Morphological Effects of Angiotensin II in Cultured Pituicytes Derived from Adult Rat Neurohypophysis
Pathak, Praveen Chandra
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Neurohypophysial astrocytes, the pituicytes, undergo morphological changes in vivo in response to dehydration and lactation, conditions that result in increased levels of oxytocin and vasopressin. The morphological changes may be an indication of events that facilitate the release of these peptide hormones into circulation. It has been shown that angiotensin II increases the rate of firing of the nerve terminals at the neurohypophysis in vivo (Akaishi et al., 1980; Okuya et al., 1987). Therefore, in four related studies, we investigated the possibility that angiotensin II receptor activation is responsible for the observed pituicyte morphological response. Pituicyte ex plants from adult Sprague-Dawley rats were maintained in culture for 13 days. In vitro studies of these pituicytes were performed to determine the subtype of the angiotensin II receptor linked to morphological changes. Contrary to expectation, angiotensin II appeared to inhibit stellation of pituicytes in a dose dependent manner. Moreover, nonspecific and specific antagonists (PD123319 and DUP753) of the angiotensin II receptor failed to block the angiotensin II response and thus, may suggest that angiotensin II is inhibiting stellation through an unknown receptor. However, the comparatively high amounts of stellation exhibited by control pituicytes suggests that caution must be exerted when interpreting the effects of neurotransmitters on pituicyte morphology.