the following example sets forth a series of tests using diabetes - susceptible mice where the mice were treated using a known gnrh antagonist . it is to be understood that this example is provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention . in this example , intact and gonadectomized non - obese mousen model of diabetes ( nod mouse ) mice were treated with gnrh agonists and antagonists to determine the effect thereof on serum igg levels and the incidence and onset of diabetes . the well - characterized nod mice were used throughout the study . male and female mice were purchased from the jackson laboratory ( bar harbor , me .). these mice are art - recognized animal models used in diabetes research . ( makino et al ., ( 1980 ) breeding of a non - obese diabetic strain of mice . exp anim , 29 , 1 - 13 ; miyazaki , a . t ., et al , ( 1985 ) predominance of t lymphocytes in pancreatic islets and spleen in prediabetic non - obese diabetic ( nod ) mice : a longitudinal study . clin exp immunol , 60 , 622 - 630 ) both intact and gonadectomized mice ( gdx ) were used . gonadectomies were performed to demonstrate an increase in the incidence of diabetes and also order to eliminate the variable of sex hormone production . to compare the effects of gnrh agonists and antagonists , gonadectomized animals were randomized at 14 to 18 days of age and begun immediately in one of the following main treatment groups : gnrh agonist ; antide ; vehicle . one group of gonadectomized males was treated with nal - glu , as an additional control . data from mice born over a period of several weeks and randomized to treatment or control groups in several different batches were combined . serum collection was staggered so that all mice were bled at the same 4 week intervals . sera for antibody measurements were stored at − 20 ° c ., and all samples from each timepoint were run in the same assay in an effort to avoid interassay variability . males were gonadectomized via a single scrotal incision under pentobarbital anesthesia . gnrh ( native decapeptide ) was purchased from bachem ( bubendorf , switzerland ). gnrh antagonist antide ( acetyl - β -[ 2 - naphthyl ]- d - ala - d - p - chloro - phe - β -[ 3 - pyridyl ]- d - ala - ser - nε -]- lys - nε -[ nicotinoyl ]- d - lys - leu - nε -[ isopropyl ]- lys - pro - d - ala - nh 2 ) was supplied by contraceptive development branch ( nichhd ) of the national institutes of health and ares - serono ( randolph , mass .). a second gnrh antagonist , nal - glu ( acetyl - d2nal1 , d4clphe2 , d3pal3 , arg5 , dglu6 ( aa ), dala10 ) was supplied by nichhd and was used on a subset of mice . all references to gnrh agonist refer to the native decapeptide . animals were injected subcutaneously in the nape of the neck six times weekly , in the a . m ., with 100 μg of gnrh or gnrh antagonist in 100 μl of vehicle consisting of 50 % propylene glycol and 50 % double distilled water . sera were collected from blood obtained every six weeks by retroorbital puncture after light isofluorane anesthesia . serum testosterone concentrations were measured by ria using a commercial kit ( coat - a - count , diagnostic products corporation , los angeles , calif .). serum lh and prolactin were measured by radioimmunoassay ( ria ) using previously described methods . ( neill , j . d . et al . ( 1971 ) development of a radioimmunoassay for rat prolactin and evaluation of the niamd rat prolactin radioimmunoassay . endocrinology , 88 , 548 - 55 ; niswender , et al . ( 1968 ) radioimmunoassay for rat luteinizing hormone with antiovine lh serum and ovine lh - 131 - i . proc soc exp biol med , 128 , 807 - 11 . total immunoglobulin g concentrations were measured by single radial immunodiffusion assay using immunodiffusion plates containing monospecific antiserum for igg ( icn biomedicals , inc ., costa mesa , calif .). serum glucoses were checked weekly using a one touch fast take meter ( lifescan , milpitas , calif .) urine was tested for glucose by urinalysis reagent strips ( miles , inc ., elkhart ind .). glycosuria was scored by comparison to reference standards on a scale of 0 to 4 as follows : negative = 0 ; 30 mg / dl = 1 ; 100 mg / dl = 2 ; 300 mg / dl = 3 ;& gt ; 1000 mg / dl = 4 . necropsies were performed on representative mice . no residual ovarian or testicular tissue was found . serum immunoglobulin measurements were compared by two - tailed student &# 39 ; s paired t - tests . percentages of mice remaining diabetes - free was assessed by mantel - haenszel methodology . ( mantel , n . ( 1966 ) evaluation of survival data and two new rank order statistics arising in its consideration . cancer chemother rep , 50 , 163 - 70 ) gonadectomy significantly increased igg levels compared to sham gonadectomy after 8 weeks of treatment . treatment of gonadectomized mice with gnrh agonist further increased igg levels compared to vehicle . in gonadectomized males , antide treatment reduced serum igg concentrations to levels seen in sham operated mice at 8 weeks . the data are shown in fig1 . in gonadectomized males , the incidence of diabetes was significantly decreased by administration of the gnrh antagonist antide . at 60 weeks of age 0 % of antide treated mice were diabetic compared to vehicle ( p = 0 . 