Effects of neurointermediate pituitary lobectomy on humoral and cell-mediated immune responses in the rat

OBJECTIVE: Chronic stress is characterized by an increased activity of the hypothalamic-pituitary-adrenocortical axis and decreased humoral and cell-mediated immune responses. In the rat, corticosterone is the principal natural immune suppressor. Neurointermediate pituitary lobectomy (NIL) in rats induces diabetes insipidus and protracted increases in basal adrenocorticotropin and corticosterone plasma levels, a situation that resembles chronic stress. In this paper, we evaluated the effects of NIL on humoral (hemagglutinin titers and footpad swelling to sheep red blood cells--SRBC) and cell-mediated immune responses (contact hypersensitivity to dinitrochlorobenzene). METHODS: The studies were conducted on NIL Wistar rats (body weight 150-200 g) 3 weeks after surgery. For comparisons, nonoperated control rats were used. RESULTS: NIL resulted in an increased water intake. Body weight gain and adrenal, thymus, and spleen weights were within the range of nonoperated controls. Eight days after SRBC immunizations a second SRBC injection into the footpad resulted in a decreased swelling response in NIL rats. The hemagglutinin titers were also reduced in the NIL rats. CONCLUSIONS: These results indicate that: (1) NIL reduces humoral immune responses and decreases the cell-mediated immune response; (2) the immune alterations are most likely due to the increased activity of the hypothalamic-pituitary-adrenocortical axis induced by NIL, and (3) NIL animals constitute a valuable paradigm to study hypothalamic-pituitary-immune interactions.