Abstract
We reported previously that a biphasic LH release (within 30 min and 90-150 min after LH-RH injection) was observed in normal menstruating baboons (non-human primates). Plasma immunoassayable LH-RH reached a maximum within 4 min after injection and was undetectable within 60 min. Plasma estrogen and progestin were elevated within 45 min. No plasma LH release with increment of plasma estrogen and progestin was observed in saline injected baboons. This study was performed to investigate the mechanism of biphasic LH release by LH-RH injection.
Synthetic LH-RH (100μg) was injected sc into four female retrochiasmatic deafferented baboons. Blood samples collected 30 and 2 min before injection and 5, 10, 15, 30, 45, 60, 90,120,150 and 180 min after injection were assayed for LH, estrogen and progestin. In four baboons plasma LH peak was observed within 30 min after injection and plasma estrogen and progestin were elevated within 45 min. However, plasma LH peak within 90-150 min was not observed. These results infer that exogenous LH-RH exerts an effect on the pituitary to release LH within 30 min after injection. Increased estrogen and progestin exert the effect on the higher brain area (extrahypothalamic area) and the anterior hypothalamus to facilitate release of endogenous LH-RH, which subsequently release LH within 90-150 min in cooperation with exogenous LH-RH which may be considered to participate LH synthesis in the pituitary. Thus, it seems likely that the extrahypothalamic area (for example; limbic system) and the anterior hypothalamus have an important role in regulating LH-RH secretion and subsequent LH release in the baboon.