0025 ; fig2 ). gnrh agonist treatment significantly increased the incidence and accelerated the timing of onset of diabetes . the of this study was to determine whether a reduction in gnrh activity was associated with an amelioration of diabetes in gonadectomized male mice susceptible to diabetes . no attempt was made to distinguish hypothalamic versus pituitary hormone effects ; likewise , no attempt was made to determine the relative importance of gonadal hormones versus hypothalamic / pituitary hormones . nevertheless , this example confirms that gnrh and / or its pituitary products appear to modify the expression of murine diabetes , and raise the hypothesis that hormones other than gonadal steroids might contribute to the well - known gender differences in expression of autoimmunity . in this example , gonadectomized mice were studied in order to eliminate the actions of gnrh on gonadal steroid production as well as gonadal feedback effects on gnrh release . this allowed a more direct assessment of the role of gnrh in modulating murine diabetes . it was found that gonadectomized nod mice treated with gnrh antagonist displayed statistically significant decreases in total igg , and delayed onset of diabetes . gnrh agonist administration resulted in reciprocal effects . gnrh antagonists might act on the immune system directly , by a direct effect on b or t lymphocytes , or indirectly , either by a reduction in gonadotropins or in cytokine production by immune cells . the prior art suggests that gnrh agonists may play a role in both b and t cell proliferation in vivo and in vitro ( marchetti , b ., et al ., ( 1989 ) luteinizing hormone - releasing hormone ( lhrh ) agonist restoration of age - associated decline of thymus weight , thymic lhrh receptors , and thymocyte proliferative capacity . endocrinology , 125 , 1037 - 45 ; morale , m . c ., et al ., ( 1991 ) blockade of central and peripheral luteinizing hormone - releasing hormone ( lhrh ) receptors in neonatal rats with a potent lhrh - antagonist inhibits the morphofunctional development of the thymus and maturation of the cell - mediated and humoral immune responses . endocrinology , 128 , 1073 - 85 ; and batticane , n ., et al ., ( 1991 ) luteinizing hormone - releasing hormone signaling at the lymphocyte involves stimulation of interleukin - 2 receptor expression . endocrinology , 129 , 277 - 86 ). for example , work demonstrating previous decreased percentages of b lymphocytes in gonadectomized lupus - prone mice treated with gnrh antagonists suggests that gnrh antagonists in some way interfere with b lymphocyte proliferation . a decrease in b lymphocyte proliferation could explain the observed reduction in serum igg and autoantibody concentrations and in decreased immune complex - mediated renal disease . inhibition of prolactin release has been shown to decrease disease severity and prolong survival in murine diabetes , whereas prolactin therapy exacerbates disease . ( mcmurray , r ., et al ., ( 1991 ) prolactin influences autoimmune disease activity in the female b / w mouse . j immunol , 147 , 3780 - 7 ) however , it was found that neither agonist nor antagonist treatment altered serum prolactin levels . thus , it is believed that the observed effects were independent of prolactin . previous reports have documented the ability of estradiol to exacerbate murine diabetes . although the feedback effects of estradiol on gnrh are complex , it is known that estradiol exerts positive feedback effects on gnrh production in some circumstances . estradiol has been shown to increase gnrh release from hypothalamic cells in vitro . ( leadem , c . a . et al ., ( 1984 ) stimulation with estrogen and progesterone of luteinizing hormone ( lh )- releasing hormone release from perifused adult female rat hypothalami : correlation with the lh surge . endocrinology , 114 , 51 - 6 . a rise estradiol is believed to contribute to the midcycle gnrh surge . ( roselli , c . e . et al . ( 1990 ) regulation of hypothalamic luteinizing hormone - releasing hormone levels by testosterone and estradiol in male rhesus monkeys . brain res , 509 , 343 - 6 ) an estrogen response element with positive regulatory effects has been identified on the 5 ′ side of the gnrh gene . ( radovick , s ., et al . ( 1991 ) evidence for direct estrogen regulation of the human gonadotropin - releasing hormone gene . j clin invest , 88 , 1649 - 55 ) based on these observations , it is possible that some of the immunostimulatory actions of estradiol may result from its positive feedback on gnrh . androgens have been shown to negatively regulate gnrh and gonadotropin production and release . ( finkelstein , j . s ., et al . ( 1991 ) sex steroid control of gonadotropin secretion in the human male . i . effects of testosterone administration in normal and gonadotropin - releasing hormone - deficient men . j clin endocrinol metab , 73 , 609 - 20 ; veldhuis , j . d ., et al . ( 1992 ) evidence that androgen negative feedback regulates hypothalamic gonadotropin - releasing hormone impulse strength and the burst - like secretion of biologically active luteinizing hormone in men . j clin endocrinol metab , 74 , 1227 - 35 ; and kalra , p . s . et al . ( 1982 ) discriminative effects of testosterone on hypothalamic luteinizing hormone - releasing hormone levels and luteinizing hormone secretion in castrated male rats : analyses of dose and duration characteristics . endocrinology , 111 , 24 - 9 ). they have also been shown to exert suppressive actions in autoimmunity : androgen treatment ameliorates murine diabetes , whereas gonadectomy of males exacerbates the disease . ( hawkins , t ., et al . ( 1993 ) the effect of neonatal sex hormones on the incidence of diabets in nonobese diabetic mice . proc . soc . exper . biol . med ., 202 , 201 - 205 ; makino , s ., et al . ( 1981 ) the effect of castration on the appearance of diabetes in nod mouse . exp anim , 30 ; fitzpatrick , f ., et al . ( 1991 ) influence of castration , along or combined
a method for reducing the incidence or delaying the onset of diabetes in diabetes - susceptible mammals is provided wherein the mammals are treated with a gonadotropin - releasing hormone antagonist . preferably , the antagonist is administered repeatedly over time by subcutaneous injection . a useful antagonist is acetyl - β -- d - ala - d - p - chloro - phe - β -- d - ala - ser - nε -- lys - nε -- d - lys - leu - nε -- lys - pro - d - ala - nh 2 . other useful antagonists are nal - glu , ppi - 149 and acryline .