Localization and Actions of Cholecystokinin in the Rat Pituitary Neurointermediate Lobe*

Abstract

Rat pituitary neural lobe contained high concentrations of cholecystokinin-like immunoreactivity (CCK-LI). Section of the pituitary stalk resulted in loss of CCK-LI, and both lactation and replacement of drinking water with 2% saline resulted in marked depletion of CCK-LI. Rats with congenital diabetes insipidus (Brattleboro strain) had a 73% reduction in CCK-LI below the levels of hooded Long-Evans controls; levels in the brain were unchanged. Release of CCK-LI, labeled dopamine and GABA in response to K depolarization was studied. There was a low fractional release of CCK-LI. Addition of sulfated CCK-8 (CCK-8) to the medium enhanced the Ca-dependent K-stimulated release of dopamine, but basal release was unaffected. GABA release was only poorly Ca-dependent and not effected by extracellular CCK-8. Vasopressin and oxytocin release were stimulated by electrical stimulation of the pituitary stalk, and were unaffected by the addition of CCK-8 to the medium. In vivo, however, the injection of 5 .mu.g CCK-8 into the 3rd ventricle resulted in increased plasma vasopressin concentrations.