We previously demonstrated that laminin, a component of basement membranes, modulates pituitary hormone secretion. In the present study, we evaluated the effect of type IV collagen, another component of this membrane, on the release of prolactin (PRL) by anterior pituitary gland from adult male rats. Hemipituitaries were incubated for 3 h with type IV collagen or antibodies against it and PRL release was studied. Rabbit IgG to type IV collagen at concentrations of 10⁻⁷ - 10⁻⁵ M had a significant stimulatory effect on PRL release, in comparison to normal rabbit serum IgG or medium alone used as controls. Type IV collagen induced a significant inhibitory effect on basal release of PRL at a concentration of 30 µg/mL. A slight decrease in PRL release was detected in thyrotropin-releasing hormone-stimulated hemipituitaries incubated with type IV collagen at all concentrations used. These results suggest that type IV collagen, similar to laminin-1, modulates PRL released from hemipituitaries, in vitro.Instituto Multidisciplinario de Biología Celular