Several authors have recognized the regional distinctiveness of cellular types in the fowl pars distalis (see review Mikami, 1958). Recently Mikami (1958) and Brasch & Betz (1971) have attempted to correlate hormone content with cell types in the chicken. Mikami (1958) divided the pars distalis into a cephalic and a caudal portion and assayed thyroid-stimulating hormone (TSH) in day-old chicks by thyroid gland weight and cell height. The cephalic lobes produced considerably heavier thyroids in the chicks whether one or two cephalic lobes were used as opposed to chicks injected with caudal lobes. Cell height showed less distinct contrasts. Brasch & Betz (1971) transplanted cephalic, middle or caudal portions of the pars distalis on to the chorioallantoic membrane of 10-day-old partially decapitated embryos. Bioassay for TSH was based on the amount of thyroidal colloid present and the height of the thyroid epithelial cells. The cephalic and middle pars distalis transplants
W. J. RADKE and R. B. CHIASSON
R. J. Kemppainen and J. L. Sartin
Beagle dogs were given saline, insulin or the dopamine antagonist, haloperidol, to examine peripheral concentrations of immunoreactive (ir)-pro-opiomelanocortin (POMC) peptides resulting from pars distalis or pars intermedia stimulation. Six beagles were given each test substance on separate occasions with and without dexamethasone pretreatment. Plasma was assayed directly for glucose, ir-ACTH, ir-α-MSH, cortisol and, after Sephadex G-50 Fine gel filtration chromatography, for ir-β-lipotrophin (ir-β-LPH) and ir-β-endorphin (ir-β-END) content. Injection of 0·5 units insulin/kg lowered (P < 0·001) plasma glucose from 4·9 ± 0·3 mmol/l (mean ± s.d., saline controls) to 2·3 ± 0·5 mmol/l, coincident with increasing ir-ACTH (9·5 ± 3·1 to 106 ± 54 pmol/l), cortisol (52 ± 27 to 221± 27 nmol/l), ir-β-LPH (not detectable to 34 ± 18 pmol/l) and ir-β-END (not detectable to 52 ± 22 pmol/l). Plasma ir-α-MSH concentrations were not affected by insulin. Pretreatment with dexamethasone abolished the ir-ACTH, cortisol, ir-β-LPH and ir-β-END increases in response to 0·75 units insulin/kg. Haloperidol (1 mg/kg) increased (P < 0·01) plasma ir-ACTH (to 103 ± 63 pmol/l), cortisol (to 243 ± 11 nmol/l), ir-β-LPH (to 16 ± 6 pmol/l), ir-β-END (to 136 ± 73 pmol/l) and additionally raised ir-α-MSH (7 ± 8 pmol/l in saline controls to 131 ± 80 pmol/l after haloperidol). Pretreatment with dexamethasone significantly (P < 0·01 ) reduced the plasma ir-ACTH (96%), cortisol (93%), ir-β-LPH (100%) and ir-β-END (55%) response to haloperidol, but the ir-α-MSH increase (117 ± 81 pmol/l) was not affected.
The pituitary distribution of ir-β-END-like peptides was determined in tissue obtained from one healthy mongrel dog. Following G-50 gel filtration chromatography of HCl extracts, 40% of the total immunoreactivity determined in an extract of pars distalis eluted near the position of human β-LPH while 60% eluted near human β-END(1–31). In contrast, over 95% of ir-β-END eluted near β-END(1–31) in the tissue extract prepared from the neurointermediate lobe.
From the in-vivo data, it appears that insulin-induced hypoglycaemia selectively activates POMC peptide secretion by the pars distalis in dogs and that this effect is totally suppressible by dexamethasone. In contrast, haloperidol appears to activate secretion of POMC peptide from both the pars distalis and pars intermedia. The dog pars distalis secretes a mixture of ir-β-LPH and ir-β-END while the pars intermedia preferentially secretes ir-β-END.
