Studies on several marsupial anterior pituitary hormones

Immune-endocrine interactions in marsupials and monotremes

Interactions between the immune and endocrine systems are not well studied in marsupials and monotremes. One exception to this is the phenomenon of semelparity, which is well covered in the literature as this is an unusual reproductive strategy amongst mammals and is only observed in some dasyurid and didelphid marsupials. Thymus involution provides a direct link between the endocrine and immune systems and warrants further study in marsupials and monotremes. The thymus is a primary immune tissue which is essential for overall immune function. Whilst the organ is large in juvenile animals, it begins to involute around puberty due to the suppressive effects of sex steroids. Thymus involution has a significant effect on the immune system, as it signals the onset of immune aging and decline in function. The output of naïve T lymphocytes by the thymus decreases, increasing susceptibility of aged individuals to infection and cancers. Understanding the links between the immune and endocrine system in marsupials and monotremes may shed light on diseases such as devil facial tumour disease (DFTD) which threatens the future of the Tasmanian devil. We hypothesise that changes in sex hormones around puberty may drive changes in the immune system, such as thymus involution, which may make devils more susceptible to DFTD as they age. In addition, the Schwann cell origin of DFTD may enable tumours to respond to sex hormones, as occurs in similar cancers in humans.

The hypothalamic-pituitary-ovarian axis and manipulations of the oestrous cycle in the brushtail possum

The main purpose of this review is to provide a comprehensive update on what is known about the regulatory mechanisms of the hypothalamic-pituitary-ovarian axis in the brushtail possum, and to report on the outcomes of attempts made to manipulate by hormonal means, these processes in the possum. Over the last 15 years, several unique features of possum reproductive physiology have been discovered. These include an extended follicular phase despite elevated concentrations of FSH during the luteal phase, and early expression of LH receptors on granulosa cells of small antral follicles, suggesting a different mechanism for the selection of a dominant follicle. The use of routine synchronisation protocols that are effective in eutherians has failed to be effective in possums, and so the ability to reliably synchronise oestrus in this species remains a challenge.

Follicle-stimulating hormone in the brushtail possum (Trichosurus vulpecula): purification, characterization, and radioimmunoassay

Follicle-stimulating hormone (FSH) was purified from brushtail possum (Trichosurus vulpecula) pituitary glands by using the following purification techniques: fractional ammonium sulfate precipitation, triazinyl-dye affinity chromatography, hydrophobic interaction chromatography, and gel filtration. A yield of 18 micrograms of FSH per gram of pituitary, with a recovery of 12%, was obtained from 1400 glands (20.3 g wet weight). The purified FSH activity per gram of protein was 1320 times more potent than the initial pituitary homogenate. Contamination with possum luteinizing hormone (LH) was < 0.02%. The amino acid composition of possum FSH was similar to that of ovine FSH. Amino-terminal sequencing for 11 cycles indicated that the alpha subunit has the same sequence as ovine FSH except for residue 7, where the possum FSH alpha subunit contains isoleucine compared to the ovine subunit which contains threonine. The beta subunit has two substitutions in the first 11 residues and does not contain the N terminal serine that is found in ovine FSH. Amino acid sequencing did not detect any contaminating proteins. Possum FSH bound possum and bovine testicular receptors with similar affinities. It was also able to stimulate in vitro cAMP production by Chinese hamster ovary cells which express recombinant FSH receptors. In the receptor assays and the bioassay possum FSH has about 21% of the potency of ovine FSH (USDA-oFSH-19-SIAFP-RP2). An RIA was developed for possum FSH using 125I-possum FSH and an antiserum raised against human FSH. The RIA has a sensitivity of 0.3 ng/ml, a 50% displacement of 2.7 ng/ml, and a cross reactivity of 0.05% against possum LH. Plasma FSH levels in male possums (10.4 +/- 2.4 ng/ml, n = 4) were higher (P < 0.05) than levels in females (1.0 +/- 0.1 ng/ml, n = 4). Five days after gonadectomizing these possums the plasma FSH levels increased (P < 0.05) to 27.1 +/- 0.2 ng/ml in the males and to 6.6 +/- 2.0 ng/ml in the females. In summary, we have purified and partially characterized possum FSH. We have also set up an RIA for the hormone and shown that males have higher levels than females and that plasma FSH increases after gonadectomy.

