Proceedings: Molecular aspects in comparative endocrinology

Posterior pituitary of the newborn marsupial possum, Trichosurus vulpecula

The fetal anterior pituitary-adrenal axis is thought to be involved in the initiation of birth in both eutherian and marsupial mammals. Little is known about the structure and function of the posterior pituitary at birth in the marsupial. Immunocytochemistry, high pressure liquid chromatography, and radioimmunoassay were used to identify vasopressin and mesotocin in the posterior pituitary of a newborn marsupial, the brushtail possum, Trichosurus vulpecula. The concentrations of vasopressin and mesotocin in the head of the newborn possum were 0.34 and 0.28 ng, respectively. The concentration of vasopressin was always greater than that of mesotocin, and the amounts of neuropeptides present in the head increased as the possum developed.

Brain content and plasma concentrations of arginine vasopressin in an Australian marsupial, the brushtail possum Trichosurus vulpecula

Arginine vasopressin (AVP) has been identified and quantified in the brain and plasma of the possum using a highly specific radioimmunoassay and high-performance liquid chromatography. Large amounts of AVP were found in the pituitary (16.3 +/- 0.56 micrograms/pituitary, n = 5) and hypothalamus (398 +/- 82.5 ng/hypothalamus), and significant amounts of AVP were also present in the cerebral cortex (26.8 +/- 11.5 ng/cortex). Plasma AVP concentrations were significantly lower (2.2 +/- 0.45 pg/ml, n = 10) during anesthesia compared to concentrations while conscious (4.5 +/- 1.19 pg/ml). Severe hemorrhage markedly increased plasma concentrations to 1091 +/- 225 pg/ml (n = 8). It was concluded that AVP is present in the possum brain, pituitary, and plasma, and that its secretion is stimulated by hypovolemia and inhibited by surgical stress.

Mesotocin and oxytocin in the brain and plasma of an australian marsupial, the northern brown bandicoot, isoodon macrourus

1. Mesotocin (MT) and oxytocin (OT) were measured in the brain and plasma of bandicoots using reverse phase high performance liquid chromatography and specific radioimmunoassays. 2. MT and OT were found in the pituitary (1.25 +/- 0.10 micrograms/MT; 0.725 +/- 0.077 micrograms/OT) and hypothalamus (38.37 +/- 6.46 ng/MT; 19.1 +/- 4.61 ng/OT). Smaller amounts were present in the cerebral cortex. 3. Basal plasma concentrations ranged from 1.5 to 8.1 pg/ml for both peptides (N = 14) and were elevated by stress. 4. It was concluded that both MT and OT are secreted by the bandicoot brain and that stress stimulates secretion.

Mesotocin in the brain and plasma of an Australian marsupial, the brushtail possum (Trichosurus vulpecula)

Oxytocic peptides extracted from the brain and plasma of the brushtail possum, Trichosurus vulpecula, were separated by reverse-phase high pressure lipid chromatography (HPLC) and quantified by specific radioimmunoassays for oxytocin (OT) and mesotocin (MT). The pituitary, hypothalamus and cerebral cortex were found to contain MT only in quantities of 3.9 +/- 0.2 (SE) ug, 17.6 +/- 0.6 ng and 21.0 +/- 2.6 ng respectively. The plasma concentration of MT varied according to the degree of stress of the possum. In anaesthetized animals values of 39.7 +/- 9.7 pg/ml (11 males) and 31.5 +/- 12.9 pg/ml (6 females) were obtained; in four conscious catheterized animals, 9.4 +/- 6.3 pg/ml. Samples taken from three anaesthetized animals during exsanguination contained 271 +/- 102 (SD) pg MT/ml. It was concluded that hypothalamic and extra-hypothalamic MT is present in the marsupial brain and that as in placental mammals, stress stimulates the secretion of mesotocin.