J. Endocr. (1988) 117, 91–96
M. O. Dada, G. T. Campbell and C. A. Blake
We analysed cell types in the pars distalis of normal young adult male and female rats with respect to their percentages and the relative volumes they occupy. In male rats the percentages of the cell types were: prolactin 49·80, GH 22·67, LH 5·04, FSH 4·22, ACTH 2·93 and TSH 2·09, The volume densities were: prolactin 20·48, GH 20·95, LH 7·34, FSH 6·73, ACTH 3·75 and TSH 3·19. In female rats the percentages of the cell types were: prolactin 52·40, GH 20·30, LH 5·89, FSH 4·06, ACTH 2·53, TSH 2·40 and the volume densities were: prolactin 28·09, GH 20·86, LH 8·11, FSH 5·46, ACTH 3·49 and TSH 2·91. The percentages of pars distalis cells which did not stain with the antisera to the six classical hormones were 17·47 in male and 16·48 in female rats.
The results suggest that (1) in both sexes the number (N) of prolactin cells > N of GH cells > N of gonadotrophs > N of TSH or ACTH cells, (2) the percentage of each cell type was similar in both sexes, (3) the volume density (Vv) of prolactin cells was greater than the Vv of GH cells in female but not in male rats and in both sexes the Vv of GH cells > the Vv of gonadotrophs > the Vv of TSH or ACTH cells, (4) in both sexes the volume (V) of prolactin cells < the V of GH cells < the V of gonadotrophs, the V of TSH cells or the V of ACTH cells, (5) the V of prolactin cells was greater in female than in male rats and (6) approximately 17% of the cells in the pars distalis of both sexes did not contain 'immunoreactive' prolactin, GH, LH, FSH, TSH or ACTH.
J. Endocr. (1984) 101, 87–94
R. N. SMITH
The innervation of the ferret's pituitary gland has been studied by means of a modification of Ranson's pyridine-silver technique.
Non-myelinated nerve fibres of characteristic appearance are present in the pars distalis. The number of these fibres is small, but their paucity may be accounted for by the varying depth of impregnation achieved. Structures resembling end-organs within the pars distalis are also described.
W. B. QUAY
Microperfusion of the tissue parenchyma of regions of the rat pituitary gland with 1:1 dilutions of India ink revealed a network of fine intercellular spaces or canaliculi throughout the pars distalis. They were demonstrable in animals of all ages from 1·5 months to over 1 year, in both sexes, and at various times during the 24 h light–darkness cycle. However, 24 h rhythms were suggested in the radial perfusion distance (P < 0·05) and tissue density (P < 0·01) of the perfused canaliculi in adult male rats. The amplitude of the 24 h rhythmicity in these pituitary canaliculi was lower than that shown recently in pineal canaliculi of the same species. Structural regularity and evidence of rhythmic and physiologically correlated changes in the pituitary canaliculi suggest that they relate to natural features rather than being only artifactual, and that analysis of their possible functional significance is appropriate.
S. PATHAK and A. FISK
Typical histological and ultrastructural changes that occur in the pars distalis of the rabbit pituitary after different periods of organ culture are described. The best technique for the maintenance of the maximum proportion of the explant was assessed by comparing cultures grown under different conditions. Explants in air with a medium buffered with N-2-hydroxyethylpiperazine-N 1-2-ethanesulphonic acid (HEPES), not previously used in organ culture, proved more satisfactory than explants in carbogen with bicarbonate-buffered 199, and cultures were maintained for more than 3 weeks.
The survival of cells was assessed on the basis of their cytological integrity; DNA- and RNA-fluorescence with acridine orange was a valuable indicator. Prolactin cells, which were few in uncultured controls, became the most common type of granular cell in long-term cultures.
Cell modifications during culture included the development of a peripheral epithelioid layer and the appearance of numerous microvilli. Microfibrils, coated or smooth vesicles, lytic bodies, desmosomes and intranuclear rods became more common and intranuclear rodlets (fibrous or membranous structures) were identified. Cells often became more electron dense during long-term culture.
Though there was an increase in the number of agranular cells during culture, identifiable granules were retained by many cells throughout culture.
