Cytological changes in the mouse anterior pituitary after neonatal thymectomy: a light ane electron microscopical study

Lymphocyte subset pattern in acromegaly

Immune function in acromegalic patients has been poorly investigated. The aim of this study was to evaluate the main surface antigen clusters of circulating lymphocytes in acromegaly. One hundred patients with active acromegaly (55 women and 45 men, aged 20-70 yr) and 200 healthy subjects sex- and age-matched with the patients (110 women and 90 men, aged 20-70 yr) were enrolled in this study. All patients and controls were born and live in Southern Italy. No patient had received octreotide, bromocriptine or corticosteroids for at least 3 months before entering the study. The analysis of lymphocyte subset pattern was performed by flow cytometry and fluorescein isothiocyanate or phycoerythrin directly conjugated monoclonal antibodies specific for the cell surface antigen clusters (CD) representing T-cell population as a whole (CD3), T helpers (CD4), T suppressors (CD8), natural killer cells (CD16) and B-cell population as a whole (CD19). Acromegalics had significantly increased levels of CD3 (67.1+/-7.2 vs 64.3+/-8.8%; p=0.03) and CD4 (37.8+/-3.5 vs 36.4+/-4.3%; p=0.004) and decreased levels of CD8 (31.4+/-3.3 vs 33.7+/-8.2%; p<0.01) and CD19 (12.1+/-3.1 vs 15.2+/-5.1; p=0.01) without age-difference. The results of the current study demonstrate an increase in T-cell activity together with a decrease in B-cell activity in a very large series of patients with active acromegaly. These data further support the existence of abnormalities of the immune system in patients with chronic GH/IGF-1 excess.

Altered functional responses with preserved morphology of gonadotrophic cells in congenitally athymic mice

Neonatal thymectomy or congenital absence of the thymus induces severe reproductive deficiencies in female mice, which are associated with reduced levels of circulating and pituitary gonadotropins. In contrast, the reproductive function is well preserved in nude males. It was therefore of interest to assess gonadotrophic cell morphology and function in congenitally athymic male mice. Circulating gonadotropins were measured under basal and stressful conditions, taking as a reference their haired counterparts. Adult normal (+/+), heterozygous nude (nu/+), and homozygous (nu/nu) CD-1 mice were subjected to 1-h immobilization stress. Serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were assessed by RIA at 0, 30, and 60 min poststress. Athymic animals showed significantly lower basal levels of serum LH and FSH than their heterozygous littermates. Immunohistochemical assessment of LH and FSH cell populations revealed a normal morphology and cell number in the athymic animals compared to their normal littermates. Immobilization stress induced a significant reduction in gonadotrophin levels, particularly LH, in normal mice but had only a weak effect in athymic animals. It is concluded that congenital athymia in the adult male mouse is associated with decreased basal levels of serum LH and FSH, in the presence of a normal gonadotroph number and morphology. The anomalous responses of athymic mice to stress do not appear to be due to primary hypopituitarism but, rather, to an altered modulation of pituitary hormone secretion. .

Underdevelopment of fetal thyroid follicular cells in athymic nude mouse (BALB/cAnNCrj-nu/nu) observed by electron microscopic morphometry

Fetal thyroid follicular cells of congenitally athymic nude mouse (BALB/cAnNCrj-nu/nu) were studied with an electron microscope. The area of the entire cell, nucleus and mitochondrion were measured and compared in athymic and euthymic fetal nude mice (BALB/cAnNCrj-nu/+) at 18 days of gestation. The mean area of cytoplasm was significantly smaller in homozygous athymic nude mice than in heterozygous euthymic ones. The mean area of the mitochondrion was also smaller in homozygous athymic nude mice, but the difference was not statistically significant. There was no significant difference between the two groups in the area of the nucleus. These findings suggest that the thyroid gland of athymic nude mice is still underdeveloped at the end of gestation as compared to that of their euthymic littermates.

The role of immunopeptides in the regulation of anterior pituitary hormone release

The anterior pituitary lobe secretes hormones that regulate the functioning of the immune system which, in turn, produces thymic hormones and interleukin proteins capable of altering neuroendocrine responsiveness. Interleukin-1 is released during inflammation and activates the hypothalamic-pituitary-adrenal axis, which subsequently diminishes the immune response. Interleukin-6 (IL-6) stimulates prolactin and growth hormone release in vitro from anterior pituitary cells which, in turn, are capable of producing IL-6. The possible production of IL-6 by the anterior pituitary in situ suggests an autocrine and/or paracrine role for this cytokine in the regulation of hormone release.

Thymic stromal elements contain an anterior pituitary hormone-stimulating activity

Conditioned medium from thymic reticular monolayers displayed time-dependent accumulations of a concentration-responsive pituitary hormone-releasing activity that has been named thymic neuroendocrine-releasing factor (TNRF). Dopamine blocked and somatostatin (SRIF) attenuated TNRF-induced prolactin (PRL) release. Conversely, SRIF had no effect on TNRF-induced growth hormone (GH) release. TNRF potentiated thyrotropin-releasing hormone (TRH)-stimulated PRL release and was additive to the effects of GH-releasing hormone (GHRH) on GH release. Anterior pituitary cells perifused with TNRF responded with immediate, sustained and reversible increases in hormone release. Partial purification revealed this activity to be greater than 10,000 in molecular weight. These data suggest that the thymus may affect pituitary function.

Immunohistochemical and electron microscopic changes in the endocrine pancreas after thymectomy

This study showed that six months after adult thymectomy blood glucose level in rats was significantly lower compared to that of control animals. The low glucose level found in thymectomized rats was accompanied by structural changes in the pancreatic islets. Electron microscopy and paraldehyde fuchsin (PAF) stained paraffin sections revealed partial degranulation of B-cells.

