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Effects of estradiol benzoate and castration on LH in experimental hyperprolactinemia
Abstract:
Female rats of the Wistar strain were rendered hyperprolactinemic by grafting one additional pituitary gland under the right kidney capsule at various ages (5 days group A; 30 days group B and 90 days group C). Age matched animals were sham operated to serve as controls. Plasma levels of PRL and LH were measured by specific double antibody RIA. Basal preoperative PRL levels were increased rapidly after grafting, reaching values over 100 ng/ml, in front of the 20 ng/ml showed by sham operated controls. Plasma LH levels were significantly decreased in all hyperprolactinemic groups as compared to controls. After Estradiol Benzoate (EB) administration all control rats showed an increase in PRL levels in a pulsatile manner with higher values found in the afternoon. PRL response in transplanted rats was less evident and with absence of pulsatility. LH responses to EB in control animals showed a biphasic pattern, with a negative feed-back in the first hours followed by a positive effect at 31 or 55 h after the injection. This pattern of response started in the control rats from group A at 19 days of age. Before that, only the negative feed-back effect was present. In grafted animals from the same group no positive feed-back effect could be detected at any time studied. In group B, a reduction in the positive feed-back effect, more evident after 90 days of hyperprolactinemia was detected. Animals of group C on the contrary showed an increased positive feed-back effect 40 days after grafting. Eight days after castration a reduction in PRL levels was detected in all groups, together with an increase in LH values. PRL values after ovariectomy were less reduced in grafted animals, and these rats also showed a less marked LH increase. This effect is more evident in group B. All these data seem to point out that hyperprolactinemia is capable of modifying the feed-back system between E2 and LH, and that the age at which hyperprolactinemia starts has a profound effect.