern. It is concluded that the expression of AgNORs--evaluated as AgNOR area/cell or AgNOR numbers/cell--is causally or indirectly coupled to DNA synthesis and, thus, AgNORs can be considered as a cell proliferation marker.

Proliferative activity of cells of the intermediate lobe of the rat pituitary during the postnatal period

Cellular proliferation was studied in the intermediate lobe (IL) of the pituitary gland of developing rats by labelling cells at the S-phase of the cell cycle with bromodeoxyuridine (BrdU). The number of BrdU-labelled cells in the IL decreased from birth until the 14th postnatal day and was low from that day until the end of the first month after birth. Throughout the postnatal period a large proportion of BrdU-labelled cells was found in the marginal layer (ML) of the IL, suggesting for the ML a role as a germinative layer of the IL during postnatal growth. Double immunostaining with anti-BrdU and anti-MSH showed that MSH cells actively proliferate as from the day of birth. Cells doubly immunostained with anti-BrdU and anti-S100 protein were first seen on the 14th postnatal day. From then onwards, most proliferating cells were labelled with either anti MSH or anti S-100 protein. This, together with the high proportion of proliferating cells found in the ML marks a clear difference with the pattern of cellular proliferation previously reported during a similar period in the anterior lobe of the rat pituitary.

Immunocytochemical study of the epithelial lining of naturally occurring cysts in the rat intermediate lobe

An immunocytochemical study of the epithelial lining of naturally occurring cysts in the rat intermediate lobe (IL) has been carried out. Paraffin-embedded sections, in which cysts were identifiable, were treated either with anti-serotonin or anti-S-100 protein sera. S-100-positive cells were intermingled with glandular cells surrounding the cyst lumen. These S-100-positive cells sent slender cytoplasmic processes as if to cover the apical surface of neighbouring cells. Rarely were 5-HT-immunopositive cells seen in the cyst epithelial lining. Most cells of the marginal layer of the IL were found reactive either to an S-100 or a-5-HT serum. The presence of an epithelial lining positive to S-100 protein sera is in keeping with the notion that cysts in the IL might form as evaginations of the epithelial lining of the pituitary cleft. The lack of correspondence between 5-HT-positive cells in the marginal layer and the cyst lining is controversial. A peculiar spatial relationship of 5-HT cells with the vascular network of the IL is suggested.

Serotonin immunoreactivity in the intermediate lobe of the rat pituitary

Immunocytochemical staining for serotonin (5-HT) in paraffin-embedded sections of rat pituitary resulted in the localization of reactive nerve fibres and cell bodies in the intermediate lobe. Immunostaining was also found in the anterior and posterior lobes. Labelled nerve fibres appear to enter the intermediate lobe from the neural lobe through the interlobular spaces. These fibres are relatively scarce and lightly stained. Neuroglandular contacts were identified between varicose nerve endings containing serotonin and immunoreactive perykarion. It is not clear whether intermediate lobe cells produced 5-HT themselves or, alternatively, these cells take in 5-HT from serotoninergic nerve terminals.

Circadian variation in the distribution of cells throughout the different phases of the cell cycle in the anterior pituitary gland of adult male rats as analysed by flow cytometry

Flow cytometric analysis of nuclei stained with propidium iodide (PI) has been used to study the distribution of cells throughout the different phases of the cell cycle in the anterior pituitary gland of adult male Sprague-Dawley rats at different times of the day. According to PI fluorescence intensity the relative numbers of cells in S phase (cells with a DNA content between that of somatic cells in interphase (2n) and that of somatic cells after duplication of the DNA prior to cell division (4n] and G2/M phase (4n) were calculated. A significant circadian rhythm was found for cells in both the S phase (P less than 0.05) and the G2/M phase (P less than 0.01). The wave of cells in S phase with a peak at the middle of the light period (14.00 h) precedes by about 6 h the wave of cells in G2/M phase (peak at 20.00 h). Most of the DNA-replicating cells were found during the early S phase at 11.00 h, advancing further up to the middle of this phase at 14.00 h. Cells were distributed homogeneously throughout the S phase at 17.00 h. These data strongly suggest that the beginning of the light period triggers a wave of cells to leave G0/G1 into S phase.

Cellular proliferation in the anterior pituitary of the rat during the postnatal period

Cellular proliferation in the anterior pituitary of 2-, 8-, 15- and 30-day-old rats was examined by injection of bromodeoxyuridine 1 h before autopsy. Bromodeoxyuridine incorporated into DNA was detected immunohistochemically by use of a monoclonal antibody. The highest rate of cell proliferation was found in 2-day-old animals; it decreased thereafter during the postnatal period. Possible toxic effects of colchicine on cellular proliferation were examined. Colchicine treatment (10 mg/kg in 8- and 30-day-old animals) significantly decreased the number of bromodeoxyuridine-labelled cells/mm2 in 8-day-old rats. Some sections were doubly immunostained for bromodeoxyuridine and various pituitary hormones. The proportion of doubly-immunostained cells to all proliferating cells was generally low, ranging from 23% at 2 days to 32% at 30 days of age.

[Distribution of the vascular network of the adenohypophysis of the rat]

From various experiments it has been suggested that the blood flow to the different parts of the adenohypophysis is not the same. By developing the peroxidase activity of the red and white blood cells we have obtained a satisfactory image of the distribution of the intrahypophysial vessels, which indicate that the organization and distribution of these vessels varies from one portion to another in the pars distalis. On the lateral portion of the gland vascular routes are irregular, whilst in the media zone they run in a sagittal plane. Between the above-mentioned portions, on either side of the edge of the pars intermedia, a rich vascular network extending along the dorsal limit, which is fed by the long portal vessels and by numerous smaller vessels from the ventral vascular chain of the pars intermedia and neural lobe, is observed.