[The mechanism of the pineal gland in inhibiting sexual receptivity of female rats treated with monosodium-L-glutamate: (III). Does it concern with the function of the pituitary gland?].

: To elucidate whether pituitary function participates in the effect of the pineal gland on sexual receptivity, monosodium L-glutamate (MSG) was used as a neurotoxin to induce hypogonadal status. Long-Evans rats were divided into four groups: (1) normal control (C), (2) pinealectomized (Px), (3) MSG-treated (MSG) and (4) pinealectomized MSG-treated (Px-MSG). Pinealectomy was performed at six weeks of age. In the first part of the experiment, the sexual receptivity was estimated at the age of 2.5 months by lordosis quotient (LQ). The result indicates that the decline of receptivity by neonatal MSG treatment can be significantly improved by pinealectomy. In the second part of the experiment, the effect of pinealectomy on pituitary function was examined by two tests including (1) post-castrational LH rise and (2) pituitary response to LHRH. Ovariectomy was performed at the age of 2.5 months. Four weeks later three consecutive blood samples were collected at 10 minute intervals for LH radioimmunoassay. Then, three doses of LHRH (100 ng, 250 ng and 500 ng/100 g of body weight) were administered separately at two-week intervals, serum samples were taken before as well as 15 and 60 minutes after LHRH administration. The results showed that there was no significant difference in serum LH levels between Px and control rats after ovariectomy. The LHRH-evoked LH elevation in Px-MSG rats was just the same as that of the MSG rats, although the LH level in MSG rats was lower than in the control rats.(ABSTRACT TRUNCATED AT 250 WORDS)