Hypophysectomy and growth hormone replacement effects on multiple immune responses in rats.

Male Fischer 344 rats were hypophysectomized at 8 weeks of age. At 10 weeks of age, one group of these animals was treated with 40 micrograms of bovine somatotropin given daily sc for 13 days. A third group was sham-operated and injected daily with saline. All animals were sacrificed on Day 14 and multiple immune responses were assessed in each rat. Immune responses assayed included specific antibody production and delayed-type hypersensitivity (DTH) reactions to antigen, natural killer (NK) cell cytotoxicity, and production of interleukin 2 (IL2). Body and lymphoid organ weights, hematologic parameters, and spleen cell numbers were also recorded. Hypophysectomized (Hx) rats had reduced antibody synthesis, DTH reactions, NK cytotoxicity, IL2 (or IL4) production, body and organ weights, rbc counts, packed cell volumes, and hematocrits compared to sham-operated controls. White blood cell counts were elevated. Treatment of Hx animals with GH restored antibody and IL2 production and thymic weights and partially restored DTH reactions. These data indicate the pituitary is important in maintaining normal immune functions, and part of this effect may be via production of GH. It is postulated that GH may act through stimulation of IL2 (or IL4).