Effect of thymus grafts of various ages on the immune system formation in CBA mice

An attempt has been made to govern the development of immunological capability in CBA mice by means of transplantation at an early postnatal period of thymus from donors of various ages. The results have shown that in thymectomized animals, apart from a well known gradual decline with the donor's age in restorative functions of the transplanted thymus, there was at the age of 22 months a phase of inhibitory influence on the recipient's immune system. In intact animals, transplantation of the thymus from a 5-day-old donor caused a decrease and that from a 22-month-old donor caused an increase in the development of the capacity for immune response. Taken together, our findings indicate an active role of the thymus both in the formation of the immune system and in its alteration with aging.

Modulation of lymphoproliferation by human growth hormone

This study was designed to investigate the capacity of human growth hormone (hGH) to induce proliferation of human peripheral blood lymphocytes (PBL) and its effect on lectin-induced lymphoproliferation, as measured by [3H]-thymidine (3H-TdR) incorporation into lymphocyte DNA. We observed that hGH itself induced lymphoproliferation. Maximal responses were reached with 50 ng/ml after 4 days and 25 ng/ml after 7 days. Anti-hGH-antiserum completely blocked the stimulatory capacity of hGH. Further evidence for the specificity of the effect was obtained by the finding that no other hormone present in the hGH preparation produced any effect on lymphocyte cultures. In contrast to its stimulatory capacity, hGH reduced the proliferative response of PBL to phytohaemagglutinin (PHA). This effect was also neutralized by anti-hgH-antiserum. These results show a direct stimulatory effect of hGH on PBL and a regulatory effect of the hormone on lectin-induced lymphoproliferation.

The morphology of the endocrine system in congenitally athymic (nude) mice

The endocrine system (adenohypophysis, thyroid, adrenals, ovaries, testes) and the submandibulary salivary gland of both female and male congenitally athymic (nu/nu) B10LP mice at various ages post partum (2, 4, 6, 8 and 12 wks) were studied morphologically and compared with their heterozygous thymus-bearing (+/nu) littermates. The animals were held under conventional conditions. The adenohypophysis of male nu/nu mice showed a decrease in size of the acidophilic cells. In the thyroid glands a slight hyperactivity of the follicles was seen in both female and male nu/nu mice in comparison with the +/nu mice. No changes were observed in the adrenals. The ovaries of the nu/nu females showed degeneration in the follicles while the corpora lutea were absent or, if present, degenerated. In the testes of nu/nu mice only a slight retardation in spermatogenesis was seen at wk 4. In the submandibular salivary glands of the nu/nu males the normal sex-dependent presence of well-developed tubular structures was absent from wk 4 onwards. The results were compared with those described in the literature for athymic mice with another genetic background and for thymectomised mice. It was concluded that alterations in immunological reactivity in athymic mice are not necessarily due to changes in the immune system, but may also be dependent on changes in endocrine function.

Quantitative studies of lymphocytes and other cell populations in the bone marrow of neonatally thymectomized C3H mice

The effects of neonatal thymectomy on the development of the lymphoid, erythroid and granulocytic cell populations in mouse bone marrow have been assessed by quantitative techniques. The numbers per unit volume of bone marrow of 17 cell types were determined in neonatally thymectomized and sham thymectomized C3H mice at two, four and eight weeks of age, and compared with those of normal C3H mice. After neonatal thymectomy the numbers of small lymphocytes, large and medium-sized lymphoid cells, and erythroid cells reached normal levels at two weeks but fell progressively to 18%, 22% and 42% of normal, respectively, by eight weeks. In sham thymectomized mice these cell populations did not differ significantly from normal. Immature and mature granulocytes were elevated in numbers two weeks after either neonatal thymectomy or sham thymectomy, suggesting a transient non-specific stimulation of granulocytopoiesis. During continuous infusion of 3H-thymidine for ten days in neonatally thymectomized mice aged four weeks and eight weeks many bone marrow small lymphocytes remained unlabeled. The results demonstrate that early postnatal development of bone marrow lymphoid and erythroid cells proceeds normally in the absence of the thymus, in accord with the concept of the bone marrow as a primary site of lymphocyte production and differentiation. In addition, some slowly-renewing small lymphocytes in bone marrow appear to be thymus-independent cells.

The isolation and amino acid sequence of an adrenocorticotrophin from the pars distalis and a corticotrophin-like intermediate-lobe peptide from the neurointermediate lobe of the pituitary of the dogfish Squalus acanthias

An adrenocorticotrophic hormone (ACTH) was isolated from extracts of the pars distalis of the pituitary of the dogfish Squalus acanthias by gel filtration and ion-exchange chromatography. It had 15% of the potency of human ACTH in promoting cortico-steroidogenesis in isolated rat adrenal cells. Sequence analysis revealed it to be a nonatria-contapeptide with the following primary structure: Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Met-Gly-Arg-Lys-Arg-Arg-Pro-Ile-Lys-Val-Tyr-Pro-Asn-Ser-Phe-Glu-Asp-Glu-Ser-Val-Glu-Asn-Met-Gly-Pro-Glu-Leu. The N-terminal tridecapeptide sequence was identical with the proposed structure of dogfish alpha-melanocyte-stimulating hormone (alpha-MSH). On comparison with human ACTH eleven amino acid differences were seen, nine of which are in the 20-39 region of the molecule which is not essential for the steroidogenic activity of ACTH. A peptide identical with the 18-39 portion of this new ACTH was similarly isolated from the neurointermediate lobe of the pituitary where considerable amounts of dogfish alpha-MSH were found. This supported our view that ACTH as well as having a distinct biological role of its own is also the precursor of alpha-MSH.