Influence of diabetes on the gonadotropin response to the negative feedback effect of testosterone and hypothalamic neurotransmitter turnover in adult male rats.

The influence of diabetes on the gonadotropin response to the negative feedback effect of testosterone (T) and hypothalamic neurotransmitter turnover rates in adult male rats was evaluated. Adult male Sprague-Dawley rats were made diabetic by an intraperitoneal injection of streptozotocin (STZ; 5 mg/100 g body weight) in citrate buffer. Vehicle-injected rats served as controls. On day 9, all rats were bilaterally castrated and treated subcutaneously on alternate days with either peanut oil or T propionate (TP) in peanut oil (100 micrograms/rat). Plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), and T concentrations were measured by specific radioimmunoassays from blood samples collected on day 1 (before castration) and 2, 4, 6, and 7 days after castration. On day 7 after castration (day 15 after vehicle or STZ treatment), 1 h before autopsy, the rats were injected intraperitoneally with saline or a tyrosine hydroxylase inhibitor, alpha-methyl-p-tyrosine (25 mg/100 g BW), for the measurement of norepinephrine (NE) and dopamine turnover in median eminence and medial basal hypothalamus (MBH). Circulating FSH, LH, PRL, and T levels were significantly lower (FSH and T: p less than 0.001; LH and PRL: p less than 0.05) in gonad-intact rats treated with STZ than in vehicle-injected animals. The castration-induced increase in plasma LH levels was attenuated in diabetic rats. The suppressive effect of T on LH secretion was significantly greater (p less than 0.001) in STZ-treated rats relative to TP-treated nondiabetic controls.(ABSTRACT TRUNCATED AT 250 WORDS)