Abstract Physiological stimuli such as dehydration and lactation/suckling of the young have been found to induce reversible changes in the relationships of neural and glial elements with the basal lamina of the neurohypophysis. Such stimulation is associated with a decline in the extent of basal lamina occupied by glial processes and an increase in nerve terminals abutting the lamina. One possible mechanism playing a role in these changes is the activation of beta-adrenergic receptors on the neurohypophysial glia (the pituicytes), since such cells in primary culture from adult rats undergo dramatic morphological transformation when stimulated with beta-adrenergic agonists. We sought to determine if changes similar to those seen in vivo and predicted from the responses of cultured cells would occur with beta-adrenergic stimulation of the isolated neurointermediate lobe in vitro. Neurointermediate lobes from adult male rats were incubated in artificial cerebrospinal fluid containing ascorbic acid alone (control) or in the same medium with either 10(-8), 10(-7) or 10(-5) M isoproterenol for 15 min after a 30-min period of preincubation in control medium. Quantitative ultrastructural analysis revealed significant decreases in pituicyte and, corresponding increases in neural, membrane abutting the basal lamina at the lower two drug concentrations. These results support the findings of other studies suggesting a beta-adrenergic mediation of pituicyte morphology and a role for beta-receptors in control of posterior pituitary function.