L. I. AGUADO, A. R. GIMÉNEZ and E. M. RODRÍGUEZ
Laboratorio de Investigaciones Endócrino-Oncológicas, Instituto de Histología y Embriología, Facultad de Ciencias Médicas, U.N.C., 5.500 Mendoza, Argentina
(Received 16 August 1976)
The secretion of prolactin by the pars distalis transplanted at a site remote from the hypothalamus was first reported by Desclin (1950). This author observed the persistence of the ovarian corpora lutea in hypophysectomized, oestrogen-treated rats bearing a pars distalis graft under the kidney capsule. Everett (1954, 1956) confirmed Desclin's findings, but in addition demonstrated that liberation of prolactin from the pituitary gland graft occurred independently of oestrogen. Mühlbock & Boot (1959) found that transplanted hypophyses release prolactin continuously. Chen, Amenomori, Lu, Voogt & Meites (1970) have determined the serum prolactin concentrations, measured by radioimmunoassay, in hypophysectomized, ovariectomized rats with 1, 2 or 4 pars distalis grafts under the kidney capsule. Under these conditions the amount of prolactin released by the transplants was judged to be similar to that
J. A. M. VAN KEMENADE
Recently it was observed that in Rana temporaria interrenal activation was paralleled by a stimulation of both basophils type 3, located in the medio—rostro—ventral region of the distal lobe, and the caudal chromophobic cells (van Kemenade, 1969). Since chromophobes were identified as cells related to the different tinctorial cell types, and believed to be a stock of undifferentiated cells (Doerr-Schott, 1968), it was supposed that basophils type 3 were the source of corticotrophin (ACTH). For a more definite localization of the frog's corticotrophic function, basophils type 3 and caudal chromophobes were separated by dividing distal lobes into a rostral and a caudal half, each half then being tested for corticotrophic activity.
From 36 hibernating male frogs, pooled rostral and pooled caudal halves of the distal lobe were each homogenized in 18 ml distilled water, and stored at −20 °C. One week after operation, groups of pars distalis-ectomized frogs were injected
R. K. RASTOGI and G. CHIEFFI
Nucleic acid and protein were assayed in the hypothalamo-hypophysial system of adult Rana esculenta during the annual reproductive cycle.
Adult frogs, weighing 25–35 g, were used and six to seven monthly determinations were made. For each determination material (pars distalis (PD), hypothalamus and cerebral cortex) was collected from five frogs and each pool of material, homogenized in 4 ml cold acetate buffer at pH 5, was analysed in duplicate for RNA, DNA and protein as described earlier (Rastogi & Chieffi, 1972).
In both sexes PD weight, and RNA:DNA and protein:DNA ratios increased during the spawning period (April-June) and thereafter declined (Fig. 1). In fact PD cells accumulated increasing amounts of granules with the approach of spawning and degranulated during July-September (cf. Rastogi & Chieffi, 1970), the latter conforming with decreased PD weight and RNA: DNA and protein: DNA ratios (Fig. 1). The DNA concentration decreased with increasing PD weight and
R. K. RASTOGI and G. CHIEFFI
The protein, RNA and DNA content was measured in the pars distalis, hypothalamus and cerebral cortex of gonadectomized frogs (Rana esculenta) and compared with the levels in captive and in wild controls. Short-term (35 days) gonadectomy increased the weight of the pars distalis and also its RNA and protein content, whilst gonadectomy for a longer period (135 days, females only) depressed these parameters below control levels. In the hypothalamus, short-term gonadectomy increased the protein concentration, and long-term gonadectomy the RNA content. Captivity alone for 135 days caused a diminution in the weight and protein content of the pars distalis, although the various parameters showed an increase which correlated with the annual reproductive cycle. The DNA content (μg/mg tissue) of the pars distalis was similar in all groups suggesting that any weight changes were not due to changes in cell numbers. Neither gonadectomy nor captivity altered the nucleic acid and protein content of the cerebral cortex. The pars distalis weighed more in female frogs and contained more RNA and protein per mg.