Purification, partial characterization, and radioimmunoassay of prolactin and growth hormone from the Bennett's wallaby

Bennett's wallaby prolactin (wPRL) and growth hormone (wGH) were purified from an aqueous extract of pituitary glands. The extract from 202 glands (6.5 g wet wt) was processed by gel filtration on Sephadex G-100, gel filtration on Sephadex G-100 SF, and then anion-exchange chromatography on DEAE-Sepharose CL-6B. The yields of wPRL and wGH were 5.2 and 15.7 mg, respectively. Since recovery of wPRL from the anion exchange column was 10%, anion exchange was performed in the presence of 20% acetonitrile in a subsequent purification. Recovery from this column was markedly increased to 42%. The purified hormones each gave a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a molecular weight under reducing conditions of 21,000 and 23,000 for GH and PRL, respectively. Each hormone was positively identified by its N-terminal amino acid sequence, which showed high sequence identity with the equivalent eutherian hormone. Semianalytical gel filtration of purified hormone was used to demonstrate that each hormone remained as a monomer in aqueous solution. Each purified hormone was tested in the heterologous PRL radioimmunoassay (RIA) which has been used in many earlier studies to measure marsupial PRL. Highly purified wPRL was less potent than ovine prolactin (5.3 compared with 1.5 ng/ml at 50% displacement) and the cross-reaction of wGH was < 0.01%. Antibodies were raised against wPRL and wGH and a homologous RIA was developed for each hormone. The sensitivity of the wPRL assay was 0.8 ng/ml which is similar to that of the heterologous PRL assay. Cross-reaction with a number of eutherian pituitary hormones or wGH was < 0.07%. The wGH assay detected 0.8 ng/ml which is similar to that of the heterologous PRL assay. Cross-reaction with a number of eutherian pituitary hormones or wGH was < 0.07%. The wGH assay detected 0.8 ng/ml, cross-reacted with GH from several eutherian species, and showed low cross-reaction with wPRL (< 0.5). In both the wPRL and wGH assays, pituitary homogenates from several species of marsupial diluted in parallel with the wallaby standard, suggesting that these assays will be of use in studies of a number of marsupial species.

Characterization of a monoclonal antibody which detects luteinizing hormone from diverse mammalian species

The present study describes the development and characterization of a monoclonal antibody (518B7) generated against bovine LH (bLH). Although 518B7 was extremely specific for LH, very low species specificity was observed. A RIA using this antibody and radioiodinated equine LH (eLH) showed good sensitivity for all mammalian LH preparations tested, with the exception of human LH (15%, relative to the eLH reference standard). Activities of most mammalian LH's ranged between approximately 50-200%. Much less activity was detected with reptilian LH (less than 1.5%). Amphibian and avian LH fractions were essentially inactive. The reactivities of LH alpha and beta subunits from a variety of mammals clearly showed that the antibody reacts with the beta subunit. Sensitive RIAs were also developed utilizing 125I-bovine and 125I-rat LH. Interestingly, all hormone preparations which showed sufficient reactivity for statistical analysis within the dose ranges used in the present study (0.01-1000 ng/tube) produced a displacement curve parallel to the reference standard. We have also validated the use of 518B7 in detecting LH in serum. Parallel dilution curves relative to purified LH reference standards were observed with equine and bovine serum samples and equine pituitary extract. High (average 94%) recoveries were also seen with bovine serum with known amounts of exogenously added bLH. Similar patterns of LH secretion were detected with a RIA based upon 125I-bLH and 518B7 and a previously described polyclonal antibody-based RIA in bovine serum samples during estrus. Thus, a monoclonal antibody for LH has been produced which can be used to develop sensitive and specific RIAs in many different mammalian species.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunolocalization of insulin, glucagon, pancreatic polypeptide, and somatostatin in the pancreatic islets of the possum, Trichosurus vulpecula

Antibodies to insulin, glucagon, pancreatic polypeptide (PP), and somatostatin were used in the immunofluorescence procedure to demonstrate localization of the four hormones in cells of the pancreatic islets of the brushtailed possum, Trichosurus vulpecula. Most pancreatic islets revealed some differences in the topographical distribution and cell number of each endocrine cell type. Insulin immunoreactive cells were observed in most islets where they occurred as groups of cells peripherally and within the islet. In several islets glucagon cells were the predominant cell population and were distributed peripherally as well as centrally. Pancreatic polypeptide cells were fewer in number and usually occurred as single cells within the islet. Cells immunoreactive to antisomatostatin serum were observed in varying numbers in the peripheral and central regions of the islet. The present immunofluorescence study demonstrates differences in the topographical distribution of the four major pancreatic hormones between a marsupial species and several of the eutherian mammals.