[Research related to hormones in Nagase analbuminemic rats]

The levels of hormones in the anterior pituitary gland and serum in Nagase analbuminemic rats (NAR) were examined. For the anterior pituitary gland, the contents of prolactin, TSH, GH, LH and FSH in male NAR were lower than those of normal rats. In female NAR, prolactin and TSH levels were also lower than those in normal rats, whereas LH, FSH and GH were unchanged. In serum, the concentrations of TSH, T3, T4, estradiol, testosterone and prolactin (female only) were examined. The serum prolactin level in female NAR was lower than that of normal rats, whereas a higher level of serum TSH was seen in NAR. Male NAR had a higher T3 level and a lower T4 level. Although the estradiol concentration in male NAR was normal, the serum testosterone level was only a quarter of that in normal rats. We investigated the reason for the low level of serum testosterone in male NAR through biochemical studies on steroid metabolism. The results indicated that the low serum concentration of testosterone in NAR was mainly attributable to decreased biosynthesis of testosterone in the testes. Prolactin is the primary hormone for experimental mammary tumorigenesis. In association with the lower prolactin level in female NAR, induction of tumors by 7, 12-dimethylbenz (a) anthracene (DMBA) was studied. NAR showed a significantly lower mammary tumor response to DMBA. The incidences of spontaneous mammary tumor in NAR and normal rats after 2 years were also compared. The incidence was much lower in NAR than in the controls. Thus the lower mammary tumor induction in NAR could mostly be ascribed to the lower level of circulating prolactin.