BACKGROUND: Pituitary pars intermedia dysfunction (PPID), a neurodegenerative disease leading to reduced dopamine production, is a common disease in aged horses. The treatment is based on administration of the dopamine agonist pergolide. This drug has been related to valvular fibrosis in humans, but the cardiovascular effect of this drug has not yet been investigated in horses.
OBJECTIVE: To determine whether pergolide induces valvular disease in horses or affects the cardiac function.
METHODS: Standard, tissue Doppler (TDE) and two-dimensional speckle tracking (STE) echocardiography were performed in horses with diagnosed PPID based on adrenocorticotropic hormone dosage. Measurements taken in horses treated with pergolide were compared with those from untreated horses with nonparametric t-tests. Furthermore, measurements from follow-up examinations performed at least three months after the initial exam were compared with a Wilcoxon signed rank test for repeated measurements in each group.
RESULTS: Twenty-three horses were included. None of the 12 horses under treatment developed valvular regurgitation. Furthermore, no differences in the measurements of the left ventricular systolic or diastolic function could be seen between the group of horses with treatment and those without treatment. Measurements taken in the follow-up exam did not differ compared to those taken in the initial exam in both groups.
CONCLUSIONS: No changes of the left ventricular function assessed by TDE and STE could be shown in a small population of horses with confirmed PPID. Treatment with pergolide did not affect the ventricular function nor induce valvular disease.

Orexin A may play a special role in animals\' sensitivity to the day length changes such as sheep. The localization of mRNA for prepro-orexin in the ovine hypothalamus was found to correspond to the pattern described in rodents. The results of that research also showed that the expression of the orexin gene depends on the length of a day and is higher during short days. Other study revealed that mRNA for orexin receptors (OxR)1 and OxR2 shows strong expression in the anterior, intermediate and posterior pituitary lobes of the rat. In addition, it was also found that in the anterior pituitary, OxR1 is more strongly expressed than OxR2. These observations indicate that the pituitary gland is capable of receiving the orexin signal. The aim of the study was to determine the interaction of season and orexin A on PRL and GH secretion by pituitary explants in short-term culture. Studies were carried out on pituitaries explants collected from lactating Polish Longwool sheep during the long (LD, May, n=5) and short day (SD, December, n=5). Glands were transected saggitally into halves, with each incubated in 2.5 ml of M-199 for 180-min in medium containing either 0 or 1000 ng/ml of orexin A. Treatment with orexin during LD increased significantly the secretion of PRL (P < 0.01) and GH (P < 0.05), compared to controls. In cultures from glands collected during SD, orexin significantly (P < 0.05) decreased the secretion of both hormones, compared to controls. We conclude that the secretion of PRL and GH from the ovine pituitary gland is negatively responsive to orexin A during SD; whereas orexin may stimulate PRL and GH secretion during LD.

The aim of this work was to study the pituitary pars intermedia in seasonally captured adult male and immature viscachas by immunohistochemistry and image analysis. The pituitary pars intermedia exhibited a well-developed parenchyma with scarce connective tissue and vascularization. It was formed by a close association of melanotrophs and folliculostellate cells. The folliculostellate cells were stellate in shape with cytoplasmic processes, and they originated follicles with PAS-positive colloid inside. The morphometric parameters of melanotrophs, follicular colloid and folliculostellate cells (S-100-ir and GFAP-ir) varied seasonally and in relation to age. These parameters showed minimal values in the adult males captured in winter and in immature animals, and they were maximal in summer. The percentage of vimentin-positive area of the folliculostellate cells was maximal in immature animals, decreased in relation to age and did not vary seasonally in the adult animals. The greatest development of pars intermedia in the adult animals in relation to the immature ones is probably related to the adults\' adaptation to the semiarid environment. The expression of the tested proteins suggests a probable neuroectodermic origin for the folliculostellate cells of the viscacha pituitary pars intermedia. In addition, the cytoplasmic processes of folliculostellate cells might originate an intercellular communication network inside the pars intermedia. The decrease in the morphometric parameters melanotrophs, follicular colloid and folliculostellate cells in winter suggests a low endocrine activity of this zone. This fact might be due to the effect of the short photoperiod and high melatonin serum levels.

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