Effects of intraventricular injections of 6‐hydroxydopamine on anterior pituitary cell proliferation

Abstract

Effects of intraventricular injections of 6-hydroxydopamine (6-OHDA; 200 micrograms/20 microliter vehicle) on anterior pituitary cell proliferation in rats have been investigated by means of the colchicine metaphase-arrest technique. In those groups of animals receiving 6-OHDA alone or 6-OHDA plus desmethylimipramine (DMI, 25 mg/kg body weight i.p.), where the mean mitotic activity rates (MMARs) were initially low at 48 hours, an increase of MMARs was observed at 96 and 144 hours after the drug injections. At 144 hours after drug administration, the MMARs values in the 6-OHDA-injected group and in the 6-OHDA + DMI-treated group were significantly higher than those in the control groups. This increase of MMARs resulted from the enhancement of acidophilic and chromophobe cell proliferation. The low MMARs at 48 hours after 6-OHDA injection are probably a result of dopamine release from damaged nerve endings; the enhancement of MMARs (particularly evident in the 6-OHDA + DMI-treated group) at 96 and 144 hours after drug administration is presumably related to a deficiency of dopaminergic control of anterior pituitary cell proliferation.

Physiological implications of pituitary trophic activity

“…A similar antiproliferative effect of dopamine agonists on the anterior pituitary is seen in organ culture (Pawlikowski et al 1978b) and in vivo under basal conditions (Lloyd et al 1975). Intraventricular injection of the neurotoxin 6-hydroxydopamine, which depletes striatal dopamine, results in a modest increase in pituitary mitotic activity, principally in the acidophilic and chromophobe compartments, when measured 4 and 12 days (but not 2 days) after the injection (Lewinski et al 1984). The authors speculated that the absence of effect at 2 days was related to a relative increase in hypothalamohypophyseal portal dopamine resulting from early dopaminergic nerve damage.…”

Pituitary Phenotypes of Mice Lacking the Notch Signalling Ligand Delta‐Like 1 Homologue

“…The five different hormone‐producing cell types within the gland are specified during embryogenesis by a cascade of transcription factors and signalling pathways , although the number of cells of each population increases after birth and can vary throughout life in response to physiological demand . These changes in cell number and function are under the control of hypothalamic and peripheral signals , although paracrine and autocrine factors are also considered to be involved . Paracrine factors are likely to regulate differentiation of the recently described multipotent progenitor, or stem cells, of the pituitary , especially for cell types such as somatotrophs (producing growth hormone; GH), where the receptor for the primary proliferative signal is restricted to the differentiated cell type .…”

Effect of intracerebroventricular injection of prostaglandin E2 on anterior pituitary cell proliferation

“…It cannot be excluded that the lack of mitoses in acidophilic cells is related to the method of i.c.v, injections employed in the present study. In the previous experiment, made in our laboratory, the analogous i.c.v, injections of ascorbic acid solution caused a striking decrease of MMAR of acidophilic cells in the rat anterior pituitary [4]. It is also possible that ethanol, which was used in the present study as one of the compounds of vehicle, enhanced the suppressive effect of i.c.v, injections on the proliferation of acidophils in the anterior pituitary.…”